Re: [time-nuts] ? phase comparison or other device
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: Juerg Koegel [EMAIL PROTECTED] Subject: [time-nuts] ? phase comparison or other device Date: Fri, 29 Jun 2007 19:08:47 +0200 Message-ID: [EMAIL PROTECTED] Another article (with practical hints) is OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE MULTIPLIER L. Sojdr, J. Cermák, R. Barillet The article (pdf file) is at present not online. It is too big for the Time Nuts annex (912k) I can send you the article direct. Where did this article show up? I'd like a copy! Cheers, Magnus ___ 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] ? phase comparison or other device
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote: Not true, there's nothing magic about amplifier saturation, any means that limits the amplifier output whilst dropping the small signal gain to a low value will have exactly the same effect. The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers. The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater. These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage. The output signal will clamp at these specified levels. http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes) http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs). A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion. A diode clamp in the feedback path will cut the noise gain to 1 when either diode turns on. The following diode clamp across the filter capacitor will reduce the noise gain to a very small value when it turns on. Both diode clamps and internal saturation will still produce some output noise although not from the amplifier input stages. Improperly done diode clamps can significantly increase harmonics. -- http://www.wearablesmartsensors.com/ http://www.softwaresafety.net/ http://www.designer-iii.com/ http://www.unusualresearch.com/ ___ 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] ? phase comparison or other device
Bob Paddock wrote: On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote: Not true, there's nothing magic about amplifier saturation, any means that limits the amplifier output whilst dropping the small signal gain to a low value will have exactly the same effect. The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers. The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater. These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage. The output signal will clamp at these specified levels. http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes) http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs). A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion. A diode clamp in the feedback path will cut the noise gain to 1 when either diode turns on. The following diode clamp across the filter capacitor will reduce the noise gain to a very small value when it turns on. Both diode clamps and internal saturation will still produce some output noise although not from the amplifier input stages. Improperly done diode clamps can significantly increase harmonics. Bob These devices are a little noisy below 100Hz. Also any noise at the input clamp level inputs appears at the output. Since these devices actually set the maximum input voltage before clamping occurs they are unsuitable when the gain is high. The distortion produced by a diode clamp is immaterial when one is only interested in the zero crossing time. 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] ? phase comparison or other device
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] These devices are a little noisy below 100Hz. Rather than constantly battle the there is to much noise, what are your thoughts on deliberately injecting out-of-band noise? As an example: http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf Overcoming Converter Nonlinearities with Dither The distortion produced by a diode clamp is immaterial when one is only interested in the zero crossing time. It depends on where the harmonics fall. -- http://www.wearablesmartsensors.com/ http://www.softwaresafety.net/ http://www.designer-iii.com/ http://www.unusualresearch.com/ ___ 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] ? phase comparison or other device
Bob Paddock wrote: These devices are a little noisy below 100Hz. Rather than constantly battle the there is to much noise, what are your thoughts on deliberately injecting out-of-band noise? As an example: http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf Overcoming Converter Nonlinearities with Dither The distortion produced by a diode clamp is immaterial when one is only interested in the zero crossing time. It depends on where the harmonics fall. Bob What is the application for which you want to use injected out of band noise? Since the performance of a well designed zero-crossing detector is equivalent to a 25 bit ADC when locating the zero-crossing, it will be difficult to replicate this performance using a lower resolution ADC even combined with out of band dithering. In practice, diode clamp circuit distortion in a zero-crossing detector isn't 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] ? phase comparison or other device
