Load and Frequency Independent Doherty Power Amplifier Back-Off Extension

IEEE Transactions on Microwave Theory and Techniques, vol. 72, pp. 3438–3451

Abstract

This article presents the principle of extending the back-off efficiency of a three-stage Doherty power amplifier (DPA) by substituting the second load modulation stage using a load transformation stage. Thereby, the DPA output combiner is split into two independent circuits so that the second peaking PA, peaking II, can act as a reflector for the DPA instead of additionally loading the combiner. The derived design equations introduce the flexibility to maintain the load of a stand-alone DPA and, therefore, the frequency response. The independence between the DPA and peaking II offers extremely large output power back-off (OBO) implementations up to 20-dB OBO while maintaining the bandwidth of a two-way DPA. With a detailed analysis of the design considerations and limitations, a design space for the DPA and RDPA combiner as well as a pure S-parameter-based bandwidth prediction and circuit design method is derived. Thereby, an ultracompact DPA combiner with an$\uplambda_0/20$-length impedance inverter is implemented. To further validate the proposed design technique, a 19-dB OBO RDPA with 80-W peak envelop power (PEP) and 35% relative bandwidth from 2.1 to 3 GHz is fabricated. Moreover, the RDPA concept can also be applied to double the OBO of the already existing DPA implementations.

Authors 5

1. Florian Dietrich Aachen Chair of High Frequency Electronics

   RWTH Aachen University

   Affiliation as printed

   Chair of High Frequency Electronics (HFE), RWTH Aachen University, Aachen, Germany

2. Muh‐Dey Wei Aachen Chair of High Frequency Electronics

   RWTH Aachen University

   Affiliation as printed

   Chair of High Frequency Electronics (HFE), RWTH Aachen University, Aachen, Germany

3. Eduard Heidebrecht Aachen Chair of High Frequency Electronics

   RWTH Aachen University

   Affiliation as printed

   Chair of High Frequency Electronics (HFE), RWTH Aachen University, Aachen, Germany

4. David Bierbüsse Aachen Chair of High Frequency Electronics

   RWTH Aachen University

   Affiliation as printed

   Chair of High Frequency Electronics (HFE), RWTH Aachen University, Aachen, Germany

5. Renato Negra Aachen Chair of High Frequency Electronics

   RWTH Aachen University

   Affiliation as printed

   Chair of High Frequency Electronics (HFE), RWTH Aachen University, Aachen, Germany