| 摘要 |
PROBLEM TO BE SOLVED: To simplify the circuit constitution and to improve the process response of an amplifier circuit which is provided in radio communication equipment, etc., and is so variable in amplification factor that the amplitude of a signal is within a specified range or an amplifier circuit for protecting trailing- stage circuits. SOLUTION: An amplifier circuit is equipped with an amplifier 14 which amplifies an input signal and is so constituted that the amplification is varied according to the source current Is of the amplifier 14 and a transistor 22 which is provided to the power line 20 of the amplifier 14 and inputs at its control terminal a DC component generated by rectifying a branch signal Ib branched from the input signal and controls the source current so that the amplification factor of the amplifier 14 becomes smaller as the amplitude of the branch signal Ib is larger.
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