Modified Three-Way Doherty Power Amplifier Design Using Simplified Transistor Model Assisted Optimization for Ultra-Wideband Applications

Abstract

This paper presents the design and realization of an ultra-wideband three-way Doherty power amplifier (DPA). A modified load modulation network (LMN) with very simple circuit structure is proposed to enhance the bandwidth of three-way DPAs. An equivalent transmission line (TL) network is employed to construct the proposed LMN, which absorbs the package and parasitic parameters of the active devices. Meanwhile, the complex combining load is also employed to further improve the broadband performance of the proposed three-way DPA. To streamline the design process for complex power amplifiers (PAs), we introduce a tailored, expedited approach that harnesses a simplified transistor behavioral model and corresponding design methodology. This methodology significantly diminishes the complexities associated with multi-way DPA designs, enabling the swift completion of initial design iterations. To validate the proposed circuit architecture and design strategy, a three-way DPA with a bandwidth spanning more than one octave is designed and fabricated using commercial Gallium Nitride (GaN) devices. The fabricated three-way DPA achieves efficiency higher than 46% at 6 dB output power back-off (OBO) throughout the band from 0.7 GHz to 2.3 GHz, with a small signal gain of 11.7–13.9 dB. At saturation, 43.9–46.4 dBm output power can be obtained with peak efficiency of 58.9–78.1% . The modulation signal test has also been completed with a 64 QAM signal which has a PAPR of 6.7 dB and a bandwidth of 10 MHz, ACPR better than −20.8 dBc has been achieved.