Ultra-Wideband Dual-Mode Doherty Power Amplifier Using Reciprocal Gate Bias for 5G Applications

A novel architecture to extend the bandwidth of the Doherty power amplifier (DPA) is presented in this article. It is illustrated that two DPA modes at different frequency bands can be realized by simply swapping the gate biases of the transistors without changing the matching circuits, and hence, ultrawide bandwidth can be achieved by using a single load modulation network in DPA. A dual-mode DPA with 2.8-4.1-GHz bandwidth for Mode I and 2.2-2.7-GHz/4.2-4.8-GHz bandwidth for Mode II using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated DPA attains a measured 7.5-11.7-dB gain and 39.2-41-dBm saturated power. 35.0%-49.7% drain efficiency is obtained at 6-dB output power back-off for the designed dual-mode bands. When driven by a ten-carrier 200-MHz OFDM signal with 7.7-dB peak-to-average power ratio, the proposed DPA achieves adjacent channel leakage ratio of better than -50 dBc after digital predistortion at 2.5 GHz/3.5 GHz/4.5 GHz with an average efficiency of 46.0%/35.7%/33.0%. This simple configuration provides a promising solution for 5G, where multiple frequency bands in sub-6 GHz will be deployed.