A Broadband Outphasing GaN Power Amplifier Based on Reconfigurable Output Combiner
Weiwei Wang, Shiping Li, Shichang Chen, Jialin Cai, Yuanchun Li, Xin Yu Zhou, Giovanni Crupi, Gaofeng Wang, Quan Xue
Abstract
This article introduces a broadband outphasing power amplifier (OPA) design in virtue of a reconfigurable output combiner. Two T-type matching structures loaded with varactors are applied to replace the transmission lines in the conventional architecture. To have broadband performance, the bias voltage applied to the varactors is adjusted when the frequency changes, ensuring proper phase shifting amounts required for outphasing operation. This technique compensates for the frequency dispersion effects inherent in the conventional combiner. Besides, to provide the subamplifiers with correct reactance compensation and impedance in a large frequency band, a postmatching network (PMN) is further employed. These design strategies help to improve the bandwidth and drain efficiency (DE) of the whole OPA. For demonstration, a prototype circuit is successfully implemented using two 10-W GaN HEMT transistors. At 6-dB back-off (BO) power, over 49.3% DE is achieved from 2.4 to 2.8 GHz, accounting for 15.4% fractional bandwidth. In addition, a minimum of 63.6% DE is maintained at saturation in the same frequency band.