[time-nuts] What is a Time-Nut grade Zero Crossing Circuit?

Didier Juges didier at cox.net
Thu Jul 31 16:25:33 EDT 2008


Can you explain #2?

I understand ECL has more jitter, so I understand excluding ECL based
comparators, but why excluding ALL comparators? It seems to me the
comparators allow tighter control of the threshold, so it sounds as if it
would help at very low frequencies, unless the higher 1/f noise of the
compartor dominates other factors.

How does the 1/f noise of a CMOS gate compare to an analog comparator?

Didier KO4BB 

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Rick Karlquist
> Sent: Thursday, July 31, 2008 3:14 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] What is a Time-Nut grade Zero 
> Crossing Circuit?
> Two things NOT to do:
> 1.  Do NOT use ECL.  CMOS is much lower jitter.
> 2.  Do NOT use a comparator to square up the sine wave.
> Especially don't use a ultrafast ECL based comparator.

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