Patent ID: 7271669

Claim:
A voltage controlled oscillator including a plurality of unit delay cells connected serially, each unit delay cell comprising: a differential amplification unit for comparing a plurality of input voltages having different phases and amplifying the comparison result; and an output driving unit, connected to both output terminals of the differential amplification units, for driving an output voltage of another output terminal with a potential of one of both output terminals, wherein the output driving unit comprises: a first NMOS transistor for driving an output voltage of a second output terminal of both output terminals with a charge of a first output terminal of both output terminals, connected to both output terminals of the differential amplification units, a gate to receive a first input voltage; and a second NMOS transistor for driving an output voltage of the first output terminal with a charge of the second output terminal, connected to both output terminals of the differential amplification units, and a gate to receive a second input voltage.