Patent ID: 7567139

Claim:
A voltage controlled oscillator for oscillating a radio frequency signal, the voltage controlled oscillator comprising: an inductor circuit including an inductor; a variable capacitance circuit including a variable capacitance element for changing a capacitance value in accordance with a voltage difference between both of two terminals thereof and including a capacitive element, for cutting a DC component, connected to the variable capacitance element, the variable capacitance circuit being connected in parallel to the inductor circuit, such that the variable capacitance circuit and the inductor circuit form a parallel resonance circuit; a negative resistance circuit for cancelling a loss caused by a parasitic resistance component of the parallel resonance circuit; and a time-switched level shift circuit for shifting a reference voltage to be output to two or more different levels in a predetermined period; wherein one terminal of the two terminals of the variable capacitance element is supplied with a control voltage for controlling an oscillation frequency, and the other terminal of the two terminals of the variable capacitance element is supplied with the reference voltage that shifts to the two or more different levels in the predetermined period and that is output from the time-switched level shift circuit, such that a capacitance value of the variable capacitance circuit changes in accordance with the reference voltage that shifts to the two or more different levels in the predetermined period.