Broadband GaAs HBT Doherty Power Amplifier Using Lumped Compensation Network and Input Phase Correction for 5G Applications

This paper presents a broadband Gallium Arsenide (GaAs) heterojunction bipolar transistor (HBT) Doherty power amplifier (DPA) that employs a lumped compensation network (LCN) and input phase correction technique for 5G applications. A LCN is utilized with an integrated impedance inverter to enhance output power back-off (OBO) efficiency across a wide frequency range. To mitigate the overdrive issue caused by the LCN under saturation, different input phase strategies are analyzed, and an on-chip coupler-based input phase correction network is introduced to maintain a constant phase difference between the carrier and peaking paths. The DPA is implemented using a 2μm GaAs HBT process and achieves broadband operation over 3.1-4.3 GHz with a fractional bandwidth exceeding 32%, covering the 5G n77 and n78 bands. Measurement results demonstrate a saturated output power of 32.73-33.77 dBm with a saturated power-added efficiency (PAE) of 39.54%-46.51%, a small-signal gain of 22.19-25.30 dB. At 6 dB OBO, the DPA maintains a PAE of 30.84%-34.95%. When tested with a 100 MHz bandwidth 64-QAM signal with 5.6 dB PAPR, the DPA achieves an average PAE of up to 34.3% and an adjacent channel power ratio (ACPR) better than -45.2 dBc after digital predistortion (DPD), demonstrating its potential for wideband 5G terminal applications.