Analysis and Design of Reconfigurable Multiband Mismatch-Resilient Quasi-Balanced Doherty Power Amplifier for Massive MIMO Systems

A novel power amplifier (PA) with wide bandwidth and load mismatch resilience is presented based on the quasi-balanced Doherty PA (QB-DPA) architecture. By reconfiguring the parallel/series QB-DPA operation modes with the nominal/exchanged biasing alternation and control of phase dispersion, the proposed QB-DPA topology can overcome the bandwidth limitations and ensure a standard Doherty profile and high efficiency and linearity against dynamic load mismatch over the operational bandwidth. Based on the theoretical analysis, a design guidance of output matching topology on phase offset implementation is presented. As a proof of concept, a physical prototype is demonstrated targeting for 1.7-2.7-GHz bandwidth. The developed QB-DPA achieves an efficiency of 56%-78% at OP1 dB and 47%-71% at 6-dB output back-off (OBO) over the in-band operation with 50-Omega load. Through reconfiguration (parallel/series mode for mismatch recovery and nominal/exchanged biasing for bandwidth extension), the developed QB-DPA demonstrates significantly improved OP1 dB variation both at center frequency 2.1 GHz and edged-frequency 1.7 and 2.6 GHz at 2:1 voltage standing wave ratio (VSWR) over 360 degrees phase span. In modulated measurement using 20-MHz longterm evolution (LTE) signals, >44.5% average efficiency and <-30.9-dBc adjacent channel power ratio (ACPR) are obtained across the wide bandwidth at matched-load condition. More importantly, for VSWR 2:1 circle, the high linearity [<5.3% error vector magnitude (EVM)] and average efficiency (>38.1%) can be experimentally maintained through reconfigurations.