[time-nuts] ? phase comparison or other device

Magnus Danielson magnus at rubidium.dyndns.org
Sat Jun 30 09:59:27 EDT 2007

From: "Ulrich Bangert" <df6jb at 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 at athlon>

> 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?

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.


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