Patent ID: 7605664

Claim:
An all digital phase locked loop system for generating an analog oscillator signal under control of a reference signal, comprising: a digitally controlled oscillator with a digital control input and an analog signal output; a digital loop filter that generates a digital control signal for the digitally controlled oscillator; a sigma-delta modulator with an input coupled to a second output of the digital loop filter, and an output providing a digital output signal; a digital adder having inputs coupled for adding an output of the digital loop filter and the output of the sigma-delta modulator, and the digital adder having an output coupled to the digital control input of the digitally controlled oscillator; a feedback divider that is coupled to the analog signal output signal to provide a divided oscillator signal; and a phase frequency detector that is coupled to the feedback divider, wherein the phase frequency detector receives the divided oscillator signal and provides an input signal to the feedback divider.