Time interval measurement limits - Page 1
Forum section: electronics / general

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 07:52:48 am
content: I wonder how time intervals and their distributions are measured and what the current state of art is in terms of resolution. Rather than a clock or a periodic signal, what I wonder is more general, measuring irregular events, either by start/stop signals or just by measuring the pulse width. Is it possible to have a resolution around 1ps or even better ?I saw there was jitter/time interval analyzers (eg Yokogawa TA520) in the past having 25ps resolution using an hybrid approach, and Keysight at the moment have a freq. counter that can do 20ps I think using interpolation. TA520 resolves two reference clock period length of time by converting it to a voltage and then reading it with a 8-bit ADC. Just by using a 16-bit ADC and if needed a better clock (it has TCXO), it should be possible to improve this a lot, correct ?

author: jonpaul
author_rank: Super Contributor
timestamp: January 03, 2022, 10:55:36 am
content: Bonjour as a digital audio researcher and transformer manufacturer since 1980s, we have used the old HP counters 5370A and 5372A but only 100 pS res.In our papers for AES we were fortunate to have Yokogawa time analyzers: Several TA320 and a like new Yokogawa TA720Those are unique as they use an interpolation with two different clocks. ~ 25 pS.Simply digitizing the input would need GHz FS rates to do better.Stanford Research has a nice counter 25 pS: SR620 s Universal Time Interval CounterThe nucleonics groups have much faster single shot , using image intensifiers, MCP gigahertz scopes, etc.If you can define the signals you measure and the aim of jitter, rise/fall, etc we can better respond.Finally in all old digital instruments like the TA320/TA720 beware of old/dead backup Li batteries, that may hold CAL constants. The TA320/720 are not simple to open and reach the batteries.Bon Chance,Jon

author: 2N3055
author_rank: Super Contributor
timestamp: January 03, 2022, 11:36:37 am
content: It is tough to add something of value after Jon but just to repeat his question:What is this for? Pure intellectual curiosity?It certainly is possible. But those are specialized instruments.Sub picosecond accuracy measurements are domain of CERN, femtosecond laser research, etc etc...I cannot think of any "normal world" electronics application of top of my head that wouldn't be served with 25ps time resolution for instance.Would you like to share what kind of exciting stuff you're been doing.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 11:51:37 am
content: Hi Jon,Quote from: jonpaul on January 03, 2022, 10:55:36 amI find it very nice how they are designed. Very simple (at least it sounds simple) but very effective.Quote from: jonpaul on January 03, 2022, 10:55:36 amI think most of these are out of question without a method like TA-series have, I mean something more hybrid with analog circuitry. I dont know about RF/microwave freq. counters, if they can be used for this purpose, and also even if they are rated 100Ghz, that is still not enough I guess. Can you give an example of such a device if you have something in mind ? I dont even know how to search.Quote from: jonpaul on January 03, 2022, 10:55:36 amThe reason I ask this question now is because I was wondering if I can measure the SPDIF jitter and I was wondering how they are measuring the oscillators. However, these are not the point of my question, I am interested to know the state of the art in this type of measurement. As far as I understand the oscillators are measured in f-domain, I guess simply because there is no device that can measure the close-in phase noise in time domain (?). I dont know if I think and calculate this right, if I have a clock 10MHz so 50ns pw, and if I want to measure deviation at 1Hz level, this requires even a better resolution than fs, so I guess not possible to do in t-domain (?). and I guess there is no need to measure SPDIF or similar jitter below 25ps. It might be possible to do this with a sampling scope to some extent, but this requires a periodic signal and it will not be better than 25ps I think.Actually my interest in time interval measurement started from somewhere else. I am interested in measuring interrupt response latency, how quick an embedded device -electronic+software- response to an input, so this is a time interval measurement with irregular events. I do this (as a hobby) using an FPGA based counter since there is no need to go below ~10ns there but it raised my interest on time interval measurement.Quote from: jonpaul on January 03, 2022, 10:55:36 amThat is very good to know as I am interested in getting one (most possibly TA520). When you say they hold CAL constants, I guess you dont mean they are dead when the battery is dead, but you mean it needs a working battery right ? Is there a way to check the status of the battery without opening up the unit, so it can be asked to the seller ?

