A common drain parallel amplifier in GaN using baseband PWM and direct filter connection for efficiency enhancement

To cope with the increasing demand for bandwidth in wireless communications coding schemes with high crest factors are employed. As a result the power amplifier (PA) is operated far below maximum output power for most of the time leading to low average efficiency in traditional designs. Therefore PA concepts providing efficiency enhancement in back off are key for efficient transmitters. Baseband PWM operated PAs in combination with direct filter connection are possible candidates. Due to the constant current of the used filters special PA structures are required. The proposed parallel common drain amplifier offers this properties. Its general operational principle is explained and an implementation study in a GaN MMIC process is presented. The designed PA operates at 2.65 GHz delivering a maximum output power of 3 W. To get optimum performance of the direct filter connection a codesign of the PA and the cavity filter included in the output matching network was done, resulting in a compact solution.