A tunable matching network for power amplifier efficiency enhancement and distortion reduction

Variable load technique has been proposed as a solution for improving the efficiency of power amplifiers at reduced drive levels. To provide variable load impedance to a transistor, various configurations for tunable matching networks may be used. However, many of them can introduce large AM-PM distortion. To avoid the degradation in linearity, a T-network that in principle causes no phase variation is presented in this work. A 1750-MHz medium power amplifier along with a tunable matching network using GaAs hyperabrupt varactor diodes is designed, fabricated, and tested. Experimental results for the power amplifier show that the power-added efficiency (PAE) at reduced power levels is enhanced when variable load is used. Meanwhile, lower AM-AM and AM-PM distortions are observed, demonstrating its potential for improving the efficiency as well as the linearity.