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 12:00:07 pm
content: Quote from: 2N3055 on January 03, 2022, 11:36:37 amYes intellectual curiosityQuote from: 2N3055 on January 03, 2022, 11:36:37 amI am possibly saying this wrong but I think the lengths are measured with an interferometer for example, so I guess optical methods make sense, but I dont know much about it so cannot convert something in electrical domain to that easily in my mind.Quote from: 2N3055 on January 03, 2022, 11:36:37 amI guess it is natural for oscillators, but they are measured differently, so it might be unnecessary, but as an example, I can pose the question to what extent can I measure an oscillator jitter in t-domain ?

author: 2N3055
author_rank: Super Contributor
timestamp: January 03, 2022, 12:44:39 pm
content: Quote from: metebalci on January 03, 2022, 12:00:07 pmJitter of a clock signal? In digital parlance it is jitter, in analog parlance we call it phase noise.There are many components to characterizing clock jitter. It also depends what are you characterizing for.Fast ADC clock for a scope? Jitter in audio systems?You usually don't measure details you don't need (not necessary for your application) and over accuracy needed (better and better measurements quickly become from more expensive to too expensive, and finally physically impossible).Engineering is art of "good enough with a bit of safety margin"...Jitter is roughly divided into random and deterministic jitter (RJ and DJ) RJ is noise process that follows Gaussian distribution. DJ is crosstalk, modulation and can be analyzed and decomposed into well defined components of causal nature, i.e. there will be discrete source of interference. Hence deterministic.DJ in clock signals is further divided into periodic jitter (PJ) and other uncorrelated jitter (crosstalk etc, from sources that have varying signals, not just simple single frequencies, like modulation of clock by nearby switcher PSU)Data dependent jitter categories usually don't apply to clock signals, unless you have a crosstalk from data lines to clock lines.. In which case DDJ is also a part of DJ...bla bla bla..There are many books about jitter, and many application specific views of it and, with that, connected measurement types.Today, jitter is mostly measured with scopes and Eye/Jitter analysis packages..In attachment , a Siglent SDG6000G AWG generator outputting 10 MHz and CCJ (Cycle to Cycle jitter) measured with SDS6000A series scope... Instruments are not synchronized and both work from their internal clocks...CCJ P-P 60ps, CCJ RMS (Stdev) 5,5ps both of them combined...

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 01:57:59 pm
content: Quote from: 2N3055 on January 03, 2022, 12:44:39 pmThanks for the info. Yes after reading a bit I learned some very basic info about the topic, and I also have a scope that can do basic jitter analysis. Like I said, my question is for general curiosity.Regarding to your demo measurement, assuming the scope has 10GS/s, so the sampling period is 100ps. How can it report something in 5ps range ? it interpolates from the samples and makes a calculation on the interpolated signal ?

author: 2N3055
author_rank: Super Contributor
timestamp: January 03, 2022, 02:14:03 pm
content: Quote from: metebalci on January 03, 2022, 01:57:59 pmYes, it is averaging and interpolation. Since source and sampling clock are not corelated, it will keep taking samples randomized around the edges, building data.. Together with trigger point interpolation you get very high resolution data..

author: jonpaul
author_rank: Super Contributor
timestamp: January 03, 2022, 02:27:45 pm
content: Rebonjour metebalci, 2N3055 many thanks,The effects and reduction of digital audio clock jitter has been our specialty for decades. Audio quality and noise depends on the entre chain: CODECS, reclocking IC, clock source, cables, EMI interference burden.1/ RE jitter of SPDIF or any encoded digital audio signal, we first recover the clock with a CODEC that takes the input and recovers data and clock. The recovered clock is then measured.2/ Please see my papers in AES since 1995, SMPTE 2014, and NAB 2017. If you send a PM I can send you links.One spec for AES/EBU is :https://tech.ebu.ch/docs/tech/tech3250.pdfGreat jitter paper from Benchmark Audio:https://benchmarkmedia.com/blogs/application_notes/12142221-jitter-and-its-effects3/ Period histogram is the best indicator and RMS jitter = statistics (Sigma)Notice that most instruments and scopes only measure the total wideband jitter, but that digital audio clock jitter is measured with a low pass filter, according to the AES standards.4/ Interfaces are highly variable in interference rejections and jitter , in descending order: AES/EBU 110 Ohm Bal, AES 2id 75 Ohm unbaql, SPDIF and last TOSLINK Optical.5/ High end studio and broadcast devices use high CMRR low Cps transformers like SC947-02LF. Most consumer interfaces use very poorly made low cost transformers.6/ See the classic Dr Steve HARRIS paper on effect of jitter on audio noise. The end result deopends on the ENOB and FS, even for a 20 kHz signal at 24 bits, the 100 pS res of TA320 is fine.7/ PC/MAC created USB and SPDIF sources have the burden of digital noise eg from the SMPS.8/ The TA320 was sufficient for all our studies and papers, with 100 pS res in histograms. TA520 is not much different, and TA720 the very best of the Yokogawas, but not needed.9/ The battery of the TA320 may not have CAL but if dead, the unit is not useable, I forget what happened.9/ I had Very poor results with most digital scopes, like Lecroy and Yokogawa DLM series, even if they have the mats and histogram functions. No expérience the Chines scopes.I hope this answers your concerns and points you in the right direction!Bon chance!Jon Paul

