文档介绍：Maddy, ., “Phase-Locked Loop”
The Electrical Engineering Handbook
Ed. Richard C. Dorf
Boca Raton: CRC Press LLC, 2000
76
Phase-Locked Loop
Introduction
Loop Filter
Noise
PLL Design Procedures
Steven L. Maddy
RLM Research Applications
Introduction
A phase-locked loop (PLL) is a system that uses feedback to maintain an output signal in a specific phase
relationship with a reference signal. PLLs are used in many areas of electronics to control the frequency and/or
phase of a signal. These applications include frequency synthesizers, analog and digital modulators and demod-
ulators, and clock recovery circuits. Figure shows the block diagram of a basic PLL system. The phase
detector consists of a device that produces an output voltage proportional to the phase difference of the two
input signals. The VCO (voltage-controlled oscillator) is a circuit that produces an ac output signal whose
frequency is proportional to the input control voltage. The divide by N is a device that produces an output
signal whose frequency is an integer (denoted by N) division of the input signal frequency. The loop filter is
a circuit that is used to control the PLL dynamics and therefore the performance of the system. The F(s) term
is used to denote the Laplace transfer function of this filter.
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