Previously I have been comparing 10 MHz frequencies using TvB's picPET
device plus a picDIV divider to get a 1 PPS signal, but I wanted more
resolution for comparing relative drift of two Rb references. I got square
wave outputs from my references (see my previous posts) and I made a simple
XOR phase detector from a single XOR gate (74LVC1G86) :
https://picasaweb.google.com/lh/photo/ofFwP8Eo1qFAzNObq69iCtMTjNZETYmyPJy0liipFm0
I have read about how nonlinear the XOR PD becomes at the endpoints (0 and
180 phase shift) although this one seems to work pretty well, and the
output looks reasonably triangular:
https://picasaweb.google.com/lh/photo/swKVhhP7NerRvMKdnW8rjtMTjNZETYmyPJy0liipFm0
There is some nonlinearity but it seems consistent from cycle to cycle. I
might be able to reduce the bumps with better circuit layout, shorter
wires, terminated lines etc. But just for playing around with my initial
data, I think I can model the shape of the response and get a more accurate
reading of instantaneous phase angle vs time. I could write some code for
this, but I suspect this wheel has been invented before... is there any
reference I should consult? I think something similar is done inside the
PIC-TIC to calibrate its response?
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