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

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.

That would then be a little sensitive to the DAC noise, which would cause jitter directly. But that DAC signal can be heavily filtered

I would need a linear ramp then. But in other threads you have shown more or less how that can be done

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.

That is sort of how they are doing the ps timebase. They use a standard timer (16 bit or whatever), max clock of 144MHz (7ns resolution). Then they add a delay line, to generate the 217ps smaller intervals

Cheers

Klaus

 

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 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

Cheers

Klaus

 

[John Larkin]

On Tue, 7 May 2019 12:45:47 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

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?

No, NO! Buy a cheap cmos crystal oscillator with a suitable jitter
spec.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Tue, 7 May 2019 15:37:52 -0400, bitrex <user@example.net> 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.

If Klaus needs an oscillator at all, he needs many MHz. A $3 quartz
crystal oscillator would have picosecond jitter. A Wein bridge
wouldn't be practical at that frequency and would have ghastly phase
noise.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

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.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

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 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

Oscillators are so cheap, there's no point in buying bare crystals and
trying to make them oscillate.

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

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

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

 

[Steve Wilson]

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?

 

[bitrex]

On 5/7/19 5:01 PM, John Larkin wrote:

On Tue, 7 May 2019 15:37:52 -0400, bitrex <user@example.net> 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.

If Klaus needs an oscillator at all, he needs many MHz. A $3 quartz
crystal oscillator would have picosecond jitter. A Wein bridge
wouldn't be practical at that frequency and would have ghastly phase
noise.

Sometimes folks assume we're all intimately familiar with the
requirements of the projects they're working on ("I'm working on my...")
sadly I'm not, sure would make my life easier if that crystal ball were
up and running. Not even sure if requirement is sine or square.

Analog Devices likes the injection-locked Wien bridge for low phase
noise, low distortion sines but at say, 10kHz. Down there the
performance of that lash-up does look amazing.

 

On Wednesday, 8 May 2019 00:27:09 UTC+2, bitrex wrote:

On 5/7/19 5:01 PM, John Larkin wrote:
On Tue, 7 May 2019 15:37:52 -0400, bitrex <user@example.net> 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.

If Klaus needs an oscillator at all, he needs many MHz. A $3 quartz
crystal oscillator would have picosecond jitter. A Wein bridge
wouldn't be practical at that frequency and would have ghastly phase
noise.



Sometimes folks assume we're all intimately familiar with the
requirements of the projects they're working on ("I'm working on my...")
sadly I'm not, sure would make my life easier if that crystal ball were
up and running. Not even sure if requirement is sine or square.

Analog Devices likes the injection-locked Wien bridge for low phase
noise, low distortion sines but at say, 10kHz. Down there the
performance of that lash-up does look amazing.

There's another thread about a 1ns sampling stage which details that I am working on a ns sample hold, that will be used for a cheap TDR function

https://groups.google.com/forum/#!topic/sci.electronics.design/Rzeziuv-4q8

Cheers

Klaus

 

[John Larkin]

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

 

[Gerhard Hoffmann]

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.

 

[bitrex]

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?

 

[bitrex]

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....

 

[Gunther Heiko Hagen]

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.

 

[Clifford Heath]

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...

 

[bitrex]

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]

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

 

[Steve Wilson]

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?

 

[John Larkin]

On Wed, 08 May 2019 02:30:11 GMT, Steve Wilson <no@spam.com> wrote:

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?

In our products, we compute a polynomial at factory cal time to
linearize the dac codes going into the ramp comparator. The poly terms
go into a cal table. That's why we can use an RC instead of a current
source.

We use a Keysight time interval counter to cal the ramps.

It takes a bit of care to avoid "stitching errors", little hickies
every time we add one digital count and jump the ramp back down.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics