Re: [time-nuts] Phase noise confusion II
On Thu, April 9, 2020 11:20 pm, Hal Murray wrote: > Suppose I measure the edge to edge times and make a histogram. How precisely can you measure the period. You would be using the rising edge as start time and stop time, with no dead time, i.e. measure the time of every period? > Can I get jitter out of that? I think that is typically referrred to as period jitter in the literature I have seen. I think you could in theory derive any other view of the timing error if you had enough measurements, and if the measurements had enough precision and accuracy. I think in practice that is difficult to achieve, otherwise there would not be need for DMTD, PLL based mix down for phase noise measurement, Miles's fancy quad ADC instruments, etc., you could just use a time interval counter for everything. Most of the jitter terminology has come from the digital communications industries, because that is typically where you care about edge position, vs. phase noise in an application where you care about modulation, noise in an RF transmitter or receiver, etc. This app note has an overview of the definitions of the various ways to measure jitter: https://www.sitime.com/sites/default/files/gated/AN10007-Jitter-and-measurement.pdf I have some small quibbles, like in section 2.1.2 it begins with the statement "Because the period jitter from a clock is random in nature with Gaussian distribution" I would rather phrase it "If the period jitter from a clock is random in nature" because there are a lot of ways that systematic noise can get into a clock and make the jitter behavior not random, or at least non-Gaussian. > Where is the clock recovery loop? I think that comes from a lot of the measurement techniques where you don't care if the clock you are measuring is slightly off of nominally perfect frequency, because the receiver will have a PLL which will track the average value of the clock, what you care about is short term variation around that average value, so the measurement techniques utilize a PLL (either physically implemented, or simulated in software) to mimic the behavior of the receiver PLL so that you effectively ignored slow variation in the average period time. On Fri, April 10, 2020 5:05 am, Dana Whitlow wrote: > Question about definition of jitter: Is it the variation in > pulse-to-pulse spacing, or is it > the variation in pulse positions with respect to a jitter-free waveform? See the document linked above, there are various distinctions made to what and how you measure the period based on how the clock is being used or what particular behavior you care about. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
Hi Back quite a while ago, I went back and visited my buddies / ex-coworkers at Motorola Franklin Park ( = the Motorola crystal / oscillator group). Based on my past experience with the yields on a “quartz bar to oscillator” fab process, I asked: How do you build a “6 sigma” oscillator? ….. The answer: You divide the process up into about 6,000 independent “points of failure”. You then postulate that those failures can only be “detected” at the final test end of things. I’m not suggesting that is a *wrong* answer, only that it was a somewhat surprising approach to solving the “problem”. Bob > On Apr 10, 2020, at 12:27 PM, Richard (Rick) Karlquist > wrote: > > > > On 4/10/2020 5:47 AM, Bob kb8tq wrote: >> Hi >> It is not at all uncommon to …. errr …. make that decision, regardless >> of what the customer might think about it :) >> Even with that sort of decision, the whole process of measuring a one >> sigma and multiplying by 6 depends very much on the underlying >> processes (noise or maybe something else ….) being well behaved / >> Gaussian sort of things. One can at least on paper construct situations >> that do not meat that “well behaved” constraint ….. >> >> Bob >> > > > A few decades ago, Motorola had a "six sigma" program > which made everyone think they were a statistician just > because they knew that buzzword. > > Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
On 4/10/2020 5:47 AM, Bob kb8tq wrote: Hi It is not at all uncommon to …. errr …. make that decision, regardless of what the customer might think about it :) Even with that sort of decision, the whole process of measuring a one sigma and multiplying by 6 depends very much on the underlying processes (noise or maybe something else ….) being well behaved / Gaussian sort of things. One can at least on paper construct situations that do not meat that “well behaved” constraint ….. Bob A few decades ago, Motorola had a "six sigma" program which made everyone think they were a statistician just because they knew that buzzword. Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
