| 摘要 |
PROBLEM TO BE SOLVED: To simplify a configuration of a changeover circuit and a signal bypass circuit in an amplification and attenuation changeover circuit and to reduce production of intermodulation distortion in a transmission signal. SOLUTION: This amplification and attenuation changeover circuit is provided with a transistor amplifier stage 1, a feedback circuit 2 that is connected between an input terminal and an output terminal of the transistor amplifier stage 1, and a changeover circuit 3 that controls application of a bias voltage to the transistor amplifier stage 1 depending on an ON or OFF state of a received switching signal to switch the transistor amplifier stage 1 into an operating state or an inoperative state. When the transistor amplifier stage 1 is switched to the operating state, the transistor amplifier stage 1 and the feedback circuit 2 apply amplification and negative feedback to a signal fed to the input terminal and provide the result of amplification and negative feedback processing to the output terminal. When the transistor amplifier stage 1 is selected to be an inoperative state, the signal fed to the input terminal is supplied to the output terminal via the feedback circuit 2.
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