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:

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:

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

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: rubiola@femto-st.fr

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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Ulrich Bangert wrote:

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

From: Dr Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Fri, 29 Jun 2007 19:52:22 +1200
Message-ID: 4684BA36.3040401@xtra.co.nz

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

From: "Ulrich Bangert" df6jb@ulrich-bangert.de
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Fri, 29 Jun 2007 09:14:02 +0200
Message-ID: 000001c7ba1d$130c2750$03b2fea9@athlon

Ulrich,

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

Magnus Danielson 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.
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.

Bruce.

From: Dr Bruce Griffiths bruce.griffiths@xtra.co.nz
Subject: Re: [time-nuts] ? phase comparison or other device
Date: Sun, 01 Jul 2007 02:15:55 +1200
Message-ID: 4686659B.8000205@xtra.co.nz

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.

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