Design of a Compact GaN MMIC Doherty Power Amplifier and System Level Analysis With X-Parameters for 5G Communications

This paper presents a monolithic microwave integrated circuit Doherty power amplifier (DPA) operating at sub-6 GHz for 5G communication applications by a 0.25- \mu \text{m} gallium nitride high-electron mobility transistor process. A compact impedance inverter and output matching of the DPA are achieved using a transmission line network and shunt capacitors. Also, the size ratio of power cells in the main and auxiliary amplifiers is optimized for a high efficiency at output power backoff (OPBO). The measured peak output power ( {P}_{\text {out}} ) and the 1-dB compression point ( {P}_{{1\,\text {dB}}} ) are 38.7 and 32.1 dBm, respectively, at 5.9 GHz. The power-added efficiency at 6-dB OPBO is up to 49.5%. Without digital predistortion (DPD), the DPA can deliver an average {P}_{\text {out}} of 23.5 dBm with error vector magnitude (EVM)