Dual‐Mode Coupler‐Based Asymmetrical Doherty Power Amplifier for Compensating Load Mismatch

ABSTRACT Though the output back‐off (OBO) range of a load insensitive Doherty power amplifier (DPA) can be improved through multi‐way load modulation techniques, it will significantly increase the circuit complexity. This paper presents an asymmetrically biased coupler‐based Doherty power amplifier (ABCB‐DPA) with two operation modes for enhancing the high efficiency power range under varying load conditions. The proposed ABCB‐DPA uses two same active devices, while different drain supply voltages are adopted by the carrier and peaking power amplifiers (PAs). Based on the asymmetrical drain bias voltage, the current as well as the OBO range of the ABCB‐DPA is analyzed. To against load variation, the ABCB‐DPA is reconfigured between parallel and serial DPA operation modes. This is achieved by reciprocally changing the gate and drain bias voltages of the two active transistors as well as the isolation terminal of the output coupler. Theoretical analysis indicates that the ABCB‐DPA can maintain good performance over an extended OBO range even under a varying load condition. A 2.0 GHz ABCB‐DPA prototype is implemented to verify the proposed method. Under a matching condition, the fabricated ABCB‐DPA achieves a saturation output power of 43.4 dBm, a saturation drain efficiency (DE) of 66.4%, and an 8 dB back‐off DE of 54.9% in two operation modes. Moreover, over the entire 2:1 VSWR circle, the fabricated ABCB‐DPA maintains a 9 dB back‐off DE of 45%.