Patent ID: 7386293

Claim:
A receiving circuit for a radio communication apparatus, comprising: an antenna for receiving a radio-frequency signal at a predetermined frequency band; a level changing section for changing a signal level of the radio-frequency signal received by the antenna; a subsequent-stage circuit for performing predetermined signal processing for the radio-frequency signal whose signal level is changed at the level changing section; a detecting section for detecting a signal level of the radio-frequency signal for which the signal processing is performed by the subsequent-stage circuit; and a control section for setting a rate of change of the radio-frequency signal, based on the signal level of the radio-frequency signal detected by the detecting section, so that the signal level of the radio-frequency signal detected by the detecting section does not exceed a first value, wherein the control section generates a control signal smaller than a predetermined level when the signal level of the radio-frequency signal detected by the detecting section is greater than a second value which is smaller than the first value, and the control section generates a control signal having the predetermined level when the signal level of the radio-frequency signal detected by the detecting section is smaller than the second value, wherein the level changing section includes: a grounded-emitter amplifying transistor; a bias circuit for applying a bias voltage to a base of the amplifying transistor; a control transistor connected to the amplifying transistor in cascode connection; and an output circuit connected to a collector of the control transistor, wherein the amplifying transistor amplifies the radio-frequency signal that is inputted to the base and to which the bias voltage is applied, wherein the control transistor controls a gain of the amplifying transistor so as to become a gain based on the control signal that is generated at the control section and is inputted to the base, and wherein the output circuit outputs the amplified radio-frequency signal from the collector of the control transistor.