Re: [time-nuts] ? phase comparison or other device

[Bob Paddock]

); SAEximRunCond expanded to false
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On Friday 29 June 2007 13:08, Juerg Koegel wrote:
> Another article (with practical hints) is> 
> OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE MULTIPLIER 
> L. Sojdr, J. Cermák, R. Barillet

> It is too big for the Time Nuts annex   (912k) 

As Juerg did not have space for the paper,
I added it to the Application Notes section
of my http://www.unusualresearch.com/
site.

If anyone else needs a home for an odd ball
paper and does not have the space or inclination
to set up a web site, I'm happy to post the papers.

Also if you need to reduce the size of a large .pdf,
you can use http://any2djvu.djvuzone.org to reduce
and OCR them.  The 912K .pdf comes in as a 127K DjVu
file.


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 http://www.unusualresearch.com/

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Bob Paddock wrote:
> "The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low 
> distortion clamping amplifiers. 
> The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or 
> greater. 
> These devices allow the designer to specify a high (VCH) and low (VCL) output 
> clamp voltage.
> The output signal will clamp at these specified levels."
>
> http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html
>
> AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 
> 57,313 bytes)
>
> http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf
>
> "So far most clamping amplifiers have relied upon an output clamping 
> architecture and are called output clamp amps (OCAs). 
> A new architecture called an input clamp amp (ICA) offers superior clamping 
> accuracy and lower distortion."
>   
Bob

A significant issue with these clamping amplifiers is that although when 
the clamp is active the signal gain is near very low, the amplifier 
noise gain is the same as when the clamp isn't active.
In contrast with a simple diode clamp, the signal gain is low when the 
clamp is conducting and the amplifier noise gain is at worst unity.
Surely this characteristic of a simple diode clamp reduces the noise 
associated with the amplifier accumulated on the low pass filter 
capacitor in a zero-crossing detector over the amplifier noise 
contribution from an equivalent zero-crossing detector using such input 
clamping amplifiers?

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Mon, 02 Jul 2007 10:02:44 +1200
Message-ID: <[EMAIL PROTECTED]>

> Bob
> 
> What is the application for which you want to use injected out of band 
> noise?
> Since the performance of a well designed zero-crossing detector is 
> equivalent to a 25 bit ADC when locating the zero-crossing, it will be 
> difficult to replicate this performance using a lower resolution ADC 
> even combined with out of band dithering.
> 
> In practice, diode clamp circuit distortion in a zero-crossing detector 
> isn't an issue.

We soon will have well-tested ZCDs of "sufficient" resolution at our hands
here on the list. They will be fairly easy to duplicate. As we combine findings
of different origins I think alot will be gained.

Now, would interferometric approaches lower our 1/f noise floor in the mixers?
I have been considering multiple insertion polyphase filters in order to
acheive the equalent of a 0/180 degree combiner network but for 10 MHz where
such approaches would be bulky unless built by coaxes, which certainly would be
possible to acheive. Any opinions?

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Bob Paddock wrote:
>> These devices are a little noisy below 100Hz.
>> 
>
> Rather than constantly battle the "there is to much noise", what are
> your thoughts on deliberately injecting out-of-band noise?
>
> As an example:
> http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf
> "Overcoming Converter Nonlinearities with Dither"
>
>   
>> The distortion produced by a diode clamp is immaterial when one is only 
>> interested in the zero crossing time.
>> 
>
> It depends on where the harmonics fall.
>
>
>   
Bob

What is the application for which you want to use injected out of band 
noise?
Since the performance of a well designed zero-crossing detector is 
equivalent to a 25 bit ADC when locating the zero-crossing, it will be 
difficult to replicate this performance using a lower resolution ADC 
even combined with out of band dithering.

In practice, diode clamp circuit distortion in a zero-crossing detector 
isn't an issue.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Bob Paddock]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]


> These devices are a little noisy below 100Hz.

Rather than constantly battle the "there is to much noise", what are
your thoughts on deliberately injecting out-of-band noise?

As an example:
http://www.analog.com/UploadedFiles/Application_Notes/319765654AN-410.pdf
"Overcoming Converter Nonlinearities with Dither"

> The distortion produced by a diode clamp is immaterial when one is only 
> interested in the zero crossing time.

It depends on where the harmonics fall.


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 http://www.softwaresafety.net/ http://www.designer-iii.com/
 http://www.unusualresearch.com/

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Bob Paddock wrote:
> On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote:
>
>   
>> Not true, there's nothing magic about amplifier saturation, any means 
>> that limits the amplifier output whilst dropping the small signal gain 
>> to a low value will have exactly the same effect.
>> 
>
> "The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low 
> distortion clamping amplifiers. 
> The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or 
> greater. 
> These devices allow the designer to specify a high (VCH) and low (VCL) output 
> clamp voltage.
> The output signal will clamp at these specified levels."
>
> http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html
>
> AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 
> 57,313 bytes)
>
> http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf
>
> "So far most clamping amplifiers have relied upon an output clamping 
> architecture and are called output clamp amps (OCAs). 
> A new architecture called an input clamp amp (ICA) offers superior clamping 
> accuracy and lower distortion."
>
>   
>> A diode clamp in the feedback path will cut the noise gain to 1 when 
>> either diode turns on. The following diode clamp across the filter 
>> capacitor will reduce the noise gain to a very small value when it turns on.
>> Both diode clamps and internal saturation will still produce some output 
>> noise although not from the amplifier input stages.
>> 
>
> Improperly done diode clamps can significantly increase harmonics.
>
>
>   
Bob

These devices are a little noisy below 100Hz.
Also any noise at the input clamp level inputs appears at the output.
Since these devices actually set the maximum input voltage before 
clamping occurs they are unsuitable when the gain is high.

The distortion produced by a diode clamp is immaterial when one is only 
interested in the zero crossing time.

Bruce


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Re: [time-nuts] ? phase comparison or other device

[Bob Paddock]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

On Saturday 30 June 2007 10:15, Dr Bruce Griffiths wrote:
   
> Not true, there's nothing magic about amplifier saturation, any means 
> that limits the amplifier output whilst dropping the small signal gain 
> to a low value will have exactly the same effect.

"The AD8036 and AD8037, from Analog Devices, are wide bandwidth, low distortion 
clamping amplifiers. 
The AD8036 is unity gain stable. The AD8037 is stable at a gain of two or 
greater. 
These devices allow the designer to specify a high (VCH) and low (VCL) output 
clamp voltage.
The output signal will clamp at these specified levels."

http://www.analog.com/en/prodDesc/0,2895,AD8036%255F0,00.html

AN-402: Replacing Output Clamping Op Amps with Input Clamping Amps (pdf, 57,313 
bytes)

http://www.analog.com/UploadedFiles/Application_Notes/374941256AN-402.pdf

"So far most clamping amplifiers have relied upon an output clamping 
architecture and are called output clamp amps (OCAs). 
A new architecture called an input clamp amp (ICA) offers superior clamping 
accuracy and lower distortion."

> A diode clamp in the feedback path will cut the noise gain to 1 when 
> either diode turns on. The following diode clamp across the filter 
> capacitor will reduce the noise gain to a very small value when it turns on.
> Both diode clamps and internal saturation will still produce some output 
> noise although not from the amplifier input stages.

Improperly done diode clamps can significantly increase harmonics.


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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

From: "Juerg Koegel" <[EMAIL PROTECTED]>
Subject: [time-nuts] ? phase comparison or other device
Date: Fri, 29 Jun 2007 19:08:47 +0200
Message-ID: <[EMAIL PROTECTED]>

> Another article (with practical hints) is
> 
>  
> 
> OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE MULTIPLIER
> 
>  
> 
> L. Sojdr, J. Cermák, R. Barillet
> 
>  
> 
> The article (pdf file) is at present not online.
> 
> It is too big for the Time Nuts annex   (912k)  
> 
> I can send you the article direct.

