Flip-flops hardened against metastability are available. I would try a track and hold before a sample and hold but I wonder how accurate it would be having to rely on the oscillator waveform. Fast sample gates are non-trivial. I believe better than either would be a time to voltage converter which just needs a set/reset flip-flop and switched current integrator. Dig up the schematic for a Tektronix 2232 oscilloscope for a "simple" example that yields 50pS resolution using late 1980s technology.
I just recently ventured into the sampling oscilloscope world with a 7S11/S-4/7T11 setup. The S-4 uses a traveling wave gate which avoids the fast sample gate problem but I would consider that the far side of esoteric since I have not studied it in detail yet. On Fri, 10 Feb 2012 17:23:46 -0800 (PST), Robert LaJeunesse <[email protected]> wrote: >Sampling unsychronized signals with a DFF is problematic, since if setup and >hold times are not met the output could oscillate and maybe settle to some >noise >driven value. I can't help thinking that if you are sampling the 10MHz >signal at >1Hz the only way to get reasonable resolution is to sample the 10MHz sinewave >signal's fastest part with tight analog sample & hold. Looking at the result >wih >a slow, low-cost 24-bit A to D chip would give tremendous resolution - if the >drift was low enough. Use the ADC over a sub-range and add a small micro for >noise filtering and averaging and one can achieve measurements result in the >10s >of femtoseconds. > >________________________________ >From: David <[email protected]> >To: Discussion of precise time and frequency measurement <[email protected]> >Sent: Fri, February 10, 2012 8:10:56 PM >Subject: Re: [time-nuts] GPS lock of the FE5680. Current experiment and >question > >All you need for this is the flip-flop. Clock the flip-flop with the >1 PPS signal and capture whether the oscillator is leading or lagging. >This requires the 10 MHz oscillator to be within 1 Hz but if you >divide it down before the comparison, you can extend this range as >needed to handle wider initial oscillator frequencies and larger >amounts of PPS jitter. > >The simple GPSDO design in QST a couple years ago did something like >this. _______________________________________________ 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.
