[time-nuts] FE-5680A clock shaping (sine -> square wave)

John Beale beale at bealecorner.com
Fri Dec 30 00:14:30 EST 2011

In case it's useful... there are many ways to get a square wave out from a 
sine wave in, but one straightforward way is with a comparator. Some work 
better than others. The slow ones won't work at all at 10 MHz, and the very 
fast comparators (MAX999, ADCMP600, LT1116 etc.) are more expensive, and 
perhaps harder to work with. I tried a MAX9013 in SO-8 package and it works 
well for the job. You can see my schematic, circuit and scope plots at the 
bottom of this page:


My circuit works best with a sine wave input amplitude above 100 mVpp. 
Below that level, the duty cycle starts to become noticeably worse. I am 
using some hysteresis, but it may not be necessary.

Previous to those pics on the page, you also see a circuit which did not 
work so well, using a MAR-1 (broadband DC-1GHz MMIC amp). It's intended as 
a linear amp, and it does not saturate in a symmetric way even with large 
input signals.

Here are a few other circuits of interest, which I did not try:

...and by the way, my FE-5680A shows a consistent -7E-12 per degree C 
temperature sensitivity (measured at case temp 42 and 52 C). Has anyone 
else measured theirs?

-john beale

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