Patent ID: 7492224

Claim:
A gain variable circuit comprising: a first load connected between a first supply voltage node, and a first output terminal that outputs a first output signal; a second load connected between the first supply voltage node, and a second output terminal that outputs a second output signal having phase reversed from a phase of the first output signal; a first differential circuit that is connected between the first and second output terminals and a first node, and that changes gains of the first and second output signals responsive to a difference between first and second complementary gain variable signals; a second differential circuit that is connected between the first and second output terminals and a second node, and that changes the gains of the first and second output signals responsive to a difference between the first and second gain variable signals; and an amplification circuit that is connected between the first and second nodes and a second supply voltage node, and that amplifies the first and second output signals responsive to a difference between first and second complementary input signals, wherein the first differential circuit comprises a first transistor that is connected between the first output terminal and the first node, and that has a state of conduction controlled by the first gain variable signal, and a second transistor that is connected between the second output terminal and the first node, and that has a state of conduction controlled by the second gain variable signal, and the second differential circuit comprises a third transistor that is connected between the first output terminal and the second node, and that has a state of conduction controlled by the second gain variable signal, and a fourth transistor that is connected between the second output terminal and the second node, and that has a state of conduction controlled by the first gain variable signal.