US 4,543,540 A · Phase locked loop with limited phase correction when in locked condition

Abstract

A phase locked loop provides limited phase correction when in lock in order to minimize the effects of noise in the periodic input signal to which the loop is locked. The phase locked loop includes a voltage controlled oscillator (VCO), a timing generation divider, a phase detector, a lock detector and an oscillator control circuit. The phase detector provides an output based upon the phase difference between rising edges of the input signal and a loop synthesized signal which is derived by the divider from an oscillator output signal. A window signal, which begins slightly before and ends slightly after an anticipated rising edge of the input signal, is also derived from the oscillator output signal. The lock detector provides a lock detect signal which indicates whether the loop is in lock. The oscillator control circuit provides an oscillator control voltage based upon the phase detector output signal, the window signal, and the lock detect signal. When the loop is in lock, changes to the oscillator control voltage based on the phase detector output are limited by the window signal. When the loop out of lock, full corrections to the oscillator control voltage based upon the phase detector output signal are permitted, so that the loop can rapidly regain the phase locked condition.

Claims13

Dependent claims

A phase locked loop comprising:

phase detector means for providing a phase detector output which is a function of a phase difference between selected signal transitions of a periodic input signal and a periodic loop synthesized signal;
oscillator means for providing a periodic oscillator output signal having a frequency which is a function of an oscillator control signal;
means for deriving the loop synthesized signal from the oscillator output signal;
means for deriving a periodic window signal from the oscillator output signal, the window signal having a pulse duration which begins before and ends after the selected signal transition of the input signal is anticipated;
lock detector means for providing a lock detect signal indicative of whether the loop is in lock;
and
means for providing the oscillator control signal as a function of the phase detector output, the window signal, and the lock detect signal, wherein changes to the oscillator control signal based upon the phase detector output are limited by the window signal when the lock detect signal indicates that the loop is in lock, and are not limited by the window signal when the lock detect signal indicates that the loop is out of lock.

4 more elements

A phase locked loop comprising:

voltage controlled oscillator (VCO) means for producing an oscillator output signal having a frequency which is function of an oscillator control voltage;
phase detector means for providing a phase detector output as a function of a phase relationship between an input signal and a loop synthesized signal which is derived from the oscillator output signal, the phase detector output indicating that the frequency of the oscillator output signal should be increased if the input signal leads the loop synthesized signal and indicating that the frequency should be decreased if the input signal trails the loop synthesized signal, and further indicating the amount of such an increase or decrease based on the amount of such lead or amount of such trailing;
loop filter capacitor means for storing the oscillator control voltage;
charge pump means for selectively changing the stored oscillator control voltage as a function of charge and discharge command signals;
lock detector means for providing a lock detect signal indicative of whether the loop is in lock based on the amount of the lead or the amount of the trailing indicated in the phase detector output integrated over selected time duration;
and
correction limiting means for producing the charge and discharge command signals based upon the phase detector output and the lock detect signal, wherein the amount of change in the oscillator control voltage produced by the charge and discharge signals is limited if the lock detector signal indicates that the loop is in lock.

4 more elements

Dependencies are inferred from the claim text.

Phase locked loop with limited phase correction when in locked condition

Life of this patent

Phase locked loop with limited phase correction when in locked condition

Life of this patent

Abstract

Claims13