[time-nuts] 5 MHZ PIC PPS Divider?
didier at cox.net
Sun Apr 13 11:09:47 EDT 2008
While the outputs change state synchronously with the clock, there may be
many gates and latches inside the chip between the clock pin and the output,
and the delay through those will be affected by temperature, supply voltage
glitches and ground bounce, things that are not necessarily very well
controlled inside the chip, so the jitter has to be more than a single
external D-latch of J-K flip-flop with a decoupling cap across it will
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Tom Van Baak
> Sent: Sunday, April 13, 2008 9:55 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] 5 MHZ PIC PPS Divider?
> > 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.
> time-nuts mailing list -- time-nuts at febo.com To unsubscribe,
> go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> Internal Virus Database is out-of-date.
> Checked by AVG.
> Version: 7.5.519 / Virus Database: 269.22.5/1358 - Release
> Date: 4/3/2008 6:36 PM
Internal Virus Database is out-of-date.
Checked by AVG.
Version: 7.5.519 / Virus Database: 269.22.5/1358 - Release Date: 4/3/2008
More information about the time-nuts