pic microcontroller discussion list <> wrote on Thursday, April 24, 2003
12:57 PM:

> A PLL (Phase Locked Loop) could be a solution.  If you don't have a
> clue about them, then learn or get someone else to do the design.
> There's got to be loads of material out there on PLLs, so I won't

There is loads of material.  Unfortunately much of it is quite confusing,
at least to me... with arbitrary 2*pi appearing in some app notes etc, and
not in others, and contradictory advice on choosing the right phase
comparator for best performance.  The PLL section in Horowitz & Hill is
still the plainest advice I've come across on the subject, it's nice to see
books still have value :-)

I've produced a PLL circuit for a low speed noisy FSK comms link.  It
works, but I can't help thinking it should work better, the VCO signal
needs quite a lot of post-filtering to get reliable data out.  If anyone
has any good pointers on FSK demodulation, choosing the right phase
comparator and loop filter design, I'd love to hear them- the FSK is a
couple of kHz, data rate a few 10's of bps.

The principle is easy to understand, and it sounds like the 'right'
solution for the OP's problem, but the practicalities seem more complex.  I
know it's not just me, I've never met anyone who claims to be expert in
PLLs in Real Life(TM), and only a few who claim to be, online...

Nigel
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