Fractional frequency synthesizer and phase locked loop utilizing fractional frequency synthesizer and method thereof
AssigneeRealtek Semiconductor Corp.
InventorsWen-Chi Wang, Tze-Chien Wang
Life of this patent
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Abstract
A fractional frequency synthesizer, applied to a phase-locked loop, includes a phase detector, a loop filter, a controllable oscillator, a first frequency divider, and a sigma-delta modulator (SDM). The phase detector generates a phase difference signal according to a reference signal and a feedback signal. The loop filter filters the phase difference signal to generate a filtered signal. The controllable oscillator generates the frequency signal according to the filtered signal. The first frequency divider generates the feedback signal by dividing a frequency of the frequency signal according to a dividing factor. The SDM determines the dividing factor according to a control signal.
Claims16
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.
A method for generating a frequency signal, comprising:
- receiving an input signal and a first feedback signal, and generating a first phase difference signal according to the input signal and the first feedback signal;
- filtering the first phase difference signal to generate a control signal;
- and
- adjusting the first feedback signal according to the control signal in a fractional frequency synthesizer;
- wherein the step of adjusting the first feedback signal comprises:
- receiving a reference signal and a second feedback signal, and generating a second phase difference signal according to the reference signal and the second feedback signal;
- filtering the second phase difference signal to generate a filtered signal;
- generating a frequency signal according to the filter signal;
- determining a frequency dividing factor according to the control signal;
- and
- dividing a frequency of the frequency signal according to the frequency dividing factor to generate the second feedback signal.
A method for generating a frequency signal, comprising:
- receiving an input signal and a first feedback signal, and generating a first phase difference signal according to the input signal and the first feedback signal;
- filtering the first phase difference signal to generate a control signal;
- and
- adjusting the first feedback signal according to the control signal in a fractional frequency synthesizer;
- wherein the step of adjusting the first feedback signal comprises:
- receiving a reference signal to output the frequency signal, wherein a frequency of the reference signal is a non-integer multiple of a frequency of the frequency signal;
- and
- adjusting the non-integer multiple according to the control signal.
Dependencies are inferred from the claim text.