Patent ID: 7697592

Claim:
A spread spectrum clock generating apparatus comprising: a phase interpolator receiving an input clock signal and a control signal, varying a phase of an output clock signal in accordance with the control signal and outputting the resultant output clock signal; and a control circuit receiving and counting the input clock signal, generating the control signal, which is for varying the phase of the output clock signal, based upon a count result, such that a frequency of the output clock makes a round trip over a predetermined frequency range, and supplying the so generated control signal to the phase interpolator, the output clock signal being frequency-modulated, the input clock signal not being derived from the output clock signal, wherein the modulated frequency of the output clock signal is obtained by taking an average (arithmetic mean) of k cycles of the input clock signal, where k comprises a predetermined positive integer, and wherein said control circuit includes a circuit for generating the control signal in such a manner that said frequency of the output clock signal makes said round trip over said frequency range, which frequency range is stipulated by predetermined first and second frequencies of mutually different frequencies, in an interval that is a prescribed multiple of a period of the input clock signal, and supplying the generated control signal to said phase interpolator.