On Tue, 21 Mar 2017 21:45:24 -0400 Bob Camp <kb...@n1k.org> wrote: > 1) You need a way to digitize the phase input with adequate resolution. If > you have a 1 second period and want 1 ns, you need a way to digitize at > a 1:1,000,000,000 sort of level. That’s in the 30 bit range so a simple > ADC isn’t going to do it alone.
That depends on how the phase difference is measured. If the whole measurement period needs to be encoded, then yes, the number of bits needed will make it difficult. But usually the input frequency range is limited, which allows to measure and encode just the difference between expected and actual arrival time of the pulse/edge. The integrated version of these PLLs (the ADPLL - all digitall PLL), if they have a real TDC, have only a resolution in the order of 7-8 bits (IIRC I've seen down to 4 bits). And then there is the class of those Bang-Bang PLL, which only encode one bit: early/late. Eventhough they are relatively crude and rely on the loopfilter to smooth things out, they perform quite well. Attila Kinali -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson _______________________________________________ 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.