Highly efficient three-stage Doherty power amplifier with adaptive driving amplifier for 3.5 GHz WiMAX applications

This paper describes a new three-stage Doherty power amplifier (DPA) with an adaptive driving amplifier inserted at the input of the carrier cell. This driving amplifier controls the input power of the carrier cell to eliminate the gate leakage current at high input power levels. Using an envelope tracking technique, the gate bias voltage of the driving amplifier is adjusted according to the input power levels. For verification, the driving amplifier, carrier, and peaking cells are fabricated using 10-W, 15-W, and 35-W GaN HEMTs, respectively, at 3.5 GHz. For a continuous wave signal, total drain efficiencies (DEs) of 37.3% and 45.6% are achieved at approximately 9.5- and 4.3-dB back-off powers (BOPs), respectively. For a worldwide interoperability for microwave access (WiMAX) signal, the proposed DPA has a total DE of 39.5 % at an 8-dB BOP.