Highly efficient linear power amplifier for 3.5 volt NADC cellular applications

A highly efficient linear power amplifier has been developed for North American Digital Cellular (NADC) mobile radio telephones operating with 3.5 volt batteries. The amplifier consists of two cascaded gain stages to achieve 25 dB gain at greater than 1 W output power with a corresponding power added efficiency of 50% at IS-136 specified ACPR linearity levels. The amplifier is realized using GaAs PHEMT devices to provide superior performance in optimizing the efficiency/linearity trade-off for this digital modulation format. Size of the amplifier is minimized by placing most of the circuitry on a single GaAs IC. An exception is the output matching circuitry where high Q lumped elements are selected to minimize loss. The circuit topology is chosen based on a design methodology where a large signal model of the PHEMT device is combined with behavior analysis techniques such that performance of the amplifier is simulated for a /spl pi//4 DQPSK modulated signal. This approach proved successful in sizing the FET devices as well as examining the performance improvements offered in using selected fundamental and harmonic terminations.