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Final Report - Binary Sampler

J

John Larkin

Jan 1, 1970
0
To All,

The final report on the Binary Sampler is available at

http://www3.sympatico.ca/add.automation/sampler/intro.htm

We are moving. This section will be removed Monday morning at 8:00 am
EST.

Thanks to all who found the information useful.

Best Wishes,

Michael R. Monett


Good grief, you again? How can you patent something that was in the GE
transistor manual in 1964? And why don't you mention me in the
credits, since I first told you about it here?

John
 
H

Helmut Sennewald

Jan 1, 1970
0
John Larkin said:
Good grief, you again? How can you patent something that was in the GE
transistor manual in 1964? And why don't you mention me in the
credits, since I first told you about it here?

Hello John,
I am interested in a copy of that appnote? from the GE manual.
Is there any link to it?

Thanks in advance
Helmut
 
J

John Larkin

Jan 1, 1970
0
Hello John,
I am interested in a copy of that appnote? from the GE manual.
Is there any link to it?

Thanks in advance
Helmut

Helmut,

I'll (re)post the pics to a.b.s.e. I did a senior EE paper in 1969,
"The Tunnel Diode Slideback Sampler", different circuits but similar
idea - a threshold sampler with integrated bang-bang feedback - and
won the student IEEE paper award, which meant I had to present the
danged thing again at a regional competition. In my paper I made most
of the same erroneous claims that MM is making now; I just never
claimed to have invented it.

The heterodyne sampler timebase idea is patented by LeCroy.

John
 
M

Mike Monett

Jan 1, 1970
0
Helmut,
I'll (re)post the pics to a.b.s.e. I did a senior EE paper in
1969, "The Tunnel Diode Slideback Sampler", different circuits but
similar idea - a threshold sampler with integrated bang-bang
feedback - and won the student IEEE paper award, which meant I had
to present the danged thing again at a regional competition. In my
paper I made most of the same erroneous claims that MM is making
now; I just never claimed to have invented it.
The heterodyne sampler timebase idea is patented by LeCroy.

Thanks for your input.

I don't claim to have invented the slideback sampler either, John.
Nor do I claim having invented Delta Modulation, nor do I claim to
have invented undersampling in conjunction with the Delta Modulator.
The references I list show this clearly.

If you look at the paper by T. M. Souders and P. S. Hetrick,
"Accurate rf voltage measurements using a sampling voltage tracker,"
IEEE Trans. Instrum. Meas., vol. IM-38, pp. 451-456, Apr. 1989, you
will see he refers to S. P. McCabe's MS thesis, "A sampling voltage
tracker for analyzing high speed waveforms", Univ. CA, Los Angeles,
1975.

In the "History of the Idea", section 1.3 on page 2, McCabe credits
Mr. Don Devendorf of the Hughes Aircraft Company for conceiving the
basic idea in 1972. He continues

"In 1974, when he presented the idea to me, it seemed that the
circuit would be much more useful when coupled with a timing
circuit which could generate a variety of strobe signals. Practice
has borne this out, and the Sampling Voltage Tracker is now used
in many applications where the use of an expensive oscilloscope is
impractical or impossible."

However, it appears that Devendorf, McCabe, Souders, and everyone
else who worked on this concept failed to note the excellent noise
rejection property obtained by undersampling the Delta Modulator or
the Tracking ADC. I show a simulation of this effect and actual data
taken from the demo circuit shown on my web site.

Everyone also seems to have missed the periodic oscillation caused
by low loop gain in the op amp, and the consequent loss of precision
in sampler output. I show this on my web page at

http://www3.sympatico.ca/add.automation/sampler/tracking.htm

The switch to an undersampled Tracking ADC solves this problem. It
is shown on the same page.

If your IEEE paper covers these issues, I would certainly like to
receive a copy. As I am moving, I will temporarily be without web
access, but you could post it here so everyone else can see it also.

The tunnel diode sampler is a different technology, and is not
really well suited for precision waveform capture. There seems to be
very few records of it being used other than in the GE manual. So
unlike the quote above and the references I list, we really don't
have proof that it functions well enough to be useful.

It is prior art, but so are all the rest of the references I list.
However, I tried to stay with references that other researchers
could obtain fairly easily. For example, you can get the Souders
paper in most good libraries, but they may not have a copy of the
old GE transistor manual. You can also get the Souders paper online:

http://makeashorterlink.com/?B10F11A76

As far as heterodyne sampling, there are probably several others
besides the Lecroy patent. For exmple, see the Ainsworth patent
5,260,670 (1993). These patents demonstrate prior art, but I believe
the description shown on my web page is the first application of
heterodyne sampling to a tracking ADC.

Again, if your IEEE paper describes these issues, please post a copy
so we can see it.

