Re: [time-nuts] Advice on 10 MHz isolation/distribution /Phase Noise of 74AC gates (John Miles)
Hello John, Your results look very interesting. The big variation with input level shows how important it is to get that right. Incidentally, I didn't blame the CMOS for the 1/f^3 slope, as that was 18dB below the OCXO's phase noise. The divider output dominated from ~100Hz outwards, and showed 1/f slope down to the noise floor. (The E5052 doesn't do added noise measurement.) I suspect that the input and output interfaces are the main barriers to achieving the potential performance. The switching threshold is roughly proportional to Vcc, so with a finite slew rate, the supply pin acts as a jitter modulator. The common practice of using a Schmitt input to square up a sine wave is likely to make things worse if anything. Increasing the slew rate with a non-saturating limiter is probably the best approach. (My measurement benefitted from starting at 100MHz where the slew rate is inherently 10 times as high.) Supply noise will amplitude modulate the output, which can also cause problems, depending on the AM-to-phase mod conversion factor of whatever it's driving into. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opo...@pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution / Phase Noise of 74AC gates (Bruce Griffiths)
Bruce wrote: A little more detail is required such as: 1) What was the divided down output of the 74AC163 compared with? The E5052B contains 2 uncorrelated test systems, and uses its 2 internal synthesisers (with separate 10MHz ref OCXOs) as references. The signal under test is split at the input, and cross-correlation is used to reduce the effect of reference noise. 2) An image of the breadboard would also be useful. It was 2 years ago, and it doesn't exist any more! The IC was an SO-16 package, stuck upside down to a piece of copper-clad board. 3) A circuit diagram showing component values and manufacturer's part nos. Circuit attached. I don't remember the supply filter resistor value, but it was probably ~100R. I adjusted the supply to give 5V on the IC when it was operating. I've read the E5052B manual but there's insufficient detail to have confidence in the calibration technique used when a square wave input is used. The E5052B doesn't tune the DUT, but digitally locks its synthesisers to the signal, so there is no VCO constant to calibrate. It uses analogue mixers as phase detectors. I assume it measures the slope at zero crossing as it appears able to work with high harmonic levels, e.g. passing undistorted signals through amplifiers driven into compression and re-measuring doesn't change the measured close-in phase noise (in the 1/f^3 region). Below 100Hz where the oscillator's phase noise dominates, the 12.5MHz curve tracks it 18dB lower, which gives confidence that the instrument has got the calibration right. >From what I understand from the manual / various application notes, the E5052B samples the baseband signal at 250MHz, and processes the whole thing in a single band. (This is how it achieves such good far-from-carrier performance. In the time it takes to do a single measurement at 1Hz offset for example, it does 128000 correlations at >6.25MHz, giving 25.5dB improvement.) From this, I think one can assume that if the cal is valid close-in, it will be valid at all offsets. I would be interested in any suggestions about possible measurement errors. The instrument settings are shown on the plot I posted yesterday. In theory, 74AC phase noise should tend to a very low value as f tends to zero, assuming the power supply is quiet, as one is just left with FETs with a low ON resistance. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opo...@pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system. 74AC163 test circuit.pdf Description: 74AC163 test circuit.pdf ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution / PhaseNoise of 74AC gates
Hi That plot is very similar to what I have seen on AC gates. The usual mumble words apply - that was > 15 years ago and semiconductor processes have changed a bit since then. Bob On Feb 26, 2010, at 5:54 AM, John Miles wrote: > Hi, Garry -- > >> I knew from other people's measurements that 74AC was capable of better >> than -160dBc/Hz when used to make a phase detector at 10MHz, but I >> wanted to do a quick feasibility check on a divider for an application a >> couple of years ago. >> >> The 74AC163 was powered from a linear bench supply via a long (many >> seconds) RC time constant plus local decoupling. I adjusted the supply >> to give 5V at the IC when it was operating. >> >> The 100MHz OCXO, which gave 18dBm into 50 ohm, was AC-coupled into the >> clock input, which was biased to half the supply voltage. The counter >> was left dividing by 16, as its propagation delay and set-up times are >> too long to programme it to divide by 10 with 100MHz clock rate. The >> output was AC-coupled directly to the E5052B input, without any >> filtering. I had to use the Qc output as the SSA doesn't work below >> 10MHz. >> >> The attached plot shows the 12.5MHz phase noise plus that of the 100MHz >> OCXO. The divider phase noise tracks 18dB below the OCXO at low offsets >> as expected, before its flicker noise and eventual noise floor >> predominate. I was primarily interested in seeing what the flicker noise >> was like, but I was surprised when I saw how low the floor was! >> >> The E5052B does the necessary calibration automatically before doing a >> measurement - from my experience with the instrument I have no reason to >> doubt the validity of the result. (The indicated 100MHz phase noise in >> the ~1-50kHz region is actually limited by the E5052B, owing to my >> setting only 100 correlations. However it shows it low enough to >> indicate that the CMOS noise dominates over that range.) >> >> I realise that a divider is very different from a simple inverter, but I >> think this gives an useful indication of what AC logic is capable of. > > Some interesting results, all right. The 74AC parts do seem to be quite > decent in the PN department. To try to corroborate your observations I ran > some residual PN tests on a 74AC04 inverter using a different measurement > technique (splitter+quadrature delay line): see http://www.ke5fx.com/ac.htm > . > > While I didn't achieve anything like the broadband floor you saw, I did find > that the close-in noise was quite a bit better than your E5052B plot showed. > It doesn't seem correct to blame your 1/f^3 slope below 1 kHz on CMOS > process noise, as it doesn't show up in a true residual test. That is more > likely to be your OCXO's PN profile, improved 18 dB by 20*log(N). It looks > virtually identical to a couple of Wenzel parts I measured awhile back > (attached). > > I agree that an edge conditioner and a clean Vcc supply could wring some > serious performance out of these chips. The power supply might account for > the broadband-floor deficit relative to your test setup; I'm not really sure > what to expect there. I made some PSU noise measurements awhile back but > the methodology was pretty bad and I don't really trust my results. Will > try to do some more in-depth tests later, to see what's really possible. > > -- john, KE5FX > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution / PhaseNoise of 74AC gates
Hi, Garry -- > I knew from other people's measurements that 74AC was capable of better > than -160dBc/Hz when used to make a phase detector at 10MHz, but I > wanted to do a quick feasibility check on a divider for an application a > couple of years ago. > > The 74AC163 was powered from a linear bench supply via a long (many > seconds) RC time constant plus local decoupling. I adjusted the supply > to give 5V at the IC when it was operating. > > The 100MHz OCXO, which gave 18dBm into 50 ohm, was AC-coupled into the > clock input, which was biased to half the supply voltage. The counter > was left dividing by 16, as its propagation delay and set-up times are > too long to programme it to divide by 10 with 100MHz clock rate. The > output was AC-coupled directly to the E5052B input, without any > filtering. I had to use the Qc output as the SSA doesn't work below > 10MHz. > > The attached plot shows the 12.5MHz phase noise plus that of the 100MHz > OCXO. The divider phase noise tracks 18dB below the OCXO at low offsets > as expected, before its flicker noise and eventual noise floor > predominate. I was primarily interested in seeing what the flicker noise > was like, but I was surprised when I saw how low the floor was! > > The E5052B does the necessary calibration automatically before doing a > measurement - from my experience with the instrument I have no reason to > doubt the validity of the result. (The indicated 100MHz phase noise in > the ~1-50kHz region is actually limited by the E5052B, owing to my > setting only 100 correlations. However it shows it low enough to > indicate that the CMOS noise dominates over that range.) > > I realise that a divider is very different from a simple inverter, but I > think this gives an useful indication of what AC logic is capable of. Some interesting results, all right. The 74AC parts do seem to be quite decent in the PN department. To try to corroborate your observations I ran some residual PN tests on a 74AC04 inverter using a different measurement technique (splitter+quadrature delay line): see http://www.ke5fx.com/ac.htm . While I didn't achieve anything like the broadband floor you saw, I did find that the close-in noise was quite a bit better than your E5052B plot showed. It doesn't seem correct to blame your 1/f^3 slope below 1 kHz on CMOS process noise, as it doesn't show up in a true residual test. That is more likely to be your OCXO's PN profile, improved 18 dB by 20*log(N). It looks virtually identical to a couple of Wenzel parts I measured awhile back (attached). I agree that an edge conditioner and a clean Vcc supply could wring some serious performance out of these chips. The power supply might account for the broadband-floor deficit relative to your test setup; I'm not really sure what to expect there. I made some PSU noise measurements awhile back but the methodology was pretty bad and I don't really trust my results. Will try to do some more in-depth tests later, to see what's really possible. -- john, KE5FX <>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution / Phase Noise of 74AC gates
Garry A little more detail is required such as: 1) What was the divided down output of the 74AC163 compared with? 2) An image of the breadboard would also be useful. 3) A circuit diagram showing component values and manufacturer's part nos. The idea being to provide sufficient information so that your measurement can be replicated using a different phase noise measurement system. This would help identify any calibration or other issues. NIST recently found that using a low noise power supply made a significant difference to the measured phase noise of ECL dividers. The data on the phase noise of CMOS dividers in the readily accessible literature is a little sketchy to say the least. This wasn't helped by the lack of a good understanding of the phase noise characteristics of a divider at the time such measurements were made. Even erroneous/anomalous results are worth discussing if only to highlight potential pitfalls when measuring phase noise. I've read the E5052B manual but there's insufficient detail to have confidence in the calibration technique used when a square wave input is used. Bruce Garry Thorp wrote: Having followed the discussion for a while, I get the feeling that some people dismissed my results on the basis that 'CMOS ICs can't be anywhere near that good, therefore the measurement must be faulty, therefore it's not even worth discussing it'. I knew from other people's measurements that 74AC was capable of better than -160dBc/Hz when used to make a phase detector at 10MHz, but I wanted to do a quick feasibility check on a divider for an application a couple of years ago. The 74AC163 was powered from a linear bench supply via a long (many seconds) RC time constant plus local decoupling. I adjusted the supply to give 5V at the IC when it was operating. The 100MHz OCXO, which gave 18dBm into 50 ohm, was AC-coupled into the clock input, which was biased to half the supply voltage. The counter was left dividing by 16, as its propagation delay and set-up times are too long to programme it to divide by 10 with 100MHz clock rate. The output was AC-coupled directly to the E5052B input, without any filtering. I had to use the Qc output as the SSA doesn't work below 10MHz. The attached plot shows the 12.5MHz phase noise plus that of the 100MHz OCXO. The divider phase noise tracks 18dB below the OCXO at low offsets as expected, before its flicker noise and eventual noise floor predominate. I was primarily interested in seeing what the flicker noise was like, but I was surprised when I saw how low the floor was! The E5052B does the necessary calibration automatically before doing a measurement - from my experience with the instrument I have no reason to doubt the validity of the result. (The indicated 100MHz phase noise in the ~1-50kHz region is actually limited by the E5052B, owing to my setting only 100 correlations. However it shows it low enough to indicate that the CMOS noise dominates over that range.) I realise that a divider is very different from a simple inverter, but I think this gives an useful indication of what AC logic is capable of. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opo...@pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution /
From: "Garry Thorp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution / Phase Noise of 74AC gates The attached plot shows the 12.5MHz phase noise plus that of the 100MHz OCXO. The divider phase noise tracks 18dB below the OCXO at low offsets as expected, before its flicker noise and eventual noise floor predominate. I was primarily interested in seeing what the flicker noise was like, but I was surprised when I saw how low the floor was! The E5052B does the necessary calibration automatically before doing a measurement - from my experience with the instrument I have no reason to doubt the validity of the result. (The indicated 100MHz phase noise in the ~1-50kHz region is actually limited by the E5052B, owing to my setting only 100 correlations. However it shows it low enough to indicate that the CMOS noise dominates over that range.) I realise that a divider is very different from a simple inverter, but I think this gives an useful indication of what AC logic is capable of. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH Gary, Hi Gary, Interesting plot, thanks for sharing. Like I said previously; logic gates absolutely have their uses in reference buffering. I have used them before, and will continue to do so. However, I think in the most demanding applications the relatively-poor 1/F noise of CMOS loses out to bipolar transistors. If one wanted to stick with a square wave reference, or implement a digital phase detector or divider other types of logic like ECL are more appropriate. Also, digital logic, even high-current ECL, is more susceptible to AM to PM conversion from power supply noise. It all depends on what you need to do. CMOS is pretty good, but can't get you that last bit of performance especially close in. Which is, after all, what a clean reference is for. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Bob Camp)