Where did this article show up? I'd like a copy!

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[John Miles]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

> John Miles wrote:
> >> The output of an opamp is always referenced to its power supply,
> >> regardless of the configuration.  If the power supply is noisy,
> >> the output is noisy.
> >>
> >
> > Beyond a few kHz this may be true, but at lower frequencies
> even a low-grade
> > opamp has excellent rejection of power supply noise.  A good opamp data
> > sheet will characterize the PSRR versus frequency.
> >
> > -- john, KE5FX
> >
> John
>
> Only when the opamp is operating within its linear region, not when the
> output is saturated.
> Opamp saturation has been proposed as a good method of reducing the
> output noise of an opamp when an amplifier is overdriven.
> This is clearly not true when power supply noise is significant, as is
> almost always the case.

Sure; I was mainly objecting to use of the term "always."  The statement
that "the output of an opamp is always referenced to its power supply" is
simply not a good model of the situation near DC, unless (as you note) the
output is saturated.

-- john, KE5FX


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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

For those of you who are unfamiliar with the bipolar transistor feedback 
limiter the attached schematic depicts it in use with both a 
noninverting and an inverting amplifier.
The output voltage swing before clamping is limited by transistor Vbe 
breakdown. However this can be oversome by adding a few diodes when a 
larger output swing is required.
Unlike the simple shunt diode feedback clamp, the circuit noise gain is 
less than 1 when the output is clamped. Off course the voltage noise at 
one of the clamp transistor bases appears at the output when the output 
is clamped. However this voltage is generally less than the power supply 
and its noise can easily be made significantly lower.


Bruce


Bipolar transistor feedback limiter.pdf
Description: Adobe PDF document
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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

John Miles wrote:
>> The output of an opamp is always referenced to its power supply,
>> regardless of the configuration.  If the power supply is noisy,
>> the output is noisy.
>> 
>
> Beyond a few kHz this may be true, but at lower frequencies even a low-grade
> opamp has excellent rejection of power supply noise.  A good opamp data
> sheet will characterize the PSRR versus frequency.
>
> -- john, KE5FX
>   
John

Only when the opamp is operating within its linear region, not when the 
output is saturated.
Opamp saturation has been proposed as a good method of reducing the 
output noise of an opamp when an amplifier is overdriven.
This is clearly not true when power supply noise is significant, as is 
almost always the case.

Bruce


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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Pete

Try changing your input stage to the configuration depicted in the 
attachment.
The input amplifier can then be something like an OP27 without affecting 
performance.
The noise spectrum at the first opamp output will actually be reduced to 
the opamp (and series resistor) input noise at frequencies outside the 
tuned circuit bandpass rather than being significantly enhanced as in 
you circuit. The first opamp will ouput also be dc stable with a zero 
signal output of around zero volts unlike your circuit.


This will do nothing for the rather large phase shift tempco, but at 
least its a more rational design.


In fact your circuit performance should improve if you just delete the 
first tuned circuit.


You still need to think about a suitable limiter that doesn't switch the 
power supply noise to the output during stauration.


Bruce


ModifiedRawsonZCDInputStage.pdf
Description: Adobe PDF document
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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Chuck Harris wrote:

>> What about the power supply noise that appears at the amplifier output 
>> during saturation?
>> Power supply noise is almost always much larger than the opamp input noise.
>> A simple resistor + diode clamp in addition to the feedback clamp will 
>> easily attenuate the output noise of an opamp with diode clamps across 
>> its feedback resistor.
>> 
>
> The output of an opamp is always referenced to its power supply,
> regardless of the configuration.  If the power supply is noisy,
> the output is noisy.
>
> -Chuck Harris
>
>   
Only when that opamp output is saturated.
When in linear operation the power supply rejection, at least at low 
frequency, is significant.

Bruce


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Re: [time-nuts] ? phase comparison or other device

[John Miles]

> The output of an opamp is always referenced to its power supply,
> regardless of the configuration.  If the power supply is noisy,
> the output is noisy.

Beyond a few kHz this may be true, but at lower frequencies even a low-grade
opamp has excellent rejection of power supply noise.  A good opamp data
sheet will characterize the PSRR versus frequency.

-- john, KE5FX


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Re: [time-nuts] ? phase comparison or other device

[Chuck Harris]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Dr Bruce Griffiths wrote:
> ); SAEximRunCond expanded to false
> Errors-To: [EMAIL PROTECTED]
> 
> Pete wrote:
>> ); SAEximRunCond expanded to false
>> Errors-To: [EMAIL PROTECTED]
>>
>> Magnus,
>>
>> This discussion is why I have allowed the ADA4899-1 to saturate in the ZCD
>> posted earlier. The transition times up & down in the second stage are 350 
>> to
>> 400 ns; thus I believe the <50ns overload recovery doesn't degrade the
>> measured jitter. With 500MHz 'scope bandwidth, the 1KHz squarewave
>> output has <1% over/under shoot & appears noise free at the zero crossing.
>>
>> The output transitions are fast enough for my HP 5370A to  show < 1ns
>> jitter over 1K or 10K samples.
>>
>> Regards,
>>
>> Pete Rawson 
>>   
> Pete
> 
> What about the power supply noise that appears at the amplifier output 
> during saturation?
> Power supply noise is almost always much larger than the opamp input noise.
> A simple resistor + diode clamp in addition to the feedback clamp will 
> easily attenuate the output noise of an opamp with diode clamps across 
> its feedback resistor.

The output of an opamp is always referenced to its power supply,
regardless of the configuration.  If the power supply is noisy,
the output is noisy.

-Chuck Harris

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Pete wrote:
> Magnus,
>
> This discussion is why I have allowed the ADA4899-1 to saturate in the ZCD
> posted earlier. The transition times up & down in the second stage are 350 
> to
> 400 ns; thus I believe the <50ns overload recovery doesn't degrade the
> measured jitter. With 500MHz 'scope bandwidth, the 1KHz squarewave
> output has <1% over/under shoot & appears noise free at the zero crossing.
>
> The output transitions are fast enough for my HP 5370A to  show < 1ns
> jitter over 1K or 10K samples.
>
> Regards,
>
> Pete Rawson 
>
>   
Pete

Try measuring your circuits output noise spectrum.
Also measure the temperature dependance of its input output phase shift.
What does this tell you about how stable its temperature needs to be to 
limit the phase shift change to a few nanosconds, or even a microsecond?

Bruce


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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Operating an opamp in saturation for extended periods in a precision 
circuit is a bad idea, as the changes in dissipation of the various 
devices in the opamp will change the opamp input offset voltage when it 
comes out of saturation. Even though modern opamps use cross coupled 
quads and other layout symmetry techniques to greatly reduce the thermal 
feedback on the chip, the effect is still finite. With input frequencies 
above a few kHz the thermal feedback isn't significant, however with the 
low frequencies typically used in this application thermal feedback is 
significant. Thermal feedback is reduced by keeping the opamp out of 
saturation and limiting the output swing to minimise the change in the 
power dissipation in the output stage transistors.

Bruce



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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Pete wrote:
> ); SAEximRunCond expanded to false
> Errors-To: [EMAIL PROTECTED]
>
> Magnus,
>
> This discussion is why I have allowed the ADA4899-1 to saturate in the ZCD
> posted earlier. The transition times up & down in the second stage are 350 
> to
> 400 ns; thus I believe the <50ns overload recovery doesn't degrade the
> measured jitter. With 500MHz 'scope bandwidth, the 1KHz squarewave
> output has <1% over/under shoot & appears noise free at the zero crossing.
>
> The output transitions are fast enough for my HP 5370A to  show < 1ns
> jitter over 1K or 10K samples.
>
> Regards,
>
> Pete Rawson 
>   
Pete

What about the power supply noise that appears at the amplifier output 
during saturation?
Power supply noise is almost always much larger than the opamp input noise.
A simple resistor + diode clamp in addition to the feedback clamp will 
easily attenuate the output noise of an opamp with diode clamps across 
its feedback resistor.

