Patent ID: 7167059

Claim:
A circuit for generating a spread spectrum clock comprising: an output node; a voltage controller oscillator (VCO) that includes an input coupled to a voltage control node (V_ctrl) for receiving a voltage signal and an output for generating a clock signal that has a frequency (F _out) dependent on the received voltage signal; and a VCO input voltage modulation mechanism, coupled to the VCO input voltage node, for modulating a voltage at the VCO input voltage node to generate a spread spectrum clock; wherein the VCO input voltage modulation mechanism uses a plurality of pull-up transistors and a plurality of pull-down transistors to selectively adjust the voltage at the VCO input voltage node; and wherein the VCO input voltage modulation mechanism uses a plurality of delay cells to selectively adjust the time between a first point and a second point on a graph of the voltage at the VCO input voltage node with respect to time.