All digital phase locked loop system and method

A system for generating an analog oscillator signal under control of a reference signal, the system 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 that is coupled to outputs from the digital loop filter and the sigma delta modulator and that is coupled to the digital control input of the digitally controlled oscillator;
• a feedback divider that is coupled to the analog signal output to provide a divided oscillator signal and a phase difference output signal;
• and
• a digital charge pump that is coupled to receive the phase difference output signal and that is coupled to provide a digitized current signal to the digital loop filter.

An apparatus comprising:

• a digitally controlled oscillator having a digital input terminal and an analog output terminal;
• a digital loop filter that generates an integer part of a digital control signal and a fractional part of the digital control signal;
• a sigma-delta modulator that is coupled to the digital loop filter so as to receive the integer part of the digital control signal;
• a digital adder that is coupled to the digital loop filter so as to receive the fractional part of the digital control signal and that is coupled to the sigma delta modulator, and wherein;
• a feedback divider that:
• is coupled to the analog output terminal;
• receives a reference signal;
• and
• generates a divided oscillator signal, a sign output signal, and a phase difference output signal;
• a phase frequency detector that is coupled to the feedback divider so as to receive the divided oscillator signal and that provides a feedback signal to the feedback divider;
• and
• a digital charge pump that is coupled to the feedback divider so as to receive the sign output signal and the phase difference output signal and that is coupled to the digital input terminal.