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Bob Paddock wrote: The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion clamping amplifiers. The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or greater. These devices allow the designer to specify a high (VCH) and low (VCL) output clamp voltage. The output signal will clamp at these specified levels. http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 bytes) http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf So far most clamping amplifiers have relied upon an output clamping architecture and are called output clamp amps (OCAs). A new architecture called an input clamp amp (ICA) offers superior clamping accuracy and lower distortion. Bob A significant issue with these clamping amplifiers is that although when the clamp is active the signal gain is near very low, the amplifier noise gain is the same as when the clamp isn't active. In contrast with a simple diode clamp, the signal gain is low when the clamp is conducting and the amplifier noise gain is at worst unity. Surely this characteristic of a simple diode clamp reduces the noise associated with the amplifier accumulated on the low pass filter capacitor in a zero-crossing detector over the amplifier noise contribution from an equivalent zero-crossing detector using such input clamping amplifiers? 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] ? phase comparison or other device
Peter, The JPL paper is the second on Enrico Rubiola's posting. Pete Rawson ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Hi Pete, 3. I read the JPL paper (more than once)... Do you have it available in electronic form (or know a link that I might download it from)? Thanks, Peter Vince (G8ZZR, London) ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Post it to Didier Juges's site? ftp.ko4bb.com User: manuals Password: manuals -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Richard (Rick) Karlquist Sent: Wednesday, June 27, 2007 7:37 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] ? phase comparison or other device I have the JPL zero crossing detector paper scanned in. (John Dick, et al, 1990 PTTI). It is definitely a must read. Do you want me to email to you? Rick Karlquist N6RK ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Pete wrote: Bruce, A few final thoughts. 1. Thanks for the critical view; it does help. 2. Like many time-nuts I have a reasonably good 10MHz source sometimes need to check out a newly acquired OXCO to ensure it can muster 1E9 or 1E10 performance (with 10x headroom). An SR620 would be ideal, but it's just too many $$ ;even used. I expect casual participants of time-nuts already have a basic, decent counter e.g. HP5335A a basic decent synthesizer e.g. PTS040, Fluke6060(?), HP3335x or 6x. Also, I assumed a coaxial level 7 mixer suitable lowpass filter would be available. 3. I read the JPL paper (more than once) developed the first three stages (modified for 1KHz bandpass) per their process. At that point the measured jitter was well under 1ns rms; which was enough to enable 1E12 resolution for 10MHz sources. I deliberately choose the ADA4899-1 opamp since it's characterized for 5V operation, low noise, fast cheap enough ($4.30/ea). It was apparent that even with 2 stages the ZCD was still under 1ns jitter; the risetime wasn't blazing, but it was obviously good enough. 4. Without PCB capability (at home now retired) even this simple circuit is tough to build; each part adds significantly to the effort when doing 1-up. So I examined the need for every part in an effort to minimize parts count, but retain jitter performance. I found that the opamp overload recovery was more than fast enough to discard the limiting without measurable deterioration in jitter. Lots of parts went away; construction became easy. 5. I went TOO FAR. The opamps I had exhibited such low offset that I DC coupled without thinking about it. WRONG answer (as you noted), Rookie mistake. I have shown the AC coupling 2nd stage feedback resistor in the revised circuit. 6. The ZCD costs $20 for parts about 2 hours to build/check out. It performs well enough to look at stable sources to 2 parts in 1E12 in 50 to 100 seconds and be confident in the data. The noise floor is easy to measure verifies functionality. Is it well designed ? NO. Could it be (much) better? Certainly. Does it work well for it's intended purpose? Yes. My assumptions about equipment may be out of line. In my case, eBay supplied everything, except the mixer, filter ADA4899-1s, so this effort didn't require much in the way of extra $$. It does what I wanted. As previously observed, the mixer should have a diplexer between it and the filter for the mixer higher order products to be terminated properly. I examined the filter input Z, as terminated, and found it to be from 150 ohms inductive to 1200 ohms inductive from 10 to 30 MHz. This suggests the use of a feedthrough termination of around 100 ohms as a first order fix. Using a 93 ohm feedthrough, no improvement, or degradation in results was noted. This could use more study. From your earlier response, I suspect you have a cheaper, better method in mind to achieve the same results. Would you detail it? Regards, Pete Rawson ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Pete Try connecting the input stage inductor and capacitor in parallel with the 6190 ohm feedback resistor, but before you do this replace the first opamp with a lower gain bandwidth (audio??) device that is unity gain stable. This will produce a first gain stage that amplifies the signal of interest as well as the noise within the tuned circuit bandwidth without unduly amplifying the noise not within the tuned circuit bandpass. The other thing you could do since you've chosen a 1kHz beat frequency is to use an audio transformer to step up the output of the mixer before amplifying it. NB dont forget to connect the transformer to ground through a capacitor that has a low impedance at 1kHz (this ensures that the dc load current at the mixer IF