Hi It is not at all uncommon to …. errr …. make that decision, regardless of what the customer might think about it :) Even with that sort of decision, the whole process of measuring a one sigma and multiplying by 6 depends very much on the underlying processes (noise or maybe something else ….) being well behaved / Gaussian sort of things. One can at least on paper construct situations that do not meat that “well behaved” constraint ….. Lots and lots of issues. If you turn back the clock, this whole thing is very similar to the 1960’s frequency stability measurement fun and games. That’s what ultimately gave us ADEV. Bob > On Apr 10, 2020, at 8:05 AM, Dana Whitlow wrote: > > I once got into that "p-p" business and it was like pulling teeth to get > the customer > even semi-reasonable. He finally agreed to stipulate that the p-p value > could be > construed as 6 X the rms value. > > Dana > > > On Fri, Apr 10, 2020 at 6:57 AM Bob kb8tq wrote: > >> Hi >> >> Which of the multitude of definitions are we talking about? >> >> One very common definition looks at peak to peak jitter and does >> not care about the center. Another looks at +/- peak to edge and >> then uses the greater of the two numbers. Other definitions look >> at RMS jitter and generally don’t care about the edge. >> >> At least to me, the biggest problem is that any time “peak” or “peak >> to peak” comes in to a calculation that involves random noise, >> things go sideways fast. People pretty much never want to >> define a confidence level (how any sigma?). They want an >> absolute number. >> >> Lots of fun >> >> Bob >> >>> On Apr 10, 2020, at 6:05 AM, Dana Whitlow wrote: >>> >>> Question about definition of jitter: Is it the variation in >>> pulse-to-pulse spacing, or is it >>> the variation in pulse positions with respect to a jitter-free waveform? >>> >>> Dana >>> >>> >>> On Thu, Apr 9, 2020 at 11:21 PM Hal Murray >> wrote: >>> rich...@karlquist.com said: > There is always an implied clock recovery loop that the the jitter is > measured against. The loop may itself affect the jitter measurement either by > cleaning up jitter or contributing to it. Interesting. I hadn't thought about it that way. Suppose I measure the edge to edge times and make a histogram. Can I >> get jitter out of that? Where is the clock recovery loop? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. >>> ___ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
Hi Which of the multitude of definitions are we talking about? One very common definition looks at peak to peak jitter and does not care about the center. Another looks at +/- peak to edge and then uses the greater of the two numbers. Other definitions look at RMS jitter and generally don’t care about the edge. At least to me, the biggest problem is that any time “peak” or “peak to peak” comes in to a calculation that involves random noise, things go sideways fast. People pretty much never want to define a confidence level (how any sigma?). They want an absolute number. Lots of fun Bob > On Apr 10, 2020, at 6:05 AM, Dana Whitlow wrote: > > Question about definition of jitter: Is it the variation in > pulse-to-pulse spacing, or is it > the variation in pulse positions with respect to a jitter-free waveform? > > Dana > > > On Thu, Apr 9, 2020 at 11:21 PM Hal Murray wrote: > >> >> rich...@karlquist.com said: >>> There is always an implied clock recovery loop that the the jitter is >>> measured against. The loop may itself affect the jitter measurement >> either by >>> cleaning up jitter or contributing to it. >> >> Interesting. I hadn't thought about it that way. >> >> Suppose I measure the edge to edge times and make a histogram. Can I get >> jitter out of that? Where is the clock recovery loop? >> >> -- >> These are my opinions. I hate spam. >> >> >> >> >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
IIRC the latter -Original Message- From: time-nuts [mailto:time-nuts-boun...@lists.febo.com] On Behalf Of Dana Whitlow Sent: 10 April 2020 11:06 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Phase noise confusion II Question about definition of jitter: Is it the variation in pulse-to-pulse spacing, or is it the variation in pulse positions with respect to a jitter-free waveform? Dana ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
rich...@karlquist.com said: > There is always an implied clock recovery loop that the the jitter is > measured against. The loop may itself affect the jitter measurement either by > cleaning up jitter or contributing to it. Interesting. I hadn't thought about it that way. Suppose I measure the edge to edge times and make a histogram. Can I get jitter out of that? Where is the clock recovery loop? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Phase noise confusion II
Perry, Typically jitter is expressed in the time domain (so many ps peak to peak for instance) Phase noise is expressed as a power ratio in the frequency domain. Otherwise they usually represent the same phenomenon. Didier On Thu, Apr 9, 2020, 6:29 PM Perry Sandeen via time-nuts < time-nuts@lists.febo.com> wrote: > Learned Gentlemen, > > The explanation by Tobias was excellent and fully answered my question. > > I think I'll be able to use my Fluke 6080AN for offset generation so the > problem will be the measurement after the mixer. > What is now called phase noise was taught to me as *jitter* over 55 years > ago. > Regards, > Perrier > > > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] Phase noise confusion II
Learned Gentlemen, The explanation by Tobias was excellent and fully answered my question. I think I'll be able to use my Fluke 6080AN for offset generation so the problem will be the measurement after the mixer. What is now called phase noise was taught to me as *jitter* over 55 years ago. Regards, Perrier ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
