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

Started by Unknown May 7, 2019
On Tue, 07 May 2019 21:37:16 GMT, Steve Wilson <no@spam.com> wrote:

>John Larkin <jjlarkin@highland_snip_technology.com> wrote: > >> It is possible to build an instant-start LC oscillator, and phase-lock >> it to a low phase noise XO, and preserve the original trigger timing >> with picosecond precision, but I can't tell how. > >"preserve the original trigger timing" <- compared to what?
Like this: https://www.dropbox.com/s/0pldde09649579k/Burst_2.jpg?dl=0 That oscillator starts instantly when an external trigger comes in, but it's phase locked to a crystal oscillator. The XO is at some random phase at trigger time. Injection locking would walk the triggered oscillator into phase with the XO, which we don't want. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Am 07.05.19 um 21:37 schrieb bitrex:
> 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.
Alone the fact that you can easily injection lock a Wien bridge oscillator is a sure sign that its frequency stability is not of prime quality. And the absence of harmonics has nothing to do with phase noise, as long as their amplitude is not that large that it causes high order sideband mixdown to baseband. (noise present around harmonics). You can have a square wave with excellent phase noise. Injection locking also does not solve any problem. If your injection source is so good, why not use it directly, without all of this ado? And if you look at the Leeson equation that defines the phase noise of an oscillator, there is a division term of (2 * Q**2), so Q is one of the most important parameters. In practical oscillators that can be even stronger than **2, depending on offset. The Leeson formula is somewhat simplified. Rohde, Rubiola and others have improved on that. Remember that the phase slope of the loop gain is effective Q. dphase/dfreq of a Wien bridge is, oh, ask LTspice. The wet sand bag. Good is different. Oscillation frequency is where phase goes through 0, so Q = dphase / dfreq at this frequency is that what counts. Jitter is phase noise integrated over all frequencies of interest. That works in the other direction, too, but there are more degrees of freedom, i.e the noise distribution close to / far from the carrier. And for telecom applications, the frequencies of interest do not include anything below 12 KHz. That's how most stuff is specc'ed because it gives better numbers. 1/f noise is ugly. You probably cannot afford that luxury of neglecting 1/f because you need absolute flight time, but if your laser link has GHz subcarriers, then that's OK. There is a German web site with a calculator: phase noise -- jitter but here it's well after midnight, so I won't search it now. Maybe tomorrow. As I wrote more than once here: timenuts group at febo.com, and www.rubiola.org The HP 54750A scope contains a time stretcher (dual slope: charge fast, discharge slowly). It has been described in HP Journal. It is even 2-stage to get more traces per second. I must admit that I love that scope. And everybody should have the HP journals in their vault. This dual slope procedure is not uncommon. I have done something similar to compare a hydrogen maser and a cesium. 5 ps resolution with somewhat worse accuracy have been reached at many places. That's about what a Stanford 620 time interval counter delivers. Good instrument. cheers, Gerhard ...and its a Wien bridge, not Wein. Also, it's not Seimens. The creator of the bridge was Wien by name; he has his name probably from the the town called Vienna abroad. Also the sausages are not Weiners but Wieners, even if from Oscar Mayer; but methinks in Vienna they call them Frankfurter. I wished I was an Oscar Meyer Weiner, because if I was an Oscar Meyer weiner, everybody would love me.
On Wed, 08 May 2019 01:30:48 +0200, Gerhard Hoffmann wrote:

