Kasper Pedersen wrote: > This is to poke my head in, and to share a simple multichannel > phase comparator/monitor that turned out to be useful. > > I have a few homebuilt boxes that will do ~100ps timestamps, > I have other uses for them, and tying them up with a single > long term experiment is unacceptable. So I needed a phase > comparator that I could rebuild in an hour if I wanted to, > something in the spirit of TVB's PIC16 divider. > Something simple. > > The idea is this: > Beat a number of 10MHz inputs against another clock frequency > using the input flipflops in a microcontroller as samplers, > sample a number of times to cover the phase circle, and > calculate the phase. Beating against 11.0592MHz gives a period > of 3456 clocks, sampling every 8 clocks gives 432 samples, that > should give 230ps resolution. Add clock jitter and aperture > jitter, and precision should be around 500ps. > How much performance can one get for $10? > > schematic: http://n1.taur.dk/timenuts/phasecomp8.pdf > samples: http://n1.taur.dk/timenuts/phasesamples.png > > When comparing a 10MHz source with itself through > a cable delay, the peak noise is 400ps. That's for a > 300-microsecond acquisition time, which means the > update rate is limited by how fast I can compute the > vector and shovel data over to a PC. When monitoring > beating 10MHz sources with an adjusted (-3ppm) > microcontroller clock, it's about 600ps peak. > When misadjusted to be -30 ppm off, it's 1.1ns peak. > > At the moment there is only a crude windows program for > turning the output into decimal plottable data, so some > programming skill or beer drinking friend with programming > skill is required, as well as knowledge of what one wants to > measure (that's usually the hard part). > > source, hex: http://n1.taur.dk/timenuts/phasecomp.zip > converter: http://n1.taur.dk/timenuts/phasehex2dec_win.zip > > I'm aware that 600ps is a very large figure in a lot of > cases but for my oscillators it's good enough. > > /Kasper Pedersen. > Kasper
Another option is to add a 10MHz gated delay line oscillator which could be phase shifted (as in a 5370A) by the PPS output of a GPS receiver. The leading edge of the PPS pulse could then be timestamped with subnanosecond resolution using this technique. 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.