Best Wishes,

Mike Monett
 
J

John Larkin

Jan 1, 1970
0
In the "History of the Idea", section 1.3 on page 2, McCabe credits
Mr. Don Devendorf of the Hughes Aircraft Company for conceiving the
basic idea in 1972. He continues

I guess he never saw the GE manual either. Or maybe he did.
However, it appears that Devendorf, McCabe, Souders, and everyone
else who worked on this concept failed to note the excellent noise
rejection property obtained by undersampling the Delta Modulator or
the Tracking ADC.

No, they were smart enough to see how bad it really is.
I show a simulation of this effect and actual data
taken from the demo circuit shown on my web site.

Everyone also seems to have missed the periodic oscillation caused
by low loop gain in the op amp, and the consequent loss of precision
in sampler output. I show this on my web page at

That's because most everybody (including me, in 1969) used a defined
feedback step size per shot, not a simple lowpass filter, which is why
yours can oscillate and the rest don't. Control theory is hardly new.
The tunnel diode sampler is a different technology, and is not
really well suited for precision waveform capture. There seems to be
very few records of it being used other than in the GE manual. So
unlike the quote above and the references I list, we really don't
have proof that it functions well enough to be useful.

It was the exact same concept, just different parts, and was as well
suited to waveform capture as is a flip flop, namely mediocre compared
to a real feedback sampler. Tek, HP, Philips, Anritsu, and LeCroy
figured this out. There's a lot to be said for getting a, say, 10-bit
linear error signal every shot instead of a 1-bit hint.

To my knowledge, the 'binary sampler' was commercialized only once,
and wasn't very successful. A diode half-bridge sampler performs
vastly better at trivial incremental expense.

John
 
M

Mike Monett

Jan 1, 1970
0
John Larkin wrote:

[...]
That's because most everybody (including me, in 1969) used a defined
feedback step size per shot, not a simple lowpass filter, which is why
yours can oscillate and the rest don't. Control theory is hardly new.

I show why the current use of this technology can oscillate, such as the
NIST sampling Tracker, and the McCabe thesis. The Tracking ADC solves it,
as shown on my web site.

An analog approach would be extremely difficult to keep balanced, and it
would have the same problem with unequal up and down charge as a pure
integrator. So I don't think your proposal would solve the problem.

[...]
It was the exact same concept, just different parts, and was as well
suited to waveform capture as is a flip flop, namely mediocre compared
to a real feedback sampler. Tek, HP, Philips, Anritsu, and LeCroy
figured this out. There's a lot to be said for getting a, say, 10-bit
linear error signal every shot instead of a 1-bit hint.

Then you pay the speed penalty when you have to average, as discussed on
my web site. Pretty soon, the averaging time exceeds the time available
for the measurement, or the system drifts. Then you cannot make the
measurement with existing technology.
To my knowledge, the 'binary sampler' was commercialized only once,
and wasn't very successful. A diode half-bridge sampler performs
vastly better at trivial incremental expense.

John

You do not talk about the noise-rejection property of the Binary Sampler,
and you do not include the poor noise figure of conventional samplers.

Then, you have to include the time spent averaging in order to compare
the results to the Binary Sampler. Also, the conventional diode sampler
has a fairly drastic rolloff with frequency, as shown on my web site.

Certainly, the diode sampler is faster and better suited for general
purpose applications. But when you have an application where the Binary
Sampler fits, it vastly outperforms the conventional diode technology.

Best Wishes,

Michael R. Monett
 
J

John Larkin

Jan 1, 1970
0
Then, you have to include the time spent averaging in order to compare
the results to the Binary Sampler. Also, the conventional diode sampler
has a fairly drastic rolloff with frequency, as shown on my web site.

Down 3 dB at 70 GHz is 'fairly drastic'? That's what you can buy today
from Tek, Agilent, LeCroy. PSPL has a 100 GHz sampler, but it's not a
whole scope. On ebay, you can get a nice 7000-series rig, 5 GHz or so,
for maybe $350.

What's the measured (not simulated) bandwidth you are actually getting
now?

John
 
M

Mike Monett

Jan 1, 1970
0
John said:
Down 3 dB at 70 GHz is 'fairly drastic'? That's what you can buy today
from Tek, Agilent, LeCroy. PSPL has a 100 GHz sampler, but it's not a
whole scope. On ebay, you can get a nice 7000-series rig, 5 GHz or so,
for maybe $350.

What's the measured (not simulated) bandwidth you are actually getting
now?

John

I think the 7000 series goes up to 12 or 14GHz, depending on the sampling
head. Yes, they are very cheap now, thanks to EBay.

As shown on my web site, the 100EP52 will track a 200 ps risetime. The
GigaComm part will probably do much better. As I mentioned on my web site,
the Binary Sampler will never be as fast as conventional sampling scopes.

