Patent ID: 8872556
Filing Date: 2014-10-28
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 generate a curve select signal using a closed loop curve search operation to select one of the plurality of operating curves in the multi-curve VCO, 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, the digital control circuit further configured to set the charge pump current to the nominal current value after an operating curve is selected.