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 _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