author: 2N3055
author_rank: Super Contributor
timestamp: January 03, 2022, 03:04:57 pm
content: Quote from: jonpaul on January 03, 2022, 02:27:45 pmJon Paul,thank you for sharing your vast knowledge and experience. As we agree, there is no need to go above the point of diminishing returns in any measurements and engineering in general.Unless the point is pushing the envelope of state of the art, in which case usually there is still reason to do so, i.e. some potential application..Scopes went a long way in last 10 years. And Siglent is a long time collaborating with LeCroy. They made great developments in last 5 years alone, and are going forward at a fast pace..Scope I have shown is a new one in mid range class that is a very promising new device.Très respectueusement,Sinisa

author: branadic
author_rank: Super Contributor
timestamp: January 03, 2022, 03:42:01 pm
content: QuoteI can imagine multiple applications, that would benefit from even more time resolution such as 1 ps or far below. For example ACAM manufactures capacitance to digital converters based on tapped delay line TDCs to measure discharge time. We've made several different capacitive sensors in the past, that benefit from the large time resolution of 22 ps and would benefit from even higher time resolution.We also made LVDT position sensors in the past based on phase difference measurement between the secondary coil signals, with phase difference being a time difference at known excitation frequency, that can be measured with TDCs.There is hope that with papers like:"1.0 Ps Resolution Time-to-Digital Converter Based-On Cascaded Time-Difference-Amplifier Utilizing Differential Logic Delay Cells""Wide-Range Time-to-Digital Converter With 1-ps Single-Shot Precision""A high resolution Time-to-Digital Converter (TDC) based on self-calibrated Digital-to-Time Converter""A 1ps Resolution Two-Step Time-to-digital Converter Using Parallel Digital-to-time"the border of the current time resolution for single chip TDCs can be pushed forward, which would enable higher resolution sensors.-branadic-

author: retroware
author_rank: Contributor
timestamp: January 03, 2022, 04:04:08 pm
content: You might want to check out the Wavecrest DTS series of time interval analyzers. Their jitter noise floor is around 5ps with an accuracy around 2ps. They are no longer produced but can still be found on various auction sites.

author: jonpaul
author_rank: Super Contributor
timestamp: January 03, 2022, 04:37:54 pm
content: The Wavecrest DTS are old monsters zero support or info...I have one if you like send a PM, happy to sell it.Jon

author: bnz
author_rank: Regular Contributor
timestamp: January 03, 2022, 04:57:05 pm
content: The Lecroy DDA-3000/WavePro 7300a has a 1ps jitter noise floor.If I remember it correctly, the trigger system is used somehow to get a better than sample resolution.

author: David Hess
author_rank: Super Contributor
timestamp: January 03, 2022, 05:15:29 pm
content: Below about 100 picoseconds, various analog error sources start showing up, including jitter in the trigger comparator based on input noise and bandwidth, so the time to whatever converter requires attention to detail and it is not simply a matter of higher resolution in the ADC. The earliest DSOs achieved 50 picosecond accuracy for 2 GS/s equivalent time sampling. 10 picoseconds (over a short duration) was possible 40 years ago in analog sampling oscilloscopes, and not long after that digital sampling oscilloscopes achieved accuracy of a couple picoseconds.At this level, some type of self calibration is required between measurements to remove drift, which made things easier for oscilloscopes because a missed sample is not a problem. If the instrument must be ready at all times, like with a time-interval analyzer, this might require duplication of the measurement circuitry so that it is always ready, or a calibration cycle could be run after every measurement to correct the previous measurement.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:15:56 pm
content: Quote from: bnz on January 03, 2022, 04:57:05 pmI have a Keysight MSOX 6000, spec says Jitter measurement floor: 600 fs rms at 6 GHz sine wave (typical). I dont fully understand how it maps to 2.5Ghz bandwidth and why it says sine wave, I didnt see any other information yet.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:18:02 pm
content: Quote from: 2N3055 on January 03, 2022, 02:14:03 pmHmm, so in effect it is a bit like sampling scope ?

author: 2N3055
author_rank: Super Contributor
timestamp: January 03, 2022, 05:22:10 pm
content: Quote from: metebalci on January 03, 2022, 05:18:02 pmKind of, yes..

