Broadband GaAs HBT Doherty Power Amplifier for 5G NR Mobile Handset

This paper proposes a broadband flat-gain Doherty power amplifier (DPA) for 5G new radio (NR) mobile handsets. It is implemented by the heterogeneous integration of GaAs HBT process for PA die and 6-layer laminate for output network. To realize wideband Doherty-operation, an on-laminate transformer with three π-shaped networks is designed. Meanwhile, the parallel coupling of on-chip spiral inductors is introduced into input quadrature power splitter and interstage matching network to extend bandwidth and reduce size. Mechanism of the proposed DPA is analyzed and a prototype is implemented for verification. For continuous-wave (CW) signal, saturation power of 36-dBm and comparable peak power added efficiency (PAE) of the DPA at 3.3, 3.75 and 4.2 GHz are realized. Within the 6-dB power back-off (PBO) range, the measured PAE is higher than 27%. Flat gain within n77 band (3.3 -4.2 GHz) is obtained, varying from 25.8 dB to 27.2 dB. Under the excitation of 5G NR 100-MHz QPSK signal, the proposed DPA delivers a PAE of 26.2% -30.3% with the averaged output power of 30 dBm in n77 band. The corresponding lower and upper adjacent channel leakage ratios (ACLRs) are measured from -32.1 dBc to -36.5 dBc without digital pre-distortion (DPD). The size of die is 1.34 × 1.44 mm2, and the occupied core area of laminate is 1.69 × 3.85 mm2.