[time-nuts] Re: Isolation amp transistors
how about grounded grid ? Bob can you get better isolation with a vaccuum tube cascode than a solid state cascode ? -glen On 07/07/2022 15:22, Bob kb8tq via time-nuts wrote: Hi On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts wrote: The 2N5179 has high base spreading resistance (decreases isolation). As does sticking a resistor (even a small one) in series with the base …. Yes, inductance is even worse. For “best isolation” in a cascode you very much want the base of the common base stage nailed to ground. Typically “lower” Ft transistors with a decent base structure are the best choice for the common base stage. Both stages benefit from low 1/F noise in the audio range if this is for a phase noise test se ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Isolation amp transistors
Hi > On Jul 6, 2022, at 1:53 PM, Richard Karlquist via time-nuts > wrote: > > The 2N5179 has high base spreading resistance (decreases isolation). As does sticking a resistor (even a small one) in series with the base …. Yes, inductance is even worse. For “best isolation” in a cascode you very much want the base of the common base stage nailed to ground. Typically “lower” Ft transistors with a decent base structure are the best choice for the common base stage. Both stages benefit from low 1/F noise in the audio range if this is for a phase noise test set. This is why people use what would normally be considered “audio” transistors …. Bob > > --- > Rick Karlquist > N6RK > > On 2022-07-06 12:18, ed breya via time-nuts wrote: > >> My favorite VHF Q is the good old 2N5179 or similar, but it appears you want >> something in surface mount, and not obsolete. I'm not familiar with the >> modern SMT stuff. If your present transistors are working, but just need a >> bit more stability, it seems it should be OK with the right scheme, and not >> the transistors' fault. >> >> Ed >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe send an email to time-nuts-le...@lists.febo.com > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Isolation amp transistors
The 2N5179 has high base spreading resistance (decreases isolation). --- Rick Karlquist N6RK On 2022-07-06 12:18, ed breya via time-nuts wrote: > My favorite VHF Q is the good old 2N5179 or similar, but it appears you want > something in surface mount, and not obsolete. I'm not familiar with the > modern SMT stuff. If your present transistors are working, but just need a > bit more stability, it seems it should be OK with the right scheme, and not > the transistors' fault. > > Ed > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer
Hi Gerhard, On 06.07.22 18:28, Gerhard Hoffmann via time-nuts wrote: Am 2022-07-05 18:04, schrieb Bob kb8tq via time-nuts: If you need that sort of isolation, it certainly can be done. NIST has papers on very simple / DIY compatible cascode amps that will do the trick. ( chain of common base stages driven by a common emitter). Some folks on the list have gone a lot further in terms of complexity than NIST did. Device wise, the cascode amps seem to work pretty well with some very humble transistors ( 2N3904 etc ). There likely are fancier parts out there, but some of the really old stuff appears to be “good enough”. I have made a new isolation amplifier but I'm absolutely not happy with the available transistors. Anything in sot-89 is either to slow ( Zetex/Diodes Inc, the 2N3904-alikes) or is much too hot. I want at least 200 MHz to have no phase shift at 100. BFQ19s gave me 1 GHz of BW. The version in the plot is already heavily sandbaged but still has quite an S21 overshoot on the high frequency end. The input-voltage to cascode current converter is especially problematic in that the smallest capacitive load on the emitter tends to make it more unstable. That spoils S11, of course. I even took the feedback from a tap of the emitter resistor. Backward isolation is 120 dB over most of the useful range but changes depending on the damping methods. Any ideas of more friendly transistors? BFQ31 were quite well-behaved but are extinct now. I still have a reel, but stuff from the secret drawer is unfair. And it's PNP. Well, what kind of parameter are you after? I suspect, you're looking for sufficiently high fT and beta. Your mentioning of too hot devices seems to imply you'd like to have these at low collector currents, probably not more than a few milliamps. Anything else to look for? Best regards, Florian ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Isolation amp transistors
