Hi The degree to which your samples converge to a specific value while being averaged is dependent on a bunch of things. The noise processes on the clock and the measured signal are pretty hard to avoid. It is *very* easy to over estimate how fast things converge.
Bob > On Apr 26, 2018, at 5:28 PM, Oleg Skydan <[email protected]> wrote: > > From: "Hal Murray" <[email protected]> > Sent: Thursday, April 26, 2018 10:28 PM > >> Is there a term for what I think you are doing? > > I saw different terms like "omega counter" or multiple time-stamp > average counter, probably there are others too. > >> If I understand (big if), you are doing the digital version of magic >> down-conversion with an A/D. I can't even think of the name for that. > > No, it is much simpler. The hardware saves time-stamps to the memory at > each (event) rise of the input signal (let's consider we have digital logic > input signal for simplicity). So after some time we have many pairs of > {event number, time-stamp}. We can plot those pairs with event number on > X-axis and time on Y-axis, now if we fit the line on that dataset the > inverse slope of the line will correspond to the estimated frequency. > > The line is fitted using linear regression. > > This technique improves frequency uncertainty as > > 2*sqrt(3)*tresolution/(MeasurementTime * sqrt(NumberOfEvents-2)) > > So If I have 2.5ns HW time resolution, and collect 5e6 events, > processing should result in 3.9ps resolution. > > Of cause this is for the ideal case. The first real life problem is > signal drift for example. > > Hope I was able to tell of what I am doing. > > BTW, I have fixed a little bug in firmware and now ADEV looks a bit better. > Probably I should look for better OCXOs. Interesting thing - the counter > processed 300GB of time-stamps data during that 8+hour run :). > > All the best! > Oleg > <1133.png>_______________________________________________ > 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. _______________________________________________ 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.
