US 4,365,211 A · Phase-locked loop with initialization loop

Abstract

An integrator and a voltage controlled oscillator produce a variable frequency output signal. A primary loop is locked to an input signal and has a narrow bandwidth allowing the output signal to precisely track the input signal. An initialization loop is locked to an internally generated reference signal and has a wide bandwidth for pulling the frequency of the output signal very close to the frequency of the reference signal. Since the frequency of the reference signal is approximately equal to the frequency of the input signal the initialization loop pulls the frequency of the output signal very close to the frequency of the input signal thus assuring locking of the primary loop. A switch selectively connects components of the primary loop to the integrator when the frequency difference between the reference signal and the output signal is small and connects components of the initialization loop to the integrator when the frequency difference between the reference signal and the output signal is large.

Claims15

Dependent claims

A phase-locked loop producing an output signal having a frequency locked to the frequency of an input signal, comprising:

means for producing the input signal;
means for producing the output signal, said output signal having a variable frequency;
first means for detecting a phase difference between said input signal and said output signal, said first phase detection means having a narrow bandwidth;
means for producing a reference signal;
second means for detecting a phase difference between said reference signal and said output signal, said second phase detection means having a wide bandwidth;
control means responsive to said second phase detection means, said control means producing a switching signal representative of the frequency difference between said reference signal and said output signal;
and switching means selectively connecting one of said first phase detection means and said second phase detection means to said means producing said output signal, said switching means being responsive to said switching signal such that when said frequency difference between said reference signal and said output signal is large said second phase detection means is connected to said means producing said output signal.

4 more elements

Dependencies are inferred from the claim text.

Phase-locked loop with initialization loop

Life of this patent

Phase-locked loop with initialization loop

Life of this patent

Abstract

Claims15