ADAPTIVE BIAS CIRCUIT FOR POWER AMPLIFIER

摘要

PURPOSE: An active bias circuit for power amplifier is provided to improve the efficiency and the linearity of the power amplifier by obtaining an optimized quiescent current value according to an output power level of the power amplifier. CONSTITUTION: A power amplifier is formed with the first transistor(Q1) for amplifying the power of an input signal. A choke coil(RFC) is connected between a power source and a collector of the first transistor. A current driver transistor is formed with the third transistor(Q3). The fourth transistor(Q4) is used for sinking the current of a base of the third transistor to an earth portion. The second transistor(Q2) is used for increasing the intensity of a collector according to the intensity of the current of the input signal. A bypass capacitor(Cb) is connected between a collector of the second transistor and the earth portion to bypass the amplified signal of the second transistor to the earth portion. The second resistance(R2) is connected between a regulated power source and the collector of the second transistor to vary a voltage of the collector of the second transistor.