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:23:46 pm
content: Quote from: 2N3055 on January 03, 2022, 05:22:10 pmVery interesting actually, I would not have thought, thanks for pointing it out.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:39:07 pm
content: Quote from: jonpaul on January 03, 2022, 02:27:45 pmWill do.Quote from: jonpaul on January 03, 2022, 02:27:45 pmThat is good to know. I was just yesterday wondering about this. I am sure there are measurements done about it, I will search.Quote from: jonpaul on January 03, 2022, 02:27:45 pmI will check the paper. SPDIF jitter is just a nice example in an area I am interested in, but I guess the numbers in ns range, so my question is not directly related to this.Quote from: jonpaul on January 03, 2022, 02:27:45 pmActually the only reason I said TA520 is as you know it has 25ps resolution like TA720.Quote from: jonpaul on January 03, 2022, 02:27:45 pmSounds a bit scaryQuote from: jonpaul on January 03, 2022, 02:27:45 pmI dont know if it is the right forum to ask this but I ask anyway, I think it is pretty basic info but my scope is new to me still. So I think my scope (MSOX 6000 @ 2.5GHz) is quite OK in terms of measuring the jitter in the SPDIF, but what I did not understand yet is SPDIF is differential manchester, and it cannot decode this (as far as I understand), and I dont understand if clock recovery is valid to be used in this case. I tried visualizing the clock recovery and it seems to be OK but I see 4x of the signal (I thought it should be 2x). If that is not right, I can I guess use constant freq. since I know it, but then there is no data on every clock because of differential manchester. Can jitter analysis be used in this case ? Another example if I want to use width measurement, there is no single width but two, x and 2x.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 05:52:10 pm
content: Quote from: branadic on January 03, 2022, 03:42:01 pmgreat info, thanks, I will check the papers.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 06:12:40 pm
content: Quote from: retroware on January 03, 2022, 04:04:08 pmI heard about it but I didnt look into. It looks pretty good, better than TA series. I need to work on these numbers, I am not totally sure if I understand them right.

author: hgl
author_rank: Regular Contributor
timestamp: January 03, 2022, 06:19:08 pm
content: I am always interested in TDCs for private use and found an interesting project on Github called jTDC .https://github.com/jobisoft/jTDCThis describes a Vernier - TDC with < 30ps resolution on a Spartan 6 FPGA .They have also built a 40nm CMOS chip with 0.8ps resolution.

author: jonpaul
author_rank: Super Contributor
timestamp: January 03, 2022, 06:41:12 pm
content: AES/EBU, SP/DIF Manchester code:https://en.wikipedia.org/wiki/AES3https://tech.ebu.ch/docs/other/aes-ebu-eg.pdfTypical codecs:https://www.akm.com/us/en/products/audio/SRChttps://www.akm.com/us/en/products/audio/ak4137eq/

author: David Hess
author_rank: Super Contributor
timestamp: January 03, 2022, 07:13:12 pm
content: Quote from: metebalci on January 03, 2022, 05:15:56 pmSomewhere a triggering decision is made, whether analog or digital, and the input noise of the trigger and signal interacts with the slew rate to produce jitter in time. A 6 GHz sine wave is a way to sort of specify the slew rate. A lower frequency sine wave would have more jitter. A square wave would presumably have less because the slew rate is higher.Analog trigger circuits often include a low noise limiting amplifier, meaning it is designed to behave benignly when saturated or cut-off, preceding the trigger to raise the slew rate lowering jitter and the effect of the comparator's noise. With enough amplification, the comparator can just be a high noise digital input and sometimes this is done.Digital trigger circuits using an ADC and then digital processing effectively have the same limits in performance due to input noise and maybe some more. Noise beyond the Nyquist frequency folds back causing aliasing so even with a perfect ADC, the trigger point is a smear of possibilities because there are many solutions to the interpolation.I think HP published an application note on this subject in connection with their timer/counters.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 07:22:57 pm
content: Quote from: hgl on January 03, 2022, 06:19:08 pmThat is great to look at, strange but I havent heard TDC acronym before, it seems that is the thing I should search for. The relatively straightforward part is also what I am doing for what I mentioned as interrupt service latency or software reaction time: "One of the key features of this implementation is its rate stability: Each input can record up to 200 MHz without a hit being overseen; a true double pulse resolution of 5ns."

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 07:41:41 pm
content: Quote from: jonpaul on January 03, 2022, 06:41:12 pmYes I checked the specs while trying to connect an SPDIF output to scope and while trying to make sense of it. I dont have an AES3 interface at the moment. I have one device also with word clock output, so it makes more sense looking at them together. I know a little bit about AKM and ESS DACs but not CODEC or SRC ICs.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 08:49:42 pm
content: Nice overview presentation from CERN (2008):https://indico.cern.ch/event/43741/contributions/1924510/attachments/939372/1332084/TIMMethods.pdfPaper it is based on (2004):https://ztc.wel.wat.edu.pl/met4_1_004.pdfSo the methods very briefly:- Coarse counting / periodic function sampling: counting the number of pulses inside the event, straightforward method, resolution can be improved by random sampling (e.g. sampling scope) and averaging- time stretching then counter: I dont know any device- time to amplitude then ADC: Yokogawa TA series, SR 620- Vernier method: HP 5370A- Tapped delay line: HP5371A, jTDC project mentioned beforeThere are some numbers on the paper about their resolution etc. but not sure what the current state-of-art is, I should find a recent paper.