port is low).. The mixer IF port should be terminated with a 10nF capacitor and a simple low pass filter consisting of say a 100uH inductor and a 1nF capacitor substituted for the 1.9MHz bandpass filter. This, as shown by the NIST paper alluded to by Magnus, will increase the mixer sensitivity considerably. You should also run the mixer with both the RF and LO ports saturated ie more than 7dBm for both of these ports. The mixer output noise at the 1KHz beat frequency will be somewhere in the vicinity of 100nV/rtHz, so if you have say a 1V peak output then the inherent jitter due to mixer noise will be around 160ps rms for a tuned circuit noise bandwidth of 100Hz. With a suitable amplifier choice you shouldn't degrade this by more than 5% or so. Achieving a resolution of better than 1E-13 in 1 second with a 10MHz input and a suitable counter is easy, provided you dont rely on the counters input circuitry to trigger on the amplified mixer output you
Re: [time-nuts] ? phase comparison or other device
Ulrich Bangert wrote: Pete, 5. Mini-circuits BLP-1.9 low pass filter. terminating the mixer if output with an lowpass/bandpass filter and NOT with an diplexer is not so good an idea. Where does the rf go? Best regards Ulrich Bangert Ulrich This depends on whether the low pass filter has a shunt capacitor at its input or a series inductor. With the shunt capacitor the RF is shunted to ground through this capacitor. With a series inductor the RF sees a relatively high input impedance and the mixer will not perform well. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Bruce, This idea is NOT intended to rival the JPL results. Instead, it's intended to be cheap, easy to replicate allow rather low cost instruments to be used to compare good sources to parts in 1E12, quickly. The 1KHz heterodyne frequency makes life much easier than 1Hz. Noisy components ground loops are still of concern, but not so hard to fix. ADA4899-1 overload recovery is 50ns (per data sheet). I've attached a rather poor schematic which doesn't show power supply decoupling or the need to pull the disable pin high. The ADA4899-1 uses 14mA per part, but it's quiet fast. Metal film resistors are fine for this low noise application all are low values to keep noise down. The inductors are easy to wind, but I found materials other than moly permalloy powder to be too noisy. Even with MPP material, cores with u200 are prone to field induced shifts which are unacceptable. Regards, Pete Rawsonattachment: ZCD5.JPG___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Pete wrote: Bruce, This idea is NOT intended to rival the JPL results. Instead, it's intended to be cheap, easy to replicate allow rather low cost instruments to be used to compare good sources to parts in 1E12, quickly. The 1KHz heterodyne frequency makes life much easier than 1Hz. Noisy components ground loops are still of concern, but not so hard to fix. ADA4899-1 overload recovery is 50ns (per data sheet). I've attached a rather poor schematic which doesn't show power supply decoupling or the need to pull the disable pin high. The ADA4899-1 uses 14mA per part, but it's quiet fast. Metal film resistors are fine for this low noise application all are low values to keep noise down. The inductors are easy to wind, but I found materials other than moly permalloy powder to be too noisy. Even with MPP material, cores with u200 are prone to field induced shifts which are unacceptable. Regards, Pete Rawson ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Pete Even so, it pays to use a well designed circuit instead of something thrown together with little understanding of what you are doing. The JPL design is not expensive and doesn't require particularly exotic wideband components or high resolution counters. There is still a noise advantage in using a 1Hz beat frequency, suitable opamps are readily available. Magnetic shielding of the inductors and/or the entire circuit is probably advisable for the best performance. The circuit diagram is sufficient to confirm my suspicions. The input stage noise gain will be high at frequencies away from the 1kHz frequency of interest. This is a very poor design. It is very easy to do much better with the same components. A 50ns overload recovery will be somewhat problematic when you are attempting 1ns or less timing jitter. A well designed and simple feedback bound circuit will be much faster. Using an inverting amplifier input stage is not optimum for noise. In fact the input stage doesn't need to use such a wideband opamp, a low noise opamp with a more modest gain bandwidth configured as a non inverting stage with gain followed by a bandpass filter will have far better performance. Only the final limiting stage needs to be fast. Also since you are using a 1kHz offset frequency it may be advantageous to use a transformer to couple the mixer output to the input stage, a stepup transformer will improve the equivalent input noise significantly even when using a somewhat noisier slower and cheaper opamp for the input stage. A low pass filter with a lower cutoff frequency than the several MHz of the BLP 1.9 is desirable between the mixer and the input amplifier, a tuned bandpass filter would be optimum but don't forget to terminate the mixer IF port in a suitable impedance at frequencies other than the beat frequency. It should be possible to combine the tuned bandpass filter and the stepup transformer. Try reading the JPL article to gain an understanding of how to do it properly. Although their design uses cascaded low pass filtered amplifiers with feedback bound circuits, the same technique can be used with bandpss filters. Since you use a 1kHz beat frequency it is advantageous to AC couple the various stages to reduce the effective output dc offset. Low frequency earth loops will limit the performance unless a different mixer with dc isolated RF. LO and IF outputs is used. Suitable mixers are available. Your claimed performance is comparable with that which can be achieved using a linear phase comparator which neither requires a mixer (other than the implicit mixer built into the phase comparator) nor a high resolution counter. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