Hello Bob, My 15mA estimate for the output stage was based on AC coupling the output, which is how I connected it. The IC is then sourcing 25mA into 100R for half the time and sinking 25mA the rest of the time, so the mean supply current drawn is 12.5mA. The extra is to allow for the IC's dissipation capacitance x 5V x 10MHz. As I was just doing this as a feasibility check, the 74AC163 was on a board on its own, powered from a linear bench supply with loads of RC filtering plus local decoupling, so no problem with interaction with other components. The input was biased to half the supply voltage, and AC coupled to the oscillator which gave ~18dBm sine wave into 50R. Slew rate wasn't much of an issue as it was being driven at 100MHz. Garry Hi Yup, that works. A couple of *very* minor points: - My guess is that your output stage will be pulling a bit more than 15 ma. This assumes you are running a 50 ohm load and a 50 ohm output impedance to deliver 13 dbm (~ 2.5 V p-p). More or less, 100 ohms from +5 to ground would be 50 ma half the time. The stage likely will pull 25 or more ma. (Says Bob who hopefully hasn't done any typos in the last minute or so). You might also want to parallel two (or more) gates to get the output current into the "safe" region. The Datum LPRO manual on page 18 shows some data for AC gates driven with very simple circuits (just bias the gate ...). The data they show would be adequate for the proposed application (if I remember the numbers right). Power supply bypassing is indeed an issue no matter how you do this. AC gates create some *major* supply line spikes. Depending on how you look at ground bounce, it might be an issue in terms of isolation. Good layout practices required The gate approach also lets you generate an "almost differential" signal without a lot of crazy effort. One 74AC86 should do the trick. Not real sure that Clay is a big fan of lots of harmonics or of filters. Bob Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opo...@pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Clay, I'm not sure what the "leadless" package looks like, so I'll check it out. The only older leadless packages I can't deal with are BGA and the leadless ceramic chip carrier. Would you send me a complete P/N to be sure I'm looking at the right thing? This would still be a very useful accessory, even if the reverse isolation results were down to 60dB. Pete On Feb 20, 2010, at 12:46 PM, life speed wrote: > From: Pete Rawson > Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution > To: Discussion of precise time and frequency measurement > > Message-ID: <1027d446-fe23-45a7-88ad-1cfd339c4...@earthlink.net> > Content-Type: text/plain; charset=us-ascii > > Clay, > > I would really like to have a copy of your test board for this effort. > I'm sure it will be a challenging layout. But it could be a very handy > piece of hardware. Supporting a PCA order would easy to do. > > Pete Rawson > > I always buy more than one PCB, 5 - 6 don't cost any more than 1. > Unfortunately, I don't think my favorite prototype shop (PCB123) will be > suitable for a layout with voids in the ground plane (reduce parasitic C) > under the opamp and R4003C on the top layer, so I will have to do a 'real' > PCB. I was also planning on using the leadless version of the part, which > could be challenging for home assembly. > > Everything is leadless these days. Gives me fits sometimes. I just went > through a nightmarish experience with a leadless ARM7 processor that needed > some wires added. I replaced it with a leaded part at a cost of 2 mm PCB > area . . . but I digress. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
> I have been thinking about how to make the measurement. I don't > normally measure OCXO phase noise. I buy them to spec and lock > my synthesizer to them, measuring phase noise at microwave > frequencies using an older Agilent E5500 system with an 8254 (?) > signal generator reference, which is an older version of their 8257. > > I was thinking I could split an OCXO signal, run one path thru > the amp, and then mix them together and put the IF output into > the E5500. I think I would need a phase shifter to ensure the > signals are in quadrature at the mixer. I guess if I had two > OCXOs I could let the E5500 control the EFC port on one, it would > then use it's internal PLL to lock the 'reference' OCXO to the > 'DUT' OCXO/amp. The E5500 manuals will talk about residual measurements to some extent. When measuring an amplifier, you can indeed use a phase shifter in one leg, but be sure to use a well-filtered test source. If you use a low-end signal generator (or any broadband generator at all, really) you need to filter the broadband noise from it, or it will degrade the apparent performance of your amp under test. I measured a few MMICs with a 3048A system using this technique here: http://www.ke5fx.com/pnamp.htm ... and a simple common-emitter amp with a transformer here, courtesy of Bruce: http://www.ke5fx.com/norton.htm On the first page you can see the importance of the filter, even when using a decent signal generator. -- john, KE5FX ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
From: Bruce Griffiths Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) The calculation is useful to help eliminate amplifiers that will not meet the phase noise floor specs. The amplifiers that remain will then need to be tested/measured for their actual phase noise. Bruce I have been thinking about how to make the measurement. I don't normally measure OCXO phase noise. I buy them to spec and lock my synthesizer to them, measuring phase noise at microwave frequencies using an older Agilent E5500 system with an 8254 (?) signal generator reference, which is an older version of their 8257. I was thinking I could split an OCXO signal, run one path thru the amp, and then mix them together and put the IF output into the E5500. I think I would need a phase shifter to ensure the signals are in quadrature at the mixer. I guess if I had two OCXOs I could let the E5500 control the EFC port on one, it would then use it's internal PLL to lock the 'reference' OCXO to the 'DUT' OCXO/amp. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
From: Pete Rawson Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution To: Discussion of precise time and frequency measurement Message-ID: <1027d446-fe23-45a7-88ad-1cfd339c4...@earthlink.net> Content-Type: text/plain; charset=us-ascii Clay, I would really like to have a copy of your test board for this effort. I'm sure it will be a challenging layout. But it could be a very handy piece of hardware. Supporting a PCA order would easy to do. Pete Rawson I always buy more than one PCB, 5 - 6 don't cost any more than 1. Unfortunately, I don't think my favorite prototype shop (PCB123) will be suitable for a layout with voids in the ground plane (reduce parasitic C) under the opamp and R4003C on the top layer, so I will have to do a 'real' PCB. I was also planning on using the leadless version of the part, which could be challenging for home assembly. Everything is leadless these days. Gives me fits sometimes. I just went through a nightmarish experience with a leadless ARM7 processor that needed some wires added. I replaced it with a leaded part at a cost of 2 mm PCB area . . . but I digress. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: From: Bruce Griffiths Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Its easy to calculate a lower bound to the amplifier phase noise floor from the signal level at the output and the amplifier output noise due to feedback resistors together with the amplifier input voltage and current noise. The actual phase noise floor may be a few dB higher. Bruce Yes, it is easy to calculate. Clay The calculation is useful to help eliminate amplifiers that will not meet the phase noise floor specs. The amplifiers that remain will then need to be tested/measured for their actual phase noise. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
From: Bruce Griffiths Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Its easy to calculate a lower bound to the amplifier phase noise floor from the signal level at the output and the amplifier output noise due to feedback resistors together with the amplifier input voltage and current noise. The actual phase noise floor may be a few dB higher. Bruce Yes, it is easy to calculate. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
life speed wrote: If I can believe the simulation (a big if) the ADA4899-1 can provide 90 dB isolation at 10 MHz, rolling up to 70 dB at 100 MHz, when configured with a gain of +2 The subcircuit model provided by ADI is useless for noise, unfortunately. I guess I'll have to build and measure, which I don't mind doing. Unless it turns out to be a waste of time, and I should have just used the transistor circuit. Clay Its easy to calculate a lower bound to the amplifier phase noise floor from the signal level at the output and the amplifier output noise due to feedback resistors together with the amplifier input voltage and current noise. The actual phase noise floor may be a few dB higher. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Clay, I would really like to have a copy of your test board for this effort. I'm sure it will be a challenging layout. But it could be a very handy piece of hardware. Supporting a PCA order would easy to do. Pete Rawson On Feb 19, 2010, at 6:17 PM, life speed wrote: > If I can believe the simulation (a big if) the ADA4899-1 can provide 90 dB > isolation at 10 MHz, rolling up to 70 dB at 100 MHz, when configured with a > gain of +2 > > The subcircuit model provided by ADI is useless for noise, unfortunately. I > guess I'll have to build and measure, which I don't mind doing. Unless it > turns out to be a waste of time, and I should have just used the transistor > circuit. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
If I can believe the simulation (a big if) the ADA4899-1 can provide 90 dB isolation at 10 MHz, rolling up to 70 dB at 100 MHz, when configured with a gain of +2 The subcircuit model provided by ADI is useless for noise, unfortunately. I guess I'll have to build and measure, which I don't mind doing. Unless it turns out to be a waste of time, and I should have just used the transistor circuit. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Hi . and thus if you drive it from a low impedance node you can get pretty good isolation. Bob On Feb 19, 2010, at 5:59 PM, Bruce Griffiths wrote: > life speed wrote: >> Message: 6 >> From: Pete Rawson >> Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution >> >> >>> Clay, >>> >>> Analog devices AD4899-1 voltage noise = 2nV/rtHz @ 10Hz; GBW = 300MHz. >>> >>> Pete Rawson >>> >> That is an interesting part. >> >> So, how does one think about reverse isolation in a feedback amp? Is the >> open-loop gain of the amp applied to the spurious signal to cancel it? The >> spurious, reduced by the ratio of the 50 ohm source impedance, to the output >> impedance of 0.7 ohms of the amp (-18 dB) appears at the inverting input . . >> . >> >> And what would appear at the non-inverting input? >> >> Off to the simulator. >> >> Clay >> >> > Reverse isolation is highest if one uses a non inverting amplifier rather > than an inverting one. > The signal at the inverting input is coupled to the non inverting input via > the differential input impedance (predominately capacitive) of the opamp. > ie finite input stage current gain and emitter base (along with package > strays) capacitances are the principal contributors at least for frequencies > where the input stage output voltage swing is small. > > Bruce > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
life speed wrote: Message: 6 From: Pete Rawson Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Clay, Analog devices AD4899-1 voltage noise = 2nV/rtHz @ 10Hz; GBW = 300MHz. Pete Rawson That is an interesting part. So, how does one think about reverse isolation in a feedback amp? Is the open-loop gain of the amp applied to the spurious signal to cancel it? The spurious, reduced by the ratio of the 50 ohm source impedance, to the output impedance of 0.7 ohms of the amp (-18 dB) appears at the inverting input . . . And what would appear at the non-inverting input? Off to the simulator. Clay Reverse isolation is highest if one uses a non inverting amplifier rather than an inverting one. The signal at the inverting input is coupled to the non inverting input via the differential input impedance (predominately capacitive) of the opamp. ie finite input stage current gain and emitter base (along with package strays) capacitances are the principal contributors at least for frequencies where the input stage output voltage swing is small. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Message: 6 From: Pete Rawson Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution >Clay, > >Analog devices AD4899-1 voltage noise = 2nV/rtHz @ 10Hz; GBW = 300MHz. > >Pete Rawson That is an interesting part. So, how does one think about reverse isolation in a feedback amp? Is the open-loop gain of the amp applied to the spurious signal to cancel it? The spurious, reduced by the ratio of the 50 ohm source impedance, to the output impedance of 0.7 ohms of the amp (-18 dB) appears at the inverting input . . . And what would appear at the non-inverting input? Off to the simulator. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Clay, Analog devices AD4899-1 voltage noise = 2nV/rtHz @ 10Hz; GBW = 300MHz. Pete Rawson On Feb 19, 2010, at 12:05 PM, life speed wrote: > Any opinions on the suitability of the TI OPA820 as a 10 MHz distribution > amp? The voltage noise is only 7 nV/rtHz @ 100 Hz (gain=2, I'll be using > g=1), which is the best I've seen so far for a wideband amp. Not as good as > the discrete transistor circuit, but it would use alot fewer parts. It only > needs to be better than a 'good' OCXO. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Hi As previously mentioned, these gizmos seem to all be spec'd out at 2V p-p into 100 or 200 ohms. The only way to figure out what happens past that is going to be to get one and see. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Friday, February 19, 2010 2:06 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Any opinions on the suitability of the TI OPA820 as a 10 MHz distribution amp? The voltage noise is only 7 nV/rtHz @ 100 Hz (gain=2, I'll be using g=1), which is the best I've seen so far for a wideband amp. Not as good as the discrete transistor circuit, but it would use alot fewer parts. It only needs to be better than a 'good' OCXO. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Any opinions on the suitability of the TI OPA820 as a 10 MHz distribution amp? The voltage noise is only 7 nV/rtHz @ 100 Hz (gain=2, I'll be using g=1), which is the best I've seen so far for a wideband amp. Not as good as the discrete transistor circuit, but it would use alot fewer parts. It only needs to be better than a 'good' OCXO. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 6 Date: Fri, 19 Feb 2010 15:17:44 - From: "Garry Thorp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hello Clay, Joining in this discussion at a rather late stage - have you considered using 74AC series gates as buffers? They provide reasonable isolation and have surprisingly low phase noise. Hi Gary, That's funny! I have already done everything you describe, and shipped synthesizers with such circuits in them. I like Fairchild UHS inverters for the logic gates. And yes, I've done the low-noise regulators constructed from voltage references, heavy filtering, and an opamp driving a BJT pass transistor (I like the NZT560A/660A). I will mention that for some applications, the Burr-Brown Reg104A is one of the few IC regulators that has suitably low noise for frequency synthesis. However, at the very limits of phase noise performance, the squaring technique is inferior to a sine wave. Not by alot, but enough that I need to stick with a sinusoid. Not to mention the other modules in the system are expecting a sine wave. Thanks, Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