author: hgl
author_rank: Regular Contributor
timestamp: January 03, 2022, 09:28:24 pm
content: Quote from: metebalci on January 03, 2022, 07:22:57 pmmore search terms ...There are among others TDC (Time to Digital Converters) and TAC (Time to Analog Converters) with subsequent analog to digital conversion. The measured time between 2 events (start and stop) is usually called TOF (Time of Flight). And the measurement units are called TIA (Time Interval Analyzer).Ich have an HP E1740A with 50ps resolution.https://www.eevblog.com/forum/testgear/hp-e1740a-time-interval-analyzer-292384/msg3718660/

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 09:34:02 pm
content: I think I have found a state-of-the-art device (photon counting and timing, LIDAR), it has 1ps resolution. So sub-picosecond resolution seems to be cutting edge.https://www.picoquant.com/products/category/tcspc-and-time-tagging-modules/hydraharp-400-multichannel-picosecond-event-timer-tcspc-module

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 09:39:19 pm
content: Quote from: hgl on January 03, 2022, 09:28:24 pmTDC was helpful, I found now the literature and research. It seems optics/quantum research (so including various imaging related things) and radar are major applications.

author: hgl
author_rank: Regular Contributor
timestamp: January 03, 2022, 10:26:03 pm
content: Quote from: metebalci on January 03, 2022, 09:34:02 pmIf you read the specifications carefully you will find :Minimum time bin width 1 psTiming precision* < 12 ps rmsTiming precision / √2* < 8.5 ps rmsThere is no temperature range or the precision over temperature specified.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 03, 2022, 10:34:48 pm
content: Quote from: hgl on January 03, 2022, 10:26:03 pmYou mean it has to be kept in a temp controlled environment ?

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2022, 02:44:48 am
content: Quote from: 2N3055 on January 03, 2022, 12:44:39 pmThese numbers are more likely the noise floor of your oscilloscope than what is actually happening. Clock jitter (phase noise) is to be analysed using a phase noise / frequency stability analyser. The problem with an oscilloscope is that it introduces too much noise in the signal path. Unfortunately the jitter or phase noise for the SDG6k don't seem to be specified in the datasheet.

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2022, 08:08:43 am
content: Rebonjour a tous:Our fine but ancient Yokogawa TA720 has 25 pS res.https://tmi.yokogawa.com/us/solutions/discontinued/ta720-time-interval-analyzers/We measured the jitter of the internal REF clock 10 MHz and discovered the limitation was the internal REF clock jitter.Used external REF CLK 10.000 MHz, Leo Bodnar GPS or Wenzel TCXOand tested the residual jitter of the same EXT REF CLK.So, intrinsic jitter of the TA720, the input stage and trigger circuit etc.RMS jitter was ~ 27..35 pS, slightly different between two channels.Your thoughts?Can others post such an intrinsic jitter test for LeCroy or Chinese scopes?Bon Chance,Jon

author: 2N3055
author_rank: Super Contributor
timestamp: January 04, 2022, 09:09:11 am
content: Quote from: nctnico on January 04, 2022, 02:44:48 amWell, 5,5 ps is combined. That is scope measuring SDG6000X. If that is noise floor for both of them, those are some epic specs for SDG6000X... And quite good for a scope.5.5ps is better than 25ps from those analyzers.What I was trying to say is that there are many ways to go about measurement.Also it isn't clear to me whether OP now talks about single shot measurements of time delay between two pulses or clock characterization for jitter, because along the way it seems that topic shifted.For clock characterization, if OP has scope with jitter/eye package (DSOX6000) that is more than enough to measure jitter of audio related clocks. No need for sub ps jitter measurements there.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 09:38:09 am
content: My scope (MSOX 6000, 20GS/s, 2.5GHz bandwidth) has spec 600fs jitter measurement floor for 6GHz sine wave. So if that is the sine wave measured, with a digital signal I guess it is not worse (as David mentioned before due to slew rate), and this spec does not mention the bandwidth (scope has max 6 GHz), but I guess having a less than max bandwidth decreases noise so again this does not increase this 600fs number.I am not 100% sure about the time base jitter relevant for the jitter analysis (or is the jitter measurement floor includes all these elements?). Time base accuracy is 2.5ps, trigger jitter is less than 3ps or 1ps depending on the setting.So from what I understand from these, measuring something like 5ps jitter should be possible, which is better than TA series time interval analyzers, and probably close to Wavetek devices.Coming back to my original question, I was not asking about a particular application of jitter measurement (and yes if the above understanding is correct, the scope is more than enough for audio related jitter measurements), but the current limits of time interval measurements. Maybe to sum up:- If my understanding of the capability of the scope is correct in terms of jitter measurement, it is very good, better than the analyzers mentioned. I was not expecting this.- However the scope (and also I think phase noise analyzers) is limited to periodic signals (clock, sine) or serial signals with embedded clock. So for irregular events, they are not a solution, but analyzers are.- To me it looks like sub-picoseconds is not possible at the moment. It seems there is a good research activity around tapped delay line based solutions close to picoseconds.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 09:40:02 am
content: Quote from: nctnico on January 04, 2022, 02:44:48 amCan a phase noise analyzer be used for non-sinusoidal and serial encoded digital signals ?

