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From: John Larkin
Subject: Re: How to increase PLL order?
Date: Tue, 10 Dec 2002 19:05:55 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On Tue, 10 Dec 2002 18:08:18 -0800, "Christopher R. Carlen"
>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.
A 4046 type II (digital/charge pump) detector driving an R-C or R-C//C
filter does give a type 2 closed loop: zero steady-state phase error.
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