Patent ID: 8503501

Claim:
A spread spectrum clock generation circuit comprising: a voltage control oscillator circuit; a voltage adder to add a first voltage for controlling a frequency of an output signal from the voltage control oscillator circuit so as to have a specified value to a second voltage for modulating the frequency and to output a sum of the first voltage and the second voltage to the voltage control oscillator circuit; a capacitor unit to output the second voltage for modulating the frequency from a second terminal thereof while a given voltage is applied to a first terminal thereof; a first charger unit coupled between the second terminal of the capacitor unit and a power supply line to charge the capacitor unit by a constant current based on a voltage of the power supply line; a second charger unit coupled to the second terminal of the capacitor unit to discharge the capacitor unit; and a switching unit to alternately make a first connection between the first charger unit and the capacitor unit and a second connection between the second charger unit and the capacitor unit in each of a plurality of different cycles to which a modulation cycle varies, wherein the first charger unit is substantially equivalent to the second charger unit in current supply capacity a digital control circuit provided for generating an output code of n bits (n=a natural number) according to the modulation cycle; a plurality of the first charger units are provided which have current supply capacities weighted by a power of 2; a plurality of the second charger units are provided, each having the same current supply capacity as a current supply capacity of the first charger unit associated with the each of the pluraliry of the second charger units; and wherein the switching unit is provided for each of the plurality of first charger units and the plurality of second charger units and the switching units are controlled according to the output code.