Spread spectrum clock generator and method for generating spread spectrum clock signal
First Claim
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1. A spread spectrum clock generator, comprising:
- a random walk modulator for generating a modulating signal according to a random walk model; and
a phase-locked loop system, in communication with the random walk modulator, for receiving the modulating signal and generating a clock signal with spread spectrum in response to the modulating signal,wherein the phase-locked loop system comprises;
a phase-frequency detector for receiving and comparing a reference clock and a feedback signal, and generating a control signal according a phase difference between the reference clock and the feedback signal;
a charge pump for generating a control voltage in response to the control signal from the phase-frequency detector;
a voltage-controlled oscillator, in communication with the charge pump, for generating the clock signal according to the control voltage from the charge pump; and
a frequency divider, in communication with the voltage-controlled oscillator and the phase-frequency detector, for receiving the clock signal from the voltage-controlled oscillator and generating the feedback signal to the phase-frequency detector by down-converting the clock signal with a frequency divisor,wherein the frequency divisor is adjusted by steps of;
providing an integer set, an interval between every successive two integers in the integer set being a constant value;
selecting one integer in the integer set as a first frequency divisor at a first time; and
selecting another integer in the integer set immediately previous or next to the selected integer as a second frequency divisor at a second time.
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Abstract
A spread spectrum clock generator for generating a spread spectrum clock signal is provided. The spread spectrum clock generator includes a phase-locked loop system and a random walk modulator. The random walk modulator generates a modulating signal according to a random walk model. Then, the phase-locked loop system generates a clock signal with spread spectrum in response to the modulating signal. A method for generating the spread spectrum clock signal using the spread spectrum clock generator is also provided.
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Citations
17 Claims
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1. A spread spectrum clock generator, comprising:
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a random walk modulator for generating a modulating signal according to a random walk model; and a phase-locked loop system, in communication with the random walk modulator, for receiving the modulating signal and generating a clock signal with spread spectrum in response to the modulating signal, wherein the phase-locked loop system comprises; a phase-frequency detector for receiving and comparing a reference clock and a feedback signal, and generating a control signal according a phase difference between the reference clock and the feedback signal; a charge pump for generating a control voltage in response to the control signal from the phase-frequency detector; a voltage-controlled oscillator, in communication with the charge pump, for generating the clock signal according to the control voltage from the charge pump; and a frequency divider, in communication with the voltage-controlled oscillator and the phase-frequency detector, for receiving the clock signal from the voltage-controlled oscillator and generating the feedback signal to the phase-frequency detector by down-converting the clock signal with a frequency divisor, wherein the frequency divisor is adjusted by steps of; providing an integer set, an interval between every successive two integers in the integer set being a constant value; selecting one integer in the integer set as a first frequency divisor at a first time; and selecting another integer in the integer set immediately previous or next to the selected integer as a second frequency divisor at a second time. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A spread spectrum clock generator, comprising:
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a phase-frequency detector for receiving and comparing a reference clock and a feedback signal, and generating a control signal according a phase difference between the reference clock and the feedback signal; a charge pump, in communication with the phase-frequency detector, for generating a control voltage in response to the control signal from the phase-frequency detector; a voltage-controlled oscillator, in communication with the charge pump, for generating a clock signal according to the control voltage from the charge pump; a frequency divider, in communication with the voltage-controlled oscillator and the phase-frequency detector, for receiving the clock signal from the voltage-controlled oscillator, and generating the feedback signal to the phase-frequency detector by down-converting the clock signal with a frequency divisor; and a random walk modulator, in communication with the frequency divider, for generating a modulating signal according to a random walk model to adjust the frequency divisor, wherein the modulating signal is a random walk sequence and the frequency divisor is adjusted according to the random walk sequence by sub-step of; providing the random walk sequence according to Brownian motion wherein each random walk value is selected from a positive integer and a negative integer with an identical absolute value, and probabilities of the two integers are the same in the random walk sequence; and obtaining a current frequency divisor by adding a corresponding random walk value in the random walk sequence to a previous frequency divisor. - View Dependent Claims (11)
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12. A method for generating a spread spectrum clock signal by a clock generator, the method comprising steps of:
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generating a modulating signal according to a random walk model; sending the modulating signal to a phase-locked loop system of the clock generator; and the phase-locked loop system generating a clock signal with spread spectrum in response to the modulating signal, wherein the step of generating the clock signal with spread spectrum comprising sub-steps of; receiving and comparing a reference clock and a feedback signal, and generating a control signal according to a phase difference between the reference clock and the feedback signal; generating a control voltage in response to the control signal; generating the clock signal according to the control voltage; and generating the feedback signal by down-converting the clock signal with a frequency divisor, wherein the modulating signal is a random walk sequence and the frequency divisor is adjusted according to the random walk sequence by sub-step of; providing the random walk sequence according to Brownian motion wherein each random walk value is selected from a positive integer and a negative integer with an identical absolute value, and probabilities of the two integers are the same in the random walk sequence; and obtaining a current frequency divisor by adding a corresponding random walk value in the random walk sequence to a previous frequency divisor. - View Dependent Claims (13, 14, 15, 16, 17)
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Specification