Hej Magnus The Frequency measurement logic (before the interpolators) appears to use a pair of 2 bit synchonisers, one for the rising edge and one for the falling edge of the internally generated frequency gate. The synchronisers synchronise the respective transitions of the frequency gate signal to the external frequency being measured. One synchroniser uses U508A + U509A the other uses U508B + U509B, so that any mismatch in propagation delays between U509A And U509B will result in a small error in the time interval. Even for ECL flipflops a propagation delay difference between U50(A and U509B of 150ps wouldn't be unusual. As far as I can tell the calibration procedures do not address this issue. The uncalibrated differential delay through the interpolation circuit source selection multiplexer will also contribute an offset. Perhaps a better assignment of propagation delay differences may be U509A and U509B 50ps, multiplexer and wiring delay mismatches 100ps.
Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
