[time-nuts] Comparing PPS from 2 GPS units
dk4xp at arcor.de
Mon Dec 17 23:27:03 UTC 2012
Am 17.12.2012 19:56, schrieb David:
> My next pretrigger generator is going the differential comparator or
> differential ECL route with a fast ramp and precision reset. I expect
> jitter to be significantly better than 10s of picoseconds for delays
> up to about 100 nanoseconds. If I get down to 10 picoseconds of
> jitter, I will be happy since I have no real way to measure much below
That should be easy to do. I did a trigger pulse & delay for a
54750A scope. You need abt. 25 nsec delay to see the trigger event.
I did it with ooold 10K ECL I still had around and a few meters of
semi rigid cable. The semi rigid is surprisingly compact when wound
on a piece of plastic tube.
There was not much difference when watching the output of an
ADCMP580 comparator, via trigger delay or via internal trigger
and waiting a few clocks with the built-in delay.
The ADCMP580 is a fine chip, btw. You get a lot of speed for
not too much money. (digikey)
I will rebuild the trigger delay over xmas, this time with
CML to remove most of a systematic error in my scope setup.
CML is much more friendly than ECL/PECL from a probing
point of view. No need to carry Vtt to the scope and have
a problematic bias tee there, or shifting the supplies
until all happens to fit...
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