An npn plus a pnp resistor ccan also be used to clamp the output of an 
opamp whilst still suppressing the noise gain to a very low value and 
prevent opamp saturation.

Bruce


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Re: [time-nuts] ? phase comparison or other device

[Pete]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Magnus,

This discussion is why I have allowed the ADA4899-1 to saturate in the ZCD
posted earlier. The transition times up & down in the second stage are 350 
to
400 ns; thus I believe the <50ns overload recovery doesn't degrade the
measured jitter. With 500MHz 'scope bandwidth, the 1KHz squarewave
output has <1% over/under shoot & appears noise free at the zero crossing.

The output transitions are fast enough for my HP 5370A to  show < 1ns
jitter over 1K or 10K samples.

Regards,

Pete Rawson 


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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Sun, 01 Jul 2007 02:15:55 +1200
Message-ID: <[EMAIL PROTECTED]>

> Magnus Danielson wrote:
> > Ulrich,
> >
> >   
> >> you are right: Both of these articles should be read with Collins's
> >> perhaps the better (and newer!) one. 
> >>
> >> There is however one question remaining for me: When I learned
> >> electronics it was generally considered bad design to let an amplifier
> >> run into limiting due to supply limitations. If limiting was needed, so
> >> was the rule, then it should be accomplished by planned feedback, say an
> >> pair of antiparallel diodes in the feedback path. Can you give some
> >> comments on whether this also applies to ZCDs or if really supply based
> >> limiting is necessary?
> >> 
> >
> > It is actually a specific design-trick on Collins behalf to saturate the
> > op-amp since this infact acts like a noise-gate. By having the output stage
> > saturated rather than operating linearly the noise as seen by the output RC
> > filter is that of only the saturated transistor and not that of the input
> > gained up. A diode limiter in the feedback path will maintain the op-amp in
> > the linear operating range and thus cause the noise to continue to polute 
> > the
> > output filter. What you can possibly acheive is the steer how deeply you run
> > into output saturation tought.
> >
> > So, in this case op-amp saturation is a key trick to increased performance.
> >
> >   
> Not true, there's nothing magic about amplifier saturation, any means 
> that limits the amplifier output whilst dropping the small signal gain 
> to a low value will have exactly the same effect.

So you don't think the input-to-output gain is greatly affected when in
saturation? That is usually what happneds IMHO.

The gain in saturation will be less than 1. Thus, early noise sources will be
dampend rather than gained. In a diode clamp they will have unity gain rather
than gained. There's the difference.

> In most cases recovery from saturation will be too slow for the later 
> stages of the ZCD.
> Those amplifiers that have fast recovery from saturation usually employ 
> internal diode clamps.
> A diode clamp in the feedback path will cut the noise gain to 1 when 
> either diode turns on. The following diode clamp across the filter 
> capacitor will reduce the noise gain to a very small value when it turns on.
> Both diode clamps and internal saturation will still produce some output 
> noise although not from the amplifier input stages.

Well, this is true. But it again shifts the noise levels from the ideal zero.

The full gain is when the output saturates, but this has the drawback in
recovery time. I think the output saturation may be better for the first stage
where as a clamped variant is better for the following stages. For the first
stage you also have the noise out of the mixer to consider.

I might buy your argument better if you'd show me that the noise of the
saturated output stage is worse than the gain-of-1 alternative. If the noise
is just slightlty worse with the clamping, then its benefits outperforms the
loss in noise margin.

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Magnus Danielson wrote:
> Ulrich,
>
>   
>> you are right: Both of these articles should be read with Collins's
>> perhaps the better (and newer!) one. 
>>
>> There is however one question remaining for me: When I learned
>> electronics it was generally considered bad design to let an amplifier
>> run into limiting due to supply limitations. If limiting was needed, so
>> was the rule, then it should be accomplished by planned feedback, say an
>> pair of antiparallel diodes in the feedback path. Can you give some
>> comments on whether this also applies to ZCDs or if really supply based
>> limiting is necessary?
>> 
>
> It is actually a specific design-trick on Collins behalf to saturate the
> op-amp since this infact acts like a noise-gate. By having the output stage
> saturated rather than operating linearly the noise as seen by the output RC
> filter is that of only the saturated transistor and not that of the input
> gained up. A diode limiter in the feedback path will maintain the op-amp in
> the linear operating range and thus cause the noise to continue to polute the
> output filter. What you can possibly acheive is the steer how deeply you run
> into output saturation tought.
>
> So, in this case op-amp saturation is a key trick to increased performance.
>
>   
Not true, there's nothing magic about amplifier saturation, any means 
that limits the amplifier output whilst dropping the small signal gain 
to a low value will have exactly the same effect.
In most cases recovery from saturation will be too slow for the later 
stages of the ZCD.
Those amplifiers that have fast recovery from saturation usually employ 
internal diode clamps.
A diode clamp in the feedback path will cut the noise gain to 1 when 
either diode turns on. The following diode clamp across the filter 
capacitor will reduce the noise gain to a very small value when it turns on.
Both diode clamps and internal saturation will still produce some output 
noise although not from the amplifier input stages.
> Cheers,
> Magnus
>   

Bruce.

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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

From: "Ulrich Bangert" <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Fri, 29 Jun 2007 09:14:02 +0200
Message-ID: <[EMAIL PROTECTED]>

> Enrico,

Ulrich,

> you are right: Both of these articles should be read with Collins's
> perhaps the better (and newer!) one. 
> 
> There is however one question remaining for me: When I learned
> electronics it was generally considered bad design to let an amplifier
> run into limiting due to supply limitations. If limiting was needed, so
> was the rule, then it should be accomplished by planned feedback, say an
> pair of antiparallel diodes in the feedback path. Can you give some
> comments on whether this also applies to ZCDs or if really supply based
> limiting is necessary?

It is actually a specific design-trick on Collins behalf to saturate the
op-amp since this infact acts like a noise-gate. By having the output stage
saturated rather than operating linearly the noise as seen by the output RC
filter is that of only the saturated transistor and not that of the input
gained up. A diode limiter in the feedback path will maintain the op-amp in
the linear operating range and thus cause the noise to continue to polute the
output filter. What you can possibly acheive is the steer how deeply you run
into output saturation tought.

So, in this case op-amp saturation is a key trick to increased performance.

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[Peter Vince]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

I've had a quick search on the internet and found references, but not 
the actual article itself.  I wonder if it could be uploaded to one 
of the archives that members of this list have?  Otherwise, please 
may I have a copy too?

Thank you,

Peter Vince  (G8ZZR, London)


>Will be glad to receive it!
>
>Please send to:
>
>[EMAIL PROTECTED]
>
>Best regards
>Ulrich Bangert
>
>> -Ursprüngliche Nachricht-
>> Von: [EMAIL PROTECTED]
>> [mailto:[EMAIL PROTECTED] Im Auftrag von Juerg Koegel
>> Gesendet: Freitag, 29. Juni 2007 19:09
>> An: Discussion of precise time and frequency measurement
>> Betreff: [time-nuts] ? phase comparison or other device
>>
>> Another article (with practical hints) is
>>
>> OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE MULTIPLIER
>> L. Sojdr, J. Cermák, R. Barillet
>>
>> The article (pdf file) is at present not online.
>> It is too big for the Time Nuts annex   (912k)
>> I can send you the article direct.
>>
>> Best regardsJuerg

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Re: [time-nuts] ? phase comparison or other device

[Ulrich Bangert]

); SAEximRunCond expanded to false
Errors-To: [EMAIL PROTECTED]

Will be glad to receive it!

