[time-nuts] Zero-Crossing Detector Design?

[Bob Camp]

HI

The Collins paper that Bruce referred to is the standard work on limiters / jitter / bandwidth. It can't and doesn't address all the possible issues in a full blown design. The math for the basic approach is all there though. 

Bob


On Jul 21, 2012, at 6:45 PM, ehydra wrote:

> Interesting discussion but I must say I had several times a
> brain-problem here ;-)
> 
> Am I right that for that this is in general not fully understood? Are there interesting papers?
> 
> I'm interested here for two points:
> 1. What is the right threshold for a comparator and on what it depends?
> Looks like bandwidth of input signal, slew-rate of the comparator, noise
> in the input signal. Maybe more.
> Surely most of all people here know how to set the trigger right practical.
> But what is the academic answer to this problem in the view of maximum S/N behind the comparator?
> 
> 
> 2. What if this is a if-strip amp with interstage filters. Maybe in the
> look of a BPSK receiver. So we can connect to time-nuts GPS interests back ;-)
> 
> 
>> Recall that the jitter of a trigger point is noise divided by
>> slew-rate.
> 
> Is it possible to expand here the explanation? Any reference?
> 
> Thanks!
> 
> - Henry
> 
> 
> Magnus Danielson schrieb:
>> You can view the schmitt trigger detector as having a state, and when
>> in proximity of the trigger point, you let the noise control when the
>> trigger point occurs.
> 
>> Schmitt trigger is a nice tool, but it can do you great harm if you
>> do not understand what it does help you with and what it doesn't help
>> you with.
>> You need to gain yourself to slew-rates where a schmitt trigger would
>> do no harm, and when you are there it will do essentially no good
>> either, as you are looking at a high slew-rate square signal.
>> So, you *can* do better than a Schmitt trigger. A schmitt trigger can
>> be sufficiently good. A schmitt trigger can work well if you have
>> filtering in front of it to significantly reduce unwanted systematic
>> noise.
> 
> 
> -- 
> ehydra.dyndns.info
> 
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