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1ns max jitter oscillator, cheap - for fast 4 diode sampler

Started by Unknown May 7, 2019
On Tuesday, 7 May 2019 17:18:48 UTC+2, John Larkin  wrote:
> On Tue, 7 May 2019 07:14:33 -0700 (PDT), klaus.kragelund@gmail.com > wrote: > > >Hi > > > >I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > > >So I need a pretty good oscillator, with low jitter > > > >I have never needed a good oscillator before, so on this topic I am totally at square one > > > >First I was thinking about an RC oscillator, and cleaning up the jitter. RC typically have 1us of jitter (found info on the web), and a crystal oscillator, standard type probably 1ns jitter. But I think that idea was crazy, a PLL clean up, would not work I guess. > > > >In order to not mess up my measurement and keep the averaging low (I could do many samples and average), I would guess I need jitter of 300ps (10%) of my 3ns reolution) > > > >But jitter is not listed as a search parameter. So where to start? (with low price in mind) > > > >Cheers > > > >Klaus > > Do you want a continuous running oscillator, namely a crystal > oscillator? That works if the measured event and the sampler timebase > can run off the same clock. Even cheap XOs have picosecond or > sub-picosecond jitter measured over short time spans. Longer spans are > trashed by low frequency phase noise, numbers in the nanoseconds per > second for cheap XOs, picoseconds per second for good OCXOs. >
That is a very good point, great catch. I will be using it in a TDR, so short pulse, and build up waveform for reflected pulse. Since I need up to 200m lenth, the maximum time from the emitted pulse to reflected is 3us. So if the jitter is slowly changing over time, it may be a lot less in only that time span. I do not know the properties of crystal jitter. Would that be sinusoidal shaped?
> Most XOs now have a jitter spec on their data sheet. Some spec > femtosecond period jitter. >
I looked at Digikey. The cheapest XO (about 0.5 USD) has 3ps jitter: https://www.sitime.com/datasheet/SiT8008 A lot better than what I need. When looking at oscillators, the cheapest (0.4 USD) also has only 3ps: https://www.sitime.com/datasheet/SiT2001 For crystals, I see no spec of jitter: https://abracon.com/Resonators/abls.pdf But, I guess that is because that makes no sense if the inverter used for the crystal is defined. For microcontrollers I never see a spec for the jitter, maybe it is horrendous I have seen jitter defined for the PLL. For example for a ST controller: https://www.st.com/resource/en/datasheet/stm32g071cb.pdf Page 76, defines 40ps jitter. Cannot see if that is from RC or crystal clock. But is most likely crystal clock. So it seems, I can use a cheap crystal for the microontroller and get a sufficient low jitter figure
> Sampling oscilloscopes typically need async triggered timebase > oscillators, which are more difficult. Jitters like 1 part in 50,000 > (jitter 20 PPM RMS times timed delay) are more common for a triggered > LC, like on an 11801. 1 part per million is possible; I'm doing that > now. > > A triggered oscillator can be phase locked to a good XO while > preserving the trigger alignment. > >
Thanks for the very good info Regards Klaus
On Tuesday, 7 May 2019 19:20:49 UTC+2, Cursitor Doom  wrote:
> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > > Hi > > > > I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > I know I'll appear a dinosaur by saying this, but you really can't beat a > good old fashioned Wien Bridge oscillator when it comes to spectral > purity and low phase noise. They certainly beat the crap out of any > digital synthesis technique IMV. > >
So I could use a Wien Bridge oscillator, or a cheap colpits? Then use the cheap crystal osc in the microcontroller to compensate the measurements (measure the colpits frequency and correct the numbers) Cheers Klaus
On Tuesday, 7 May 2019 21:39:08 UTC+2, bitrex  wrote:
> On 5/7/19 3:08 PM, Tom Gardner wrote: > > On 07/05/19 18:20, Cursitor Doom wrote: > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > >> > >>> Hi > >>> > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > >> > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > >> good old fashioned Wien Bridge oscillator when it comes to spectral > >> purity and low phase noise. They certainly beat the crap out of any > >> digital synthesis technique IMV. > > > > No, but that statement is about as sensible as almost > > all your statements. > > He's right about the spectral purity and the phase noise can be cleaned > up by injection-locking it.
How do you clean up the oscillator by injection? Got an example? Cheers Klaus
On Tuesday, May 7, 2019 at 3:08:42 PM UTC-4, Tom Gardner wrote:
> On 07/05/19 18:20, Cursitor Doom wrote: > > On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > > >> Hi > >> > >> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > > > I know I'll appear a dinosaur by saying this, but you really can't beat a > > good old fashioned Wien Bridge oscillator when it comes to spectral > > purity and low phase noise. They certainly beat the crap out of any > > digital synthesis technique IMV. > > No, but that statement is about as sensible as almost > all your statements.
