Three-State Matching Technique for Designing Large Back-Off Doherty Power Amplifier

This paper presents a systematic design methodology for asymmetric Doherty power amplifiers (ADPAs) that explicitly considers multiple operational regions in the design of output matching networks. To enhance efficiency in the output back-off (OBO) region, the proposed approach employs Three-State Matching (TSM), in which the load-modulated impedance of the main amplifier is transformed into the transistor's optimal impedance at three distinct operating points. The method further incorporates an optimization process based on the optimal region (OR), where the input impedance trajectory of the matching networks is confined within the region identified by load-pull and source-pull simulations. To extend bandwidth, a post-matching network is employed to achieve robust impedance transformation. To validate the proposed technique, an ADPA utilizing 10 W and 30 W GaN HEMT devices was designed and fabricated for the n78 band (3.3-3.8 GHz) of 5G systems. Continuous-wave (CW) measurements confirm an OBO region of 9.5 dB with drain efficiency exceeding 45% across the target bandwidth. The results demonstrate that the proposed TSM-based design methodology effectively addresses efficiency degradation in the OBO region while ensuring wideband operation for next-generation wireless communication systems.