Patent ID: 7279994

Claim:
A variable capacitance circuit comprising: variable capacitance means, formed such that variable capacitance elements whose capacitance values change according to a voltage value of a supplied capacitance control voltage are connected so as to be paired and a plurality pairs of variable capacitance elements are connected in parallel forming multiple stages; a bias voltage generation means for generating bias voltages of different voltage values based on a constant voltage from a constant voltage source; and an on-off switch for a variable capacitance function, in which if the variable capacitance function of the variable capacitance means is turned on, the variable capacitance function of the variable capacitance means is turned on by supplying the bias voltage of each voltage value generated by the bias voltage generation means to the variable capacitance element of each stage of the variable capacitance means, and if the variable capacitance function of the variable capacitance means is turned off, the variable capacitance function of the variable capacitance means is turned off by grounding the bias voltage of each voltage value generated by the bias voltage generation means, the bias voltage each being supplied to the variable capacitance element of each stage of the variable capacitance means, wherein the bias voltage generation means generates a plurality of bias voltages of different voltage values by dividing the constant voltage of the constant voltage source by using a plurality of resistors, and wherein the variable capacitance means is formed such that a drain and a source of each of CMOS transistors, which are the variable capacitance elements, are connected, a connection point between the drain and the source of each of the CMOS transistors are commonly connected to a terminal to which the capacitance control voltage is supplied, and bases of each of the CMOS transistors are connected to the bias voltage generation means so as to be supplied the bias voltage of any one of the voltage values.