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SPREAD SPECTRUM CONTROL PLL CIRCUIT AND ITS START-UP METHOD

  • US 20100127739A1
  • Filed: 03/18/2008
  • Published: 05/27/2010
  • Est. Priority Date: 05/30/2007
  • Status: Active Grant
First Claim
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1. A spread spectrum control PLL circuit for outputting a spread spectrum clock signal based on an input reference clock signal, comprising:

  • a charge pump circuit configured to switch charging and discharging of a charging current, depending on a phase difference between a feedback clock signal based on an output clock signal of the PLL circuit and the reference clock signal;

    a loop filter circuit having a filter capacitor which is charged and discharged using the charging current output from the charge pump circuit;

    a voltage controlled oscillator configured to oscillate at a frequency depending on an input control voltage; and

    a calibration circuit configured to adjust at least one of one of the charging current of the charge pump circuit and a capacitance value of the filter capacitor and a gain of the voltage controlled oscillator, depending on a frequency of the reference clock signal.

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