Design of Wideband Doherty Power Amplifier Using Inverse Continuous Class-F Mode

This paper presents the theory and design method of a wideband Doherty power amplifier (DPA) using inverse continuous class-F mode (ICFM). It is illustrated that continuous class-F-1 mode impedance condition can be achieved for Doherty operation using a simple load modulation network (LMN). The required LMN parameters and corresponding load modulation process are analyzed and calculated in theory. The post-matching architecture is then employed to realize the proposed ICFM-DPA with equivalent transmission line (TL) based LMN, which absorbs the parasitic and package parameters of the active devices. To validate the proposed ICFM-DPA architecture and design method, a physical DPA prototype using commercial gallium nitride (GaN) transistors is then designed and implemented with wider than 44% fractional bandwidth. The fabricated ICFM-DPA achieves saturated output power of 42.6-43.3 dBm with peak efficiency of 66.0%-74.6% throughout the target bandwidth. At 6 dB output power back-off (OBO), 57.0%-61.5% back-of efficiency is obtained by the implemented ICFM-DPA with power gain of 13.5-16 dB.