Linearity-Enhanced Quasi-Balanced Doherty Power Amplifier With Mismatch Resilience Through Series/Parallel Reconfiguration for Massive MIMO

A reconfigurable series/parallel quasi-balanced Doherty power amplifier (QB-DPA) is presented with a unique capability of maintaining high linearity and high efficiency against load mismatch, which is highly desirable for massive multiple-input–multiple-output (MIMO) and active array applications. Based on the new QB-DPA topology derived from an ideal balanced amplifier, it is, for the first time, discovered that QB-DPA can be reconfigured between series- and parallel-DPA modes by setting the isolation-port loading to the ground and open circuit, respectively, and exchanging the roles of main and auxiliary amplifiers. Expanding from the ideal Doherty modes, the isolation port can be loaded with small reactance (susceptance) for linearity enhancement of series (parallel) QB-DPA. Furthermore, by leveraging the symmetry of series and parallel modes with complementary sensitivities to load impedance/admittance, it is theoretically proved that the QB-DPA can be strongly mismatch-resilient. Based upon the comprehensive and conclusive theoretical analysis, a physical prototype demonstration is practically presented using the GaN technology at 3.5 GHz. In modulated measurement using Long-Term Evolution (LTE) signals, the developed QB-DPA exhibits excellent linearity, e.g., <1.6% error vector magnitude (EVM) and high average efficiency of 45% at the rated averaged power in the nominal 50-
$\Omega $
condition, which compares favorably with state of the art. More importantly, through only a two-state adaption (using silicon-on-insulator (SOI)-based switches) of reactive loading at the output isolation port together with optimized gate biasing, the high linearity (<4% EVM) and average efficiency (>31%) can be experimentally maintained up to 2.5:1 of voltage standing wave ratio.