A spread-spectrum clock generator with direct VCO modulation in open-loop

Abstract

A new topology is proposed to achieve a spread-spectrum clock generator. It employs a new modulation filter, consisting of two capacitors and a resistor. The modulated triangular waveform is formed at the center of the control voltage coming from the segregated PLL. A definite advantage is that the spreading behavior does not affect the bandwidth of the PLL. Moreover, the modulation filter consumes smaller chip area because a larger resistor can be utilized for the required bandwidth.