Patent ID: 7538626

Claim:
A voltage controlled oscillator circuit comprising: a ring oscillator including a plurality of delay circuits that are connected like a ring; and a voltage to current converter circuit for converting input voltage into a control current that corresponds to voltage of the input voltage to control current flowing in the ring oscillator, wherein each of the plurality of delay circuits comprises first and second transistors, the voltage to current converter circuit comprises first and second current switching circuits, the first and second current switching circuits comprise shunt circuits, respectively, the first current switching circuit and the first transistor together form a first current mirror circuit, and the second current switching circuit and the second transistor together form a second current mirror circuit, and wherein, by turning on and off the shunt circuits, current flowing through the first transistor of the first current mirror circuit is controlled and current flowing through the second transistor of the second current mirror circuit is controlled so as to change an oscillation frequency of the ring oscillator.