But it really doesn't matter how cheap the current technology scopes are or
how much bandwidth they have if they cannot make the required measurement.

It would be difficult to package a HP or Textronix 70GHz scope in a small
battery-powered instrument for remote applications, and the price would be
prohibitive. If you used a homemade conventional diode sampler, you would
end up with poorer performance than the Binary Sampler offers.

You also keep forgetting the noise-rejection property of the Binary Sampler.
In production applications, time is money. If you can make a measurement
much faster, it generally pays for itself quickly. As shown on my web site,
the difference can be quite dramatic.

As I said before, none of these approaches will suit all applications. But
where the Binary Sampler suits a need, it does so very well, and there
happens to be a great deal of interest in it, primarily in Europe.

Best Wishes,

Michael R. Monett
 
J

John Larkin

Jan 1, 1970
0
I think the 7000 series goes up to 12 or 14GHz, depending on the sampling
head. Yes, they are very cheap now, thanks to EBay.

As shown on my web site, the 100EP52 will track a 200 ps risetime. The
GigaComm part will probably do much better. As I mentioned on my web site,
the Binary Sampler will never be as fast as conventional sampling scopes.

All I saw on the web site seemed to be simulations. Was Fig 2 an
actual measurement?
But it really doesn't matter how cheap the current technology scopes are or
how much bandwidth they have if they cannot make the required measurement.

It would be difficult to package a HP or Textronix 70GHz scope in a small
battery-powered instrument for remote applications, and the price would be
prohibitive. If you used a homemade conventional diode sampler, you would
end up with poorer performance than the Binary Sampler offers.

Handheld battery-powered 150-200 ps TDRs use conventional diode
samplers and are in everyday use; they look like calculators and are
commodities these days. It takes very little power to run a diode
sampler, even a fast one, certainly less than what a couple of EL
chips burn up.

The only time I tried making my own half-bridge sampler I got about 5
GHz, 70 ps risetime, using a mediocre SOT-23 dual schottky and a
flea-market SRD.
You also keep forgetting the noise-rejection property of the Binary Sampler.

You keep forgetting how bad it is. Median-seeking simulates well with
perfectly symmetric noise, but sucks in real life. True averaging is
correct. Besides, I'd rather have averaging be a option (as for eye
diagrams or jitter measurements) than be mandatory.
In production applications, time is money. If you can make a measurement
much faster, it generally pays for itself quickly. As shown on my web site,
the difference can be quite dramatic.

No human-readable waveform display needs more than 512 data points,
1024 to ensure overkill. At 200 KSPS, like an older conventional
sampler, that's 200 waveforms a second, more than anybody can use. 512
points, 32x averaging still gives 12 waveforms per second. The reason
sampling scopes don't sample faster is certainly not because they
can't be made to do it, but rather because nobody cares.

The heterodyne timebase *must* sample the entire period of the
waveform, even if just one region is of interest, which is the common
case. Zooming a region becomes a huge PITA. And 'sample' is a
misnomer, since each 'point' must be, effectively, sampled thousands
of times by the nature of the 1-bit information stream. And jitter is
a real bear for a heterodyme timebase... your claim of 10 ps jitter
between two plain vanilla crystal oscillators, over one second, is
incredible: 1 ns would be pretty good.

'Binary sampling' is a cute trick, is at least 40 years old, and isn't
especially useful. I wish I'd never told you about it.

John
 
R

Russell Shaw

Jan 1, 1970
0
John said:
Down 3 dB at 70 GHz is 'fairly drastic'? That's what you can buy today
from Tek, Agilent, LeCroy. PSPL has a 100 GHz sampler, but it's not a
whole scope. On ebay, you can get a nice 7000-series rig, 5 GHz or so,
for maybe $350.

What's the measured (not simulated) bandwidth you are actually getting
now?

Anyone can make a high speed sampling gate. The real trick is
to make the triggering circuit decent at 10GHz.
 
M

Mike Monett

Jan 1, 1970
0
John said:
[...]
I think the 7000 series goes up to 12 or 14GHz, depending on the
sampling head. Yes, they are very cheap now, thanks to EBay.
As shown on my web site, the 100EP52 will track a 200 ps
risetime. The GigaComm part will probably do much better. As I
mentioned on my web site, the Binary Sampler will never be as
fast as conventional sampling scopes.
All I saw on the web site seemed to be simulations. Was Fig 2 an
actual measurement?

The Binary Sampler is now mirrored at

http://www.smg.uni-karlsruhe.de/add.automation

Where I use simulated data in the description, I clearly mark the
figure and show in the text it is simulated. In the "Binary Sampler
vs Conventional Sampling" page at

http://smg.iwk.uni-karlsruhe.de/add.automation/binsamp.htm

Figs. 1 and 2 are simulated noise with a conventional sampler. Figs.
3 and 4 are actual data from the Binary Sampler.

