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

[Don Latham]

Heck- for a really good risetime, all you need is a mercury-wetted relay
:-)
Don

David
> What kind of performance would you expect in this application?  Low
> jitter?  50 ohm output?  TTL or better signal levels?  Fast rise and
> fall times?  Duty cycle correction?
>
> After reading your post I was thinking about how to go about it and
> ended up with an 8 transistor discrete design using a differential
> amplifier input and pair of current mirror transconductance amplifiers
> for the output.  I have been looking into designing a pulse generator
> for oscilloscope calibration and have an interest in GPSDOs so maybe I
> will prototype this as well just to see what kind of performance a
> bunch of 2N3904 and 2N4401 jelly bean transistors can provide.
>
> On Thu, 29 Dec 2011 21:14:30 -0800, John Beale <beale at bealecorner.com>
> wrote:
>
>>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:
>>
>>https://picasaweb.google.com/bealevideo/FE5680A
>>
>>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:
>>http://www.ko4bb.com/~bruce/CLKSHPR.html
>>http://www.ko4bb.com/Timing/ClockShaper.php
>
>
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-- 
"Neither the voice of authority nor the weight of reason and argument
are as significant as experiment, for thence comes quiet to the mind."
R. Bacon
"If you don't know what it is, don't poke it."
Ghost in the Shell


Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
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