[time-nuts] Re: PLL subharmonic spurs

[mail at vresearch.pt]

Hi All,

After 17 years from my PhD on EE I humbly learn a lot every day on different
areas. I treat my students, colleagues, hobbyist, etc. with all the respect
they deserve.

Thanks for the educated answers given. I own all the book references stated
that are well known (e.g., Roland Best [3], Floyd Gardner [4], Den Banerjee
[5]) but there are some specific aspects that they do not address with
enough detail (and even would make no sense for the publication goal
perspective). I consider that Roland Best and Den Banerjee books give much
more insight than Floyd Gardner. Also, no doubt that Den Banerjee book is
more practical oriented than the others and still there are some spurs
modelling as well.

I like to address the problems by an academic perspective at first place.
I'm looking the formal/mathematical aspects of spurs (amplitude estimation,
modelling, etc.) on voltage and current PFDs that probably can only be found
on specific papers. I'll look carefully at references [1] and [2] "Causes of
PLL spurs and their modeling". As been said it's a not trivial matter and at
the end I will get on simulation and prototyping sooner than I expect as
time is not on my side.

End of story.

-----Original Message-----
From: Attila Kinali <attila at kinali.ch> 
Sent: 7 de fevereiro de 2022 14:05
To: glenlist at cortexrf.com.au; Discussion of precise time and frequency
measurement <time-nuts at lists.febo.com>
Subject: [time-nuts] Re: PLL subharmonic spurs

On Mon, 7 Feb 2022 09:51:27 +1100
glen english LIST <glenlist at cortexrf.com.au> wrote:

> If you are interested in harmonics of the reference frequency at the 
> input to the phase detector, this will be entirely defined by the 
> fourier series of the source. Get yourself a 2nd year EE student, 
> they'll have this info for you.

I do not think that this tone is warranted here.

First of all, nothing about PLL is trivial. Especially not their non-linear
and non-ideal behaviour. I know many EEs who do not fully understand these,
much less have mastered them. Heck, I barely understand these and I am
considered the local PLL-"expert" where I am.
And it gets only worse the more closely one models the parts of a PLL, most
of which are quite far from their usually modeled ideal behaviour.

Second, keep in mind that many people on the time-nuts mailinglist are
hobbyists who came here through various paths. Very few of those have the
mathematical background to read and understand the textbooks on PLLs, much
less to calculate something that is not in there. Yes, we have quite a few
engineers and scientists with a very high level here. While I do hold these
engineers and scientists to a higher standard and expect them to write mails
according to that level of knowledge and understading, I do not apply that
to the majority on time-nuts. Especially not someone who is new on the list
and whose background is not known. And neither should you.


But back to the topic at hand....

[1] Gives an easy, though probably not very accurate way how to calculate
some of the spurs caused by current leakage.

A more complete analysis, can be found in [2].

For general discussion about PLLs and their behaviour, I would recommend
Best's book [3] (which OP already has) and Gardner [4]. The latter is quite
a bit more theoretical and more complete in its treatment of PLL behaviour,
but also quite a bit harder to apply to a design.

Another book that I quite recommend is [5], written by a TI engineer, which
focuses on the practical aspects of discrete PLL circuit design and the
difficulties faced there. It contains some discussion of spurs, but I don't
remember whether it had a in-depth discussion of the reference spurs.

Sorry that I can't give a more to the point answer. I haven't looked into
the the spur behaviour of PLL yet and thus have only the most basic knowlege
about it.

			Attila Kinali


[1] "A Simple Method to Accurately Predict PLL Reference Spur Levels Due to
Leakage Current", by Azarian and Ezell, Linear Application Note 143,
2013
https://www.analog.com/media/en/technical-documentation/application-notes/an
143f.pdf

[2] "Causes of PLL spurs and their modeling", by Biswas and Bhattacharyya,
2019
https://doi.org/10.1007/s10470-019-01477-z

[3] "Phase-Locked Loops - Design, Simulation and Applications", by Roland
Best, 5th edition 2003

[4] "Phaselock Techniques" by Floyd Gardner, 3rd edition, 2005

[5] "PLL Performance, Simulation, and Design", by Dean Banerjee, 5th
edition, 2017 http://www.ti.com/lit/ug/snaa106c/snaa106c.pdf
--
The driving force behind research is the question: "Why?"
There are things we don't understand and things we always wonder about. And
that's why we do research.
		-- Kobayashi Makoto
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