Patent ID: 7236039

Claim:
A spread spectrum clock generating apparatus comprising: a phase interpolator for receiving an input clock signal and a control signal, varying phase of an output clock signal in accordance with said control signal to output the resultant output clock signal; and a control circuit for receiving and counting the input clock signal, generating said control signal, which is for varying the phase of the output clock signal and frequency-modulating the input signal, based upon result of the count, and supplying the generated control signal to said phase interpolator, wherein said control circuit, responsive to a frequency-modulation starting signal which is supplied thereto at any timing, starts output of said control signal, at a timing at which the frequency of the output clock signal is equal to the frequency of the input clock signal, and responsive to a frequency-modulation stop signal which is supplied thereto at any timing, stops output of said control signal, at a timing at which the frequency of the output clock signal is equal to the frequency of the input clock signal.