Voltage controlled oscillator, and pll circuit and radio communication device each including the same

A voltage controlled oscillator comprising:

• an inductor circuit that includes an inductor;
• a plurality of C-coupling type variable capacitance circuits each of which includes two variable capacitance elements connected in series and two blocking capacitors connected to both ends of the two variable capacitance elements for blocking a direct current component;
• at least one direct-coupling type variable capacitance circuit that includes two variable capacitance elements connected in series;
• a negative resistance circuit;
• and
• a reference voltage generating section that generates a plurality of reference voltages to be supplied to said plurality of C-coupling type variable capacitance circuits, respectively, wherein:
• said inductor circuit, said plurality of C-coupling type variable capacitance circuits, said at least one direct-coupling type variable capacitance circuit, and said negative resistance circuit are connected in parallel;
• said plurality of reference voltages are inputted to terminals of the variable capacitance elements of said plurality of C-coupling type variable capacitance circuits, respectively;
• a control voltage for feedback control of an oscillation frequency is inputted to the other terminals of the variable capacitance elements of said plurality of C-coupling type variable capacitance circuits and terminals of the variable capacitance elements of said at least one direct-coupling type variable capacitance circuit;
• and
• a variable capacitance circuit with the greatest threshold voltage about which a variation range of a capacitance value thereof is centered and a variable capacitance circuit with the smallest threshold voltage about which a variation range of a capacitance value thereof is centered are at least C-coupling type variable capacitance circuits.