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From: "Christopher R. Carlen"
Subject: Re: How to increase PLL order?
Date: Tue, 10 Dec 2002 18:08:18 -0800
Organization: Sandia National Laboratories, Albuquerque, NM USA
NNTP-Posting-Date: Wed, 11 Dec 2002 01:06:32 +0000 (UTC)
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Bill Sloman wrote:
> According to chapter 2 of Floyd M. Gardner's "Phaselock Techniques"
> (ISBN 0-471-04294-3) you need a second order control loop, which is to
> say an integrator in the feed-back path (in addition to the integrator
> formed by the voltage-controlled oscillator) to get a zero phase error
> at an arbitrary (but stable) frequency.
> The nature of the phase detector has nothing to do with Christopher
> Carlen's problem. A digital phase-frequency detector comes into lock
> much more nicely and quite a lot faster than a simple
> multiplying/exclusive-OR phase detector, but once the loop is locked
> both forms of phase detector give an error signal directly
> proportional to phase error, and you have to feed this into an
> integrator this if you want an arbitrary voltage output (and
> frequency) at zero phase error.
Yeah, that's what I think too!
> To get a zero phase error when tracking a linearly varying frequency
> you have to go to a third order loop (with two integrators in the
> feed-back path) and to get zero phase error when tracking a frequency
> which is increaising or decreasing at a constantly
> accelerating/decelerating rate you need a fourth order loop, and so
Well fortunately, I just need the second order.
Thanks for the input.
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
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