[time-nuts] Zero-Crossing Detector Design?

Richard (Rick) Karlquist richard at karlquist.com
Sun Sep 16 19:46:21 UTC 2012



On 9/16/2012 12:03 PM, Gerhard Hoffmann wrote:
> Am 20.07.2012 00:57, schrieb Richard (Rick) Karlquist:
>> A fast comparator seems like a good idea, and it
>> is simple, however it is actually the last thing
>> you want to use.  High thermal sensitivity and high jitter.
>>
>> Rick
>>
>> On 7/19/2012 1:35 PM, Dan Kemppainen wrote:
>>> Or use a fast comparator such as an ADCMP600 series. Much lower delays,
>>> and faster rising/falling edges.
>>> FYI, I've had good luck with this at 30Mhz. You could transformer couple
>>> this one, or simply couple it through a cap.
>
> The ADCMP580 could be an excellent choice for the output stage
> of a Collins type device. Running quite cool and showing only
> 180 ps _total_ delay is a good start.
>
> Good rise/fall times on home-etched 0.5 mm FR4 (and some semi-rigid):
>
> http://www.imagesup.de/bild-_Mgif-119362.htm
>
>
> regards, Gerhard, dk4xp

Again, a really high speed comparator necessarily has a really broad
bandwidth, meaning its noise bandwidth is large.  This means more
noise and more jitter than a lower speed comparator.  The comparator
cited is much faster than necessary for 30 MHz, by orders of magnitude.

Rick N6RK



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