Frequency/phase locked loop circuit using digitally controlled o

Details Frequency/phase locked loop circuit using digitally controlled o Frequency/phase locked loop circuit using digitally controlled o

1980-08-04

1983-04-19

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Afc with logic elements

331 17, 331 25, 331 27, 331 34, H03L 714

Patent

active

043807429

ABSTRACT:
A circuit for synchronizing the frequency and/or phase of an output frequency signal (f.sub.0) to a reference frequency signal (f.sub.ref) is disclosed. A digitally controlled oscillator produces an output frequency signal which varies dependent upon an input digital signal which also is varied. A comparator means is coupled to the oscillator and the reference signal for determining the presence or absence of a frequency or phase difference between the output frequency signal and the reference frequency signal and generates a digital signal to the oscillator indicating whether the output frequency signal should be increased or decreased. In one embodiment, the comparator means comprises an up/down counter and the digitally controlled oscillator comprises a digital-to-analog converter (DAC) coupled to an oscillator circuit. The output of the oscillator circuit (f.sub.0) is fed back through a divide by N counter circuit. The most significant digit (MSB) of the counter is connected to the up/down terminal of the up/down counter. The reference frequency signal is connected to the clock terminal of the up/down counter and through gating circuitry to the clear terminal of the divide by N counter. The up/down counter determines whether the reference frequency signal or the output frequency signal occurs first and generates a digital signal to the DAC and oscillator which adjusts the oscillator either upward or downward until the divided down oscillator signal is in synchronization with the reference signal.

REFERENCES:
patent: 3271688 (1966-09-01), Gschwind et al.
patent: 3484712 (1969-12-01), Foote et al.
patent: 3824483 (1974-07-01), Margala et al.
patent: 3840821 (1974-10-01), Conway
patent: 3989931 (1976-11-01), Phillips
patent: 4144489 (1979-03-01), Ward et al.
patent: 4166249 (1979-08-01), Lynch
patent: 4309662 (1982-01-01), Baudoux

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