Phase locked loop having circuit for recovering from oscillation

Details Phase locked loop having circuit for recovering from oscillation Phase locked loop having circuit for recovering from oscillation

1989-11-30

1990-11-06

Grimm, Siegfried H.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Afc with logic elements

331 16, 331 25, H03L 718

Patent

active

049689517

ABSTRACT:
A phase locked loop for extracting an output signal synchronized with an input signal. The present invention is structured so that a phase locked loop can prevent loss of control due to high frequency noise generated by a level conversion circuit in the feedback loop after oscillation of the VCO has stopped due to a failure. The phase locked loop includes an exchange circuit connected between an output of the phase detector and an input to the feedback loop. When the exchange circuit determines that the output of the phase detector is below a reference voltage, it applies a signal having a frequency which is lower than that of the input signal to the phase detector in place of a signal from a frequency divider in the feedback loop. In such a case, the phase detector outputs a pulse signal which restarts oscillation of the VCO and leads to normal phase control operation.

REFERENCES:
patent: 4135165 (1979-01-01), Coe

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