Hi Ok, this is a non-trivially difficult problem. You get into a number of issues that are *very* specific to your exact circuit. Often simulation is the most practical way to work out “what’s what”.
Bob > On Feb 6, 2022, at 5:27 PM, [email protected] wrote: > > Hi Bob, > > Thank you for clarifying. On Roland Best's book he states that for some phase > detectors there are also subharmonics that will be generated (~ 1/20 > reference frequency) but in fact the spurs I'm really interested to estimate > are multiple of the reference frequency (i.e. at the input of phase > detector). There are a few equations to estimate the reference spurs but I'm > chasing the source material. > > Regards, > Vasco Soares > > -----Original Message----- > From: Bob kb8tq <[email protected]> > Sent: 6 de fevereiro de 2022 19:08 > To: Discussion of precise time and frequency measurement > <[email protected]> > Subject: [time-nuts] Re: PLL subharmonic spurs > > Hi > > Just to clarify: > > “Sub Harmonics” is a term often used to describe spurs at carrier / N where N > is pretty small. If N = 4 you would be looking for spurs at 0.25, 0.5, 0.75, > 1.25, 1.5 and 1.75 times the carrier frequency. This would be a common way to > talk about them in the context of “sub harmonics are 120 db down”. > > Indeed if your PLL has a reference at 1/4 the output carrier the same term > might be used. That would be an unusual case, but possible. > > In a more conventional PLL, the reference is a (very) small fraction of the > carrier. The term “reference spurs” is typically used to describe them. > They still are at some fraction of the carrier, but the “N” value is quite > large. It is more convienient to look at them as ref x 1, ref x 2 , ref x 3 > rather than carrier / 3896. > > Typically reference spurs are part of a PLL and sub-harmonics are part of a > multiplier chain. No, it does not have to be that way, but it is how the > terms usually show up. > > Again, only trying to clarify what sort of spurs you are chasing. > > Bob > >> On Feb 6, 2022, at 1:21 PM, [email protected] wrote: >> >> Hi All, >> >> I'm searching for a good reference to calculate the PSD of subharmonic spurs >> on an integer PLL. Roland Best uses a reference on his PLL book: "Volgers, >> B.: "Phase-Locked Loop Circuits: 74HC/HCT4046A & 74HC/HCTR7046A HCMOS >> Designer’s Guide", Signetics/Phillips Components. (Ordering Code: >> 98-2908350)". Does anyone can help? >> >> Regards, >> Vasco Soares >> _______________________________________________ >> time-nuts mailing list -- [email protected] -- To unsubscribe >> send an email to [email protected] To unsubscribe, go to and >> follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] To unsubscribe, go to and follow the > instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send an > email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
