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Spread spectrum clock generator and method for generating spread spectrum clock signal

  • US 9,191,128 B2
  • Filed: 12/17/2013
  • Issued: 11/17/2015
  • Est. Priority Date: 12/17/2013
  • Status: Active Grant
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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