Extension of High-Efficiency Range of Doherty Amplifier by Using Complex Combining Load

In this paper, a novel Doherty power amplifier (DPA) configuration with a complex combining load (CCL) is presented to extend the high-efficiency range of the amplifier. Theoretical analysis of dynamic load span, current ratio, and drain efficiency reveals that CCL can offer a new degree of freedom to boost the output back-off (OBO) of the DPA. For verification, a 2-GHz equal-cell GaN HEMT-based DPA is simulated, prototyped, and measured with both complex and resistive combining loads (RCLs). Under continuous wave (CW) excitation, measurement results show that the proposed DPA can attain an OBO of 9.1 dB, which is 3.6 dB higher than that of the RCL design. In addition, by the use of single-carrier WCDMA signal with peak-to-average power ratio of 9.6 dB and at an average output power of 33.2 dBm, the proposed design is found to deliver an average drain efficiency of 57.4%. In the absence of multi-cell or enlarged auxiliary device, this approach offers a low-cost and simple DPA solution with extended OBO, as well as good Doherty behavior.