Please send to:

[EMAIL PROTECTED]

Best regards
Ulrich Bangert

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Juerg Koegel
> Gesendet: Freitag, 29. Juni 2007 19:09
> An: Discussion of precise time and frequency measurement
> Betreff: [time-nuts] ? phase comparison or other device
> 
> 
> Another article (with practical hints) is
> 
>  
> 
> OPTIMIZATION OF DUAL-MIXER TIME-DIFFERENCE MULTIPLIER
> 
>  
> 
> L. Sojdr, J. Cermák, R. Barillet
> 
>  
> 
> The article (pdf file) is at present not online.
> 
> It is too big for the Time Nuts annex   (912k)  
> 
> I can send you the article direct.
> 
>  
> 
> Best regardsJuerg
> ___
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> 


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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

A link to reference 6 in the Collins paper on the design of low jitter 
hard limiters:

http://tmo.jpl.nasa.gov/progress_report/42-107/107D.PDF

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Fri, 29 Jun 2007 19:52:22 +1200
Message-ID: <[EMAIL PROTECTED]>

> Ulrich Bangert wrote:
> > Enrico,
> >
> > you are right: Both of these articles should be read with Collins's
> > perhaps the better (and newer!) one. 
> >
> > There is however one question remaining for me: When I learned
> > electronics it was generally considered bad design to let an amplifier
> > run into limiting due to supply limitations. If limiting was needed, so
> > was the rule, then it should be accomplished by planned feedback, say an
> > pair of antiparallel diodes in the feedback path. Can you give some
> > comments on whether this also applies to ZCDs or if really supply based
> > limiting is necessary?
> >
> > Best regards
> > Ulrich Bangert 
> >
> >   
> Ulrich
> 
> Diode clamps are usually essential particularly with opamps as in most 
> cases their recovery from input overdrive is otherwise too slow to be 
> useful in such circuits.
> The Collins paper also indicates, as I suspected, that the -5v and +5V 
> clamp levels used in the JPL ZCD are somewhat arbitrary and lower clamp 
> levels can be used.

The clamp levels is gain-wise not very relevant since in the next gainstage
they will be clamped out anyways. The lowpass filtering in each stage will
integrate the clamp levels such that the rise and fall positions will be
shifted from their "true" positions by the clamp level and these shifts will
not have an zero mean. However, if the clamp levels are stable they are less of
a problem. The main clamp level effect will be time-shift and as long as the
levels are stable this time-shift will be stable.

I must have a propper reading of the Collins paper, but I will do that
tomorrow. Refreshing new info from the JPL ZCD paper which confirmed my
initial thoughts while introducing the noise aspect. It did bug me that the
noise may not be continous so the Collins findings in that respect was fairly
obvious. However, it seems like he is not caring about the noise level during
the clamping time, which would make his noise estimates somewhat
over-optimistic. But then again, I haven't given the paper a propper read-
through.

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Ulrich Bangert wrote:
> Enrico,
>
> you are right: Both of these articles should be read with Collins's
> perhaps the better (and newer!) one. 
>
> There is however one question remaining for me: When I learned
> electronics it was generally considered bad design to let an amplifier
> run into limiting due to supply limitations. If limiting was needed, so
> was the rule, then it should be accomplished by planned feedback, say an
> pair of antiparallel diodes in the feedback path. Can you give some
> comments on whether this also applies to ZCDs or if really supply based
> limiting is necessary?
>
> Best regards
> Ulrich Bangert 
>
>   
Ulrich

Diode clamps are usually essential particularly with opamps as in most 
cases their recovery from input overdrive is otherwise too slow to be 
useful in such circuits.
The Collins paper also indicates, as I suspected, that the -5v and +5V 
clamp levels used in the JPL ZCD are somewhat arbitrary and lower clamp 
levels can be used.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Ulrich Bangert]

Enrico,

you are right: Both of these articles should be read with Collins's
perhaps the better (and newer!) one. 

There is however one question remaining for me: When I learned
electronics it was generally considered bad design to let an amplifier
run into limiting due to supply limitations. If limiting was needed, so
was the rule, then it should be accomplished by planned feedback, say an
pair of antiparallel diodes in the feedback path. Can you give some
comments on whether this also applies to ZCDs or if really supply based
limiting is necessary?

Best regards
Ulrich Bangert 

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Enrico Rubiola
> Gesendet: Donnerstag, 28. Juni 2007 16:25
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] ? phase comparison or other device
> 
> 
> Dear time-nuts,
> there is another article about zero crossing detection,
> comes after the very wise article written by my friend J. 
> Dick Cheers, Enrico
> 
http://rubiola.org/hidden/collins96comm-zero-crossing-detector.pdf
http://rubiola.org/hidden/dick90ptti-dual-mixer-dc-amplifier.pdf


Enrico Rubiola
professor of electronics

web:http://rubiola.org
e-mail: [EMAIL PROTECTED]

FEMTO-ST Institute
32 av. de l'Observatoire
25044 Besancon, FRANCE
voice:  +33(0)381.853940 (E.Rubiola)
voice:  +33(0)381.853999 (switchboard)
fax:+33(0)381.853998


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Re: [time-nuts] ? phase comparison or other device

[Pete]

Peter,

The JPL paper is the second on Enrico Rubiola's posting.

Pete Rawson

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Re: [time-nuts] ? phase comparison or other device

[Enrico Rubiola]

Dear time-nuts,
there is another article about zero crossing detection,
comes after the very wise article written by my friend J. Dick
Cheers,
Enrico

http://rubiola.org/hidden/collins96comm-zero-crossing-detector.pdf
http://rubiola.org/hidden/dick90ptti-dual-mixer-dc-amplifier.pdf


Enrico Rubiola
professor of electronics

web:http://rubiola.org
e-mail: [EMAIL PROTECTED]

FEMTO-ST Institute
32 av. de l'Observatoire
25044 Besancon, FRANCE
voice:  +33(0)381.853940 (E.Rubiola)
voice:  +33(0)381.853999 (switchboard)
fax:+33(0)381.853998


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Re: [time-nuts] ? phase comparison or other device

[John Ackermann N8UR]

Rick, I'd love to have it, too... I've seen references for quite a 
while, but never been able to get the actual document.

Thanks,

John


Richard (Rick) Karlquist wrote:
> I have the JPL zero crossing detector paper scanned in.
> (John Dick, et al, 1990 PTTI).  It is definitely a must
> read.
> 
> Do you want me to email to you?
> 
> Rick Karlquist N6RK
> 
>> -Original Message-
>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
>> Behalf Of Peter Vince
>> Sent: Wednesday, June 27, 2007 11:55 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] ? phase comparison or other device
>>
>>
>> Hi Pete,
>>
>>> 3. I read the JPL paper (more than once)...
>> Do you have it available in electronic form (or know a link that I 
>> might download it from)?
>>
>>  Thanks,
>>
>>  Peter Vince  (G8ZZR, London)
>>
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> 
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> 


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Re: [time-nuts] ? phase comparison or other device

[Didier Juges]

That will be welcome of course.
Please note that I will be out of the country for a week starting 
tomorrow (June 28), so anything uploaded will have to wait until my 
return to be found at the usual place.
However, anything uploaded can be immediately downloaded using ftp and 
the same login account as for uploading.

