Hi Convergence in a PLL has no absolute definition. In some cases 45 degree phase error = all is running fine.
I would simply track GPS time vs OCXO time and declare it ok when it's inside some magic number of nanoseconds. Bob On Aug 30, 2013, at 7:08 PM, Bob Stewart <[email protected]> wrote: > I finally (think I) understand enough about my hardware and the data that my > PLL is working! Now for the hard part: When do I decide it's converged? I > believe that the maximum time in seconds till convergence is on the order of: > > (OCXO range / DAC range) / (error count * DAC volts per step) > > where: > "OCXO range": the tuning range of the OCXO in Hz - let's use 8 Hz > "DAC range" is the voltage range of the DAC from bottom to top - let's use 6 V > "error count": the number of DAC steps till convergence > "DAC volts per step": voltage change for one step of the DAC - let's use > .0003 volts per step > > For example, discounting the UT+ sawtooth and OCXO stability, the last 1 step > of the DAC until complete convergence could take up to: (6/8) / (1 * .0003) > ~ = 2500 seconds until convergence. Two steps away would be ~1250, three > steps ~833, etc. > > So my dilemma is to pick a number when it's safe to say that the PLL is > converged. Do I just wait until there is 2500 seconds between DAC changes or > do I pick a lower number? And, conversely, when I do say it's no longer > converged? Or have I just got it all wrong? (Apologies if I've gotten > terminology wrong.) > > The methodology is similar to a Bang-Bang PLL. I keep a running track > of the OCXO error count per 1PPS, and if it over-counts twice, the DAC is > reduced one step, and if it under-counts twice then the DAC is > increased. Any 1PPS where the count is correct is thrown out. The name > "Bang-Bang PLL" doesn't seem appropriate, so I think this should be > called a "Tick-Tock PLL". =) > > Bob - AE6RV > _______________________________________________ > 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.
