Design of a 12dB back-off asymmetric Doherty power amplifier using reactive output impedance

抄録

This paper presents a method to extend the back-off range of an asymmetric Doherty power amplifier (DPA) to 12dB using a reactive output impedance of the peaking amplifier. An analytical method is employed to determine the desired reactive output impedance for specific output power back-off (OPBO) range. Then, a peaking output matching network is designed to achieve the desired impedance to enlarge the efficiency of the carrier amplifier. When compared with conventional design, the OPBO range can be improved by about 2dB using the proposed method. For verification, a 3.4-3.6GHz asymmetric DPA with enhanced OPBO range was designed using 10 and 30W GaN HEMT transistors. The measured efficiencies of 47%-49% at 12dB back-off and 63%-66% at saturation are obtained over the whole frequency range. For a 40MHz LTE signal at 3.5GHz, the adjacent channel leakage ratio is -50dBc after linearization with an average efficiency of higher than 50%.