In the "Smoothing and Slew Rate Detect" page at

http://smg.iwk.uni-karlsruhe.de/add.automation/smooth.htm

Figs. 1 and 2 are actual data from the Binary Sampler.
Handheld battery-powered 150-200 ps TDRs use conventional diode
samplers and are in everyday use; they look like calculators and
are commodities these days. It takes very little power to run a
diode sampler, even a fast one, certainly less than what a couple
of EL chips burn up.

Yes, they are a marvel of low cost design. Any idea what the
bandwidth is? I'd guess perhaps 1 GHz or so. Perfectly adequate for
the application.

For other applications, such as OTDR, averaging is needed to improve
the SNR. I watched a line crew using a commercial unit, and it had
to average 1,000 waveforms to get a result. This took a long time,
and they had to repeat it each time they changed fibres.
The only time I tried making my own half-bridge sampler I got
about 5 GHz, 70 ps risetime, using a mediocre SOT-23 dual schottky
and a flea-market SRD.

Interesting. Got the part numbers? Of course, you have the same
problem with noise and low sample rate.
You keep forgetting how bad it is. Median-seeking simulates well
with perfectly symmetric noise, but sucks in real life. True
averaging is correct. Besides, I'd rather have averaging be a
option (as for eye diagrams or jitter measurements) than be
mandatory.

The Binary Sampler does not respond to the amplitude of the error,
so it cannot respond to the median. It only reponds to the direction
of the error, which tends to zero in Gaussian noise.

As Souders points out in "The effects of timing jitter in sampling
systems," IEEE Trans. Instrum. Meas., vol. IM-39, Feb. 1991,
averaging causes significant errors at slope changes.

Since the Binary Sampler only responds to the direction of the
error, and not the magnitude, it gives greater accuracy than
conventional sampling under these conditions.

Yes, you cannot measure noise with the Binary Sampler, as I mention
on my web site. You need a conventional sampler or digitizer. But
for many applications, the noise is well-defined and does not
change.
No human-readable waveform display needs more than 512 data
points, 1024 to ensure overkill. At 200 KSPS, like an older
conventional sampler, that's 200 waveforms a second, more than
anybody can use. 512 points, 32x averaging still gives 12
waveforms per second. The reason sampling scopes don't sample
faster is certainly not because they can't be made to do it, but
rather because nobody cares.

The required number of data points depends on what you need to
measure. The 200KSPS is a real problem when you have to use
averaging. Heterodyne sampling can be 1,000 times faster, so you get
higher precision and faster throughput.
The heterodyne timebase *must* sample the entire period of the
waveform, even if just one region is of interest, which is the
common case. Zooming a region becomes a huge PITA. And 'sample' is
a misnomer, since each 'point' must be, effectively, sampled
thousands of times by the nature of the 1-bit information stream.

You can use heterodyne sampling or a conventional delayed trigger,
depending on the application. The conventional trigger will probably
have more jitter and poor linearity.

The point is you have a choice with the Binary Sampler. With a
conventional sampler, you have no choice and are stuck with the low
sample rate.
And jitter is a real bear for a heterodyme timebase... your claim
of 10 ps jitter between two plain vanilla crystal oscillators,
over one second, is incredible: 1 ns would be pretty good.

The jitter spec is 25 picoseconds rms, and is pretty typical for
these oscillators at 1MHz. I measured 24.7 ps with the HP5370A. I
think the measurement interval was 10 seconds.

I wrote the manufacturer and asked what the jitter spec was over a 1
second interval. He did not have that information, but another
similar vendor said the 1 second jitter was about 1/2.5 of the spec.

I used a factor of 3.5 in the calculations to be conservative when
comparing the Binary Sampler to the conventional sampler. This gave
the conventional sampler a significant advantage, but the Binary
Sampler still beat it.
'Binary sampling' is a cute trick, is at least 40 years old, and
isn't especially useful. I wish I'd never told you about it.

Sorry John, this is simply not true.

You sent me the GE tunnel diode sampler gif via email after I had
posted the description of the Binary Sampler to the web. You did not
include a description of how the GE circuit worked, and you did not
provide that information until much later.

When you saw the information I had posted to the web, you claimed it
would rail. Clearly, you did not understand it.

Yes, as I show in the references, the basic idea has been around a
long time. But nobody noticed the noise-rejection properties, or
that the pure integrator would oscillate.

Best Wishes,

Mike
 
J

John Larkin

Jan 1, 1970
0
John Larkin wrote:
[...]
What's the measured (not simulated) bandwidth you are actually
getting now?
John
I think the 7000 series goes up to 12 or 14GHz, depending on the
sampling head. Yes, they are very cheap now, thanks to EBay.
As shown on my web site, the 100EP52 will track a 200 ps
risetime. The GigaComm part will probably do much better. As I
mentioned on my web site, the Binary Sampler will never be as
fast as conventional sampling scopes.
All I saw on the web site seemed to be simulations. Was Fig 2 an
actual measurement?

