| 摘要 |
PROBLEM TO BE SOLVED: To variably set an output power without damaging signal quality and also to ensure power efficiency to be sufficiently highly. SOLUTION: This amplifier is provided with connecting transistors 21 and 22 in multistage which perform power amplification of a high frequency signal, a bias current setting circuit 23 which variably sets the bias current of the transistor 22 on the last stage according to requested output power and adjusts its power efficiency and a feedback circuit 24, which feedbacks the output of the transistor on the last stage to the transistor of the preceding sage side and maintains entire gain of the amplifier. Then, the amplifier varies the output power, while maintaining the power efficiency high and signal quality at a constant level by holding the entire gain at a constant level.
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