Hmm, Well I know little of phase noise, but if it's at all related to harmonic distortion... Then I will say I've built a little Wien bridge oscillator (audio) with light bulb AGC (ala Jim Williams, ala Bill Hewlett) And it's slick. The 2nd harmonic is hard to see without fancy kit and the 3rd harmonic is ~70 dB down. Which is better than my Rigol DDS Sig Gen. (about -70 dB 2nd and -60 on 3rd) I'm not sure my objection has anything to do with ns phase noise. George H.
On Tuesday, May 7, 2019 at 3:47:01 PM UTC-4, klaus.k...@gmail.com wrote:
> On Tuesday, 7 May 2019 21:39:08 UTC+2, bitrex wrote: > > On 5/7/19 3:08 PM, Tom Gardner wrote: > > > On 07/05/19 18:20, Cursitor Doom wrote: > > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > >> > > >>> Hi > > >>> > > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > >> > > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > > >> good old fashioned Wien Bridge oscillator when it comes to spectral > > >> purity and low phase noise. They certainly beat the crap out of any > > >> digital synthesis technique IMV. > > > > > > No, but that statement is about as sensible as almost > > > all your statements. > > > > He's right about the spectral purity and the phase noise can be cleaned > > up by injection-locking it. > > How do you clean up the oscillator by injection? Got an example?
Yeah me too. Curious minds want to know. In my very limited experience, the spectral purity depended on how 'strong' the AGC was. George H.
> > Cheers > > Klaus
On Tuesday, May 7, 2019 at 4:01:58 PM UTC-4, George Herold wrote:
> On Tuesday, May 7, 2019 at 3:47:01 PM UTC-4, klaus.k...@gmail.com wrote: > > On Tuesday, 7 May 2019 21:39:08 UTC+2, bitrex wrote: > > > On 5/7/19 3:08 PM, Tom Gardner wrote: > > > > On 07/05/19 18:20, Cursitor Doom wrote: > > > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > > >> > > > >>> Hi > > > >>> > > > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > > >> > > > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > > > >> good old fashioned Wien Bridge oscillator when it comes to spectral > > > >> purity and low phase noise. They certainly beat the crap out of any > > > >> digital synthesis technique IMV. > > > > > > > > No, but that statement is about as sensible as almost > > > > all your statements. > > > > > > He's right about the spectral purity and the phase noise can be cleaned > > > up by injection-locking it. > > > > How do you clean up the oscillator by injection? Got an example? > > Yeah me too. Curious minds want to know. > In my very limited experience, the spectral purity depended on > how 'strong' the AGC was. > > George H. > > > > Cheers > > > > Klaus
This maybe. https://www.analog.com/en/technical-articles/injection-lock-a-wien-bridge-oscillator.html GH
On Tuesday, May 7, 2019 at 4:08:37 PM UTC-4, George Herold wrote:
> On Tuesday, May 7, 2019 at 4:01:58 PM UTC-4, George Herold wrote: > > On Tuesday, May 7, 2019 at 3:47:01 PM UTC-4, klaus.k...@gmail.com wrote: > > > On Tuesday, 7 May 2019 21:39:08 UTC+2, bitrex wrote: > > > > On 5/7/19 3:08 PM, Tom Gardner wrote: > > > > > On 07/05/19 18:20, Cursitor Doom wrote: > > > > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > > > >> > > > > >>> Hi > > > > >>> > > > > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > > > >> > > > > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > > > > >> good old fashioned Wien Bridge oscillator when it comes to spectral > > > > >> purity and low phase noise. They certainly beat the crap out of any > > > > >> digital synthesis technique IMV. > > > > > > > > > > No, but that statement is about as sensible as almost > > > > > all your statements. > > > > > > > > He's right about the spectral purity and the phase noise can be cleaned > > > > up by injection-locking it. > > > > > > How do you clean up the oscillator by injection? Got an example? > > > > Yeah me too. Curious minds want to know. > > In my very limited experience, the spectral purity depended on > > how 'strong' the AGC was. > > > > George H. > > > > > > Cheers > > > > > > Klaus > > This maybe. > https://www.analog.com/en/technical-articles/injection-lock-a-wien-bridge-oscillator.html > > GH
OK last thing. I stuck my Wien bridge on the good SRS 720 spectrum analyzer and the 3rd was ~90 db down. (my above 70 dB number was measuring on a 'scope, not so good.) GH FFT.)
On 2019-05-07 21:37, bitrex wrote:
> On 5/7/19 1:20 PM, Cursitor Doom wrote: >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: >> >>> Hi >>> >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) >> >> I know I'll appear a dinosaur by saying this, but you really can't beat a >> good old fashioned Wien Bridge oscillator when it comes to spectral >> purity and low phase noise. They certainly beat the crap out of any >> digital synthesis technique IMV. >> >> >> >> > > In a rare moment of partial agreement with my arch-nemesis "Cursitor > Doom" an injecton-locked Wien bridge oscillator can provide a > near-perfect combination of very low phase noise and very low wideband > noise floor and distortion. And certainly meets the low-price requirement.
