Forums

Phase Noise vs. Jitter

Started by Cursitor Doom September 14, 2019
Gentlemen,

I thought these terms were effectively the same thing, but now I'm not so 
sure. 
Taking a square waveform of uniform amplitude for the sake of simplicity, 
AFAIAA, if I'm looking at such a wave in the time domain with an 
oscilloscope and I'm seeing intermittent thickening of the vertical 
portions of the trace, that's jitter. But if the frequency of the wave is 
more slowly varying, then that's phase noise, which can be observed with 
a spectrum analyser (frequency domain) as the presence of unwanted 
sidebands on what would be an otherwise infinitely thin vertical peak if 
the wave had perfect spectral purity. Do I have that right? 
<cue massive argument, probably>

TIA



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On Sun, 15 Sep 2019 00:25:46 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>Gentlemen, > >I thought these terms were effectively the same thing, but now I'm not so >sure. >Taking a square waveform of uniform amplitude for the sake of simplicity, >AFAIAA, if I'm looking at such a wave in the time domain with an >oscilloscope and I'm seeing intermittent thickening of the vertical >portions of the trace, that's jitter. But if the frequency of the wave is >more slowly varying, then that's phase noise, which can be observed with >a spectrum analyser (frequency domain) as the presence of unwanted >sidebands on what would be an otherwise infinitely thin vertical peak if >the wave had perfect spectral purity. Do I have that right? ><cue massive argument, probably> > >TIA
There's a math operation that maps one into the other, at least for wideband noise and RMS jitter. There are several calculators online. One of the guys here did this: https://www.dropbox.com/s/zkhw9nlkwurcy7q/PhaseNoise102.exe?dl=0 In the telecom business, stuff below 0.1 Hz is called "wander" and faster wiggles are "jitter."
On Saturday, September 14, 2019 at 8:25:51 PM UTC-4, Cursitor Doom wrote:
> Gentlemen, > > I thought these terms were effectively the same thing, but now I'm not so > sure. > Taking a square waveform of uniform amplitude for the sake of simplicity, > AFAIAA, if I'm looking at such a wave in the time domain with an > oscilloscope and I'm seeing intermittent thickening of the vertical > portions of the trace, that's jitter. But if the frequency of the wave is > more slowly varying, then that's phase noise, which can be observed with > a spectrum analyser (frequency domain) as the presence of unwanted > sidebands on what would be an otherwise infinitely thin vertical peak if > the wave had perfect spectral purity. Do I have that right? > <cue massive argument, probably> > > TIA > > > > -- > This message may be freely reproduced without limit or charge only via > the Usenet protocol. Reproduction in whole or part through other > protocols, whether for profit or not, is conditional upon a charge of > GBP10.00 per reproduction. Publication in this manner via non-Usenet > protocols constitutes acceptance of this condition.
What you seem to be talking about is like the old turntables which has specs for "wow" and "flutter". One was fast and the other slow. Same but different. Or not so different really, they just produced different effects on the sound and usually had different causes, but both are just variations in the speed of the platter. Likewise your jitter and phase noise are the same thing, just different parts of the frequency spectrum. Same but different. Why do you care exactly? How are you using this? -- Rick C. - Get 2,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
On Sunday, September 15, 2019 at 2:08:22 PM UTC+10, Rick C wrote:
> On Saturday, September 14, 2019 at 8:25:51 PM UTC-4, Cursitor Doom wrote: > > Gentlemen, > > > > I thought these terms were effectively the same thing, but now I'm not so > > sure. > > Taking a square waveform of uniform amplitude for the sake of simplicity, > > AFAIAA, if I'm looking at such a wave in the time domain with an > > oscilloscope and I'm seeing intermittent thickening of the vertical > > portions of the trace, that's jitter. But if the frequency of the wave is > > more slowly varying, then that's phase noise, which can be observed with > > a spectrum analyser (frequency domain) as the presence of unwanted > > sidebands on what would be an otherwise infinitely thin vertical peak if > > the wave had perfect spectral purity. Do I have that right? > > <cue massive argument, probably> > > > > TIA > > > > > > > > -- > > This message may be freely reproduced without limit or charge only via > > the Usenet protocol. Reproduction in whole or part through other > > protocols, whether for profit or not, is conditional upon a charge of > > GBP10.00 per reproduction. Publication in this manner via non-Usenet > > protocols constitutes acceptance of this condition. > > What you seem to be talking about is like the old turntables which has specs for "wow" and "flutter". One was fast and the other slow. Same but different. Or not so different really, they just produced different effects on the sound and usually had different causes, but both are just variations in the speed of the platter. > > Likewise your jitter and phase noise are the same thing, just different parts of the frequency spectrum. Same but different. > > Why do you care exactly? How are you using this?
Actually "jitter" is variation in period, and is measured once per period, and phase noise is variation from an ideal - perfectly regular - waveform and is integrated over the whole period. It's not always a particularly useful distinction, but Cursitor Doom doesn't think about what he's doing. -- Bill Sloman, Sydney
On Sat, 14 Sep 2019 21:08:18 -0700, Rick C wrote:
 
