Phase locked loop system having locking and tracking modes of operation

摘要

An embodiment pertains to a phase locked loop (PLL) circuit. The PLL includes a voltage controlled oscillator which outputs a signal at a desired frequency. A phase detector is coupled to an output from the voltage controlled oscillator. The phase detector compares the phase of a signal output from the voltage controlled oscillator (VCO) with the phase of a reference signal. A loop filter is coupled to the VCO and the phase detector. The loop filter has a locking mode of operation for locking the phase of the VCO signal to the phase of the reference signal. The loop filter can subsequently be placed in a tracking mode of operation which adjusts the phase of the VCO signal to track the phase of the reference signal.