author: hgl
author_rank: Regular Contributor
timestamp: January 04, 2022, 09:46:22 am
content: Quote from: metebalci on January 03, 2022, 10:34:48 pmI just miss the specs. In the order of a picosecond, everything plays a role. Light in a vacuum travels only about 0.3 millimeters in this time. Electrical signals are only slightly slower.The effects can be calibrated and stored in correction tables, but not over any temperature range.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 09:46:42 am
content: Quote from: jonpaul on January 04, 2022, 08:08:43 amTwo related further questions:- how is the jitter noise floor of a scope measured ? with a much lower phase noise oscillator, so whatever seen is the noise ?- if a low phase noise external ref clk is provided to the scope, is the jitter noise floor also decreased ? Coming back to my scope's 600fs jitter noise floor number, I am trying to calculate this but I am probably not doing it right, if 600fs is translated to a 10MHz oscillator, how much phase noise is this ? Lets say I am measuring a 20 MHz signal, and if it matters lets say the measurement channel bandwidth is 1Ghz.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 09:51:11 am
content: Quote from: hgl on January 04, 2022, 09:46:22 amThanks for putting this in the context of light, I missed thatSo it is probable other things limit the sub-picosecond resolutions.

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2022, 10:20:47 am
content: Speed of light, is 299792 km/sec so 25 pS is ~ 0.7 cm and 5 pS is 0.15 cm.Jon

author: hgl
author_rank: Regular Contributor
timestamp: January 04, 2022, 10:32:59 am
content: With this device you can measure repetitive time intervals with 1ps (histogram bin) resolution, an average accuracy of 12.5 ps with a standard deviation of 8.5ps.For single shot intervals you can define one channel as start signal and the other channels as stop signal to measure (T2 mode). Maybe also with 1ps resolution, but with what accuracy ?

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 10:57:31 am
content: Quote from: hgl on January 04, 2022, 10:32:59 amI also realized I am not always using the term resolution correctly or as I intend, I naturally dont mean a display or empty resolution. What I have in mind is naturally accuracy, or at least not very different accuracy and resolution numbers. If I am not wrong, TA series has much worse accuracy numbers in ns level. Wavecrest says <2ps accuracy and 3<ps noise floor which are pretty good. The scope has ~1ppm time base accuracy, so I guess it means for 10MHz signal it is also in ps range. For this device, I assumed it is average number in 10ps region.

author: nctnico
author_rank: Super Contributor
timestamp: January 04, 2022, 12:30:18 pm
content: Quote from: 2N3055 on January 04, 2022, 09:09:11 amNo. The 25ps number is for single shot measurements peak-to-peak.QuoteThat is true.

author: ramon
author_rank: Regular Contributor
timestamp: January 04, 2022, 01:02:57 pm
content: Quote from: metebalci on January 03, 2022, 09:34:02 pmThere is also another whole universe under this keywords: "OTN Jitter femtoseconds" "800G jitter femtoseconds"Are you close to Interlaken? There was a protocol named Interlaken that started the path to 10G and above ... many years ago.

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2022, 01:40:03 pm
content: Meta:Resolution is the smallest distinguishable change, eg a DVM has 5 digits or a divider has a 0.001% resolution.Accuracy is the error in a measurement eg a 10.0000 V ref has a rated accuracy of +/- 50 ppm.Jitter is a statistic of a set of period samples. It is the peak to peak or RMS difference between the nominal (center) periodSuggest to read the Dr Steve Harris Crystal Semi“The Effects of Sampling Clock Jitter on Nyquist Sampling Analog-to-Digital Converters and Oversampling Delta-Sigma ADCs,” Journal ofAudio Engineering Society, Vol. 38, pp. 537- 542, Jul/Aug 1990Also the fine Audio Precision Jitter papers by Dr Julian DUNN (RIP)http://www.audiophilleo.com/zh_hk/docs/Dunn-AP-tn23.pdfBest Regards,Jon

author: hgl
author_rank: Regular Contributor
timestamp: January 04, 2022, 01:46:52 pm
content: Quote from: jonpaul on January 04, 2022, 10:20:47 am1km = 1E6 mm;1s = 1E12 ps;299792 * 1E6 / 1E12 = 299792 / 1E6 = 0.299792 mm/ps

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 03:30:48 pm
content: Quote from: ramon on January 04, 2022, 01:02:57 pmGood idea to look at these and even before optical networks PCIe 4 has 500fs jitter spec. Are they looking into these signals in time domain ? Anyone knows the jitter floor of very expensive scopes ?Maybe like 2h to InterlakenI didnt know the protocol

