| 摘要 |
A power amplifier circuit comprises an amplifying transistor and a dc bias circuit. The dc bias circuit comprises a first transistor in a current mirror with the amplifying transistor, and a second transistor to provide the base currents to both the amplifying transistor and the first transistor. A dc bias power source is coupled to the base of the second transistor through a resistor and an inductor connected in series. A bypass capacitor is coupled between a ground and a node between the resistor and the inductor. Thus, the reduced voltage drop across the base-emitter junction of the amplifying transistor due to an increased input power is compensated. Furthermore, by properly scaling the emitter area ratio between the amplifying transistor and the first transistor, and/or the ratio between a bias resistor and a corresponding resistor coupled with the mirroring first transistor, the quiescent current in the amplifying transistor can be made to be in direct proportion to that of the first transistor.
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