3-Way Doherty Power Amplifiers: Design Guidelines and MMIC Implementation at 28 GHz

This article presents the design strategy and the implementation of a three-way Doherty power amplifier (DPA3W) to enhance the efficiency at deep power back-off. Theoretical design equations are derived, based on which design charts are drawn to explore the available design space, accounting for practical constraints related to the available technology and selected application. The proposed design strategy is demonstrated by the design, fabrication and experimental characterization of a three-way multistage Doherty amplifier optimized for efficiency peaks at 6 and 12 dB back-off. The amplifier is realized on the WIN Semiconductors 150 nm GaN-SiC high-electron-mobility transistor (HEMT) monolithic process at 28 GHz, targeting 5G applications. The prototype achieves saturated output power in excess of 34 dBm and power added efficiency of the order of 15% from 6 to 12 dB back-off, demonstrating competitive performance and a good agreement between simulations and measurements, thus validating the approach.