A Reconfigurable Hybrid Series/Parallel Doherty Power Amplifier With Antenna VSWR Resilient Performance for MIMO Arrays

Antenna load impedance variations typically cause significant power amplifier (PA) performance degradation, including output power, large-signal linearity, and peak/average PA efficiency, which are especially critical for modern millimeter-wave (mm-Wave) communications with spectrally efficient complex modulations. To address this problem, we propose a reconfigurable hybrid series/parallel Doherty PA with a 90°coupler-based active load modulation network. By reconfiguring the series/parallel Doherty operation modes, the strengths of the Main/Auxiliary PAs, and their relative phase, linear output power (OP1dB), as well as peak output power (Psat) and energy efficiency (PAEpeakand PAE1dB) of the PA can be largely restored under full-span 360° antenna impedance variations. The theoretical analysis and design guidelines are both presented in this article. As a proof of concept, a 39-GHz reconfigurable hybrid series/parallel Doherty PA is fabricated in the Global Foundries 45-nm RF CMOS silicon on insulator (SOI) process with a 2-V PA supply and 1-V driver supply. At 39 GHz, the PA achieves a 33.3% peak power-added efficiency (PAE) at 20.8-dBm Psatand 32.2% PAE1dBat 20.2-dBm OP1dBat a nominal 50-Ω load. The reconfigured PA demonstrates an 18.5-19.12-dBm OP1dBwith a high PAE1dBof 20.6%-25.3% at 3:1 antenna voltage standing wave ratio (VSWR) over 360° angles. The PA achieves an rms error vector magnitude (EVM) of -23.6 dB/-22.8 dB/-23.1 dB at an average Poutof 13.8 dBm/12.2 dBm/11.5 dBm with 100 MSym/S/500 MSym/S/1 GSym/S single-carrier 64-quadratic amplitude modulation (QAM) signal, respectively, at a nominal load of 50 Ω. A greater-than 11.2-dBm average Poutis achieved at an rms EVM of -24 dB under a full-span 3:1 antenna VSWR with a 100-MSym/S 64-QAM signal.