Hi Mark, On 2020-01-21 19:41, Mark Haun wrote: > Hi Attila, > > On Tue, 21 Jan 2020 15:08:16 +0100 > Attila Kinali <[email protected]> wrote: >> On Tue, 21 Jan 2020 01:15:45 +0100 >> Attila Kinali <[email protected]> wrote: >>> You don't need a high performance ADC for the reference as you are >>> dealing with a narrow band signal of known frequency. Even a 10bit >>> or 8bit ADC would be good enough. You can even go and sample at >>> half frequency and save both money and power. >> I just spend a few minutes looking at ADCs and found the LTC2256-12 >> and its faster sister LTC2257-12. They go for ~15USD at quantity 1. >> Both have 170fs RMS apperture jitter and do 25Msps and 40Msps >> respectively. 3dB BW is 800MHz, so more then good enough to even use >> the 100MHz output of an hydrogen maser, if you want a really good >> reference ;-) >> >> Power consumption at max sample rate are 34mW and 47mW respectively. >> That's slightly more than a PLL would use (~20mW, plus maybe another >> 5mW to 10mW for the opamps in the loopfilter). Power consumption goes >> down a bit with decreasing sample rate, but not as much as one would >> hope for. > I hope you will indulge one more newbie question on the analog PLL > option... as I have approximately zero experience designing them. > > What are the adverse consequences of using large divisors in the loop, > as would be required for my odd OCXO frequency? E.g. on paper, it would > seem that I could use 80 MHz / 625 = 16.384 MHz / 128 = 128 kHz PFD > frequency. How would this differ from a more "normal" ref clock > frequency of 10 or 16 MHz with smaller divisors?
>From my experience, such factors and rate of phase comparator is relatively easy to work with and get to work reasonably well for most purposes. I recommend you to use a PI-loop. For a step-up you want to keep the PLL bandwidth fairly large, and that helps making it easy. I've been tempted to do a bunch of such loops in various kinds of equipment to solve issues. I should to more of them. One should have a nice little lock-up board to just apply. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
