Patent ID: 8416461

Claim:
A spread spectrum clock generator comprising: a phase difference detector configured to detect phase difference between an input clock signal and a feedback clock signal while outputting a phase difference signal; a current supplying device configured to supply a current depending on the phase difference signal output from the phase difference detector; a smoothing device configured to convert the current output from the current supplying device to a voltage while smoothing the voltage; a voltage controlled oscillator configured to generate a spread spectrum clock signal having a frequency depending on the smoothed voltage; a modulation signal generator configured to generate a modulation signal having an amplitude depending on a modulation width set value; an adder configured to input a signal obtained by adding the modulation signal generated by the modulation signal generator and the smoothed voltage output from the smoothing device to the voltage controlled oscillator so that the voltage controlled oscillator generates the spread spectrum clock signal according to the input signal; a divider configured to divide the spread spectrum clock signal output by the voltage controlled oscillator to feed back the signal to the phase difference detector as the feedback clock signal; and a modulation width detector configured to detect a modulation width of the spread spectrum clock signal generated by the voltage controlled oscillator while comparing the detected modulation width with a predetermined modulation width target value to update the modulation width set value in such a manner that difference between the detected modulation width and the modulation width target value is narrowed, followed by feeding back the updated modulation width set value to the modulation signal generator.