http://www.ko4bb.com/ham_radio/Manuals/1_Upload_Instructions.html

Didier KO4BB


John Miles wrote:
> Post it to Didier Juges's site?
>
> ftp.ko4bb.com
> User: manuals
> Password: manuals
>
> -- john, KE5FX
>
>   
>> -Original Message-
>> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
>> Behalf Of Richard (Rick) Karlquist
>> Sent: Wednesday, June 27, 2007 7:37 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: Re: [time-nuts] ? phase comparison or other device
>>
>>
>> I have the JPL zero crossing detector paper scanned in.
>> (John Dick, et al, 1990 PTTI).  It is definitely a must
>> read.
>>
>> Do you want me to email to you?
>>
>> Rick Karlquist N6RK
>>
>> 
>
> ___
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Re: [time-nuts] ? phase comparison or other device

[John Miles]

Post it to Didier Juges's site?

ftp.ko4bb.com
User: manuals
Password: manuals

-- john, KE5FX

> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Behalf Of Richard (Rick) Karlquist
> Sent: Wednesday, June 27, 2007 7:37 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] ? phase comparison or other device
> 
> 
> I have the JPL zero crossing detector paper scanned in.
> (John Dick, et al, 1990 PTTI).  It is definitely a must
> read.
> 
> Do you want me to email to you?
> 
> Rick Karlquist N6RK
> 

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Re: [time-nuts] ? phase comparison or other device

[Richard \(Rick\) Karlquist]

I have the JPL zero crossing detector paper scanned in.
(John Dick, et al, 1990 PTTI).  It is definitely a must
read.

Do you want me to email to you?

Rick Karlquist N6RK

> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Behalf Of Peter Vince
> Sent: Wednesday, June 27, 2007 11:55 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] ? phase comparison or other device
> 
> 
> Hi Pete,
> 
> >3. I read the JPL paper (more than once)...
> 
> Do you have it available in electronic form (or know a link that I 
> might download it from)?
> 
>   Thanks,
> 
>   Peter Vince  (G8ZZR, London)
> 
> ___
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Re: [time-nuts] ? phase comparison or other device

[Peter Vince]

Hi Pete,

>3. I read the JPL paper (more than once)...

Do you have it available in electronic form (or know a link that I 
might download it from)?

Thanks,

Peter Vince  (G8ZZR, London)

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Pete wrote:
> Bruce,
>
> A few final thoughts.
>
> 1. Thanks for the critical view; it does help.
>
> 2. Like many time-nuts I have a reasonably good 10MHz source &
> sometimes need to check out a newly acquired OXCO to ensure
> it can muster 1E9 or 1E10 performance (with 10x headroom).
> An SR620 would be ideal, but it's just too many $$ ;even used.
> I expect "casual" participants of time-nuts already have a basic,
> decent counter e.g. HP5335A & a basic decent synthesizer
> e.g. PTS040, Fluke6060(?), HP3335x or 6x. Also, I assumed a
> coaxial level 7 mixer & suitable lowpass filter would be available.
>
> 3. I read the JPL paper (more than once) & developed the first three
> stages (modified for 1KHz bandpass) per their process. At that point
> the measured jitter was well under 1ns rms; which was enough to enable
> 1E12 resolution for 10MHz sources. I deliberately choose the ADA4899-1
> opamp since it's characterized for 5V operation, low noise, fast & cheap
> enough ($4.30/ea). It was apparent that even with 2 stages the ZCD
> was still under 1ns jitter; the risetime wasn't blazing, but it was 
> obviously
> good enough.
>
> 4. Without PCB capability (at home & now retired) even this simple
> circuit is tough to build; each part adds significantly to the effort 
> when
> doing 1-up. So I examined the need for every part in an effort to
> minimize parts count, but retain jitter performance. I found that the
> opamp overload recovery was more than fast enough to discard the
> limiting without measurable deterioration in jitter. Lots of parts went
> away; construction became easy.
>
> 5. I went TOO FAR. The opamps I had exhibited such low offset that I
> DC coupled without thinking about it. WRONG answer (as you noted),
> Rookie mistake. I have shown the AC coupling & 2nd stage feedback
> resistor in the revised circuit.
>
> 6. The ZCD costs <$20 for parts & about 2 hours to build/check out.
> It performs well enough to look at stable sources to 2 parts in 1E12
> in 50 to 100 seconds and be confident in the data. The noise floor is
> easy to measure & verifies functionality.
>
> Is it "well designed" ? NO. Could it be (much) better? Certainly.
> Does it work well for it's intended purpose? Yes.
>
> My assumptions about equipment may be out of line. In my case, eBay
> supplied everything, except the mixer, filter & ADA4899-1s, so this
> effort didn't require much in the way of extra $$. It does what I wanted.
>
> As previously observed, the mixer should have a diplexer between it and
> the filter for the mixer higher order products to be terminated properly.
> I examined the filter input Z, as terminated, and found it to be from 150
> ohms inductive to 1200 ohms inductive from 10 to 30 MHz. This suggests
> the use of a feedthrough termination of around 100 ohms as a first order
> fix. Using a 93 ohm feedthrough, no improvement, or degradation in 
> results
> was noted. This could use more study.
>
>> From your earlier response, I suspect you have a cheaper, better method
> in mind to achieve the same results. Would you detail it?
>
> Regards,
> Pete Rawson
> 
>
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Pete

Try connecting the input stage inductor and capacitor in parallel with 
the 6190 ohm feedback resistor, but before you do this replace the first 
opamp with a lower gain bandwidth (audio??) device that is unity gain 
stable. This will produce a first gain stage that amplifies the signal 
of interest as well as the noise within the tuned circuit bandwidth 
without unduly amplifying the noise not within the tuned circuit bandpass.
The other thing you could do since you've chosen a 1kHz beat frequency 
is to use an audio transformer to step up the output of the mixer before 
amplifying it. NB dont forget to connect the transformer to ground 
through a capacitor that has a low impedance at 1kHz (this ensures that 
the dc load current at the mixer IF port is low)..

The mixer IF port should be terminated with a 10nF capacitor and a 
simple low pass filter consisting of say a 100uH inductor and a 1nF 
capacitor substituted for the 1.9MHz bandpass filter.
This, as shown by the NIST paper alluded to by Magnus, will increase the 
mixer sensitivity considerably. You should also run the mixer with both 
the RF and LO ports saturated ie more than 7dBm for both of these ports.

The mixer output noise at the 1KHz beat frequency will be somewhere in 
the vicinity of 100nV/rtHz, so if you have say a 1V peak output then the 
inherent jitter due to mixer noise will be around 160ps rms for a tuned 
circuit noise bandwidth of 100Hz. With a suitable amplifier choice you 
shouldn't degrade this by more than 5% or so. Achieving a resolution of 
better than 1E-13 in 1 second with a 10MHz input and a suitable counter 
is easy, provided you dont 

Re: [time-nuts] ? phase comparison or other device

[Pete]

Bruce,

A few final thoughts.

1. Thanks for the critical view; it does help.

2. Like many time-nuts I have a reasonably good 10MHz source &
sometimes need to check out a newly acquired OXCO to ensure
it can muster 1E9 or 1E10 performance (with 10x headroom).
An SR620 would be ideal, but it's just too many $$ ;even used.
I expect "casual" participants of time-nuts already have a basic,
decent counter e.g. HP5335A & a basic decent synthesizer
e.g. PTS040, Fluke6060(?), HP3335x or 6x. Also, I assumed a
coaxial level 7 mixer & suitable lowpass filter would be available.

3. I read the JPL paper (more than once) & developed the first three
stages (modified for 1KHz bandpass) per their process. At that point
the measured jitter was well under 1ns rms; which was enough to enable
1E12 resolution for 10MHz sources. I deliberately choose the ADA4899-1
opamp since it's characterized for 5V operation, low noise, fast & cheap
enough ($4.30/ea). It was apparent that even with 2 stages the ZCD
was still under 1ns jitter; the risetime wasn't blazing, but it was 
obviously

good enough.