The Binary Sampler is now mirrored at

http://www.smg.uni-karlsruhe.de/add.automation

Where I use simulated data in the description, I clearly mark the
figure and show in the text it is simulated. In the "Binary Sampler
vs Conventional Sampling" page at

http://smg.iwk.uni-karlsruhe.de/add.automation/binsamp.htm

Figs. 1 and 2 are simulated noise with a conventional sampler. Figs.
3 and 4 are actual data from the Binary Sampler.

In the "Smoothing and Slew Rate Detect" page at

http://smg.iwk.uni-karlsruhe.de/add.automation/smooth.htm

Figs. 1 and 2 are actual data from the Binary Sampler.
Handheld battery-powered 150-200 ps TDRs use conventional diode
samplers and are in everyday use; they look like calculators and
are commodities these days. It takes very little power to run a
diode sampler, even a fast one, certainly less than what a couple
of EL chips burn up.

Yes, they are a marvel of low cost design. Any idea what the
bandwidth is? I'd guess perhaps 1 GHz or so. Perfectly adequate for
the application.

For other applications, such as OTDR, averaging is needed to improve
the SNR. I watched a line crew using a commercial unit, and it had
to average 1,000 waveforms to get a result. This took a long time,
and they had to repeat it each time they changed fibres.
The only time I tried making my own half-bridge sampler I got
about 5 GHz, 70 ps risetime, using a mediocre SOT-23 dual schottky
and a flea-market SRD.

Interesting. Got the part numbers? Of course, you have the same
problem with noise and low sample rate.
You keep forgetting how bad it is. Median-seeking simulates well
with perfectly symmetric noise, but sucks in real life. True
averaging is correct. Besides, I'd rather have averaging be a
option (as for eye diagrams or jitter measurements) than be
mandatory.

The Binary Sampler does not respond to the amplitude of the error,
so it cannot respond to the median. It only reponds to the direction
of the error, which tends to zero in Gaussian noise.

As Souders points out in "The effects of timing jitter in sampling
systems," IEEE Trans. Instrum. Meas., vol. IM-39, Feb. 1991,
averaging causes significant errors at slope changes.

Since the Binary Sampler only responds to the direction of the
error, and not the magnitude, it gives greater accuracy than
conventional sampling under these conditions.

Yes, you cannot measure noise with the Binary Sampler, as I mention
on my web site. You need a conventional sampler or digitizer. But
for many applications, the noise is well-defined and does not
change.
No human-readable waveform display needs more than 512 data
points, 1024 to ensure overkill. At 200 KSPS, like an older
conventional sampler, that's 200 waveforms a second, more than
anybody can use. 512 points, 32x averaging still gives 12
waveforms per second. The reason sampling scopes don't sample
faster is certainly not because they can't be made to do it, but
rather because nobody cares.

The required number of data points depends on what you need to
measure. The 200KSPS is a real problem when you have to use
averaging. Heterodyne sampling can be 1,000 times faster, so you get
higher precision and faster throughput.
The heterodyne timebase *must* sample the entire period of the
waveform, even if just one region is of interest, which is the
common case. Zooming a region becomes a huge PITA. And 'sample' is
a misnomer, since each 'point' must be, effectively, sampled
thousands of times by the nature of the 1-bit information stream.

You can use heterodyne sampling or a conventional delayed trigger,
depending on the application. The conventional trigger will probably
have more jitter and poor linearity.

The point is you have a choice with the Binary Sampler. With a
conventional sampler, you have no choice and are stuck with the low
sample rate.
And jitter is a real bear for a heterodyme timebase... your claim
of 10 ps jitter between two plain vanilla crystal oscillators,
over one second, is incredible: 1 ns would be pretty good.

The jitter spec is 25 picoseconds rms, and is pretty typical for
these oscillators at 1MHz. I measured 24.7 ps with the HP5370A. I
think the measurement interval was 10 seconds.

I wrote the manufacturer and asked what the jitter spec was over a 1
second interval. He did not have that information, but another
similar vendor said the 1 second jitter was about 1/2.5 of the spec.

We have, of late, done extensive testing on commercial crystal
oscillators, with reference to jitter in the single-cycle range (which
is what they spec, generally) out to seconds. A 3$ AT-in-a-can
oscillator may well have ps sing;e-cycle jitter, but has a nasty
corner in the millisecond range and increases to, typically, a
nanosecond or three at one second delay. Thermally shielding it helps,
a decent TCXO is better, ovenizing an SC-cut is better still, but
picoseconds jitter per second of delay is *very* difficult.
Sorry John, this is simply not true.

