[sdiy] Phase-locked loops and the root of my headache

[Magnus Danielson]

From: "Jon Darby" <jdarby at lplizard.com>
Subject: Re: [sdiy] Phase-locked loops and the root of my headache
Date: Fri, 31 Aug 2001 18:47:37 -0400

G'day Jon,

> Thanks, Magnus,

Anytime.... 

> I appreciate the primer.

Sure...

> What is a typical application of the phase-locked loop?

Tracking a frequency but with another oscillator sounds like a usefull
app. You can also have the tracking VCO to operate on an
overtone. This you can acheive by simply put a frequency divider in
the feedback path from the oscillator to the detector. You can also
acheive non-even stepups by making an initial division of the input
signal. Things like taking the 5/4 overtone etc. I let your
imagination figure out where things like that can be usefull.

You can also use them to dampen the jitter (phasemodulation) of a
signal while having it tracking the frequency of the input. This is
more a telecommunication thing, but possibly of use in music too.

Depending on the loopfilter the tracking may be more or less
"sluggish" and this could possibly have an interesting effect. Another
things is when the PLL is out of lock, then it "beats" in
frequency. This beating also occurs as it acheives lock. I haven't
actually listened to it, but it might be usefull in musical applications.

You can also use PLLs as detection of phase or frequency modulation.

> I can kind of pick up smatterings of filter
> applications, but don't understand what role it plays.

It filters, but not in the fashion you might expect. It can act as a
sort of very narrowband bandpass filter which automatically tracks the
centerfrequency of the signal. It does filter (lowpass commonly) phase
deviations of a signal. It is not very near your average analogue
linear filter.

> I'll look for the
> book tonight. The 4046 seems really interesting from the datasheet and I
> feel like I'm beginning to take that first dive into Lake Understanding The
> Application of Electronic Components.

Ah! Don't forget your towel!

Do make a few experiments with the 4046, it is fun and it can be
usefull in the future.

Cheers,
Magnus