A Compact Ka-Band Integrated Doherty Amplifier With Reconfigurable Input Network

In this paper, we present the design of an ultracompact monolithic millimeter-wave integrated circuit Doherty power amplifier (DPA) using a novel reconfigurable input network at Ka-band. The proposed input network is formed by a compact broadside coupler and two additional field-effect transistors. By reconfiguring the relative phase offset between the main and auxiliary amplifiers, the DPA can be postoptimized to achieve high efficiency and maximal power gain flatness. More importantly, the DPA can be tuned for the highest performance at different frequencies. To verify the concept, a DPA is fabricated in a 0.15-μm enhancement mode Gallium Arsenide (GaAs) process and exhibits a measured output power of 26.5 dBm and gain of 11.8 dB at 28 GHz. The peak power-added efficiency (PAE) is 42%, and the PAE at 6-dB output power backoff (PBO) is 31%, respectively. With reconfigurable capability, the DPA can maintain high performance over a 3-GHz frequency band from 26.5 to 29.5 GHz. To the best of the authors' knowledge, the proposed DPA achieves among the highest backoff PAE over a wide bandwidth at Ka-band.