4. Without PCB capability (at home & now retired) even this simple
circuit is tough to build; each part adds significantly to the effort when
doing 1-up. So I examined the need for every part in an effort to
minimize parts count, but retain jitter performance. I found that the
opamp overload recovery was more than fast enough to discard the
limiting without measurable deterioration in jitter. Lots of parts went
away; construction became easy.

5. I went TOO FAR. The opamps I had exhibited such low offset that I
DC coupled without thinking about it. WRONG answer (as you noted),
Rookie mistake. I have shown the AC coupling & 2nd stage feedback
resistor in the revised circuit.

6. The ZCD costs <$20 for parts & about 2 hours to build/check out.
It performs well enough to look at stable sources to 2 parts in 1E12
in 50 to 100 seconds and be confident in the data. The noise floor is
easy to measure & verifies functionality.

Is it "well designed" ? NO. Could it be (much) better? Certainly.
Does it work well for it's intended purpose? Yes.

My assumptions about equipment may be out of line. In my case, eBay
supplied everything, except the mixer, filter & ADA4899-1s, so this
effort didn't require much in the way of extra $$. It does what I wanted.

As previously observed, the mixer should have a diplexer between it and
the filter for the mixer higher order products to be terminated properly.
I examined the filter input Z, as terminated, and found it to be from 150
ohms inductive to 1200 ohms inductive from 10 to 30 MHz. This suggests
the use of a feedthrough termination of around 100 ohms as a first order
fix. Using a 93 ohm feedthrough, no improvement, or degradation in results
was noted. This could use more study.


From your earlier response, I suspect you have a cheaper, better method

in mind to achieve the same results. Would you detail it?

Regards,
Pete Rawson 
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Re: [time-nuts] ? phase comparison or other device

[Magnus Danielson]

From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Mon, 25 Jun 2007 20:37:29 +1200
Message-ID: <[EMAIL PROTECTED]>

> Ulrich Bangert wrote:
> > Pete,
> >
> >   
> >>>>  5. Mini-circuits BLP-1.9 low pass filter.
> >>>> 
> >
> > terminating the mixer if output with an lowpass/bandpass filter and NOT
> > with an diplexer is not so good an idea. Where does the rf go?
> >
> > Best regards
> > Ulrich Bangert
> >
> >   
> Ulrich
> 
> This depends on whether the low pass filter has a shunt capacitor at its 
> input or a series inductor.
> With the shunt capacitor the RF is shunted to ground through this capacitor.
> With a series inductor the RF sees a relatively high input impedance and 
> the mixer will not perform well.

Depends on what you want to acheive. NIST made some experiments and found that
this was indeed what increased the gain in the frequency comparisions they
made. They where infact a bit supprised as this was contruary to what they
beleived. It's in the NIST archive, but I could pull the document number out if
given some chance to dig around.

So, what is normally a good thing in RF may not necessarilly be the best
strategy for frequency comparision, at least when it comes to mixers.

Cheers,
Magnus

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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Ulrich Bangert wrote:
> Pete,
>
>   
  5. Mini-circuits BLP-1.9 low pass filter.
 
>
> terminating the mixer if output with an lowpass/bandpass filter and NOT
> with an diplexer is not so good an idea. Where does the rf go?
>
> Best regards
> Ulrich Bangert
>
>   
Ulrich

This depends on whether the low pass filter has a shunt capacitor at its 
input or a series inductor.
With the shunt capacitor the RF is shunted to ground through this capacitor.
With a series inductor the RF sees a relatively high input impedance and 
the mixer will not perform well.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Ulrich Bangert]

Pete,

> > >  5. Mini-circuits BLP-1.9 low pass filter.

terminating the mixer if output with an lowpass/bandpass filter and NOT
with an diplexer is not so good an idea. Where does the rf go?

Best regards
Ulrich Bangert

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Pete
> Gesendet: Sonntag, 24. Juni 2007 03:38
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] ? phase comparison or other device
> 
> 
> Here is a scheme that seems to work well for comparing stable 
> frequency sources in the range of 10 to 100 second 
> measurement intervals.
> 
> Objective - Measure frequency to +/-2E-12 in less than 1 minute.
> 
> Method - Heterodyne DUT output to 1KHz with a master 
> reference source +
> mixer feeding a tuned zero crossing detector 
> + counter.
> 
> Equipment - 1. Master reference source at 5 or 10 MHz, e.g. 
> "mature" OXCO or
>GPSDO.
> 2. Synthesizer set to DUT - 1KHz, locked 
> to reference
>source. The synthesizer averaged 
> output must settle 
> to
> 10uHz in 10 seconds, e.g. HP 3335A or 3336C.
> PTS 040 should work fine, also.
> 3. 9 digit/s counter, locked to reference 
> source with
> selectable gate time. An input LPF 
> (100KHz) helps,
> e.g. HP 5335A.
> 4. Mini-circuits ZRPD-1 mixer. Other 
> level 7 mixers
>  should work, but haven't been tested.
> 5. Mini-circuits BLP-1.9 low pass filter. 
> Other filters
> should work, but haven't been tested.
> 6. Tuned zero crossing detector, accepts 
> 0 to 5dBm 1KHz
> sinewave input & outputs 1KHz 
> squarewave to counter
> with less than 1nS rms jitter.
> 
> Setup - DUT set to +7dBm connects to mixer LO port. 
> Synthesizer set to DUT -
> 1KHz at +4dBm connects to mixer RF port. BLP-1.9 
> connects to
>  mixer IF port. ZCD input connects to BLP-1.9. 
> Counter connects 
> to ZCD
>  output & set for 5 to 10 second gate time. The 
> DUT frequency =
>  synthesizer setting + counter frequency;
>  10uHz digit = 1E-12 for 10MHz DUT.
> 
> The ZCD - Made from 2 Analog devices ADA4899-1, inverting 
> configuration,
>   cascaded, using +/- 2.5 volt power 
> supplies. Both amps 
> have their
>   non-inverting pins connected (only) to a 
> 100 ohm resistor 
> to ground.
>   Both amps have 5uF//5mH to ground on their 
> inverting 
> inputs. The
>   input amp has Rin = 422 ohms and Rf = 6190 
> ohms. The 
> output amp
>   has Rin = 562 ohms and Rf = open. The 
> output amp output 
> pin has
>   2ea 100 ohm resistors in series to ground. 
> The counter is 
> connected
>   to the common point of the 100 ohm 
> resistors. Nominal 
> supply bypassing
>   is required. Battery supplies at +/- 3 
> volts help isolate 
> noise sources.
> 
> Only 2 ZCD parts aren't junk box items. The Analog Devices 
> ADA4899-1 are in distributor stock as SMT parts only. The 5mH 
> inductors are hand wound on MPP toroid cores. 133 turns on a 
> 55438 core or 114 turns on 2 stacked 55521 
> cores
> using 22 or 24 AWG wire work fine. Other MPP cores will work, 
> but limit Bmax to 50mT at 1KHz & 0.5V rms. Gapped ferrites 
> are too noisy. The 5uF caps are polypropylene or mylar film types.
> 
> Noise floor measurements using HP5335A opt 010 as reference 
> source & 1KHz counter + HP3336C synthesizer yielded Favg = 
> 10,000,000.000 001 5 Hz and Fdev = 4.3 uHz for 36 samples at 
> 5.7 second gate time per sample. 10 sample groups are within 
> +/- 2E-12.
> 
> Pete Rawson
> 
> 
> 
> 
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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

WB6BNQ wrote:
> Bruce,
>
> Can you provide a link to the JPL system you reference above ?
>
> Thank you,
>
> BillWB6BNQ
>
>   
Bill

http://ntrs.nasa.gov/index.jsp?method=order&oaiID=19910016462 


There is also, or was, a free to download source for this paper 
somewhere, which I cant recall.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[WB6BNQ]