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 05:34:05 pm
content: Quote from: jonpaul on January 04, 2022, 01:40:03 pmWhat I mean is sometimes there is a too large gap between accuracy and resolution, the spec of TA520 is a little like that, if I read correct, display resolution is 25ps, but accuracy is at best +-1ns. 40x difference. On the other hand and again if I read this correct, Wavecrest DTS 2075 has 800fs resolution and less than 2ps accuracy, so around 2x. I didnt fully calculate but it is also not that different for the scope I think.Just thinking loudly.. also maybe for jitter measurement precision is more important, for irregular time intervals accuracy is. Not sure if precision and accuracy numbers are same for these devices, precision is not given, maybe it is same as accuracy.

author: jonpaul
author_rank: Super Contributor
timestamp: January 04, 2022, 06:47:11 pm
content: Hello again,1/ Wavecreest: 1990s diansaurs, cant get them runnong, used old windows I recall.2/ I never saw or used the comparisons you make re jitter.The accuracy of PERIOD depends on the REF clock of the scope or analyzer. Never an issue!The jitter is a statistical number derived from a period sample set.The resolution is the minimum increment in a jitter measurement, eg a histogram is 100 pS in TA320 and 25 pS in TA720.Sub pS measurements are best researched at your local Swiss facilities:CERN near Genève and ETH in Zurich also Zurich Instruments.Kind Regards,Jon

author: David Hess
author_rank: Super Contributor
timestamp: January 04, 2022, 07:18:26 pm
content: Quote from: metebalci on January 03, 2022, 08:49:42 pmBruce from the Time-Nuts email listhas a pagewhich describes the major methods. Modern DSOs with "digital triggering" use transition midpoint timing and no separate trigger circuit path. Old DSOs use dual slope/ramp because they had no requirement for faster operation.Quote from: metebalci on January 04, 2022, 09:46:42 amThat is right.QuoteNo, because the much faster internal sampling clock is phase locked to the external reference, so only long term jitter is improved.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 04, 2022, 07:24:37 pm
content: Quote from: jonpaul on January 04, 2022, 06:47:11 pmDepends on what you want to do. For frequency and time interval measurements, the DTS 2050/2070 series are supported by Timelab so data collection is painless if you have GPIB. The data can be exported for use in other programs.While reading the manual for my DTS-2077, I came across the section on "strobing voltmeter" and realized it could be used as a subsampling scope with a 100 Gsps equivalent sampling rate. I threw together a *very* crude proof-of-concept program and captured the data shown in the attached graph. The X-axis is units of 100 ps. The Y-axis is volts. There are various limitations (trigger, memory, etc.) so I don't know if it's actually practical to use the beast as a scope.Ed

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: January 04, 2022, 07:47:04 pm
content: Carmel Instruments makes PXIe time interval analyzers that have single edge jitter of about 2psec rmshttps://www.carmelinst.com/products/counters-time-interval-analyzers

author: metebalci
author_rank: Frequent Contributor
timestamp: January 04, 2022, 08:10:33 pm
content: Quote from: David Hess on January 04, 2022, 07:18:26 pmGreat, thanksQuote from: David Hess on January 04, 2022, 07:18:26 pmOK nice, I will soon have a low phase noise oscillator, I will try to see which one has lower noise.Quote from: David Hess on January 04, 2022, 07:18:26 pmMaybe it is difficult to answer briefly but can you tell why only the long term jitter is improved ? or where can I look ? I ask because I thought PLL transfers some portion of the phase noise of the reference to output, so why there would be no change here ?

author: David Hess
author_rank: Super Contributor
timestamp: January 04, 2022, 11:03:27 pm
content: Quote from: metebalci on January 04, 2022, 08:10:33 pmThe PLL combines the noise spectrums based on its breakpoint frequency, which is necessarily below its Nyquist frequency. So the phase noise and jitter can only be improved at lower frequencies where the PLL is influencing the output, which only affects long term jitter. Of course if it is long term jitter that you want to improve, then that is well worthwhile.Measuring the jitter will likely involve a low phase noise crystal oscillator while the DSO is relying on a PLL multiplied VCO so it should not be difficult to find a difference. You might remember a couple years ago where the Rigol DS1000Z series was revealed to have problems with very high jitter at low frequencies because of a design error in its PLL.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 05, 2022, 06:51:16 am
content: Quote from: David Hess on January 04, 2022, 11:03:27 pmI realized I was mistaken in something in how PLL works. Many thanks David.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 05, 2022, 06:57:58 am
content: Quote from: maxwell3e10 on January 04, 2022, 07:47:04 pmAnother cool device, I didnt find info about how it exactly works

author: 1audio
author_rank: Frequent Contributor
timestamp: January 09, 2022, 07:03:47 pm
content: RE HP5370 The resolution floor is 20 pShttps://www.febo.com/pages/hp5370b/

