CHARGE PUMP FOR PHASE-LOCKED LOOP

摘要

A current generator for a phase-locked loop arranged to generate an output signal having predetermined frequency-relationship with a reference signal, the phase-locked loop comprising a signal generator arranged to generate the output signal, a divider arranged to receive the output signal and divide the output signal to form a feedback signal, the divider being arranged to vary the divisor by which the output signal is divided, a comparison unit arranged to compare the feedback signal with the reference signal and output a first error signal indicative of the phase-difference between the feedback signal and the reference signal to the current generator and a loop filter arranged to filter a current signal output by the current generator to form a control signal for controlling the signal generator, the current generator being capable of receiving the first error signal and generating a current in dependence thereon, receiving a second error signal indicative of an error in the feedback signal caused by the variation of the divisor by which the output signal is divided and generating a current having a magnitude and sign that is dependent on that error and combining the currents generated in dependence on the first error signal and the second error signal to form a current signal output to the loop filter that is representative of an overall error in the output signal of the phase-locked loop relative to the reference signal.