Energy-efficient doherty power amplifier MMIC and beamforming-oriented digital predistortion for 5G massive MIMO application

We present an energy-efficient Ka-band asymmetrical Doherty power amplifier (DPA) MMIC in a 0.15-μm E-mode GaAs pHEMT process in this paper, which is dedicated for 5G massive MIMO application. A novel design method is employed to remove the offset line behind the main power amplifier, resulting in a compact chip size of 2.1 mm × 1.7 mm, and a large bandwidth of 2.8 GHz. The DPA achieves a saturation output power of 25.7 dBm-26.8 dBm, a peak PAE of 31%-38%, and a PAE at 7 dB back-off of 21%-30% from 29 GHz to 31.8 GHz. In addition, a beamforming-oriented digital predistortion (DPD) scheme for 5G Massive MIMO system is proposed to reduce the number of feedback paths and predistorters, this technique includes only one predistorter and a shared feedback path for the whole array, which greatly simplifies the conventional massive MIMO hybrid beamforming transmitters. The experimental results show that the proposed technique and linearization angle range broadening method achieve up to 15 dB adjacent channel power ratio (ACPR) improvement and 10° linearization angle range in main beam direction.