WB6BNQ wrote: Bruce, Can you provide a link to the JPL system you reference above ? Thank you, BillWB6BNQ Bill http://ntrs.nasa.gov/index.jsp?method=orderoaiID=19910016462 http://ntrs.nasa.gov/index.jsp?method=orderoaiID=19910016462 There is also, or was, a free to download source for this paper somewhere, which I cant recall. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Pete, 5. Mini-circuits BLP-1.9 low pass filter. terminating the mixer if output with an lowpass/bandpass filter and NOT with an diplexer is not so good an idea. Where does the rf go? Best regards Ulrich Bangert -Ursprüngliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Pete Gesendet: Sonntag, 24. Juni 2007 03:38 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] ? phase comparison or other device Here is a scheme that seems to work well for comparing stable frequency sources in the range of 10 to 100 second measurement intervals. Objective - Measure frequency to +/-2E-12 in less than 1 minute. Method - Heterodyne DUT output to 1KHz with a master reference source + mixer feeding a tuned zero crossing detector + counter. Equipment - 1. Master reference source at 5 or 10 MHz, e.g. mature OXCO or GPSDO. 2. Synthesizer set to DUT - 1KHz, locked to reference source. The synthesizer averaged output must settle to 10uHz in 10 seconds, e.g. HP 3335A or 3336C. PTS 040 should work fine, also. 3. 9 digit/s counter, locked to reference source with selectable gate time. An input LPF (100KHz) helps, e.g. HP 5335A. 4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers should work, but haven't been tested. 5. Mini-circuits BLP-1.9 low pass filter. Other filters should work, but haven't been tested. 6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz sinewave input outputs 1KHz squarewave to counter with less than 1nS rms jitter. Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT - 1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to mixer IF port. ZCD input connects to BLP-1.9. Counter connects to ZCD output set for 5 to 10 second gate time. The DUT frequency = synthesizer setting + counter frequency; 10uHz digit = 1E-12 for 10MHz DUT. The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration, cascaded, using +/- 2.5 volt power supplies. Both amps have their non-inverting pins connected (only) to a 100 ohm resistor to ground. Both amps have 5uF//5mH to ground on their inverting inputs. The input amp has Rin = 422 ohms and Rf = 6190 ohms. The output amp has Rin = 562 ohms and Rf = open. The output amp output pin has 2ea 100 ohm resistors in series to ground. The counter is connected to the common point of the 100 ohm resistors. Nominal supply bypassing is required. Battery supplies at +/- 3 volts help isolate noise sources. Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521 cores using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax to 50mT at 1KHz 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are polypropylene or mylar film types. Noise floor measurements using HP5335A opt 010 as reference source 1KHz counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample groups are within +/- 2E-12. Pete Rawson ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi- bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Here is a scheme that seems to work well for comparing stable frequency sources in the range of 10 to 100 second measurement intervals. Objective - Measure frequency to +/-2E-12 in less than 1 minute. Method - Heterodyne DUT output to 1KHz with a master reference source + mixer feeding a tuned zero crossing detector + counter. Equipment - 1. Master reference source at 5 or 10 MHz, e.g. mature OXCO or GPSDO. 2. Synthesizer set to DUT - 1KHz, locked to reference source. The synthesizer averaged output must settle to 10uHz in 10 seconds, e.g. HP 3335A or 3336C. PTS 040 should work fine, also. 3. 9 digit/s counter, locked to reference source with selectable gate time. An input LPF (100KHz) helps, e.g. HP 5335A. 4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers should work, but haven't been tested. 5. Mini-circuits BLP-1.9 low pass filter. Other filters should work, but haven't been tested. 6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz sinewave input outputs 1KHz squarewave to counter with less than 1nS rms jitter. Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT - 1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to mixer IF port. ZCD input connects to BLP-1.9. Counter connects to ZCD output set for 5 to 10 second gate time. The DUT frequency = synthesizer setting + counter frequency; 10uHz digit = 1E-12 for 10MHz DUT. The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration, cascaded, using +/- 2.5 volt power supplies. Both amps have their non-inverting pins connected (only) to a 100 ohm resistor to ground. Both amps have 5uF//5mH to ground on their inverting inputs. The input amp has Rin = 422 ohms and Rf = 6190 ohms. The output amp has Rin = 562 ohms and Rf = open. The output amp output pin has 2ea 100 ohm resistors in series to ground. The counter is connected to the common point of the 100 ohm resistors. Nominal supply bypassing is required. Battery supplies at +/- 3 volts help isolate noise sources. Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521 cores using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax to 50mT at 1KHz 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are polypropylene or mylar film types. Noise floor measurements using HP5335A opt 010 as reference source 1KHz counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample groups are within +/- 2E-12. Pete Rawson ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Pete wrote: Here is a scheme that seems to work well for comparing stable frequency sources in the range of 10 to 100 second measurement intervals. Objective - Measure frequency to +/-2E-12 in less than 1 minute. Method - Heterodyne DUT output to 1KHz with a master reference source + mixer feeding a tuned zero crossing detector + counter. Equipment - 1. Master reference source at 5 or 10 MHz, e.g. mature OXCO or GPSDO. 2. Synthesizer set to DUT - 1KHz, locked to reference source. The synthesizer averaged output must settle to 10uHz in 10 seconds, e.g. HP 3335A or 3336C. PTS 040 should work fine, also. 3. 9 digit/s counter, locked to reference source with selectable gate time. An input LPF (100KHz) helps, e.g. HP 5335A. 4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers should work, but haven't been tested. 5. Mini-circuits BLP-1.9 low pass filter. Other filters should work, but haven't been tested. 6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz sinewave input outputs 1KHz squarewave to counter with less than 1nS rms jitter. Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT - 1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to mixer IF port. ZCD input connects to BLP-1.9. Counter connects to ZCD output set for 5 to 10 second gate time. The DUT frequency = synthesizer setting + counter frequency; 10uHz digit = 1E-12 for 10MHz DUT. The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration, cascaded, using +/- 2.5 volt power supplies. Both amps have their non-inverting pins connected (only) to a 100 ohm resistor to ground. Both amps have 5uF//5mH to ground on their inverting inputs. The input amp has Rin = 422 ohms and Rf = 6190 ohms. The output amp has Rin = 562 ohms and Rf = open. The output amp output pin has 2ea 100 ohm resistors in series to ground. The counter is connected to the common point of the 100 ohm resistors. Nominal supply bypassing is required. Battery supplies at +/- 3 volts help isolate noise sources. Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521 cores using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax to 50mT at 1KHz 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are polypropylene or mylar film types. Noise floor measurements using HP5335A opt 010 as reference source 1KHz counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample groups are within +/- 2E-12. Pete Rawson I am confused the opamp circuitry as described seems to be almost exactly the inverse of what is required. Please send a schematic so I can check. Are the MPP cores powdered iron or ferrite? The phase stability of the bandpass filters is critical as is any phase instability like that exhibited by ferrite cores. The overdrive recovery characteristics of the ADA4889-1 are not specified, how fast does it actually recover from overdrive? One can do considerably better than this (JPL have a system with a resolution of around 1E-15/Tau 1Hz offset, 100MHz input) with lower offset frequencies and a well designed amplifier and cascaded limiters, however low frequency ground loops are problematic. Optical isolation is almost mandatory. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] ? phase comparison or other device
Bill Janssen wrote: I thought that someone was designing a circuit that could be used to compare two oscillators. What happened to that project? I now have a HP 5370A so I have something, but I would like to make simultaneous measurements on three or four precision clocks.I am not qualified to design a state of the art device, so I am looking for others to do that. Thanks Bill K7NOM ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts Bill Ulrich and I have designed and Ulrich is currently testing a CPLD implementation of the improved version of the HP K34-5991A linear phase detector. It includes programmable prescalers (1-256) so that frequency like 10MHz and 5MHz for example can be compared. The maximum input frequency is about 50MHz. It has 2 quadrature phase outputs. The prescalers also allow the phase detector gain to be adjusted. The phase detector has a triangular wave characteristic with a period of 4 cycles of the input frequency to the phase detector (ie at the built in prescaler output). Preliminary results using a very crude kitchen table breadboard indicate that instabilities of a few parts in 1E12 are easily seen within an hour or so. Sensitivity is likely to be much better than this but a 10X prescaler was used on each 10MHz input. Comparing 3 or 4 standards requires using a set of distribution amplifiers plus a set of linear phase comparators to achieve the desired configuration. This is more flexible than trying to anticipate exactly how many channels a user may want, it also has less crosstalk than an implementation with more than 2 input frequencies to a single board or CPLD. With external prescalers the maximum input frequency can be extended to 100MHz or more. Bruce ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