> Why do you care exactly? How are you using this?
A recent acquaintance of mine has built some fancy super-fast (to me) oscillator which he wants to hook up to one of my SAs to check for stability and purity. I don't want to look an ass if he asks me something technical that's above my pay-grade and as a mere hobbyist, my-pay grade is pretty low. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
On Sat, 14 Sep 2019 20:06:46 -0700, jlarkin wrote:

> There's a math operation that maps one into the other, at least for > wideband noise and RMS jitter. There are several calculators online.
I don't want a mathematical explanation, though; just an intuitive one.
> In the telecom business, stuff below 0.1 Hz is called "wander" and > faster wiggles are "jitter."
In that case I've discovered a new phenomenon I've dubbed "twitch". :-) "Exe files can't be previewed" it says on your link. Let's try re-phrasing it thus: phase noise produces sidebands. Does jitter? -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
On Sunday, September 15, 2019 at 7:14:27 PM UTC+10, Cursitor Doom wrote:
> On Sat, 14 Sep 2019 20:06:46 -0700, jlarkin wrote: > > > There's a math operation that maps one into the other, at least for > > wideband noise and RMS jitter. There are several calculators online. > > I don't want a mathematical explanation, though; just an intuitive one.
Something dumbed down enough for Cursitor Doom to understand.
> > In the telecom business, stuff below 0.1 Hz is called "wander" and > > faster wiggles are "jitter." > > In that case I've discovered a new phenomenon I've dubbed "twitch". :-) > > "Exe files can't be previewed" it says on your link. > > Let's try re-phrasing it thus: phase noise produces sidebands. Does > jitter?
The kind of deviations from the ideal perfectly repetitive waveform that constitute phase noise, and can be characterised as jitter, show up as low level sidebands on the Fourier transform of a noisy and jittery waveform. -- Bill Sloman, Sydney
Bill Sloman <bill.sloman@ieee.org> wrote in
news:b12adec6-6c84-438b-877c-f010a60b8106@googlegroups.com: 

> On Sunday, September 15, 2019 at 7:14:27 PM UTC+10, Cursitor Doom > wrote: >> On Sat, 14 Sep 2019 20:06:46 -0700, jlarkin wrote: >> >> > There's a math operation that maps one into the other, at least >> > for wideband noise and RMS jitter. There are several >> > calculators online. >> >> I don't want a mathematical explanation, though; just an >> intuitive one. > > Something dumbed down enough for Cursitor Doom to understand. > >> > In the telecom business, stuff below 0.1 Hz is called "wander" >> > and faster wiggles are "jitter." >> >> In that case I've discovered a new phenomenon I've dubbed >> "twitch". :-) >> >> "Exe files can't be previewed" it says on your link. >> >> Let's try re-phrasing it thus: phase noise produces sidebands. >> Does jitter? > > The kind of deviations from the ideal perfectly repetitive > waveform that constitute phase noise, and can be characterised as > jitter, show up as low level sidebands on the Fourier transform of > a noisy and jittery waveform. >
clock jitter. <https://about.keysight.com/en/newsroom/imagelibrary/2006/02may- em06067/> <https://about.keysight.com/en/newsroom/imagelibrary/2006/02may- em06067/image001.jpg>
Bill Sloman <bill.sloman@ieee.org> wrote in
news:ac91c001-a3a0-4aa6-8243-f600aa23c606@googlegroups.com: 

