Charge pump circuit

Details Charge pump circuit Charge pump circuit

1990-06-13

1991-11-26

Pascal, Robert J.

Oscillators

Automatic frequency stabilization using a phase or frequency...

Particular error voltage control

331 25, H03L 700

Patent

active

050686267

ABSTRACT:
A charge pump circuit for charging a capacitor in response to a phase difference between first and second input signals comprises a constant current source for providing a first constant current; a constant current sink for absorbing a second constant current; a circuit for substantially equalizing the magnitudes of the first and second constant currents; and a switching circuit for providing the first constant current and the second constant current flowing in opposed directions to the capacitor through an output terminal of the charge pump circuit in response to the phase difference between the first and second input signals to produce a voltage level across the capacitor corresponding to the phase difference. In a phase locked loop system employing such a charge pump circuit, a phase comparator produces a phase difference signal for controlling the provision of the first and second constant currents by the switching circuit to the capacitor. The capacitor acts as a loop filter supplying the voltage thereacross as a control voltage to a voltage controlled oscillator of the phase locked loop system.

REFERENCES:
patent: 4636748 (1987-01-01), Latham, II
patent: 4668918 (1987-05-01), Adams

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