In the Frequency Divider design I did back in 2008, I used 4 outputs from a 74AC541 in parallel for each output frequency, with a 180 ohm resistor in series with each output. Unused inputs were of course tied to ground. Output impedance of each driver in the '541 should be around 20-25 ohms, so the whole ensemble should give about 50 ohms output impedance (certainly when loaded with 50 ohms, the output voltage was almost exactly 2.5V). With this setup you can safely short the output to ground with no damage (max draw per output pin of about 25mA which is half the maximum rating of 50mA per output pin). Using a four layer board (power and ground planes), I didn't see much sign of ground bounce, just some overshoot on the 0V to 5V transitions. Dave -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Camp Sent: 19 February 2010 17:30 To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hi Yup, that works. A couple of *very* minor points: - My guess is that your output stage will be pulling a bit more than 15 ma. This assumes you are running a 50 ohm load and a 50 ohm output impedance to deliver 13 dbm (~ 2.5 V p-p). More or less, 100 ohms from +5 to ground would be 50 ma half the time. The stage likely will pull 25 or more ma. (Says Bob who hopefully hasn't done any typos in the last minute or so). You might also want to parallel two (or more) gates to get the output current into the "safe" region. The Datum LPRO manual on page 18 shows some data for AC gates driven with very simple circuits (just bias the gate ...). The data they show would be adequate for the proposed application (if I remember the numbers right). Power supply bypassing is indeed an issue no matter how you do this. AC gates create some *major* supply line spikes. Depending on how you look at ground bounce, it might be an issue in terms of isolation. Good layout practices required The gate approach also lets you generate an "almost differential" signal without a lot of crazy effort. One 74AC86 should do the trick. Not real sure that Clay is a big fan of lots of harmonics or of filters. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Garry Thorp Sent: Friday, February 19, 2010 10:18 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hello Clay, Joining in this discussion at a rather late stage - have you considered using 74AC series gates as buffers? They provide reasonable isolation and have surprisingly low phase noise. A single 74AC04 inverter gives over 40dB reverse isolation at 10MHz, so 3 cascaded gates would give more than enough. You would need to use a separate IC for each stage to achieve the isolation, but they are cheap! With a series output resistor, a 74AC gate with 5V supply will give ~13dBm while providing a 50R source match. Adding a series tuned circuit will give a sine wave if required. At 10MHz the first 2 stages will draw ~2mA and the output stage ~15mA (as a matched 50R source), so the necessary isolation between power supplies can readily be achieved by using separate RC filter chains to each IC. I haven't measured the phase noise of an AC04, but I have tried dividing a low-noise 100MHz OCXO using a 74AC163. At 100MHz, the OCXO's phase noise was ~-80dBc/Hz at 1Hz offset, -110 at 10Hz, -140 at 100Hz, ~-166 at 1kHz and ~-180 at 10kHz and beyond. Taking the Qc output of the AC163, the phase noise at 12.5MHz showed the theoretical 18dB reduction at low offsets, i.e. ~-98 at 1Hz and -128 at 10Hz. It then went into a flicker of phase region, ~-155 at 100Hz and -165 at 1kHz, reaching a floor of ~-178dBc/Hz by ~100kHz offset. Extrapolating the flicker region downwards suggests the divider output phase noise would be ~-145 at 10Hz and -135 at 1Hz. Intuitively, I wouldn't expect an inverter to have worse phase noise than a counter from the same family. Cascading 3 inverters would increase the flicker phase noise by ~5dB, which I think would still be well within the spec you gave earlier. This approach has the advantage that it can be done without transformers or inductors (unless you need a sine wave output). Digital inputs need a high slew rate to achieve low phase noise, so if your oscillator has a sine wave output you would probably need to square it up with a (non-saturating) limiter such as a common-base driving into a Schottky diode limiter, or a long-tailed pair. As CMOS is a saturating logic family, low-noise power supply is vital. The input switching threshold is approximately half the supply voltage, so supply noise + non-infinite slew rate = jitter. The lowest-noise LDO regulators are probably not good enough. However this is a (
Re: [time-nuts] Advice on 10 MHz isolation/distribution
OR could AC couple it into the load, so you are not wasting all that DC peak current. IF you really want to reduce the gate load and its output current then Use a 2 to one AC coupled divider. Provides 200 Ohms AC load to the driver, 50 Ohms to the load, and could be driven with a single output gate. Also provides a high pass filter to reduce some of that low freq PS noise, especially if the input is AC coupled correctly. ws *** [time-nuts] Advice on 10 MHz isolation/distribution Bob Camp lists at cq.nu Fri Feb 19 17:30:04 UTC 2010 Previous message: [time-nuts] Advice on 10 MHz isolation/distribution Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] Hi Yup, that works. A couple of *very* minor points: - My guess is that your output stage will be pulling a bit more than 15 ma. This assumes you are running a 50 ohm load and a 50 ohm output impedance to deliver 13 dbm (~ 2.5 V p-p). More or less, 100 ohms from +5 to ground would be 50 ma half the time. The stage likely will pull 25 or more ma. (Says Bob who hopefully hasn't done any typos in the last minute or so). You might also want to parallel two (or more) gates to get the output current into the "safe" region. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Hi Yup, that works. A couple of *very* minor points: - My guess is that your output stage will be pulling a bit more than 15 ma. This assumes you are running a 50 ohm load and a 50 ohm output impedance to deliver 13 dbm (~ 2.5 V p-p). More or less, 100 ohms from +5 to ground would be 50 ma half the time. The stage likely will pull 25 or more ma. (Says Bob who hopefully hasn't done any typos in the last minute or so). You might also want to parallel two (or more) gates to get the output current into the "safe" region. The Datum LPRO manual on page 18 shows some data for AC gates driven with very simple circuits (just bias the gate ...). The data they show would be adequate for the proposed application (if I remember the numbers right). Power supply bypassing is indeed an issue no matter how you do this. AC gates create some *major* supply line spikes. Depending on how you look at ground bounce, it might be an issue in terms of isolation. Good layout practices required The gate approach also lets you generate an "almost differential" signal without a lot of crazy effort. One 74AC86 should do the trick. Not real sure that Clay is a big fan of lots of harmonics or of filters. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Garry Thorp Sent: Friday, February 19, 2010 10:18 AM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hello Clay, Joining in this discussion at a rather late stage - have you considered using 74AC series gates as buffers? They provide reasonable isolation and have surprisingly low phase noise. A single 74AC04 inverter gives over 40dB reverse isolation at 10MHz, so 3 cascaded gates would give more than enough. You would need to use a separate IC for each stage to achieve the isolation, but they are cheap! With a series output resistor, a 74AC gate with 5V supply will give ~13dBm while providing a 50R source match. Adding a series tuned circuit will give a sine wave if required. At 10MHz the first 2 stages will draw ~2mA and the output stage ~15mA (as a matched 50R source), so the necessary isolation between power supplies can readily be achieved by using separate RC filter chains to each IC. I haven't measured the phase noise of an AC04, but I have tried dividing a low-noise 100MHz OCXO using a 74AC163. At 100MHz, the OCXO's phase noise was ~-80dBc/Hz at 1Hz offset, -110 at 10Hz, -140 at 100Hz, ~-166 at 1kHz and ~-180 at 10kHz and beyond. Taking the Qc output of the AC163, the phase noise at 12.5MHz showed the theoretical 18dB reduction at low offsets, i.e. ~-98 at 1Hz and -128 at 10Hz. It then went into a flicker of phase region, ~-155 at 100Hz and -165 at 1kHz, reaching a floor of ~-178dBc/Hz by ~100kHz offset. Extrapolating the flicker region downwards suggests the divider output phase noise would be ~-145 at 10Hz and -135 at 1Hz. Intuitively, I wouldn't expect an inverter to have worse phase noise than a counter from the same family. Cascading 3 inverters would increase the flicker phase noise by ~5dB, which I think would still be well within the spec you gave earlier. This approach has the advantage that it can be done without transformers or inductors (unless you need a sine wave output). Digital inputs need a high slew rate to achieve low phase noise, so if your oscillator has a sine wave output you would probably need to square it up with a (non-saturating) limiter such as a common-base driving into a Schottky diode limiter, or a long-tailed pair. As CMOS is a saturating logic family, low-noise power supply is vital. The input switching threshold is approximately half the supply voltage, so supply noise + non-infinite slew rate = jitter. The lowest-noise LDO regulators are probably not good enough. However this is a (relatively!) straightforward low-frequency problem, that can be solved by using a heavily filtered voltage reference with a low-noise op amp buffer or Darlington emitter follower. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclo
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Hello Clay, Joining in this discussion at a rather late stage - have you considered using 74AC series gates as buffers? They provide reasonable isolation and have surprisingly low phase noise. A single 74AC04 inverter gives over 40dB reverse isolation at 10MHz, so 3 cascaded gates would give more than enough. You would need to use a separate IC for each stage to achieve the isolation, but they are cheap! With a series output resistor, a 74AC gate with 5V supply will give ~13dBm while providing a 50R source match. Adding a series tuned circuit will give a sine wave if required. At 10MHz the first 2 stages will draw ~2mA and the output stage ~15mA (as a matched 50R source), so the necessary isolation between power supplies can readily be achieved by using separate RC filter chains to each IC. I haven't measured the phase noise of an AC04, but I have tried dividing a low-noise 100MHz OCXO using a 74AC163. At 100MHz, the OCXO's phase noise was ~-80dBc/Hz at 1Hz offset, -110 at 10Hz, -140 at 100Hz, ~-166 at 1kHz and ~-180 at 10kHz and beyond. Taking the Qc output of the AC163, the phase noise at 12.5MHz showed the theoretical 18dB reduction at low offsets, i.e. ~-98 at 1Hz and -128 at 10Hz. It then went into a flicker of phase region, ~-155 at 100Hz and -165 at 1kHz, reaching a floor of ~-178dBc/Hz by ~100kHz offset. Extrapolating the flicker region downwards suggests the divider output phase noise would be ~-145 at 10Hz and -135 at 1Hz. Intuitively, I wouldn't expect an inverter to have worse phase noise than a counter from the same family. Cascading 3 inverters would increase the flicker phase noise by ~5dB, which I think would still be well within the spec you gave earlier. This approach has the advantage that it can be done without transformers or inductors (unless you need a sine wave output). Digital inputs need a high slew rate to achieve low phase noise, so if your oscillator has a sine wave output you would probably need to square it up with a (non-saturating) limiter such as a common-base driving into a Schottky diode limiter, or a long-tailed pair. As CMOS is a saturating logic family, low-noise power supply is vital. The input switching threshold is approximately half the supply voltage, so supply noise + non-infinite slew rate = jitter. The lowest-noise LDO regulators are probably not good enough. However this is a (relatively!) straightforward low-frequency problem, that can be solved by using a heavily filtered voltage reference with a low-noise op amp buffer or Darlington emitter follower. Garry Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State. The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opo...@pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: The TI THS3201-EP was looking pretty good for a high speed opamp. But the input current noise graph doesn't go below 100 KHz and is climbing pretty steeply at that point. Clay Most current feedback opamps tend to have high inverting input noise current at low frequencies. A wideband voltage feedback opamp may be a better fit but the input voltage noise may be an issue. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi The reason to consider transformers is that they cut out 2/3 of the parts in the circuit and significantly reduce the noise. Bob On Feb 18, 2010, at 6:33 PM, life speed wrote: > Message: 5 > Date: Thu, 18 Feb 2010 17:13:55 -0500 > From: "Bob Camp" > Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution > (Clay) > To: "'Discussion of precise time and frequency measurement'" > > Message-ID: <13d264786a8a41e781bb4e53c1dd9...@vectron.com> > Content-Type: text/plain;charset="iso-8859-1" > >> Hi >> >> Have you looked into any actual data on small rf transformers under >> vibration at 10 MHz? > > Hi, > > No. I have experience with low-noise designs under vibration, however. What > is the compelling reason for even considering such a device when a design is > available that doesn't need it? Sounds like risk without an upside to me. > > >> The phase noise of your reference is going to head up by your +56 db. As >> long as the transformer's impact is well below the reference, it will not >> show up in the output signal. > > any spur larger than -130 dBc will be an issue. It doesn't take much vibe to > do that. And the synthesizer has to operate under 10g RMS. > >> Noise at the load is a problem, no matter how it gets there. Transmission >> may not be inside your scope -yet. It's still an issue that directly impacts >> what you are trying to do. > > Only one device is at the end of a long cable, with reduced performance > expectations. The others are local and share a common ground. > > I am familiar with the various types of capacitors properties and frequencies. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
The TI THS3201-EP was looking pretty good for a high speed opamp. But the input current noise graph doesn't go below 100 KHz and is climbing pretty steeply at that point. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 5 Date: Thu, 18 Feb 2010 17:13:55 -0500 From: "Bob Camp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) To: "'Discussion of precise time and frequency measurement'" Message-ID: <13d264786a8a41e781bb4e53c1dd9...@vectron.com> Content-Type: text/plain; charset="iso-8859-1" >Hi > > Have you looked into any actual data on small rf transformers under > vibration at 10 MHz? Hi, No. I have experience with low-noise designs under vibration, however. What is the compelling reason for even considering such a device when a design is available that doesn't need it? Sounds like risk without an upside to me. >The phase noise of your reference is going to head up by your +56 db. As >long as the transformer's impact is well below the reference, it will not >show up in the output signal. any spur larger than -130 dBc will be an issue. It doesn't take much vibe to do that. And the synthesizer has to operate under 10g RMS. >Noise at the load is a problem, no matter how it gets there. Transmission >may not be inside your scope -yet. It's still an issue that directly impacts >what you are trying to do. Only one device is at the end of a long cable, with reduced performance expectations. The others are local and share a common ground. I am familiar with the various types of capacitors properties and frequencies. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hal Murray wrote: The problem is modulation of the reference signal via relative movement of the transformer guts. While I understand there are ways to 'harden' magnetic devices, my application is far too sensitive to even consider a magnetic approach given the availability of alternatives. Any spurious signals present on the 10 MHz reference will be increased by 56 dB by the phase-locked loop. Capacitors are piezoelectric too. Does anybodyhave any handy numbers for this sort of stuff? Most high K ceramic caps are ferroelectric below the Curie temperature and paraelectic above that. The resultant capacitance nonlinearity can allow low frequency noise to phase modulate a capacitor coupled RF signal if the phase shift due to the capacitor is sufficiently large. Yet another reason to avoid high K ceramic capacitors or at least ensure that the RF phase shift due to such capacitors is sufficiently small. Low frequency magnetic fields can phase modulate transformer coupled RF signals by modulating the transformer phase shift. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi Vibration modulates lead inductance. That's true even on SMT semiconductors.. It's true big time for leaded parts of the axial persuasion. Weather the amount of change matters to you is another thing entirely. If you stick with NPO even for the bypass caps, the piezo stuff is not going to be a big issue. Bob On Feb 18, 2010, at 5:48 PM, Hal Murray wrote: > >> The problem is modulation of the reference signal via relative >> movement of the transformer guts. While I understand there are ways >> to 'harden' magnetic devices, my application is far too sensitive to >> even consider a magnetic approach given the availability of >> alternatives. Any spurious signals present on the 10 MHz reference >> will be increased by 56 dB by the phase-locked loop. > > Capacitors are piezoelectric too. > > Does anybodyhave any handy numbers for this sort of stuff? > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
