Efficient solutions for GaN power amplifiers

Over the past decade, wireless applications have expanded rapidly across sectors like cellular networks, vehicular communication, and industrial systems. The transition to 5G addresses these needs with enhanced reliability, low latency, and cost-effective solutions. To meet gigabit-level wireless traffic, millimeter-wave frequencies are essential. RF power amplifiers (PAs) are critical to boosting signals but face challenges with high peak-to-average-power-ratio (PAPR) signals in modern modulation schemes. Recent semiconductors such as Gallium Nitride (GaN) are promising solutions due to high power density and potential for integration. Moreover, dynamic adjustment of PA performance and multi-band operation are increasingly important. While many solutions exist, bandwidth and frequency constraints limit their commercial impact. Two key areas are addressed in this thesis for improving GaN PA efficiency. First, it delves into the impact of trapping effects, which can significantly degrade device performance. A new characterization technique is developed, based on drain current transient (DCT) measurements, to assess figures of merit such as gate and drain lag, trap activation energy, cross-section, and carrier density reduction. This approach reduces characterization time while providing valuable insights into the relationship between the physical structure of HEMTs and their susceptibility to trapping effects. The second focus is on integrating varactor devices into PA output matching networks to enable reconfigurable architectures. Existing GaN-on-SiC diodes are characterized to assess their viability as integrated alternatives to discrete components. After this preliminary research, the extraction of suitable models to allow CAD simulations is required. A novel automatic modeling procedure, employing vector network measurements, is developed to accurately characterize and model varactor device behavior. This procedure generates a lumped-element circuit representation, facilitating the simulation and optimization of the matching network for improved PA efficiency and adaptability. A matching network integrating varactors is also proposed and a preliminary evaluation of PAs with modified varactor devices is presented.