Phase-locked loop having charge pump driven with preserved energ

Details Phase-locked loop having charge pump driven with preserved energ Phase-locked loop having charge pump driven with preserved energ

1992-06-15

1995-03-21

Chin, Stephen

Pulse or digital communications

Synchronizers

Phase displacement, slip or jitter correction

331 25, H03D 324, H03L 700

Patent

active

054003725

ABSTRACT:
A frequency synthesizer comprises a voltage controlled oscillator, and a variable frequency divider for dividing the VCO frequency according to the frequency of a communication channel. The output of frequency divider is compared with a reference frequency and a phase difference of first polarity and a phase difference of second polarity are detected. A charge-control voltage is generated with a duration variable with the phase difference of first polarity and a discharge-control voltage with a duration variable with the phase difference of second polarity. First and second integrators are coupled respectively to outputs of the phase comparator for respectively smoothing waveforms of the control voltages. Energy is injected into a charge pump in response to the smoothed charge-control voltage and drained from it in response to the smoothed discharge-control voltage to produce a frequency control signal for coupling to the VCO. To achieve instant switching between adjacent channels, a differentiator is coupled across the outputs of the phase comparator for preserving part of energy to be supplied to or drained from the charge pump until sufficient energy is stored.

REFERENCES:
patent: 4611239 (1986-09-01), Shanley, II
patent: 5151665 (1992-09-01), Wentzler

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