> The problem is modulation of the reference signal via relative > movement of the transformer guts. While I understand there are ways > to 'harden' magnetic devices, my application is far too sensitive to > even consider a magnetic approach given the availability of > alternatives. Any spurious signals present on the 10 MHz reference > will be increased by 56 dB by the phase-locked loop. Capacitors are piezoelectric too. Does anybodyhave any handy numbers for this sort of stuff? -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi Have you looked into any actual data on small rf transformers under vibration at 10 MHz? A change of a nH isn't the same thing at 10 MHz as at 6.3 GHz. An air core coil in the signal path at 6G would indeed be an issue. A circulator likely would not be. An RF transformer at 10 MHz has a lot more in common with the 6GHz circulator than with the 6GHz air core coil. The phase noise of your reference is going to head up by your +56 db. As long as the transformer's impact is well below the reference, it will not show up in the output signal. I would bet you an order of fries at the local MacDonald's that the single ended transmission of the signal will pick up far more noise than anything a properly constructed rf transformer will do at 10 MHz. Noise at the load is a problem, no matter how it gets there. Transmission may not be inside your scope -yet. It's still an issue that directly impacts what you are trying to do. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Thursday, February 18, 2010 4:47 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) Message: 5 Date: Thu, 18 Feb 2010 11:11:18 -0800 From: Hal Murray Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) > Thank you, but I require a circuit without transformers > for reasons of vibration susceptibility. Is the problem wires moving relative to eachother within the transformer or the whole transformer moving relative to the local magnetic field? Does it help to pot things in epoxy or varnish or ...? Years ago, when I took the lid off a small mini-circuits transformer it was just a few turns on a toroid. Something like varnish would be easy to apply. Hal, The problem is modulation of the reference signal via relative movement of the transformer guts. While I understand there are ways to 'harden' magnetic devices, my application is far too sensitive to even consider a magnetic approach given the availability of alternatives. Any spurious signals present on the 10 MHz reference will be increased by 56 dB by the phase-locked loop. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 5 Date: Thu, 18 Feb 2010 11:11:18 -0800 From: Hal Murray Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) > Thank you, but I require a circuit without transformers > for reasons of vibration susceptibility. Is the problem wires moving relative to eachother within the transformer or the whole transformer moving relative to the local magnetic field? Does it help to pot things in epoxy or varnish or ...? Years ago, when I took the lid off a small mini-circuits transformer it was just a few turns on a toroid. Something like varnish would be easy to apply. Hal, The problem is modulation of the reference signal via relative movement of the transformer guts. While I understand there are ways to 'harden' magnetic devices, my application is far too sensitive to even consider a magnetic approach given the availability of alternatives. Any spurious signals present on the 10 MHz reference will be increased by 56 dB by the phase-locked loop. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
> -Original Message- > > > > Lastly, my customer, the system designer, would now like to be able to add > > a switch function to the > 10 MHz distribution. I will have to check and see if switching of bias > current to these two-stage > transistor amp circuits can accomplish this function. Jelly-bean analog > switches are unlikely, I > think, to have the requisite noise and isolation performance. Nothing like > hitting a moving target. > > > > Clay > > > > > One way to achieve high isolation using analog switches is to use a T > switch configuration. > > Or a SPDT relay. I don't know if they'd meet your vibe requirement, though. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: Date: Thu, 18 Feb 2010 15:22:40 +1300 From: Bruce Griffiths Clay What's the effect of assigning the same label (Vout_2) to the outputs of both output amplifiers as shown in your circuit schematic? Bruce Hi Bruce, Duplication of the Vout_2 net labels (copy and paste is great) did not help the isolation. Neither did the 10 ohm base resistors. Now that the schematic is correct, the base resistors do not ruin the noise performance. Sigh . . . So this circuit looks like it will work well (I also get 100 dB simulated isolation between outputs, as well as noise of less than 2 nV/rtHz). I do believe isolation is important, as there are several subsystems using (and possibly trying to contaminate) the reference. I don't know all the details of each subsystem, and may not be privy to such info. So I can't put a number on the required isolation, but 20 log N applied to spurious within the PLL bandwidth is very unforgiving. The opamp solution is appealing, but I am unsure if it will work. My favorite low-noise parts right now are the TI OPA211, and the Analog AD797. I know the AD797 can be a bit tricky to tame oscillations. They both are probably difficult when configured for more than 10 MHz BW. I will run some simulations, but at 2V p-p into 50 ohms (10 dBm) the required rails would need to be more than 5V, although I have 15V available. I am unsure of the distortion performance at 20 mA peak output drive. Although the AD797 can source more current, neither amp is specified with good distortion numbers at 50 ohm loads. They always show audio (600 ohm) loads for their good THD numbers. I need to provide harmonics lower than 30 dBc. At first glance it does not look a likely solution. The AD797 will not work well at 10MHz its intended for audio use. The OPA211 is also unsuited, it just doesnt have enough bandwidth. You need to use wide bandwidth opamps (GBW 200MHz or more). Lastly, my customer, the system designer, would now like to be able to add a switch function to the 10 MHz distribution. I will have to check and see if switching of bias current to these two-stage transistor amp circuits can accomplish this function. Jelly-bean analog switches are unlikely, I think, to have the requisite noise and isolation performance. Nothing like hitting a moving target. Clay One way to achieve high isolation using analog switches is to use a T switch configuration. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Date: Thu, 18 Feb 2010 15:22:40 +1300 From: Bruce Griffiths Clay What's the effect of assigning the same label (Vout_2) to the outputs of both output amplifiers as shown in your circuit schematic? Bruce Hi Bruce, Duplication of the Vout_2 net labels (copy and paste is great) did not help the isolation. Neither did the 10 ohm base resistors. Now that the schematic is correct, the base resistors do not ruin the noise performance. Sigh . . . So this circuit looks like it will work well (I also get 100 dB simulated isolation between outputs, as well as noise of less than 2 nV/rtHz). I do believe isolation is important, as there are several subsystems using (and possibly trying to contaminate) the reference. I don't know all the details of each subsystem, and may not be privy to such info. So I can't put a number on the required isolation, but 20 log N applied to spurious within the PLL bandwidth is very unforgiving. The opamp solution is appealing, but I am unsure if it will work. My favorite low-noise parts right now are the TI OPA211, and the Analog AD797. I know the AD797 can be a bit tricky to tame oscillations. They both are probably difficult when configured for more than 10 MHz BW. I will run some simulations, but at 2V p-p into 50 ohms (10 dBm) the required rails would need to be more than 5V, although I have 15V available. I am unsure of the distortion performance at 20 mA peak output drive. Although the AD797 can source more current, neither amp is specified with good distortion numbers at 50 ohm loads. They always show audio (600 ohm) loads for their good THD numbers. I need to provide harmonics lower than 30 dBc. At first glance it does not look a likely solution. Lastly, my customer, the system designer, would now like to be able to add a switch function to the 10 MHz distribution. I will have to check and see if switching of bias current to these two-stage transistor amp circuits can accomplish this function. Jelly-bean analog switches are unlikely, I think, to have the requisite noise and isolation performance. Nothing like hitting a moving target. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution SRS FS700
Using an amplifier with AGC like the MC1590 is a sure method of ensuring high flicker phase noise and a high phase noise floor. The emitter followers by themselves provide insufficient reverse isolation for most applications. Usually one requires 0dB (or perhaps more) gain so that an input preamp with at least 6dB gain is required. The widespread use of inductors precludes this circuit from consideration if one wishes to avoid magnetic components. Another issue for some applications is the relatively high dc emitter current required by the emitter followers to produce the desired RF output level. For some applications this may be an issue. Bruce Bob Camp wrote: Hi Boy, that's an old circuit. I don't think I would want to try to buy the chips in the "front end" of that amp. I also suspect the front end is a bit noisy. The output stuff with the 3904's looks very reproducible though. That end of it certainly is worth looking at. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Electronics and Books Sent: Thursday, February 18, 2010 9:54 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Advice on 10 MHz isolation/distribution SRS FS700 An easy way to make a 10 MHz distribution amplifier is the one from Stanford Research. Manual can be find at : http://www.thinksrs.com/downloads/man.htm Download FS700 The schematics are in the back of the manual. Met vriendelijke groeten Regards electronicsandbo...@yahoo.com http://www.ElectronicsAndBooks.tk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
> Thank you, but I require a circuit without transformers > for reasons of vibration susceptibility. Is the problem wires moving relative to eachother within the transformer or the whole transformer moving relative to the local magnetic field? Does it help to pot things in epoxy or varnish or ...? Years ago, when I took the lid off a small mini-circuits transformer it was just a few turns on a toroid. Something like varnish would be easy to apply. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 6 Date: Thu, 18 Feb 2010 06:53:47 -0800 (PST) Subject: [time-nuts] Advice on 10 MHz isolation/distribution SRS FS700 An easy way to make a 10 MHz distribution amplifier is the one from Stanford Research. Manual can be find at : http://www.thinksrs.com/downloads/man.htm Download FS700 The schematics are in the back of the manual. Met vriendelijke groeten Regards Thank you, but I require a circuit without transformers for reasons of vibration susceptibility. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution SRS FS700
Hi Boy, that's an old circuit. I don't think I would want to try to buy the chips in the "front end" of that amp. I also suspect the front end is a bit noisy. The output stuff with the 3904's looks very reproducible though. That end of it certainly is worth looking at. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Electronics and Books Sent: Thursday, February 18, 2010 9:54 AM To: Discussion of precise time and frequency measurement Subject: [time-nuts] Advice on 10 MHz isolation/distribution SRS FS700 An easy way to make a 10 MHz distribution amplifier is the one from Stanford Research. Manual can be find at : http://www.thinksrs.com/downloads/man.htm Download FS700 The schematics are in the back of the manual. Met vriendelijke groeten Regards electronicsandbo...@yahoo.com http://www.ElectronicsAndBooks.tk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Advice on 10 MHz isolation/distribution SRS FS700
An easy way to make a 10 MHz distribution amplifier is the one from Stanford Research. Manual can be find at : http://www.thinksrs.com/downloads/man.htm Download FS700 The schematics are in the back of the manual. Met vriendelijke groeten Regards electronicsandbo...@yahoo.com http://www.ElectronicsAndBooks.tk ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
Clay What's the effect of assigning the same label (Vout_2) to the outputs of both output amplifiers as shown in your circuit schematic? Bruce life speed wrote: Date: Fri, 12 Feb 2010 15:32:55 -0500 From: Bob Camp Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hi There are a few differences between what you are simulating and the schematics Bruce posted earlier. The collectors of the input stages (q1, q4 and q7) seem have to come unglued from the bases of the output stages. The 95 ohm / 100 nf roll off networks seem to have vanished from the emitters of Q1 and Q7. There are a few other minor things. I suspect that once you get it back to a node-node feedback circuit, the impedance at the splitting point will drop and the isolation will go up quite a bit. Bob Hi Bob, I see I fumbled the mouse, thanks. I had to spend a couple days working on other parts of the design, but I am back at the 10 MHz circuit again. I don't see the RC networks in the emitters of Q1, Q7 in the original schematic (design 3), although I tried them and also with a 1.6K ohm resistor and did not see much difference. I notice that the gain of 2 (6 dB voltage gain) happens in the first stage, and the second stages seem to have an equal amount of loss, which is a reasonable outcome for buffer/isolator circuit. The isolation, while improved, seems to be only 50 dB from Vout_1 to Vout_2. To make this circuit really effective, I think I would have to parallel two Q4/Q1 two-stage amps. Either that, or there are still some mistakes. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution
life speed wrote: Date: Fri, 12 Feb 2010 15:32:55 -0500 From: Bob Camp Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution Hi There are a few differences between what you are simulating and the schematics Bruce posted earlier. The collectors of the input stages (q1, q4 and q7) seem have to come unglued from the bases of the output stages. The 95 ohm / 100 nf roll off networks seem to have vanished from the emitters of Q1 and Q7. There are a few other minor things. I suspect that once you get it back to a node-node feedback circuit, the impedance at the splitting point will drop and the isolation will go up quite a bit. Bob Hi Bob, I see I fumbled the mouse, thanks. I had to spend a couple days working on other parts of the design, but I am back at the 10 MHz circuit again. I don't see the RC networks in the emitters of Q1, Q7 in the original schematic (design 3), although I tried them and also with a 1.6K ohm resistor and did not see much difference. I notice that the gain of 2 (6 dB voltage gain) happens in the first stage, and the second stages seem to have an equal amount of loss, which is a reasonable outcome for buffer/isolator circuit. The isolation, while improved, seems to be only 50 dB from Vout_1 to Vout_2. To make this circuit really effective, I think I would have to parallel two Q4/Q1 two-stage amps. Either that, or there are still some mistakes. Clay Clay Your design is subtly different from the one I posted. The output amplifiers should have about 1K6 from the ZTX5179 emitter to ground not the 95 ohms in series with 1k6 shunted by 100nF. Among other effects your version will exhibit significant distortion unless the current in the output transistors is increased. You've also reduce R9 R10 and R12 to 10 ohms?? This significantly reduces the RF loop gain. In particular the open loop RF gain of the ZTX5179 input device drops to little more than unity. They should be about 1K or so. If you do the analysis correctly you will find that they have little effect on the RF or low frequency noise. My simulations indicate Vout-1 to Vout_2 is around 100dB at 10MHz with the correct values for R9, R10 and R12. This may be slightly optimistic. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