Dr Bruce Griffiths wrote:

> Pete wrote:
> > Here is a scheme that seems to work well for comparing stable frequency
> > sources in the range of 10 to 100 second measurement intervals.
> >
> > Objective - Measure frequency to +/-2E-12 in less than 1 minute.
> >
> > Method - Heterodyne DUT output to 1KHz with a master reference source +
> > mixer feeding a tuned zero crossing detector + counter.
> >
> > Equipment - 1. Master reference source at 5 or 10 MHz, e.g. "mature" OXCO or
> >GPSDO.
> > 2. Synthesizer set to DUT - 1KHz, locked to reference
> >source. The synthesizer averaged output must settle
> > to
> > 10uHz in 10 seconds, e.g. HP 3335A or 3336C.
> > PTS 040 should work fine, also.
> > 3. 9 digit/s counter, locked to reference source with
> > selectable gate time. An input LPF (100KHz) helps,
> > e.g. HP 5335A.
> > 4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers
> >  should work, but haven't been tested.
> > 5. Mini-circuits BLP-1.9 low pass filter. Other filters
> > should work, but haven't been tested.
> > 6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz
> > sinewave input & outputs 1KHz squarewave to counter
> > with less than 1nS rms jitter.
> >
> > Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT -
> > 1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to
> >  mixer IF port. ZCD input connects to BLP-1.9. Counter connects
> > to ZCD
> >  output & set for 5 to 10 second gate time. The DUT frequency =
> >  synthesizer setting + counter frequency;
> >  10uHz digit = 1E-12 for 10MHz DUT.
> >
> > The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration,
> >   cascaded, using +/- 2.5 volt power supplies. Both amps
> > have their
> >   non-inverting pins connected (only) to a 100 ohm resistor
> > to ground.
> >   Both amps have 5uF//5mH to ground on their inverting
> > inputs. The
> >   input amp has Rin = 422 ohms and Rf = 6190 ohms. The
> > output amp
> >   has Rin = 562 ohms and Rf = open. The output amp output
> > pin has
> >   2ea 100 ohm resistors in series to ground. The counter is
> > connected
> >   to the common point of the 100 ohm resistors. Nominal
> > supply bypassing
> >   is required. Battery supplies at +/- 3 volts help isolate
> > noise sources.
> >
> > Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in
> > distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP
> > toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521
> > cores
> > using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax
> > to 50mT at 1KHz & 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are
> > polypropylene or mylar film types.
> >
> > Noise floor measurements using HP5335A opt 010 as reference source & 1KHz
> > counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and
> > Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample
> > groups are within +/- 2E-12.
> >
> > Pete Rawson
> >
> >
> I am confused the opamp circuitry as described seems to be almost
> exactly the inverse of what is required.
> Please send a schematic so I can check.
>
> Are the MPP cores powdered iron or ferrite?
> The phase stability of the bandpass filters is critical as is any phase
> instability like that exhibited by ferrite cores.
>
> The overdrive recovery characteristics of the ADA4889-1 are not
> specified, how fast does it actually recover from overdrive?
>
> One can do considerably better than this (JPL have a system with a
> resolution of around 1E-15/Tau 1Hz offset, 100MHz input) with lower
> offset frequencies and a well designed amplifier and cascaded limiters,
> however low frequency ground loops are problematic.
> Optical isolation is almost mandatory.
>
> Bruce
>
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Bruce,

Can you provide a link to the JPL system you reference above ?

Thank you,

BillWB6BNQ



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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Pete wrote:
> Bruce,
>
> This idea is NOT intended to rival the JPL results. Instead,
> it's intended to be cheap, easy to replicate & allow rather
> low cost instruments to be used to compare good sources
> to parts in 1E12, quickly. The 1KHz heterodyne frequency
> makes life much easier than 1Hz. Noisy components &
> ground loops are still of concern, but not so hard to fix.
>
> ADA4899-1 overload recovery is <50ns (per data sheet).
>
> I've attached a rather poor schematic which doesn't show
> power supply decoupling or the need to pull the disable pin high. The 
> ADA4899-1 uses 14mA per part, but it's
> quiet & fast. Metal film resistors are fine for this low
> noise application & all are low values to keep noise down.
>
> The inductors are easy to wind, but I found materials other
> than moly permalloy powder to be too noisy. Even with
> MPP material, cores with u>200 are prone to field induced
> shifts which are unacceptable.
>
> Regards,
> Pete Rawson
> 
>
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Pete

Even so, it pays to use a well designed circuit instead of something 
thrown together with little understanding of what you are doing.
The JPL design is not expensive and doesn't require particularly exotic 
wideband components or high resolution counters.
There is still a noise advantage in using a 1Hz beat frequency, suitable 
opamps are readily available.

Magnetic shielding of the inductors and/or the entire circuit is 
probably advisable for the best performance.

The circuit diagram is sufficient to confirm my suspicions.

The input stage noise gain will be high at frequencies away from the 
1kHz frequency of interest.
This is a very poor design.
It is very easy to do much better with the same components.
A 50ns overload recovery will be somewhat problematic when you are 
attempting 1ns or less timing jitter.
A well designed and simple feedback bound circuit will be much faster.
Using an inverting amplifier input stage is not optimum for noise.

In fact the input stage doesn't need to use such a wideband opamp, a low 
noise opamp with a more modest gain bandwidth configured as a non 
inverting stage with gain followed by a bandpass filter will have far 
better performance.
Only the final limiting stage needs to be fast.

Also since you are using a 1kHz offset frequency it may be advantageous 
to use a transformer to couple the mixer output to the input stage, a 
stepup transformer will improve the equivalent input noise significantly 
even when using a somewhat noisier slower and cheaper opamp for the 
input stage.

A low pass filter with a lower cutoff frequency than  the several  MHz  
of the  BLP 1.9 is desirable between the mixer and the input amplifier, 
a tuned bandpass filter would be optimum but don't forget to terminate 
the mixer IF port in a suitable impedance at frequencies other than the 
beat frequency. It should be possible to combine the tuned bandpass 
filter and the stepup transformer.

Try reading the JPL article to gain an understanding of how to do it 
properly.
Although their design uses cascaded low pass filtered amplifiers with 
feedback bound circuits, the same technique can be used with bandpss 
filters.
Since you use a 1kHz beat frequency it is advantageous to AC couple the 
various stages to reduce the effective output dc offset.
Low frequency earth loops will limit the performance unless a different 
mixer with dc isolated RF. LO and IF outputs is used.
Suitable mixers are available.

Your claimed performance is comparable with that which can be achieved 
using a linear phase comparator which neither requires a mixer (other 
than the implicit mixer built into the phase comparator) nor a high 
resolution counter.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Pete]

Bruce,

This idea is NOT intended to rival the JPL results. Instead,
it's intended to be cheap, easy to replicate & allow rather
low cost instruments to be used to compare good sources
to parts in 1E12, quickly. The 1KHz heterodyne frequency
makes life much easier than 1Hz. Noisy components &
ground loops are still of concern, but not so hard to fix.

ADA4899-1 overload recovery is <50ns (per data sheet).

I've attached a rather poor schematic which doesn't show
power supply decoupling or the need to pull the disable 
pin high. The ADA4899-1 uses 14mA per part, but it's

quiet & fast. Metal film resistors are fine for this low
noise application & all are low values to keep noise down.

The inductors are easy to wind, but I found materials other
than moly permalloy powder to be too noisy. Even with
MPP material, cores with u>200 are prone to field induced
shifts which are unacceptable.

