VARIABLE CAPACITY CIRCUIT AND CONTROL METHOD OF VARIABLE CAPACITY CIRCUIT

To present a variable capacity circuit and a control method of variable capacity capable of extending a variable capacity width of a variable capacity element to a maximum extent without increasing an element area of the variable capacity element or varying the level of control voltage, a variable capacity circuit 2 comprises a capacity value control circuit 11, varactors VA1 and VA2, and resistance elements R1 and R2. The capacity value control circuit 11 issues a variable output voltage CNTOUT depending on input control voltage VT, and controls the potentials at both ends of the varactors simultaneously. The output voltage CNTOUT is variably adjusted so as to have a negative correlation to the control voltage VT. Variable width of terminal voltage VD can be extended from a variable width SA1 to a variable width SA1a (range is +/−(Vcc1)). As a result, as shown in FIG. 5B, the changeable area of a varactor capacity value CV can be extended from a changeable area CA1 to a changeable area CA1a.