| 摘要 |
Disclosed is a power amplifier having highly stable and excellent controllability, and having low noise in comparison with conventional power amplifiers. With the power amplifier, a differential amplifier made up of transistors Q 1 , Q 2 is provided in the initial stage thereof, and baluns doubling as inter-stage matching circuits, comprised of Cp 1 , Cp 2 , Lp 1 , and Ct 1 , Ct 2 , Lt 1 , respectively, are provided between the initial stage, and a second stage while an unbalanced single-ended circuit is provided in the second stage. The differential amplifier has an emitter-coupled type configuration for coupling both emitters with each other, and output control of the amplifier in the initial stage is executed by varying current of a current source coupled to both the emitters.
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