Regards,
Pete Rawson<>___
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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Pete wrote:
> Here is a scheme that seems to work well for comparing stable frequency
> sources in the range of 10 to 100 second measurement intervals.
>
> Objective - Measure frequency to +/-2E-12 in less than 1 minute.
>
> Method - Heterodyne DUT output to 1KHz with a master reference source +
> mixer feeding a tuned zero crossing detector + counter.
>
> Equipment - 1. Master reference source at 5 or 10 MHz, e.g. "mature" OXCO or
>GPSDO.
> 2. Synthesizer set to DUT - 1KHz, locked to reference
>source. The synthesizer averaged output must settle 
> to
> 10uHz in 10 seconds, e.g. HP 3335A or 3336C.
> PTS 040 should work fine, also.
> 3. 9 digit/s counter, locked to reference source with
> selectable gate time. An input LPF (100KHz) helps,
> e.g. HP 5335A.
> 4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers
>  should work, but haven't been tested.
> 5. Mini-circuits BLP-1.9 low pass filter. Other filters
> should work, but haven't been tested.
> 6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz
> sinewave input & outputs 1KHz squarewave to counter
> with less than 1nS rms jitter.
>
> Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT -
> 1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to
>  mixer IF port. ZCD input connects to BLP-1.9. Counter connects 
> to ZCD
>  output & set for 5 to 10 second gate time. The DUT frequency =
>  synthesizer setting + counter frequency;
>  10uHz digit = 1E-12 for 10MHz DUT.
>
> The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration,
>   cascaded, using +/- 2.5 volt power supplies. Both amps 
> have their
>   non-inverting pins connected (only) to a 100 ohm resistor 
> to ground.
>   Both amps have 5uF//5mH to ground on their inverting 
> inputs. The
>   input amp has Rin = 422 ohms and Rf = 6190 ohms. The 
> output amp
>   has Rin = 562 ohms and Rf = open. The output amp output 
> pin has
>   2ea 100 ohm resistors in series to ground. The counter is 
> connected
>   to the common point of the 100 ohm resistors. Nominal 
> supply bypassing
>   is required. Battery supplies at +/- 3 volts help isolate 
> noise sources.
>
> Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in
> distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP
> toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521 
> cores
> using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax
> to 50mT at 1KHz & 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are
> polypropylene or mylar film types.
>
> Noise floor measurements using HP5335A opt 010 as reference source & 1KHz
> counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and
> Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample
> groups are within +/- 2E-12.
>
> Pete Rawson
>
>   
I am confused the opamp circuitry as described seems to be almost 
exactly the inverse of what is required.
Please send a schematic so I can check.

Are the MPP cores powdered iron or ferrite?
The phase stability of the bandpass filters is critical as is any phase 
instability like that exhibited by ferrite cores.

The overdrive recovery characteristics of the ADA4889-1 are not 
specified, how fast does it actually recover from overdrive?

One can do considerably better than this (JPL have a system with a 
resolution of around 1E-15/Tau 1Hz offset, 100MHz input) with lower 
offset frequencies and a well designed amplifier and cascaded limiters, 
however low frequency ground loops are problematic.
Optical isolation is almost mandatory.

Bruce

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Re: [time-nuts] ? phase comparison or other device

[Pete]

Here is a scheme that seems to work well for comparing stable frequency
sources in the range of 10 to 100 second measurement intervals.

Objective - Measure frequency to +/-2E-12 in less than 1 minute.

Method - Heterodyne DUT output to 1KHz with a master reference source +
mixer feeding a tuned zero crossing detector + counter.

Equipment - 1. Master reference source at 5 or 10 MHz, e.g. "mature" OXCO or
   GPSDO.
2. Synthesizer set to DUT - 1KHz, locked to reference
   source. The synthesizer averaged output must settle 
to
10uHz in 10 seconds, e.g. HP 3335A or 3336C.
PTS 040 should work fine, also.
3. 9 digit/s counter, locked to reference source with
selectable gate time. An input LPF (100KHz) helps,
e.g. HP 5335A.
4. Mini-circuits ZRPD-1 mixer. Other level 7 mixers
 should work, but haven't been tested.
5. Mini-circuits BLP-1.9 low pass filter. Other filters
should work, but haven't been tested.
6. Tuned zero crossing detector, accepts 0 to 5dBm 1KHz
sinewave input & outputs 1KHz squarewave to counter
with less than 1nS rms jitter.

Setup - DUT set to +7dBm connects to mixer LO port. Synthesizer set to DUT -
1KHz at +4dBm connects to mixer RF port. BLP-1.9 connects to
 mixer IF port. ZCD input connects to BLP-1.9. Counter connects 
to ZCD
 output & set for 5 to 10 second gate time. The DUT frequency =
 synthesizer setting + counter frequency;
 10uHz digit = 1E-12 for 10MHz DUT.

The ZCD - Made from 2 Analog devices ADA4899-1, inverting configuration,
  cascaded, using +/- 2.5 volt power supplies. Both amps 
have their
  non-inverting pins connected (only) to a 100 ohm resistor 
to ground.
  Both amps have 5uF//5mH to ground on their inverting 
inputs. The
  input amp has Rin = 422 ohms and Rf = 6190 ohms. The 
output amp
  has Rin = 562 ohms and Rf = open. The output amp output 
pin has
  2ea 100 ohm resistors in series to ground. The counter is 
connected
  to the common point of the 100 ohm resistors. Nominal 
supply bypassing
  is required. Battery supplies at +/- 3 volts help isolate 
noise sources.

Only 2 ZCD parts aren't junk box items. The Analog Devices ADA4899-1 are in
distributor stock as SMT parts only. The 5mH inductors are hand wound on MPP
toroid cores. 133 turns on a 55438 core or 114 turns on 2 stacked 55521 
cores
using 22 or 24 AWG wire work fine. Other MPP cores will work, but limit Bmax
to 50mT at 1KHz & 0.5V rms. Gapped ferrites are too noisy. The 5uF caps are
polypropylene or mylar film types.

Noise floor measurements using HP5335A opt 010 as reference source & 1KHz
counter + HP3336C synthesizer yielded Favg = 10,000,000.000 001 5 Hz and
Fdev = 4.3 uHz for 36 samples at 5.7 second gate time per sample. 10 sample
groups are within +/- 2E-12.

Pete Rawson




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Re: [time-nuts] ? phase comparison or other device

[Dr Bruce Griffiths]

Bill Janssen wrote:
> I thought that someone was designing a circuit that could be used to compare
> two oscillators.
>
> What happened to that project?  I now have a HP 5370A so I have 
> something, but
> I would like to make simultaneous measurements on three or four "precision"
> clocks.I am not qualified to design a "state of the art" device, so I am 
> looking for others
> to do that.
>
> Thanks
> Bill K7NOM
>
>
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>   
Bill

Ulrich and I have designed and Ulrich is currently testing a CPLD 
implementation of the improved version of the HP K34-5991A linear phase 
detector.
It includes programmable prescalers (1-256) so that frequency like 10MHz 
and 5MHz for example can be compared. The maximum input frequency is 
about 50MHz.
It has 2 quadrature phase outputs. The prescalers also allow the phase 
detector gain to be adjusted. The phase detector has a triangular wave 
characteristic with a period of 4 cycles of the input frequency to the 
phase detector (ie at the built in prescaler output).

Preliminary results using a very crude kitchen table "breadboard" 
indicate that instabilities of a few parts in 1E12 are easily seen 
within an hour or so.
Sensitivity is likely to be much better than this but a 10X prescaler 
was used on each 10MHz input.

Comparing 3 or 4 standards requires using a set of distribution 
amplifiers plus a set of linear phase comparators to achieve the desired 
configuration.
This is more flexible than trying to anticipate exactly how many 
channels a user may want, it also has less crosstalk than an 
implementation with more than 2 input frequencies to a single board or CPLD.

With external prescalers the maximum input frequency can be extended to 
100MHz or more.

Bruce

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