Improved phase linearity in source field plate AlGaN/GaN HEMTs

The benefits of using source field plate (FPS) in AlGaN/GaN HEMTs to reduce the phase distortion in efficient power amplifiers (PAs) is demonstrated in this contribution. The link between phase distortion of a PA and the drain-to-gate feedback parasitic capacitance of the transistor is shown. This link leads to critical phase nonlinearity expecially when architectures based on output load modulation, as the Doherty topology, are adopted. The FPS effect in reducing the feedback parasitic capacitance and, thus, the AM/PM distortion of the PA is verified. For experimental validation two AlGaN/GaN HEMT structures, with and without FPS, are realized and compared in order to extract the effects of FPS. Source-load pull characterizations are performed on both structures in order to verify the benefits of FPS on phase distortion, both in fixed and modulated output load conditions.