Patent ID: 8421508

Claim:
A spread spectrum clock generator comprising: a phase comparator configured to detect a phase difference between a reference input clock signal and a feedback signal and output a control voltage in line with the phase difference; a voltage controlled oscillator configured to generate an output clock signal with a frequency in line with the control voltage; a phase selector configured to equally divide one cycle of the output clock signal into a predetermined number of phases and select any of the phases, generate a phase shift clock signal having a rising edge at the selected phase, and transmit the phase shift clock signal to the phase comparator as the feedback signal; a phase controller configured to decide a phase of the rising edge of the phase shift clock signal so that the phase shift clock signal has a cycle different from the cycle of the output clock signal by a first phase shift amount and control the phase selector to select the decided phase, and generate a second phase shift amount which cyclically varies in a predetermined range, decide the rising edge of the phase shift clock signal to add the second phase shift amount to the first phase shift amount and subject the output clock signal to spread spectrum modulation by the cyclically varying second phase shift amount.