One issue with opamps may be the distortion as few of the high frequency ones have distortion data for more than 2Vpp output. Its can be little optimistic to scale from this if they plot distortion vs input (or output level) or give IP2 and IP3 specs. +10dB in 50 ohms requires 4V pp at the opamp output if the output impedance is matched to the coax. Yes, transformers make the design much easier as it allows use of single transistor CE stages with series transformer feedback to set the output impedance whilst not requiring excessive collector current. At 10MHz the reverse isolation of such a stage can easily be 40dB or so. Bruce Bob Camp wrote: Hi There's also the "throw everything at it" approach. Use something like common base stages for the input and op amps for the outputs. Boost the level into the op amps and pad it at the outputs. You might get what you need. More parts than a pure op amp design, more current. Likely easier to get running. Lots easier to do with a couple transformers in there. Bob On Feb 12, 2010, at 11:02 PM, Bruce Griffiths wrote: The only data available seems to be John Ackermann's measurements on the TADD-1 distribution amp. Unfortunately the opamp used is now obsolete or about to be. Most recent discrete designs (not the HP5087 amplifiers) that I have seen phase noise data for, have significantly lower flicker phase noise and phase noise floors, particularly at 10MHz. Bruce Bob Camp wrote: Hi I have no data, but I believe that in the real application, the phase noise would not be degraded by a good low noise RF op amp / buffer amp. About all you can do for flicker noise data is to look at what they do supply and make an guess based on how the noise rolls up over the range they do show. An op amp circuit would certainly would take fewer parts, and likely more current. No free lunch Bob On Feb 12, 2010, at 10:11 PM, Bruce Griffiths wrote: In the later version the input amplifier has a gain of 2x and the output amplifiers have unity gain. Whilst the reverse isolation (and output impedance) can be improved by using a complementary symmetry emitter follower output stage, one has to ask at that point is the performance gain worth it? One has then in effect built a high open loop gain discrete current feedback opamp that has a somewhat lower input noise than a wide band IC opamp but it0 uses more components. The problem with wide bandwidth opamps is there is very little data available on their RF flicker noise. The measurement data I have seen for an isolation amp using a 2N5179 and a 2N3904 in a Sziklair pair configuration as the input stage indicates that it doesn't seem to noticeably degrade the phase noise of a 10811A. However no residual phase noise measurements have been made. Bruce Bob Camp wrote: Hi Since it's the input stage, it's likely the point most impacted by a higher flicker noise part. That might make one want to look at alternatives. Of course, it's not real clear that a super low noise amp is needed in this case. Bob On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: The series RC to ground keeps the high frequency impedance seen by Q1 and Q7 low so that the base current noise which increases significantly as the frequency approaches the ft of these transistors. However such a series RC network does little to suppress the the rise due to gain peaking. A shunt capacitor from the output stage collectors to the output stage bases is much more effective for the 2x gain stage. Such a capacitor increases the noise for the 1x gain White emitter follower. Using an input transistor with higher bandwidth is more effective in this case. Bruce Bob Camp wrote: Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: life speed wrote: Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's)
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi There's also the "throw everything at it" approach. Use something like common base stages for the input and op amps for the outputs. Boost the level into the op amps and pad it at the outputs. You might get what you need. More parts than a pure op amp design, more current. Likely easier to get running. Lots easier to do with a couple transformers in there. Bob On Feb 12, 2010, at 11:02 PM, Bruce Griffiths wrote: > The only data available seems to be John Ackermann's measurements on the > TADD-1 distribution amp. > Unfortunately the opamp used is now obsolete or about to be. > Most recent discrete designs (not the HP5087 amplifiers) that I have seen > phase noise data for, have significantly lower flicker phase noise and phase > noise floors, particularly at 10MHz. > > Bruce > > Bob Camp wrote: >> Hi >> >> I have no data, but I believe that in the real application, the phase noise >> would not be degraded by a good low noise RF op amp / buffer amp. About all >> you can do for flicker noise data is to look at what they do supply and make >> an guess based on how the noise rolls up over the range they do show. >> >> An op amp circuit would certainly would take fewer parts, and likely more >> current. No free lunch >> >> Bob >> >> >> On Feb 12, 2010, at 10:11 PM, Bruce Griffiths wrote: >> >> >>> In the later version the input amplifier has a gain of 2x and the output >>> amplifiers have unity gain. >>> >>> Whilst the reverse isolation (and output impedance) can be improved by >>> using a complementary symmetry emitter follower output stage, one has to >>> ask at that point is the performance gain worth it? >>> >>> One has then in effect built a high open loop gain discrete current >>> feedback opamp that has a somewhat lower input noise than a wide band IC >>> opamp but it0 uses more components. >>> >>> The problem with wide bandwidth opamps is there is very little data >>> available on their RF flicker noise. >>> >>> The measurement data I have seen for an isolation amp using a 2N5179 and a >>> 2N3904 in a Sziklair pair configuration as the input stage indicates that >>> it doesn't seem to noticeably degrade the phase noise of a 10811A. However >>> no residual phase noise measurements have been made. >>> >>> Bruce >>> >>> Bob Camp wrote: >>> Hi Since it's the input stage, it's likely the point most impacted by a higher flicker noise part. That might make one want to look at alternatives. Of course, it's not real clear that a super low noise amp is needed in this case. Bob On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: > The series RC to ground keeps the high frequency impedance seen by Q1 and > Q7 low so that the base current noise which increases significantly as > the frequency approaches the ft of these transistors. > However such a series RC network does little to suppress the the rise due > to gain peaking. > A shunt capacitor from the output stage collectors to the output stage > bases is much more effective for the 2x gain stage. > > Such a capacitor increases the noise for the 1x gain White emitter > follower. > Using an input transistor with higher bandwidth is more effective in this > case. > > Bruce > > Bob Camp wrote: > > >> Hi >> >> I suspect your noise spike can be cured by a series R-C to ground from >> the junction of Q1 base, Q7 base and all the other stuff. Something is >> going to have to set a high frequency roll off. With no coils some combo >> of R and C is going to have to do it. >> >> You might also try returning all of the upper emitter resistor bypasses >> to ground rather than B+. Another alternative would be emitter to >> emitter bypass as shown on the JPL schematic. I'm guessing both would >> improve isolation in a real world circuit. >> >> Bob >> >> >> On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: >> >> >> >> >>> life speed wrote: >>> >>> >>> Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
The only data available seems to be John Ackermann's measurements on the TADD-1 distribution amp. Unfortunately the opamp used is now obsolete or about to be. Most recent discrete designs (not the HP5087 amplifiers) that I have seen phase noise data for, have significantly lower flicker phase noise and phase noise floors, particularly at 10MHz. Bruce Bob Camp wrote: Hi I have no data, but I believe that in the real application, the phase noise would not be degraded by a good low noise RF op amp / buffer amp. About all you can do for flicker noise data is to look at what they do supply and make an guess based on how the noise rolls up over the range they do show. An op amp circuit would certainly would take fewer parts, and likely more current. No free lunch Bob On Feb 12, 2010, at 10:11 PM, Bruce Griffiths wrote: In the later version the input amplifier has a gain of 2x and the output amplifiers have unity gain. Whilst the reverse isolation (and output impedance) can be improved by using a complementary symmetry emitter follower output stage, one has to ask at that point is the performance gain worth it? One has then in effect built a high open loop gain discrete current feedback opamp that has a somewhat lower input noise than a wide band IC opamp but it0 uses more components. The problem with wide bandwidth opamps is there is very little data available on their RF flicker noise. The measurement data I have seen for an isolation amp using a 2N5179 and a 2N3904 in a Sziklair pair configuration as the input stage indicates that it doesn't seem to noticeably degrade the phase noise of a 10811A. However no residual phase noise measurements have been made. Bruce Bob Camp wrote: Hi Since it's the input stage, it's likely the point most impacted by a higher flicker noise part. That might make one want to look at alternatives. Of course, it's not real clear that a super low noise amp is needed in this case. Bob On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: The series RC to ground keeps the high frequency impedance seen by Q1 and Q7 low so that the base current noise which increases significantly as the frequency approaches the ft of these transistors. However such a series RC network does little to suppress the the rise due to gain peaking. A shunt capacitor from the output stage collectors to the output stage bases is much more effective for the 2x gain stage. Such a capacitor increases the noise for the 1x gain White emitter follower. Using an input transistor with higher bandwidth is more effective in this case. Bruce Bob Camp wrote: Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: life speed wrote: Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay Clay One can always use a smaller resistor in series with an RF choke that has no resonances in the region of interest. The attached circuit schematic illustrates one meth
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi I have no data, but I believe that in the real application, the phase noise would not be degraded by a good low noise RF op amp / buffer amp. About all you can do for flicker noise data is to look at what they do supply and make an guess based on how the noise rolls up over the range they do show. An op amp circuit would certainly would take fewer parts, and likely more current. No free lunch Bob On Feb 12, 2010, at 10:11 PM, Bruce Griffiths wrote: > In the later version the input amplifier has a gain of 2x and the output > amplifiers have unity gain. > > Whilst the reverse isolation (and output impedance) can be improved by using > a complementary symmetry emitter follower output stage, one has to ask at > that point is the performance gain worth it? > > One has then in effect built a high open loop gain discrete current feedback > opamp that has a somewhat lower input noise than a wide band IC opamp but it0 > uses more components. > > The problem with wide bandwidth opamps is there is very little data available > on their RF flicker noise. > > The measurement data I have seen for an isolation amp using a 2N5179 and a > 2N3904 in a Sziklair pair configuration as the input stage indicates that it > doesn't seem to noticeably degrade the phase noise of a 10811A. However no > residual phase noise measurements have been made. > > Bruce > > Bob Camp wrote: >> Hi >> >> Since it's the input stage, it's likely the point most impacted by a higher >> flicker noise part. That might make one want to look at alternatives. >> >> Of course, it's not real clear that a super low noise amp is needed in this >> case. >> >> Bob >> >> On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: >> >> >>> The series RC to ground keeps the high frequency impedance seen by Q1 and >>> Q7 low so that the base current noise which increases significantly as the >>> frequency approaches the ft of these transistors. >>> However such a series RC network does little to suppress the the rise due >>> to gain peaking. >>> A shunt capacitor from the output stage collectors to the output stage >>> bases is much more effective for the 2x gain stage. >>> >>> Such a capacitor increases the noise for the 1x gain White emitter follower. >>> Using an input transistor with higher bandwidth is more effective in this >>> case. >>> >>> Bruce >>> >>> Bob Camp wrote: >>> Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: > life speed wrote: > > >> Message: 2 >> Date: Fri, 12 Feb 2010 12:12:29 +1300 >> From: Bruce Griffiths >> The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier >> sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of >> the output amplifiers. >> >> The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that >> drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 >> respectively) each with a gain of 2x (6dB). >> The input amplifier is essentially a white emitter follower with a >> complementary symmetry output stage (shown in transistor electronics >> books from the 1960's) where an input CE transistor drives a >> complementary pair of CE transistors with feedback from the common >> collectors of the 2 output transistors to the input transistor emitter. >> In effect its merely a very simple unity gain opamp. Its usually best to >> ensure that the CE output stage pair provide the dominant open loop >> pole. Using a higher ft (2 to 3x) input transistor than the output pair >> is the usual way of ensuring this. >> >> Well, it is so obvious now that you explained it. I had forgot about >> the need for one of the stages to set the dominant pole. >> >> Thanks Bruce and Bob for sharing your obsession with frequency controls. >> I'll simulate this further, and have a prototype PCB built within the >> next few weeks. I did notice the resistor at the base of Q2,5,8 is >> responsible for significant noise. I'll have to be careful with the >> bias circuit. >> >> Have to get busy for now, but I will report back with results. >> >> Best regards, >> >> Clay >> >> >> >> > Clay > > One can always use a smaller resistor in se
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
