Phase-locked loop circuit capable of adjusting the frequency range of spread spectrum clock
AssigneeRealtek Semiconductor Corp.
InventorHorng-Der Chang
Life of this patent
Estimating the term…
Abstract
A circuit includes a first voltage-controlled oscillator (VCO) that generates a feedback clock. The circuit further includes a phase frequency detector, a charge pump and a loop filter that together receive a reference clock and the feedback clock, and in response thereto, generates a first voltage signal. The circuit further includes a timing generator that generates a control signal having varying periods, and a voltage modulator that receives the first voltage signal and the control signal, and in response thereto, generates a second voltage signal and a third voltage signal. The second voltage signal is provided to the first VCO. The circuit also includes a second VCO that receives the third voltage signal and which outputs a spread spectrum clock.
Claims18
A phase-locked loop circuit, comprising:
- a first voltage-controlled oscillator (VCO) that generates a feedback clock;
- a phase frequency detector that receives a reference clock and the feedback clock, and in response thereto generates a first control signal that is dependent upon the phase difference and the frequency difference between the reference clock and the feedback clock;
- a charge pump that receives the first control signal from the phase frequency detector;
- a loop filter coupled to the charge pump to generate a first voltage signal;
- a timing generator that generates a second control signal having varying periods;
- a voltage modulator that receives the first voltage signal and the second control signal, and in response thereto generates a second voltage signal and a third voltage signal, with the second voltage signal provided to the first VCO;
- and
- a second VCO that receives the third voltage signal and which outputs a spread spectrum clock.
A circuit that receives a reference clock, and includes:
- a first voltage-controlled oscillator (VCO) that generates a feedback clock;
- a phase frequency detector, a charge pump and a loop filter that together receives the reference clock and the feedback clock, and in response thereto generates a first voltage signal;
- a timing generator that generates a control signal having varying periods;
- a voltage modulator that receives the first voltage signal and the control signal, and in response thereto generates a second voltage signal and a third voltage signal, with the second voltage signal provided to the first VCO;
- and
- a second VCO that receives the third voltage signal and which outputs a spread spectrum clock.
Dependencies are inferred from the claim text.