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 (OP
_1
dB
), as well as peak output power (P
_sat
) and energy efficiency (PAE
_peak
and PAE
_1
dB
) 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 P
_sat
and 32.2% PAE
_1
dB
at 20.2-dBm OP
_1
dB
at a nominal 50-Ω load. The reconfigured PA demonstrates an 18.5-19.12-dBm OP
_1
dB
with a high PAE
_1
dB
of 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 P
_out
of 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 P
_out
is achieved at an rms EVM of -24 dB under a full-span 3:1 antenna VSWR with a 100-MSym/S 64-QAM signal.