Design and analysis of three-way Doherty power amplifier with self-adaptive bias network

Abstract

This article presents a novel three-way Doherty power amplifier (DPA) incorporating a diode-based self-adaptive bias network (SABN) to extend the output power back-off (OBO) range and mitigate gain compression. The SABN dynamically adjusts the gate bias of the peaking devices based on input power, leveraging the rectification characteristics of a series-connected diode array. A comprehensive theoretical analysis is provided to illustrate the SABN’s operating principle and its impact on OBO extension and source termination. Following detailed design guidelines, a prototype is implemented using commercial gallium nitride high electron mobility transistors (GaN HEMTs) CG2H40010F. Measurement results demonstrate that the proposed DPA achieves a 10-dB OBO range with drain efficiency (DE) between 43% and 61% in back-off and saturated DE of 64%–74% over 1.6–2.15-GHz bandwidth (29.3% fractional bandwidth). The proposed DPA effectively alleviates gain compression in the peaking branch and maintains high efficiency across the targeted frequency band. When evaluated using the 20-MHz long-term evolution (LTE) signals at an average output power of around 35 dBm, the proposed DPA achieves the adjacent channel power ratio (ACPR) better than −47 dBc after linearization. To the best of the authors’ knowledge, this is the first work to employ an adaptive bias network (ABN) in a PCB-level three-way GaN-based DPA.