Voltage-controlled oscillator, and pll circuit, fll circuit, and wireless communication device using the same

A voltage-controlled oscillator that generates a local oscillation signal, the voltage-controlled oscillator comprising:

• an inductor circuit including inductors that are connected in series;
• a variable capacitance circuit including variable capacitors that are connected in series, each of the variable capacitors changing a capacitance value depending on a difference in electrical potentials between both terminals of each of the variable capacitors;
• at least one capacitance switching circuit that includes a capacitive element and a switching element;
• a negative resistance circuit;
• and
• a control section that applies a power-supply voltage to a connection point between the inductors, wherein
• the inductor circuit, the variable capacitance circuit, the at least one capacitance switching circuit, and the negative resistance circuit are parallelly connected to each other,
• a control voltage is applied to a connection point between the variable capacitors and a control signal is inputted into the capacitance switching circuit, and
• the control section changes the power-supply voltage in association with a temperature change, so as to maintain the oscillation frequency of the local oscillation signal at a constant regardless of a temperature change.