Is so. I told you about the d-flop feedback sampler in s.e.d. on Jan
8, 2001, after which you decided you invented it, and announced you
had "broken Shannon's Law" with it.

Fortunately, Google archives all this stuff:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
What sort of net TDR time resolution do you need? How much can you afford to
undersample (ie, how many repetitions are you willing to expend to acquire the
entire waveform?) If the answer is 'very many', there are some truly evil
tricks to build an effective sampling oscilloscope without a lot of parts.

John

John,

That would be *very* interesting - do you have the time to explain
further?

How do you get a sampling bridge without taking a Tek or HP scope
apart?

Best Regards,

Michael R. Monett

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

etc.


It's amazing how many people find a concept, obsess on it, and soon
decide they invented it themselves.
You sent me the GE tunnel diode sampler gif via email after I had
posted the description of the Binary Sampler to the web.

Again, after I told you about it. All archived.
You did not
include a description of how the GE circuit worked, and you did not
provide that information until much later.

Why would a simple schematic need an explanation?
When you saw the information I had posted to the web, you claimed it
would rail. Clearly, you did not understand it.

As if!
Yes, as I show in the references, the basic idea has been around a
long time. But nobody noticed the noise-rejection properties, or
that the pure integrator would oscillate.

You assume that decades of engineers (including Shannon, and the
staffs of HP and Tek, and of course your humble correspondent) are
stupid, and you are smarter. Not likely.

John
 
J

John Larkin

Jan 1, 1970
0
Anyone can make a high speed sampling gate. The real trick is
to make the triggering circuit decent at 10GHz.

That's not all that bad either. The HP 135 sampling scope did around
20 ps jitter in 1960, with tubes.

John
 
M

Mike Monett

Jan 1, 1970
0
John Larkin wrote:

[...]
We have, of late, done extensive testing on commercial crystal
oscillators, with reference to jitter in the single-cycle range (which
is what they spec, generally) out to seconds. A 3$ AT-in-a-can
oscillator may well have ps sing;e-cycle jitter, but has a nasty
corner in the millisecond range and increases to, typically, a
nanosecond or three at one second delay. Thermally shielding it helps,
a decent TCXO is better, ovenizing an SC-cut is better still, but
picoseconds jitter per second of delay is *very* difficult.

The spec is 25 ps. The HP5370 measures 24.7ps over an interval of 10
seconds or greater. The Binary sampler would not display a 200ps risetime edge
that had 1 ns of jitter. I have tried using an AD DDS with 330ps rms jitter,
and can post the response of the Binary Sampler. The 200 ps risetime shows
jagged edges. These disppear using the Hosonic 1 MHz crystals.

Perhaps there is something wrong with your instrumentation. Please check using
your HP5370.
Is so. I told you about the d-flop feedback sampler in s.e.d. on Jan
8, 2001, after which you decided you invented it, and announced you
had "broken Shannon's Law" with it.

Fortunately, Google archives all this stuff:

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


John,

That would be *very* interesting - do you have the time to explain
further?

How do you get a sampling bridge without taking a Tek or HP scope
apart?

Best Regards,

Michael R. Monett

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

etc.

Yes, John. We were discussing using a binary search to locate the sample
point. You showed a simple D flop. It had to work since a similar concept is
used in flash converters.

However, this was open loop. I closed the loop with an integrator. You said it
would rail.
It's amazing how many people find a concept, obsess on it, and soon
decide they invented it themselves.

Sorry John, I do not claim credit for Delta Modulation, the Tracking ADC, or
the configuration shown in McCabe's thesis or the Souders NIST paper.
Again, after I told you about it. All archived.


Why would a simple schematic need an explanation?

Perhaps you are familiar with the circuit. To someone who has never used a
tunnel diode, it is incomprehensible. However, it is irrelevant. The basic
concept of the Binary Sampler was invented in 1972.

Sure you did, John. Just look further in the same thread.
You assume that decades of engineers (including Shannon, and the
staffs of HP and Tek, and of course your humble correspondent) are
stupid, and you are smarter. Not likely.

John

John, conventional sampling techniques are interesting from a theoretical and
practical point of view. The complexity attracts very intelligent people, and
many spend their entire careers on it, such as Agoston.

The thought of looking for a simpler approach is not part of their thinking. I
was looking for a simpler approach, and was amazed to find the excellent
noise-rejection properties of the Binary Sampler. To my knowledge, there are
no other references to this phenomenon. If you can find one, please let me
know.

In the meantime, I am moving and have to shut down, so you get the last shot.
I appreciate the excellent discussion and the time you have spent.

Thanks John!