author: Echo88
author_rank: Frequent Contributor
timestamp: January 10, 2022, 12:18:08 am
content: TAPR-TICC:https://github.com/TAPR/TICC60ps resolution open source counterhttps://tapr.org/product/tapr-ticc/

author: metebalci
author_rank: Frequent Contributor
timestamp: January 12, 2022, 06:57:50 am
content: Quote from: Echo88 on January 10, 2022, 12:18:08 amThanks. I did not know there are TDC ICs like the TI one used in this project.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 21, 2022, 08:00:53 pm
content: This IC TDC7200 is pretty nice. I made a small prototype to measure the time it takes to set two GPIO lines to high immediately one after other on a RPi, and it works flawlessly. I think the error is around ±50ps assuming the external clock is good enough.For example:Quote

author: hgl
author_rank: Regular Contributor
timestamp: January 22, 2022, 08:49:23 pm
content: Can you show us exactly what you did ?

author: metebalci
author_rank: Frequent Contributor
timestamp: January 23, 2022, 09:07:06 am
content: Quote from: hgl on January 22, 2022, 08:49:23 pmI mounted the IC on a DIP adapter and put on the breadboard, connected the SPI and other relevant lines (ENABLE, INTB, TRIGG, START, STOP) to a RPi. I am powering both from a power supply (5V for RPi, 3.3V for TDC), and using the waveform generator of the scope for CLOCK at the moment. I tried 2MHz and 5MHz for the CLOCK, both works fine, 10MHz is not working, I guess because of the breadboard. I wrote two programs on RPi, one for measuring (tia), one for device simulation (dut).I checked some measurements with the scope and they are roughly correct.I uploaded the programs here:https://github.com/metebalci/tdc7200_demo

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: January 23, 2022, 11:05:20 am
content: Quote from: edpalmer42 on January 04, 2022, 07:24:37 pmWhat's the risetime of this pulse source?Leo

author: edpalmer42
author_rank: Super Contributor
timestamp: January 23, 2022, 05:29:35 pm
content: Quote from: Leo Bodnar on January 23, 2022, 11:05:20 amIt's a 74AC04 inverter. I don't know what the risetime is speced at. The only spec the datasheets give is propagation delay. I paralleled two gates and included a resistive attenuator to reduce the output voltage while still providing a 50 ohm source impedance. It's intended use is to connect to a Wavecrest DTS-2077 which has a maximum input voltage of 1V2 and, I think, a damage level of 1V7. The resistive attenuator keeps even the open-circuit voltage to a safe level.Ed

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: January 23, 2022, 10:06:49 pm
content: Quote from: edpalmer42 on January 23, 2022, 05:29:35 pmOh, so the whole chart is 1300 x 100ps = 130ns, correct? 10/90 risetime then looks like about 2ns?Leo

author: edpalmer42
author_rank: Super Contributor
timestamp: January 23, 2022, 11:10:59 pm
content: Quote from: Leo Bodnar on January 23, 2022, 10:06:49 pmCorrect. If not for the wiggles at the top, risetime might have been < 1ns. Most annoying!However, I set my trigger voltage to about 0V25 to get the best slew rate so the wiggles aren't an issue.Ed

author: hgl
author_rank: Regular Contributor
timestamp: January 24, 2022, 03:43:00 pm
content: [quoteQuote from: metebalci on January 21, 2022, 08:00:53 pm

author: metebalci
author_rank: Frequent Contributor
timestamp: January 24, 2022, 05:12:45 pm
content: Quote from: hgl on January 24, 2022, 03:43:00 pm

author: hgl
author_rank: Regular Contributor
timestamp: January 24, 2022, 06:16:38 pm
content: 12 ns are the minimum time between start and stop signal and is mode independent. TICC runs in Mode 2 and a minimum of 300 ns TOF.My minumum is 100ns TOF in Mode 1. And the course counter I had chosen 5 stop pulses because I thought I could average them. The longer the times become the more scattered the results and you do not get a higher resolution.There is also the AS6501 with 2 channels, which claims 10ps resolution. I have ordered 2 for testing.

author: metebalci
author_rank: Frequent Contributor
timestamp: January 24, 2022, 07:28:51 pm
content: Quote from: hgl on January 24, 2022, 06:16:38 pmThe minimum interval in recommended conditions in the datasheet is different for modes, 12ns vs. 2xTclock. Maybe 12ns also works even if no clock rise happens in mode 2 but even if it is the case it doesnt look like it is recommended.I will check AS6501, thanks for mentioning.

author: David Hess
author_rank: Super Contributor
timestamp: January 24, 2022, 10:01:32 pm
content: Some time interval measurement methods have difficulty measuring very short periods, so they have a minimum pulse width which is much greater than their resolution. On a digital storage oscilloscope this is not a problem because the trigger can be compared to a later sampling clock edge.This can be worked around in the design, and negative time can even be measured, but it is tricky.