Phase frequency detector using shift register

Oscillators – Automatic frequency stabilization using a phase or frequency... – Afc with logic elements

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331 8, 331 27, 331DIG2, 328134, 307526, H03D 1300, H03L 718

Patent

active

044595590

ABSTRACT:
An improvement in a phase locked loop comprising a VCO for generating a signal S.sub.VCO of frequency f.sub.VCO, a divider for dividing f.sub.VCO to produce a signal S.sub.N of frequency f.sub.N, a reference signal generator for generating a reference signal S.sub.R of frequency f.sub.R, and with said VCO responsive to a particular value E.sub.c of a variable control signal e.sub.c to cause f.sub.N =f.sub.R for a given value of N, the improvement consisting of a phase/frequency detector for detecting and correcting frequency and phase differences between S.sub.N and S.sub.R to cause f.sub.N =f.sub.R and comprising a three stage left/right shift register responsive to one of signals S.sub.N or S.sub.R to shift binary O's into the first stage thereof in the right direction and responsive to the other of signals S.sub.N or S.sub.R to shift binary 1's into the third stage thereof in the left direction. Also provided is a bit detector responsive to the 1's and 0's in the center stage of the shift register to produce a control signal e.sub.c either above or below E.sub.c when f.sub.N is greater or less than f.sub.R. The VCO is responsive to the control signal e.sub.c to change the frequency f.sub.VCO of its output signal S.sub.VCO so that f.sub.N =f.sub.R and e.sub.c =E.sub.c.

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Breikss, Ivar, "Shift Register Simplifies Design of Phase Comparator", Electronics, Jan. 19, 1970, p. 93.

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