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This article presents a broadband fully integrated Doherty power amplifier (DPA) using a continuous-mode combining load. It is illustrated that the continuous-mode impedance condition in back-off and saturation for Doherty operation can be achieved with a simple impedance inverter network (IIN) that can be realized using lumped components in gallium nitride (GaN) monolithic microwave integrated circuits (MMICs). A DPA was designed and fabricated using the 250-nm GaN process to validate the proposed architecture and design methodology. The fabricated DPA chip attains around 8 W saturated power from 4.1 to 5.6 GHz. About 38.5%–46.5% drain efficiencies are achieved at 6-dB output power back-off within the entire design band. When driven by a 100-MHz OFDM signal with 6.5-dB peak-to-average power ratio (PAPR), the proposed DPA achieves better than −45-dBc adjacent channel leakage ratio (ACLR) and higher than 38% average efficiency at 4.4 and 5.2 GHz after digital predistortion.
Pang et al. (Wed,) studied this question.