Waveform generating circuit and spread spectrum clock generator

摘要

A spread spectrum clock generator is provided which improves the spread spectrum effect with little increasing the circuit cost by modifying the shape of a triangular wave used for frequency modulation by as simple method. The output signal of the modulation waveform generating circuit has such a modulation waveform as indicated by solid lines in FIG. 2 A. The modulation waveform is input to a VCO (voltage-controlled oscillator). In response to the modulation waveform, the oscillation frequency of the VCO is modulated, and the output clock that varies its frequency as illustrated in FIG. 2 B is obtained. The frequency transition of the output clock involves such temporal variations as indicated by solid lines in FIG. 2 C.