Efficiency versus linearity trade-off in an S-band class-AB power amplifier

This paper presents a design strategy to simultaneously optimize the efficiency and linearity of a single-device class-AB power amplifier, given minimum output power and gain requirements. The adopted linearity metric is the highest inter-modulation distortion in a two-tone test with 20MHz spacing. The simultaneous selection of optimum source and load terminations that provide the best trade-off among all of the requirements is described in detail, and the synthesis of the matching networks is then presented. A prototype is developed based on a 6W packaged GaN device around 3.5 GHz, manufactured and measured. According to the measured results, the amplifier achieves output power higher than 38dBm with associated gain higher than 12 dB and saturated power-added efficiency in excess of 73% in a single-tone test at 3.25 GHz, while providing a 33% power-added efficiency and -30 dBc inter-modulation distortion in the 20MHz two-tone test.