> On Sunday, September 15, 2019 at 2:08:22 PM UTC+10, Rick C wrote: >> On Saturday, September 14, 2019 at 8:25:51 PM UTC-4, Cursitor >> Doom wrote: >> > Gentlemen, >> > >> > I thought these terms were effectively the same thing, but now >> > I'm not > so >> > sure. >> > Taking a square waveform of uniform amplitude for the sake of >> > simplicit > y, >> > AFAIAA, if I'm looking at such a wave in the time domain with >> > an oscilloscope and I'm seeing intermittent thickening of the >> > vertical portions of the trace, that's jitter. But if the >> > frequency of the wave > is >> > more slowly varying, then that's phase noise, which can be >> > observed wit > h >> > a spectrum analyser (frequency domain) as the presence of >> > unwanted sidebands on what would be an otherwise infinitely >> > thin vertical peak i > f >> > the wave had perfect spectral purity. Do I have that right? >> > <cue massive argument, probably> >> > >> > TIA >> > >> > >> > >> > -- >> > This message may be freely reproduced without limit or charge >> > only via > >> > the Usenet protocol. Reproduction in whole or part through >> > other protocols, whether for profit or not, is conditional upon >> > a charge of > >> > GBP10.00 per reproduction. Publication in this manner via >> > non-Usenet protocols constitutes acceptance of this condition. >> >> What you seem to be talking about is like the old turntables >> which has sp > ecs for "wow" and "flutter". One was fast and the other slow. > Same but different. Or not so different really, they just > produced different effects on the sound and usually had different > causes, but both are just variations in the speed of the platter. >> >> Likewise your jitter and phase noise are the same thing, just >> different p > arts of the frequency spectrum. Same but different. >> >> Why do you care exactly? How are you using this? > > Actually "jitter" is variation in period, and is measured once per > period, and phase noise is variation from an ideal - perfectly > regular - waveform and is integrated over the whole period. > > It's not always a particularly useful distinction, but Cursitor > Doom doesn't think about what he's doing. >
<https://www.keysight.com/upload/cmc_upload/All/PhaseNoise_webcast19J ul12.pdf> A really good piece on it.
On Sun, 15 Sep 2019 09:14:23 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

>On Sat, 14 Sep 2019 20:06:46 -0700, jlarkin wrote: > >> There's a math operation that maps one into the other, at least for >> wideband noise and RMS jitter. There are several calculators online. > >I don't want a mathematical explanation, though; just an intuitive one. > >> In the telecom business, stuff below 0.1 Hz is called "wander" and >> faster wiggles are "jitter." > >In that case I've discovered a new phenomenon I've dubbed "twitch". :-) > >"Exe files can't be previewed" it says on your link.
Download it and run it. It's cool and perfectly safe.
> >Let's try re-phrasing it thus: phase noise produces sidebands. Does >jitter?
Sure. If the period of a signal isn't exactly constant, then it's frequency is being modulated. And FM makes spectral components in addition to the main frequency spike. If the jitter is fast and random, the frequency-domain noise floor is wideband, so a spectrum analyzer might not show classic sidebands, just an elevated noise floor. But some kind of systematic jitter, like time wobble caused by power supply ripple, will make classic looking sidebands around the main frequency line; FM. I often measure jitter as a function of time. The shortest time is a single cycle of a waveform, which is what you usually see on a scope. But you can measure one rising edge relative to the 10th edge away, or the millionth one. A graph of jitter vs time correlates directly with the phase noise graph of the oscillator. Low frequency phase noise makes long-timebase jitter. You can, in theory, measure the jitter of a 1-year time delay; it will be huge. A cheap crystal oscillator will have maybe 10 nanoseconds of RMS jitter when it's used to time out one second of delay. A really good OCXO will have a few picoseconds. The phase noise plots are indicators of the jitter behavior. Allan variance is one formal way of expressing the complex phase noise/jitter of an oscillator.