Bruce Griffiths wrote: > John Ackermann N8UR wrote: > >> Thanks, Bruce. I considered the idea of a multiplier but would like to >> use a software-only solution if I can. That's not only for simplicity, >> but also to eliminate additional sources of jitter; the experiment I >> have in mind is to test the second-to-second noise (and short term noise >> trends) of GPS and other PPS sources,* so I'm looking for as stable a >> reference as I can get. The additional noise from a mulitplier may be >> small, but I want to minimize the number of unknowns. >> >> Thanks! >> >> John >> >> * I realize that I'll also be limited by counter resolution. >> ---- >> >> > John > > 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. > > Measuring the PPS output jitter of the PIC will be somewhat challenging > as It I would expect it to be somewhat less than 100ps. > 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 > > John
It is also possible to use a frequency doubler to generate 10MHz from the 5MHz input to drive the PIC and resynchronise the resultant PPS output from the PIC to the 5MHz input using an external D flipflop. This will remove the jitter due to both the frequency divider and the PIC. Using a low phase shift filter (ie none ) at the doubler output will ensure a relatively stable delay between the 5MHz zero crossing and the 10MHz doubler output. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