> ...and its a Wien bridge, not Wein. Also, it's not Seimens. > The creator of the bridge was Wien by name; he has his name probably > from the the town called Vienna abroad. Also the sausages are not > Weiners but Wieners, even if from Oscar Mayer; but methinks in Vienna > they call them Frankfurter.
You're showing your misunderstanding of Wurst is only eclipsed by your misunderstanding of electronics.
> I wished I was an Oscar Meyer Weiner, because if I was an Oscar Meyer > weiner, everybody would love me.
Dream on.
On 5/7/19 4:57 PM, John Larkin wrote:
> On Tue, 7 May 2019 15:39:04 -0400, bitrex <user@example.net> 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. > > A sampler time base needs to stay phase coherent to a trigger. > Injection locking whacks randomly the phase. We care about time, not > frequency. > > It is possible to build an instant-start LC oscillator, and phase-lock > it to a low phase noise XO, and preserve the original trigger timing > with picosecond precision, but I can't tell how. > > But Klaus can do a totally synchronous system, for TDR, so doesn't > need a triggered oscillator. Could do a simple all analog ramp for the > timebase. > >
It was entirely unclear to me whether OP was looking for a timebase oscillator or a test oscillator for the sampler! to measure the performance of the sampler with a signal. I guess the part about RC oscillator threw me - why would you use an RC oscillator for a sampling timebase.....????? In any case there's nothing intrinsically high phase noise about the Wien bridge topology or injection locking. it all depends on the implementation....
On 5/7/19 5:16 PM, whit3rd wrote:
> On Tuesday, May 7, 2019 at 10:20:49 AM UTC-7, Cursitor Doom wrote: >> On Tue, 07 May 2019 07:14:33 -0700, klaus.kragelund wrote: > >>> I'm working on my ~3ns 4 diode sampler (preferable 1ns if possible) > [and want a low-jitter oscillator] > >> 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. > > The best timing performance requires significant stored energy, > if only for Heisenberg uncertainty principles. That means LC beats RC > circuitry (the resistors don't store energy, they just waste it). A rock > has the full momentum of the standing wave acoustics, so a crystal is better > than LC. Short of maser/resonant cavity references, the possibilities are good > for plain old wires as delay lines (distributed L, C) also. > > World-class timing uses superconducting cavities, if that matters. >
There's nothing intrinsic about the poor, besmirched Wien bridge oscillator topology that makes it intrinsically low Q, intrinsically high phase noise, or any of these scurrilous accusations against it! And the topology is already used in ICs to generate accurate sampling clocks, as a matter-of-fact. Do they usually put inductors in ICs?
On 8/5/19 10:21 am, bitrex wrote:
> there's nothing intrinsically high phase noise about the > Wien bridge topology or injection locking. it all depends on the > implementation....
Injection of phase adjustments doesn't cause phase noise? Tell us another joke, please...
On 5/7/19 8:56 PM, Clifford Heath wrote:
> On 8/5/19 10:21 am, bitrex wrote: >> there's nothing intrinsically high phase noise about the Wien bridge >> topology or injection locking. it all depends on the implementation.... > > Injection of phase adjustments doesn't cause phase noise? > Tell us another joke, please...
Are you hoping for -infinity dBc? No indeed you can't have that sorry
John Larkin <jjlarkin@highland_snip_technology.com> wrote:

> On Tue, 07 May 2019 21:37:16 GMT, Steve Wilson <no@spam.com> wrote:
>>John Larkin <jjlarkin@highland_snip_technology.com> wrote:
>>> It is possible to build an instant-start LC oscillator, and phase-lock >>> it to a low phase noise XO, and preserve the original trigger timing >>> with picosecond precision, but I can't tell how.
>>"preserve the original trigger timing" <- compared to what?
> Like this:
> https://www.dropbox.com/s/0pldde09649579k/Burst_2.jpg?dl=0
> That oscillator starts instantly when an external trigger comes in, > but it's phase locked to a crystal oscillator. The XO is at some > random phase at trigger time. Injection locking would walk the > triggered oscillator into phase with the XO, which we don't want.
So you count cycles until you reach the desired time, then start a fast ramp to set the vernier delay. How you measure the vernier delay time?
On Tue, 7 May 2019 14:07:00 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

>On Tuesday, 7 May 2019 22:50:59 UTC+2, John Larkin wrote: >> On Tue, 7 May 2019 12:42:22 -0700 (PDT), klaus.kragelund@gmail.com >> wrote: >> >> >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. >> > >> >> The simplest timebase is a linear RC ramp and a comparator and a DAC, >> no clock at all. RMS jitter of 1 part in 20,000 isn't difficult, >> 1:50000 is challenging. So 3 us/20000 would be 150 ps RMS jitter, >> which is probably OK. The echo from 200m of coax will be very soft, >> and you can average to reduce displayed jitter. Cheat a little. >> >> You can switch the ramp capacitor or charging current to have a couple >> of different delay ranges, and get less jitter on the short range. >> >> A TDR can use the same clock for the launch pulse as for counting >> coarse timebase delay, so an XO for coarse counts and a vernier ramp >> for fine delays could hugely reduce sampling jitter. Like say, a 50 >> MHz clock followed by a 20 ns analog ramp. >> >> > >I was actually going the digital way > >Clean clock to drive the microcontroller that generates the TDR pulse with a HR timer > >The microcontroller has picosecond timing > >https://www.st.com/resource/en/datasheet/stm32f334k6.pdf > >Page 80, 217ps
I'd be skeptical of the jitter. Resolution is cheap. A lot is going on in a uP chip.
> >I will let that HR timer trigger the 4 diode sampler, then use slow aquisition to sample and store for later analysis > > >But, your way may be cheaper
Here's a cheap semi-linear ramp delay: https://www.dropbox.com/s/hu6ltipwyi8f2go/Timebase_Ramp.JPG?dl=0 Making two ranges would't be hard. Switch the cap or the charging current. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 8/5/19 11:22 am, bitrex wrote:
> On 5/7/19 8:56 PM, Clifford Heath wrote: >> On 8/5/19 10:21 am, bitrex wrote: >>> there's nothing intrinsically high phase noise about the Wien bridge >>> topology or injection locking. it all depends on the implementation.... >> >> Injection of phase adjustments doesn't cause phase noise? >> Tell us another joke, please... > > Are you hoping for -infinity dBc? No indeed you can't have that sorry
Duh. But start with high Q (low phase noise, low resistance->Johnson noise, LC not RC) and you need smaller kicks to injection lock. Varicap tuning to reduce the frequency deviation would also allow smaller injections - you could still use a phase detector to PLL the tuning.