In the later version the input amplifier has a gain of 2x and the output amplifiers have unity gain. Whilst the reverse isolation (and output impedance) can be improved by using a complementary symmetry emitter follower output stage, one has to ask at that point is the performance gain worth it? One has then in effect built a high open loop gain discrete current feedback opamp that has a somewhat lower input noise than a wide band IC opamp but it0 uses more components. The problem with wide bandwidth opamps is there is very little data available on their RF flicker noise. The measurement data I have seen for an isolation amp using a 2N5179 and a 2N3904 in a Sziklair pair configuration as the input stage indicates that it doesn't seem to noticeably degrade the phase noise of a 10811A. However no residual phase noise measurements have been made. Bruce Bob Camp wrote: Hi Since it's the input stage, it's likely the point most impacted by a higher flicker noise part. That might make one want to look at alternatives. Of course, it's not real clear that a super low noise amp is needed in this case. Bob On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: The series RC to ground keeps the high frequency impedance seen by Q1 and Q7 low so that the base current noise which increases significantly as the frequency approaches the ft of these transistors. However such a series RC network does little to suppress the the rise due to gain peaking. A shunt capacitor from the output stage collectors to the output stage bases is much more effective for the 2x gain stage. Such a capacitor increases the noise for the 1x gain White emitter follower. Using an input transistor with higher bandwidth is more effective in this case. Bruce Bob Camp wrote: Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: life speed wrote: Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay Clay One can always use a smaller resistor in series with an RF choke that has no resonances in the region of interest. The attached circuit schematic illustrates one method of biasing for which the emitter current of the input transistor can be largely sourced via a resistor rather than from the collector current of the npn output transistor. My simulations indicate if that one uses 2N3904's as the input device rather than the 2N5179's shown that there is an enormous peak in the output noise spectrum at around 150-200MHz or so. When the 2N5179 is used this noise peak is much smaller and broader. Use the same bias divider bypassing techniques that NIST used including the use of electrolytic caps (they used tantalum caps) to reduce the low frequency noise from the power supply. The ceramic bypass caps ensure sufficient isolation between stages. Simulating the reverse isolation with realistic component parasitics is always informative/useful. Bruce ___ time-nuts mailing list -- time
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi Since it's the input stage, it's likely the point most impacted by a higher flicker noise part. That might make one want to look at alternatives. Of course, it's not real clear that a super low noise amp is needed in this case. Bob On Feb 12, 2010, at 8:46 PM, Bruce Griffiths wrote: > The series RC to ground keeps the high frequency impedance seen by Q1 and Q7 > low so that the base current noise which increases significantly as the > frequency approaches the ft of these transistors. > However such a series RC network does little to suppress the the rise due to > gain peaking. > A shunt capacitor from the output stage collectors to the output stage bases > is much more effective for the 2x gain stage. > > Such a capacitor increases the noise for the 1x gain White emitter follower. > Using an input transistor with higher bandwidth is more effective in this > case. > > Bruce > > Bob Camp wrote: >> Hi >> >> I suspect your noise spike can be cured by a series R-C to ground from the >> junction of Q1 base, Q7 base and all the other stuff. Something is going to >> have to set a high frequency roll off. With no coils some combo of R and C >> is going to have to do it. >> >> You might also try returning all of the upper emitter resistor bypasses to >> ground rather than B+. Another alternative would be emitter to emitter >> bypass as shown on the JPL schematic. I'm guessing both would improve >> isolation in a real world circuit. >> >> Bob >> >> >> On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: >> >> >>> life speed wrote: >>> Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay >>> Clay >>> >>> One can always use a smaller resistor in series with an RF choke that has >>> no resonances in the region of interest. >>> >>> The attached circuit schematic illustrates one method of biasing for which >>> the emitter current of the input transistor can be largely sourced via a >>> resistor rather than from the collector current of the npn output >>> transistor. >>> >>> My simulations indicate if that one uses 2N3904's as the input device >>> rather than the 2N5179's shown that there is an enormous peak in the output >>> noise spectrum at around 150-200MHz or so. >>> When the 2N5179 is used this noise peak is much smaller and broader. >>> >>> Use the same bias divider bypassing techniques that NIST used including the >>> use of electrolytic caps (they used tantalum caps) to reduce the low >>> frequency noise from the power supply. The ceramic bypass caps ensure >>> sufficient isolation between stages. >>> Simulating the reverse isolation with realistic component parasitics is >>> always informative/useful. >>> >>> Bruce >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
The series RC to ground keeps the high frequency impedance seen by Q1 and Q7 low so that the base current noise which increases significantly as the frequency approaches the ft of these transistors. However such a series RC network does little to suppress the the rise due to gain peaking. A shunt capacitor from the output stage collectors to the output stage bases is much more effective for the 2x gain stage. Such a capacitor increases the noise for the 1x gain White emitter follower. Using an input transistor with higher bandwidth is more effective in this case. Bruce Bob Camp wrote: Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: life speed wrote: Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay Clay One can always use a smaller resistor in series with an RF choke that has no resonances in the region of interest. The attached circuit schematic illustrates one method of biasing for which the emitter current of the input transistor can be largely sourced via a resistor rather than from the collector current of the npn output transistor. My simulations indicate if that one uses 2N3904's as the input device rather than the 2N5179's shown that there is an enormous peak in the output noise spectrum at around 150-200MHz or so. When the 2N5179 is used this noise peak is much smaller and broader. Use the same bias divider bypassing techniques that NIST used including the use of electrolytic caps (they used tantalum caps) to reduce the low frequency noise from the power supply. The ceramic bypass caps ensure sufficient isolation between stages. Simulating the reverse isolation with realistic component parasitics is always informative/useful. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: I seem to not be accomplishing much isolation from output to input, as well as output to output. Have I fumbled PSPICE somehow? For each simulation, Vac was set separately, with V1=0.707V at the input, while V6=0V at the output (sim1). Then V1=0V, and V6=0.01V (sim2). Clay Your schematic shows no connection from the collector of the npn input transistor to the base of the pnp output transistor in any of the stages. There should be a direct connection from Q4 collector to Q6 base Q1 collector to Q3 base Q7 collector to Q9 base It usually pays to check the dc voltages and currents before beginning an AC or transient analysis to see if they are what you would expect. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi There are a few differences between what you are simulating and the schematics Bruce posted earlier. The collectors of the input stages (q1, q4 and q7) seem have to come unglued from the bases of the output stages. The 95 ohm / 100 nf roll off networks seem to have vanished from the emitters of Q1 and Q7. There are a few other minor things. I suspect that once you get it back to a node-node feedback circuit, the impedance at the splitting point will drop and the isolation will go up quite a bit. Bob On Feb 12, 2010, at 2:57 PM, life speed wrote: > I seem to not be accomplishing much isolation from output to input, as well > as output to output. Have I fumbled PSPICE somehow? For each simulation, > Vac was set separately, with V1=0.707V at the input, while V6=0V at the > output (sim1). Then V1=0V, and V6=0.01V (sim2). > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
I seem to not be accomplishing much isolation from output to input, as well as output to output. Have I fumbled PSPICE somehow? For each simulation, Vac was set separately, with V1=0.707V at the input, while V6=0V at the output (sim1). Then V1=0V, and V6=0.01V (sim2). clay_schem1.pdf Description: Adobe PDF document clay_sim1.pdf Description: Adobe PDF document clay_sim2.pdf Description: Adobe PDF document ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi It's the one that Bruce posted earlier. Actually it showed up as a double post for some odd reason. I opened the whole "hybrid" thing by referring to it. Bob On Feb 12, 2010, at 11:32 AM, life speed wrote: > Message: 3 > Date: Thu, 11 Feb 2010 23:02:30 -0500 > From: Bob Camp > Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution > (Clay) > > Hi > > I suspect your noise spike can be cured by a series R-C to ground from the > junction of Q1 base, Q7 base and all the other stuff. Something is going to > have to set a high frequency roll off. With no coils some combo of R and C is > going to have to do it. > > You might also try returning all of the upper emitter resistor bypasses to > ground rather than B+. Another alternative would be emitter to emitter bypass > as shown on the JPL schematic. I'm guessing both would improve isolation in a > real world circuit. > > Bob > > Hi Bob, > > Please provide a link to the JPL schematic. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 3 Date: Thu, 11 Feb 2010 23:02:30 -0500 From: Bob Camp Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob Hi Bob, Please provide a link to the JPL schematic. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi I suspect your noise spike can be cured by a series R-C to ground from the junction of Q1 base, Q7 base and all the other stuff. Something is going to have to set a high frequency roll off. With no coils some combo of R and C is going to have to do it. You might also try returning all of the upper emitter resistor bypasses to ground rather than B+. Another alternative would be emitter to emitter bypass as shown on the JPL schematic. I'm guessing both would improve isolation in a real world circuit. Bob On Feb 11, 2010, at 8:34 PM, Bruce Griffiths wrote: > life speed wrote: >> Message: 2 >> Date: Fri, 12 Feb 2010 12:12:29 +1300 >> From: Bruce Griffiths >> The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier >> sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of >> the output amplifiers. >> >> The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that >> drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 >> respectively) each with a gain of 2x (6dB). >> The input amplifier is essentially a white emitter follower with a >> complementary symmetry output stage (shown in transistor electronics >> books from the 1960's) where an input CE transistor drives a >> complementary pair of CE transistors with feedback from the common >> collectors of the 2 output transistors to the input transistor emitter. >> In effect its merely a very simple unity gain opamp. Its usually best to >> ensure that the CE output stage pair provide the dominant open loop >> pole. Using a higher ft (2 to 3x) input transistor than the output pair >> is the usual way of ensuring this. >> >> Well, it is so obvious now that you explained it. I had forgot about the >> need for one of the stages to set the dominant pole. >> >> Thanks Bruce and Bob for sharing your obsession with frequency controls. >> I'll simulate this further, and have a prototype PCB built within the next >> few weeks. I did notice the resistor at the base of Q2,5,8 is responsible >> for significant noise. I'll have to be careful with the bias circuit. >> >> Have to get busy for now, but I will report back with results. >> >> Best regards, >> >> Clay >> >> > Clay > > One can always use a smaller resistor in series with an RF choke that has no > resonances in the region of interest. > > The attached circuit schematic illustrates one method of biasing for which > the emitter current of the input transistor can be largely sourced via a > resistor rather than from the collector current of the npn output transistor. > > My simulations indicate if that one uses 2N3904's as the input device rather > than the 2N5179's shown that there is an enormous peak in the output noise > spectrum at around 150-200MHz or so. > When the 2N5179 is used this noise peak is much smaller and broader. > > Use the same bias divider bypassing techniques that NIST used including the > use of electrolytic caps (they used tantalum caps) to reduce the low > frequency noise from the power supply. The ceramic bypass caps ensure > sufficient isolation between stages. > Simulating the reverse isolation with realistic component parasitics is > always informative/useful. > > Bruce > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay Clay One can always use a smaller resistor in series with an RF choke that has no resonances in the region of interest. The attached circuit schematic illustrates one method of biasing for which the emitter current of the input transistor can be largely sourced via a resistor rather than from the collector current of the npn output transistor. My simulations indicate if that one uses 2N3904's as the input device rather than the 2N5179's shown that there is an enormous peak in the output noise spectrum at around 150-200MHz or so. When the 2N5179 is used this noise peak is much smaller and broader. Use the same bias divider bypassing techniques that NIST used including the use of electrolytic caps (they used tantalum caps) to reduce the low frequency noise from the power supply. The ceramic bypass caps ensure sufficient isolation between stages. Simulating the reverse isolation with realistic component parasitics is always informative/useful. Bruce <>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 2 Date: Fri, 12 Feb 2010 12:12:29 +1300 From: Bruce Griffiths The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. Well, it is so obvious now that you explained it. I had forgot about the need for one of the stages to set the dominant pole. Thanks Bruce and Bob for sharing your obsession with frequency controls. I'll simulate this further, and have a prototype PCB built within the next few weeks. I did notice the resistor at the base of Q2,5,8 is responsible for significant noise. I'll have to be careful with the bias circuit. Have to get busy for now, but I will report back with results. Best regards, Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
