This has been a great conversation as I have tinkered with classical filters forever. But the fact is with micros so cheap the flexibility they add to the loop filtering is quite nice. Essentially droop-less filters with silly time constants and then other math on the data. That may or may-not improve behaviors. Regards Paul WB8TSL
On Wed, Mar 22, 2017 at 5:51 PM, Bob kb8tq <kb...@n1k.org> wrote: > Hi > > > > On Mar 22, 2017, at 7:50 AM, Attila Kinali <att...@kinali.ch> wrote: > > > > 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. > > We started out with an XOR that has a 50/50 duty cycle. An early /late > process only works if you run the outputs through an ADC and calibrate > them to some degree. Then you are right back to a lot of resolution time > wise. > > Bob > > > > > 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. > > _______________________________________________ > 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. > _______________________________________________ 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.