Hi Chris, > In theory what is the best you can do using division of a 10MHz signal.
Answer: with a 10 MHz PIC the best you can do in theory is +/- 200 ns on every 32 kHz edge, with no accumulating phase error, and perfect frequency accuracy for tau 1 s and above. And my divider meets theory. Details on how the "leap cycle" method works is in the source code: http://leapsecond.com/pic/src/pd30.asm > It's really not very good the period of the 32768 hz output will always be > "off". True, whether a PIC or DDS or PLL the period will always be "off", to some degree, over some interval. So the question is how much is it off and when does it matter or what's the spec. It's standard phase noise, jitter, and ADEV stuff. I'm not sure of Martyn's goal, but what I use these 10MHz-to-32kHz dividers for is replacing poor 32 kHz timekeeping with superb 10 MHz-based timekeeping (e.g., OCXO, Rb, Cs, GPSDO). Lots of boards, sensors, loggers, RTC, quartz wall clocks use 32 kHz as a timebase. They either have a 1-pin input for a 32 kHz clock, or a 2-pin 32 kHz crystal. Either way, the PIC output can be used to drive the input pin, and voila! you've now improved the timekeeping by a factor of thousands to millions. These little PIC's run at 2 to 5 V so its very convenient. > I think the best way is to divide the 10MHz signal by some power of five > (like 78125) then use that to phase lock your 32768 oscillator. In other > words use the 10MHz signal to discipline the 32K crystal. Right, the extra complexity of a PLL and VCO-tunable 32 kHz tuning fork crystal (?) would be useful if the end goal were a 32 kHz, low phase noise, pure sinewave, 50R output, as if a bench instrument. But for driving 32 kHz CMOS IC timekeeping inputs, the low-jitter square wave from the PIC alone does the job. /tvb _______________________________________________ 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.