Best Wishes,

Michael R. Monett
 
J

John Larkin

Jan 1, 1970
0
The spec is 25 ps. The HP5370 measures 24.7ps over an interval of 10
seconds or greater. The Binary sampler would not display a 200ps risetime edge
that had 1 ns of jitter. I have tried using an AD DDS with 330ps rms jitter,
and can post the response of the Binary Sampler. The 200 ps risetime shows
jagged edges. These disppear using the Hosonic 1 MHz crystals.

This is complex. I guess what really matters is the phase noise during
the real time interval that it takes the two oscillators to
differentially traverse the risetime. For two 1 MHz oscillators 1 Hz
apart, they sweep 1 microsecond per second, so they sweep across 200
ps in 200 usec. Yeah, cheap oscillators are this good. The jitter
*between* waveform features say 200 nsec apart (swept in 200
milliseconds of real time) will be far worse. The math is a bitch
here.
Perhaps there is something wrong with your instrumentation. Please check using
your HP5370.

The best a 5370 ever does is about 30 ps RMS, and it of course gets
worse over long timebases due to oscillator phase noise. A 5370B also
has an interesting jitter bump around 4 milliseconds, for reasons
unknown. My Tek 11801A scope hits about 1.5 ps RMS, but only for
short, sub-usec timebase delays.

The only real way to measure the phase noise (or, time domain,
jitter-versus-delay) over long timebases is to play two identical
gadgets off against each other, carefully.

Oh, a few more interesting points about the 1-bit sampler:

PC Instruments did a commercial version for a while, and I'm fairly
sure the Hypres 50 GHz superconductive sampling scope (it needed 120
VAC plus a jug of liquid helium) was too. Both are out of production.

An EP dflop does make a nice infinite-gain phase detector, capable of
sub-ps locking in a PLL.

Another - noisy - way to architect the sampler is to use a DAC for the
feedback, but use a successive-approximation register rather than a
counter. So for n-bit digitizing, you only need n samples.

You heard it here first.

John
 
M

Mike Monett

Jan 1, 1970
0
John said:
This is complex. I guess what really matters is the phase noise during
the real time interval that it takes the two oscillators to
differentially traverse the risetime. For two 1 MHz oscillators 1 Hz
apart, they sweep 1 microsecond per second, so they sweep across 200
ps in 200 usec. Yeah, cheap oscillators are this good. The jitter
*between* waveform features say 200 nsec apart (swept in 200
milliseconds of real time) will be far worse. The math is a bitch
here.

I'm not so sure I follow you here. The two positive transitions in the Binary
Sampler data are 1uS apart, and the one on the right side of the graph is identical
to the one on the left.

We start recording data on the first phase match between the two oscillators. They
are free-running, and show another phase match 1uS later. I guess the question is
exactly how far apart are the two positive transitions. I can measure this to
better than 1 ps in the graphics, so I will take a look after moving.
The best a 5370 ever does is about 30 ps RMS, and it of course gets
worse over long timebases due to oscillator phase noise.

The manuals are out of reach, but I believe a self-check for the HP5370 is to
connect a coax between the rear panel 10MHz output and the input on the front
panel. I measured 17ps rms, which I use in difference of squares to obtain the 25
ps jitter of the crystal. I also have the high stability crystal option.
A 5370B also
has an interesting jitter bump around 4 milliseconds, for reasons
unknown. My Tek 11801A scope hits about 1.5 ps RMS, but only for
short, sub-usec timebase delays.

The only real way to measure the phase noise (or, time domain,
jitter-versus-delay) over long timebases is to play two identical
gadgets off against each other, carefully.

Yes! Exactly. Wenzel has some great info and circuits on doing this, and I plan to
get one set up as soon as possible.
Oh, a few more interesting points about the 1-bit sampler:

PC Instruments did a commercial version for a while, and I'm fairly
sure the Hypres 50 GHz superconductive sampling scope (it needed 120
VAC plus a jug of liquid helium) was too. Both are out of production.

An EP dflop does make a nice infinite-gain phase detector, capable of
sub-ps locking in a PLL.

Probably would work very well. The EP52 jitter spec is 200fs, so all you need is a
good reference and a low-noise vco. If the circuit is arranged the right way, it
looks like the Binary Sampler, so you get the same noise-rejection.
Another - noisy - way to architect the sampler is to use a DAC for the
feedback, but use a successive-approximation register rather than a
counter. So for n-bit digitizing, you only need n samples.

You heard it here first.

I think NIST uses a similar concept in their current version of the Sampling
Voltage Tracker. See reference [13], O. B. Laug, T. M. Souders, and D. R. Flach, "A
custom integrated circuit comparator for high-performance sampling applications,"
IEEE Trans. Instrum. Meas., vol. 41, pp. 850-855, Dec. 1992.

They use a SAR for the first few bits, then switch to a single bit increment to get
the last bits. They pretty much have to do something like this, since you cannot do
a binary search on noisy data.

