Design Scheme for Dual-Band Three Stage Doherty Power Amplifiers

This paper presents the analysis and design of dual-band/three stage Doherty Power Amplifier (DPA). The DPA is implemented using three 10-W packaged GaN-HEMT devices from CREE, with the target of high drain efficiency at 6 and 9-dB output power back-off (OPBO), while operating at 1.7 GHz and 2.4 GHz. At 1.7 GHz, the drain efficiency is better than 51% at both 6 and 9 dB OPBO. The corresponding drain efficiency measured at 2.4 GHz is better than 45.5% for both 6 and 9 dB OPBO. The concurrent operation with simultaneous excitation at 1.7 GHz and 2.4 GHz, results into the aggregated efficiency better than 41% upto 9 dB OPBO. The modulated measurement at 1.7 GHz using one carrier WCDMA signal of 7 dB PAPR shows average efficiency of 53.25%. However, with the input excitation of 5 MHz WiMax signal of 7 dB PAPR at 2.4 GHz, the average efficiency is about 51%. The designed DPA is linearized using digital predistortion with proper mask qualification for both WCDMA and WiMax signals.