While Wien bridge oscillators may have low distortion and therefore good spectral purity, they certainly aren't low noise. I mean, even the frequency-selective part is lossy, dissipative and therefore noisy. Jitter is the uncertainty in the timing of some level crossing. This uncertainty depends on the noise level and on the rate of change of the signal around that level crossing. To get low jitter, you want the noise to be as low as possible and you want to cross the decision level as fast as possible. So you want a low-loss resonator, a low noise feedback amplifier, high oscillation amplitude and high frequency. That pretty much rules out a Wien bridge oscillator, or any RC oscillator for that matter. For timing a fast sampler, jitter performance doesn't need to be stellar. It shouldn't be too hard to get jitter in the few tens of picoseconds ballpark, even with an RC oscillator. Jeroen Belleman
On Tuesday, 7 May 2019 22:27:27 UTC+2, George Herold  wrote:
> On Tuesday, May 7, 2019 at 4:08:37 PM UTC-4, George Herold wrote: > > On Tuesday, May 7, 2019 at 4:01:58 PM UTC-4, George Herold wrote: > > > On Tuesday, May 7, 2019 at 3:47:01 PM UTC-4, klaus.k...@gmail.com wrote: > > > > On Tuesday, 7 May 2019 21:39:08 UTC+2, bitrex wrote: > > > > > On 5/7/19 3:08 PM, Tom Gardner wrote: > > > > > > On 07/05/19 18:20, Cursitor Doom wrote: > > > > > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > > > > > >> > > > > > >>> Hi > > > > > >>> > > > > > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > > > > > >> > > > > > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > > > > > >> good old fashioned Wien Bridge oscillator when it comes to spectral > > > > > >> purity and low phase noise. They certainly beat the crap out of any > > > > > >> digital synthesis technique IMV. > > > > > > > > > > > > No, but that statement is about as sensible as almost > > > > > > all your statements. > > > > > > > > > > He's right about the spectral purity and the phase noise can be cleaned > > > > > up by injection-locking it. > > > > > > > > How do you clean up the oscillator by injection? Got an example? > > > > > > Yeah me too. Curious minds want to know. > > > In my very limited experience, the spectral purity depended on > > > how 'strong' the AGC was. > > > > > > George H. > > > > > > > > Cheers > > > > > > > > Klaus > > > > This maybe. > > https://www.analog.com/en/technical-articles/injection-lock-a-wien-bridge-oscillator.html > > > > GH > > OK last thing. I stuck my Wien bridge on the good SRS 720 spectrum analyzer and the 3rd was ~90 db down. (my above 70 dB number was measuring on a 'scope, not so good.) >
That's the next thing. I need to find a scope that is good enough to measure the jitter. One of my work colleagues has one. At home I have a TDS744A, which has 80ps jitter. So I can use that for rough measurements
On Tuesday, 7 May 2019 22:32:01 UTC+2, Jeroen Belleman  wrote:
> On 2019-05-07 21:37, bitrex wrote: > > On 5/7/19 1:20 PM, Cursitor Doom wrote: > >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > >> > >>> Hi > >>> > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > >> > >> I know I'll appear a dinosaur by saying this, but you really can't beat a > >> good old fashioned Wien Bridge oscillator when it comes to spectral > >> purity and low phase noise. They certainly beat the crap out of any > >> digital synthesis technique IMV. > >> > >> > >> > >> > > > > In a rare moment of partial agreement with my arch-nemesis "Cursitor > > Doom" an injecton-locked Wien bridge oscillator can provide a > > near-perfect combination of very low phase noise and very low wideband > > noise floor and distortion. And certainly meets the low-price requirement. > > While Wien bridge oscillators may have low distortion and therefore > good spectral purity, they certainly aren't low noise. I mean, even > the frequency-selective part is lossy, dissipative and therefore > noisy. > > Jitter is the uncertainty in the timing of some level crossing. > This uncertainty depends on the noise level and on the rate of > change of the signal around that level crossing. To get low jitter, > you want the noise to be as low as possible and you want to cross > the decision level as fast as possible. > > So you want a low-loss resonator, a low noise feedback amplifier, > high oscillation amplitude and high frequency. That pretty much > rules out a Wien bridge oscillator, or any RC oscillator for > that matter. > > For timing a fast sampler, jitter performance doesn't need to > be stellar. It shouldn't be too hard to get jitter in the few > tens of picoseconds ballpark, even with an RC oscillator. >
So for RC osc, I would need: Good filtering on the waveform Fast comparator with steady trigger treshold Good PSSR Circuit isolated from noise sources Cheers Klaus