SPREAD SPECTRUM CLOCK GENERATOR, CIRCUIT DEVICE, IMAGE READING DEVICE, IMAGE FORMING DEVICE AND SPREAD SPECTRUM CLOCK GENERATING METHOD

摘要

PROBLEM TO BE SOLVED: To enable a frequency modulation width to be adjusted with high accuracy.;SOLUTION: A spread spectrum clock generator (SSCG) includes: a phase comparator 2 detecting a phase difference between an input clock and a feedback clock; a charge pump 3 supplying current depending on a phase difference signal from the phase comparator 2; a loop filter 4 converting an output of the charge pump 3 into a voltage to be smoothed; a voltage control oscillator 6 generating a clock of a frequency according to an input voltage; and a modulation generator 8 generating a modulation signal having an amplitude depending on a modulation width set value. The SSCG further includes a modulation width detector 10 applying to the voltage control oscillator 6 a signal in which the output of the loop filter 4 and the modulation signal output from the modulation generator 8 are added, detecting a modulation width of the spread spectrum clock generated by the voltage control oscillator 6 when the spread spectrum clock is generated, comparing the modulation width detected with a modulation width target value, and feeding back the modulation width set value newly calculated to the modulation generator 8 in order to narrow a difference between the detected modulation width and the modulation width target value.;COPYRIGHT: (C)2011,JPO&INPIT