Patent ID: 7477676

Claim:
The spread spectrum clock generator comprising: a phase locked loop which comprises a phase comparator to which a reference clock is input, a voltage control oscillator which generates an oscillation frequency that is variable in response to said phase comparator output, and a first divider which divides said voltage control oscillator output by an alterable division number, wherein said first divider output is fed back to said phase comparator; a disturbance signal generator which includes at least one signal generator to generate a function of digital representation and which generates a disturbance signal with a band limiting characteristic that is variable, depending on said function; at least one quantizer which converts non-integral data in the fraction part included in an output of said disturbance signal generator to an integer by integral approximation; a control circuit which controls division number change on said first divider; and a changing means for externally changing a disturbance signal type to be generated by said disturbance signal generator and a type of said quantizer wherein: said disturbance signal generator comprises: a plurality of signal generators which operate, based on a first internal clock; a first selector which selects an output of one of said plurality of signal generators, according to a first select signal; and a variable filter which removes out-of-band noise from a signal output from said first selector and outputs the signal as a disturbance signal.