[time-nuts] Zero-Crossing Detector Design?

ehydra ehydra at arcor.de
Sat Jul 21 22:45:50 UTC 2012


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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