Hi Why not do a FLL based on the counter and let the TDC run at 5 MHz (with 5X the resolution)?
It’s reasonable to believe that if you run the FLL for a while you will get things quite close. That should allow you to run the TDC at 10 MHz. Bob > On Sep 26, 2015, at 7:22 AM, Jim Harman <j99har...@gmail.com> wrote: > > Good question Will. > > First, it divides the 10 MHz down to 1 MHz, so the oscillator would have to > be off by 10 Hz for it to lock onto the wrong cycle. > > Second, the full implementation also feeds 5 MHz from the oscillator into > one of the processor's counters and checks the count every second. It > performs several checks on this to detect if the frequency is way off, > missed PPS, etc. > > On Sat, Sep 26, 2015, 12:15 AM Will <zl1...@gmx.com> wrote: > >> Hi, >> >> I'm new and trying to get to grips with things. >> >> If I understand correctly, please forgive if I have it wrong, This >> locks a 10MHz signal to a 1Hz (1pps) signal. What makes it lock to 10 >> 000 000Hz instead of 999 999Hz or 10 000 001Hz? Just the hope that the >> 10MHz is exactly that? >> >> Cheers, >> Will >> >> On 26/09/15 08:32, Jim Harman wrote: >>> To further demonstrate the Diode - R- C- approach, here (hopefully) is a >>> screenshot of the raw DAC output vs time on my Arduino Micro (32u4) based >>> system. For this test the oscillator is free running with an error of >> about >>> 1 usec per 460 sec or 2.17x10^-9. The horizontal scale is 125 sec/div >> (1000 >>> sec total) and the vertical is 1024 DAC counts (0-2.56 V) which >>> corresponds to 1 usec of offset between the oscillator and the reference. >>> >>> You can see that there is some curvature because the capacitor is being >>> charged through a resistor and not a true current source, but as I >>> mentioned earlier this does not affect the system's ability to lock the >>> oscillator to the pps reference. When locked with a time constant of 1000 >>> sec, the phase detector output is almost always less than +/- 100 counts >>> from the setpoint of 500. >>> >>> The noise is due mostly to jitter in my PPS reference, which is generated >>> by an Adafruit GPS module. Presumably it would be less if I had a real >>> timing receiver. >>> >>> >>> . >>> If the inserted image does not come through, I will re-send as an >>> attachment. >>> >>>> -- >>> --Jim Harman >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
