Patent ID: 7548121

Claim:
A frequency signal generator, comprising: a first phase detector configured to receive an input signal and a first feedback signal and generate a first phase difference signal according to the input signal and the first feedback signal; a first loop filter, coupled to the first phase detector, configured to filter the first phase difference signal to generate a control signal; and a fractional frequency synthesizer, coupled to the first loop filter and the first phase detector, configured to adjust the first feedback signal according to the control signal; wherein the fractional frequency synthesizer comprises: a second phase detector configured to receive a reference signal and a second feedback signal to generate a second phase difference signal; a second loop filter, coupled to the second phase detector, configured to filter the second phase difference signal to generate a filtered signal a controllable oscillator, coupled to the second phase detector, configured to generate a frequency signal according to the filtered signal; a first frequency divider, coupled to the controllable oscillator, configured to divide a frequency of the frequency signal to generate the second feedback signal; and a modulator, coupled to the first frequency divider and the first loop filter, configured to generate a sigma-delta output signal according to the control signal and determine a frequency dividing factor of the first frequency divider according to the sigma-delta output signal.