Patent ID: 8643415

Claim:
A filter circuit in a phase-locked loop circuit including a phase and frequency detector configured to receive an input signal and a feedback signal and generate one or more control signals for controlling a charge pump in response to the phase difference between the input signal and the feedback signal, wherein the charge pump is coupled to receive a charge pump current from a bias generator and, in response to the one or more control signals generated by the phase and frequency detector, the charge pump provides the charge pump current generated by the bias generator to drive a control voltage node to control a voltage-controlled oscillator to generate an output signal having a fixed relation to the phase of the input signal, the filter circuit comprising: a capacitor coupled between the control voltage node and a first node; and a variable resistive element coupled between the first node and a ground potential and coupled to the bias generator, the variable resistive element having a resistance value that is varied in response to a current proportional and related to the charge pump current of the charge pump so that the resistance value of the variable resistive element varies with changes in the charge pump current.