The problem with this approach is you lose the memory of the previous sample, so
you lose the noise-rejection property of the Binary Sampler, and have to average to
get rid of the noise. Then you run into system drift over long averaging times.
Back in the same problem again:)

Thanks, John. Very good discussion! I'm pulling the plug now - see you after I get
to Midland.

Best Wishes,

Michael R. Monett
 
M

Mike

Jan 1, 1970
0
This is complex. I guess what really matters is the phase noise during
the real time interval that it takes the two oscillators to
differentially traverse the risetime. For two 1 MHz oscillators 1 Hz
apart, they sweep 1 microsecond per second, so they sweep across 200
ps in 200 usec. Yeah, cheap oscillators are this good. The jitter
*between* waveform features say 200 nsec apart (swept in 200
milliseconds of real time) will be far worse. The math is a bitch
here.

It's not as bad as you think, especially if you can neglect flicker noise.
The flicker noise assumption is generally valid over short time intervals,
but not over periods of one second. It should be noted that flicker noise
makes the problems worse, not better, so neglecting it gives optimistic
results.

Assuming you can neglect flicker noise, the accumulated jitter of the
oscillator is simply the period to period jitter multiplied by sqrt(N),
where N is the number of cycles. This is the same as the standard deviation
of a one-dimensional random walk after N steps. The math for this is easy -
it's essentially one integral, and can be found in many statistics books. I
can post a derivation on abse if you're interested.

So, if you have a 1 MHz crystal oscillator with 25ps cycle-to-cycle jitter,
the jitter over 1 second will be 25ns, relative to a perfect clock.
Relative to another imperfect oscillator, it will be sqrt(2) times larger,
since both oscillators are random-walking in different directions.

I don't know what Mike's measuring - we'd need to see his test setup to be
sure, but 24.7ps over 10 seconds or greater is hard to believe. The HP5370
he's using claims an absolute accuracy of 65ps over a 10s interval, as long
as the external timebase is that accurate, and a relative accuracy of 20ps.
With an absolute accuracy of 65ps, any measurement of 24.7ps over the same
interval would appear to be meaningless.

-- Mike --
 
J

John Larkin

Jan 1, 1970
0
It's not as bad as you think, especially if you can neglect flicker noise.
The flicker noise assumption is generally valid over short time intervals,
but not over periods of one second. It should be noted that flicker noise
makes the problems worse, not better, so neglecting it gives optimistic
results.

Assuming you can neglect flicker noise, the accumulated jitter of the
oscillator is simply the period to period jitter multiplied by sqrt(N),
where N is the number of cycles. This is the same as the standard deviation
of a one-dimensional random walk after N steps. The math for this is easy -
it's essentially one integral, and can be found in many statistics books. I
can post a derivation on abse if you're interested.

So, if you have a 1 MHz crystal oscillator with 25ps cycle-to-cycle jitter,
the jitter over 1 second will be 25ns, relative to a perfect clock.
Relative to another imperfect oscillator, it will be sqrt(2) times larger,
since both oscillators are random-walking in different directions.

I don't know what Mike's measuring - we'd need to see his test setup to be
sure, but or greater is hard to believe. The HP5370
he's using claims an absolute accuracy of 65ps over a 10s interval, as long
as the external timebase is that accurate, and a relative accuracy of 20ps.
With an absolute accuracy of 65ps, any measurement of 24.7ps over the same
interval would appear to be meaningless.

-- Mike --

Hi, Mike,

When I said the math is a bitch, I didn't mean it was hard to do,
rather that the consequences are nasty for a heterodyne timebase.

What MM's doing is using a 1 MHz oscillator to make a fast edge, and
using a separate 1.000001 MHz oscillator as the timebase trigger for a
sampler. So he's effectively sweeping 1 usec of equivalent time in 1
second of real time, theoretically at 1 ps per sample. The question I
had was the effect of oscillator phase noise in such a situation,
especially using non-ovenized oscillators. A simple XO will typically
accumulate about 1 ns error per second, often worse, so his timebase
will jitter about like that. But a single 200 ps edge is swept in 200
usec of real time, and the jitter *during* that single edge won't be
bad. Of course, that edge will effectively wobble and wander around in
time on successive sweeps.

$3 Digikey-type crystal oscillators can, with luck, have maybe 10-30
ps RMS jitter cycle-to-cycle, and accumulate jitter over longer
intervals. There will typically be a jitter corner in the millisecond
time frame, sloping up to, as I estimated, a ns or more at 1 second.
Local transient temperature variations can make this much worse.

When MM says "24.7ps over 10 seconds" I think he's actually measuring
cycle-to-cycle jitter, but taking 10 seconds to make the ensemble
measurement. That's a whale different from using the same oscillator
to time a 10-second period, and measuring the jitter of *that*. No
simple oscillator is going to be steady to a couple parts in 1e12 over
10 seconds.

John
 
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