Gerhard wrote: "I have made a new isolation amplifier but I'm absolutely not happy with the available transistors. Anything in sot-89 is either to slow ( Zetex/Diodes Inc, the 2N3904-alikes) or is much too hot. I want at least 200 MHz to have no phase shift at 100. BFQ19s gave me 1 GHz of BW. The version in the plot is already heavily sandbaged but still has quite an S21 overshoot on the high frequency end. The input-voltage to cascode current converter is especially problematic in that the smallest capacitive load on the emitter tends to make it more unstable. That spoils S11, of course. I even took the feedback from a tap of the emitter resistor. Backward isolation is 120 dB over most of the useful range but changes depending on the damping methods. Any ideas of more friendly transistors? BFQ31 were quite well-behaved but are extinct now. I still have a reel, but stuff from the secret drawer is unfair. And it's PNP." Gerhard, what sort of damping are you using? I think the simplest is a small series base resistor on any common-base stage like the cascode upper Q. The same thing should help on the lower transconductance converter Q. If added base R degrades LF/MF performance too much, maybe lossy ferrite beads would do instead. My favorite VHF Q is the good old 2N5179 or similar, but it appears you want something in surface mount, and not obsolete. I'm not familiar with the modern SMT stuff. If your present transistors are working, but just need a bit more stability, it seems it should be OK with the right scheme, and not the transistors' fault. Ed ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On Tue, July 5, 2022 5:27 am, Mike Monett via time-nuts wrote: > The phase-frequency detector has zero ripple at lock. The PF detector also locks at 0 degrees offset. How do you get the demodulated phase noise out of that? The point of the a diode mixer is that it locks at quadrature, and the output is 0V DC at that point, but any instantaneous phase offset (i.e. phase noise from reference and DUT) shows up as AC signal at the output. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Mike, He was using an analog mixer, but your comment about XOR mixer does not apply to analog mixers. Your oversimplification that analog mixer and XOR gates being the same thing does not apply here, and thus the assigned missbehavior does not carry over to the analog mixer case. Cheers, Magnus On 2022-07-05 12:27, Mike Monett via time-nuts wrote: Eric, Another problem I forgot to mention, the exclusive-or phase detector has a severe output ripple. This will cause frequency shift in the oscillator frequency which will show up in the measurements. The phase-frequency detector has zero ripple at lock. There is a small transient at the sample time, but this is easily filtered with a simple low pass filter. With zero ripple in the output, the PFD will not cause any shift in the oscillator frequency. This will not cause any error in the measurements. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
Hi, On 2022-07-05 12:13, Mike Monett via time-nuts wrote: You stated: Mike, The phase detector is an ADE-1 mixer, the IF output of the mixer goes into a loop filter that has a corner frequency of about 0.2Hz to enable Phase noise measurements down to 1Hz offset That is your problem. A double balanced mixer is an exclusive-or phase detector. The lock range is determined by the loop bandwidth, as you have found. The phase-frequency detector is completely different. It will lock to any signal in the lock range, independent of loop bandwidth. You can have a bandwidth of 0.001 Hz, and it will still lock. Think of what this could do for your phase measurements. Actually, there is two schools here. There is the school of stateless phase-detectors (such as mixers) and the school of stateful phase-detectors (such as three-state mixers). Now, in the school of stateless phase-detectors, mixers, XOR-gates, samplers etc. the capture range becomes dependent on the loop gain. For passive lag filters, you will need a significant static phase-difference on the input to provide the state of the EFC to compensate on the frequency. It's very simply that the DC volt difference coming out of the detectors, through the DC gain of the filter is then what becomes the EFC. In active lag filters, you add additional gain, and this requires lower phase detector voltage to support the same EFC error. Both these actually have an implicit state in the phase detector to compensate the lack of state elsewhere. It is just not that the phase detector holds explicit state. In PI filters, the state of the frequency error is moved from the phase detector to the filter. The integrator has close to infinity in DC gain (naturally limited in practice, but for many purposes we can assume it being infinite) such that it drives the DC phase offset out of the phase detector to zero and builds up the needed EFC state in the integrator capacitor. This have the benefit that capture range is in theory unlimited, but even if the actual range is in practice limited, it is so wide that we can treat it as infinite for most cases. The PI loop those do not need any form of aiding to lock up. However, aiding it can increase lock-up time. You could either pre-trim the EFC or you could increase the PLL bandwidth to achieve quick lockup. The later is actually very simple and has very huge impact. The thing people do wrong with PI filters is to scale the bandwidth on the output side of the integrator. This is wrong, as one then needs to scale the output to maintain the acquired state to match the needed EFC. The right way to do it is to scale it on the input side. That way the scaling to EFC is maintained and no state-scaling is needed. As one scales the bandwidth through I one needs to scale P accordingly to maintain good damping properties. Fairly simple PI-loop setups allow for good lockup and stability properties. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