life speed wrote: Message: 1 Date: Thu, 11 Feb 2010 12:42:27 -0500 From: "Bob Camp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Hi I really should learn how to read the whole message Cancel the second request on vibe info. - The gotcha with vibration isolation is that it will stop working at some lower frequency. Aircraft have plenty of vibration running around at low frequencies. That all sounds like bad news. Actually it's not. Since the phase noise isn't going to be all that good below the cutoff of the isolation, the amp doesn't need to sweat super low phase noise very close in. That can make the choice of transistors easier. Bob Thanks Bob. I am aware of all the vibe issues, low freq corner, resonance peaking, etc. And yes, I have seen the Wenzel spreadsheet. Wenzel is a good resource for info. These issues have all been looked into. The phase noise numbers are what is predicted under vibration (10 Hz number might degrade a few dB). The amplifier will need to be better. 1 Hz< -100 dBc/Hz 10 Hz< -125 dBc/Hz 100 Hz< -140 dBc/Hz 1 KHz< -150 dBc/Hz 10 KHz< -155 dBc/Hz Are you aware of any bipolars that are better than others in 1/F noise performance? I noticed Gerhard Hoffman's design used BFG198 and BFG31, although those are SOT223 parts, which are somewhat large for my design. If I'm not mistake 'low saturation' correlates to low 1/F noise . . . I simulated the circuit with two outputs you sent in .GIF format. It appears to be tuned to a somewhat lower frequency than 10 MHz, perhaps 10 KHz to 1 MHz where the overall gain is near 0 dB, and the phase shift is near 0. I am using MMBT3904 transistors with Ft near 250 MHz. Perhaps that is the issue. Clay The input npn transistors for each stage have a collector current of around 2mA the ft of a 2N3904 is relatively low at such currents. Use a transistor with a higher ft (at 2mA) like a 2N5179 or its SMT equivalent for the input transistor. Increasing the collector current of the input transistor will also help. There will be a nonzero phase shift at 10MHz due to the finite bandwidth of the transistors used. To a first approximation the phase shift is equivalent to a fixed delay. This phase shift is relatively unimportant and should have a low tempco. The gain of the amplifier is more important. LTSpice predicts an output distortion below -40dBc with a 10MHz input and +10dBm output. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi If you dig into the data on some of the conventional isolation amp designs, their noise floors are down around -150 dbc / Hz in the 1 to 10 Hz range. Taking out the transformers and going to a push pull output might bump things up into the -140's in the 1 to 10 Hz range. Essentially you are building the "old NIST amp" in the paper: http://tf.boulder.nist.gov/general/pdf/498.pdf That's not to say that the old NIST amp is the best way to go, only that the close in noise performance should be similar to that amplifier. Simple answer = the 2N3904 / 2N3906 should be fine for what you are trying to do. You can find lower noise parts that don't have enough Ft to be useful. You can also find RF parts that have great Ft, great broadband noise, and lousy flicker noise. Bob On Feb 11, 2010, at 5:57 PM, life speed wrote: > Message: 1 > Date: Thu, 11 Feb 2010 12:42:27 -0500 > From: "Bob Camp" > Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution > amplifier(Clay) > > Hi > > I really should learn how to read the whole message > > > > Cancel the second request on vibe info. > > - > > The gotcha with vibration isolation is that it will stop working at some > lower frequency. Aircraft have plenty of vibration running around at low > frequencies. > > That all sounds like bad news. Actually it's not. Since the phase noise > isn't going to be all that good below the cutoff of the isolation, the amp > doesn't need to sweat super low phase noise very close in. That can make the > choice of transistors easier. > > Bob > > Thanks Bob. I am aware of all the vibe issues, low freq corner, resonance > peaking, etc. And yes, I have seen the Wenzel spreadsheet. Wenzel is a good > resource for info. These issues have all been looked into. The phase noise > numbers are what is predicted under vibration (10 Hz number might degrade a > few dB). The amplifier will need to be better. > > 1 Hz < -100 dBc/Hz > 10 Hz < -125 dBc/Hz > 100 Hz < -140 dBc/Hz > 1 KHz < -150 dBc/Hz > 10 KHz < -155 dBc/Hz > > Are you aware of any bipolars that are better than others in 1/F noise > performance? I noticed Gerhard Hoffman's design used BFG198 and BFG31, > although those are SOT223 parts, which are somewhat large for my design. If > I'm not mistake 'low saturation' correlates to low 1/F noise . . . > > I simulated the circuit with two outputs you sent in .GIF format. It appears > to be tuned to a somewhat lower frequency than 10 MHz, perhaps 10 KHz to 1 > MHz where the overall gain is near 0 dB, and the phase shift is near 0. I am > using MMBT3904 transistors with Ft near 250 MHz. Perhaps that is the issue. > > Clay > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier (Clay)
life speed wrote: Message: 2 Date: Thu, 11 Feb 2010 07:54:40 -0500 From: Bob Camp Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob Message: 6 Date: Fri, 12 Feb 2010 04:09:08 +1300 From: Bruce Griffiths Yes implementing an exact copy without using a hybrid would be difficult. However for 10MHz use, its probably not too difficult since that isolation amplifier is intended for a 100MHz signal and the requirement is for 10MHz operation. If the transistor ft's are reduced by a factor of 10 or so it shouldn't be too much of a problem. At 10MHz 2N3906 and 2N3904 transistors should suffice. Bruce Hi Bruce, Thanks for the tips. I've been trying to follow the circuits you posted. The first one, in .PNG format, looks like a common-base complementary (push-pull) stage followed by a common-emitter complementary stage to provide the low impedance output. The second circut in .GIF fromat I am having a bit more trouble understanding. I see that V6, 7 are at the outputs and just used for to simulate isolation. V1 is the input? V1 is indeed the input. Are Q5,6 used to set the bias point of Q4? Are V2,3,4 just there to bias the transistors for simulation purposes, and this would be accomplished another way in a real implementation? The output (collectors of Q5, Q6 emitter of Q4) of the input amplifier sets the dc voltage at the inputs ( Q1 base, Q7 base respectively) of the output amplifiers. The circuit consists of a unity gain input amplifier (Q4, Q5, Q6) that drives a pair of output amplifiers (Q1, Q2, Q3 and Q7, Q8, Q9 respectively) each with a gain of 2x (6dB). The input amplifier is essentially a white emitter follower with a complementary symmetry output stage (shown in transistor electronics books from the 1960's) where an input CE transistor drives a complementary pair of CE transistors with feedback from the common collectors of the 2 output transistors to the input transistor emitter. In effect its merely a very simple unity gain opamp. Its usually best to ensure that the CE output stage pair provide the dominant open loop pole. Using a higher ft (2 to 3x) input transistor than the output pair is the usual way of ensuring this. The output stages can be viewed as simple 3 transistor current feedback opamps with a nominal gain of about 2x (6dB). The output stage gain being adjusted in this case for an overall gain of 0dB when driving a 50 ohm load. The 47 ohm resistors in series with the outputs match the output impedance to that of a 50 ohm cable. With a closed loop gain of 2 ensuring that the ft of the input transistor is greater (>2x) than that of the output stage transistors is less critical. Both output transistors contribute to the RF output signal. The npn output transistor are also used to set the operating current of the output stage. The resistor in series with the npn output transistor emitter is bypassed for RF so that the full gain of this transistor is available at RF. Using a complementary symmetry output stage allows the dc collector current of the output stage to be reduced to about half that required if the npn output stage transistor were merely acting as a fixed current source. Yes the 1.7V dc sources are only included for the simulation. I just wanted to illustrate the principles without getting into too much detail in that post. In practice one could either use a LED or a resistive voltage divider buffered by a pnp emitter follower (either method provides a degree of temperature compensation for Vbe tempco of the npn output transistors) . Either one uses independent biasing for each npn CE device, or elaborate RC filtering (at least an independent 2 stage filter for each transistor ) to avoid degrading the RF reverse isolation via the RF impedance of the common 1.7V bias circuit. As noted in a later post, using unity gain output amplifiers with a 2x gain input stage allows the total dc current to be reduced below that of when the input stage has unity gain and the output stages have voltage gain of 2X. Please explain the comment regarding the hybrid. Are you and Bob referring to a 90 degree hybrid coupler, or other quadrature method like a transmission line transformer? What would be the purpose of such a device? Would it be too much to ask for a description of these circuits? I suppose we all have our areas of expertise, and transistor isolation amps are somewhat new to me. Thanks again for all the help. Clay PS - yes, the OCXO is vibe isolated. And you are certainly correct about long runs of single-ended coax being susceptible to noise. The system designer has accepted this and allowed for some degradation. But I will look into the practicality of implementing a differential line for the long run of 10 MHz cable. However, I will still need to implement traditional coaxial isolated 10 MHz outputs. Bruce ___
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 1 Date: Thu, 11 Feb 2010 12:42:27 -0500 From: "Bob Camp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Hi I really should learn how to read the whole message Cancel the second request on vibe info. - The gotcha with vibration isolation is that it will stop working at some lower frequency. Aircraft have plenty of vibration running around at low frequencies. That all sounds like bad news. Actually it's not. Since the phase noise isn't going to be all that good below the cutoff of the isolation, the amp doesn't need to sweat super low phase noise very close in. That can make the choice of transistors easier. Bob Thanks Bob. I am aware of all the vibe issues, low freq corner, resonance peaking, etc. And yes, I have seen the Wenzel spreadsheet. Wenzel is a good resource for info. These issues have all been looked into. The phase noise numbers are what is predicted under vibration (10 Hz number might degrade a few dB). The amplifier will need to be better. 1 Hz < -100 dBc/Hz 10 Hz < -125 dBc/Hz 100 Hz < -140 dBc/Hz 1 KHz < -150 dBc/Hz 10 KHz < -155 dBc/Hz Are you aware of any bipolars that are better than others in 1/F noise performance? I noticed Gerhard Hoffman's design used BFG198 and BFG31, although those are SOT223 parts, which are somewhat large for my design. If I'm not mistake 'low saturation' correlates to low 1/F noise . . . I simulated the circuit with two outputs you sent in .GIF format. It appears to be tuned to a somewhat lower frequency than 10 MHz, perhaps 10 KHz to 1 MHz where the overall gain is near 0 dB, and the phase shift is near 0. I am using MMBT3904 transistors with Ft near 250 MHz. Perhaps that is the issue. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Hi There's a quick and dirty phase noise to vibration spread sheet here: http://www.wenzel.com/documents/spread.htm You may want to plug in some numbers and see what you get. A lot is going to depend on your oscillator's sensitivity, vibration isolation setup, and the operational (as opposed to survival) vibration profile. The added noise may take you into an area where a high speed op-amp based design is quite adequate. Some topologies might also help with generating a balanced output feed. One downside to op amps would be power. Most of the circuits that have been tossed around are already a bit outside the original budget you came up with. That may or may not be significant in your case. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Thursday, February 11, 2010 1:05 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay) Message: 6 Date: Thu, 11 Feb 2010 12:38:58 -0500 From: "Bob Camp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Hi I'll grab the one on the hybrid. In this case hybrid is referring to a construction technique. The circuit shown was originally fabricated in a TO-8 package with chip and wire construction. It was certainly made using thin film or thick film technology on a substrate. Based on the number of components and size of the part, I'd bet that the resistors were printed on the substrate. When you are using that kind of construction approach there are some good things that happen and some bad things. The circuit topology is modified to work with the construction technique. In this case the Ft's of the transistors are quite high. Taming them on a substrate (alumina or glass) is a very different thing than doing it on a PC board. --- Is your OCXO vibration isolated? -- Bob OK, you're talking about chip-and-wire, or hybrid construction. Really, at 10 MHz, that seems unnecessary. Of course, PCB construction will introduce some parasitics. Transistors with lower Ft could be used. Additionally, there are bandwidth-limiting techniques like adding feedback capacitance. I suppose this would come at the expense of high-frequency isolation. But for my application isolation is important in the 10's of MHz, not much higher. Having built a couple transistor circuits over the years, I am aware of what can happen when a transistor in a low frequency circuit has an Ft of multiple GHz. Usually oscillations. I imagine a high Ft enables the isolation to extend to very high frequencies. Yes the OCXO is vibration isolated or the system wouldn't produce good phase noise in operation. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution (Clay)
Message: 6 Date: Thu, 11 Feb 2010 12:38:58 -0500 From: "Bob Camp" Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Hi I'll grab the one on the hybrid. In this case hybrid is referring to a construction technique. The circuit shown was originally fabricated in a TO-8 package with chip and wire construction. It was certainly made using thin film or thick film technology on a substrate. Based on the number of components and size of the part, I'd bet that the resistors were printed on the substrate. When you are using that kind of construction approach there are some good things that happen and some bad things. The circuit topology is modified to work with the construction technique. In this case the Ft's of the transistors are quite high. Taming them on a substrate (alumina or glass) is a very different thing than doing it on a PC board. --- Is your OCXO vibration isolated? -- Bob OK, you're talking about chip-and-wire, or hybrid construction. Really, at 10 MHz, that seems unnecessary. Of course, PCB construction will introduce some parasitics. Transistors with lower Ft could be used. Additionally, there are bandwidth-limiting techniques like adding feedback capacitance. I suppose this would come at the expense of high-frequency isolation. But for my application isolation is important in the 10's of MHz, not much higher. Having built a couple transistor circuits over the years, I am aware of what can happen when a transistor in a low frequency circuit has an Ft of multiple GHz. Usually oscillations. I imagine a high Ft enables the isolation to extend to very high frequencies. Yes the OCXO is vibration isolated or the system wouldn't produce good phase noise in operation. Clay ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay)
Hi I really should learn how to read the whole message Cancel the second request on vibe info. - The gotcha with vibration isolation is that it will stop working at some lower frequency. Aircraft have plenty of vibration running around at low frequencies. That all sounds like bad news. Actually it's not. Since the phase noise isn't going to be all that good below the cutoff of the isolation, the amp doesn't need to sweat super low phase noise very close in. That can make the choice of transistors easier. Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Thursday, February 11, 2010 12:27 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Message: 2 Date: Thu, 11 Feb 2010 07:54:40 -0500 From: Bob Camp Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob Message: 6 Date: Fri, 12 Feb 2010 04:09:08 +1300 From: Bruce Griffiths Yes implementing an exact copy without using a hybrid would be difficult. However for 10MHz use, its probably not too difficult since that isolation amplifier is intended for a 100MHz signal and the requirement is for 10MHz operation. If the transistor ft's are reduced by a factor of 10 or so it shouldn't be too much of a problem. At 10MHz 2N3906 and 2N3904 transistors should suffice. Bruce Hi Bruce, Thanks for the tips. I've been trying to follow the circuits you posted. The first one, in .PNG format, looks like a common-base complementary (push-pull) stage followed by a common-emitter complementary stage to provide the low impedance output. The second circut in .GIF fromat I am having a bit more trouble understanding. I see that V6, 7 are at the outputs and just used for to simulate isolation. V1 is the input? Are Q5,6 used to set the bias point of Q4? Are V2,3,4 just there to bias the transistors for simulation purposes, and this would be accomplished another way in a real implementation? Please explain the comment regarding the hybrid. Are you and Bob referring to a 90 degree hybrid coupler, or other quadrature method like a transmission line transformer? What would be the purpose of such a device? Would it be too much to ask for a description of these circuits? I suppose we all have our areas of expertise, and transistor isolation amps are somewhat new to me. Thanks again for all the help. Clay PS - yes, the OCXO is vibe isolated. And you are certainly correct about long runs of single-ended coax being susceptible to noise. The system designer has accepted this and allowed for some degradation. But I will look into the practicality of implementing a differential line for the long run of 10 MHz cable. However, I will still need to implement traditional coaxial isolated 10 MHz outputs. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay)
