Push-pull spread spectrum clock signal generator
AssigneeIntegrated Device Technology, Inc.
InventorDaniel M. Clementi
Life of this patent
Estimating the term…
Abstract
A spread spectrum clock signal generator modulates a reference clock signal based on a spread spectrum frequency profile and includes a phase-lock loop for generating a spread spectrum clock signal by aligning a phase of the modulated reference clock signal with a phase of the spread spectrum clock signal. The spread spectrum clock signal generator also includes a loop modulator for modulating the spread spectrum clock signal based on the spread spectrum frequency profile. Because the spread spectrum clock signal generator modulates both the reference clock signal and the spread spectrum clock signal based on the spread spectrum frequency profile, the spread spectrum clock signal has a non-distorted frequency profile and low phase jitter.
Claims20
A system for generating a spread spectrum clock signal, comprising:
- a reference clock signal modulator configured to generate a modulated reference clock signal by modulating a reference clock signal based on a spread spectrum frequency profile, the reference clock signal modulator further configured to generate a modulation direction signal indicating a modulation frequency direction of the spread spectrum frequency profile;
- a phase-lock loop coupled to the reference clock signal modulator and configured to generate a loop phase error signal indicating a phase difference between the modulated reference clock signal and a spread spectrum clock signal, the phase-lock loop further configured to generate the spread spectrum clock signal based on the modulated reference clock signal and a loop modulation signal;
- and
- a loop modulator coupled to the reference clock signal modulator and the phase-lock loop, the loop modulator configured to generate the loop modulation signal based on the modulation direction signal and the loop phase error signal for minimizing a phase-modulation amplitude difference between a phase-modulation amplitude of the modulated reference clock signal and a phase-modulation amplitude of the spread spectrum clock signal.
A system for generating a spread spectrum clock signal, the system comprising:
- a profile generator configured to generate a spread spectrum profile signal indicating a spread spectrum frequency profile and a modulation direction signal indicating a modulation frequency direction of the spread spectrum frequency profile;
- a sequencer coupled to the profile generator and configured to generate a sequencing signal based on the spread spectrum profile signal, the sequencing signal indicating a sequence of divisors for dividing a fundamental frequency of the reference clock signal;
- a frequency divider coupled to the profile generator and the sequencer, the frequency divider configured to generate a modulated reference clock signal by dividing a fundamental frequency of the reference clock signal by the sequence of divisors indicated by the sequencing signal;
- a loop phase detector coupled to the frequency divider and configured to generate a loop phase error signal indicating a phase difference between the modulated reference clock signal and the spread spectrum clock signal;
- a loop modulator coupled to the profile generator and the loop phase detector, the loop modulator configured to generate a loop modulation signal based on the modulation direction signal and the loop phase error signal for minimizing a phase-modulation amplitude difference between a phase-modulation amplitude of the modulated reference clock signal and a phase-modulation amplitude of the spread spectrum clock signal;
- a loop charge pump coupled to the loop phase detector and configured to generate a loop charge pump signal based on the loop phase error signal, the loop charge pump signal indicating the phase difference between the modulated reference clock signal and the spread spectrum clock signal;
- a loop filter coupled to the loop charge pump and configured to generate a loop oscillation control signal by low-pass filtering the loop charge pump signal and combining the loop charge pump signal with the loop modulation signal;
- and
- a loop voltage-controlled oscillator coupled to the loop filter and the loop phase detector, the loop voltage-controlled oscillator configured to generate the spread spectrum clock signal based on the loop oscillation control signal.
A method of generating a spread spectrum clock signal, the method comprising:
- receiving a reference clock signal;
- generating a modulated reference clock signal by modulating the reference clock signal based on a spread spectrum frequency profile;
- generating a modulation direction signal indicating a modulation frequency direction of the spread spectrum frequency profile;
- generating a loop phase error signal indicating a phase difference between the modulated reference clock signal and the spread spectrum clock signal;
- generating a loop modulation signal based on the modulation direction signal and the loop phase error signal for minimizing a phase-modulation amplitude difference between a phase of the modulated reference clock signal and a phase of the spread spectrum clock signal;
- and
- generating the spread spectrum clock signal based on the modulated reference clock signal and the loop modulation signal.
Dependencies are inferred from the claim text.