Patent ID: 8106718

Claim:
A voltage controlled oscillator outputting a differential signal, comprising: an inductor connected to a first power supply supplying first voltage; first and second transistors of which drain electrodes are connected to one terminal and the other terminal of the inductor, respectively and for differential switching; first and second variable capacitors that are connected between the first transistor and the second transistor in serial and connected to the inductor in parallel; a third transistor of which a drain electrode is connected to a source electrode of the first transistor and a gate electrode is connected to a first node connected to the inductor, the second variable capacitor, and the second transistor; a fourth transistor of which a drain electrode is connected to a source electrode of the second transistor and a gate electrode is connected to a second node connected to the inductor, the first variable capacitor, and the first transistor; a first capacitor that is connected to the first transistor in parallel and of which one terminal is connected to the second node; a second capacitor of which one terminal is connected to a third node connected to the source electrode of the first transistor and the drain electrode of the third transistor and the first capacitor; a third capacitor that is connected to the second transistor in parallel and of which one terminal is connected to the first node; and a fourth capacitor of which one terminal is connected to the third capacitor and a fourth node connected to the source electrode of the second transistor and the drain electrode of the fourth transistor, wherein: when bias voltage is applied to the gate electrode of the first transistor to be turned on, negative resistance is generated by voltage applied to the first capacitor and the second capacitor through the first transistor, and when voltage outputted through the first node is applied to the gate electrode of the third transistor to be turned on, the voltage is additionally increased to the first capacitor and the second capacitor by the third transistor to increase the negative resistance.