Patent ID: 7795979

Claim:
An automatic gain control circuit comprising: a radio frequency amplifying circuit for amplifying a received radio frequency signal with a variably set gain; an attenuating circuit for controlling the received radio frequency signal to have a variably set attenuation degree; and a bypass switch connected in series to the attenuating circuit, wherein an input/output node of a series circuit constituted by the attenuating circuit and the bypass switch and that of the radio frequency amplifying circuit are connected to each other to connect the series circuit and the radio frequency amplifying circuit in parallel, wherein the radio frequency amplifying circuit includes: a first nMOS transistor to be operated as a source grounding amplifier for amplifying an input signal; second and third nMOS transistors for carrying out a control to turn ON/OFF a current path of the first nMOS transistor; and a fourth nMOS transistor which is cascode connected to the first nMOS transistor, wherein the second nMOS transistor is connected in series to the first nMOS transistor and a source of the second nMOS transistor is grounded, a drain of the third nMOS transistor is connected to a gate of the fourth nMOST transistor and a source of the third nMOS transistor is grounded, and a predetermined control signal is applied to a gate of the third nMOS transistor and a signal obtained by inverting a logic of the predetermined control signal is applied to a gate of the second nMOS transistor.