[time-nuts] 5 MHZ PIC PPS Divider?

Tom Van Baak tvb at LeapSecond.com
Sun Apr 13 10:55:29 EDT 2008

> If minimising the PPS jitter, is important adding a single D flipflop to 
> resynchronise the output PPS signal to the 5MHz input will be worthwhile.
> A relatively complex chip like a PIC is likely to produce a PPS output 
> signal with a jitter much greater than that produced by a single flipflop.

Bruce, double check the PIC data sheet and see if this is really
true. They are not complex chips; they run DC to 10 MHz, and
all outputs are synchronous with the clock.

> Measuring the PPS output jitter of the PIC will be somewhat challenging 
> as It I would expect it to be somewhat less than 100ps.

I think way less. I measured it with a 5370B when I designed
the divider ten years ago. But I'll measure it again for you
using better equipment.

> The corresponding output jitter at the resynchronising flipflop output 
> should be significantly less than 10ps even for a 74HC74.
> In this case only the flipflop's random jitter is significant as the 
> frequency and duty cycle of the PPS input to the flipflop are constant 
> apart from the effects of jitter.
> Bruce

This would be an interesting experiment.


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