Patent ID: 7639053

Claim:
A spread spectrum clock generator, comprising: a phase frequency detector, for generating a phase difference signal according to a frequency divided signal and a reference signal with a reference frequency; a charge pump, for receiving the phase difference signal and generating an output current according to the phase difference signal; a loop filter, for receiving the output current and converting the output current to a voltage-controlled signal; a voltage-controlled oscillator, for receiving the voltage-controlled signal and generating a plurality of voltage-controlled output signals, wherein the plurality of voltage-controlled output signals have a specific phase difference and a same voltage-controlled frequency; a dual fractional modulus divider, for receiving the plurality of voltage-controlled output signals and a control signal, and generating a first signal though dividing the voltage-controlled frequency by (N−a) or (N+b); a frequency dividing circuit, for receiving the first signal and generating the frequency divided signal to the phase frequency detector and the control signal to the dual fractional modulus divider; and a delta-sigma modulator, for controlling the frequency dividing circuit and the dual fractional modulus divider to have an equivalent divided value of (N+b)S+(N−a)(P−S) though receiving the frequency divided signal and a control word; wherein N, P, and S are integers, and a, b are fractional numbers, and S can be adjusted by the delta-sigma modulator.