From: Jim Thompson
Subject: Re: How to increase PLL order?
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Date: Wed, 11 Dec 2002 03:12:27 GMT
NNTP-Posting-Date: Tue, 10 Dec 2002 22:12:27 EST
Organization: Cox Communications
On Tue, 10 Dec 2002 19:05:55 -0800,
John Larkin ,
In Newsgroup: sci.electronics.design,
Entitled: "Re: How to increase PLL order?",
Wrote the following:
|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.
Absolutely! Methinks Chris has some cockpit errors in his
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| Jim-T@analog_innovations.com Fax:(480)460-2142 | Brass Rat |
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