Hi I'll grab the one on the hybrid. In this case hybrid is referring to a construction technique. The circuit shown was originally fabricated in a TO-8 package with chip and wire construction. It was certainly made using thin film or thick film technology on a substrate. Based on the number of components and size of the part, I'd bet that the resistors were printed on the substrate. When you are using that kind of construction approach there are some good things that happen and some bad things. The circuit topology is modified to work with the construction technique. In this case the Ft's of the transistors are quite high. Taming them on a substrate (alumina or glass) is a very different thing than doing it on a PC board. --- Is your OCXO vibration isolated? -- Bob -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of life speed Sent: Thursday, February 11, 2010 12:27 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier(Clay) Message: 2 Date: Thu, 11 Feb 2010 07:54:40 -0500 From: Bob Camp Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob Message: 6 Date: Fri, 12 Feb 2010 04:09:08 +1300 From: Bruce Griffiths Yes implementing an exact copy without using a hybrid would be difficult. However for 10MHz use, its probably not too difficult since that isolation amplifier is intended for a 100MHz signal and the requirement is for 10MHz operation. If the transistor ft's are reduced by a factor of 10 or so it shouldn't be too much of a problem. At 10MHz 2N3906 and 2N3904 transistors should suffice. Bruce Hi Bruce, Thanks for the tips. I've been trying to follow the circuits you posted. The first one, in .PNG format, looks like a common-base complementary (push-pull) stage followed by a common-emitter complementary stage to provide the low impedance output. The second circut in .GIF fromat I am having a bit more trouble understanding. I see that V6, 7 are at the outputs and just used for to simulate isolation. V1 is the input? Are Q5,6 used to set the bias point of Q4? Are V2,3,4 just there to bias the transistors for simulation purposes, and this would be accomplished another way in a real implementation? Please explain the comment regarding the hybrid. Are you and Bob referring to a 90 degree hybrid coupler, or other quadrature method like a transmission line transformer? What would be the purpose of such a device? Would it be too much to ask for a description of these circuits? I suppose we all have our areas of expertise, and transistor isolation amps are somewhat new to me. Thanks again for all the help. Clay PS - yes, the OCXO is vibe isolated. And you are certainly correct about long runs of single-ended coax being susceptible to noise. The system designer has accepted this and allowed for some degradation. But I will look into the practicality of implementing a differential line for the long run of 10 MHz cable. However, I will still need to implement traditional coaxial isolated 10 MHz outputs. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier (Clay)
Message: 2 Date: Thu, 11 Feb 2010 07:54:40 -0500 From: Bob Camp Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob Message: 6 Date: Fri, 12 Feb 2010 04:09:08 +1300 From: Bruce Griffiths Yes implementing an exact copy without using a hybrid would be difficult. However for 10MHz use, its probably not too difficult since that isolation amplifier is intended for a 100MHz signal and the requirement is for 10MHz operation. If the transistor ft's are reduced by a factor of 10 or so it shouldn't be too much of a problem. At 10MHz 2N3906 and 2N3904 transistors should suffice. Bruce Hi Bruce, Thanks for the tips. I've been trying to follow the circuits you posted. The first one, in .PNG format, looks like a common-base complementary (push-pull) stage followed by a common-emitter complementary stage to provide the low impedance output. The second circut in .GIF fromat I am having a bit more trouble understanding. I see that V6, 7 are at the outputs and just used for to simulate isolation. V1 is the input? Are Q5,6 used to set the bias point of Q4? Are V2,3,4 just there to bias the transistors for simulation purposes, and this would be accomplished another way in a real implementation? Please explain the comment regarding the hybrid. Are you and Bob referring to a 90 degree hybrid coupler, or other quadrature method like a transmission line transformer? What would be the purpose of such a device? Would it be too much to ask for a description of these circuits? I suppose we all have our areas of expertise, and transistor isolation amps are somewhat new to me. Thanks again for all the help. Clay PS - yes, the OCXO is vibe isolated. And you are certainly correct about long runs of single-ended coax being susceptible to noise. The system designer has accepted this and allowed for some degradation. But I will look into the practicality of implementing a differential line for the long run of 10 MHz cable. However, I will still need to implement traditional coaxial isolated 10 MHz outputs. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Yes implementing an exact copy without using a hybrid would be difficult. However for 10MHz use, its probably not too difficult since that isolation amplifier is intended for a 100MHz signal and the requirement is for 10MHz operation. If the transistor ft's are reduced by a factor of 10 or so it shouldn't be too much of a problem. At 10MHz 2N3906 and 2N3904 transistors should suffice. Bruce Bob Camp wrote: Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob On Feb 10, 2010, at 11:30 PM, Bruce Griffiths wrote: Clay Circuit schematic for a more recent JPL isolation amplifier design is attached. Bruce life speed wrote: Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Hi Implementing that circuit without using a hybrid would be a bit of a challenge. Bob On Feb 10, 2010, at 11:30 PM, Bruce Griffiths wrote: > Clay > > Circuit schematic for a more recent JPL isolation amplifier design is > attached. > > Bruce > > life speed wrote: >> Avoiding transformers and inductors will make it virtually impossible to >> achieve very low phase noise as the dc gain from say the base of any >> transistor in the chain to the output will degrade the flicker phase >> noise. Using transformers or using an inductor to shunt any collector >> resistors reduces the flicker phase modulation to low levels. >> >> JPL in the past has built capacitively coupled complementary symmetry >> isolation amplifiers that avoid transformers but suffer from dc loop >> gains of around 3 or so. >> >> Using complementary symmetry can be a good way of keeping the dc current >> down. >> >> How much reverse isolation do you need? >> How low does the phase noise floor need to be? >> What about flicker phase noise, how low does that need to be? >> >> Bruce >> >> Right, what do I really need? I only have a really good 10 MHz OCXO crystal >> oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, >> - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium >> clock, living in the world of practical realities here. Of course I would >> like to be 3 - 6 dB better than the OCXO numbers. >> >> Reverse isolation is my primary interest in the distribution amplifier >> approach, although the OCXO is good enough that a sloppy approach could >> contaminate the phase noise also. I would like to accomplish at least 100 >> dB reverse isolation at frequencies below 20 MHz, but more is better in this >> case. The 10 MHz is running all over a noisy aircraft, to potentially noisy >> receivers. >> >> In reading up on the subject, I have come to understand that DC gain is the >> bane of close-in phase noise. Given that flicker noise is such a headache >> for we frequency synthesizer designers, I guess this should come as no >> surprise. >> >> Clay (AKA Lifespeed) >> >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Clay If the first stage has a voltage gain of 2x then the total dc current can be reduced as the output stages no longer need to drive the feedback 100 ohm resistor connected to ground at RF. The attached circuit schematic also includes faster input transistors in each 3 transistor feedback circuit to improve stability and increase the reverse isolation slightly. Bruce Bruce Griffiths wrote: Clay You could try something like the attached circuit schematic. Austron used buffer amplifiers like this albeit without the complementary symmetry output stage. There are no transformers and the dc gain is low. Simulated reverse isolation at 10MHz is around 120dB. Simulated crosstalk between the 2 outputs is around -100dB at 10MHz. The transistor models used usually predict reverse isolation reasonably accurately at 10MHz. The phase noise floor should be around -170dBc/Hz or less at 100kHz offset. V1 is the input signal. The 50 ohm sources V6, V7 shown at the outputs are used for simulation purposes (reverse isolation and crosstalk). Off course, more elaborate power supply decoupling will be necessary to avoid degrading reverse isolation and crosstalk. If you are really desperate to reduce the dc current the output transistors could be operated in class B. However the distortion will increase a little. Bruce life speed wrote: Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) <>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Attn: John Ackermann Not sure what happened to produce 2 identical posts but as far as I can tell I only posted this once. Bruce Bruce Griffiths wrote: Clay Circuit schematic for a more recent JPL isolation amplifier design is attached. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Clay Circuit schematic for one of the JPL isolation amplifiers is attached. Unfortunately (apart from the few I and others may have) these transistors are difficult to obtain. However modern equivalents could be substituted. Bruce life speed wrote: Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. <>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Clay You could try something like the attached circuit schematic. Austron used buffer amplifiers like this albeit without the complementary symmetry output stage. There are no transformers and the dc gain is low. Simulated reverse isolation at 10MHz is around 120dB. Simulated crosstalk between the 2 outputs is around -100dB at 10MHz. The transistor models used usually predict reverse isolation reasonably accurately at 10MHz. The phase noise floor should be around -170dBc/Hz or less at 100kHz offset. V1 is the input signal. The 50 ohm sources V6, V7 shown at the outputs are used for simulation purposes (reverse isolation and crosstalk). Off course, more elaborate power supply decoupling will be necessary to avoid degrading reverse isolation and crosstalk. If you are really desperate to reduce the dc current the output transistors could be operated in class B. However the distortion will increase a little. Bruce life speed wrote: Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. <>___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Hi Is your OCXO vibration isolated? If not and it's got "typical" g sensitivity, your phase noise in an aircraft may be much worse than the static numbers. If you are sending the signal a distance to your systems, a balanced feed may be the only way you will deliver a clean signal at the far end. Bob -- From: "life speed" Sent: Wednesday, February 10, 2010 10:03 PM To: Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce Right, what do I really need? I only have a really good 10 MHz OCXO crystal oscillator to distribute, so about -120 dBc at 10 Hz, -140 dBc/Hz at 100 Hz, - 150 dBc/Hz at 1KHz, and -155 dBc/Hz noise floor. No maser or cesium clock, living in the world of practical realities here. Of course I would like to be 3 - 6 dB better than the OCXO numbers. Reverse isolation is my primary interest in the distribution amplifier approach, although the OCXO is good enough that a sloppy approach could contaminate the phase noise also. I would like to accomplish at least 100 dB reverse isolation at frequencies below 20 MHz, but more is better in this case. The 10 MHz is running all over a noisy aircraft, to potentially noisy receivers. In reading up on the subject, I have come to understand that DC gain is the bane of close-in phase noise. Given that flicker noise is such a headache for we frequency synthesizer designers, I guess this should come as no surprise. Clay (AKA Lifespeed) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
Hi How quiet does in need to be (phase noise)? How clean does it need to be (harmonics)? How much isolation / how much gain do you need? How well do the outputs need to be matched / do you need a broad band match? Does the issue with transformers also extend to other inductors? Is cost / military components / small size / radiation tolerance an issue? The answer to your question could be any of several bipolar transistor circuits, op amps, right up to "can't be done" based on some of the answers. Bob -- From: "life speed" Sent: Wednesday, February 10, 2010 8:27 PM To: Subject: [time-nuts] Advice on 10 MHz isolation/distribution amplifier Hello everyone, I am new to this list, happened across it while searching on distribution amplifiers. I need to design a 10 MHz isolation/distribution amplifier with two outputs for a high-vibration wide temperature range environment. I was considering using a design based on the NIST article 'A new 5 and 10 MHz distribution amp', most likely the third incarnation, as I cannot tolerate modulation of the signal via the transformer. I have looked at the work by Gerhard Hoffman, which is impressive. However, the transformer remains. I should mention I am also limited to 15V power supply, and need to output into 50 ohms at 10 dBm. Ideally DC current will be minimized, preferably 20 - 30 mA per channel. I can generate a negative power supply if necessary, but would prefer not to. If anybody can offer tips so I don't undertake to reinvent the wheel, it would be appreciated. Thanks in advance, - Lifespeed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Advice on 10 MHz isolation/distribution amplifier
life speed wrote: Hello everyone, I am new to this list, happened across it while searching on distribution amplifiers. I need to design a 10 MHz isolation/distribution amplifier with two outputs for a high-vibration wide temperature range environment. I was considering using a design based on the NIST article 'A new 5 and 10 MHz distribution amp', most likely the third incarnation, as I cannot tolerate modulation of the signal via the transformer. I have looked at the work by Gerhard Hoffman, which is impressive. However, the transformer remains. I should mention I am also limited to 15V power supply, and need to output into 50 ohms at 10 dBm. Ideally DC current will be minimized, preferably 20 - 30 mA per channel. I can generate a negative power supply if necessary, but would prefer not to. If anybody can offer tips so I don't undertake to reinvent the wheel, it would be appreciated. Thanks in advance, - Lifespeed Avoiding transformers and inductors will make it virtually impossible to achieve very low phase noise as the dc gain from say the base of any transistor in the chain to the output will degrade the flicker phase noise. Using transformers or using an inductor to shunt any collector resistors reduces the flicker phase modulation to low levels. JPL in the past has built capacitively coupled complementary symmetry isolation amplifiers that avoid transformers but suffer from dc loop gains of around 3 or so. Using complementary symmetry can be a good way of keeping the dc current down. How much reverse isolation do you need? How low does the phase noise floor need to be? What about flicker phase noise, how low does that need to be? Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Advice on 10 MHz isolation/distribution amplifier
Hello everyone, I am new to this list, happened across it while searching on distribution amplifiers. I need to design a 10 MHz isolation/distribution amplifier with two outputs for a high-vibration wide temperature range environment. I was considering using a design based on the NIST article 'A new 5 and 10 MHz distribution amp', most likely the third incarnation, as I cannot tolerate modulation of the signal via the transformer. I have looked at the work by Gerhard Hoffman, which is impressive. However, the transformer remains. I should mention I am also limited to 15V power supply, and need to output into 50 ohms at 10 dBm. Ideally DC current will be minimized, preferably 20 - 30 mA per channel. I can generate a negative power supply if necessary, but would prefer not to. If anybody can offer tips so I don't undertake to reinvent the wheel, it would be appreciated. Thanks in advance, - Lifespeed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
