A source modulated amplifier in GaN designed for baseband PWM and direct filter connection

Abstract

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 source modulated amplifier offers these properties. Its general operational principle is presented and an implementation study in a GaN MMIC process was carried out. The designed PA operates at 2.65 GHz delivering a maximum output power of 3W. 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 performed, resulting in a compact solution.

Equivalent load impedance of pulse width modulation excited band pass filters

“…This problem can be solved by removing the isolator as depicted in Figure 1b and integrating the filter into the matching network [4][5][6][7][8]. The reflections of the filter are now used to achieve efficiency enhancement [4][5][6][7][9][10][11][12][13]. All these methods have in common that they use BB PWM to drive the PA and the following BPF.…”