Patent ID: 7847640

Claim:
A voltage controlled oscillator controlling an oscillation frequency based on a control voltage supplied from an external control voltage terminal, the voltage controlled oscillator comprising: a reference bias voltage circuit generating a reference bias voltage by adjusting a reference voltage; and a gain adjustment circuit adjusting a gain of the control voltage, wherein the gain adjustment circuit includes (i) a plurality of resistances and (ii) a plurality of switching elements, wherein the gain adjustment circuit controls the plurality of switching elements and forms a voltage dividing circuit between the reference bias voltage and the external control voltage terminal to generate an automatic frequency control (AFC) voltage, wherein the reference bias voltage circuit includes (i) a plurality of serial resistances between the reference voltage and a ground and (ii) a switch coupled in parallel to at least one of the serial resistances, and wherein the reference bias voltage circuit controls the switch and changes a voltage dividing ratio of the serial resistances to set the reference bias voltage.