Charge pump circuit.

摘要

A charge pump circuit (21) for charging a capacitor (C1,C2) in response to a phase difference between first and second input signals comprises a constant current source (Q3) for providing a first constant current (i3); a constant current sink (Q6) for absorbing a second constant current (i6); circuit (11,12) for substantially equalizing the magnitudes of the first and second constant currents; and a switching circuit (Q4,Q5) for providing the first constant current and the second constant current flowing in opposed directions to the capacitor through an output terminal (T2) 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 (4) 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 (22) supplying the voltage thereacross as a control voltage to a voltage controlled oscillator (7) of the phase locked loop system.