Patent ID: 9048848
Filing Date: 2015-06-02
Classification: H03L

Abstract:
1. A phase-locked loop circuit using a multi-curve voltage-controlled oscillator (VCO) having a plurality of operating curves, each operating curve corresponding to a different frequency range over a control voltage range, the phase-locked loop configured to receive an input signal having a reference frequency and to generate a control voltage to control the multi-curve VCO to generate an output signal using the one of the plurality of operating curves, the output signal having a fixed relation to the phase of the input signal, the phase-locked loop circuit comprises: a phase and frequency detector configured to receive the 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, the feedback signal being related to the output signal, the charge pump providing a charge pump current to drive a control voltage node to generate the control voltage to control the multi-curve VCO; and a digital control circuit configured to perform a closed loop curve search operation to select one of the plurality of operating curves in the multi-curve VCO and to perform a curve tracking operation using the selected operating curve, the selected operating curve being used by the VCO to generate an output signal with an output frequency being equal or close to a target frequency of the phase-locked loop, wherein the digital control circuit is configured to increase the charge pump current above a nominal current value during the closed loop curve search operation to select one of the plurality of operating curves in the multi-curve VCO and the digital control circuit is further configured to set the charge pump current to the nominal current value during the curve tracking operation.