A Fully Integrated C-Band GaN MMIC Doherty Power Amplifier With High Efficiency and Compact Size for 5G Application

Abstract

This paper presents a fully integrated C-band Doherty power amplifier (DPA) based on a 0.25-μm GaN-HEMT process for the 5G massive MIMO application. The performance degradation caused by nonlinear output capacitance is analyzed, and a novel compensation technique is proposed. A low-Q output network is employed to broaden the bandwidth, and its insertion loss in the back-off region is demonstrated to be mainly decided by the Q-factor of the drain bias inductor of the main PA. Hence, by adopting on-chip transmission lines with high Q-factors for drain biasing, a full integration, and a low loss can be achieved simultaneously. Reversed uneven power splitting and back-off input matching are proposed for gain enhancement. The fabricated DPA demonstrates a small-signal gain of 8.6-11.6 dB, an output power of 40.4-41.2 dBm, a 6-dB back-off drain efficiency (DE) of 47% - 50%, and a saturation DE of 55%-63% across a wide bandwidth from 4.5 to 5.2 GHz, with an ultra-compact size of 2.2 mm × 2.1 mm. Using a 40-MHz LTE signal with a 7.7-dB peak-to-average power ratio at the carrier frequency of 4.9 GHz, the measured average output power and efficiency are 33 dBm and 43%, respectively. The raw adjacent channel power ratio is -29 dBc and is improved to -46 dBc by applying digital predistortion.