Device-Level Intrinsic Linearity Optimization of GaN Power FETs BAsed on Volterra Series Technique for Highly Linear RF Power Amplifier Design
Final Report Abstract
This project aimed to characterize and model GaN HEMT linearity, in form of IMD behavior, with Volterra series techniques, in order to obtain a deeper insight into the relationships between improvements of this performance and physical device effects, like those produced by field-plate structures. The research activities in the project have carefully crafted a novel modeling strategy, regarding the most important aspects like an improved extraction of extrinsic parameters of the small-signal model, the thorough identification of Volterra series coefficients and the measurement techniques for vectorial IMD characterization. The implementation of our measurement setup to the specific characterization with two-tone input signals with capture of full spectra, that is, with magnitude and phase information took more time than expected. This difficulty and delay represent the main unexpected setback in the development of the project, whereas it is worth noting that the extra work was well worth it, regarding the astoundingly good agreements of model predictions with measurements that were obtained during the project. As results of the project, accurate IMD predictions have been obtained for different device sizes and different field-plate structure. The IMD models with Volterra series that have been created have the ability to separate vectorial components of the IMD products and relate them to model parameters that directly represent physical device effects. For example, vectorial IMD analysis has shown mutual cancellations of IMD components related to different model parameters, which result in an improved linearity As final contribution of this project an extension of Volterra series model to large-signal operation has been applied successfully for GaN HEMTs for the first time.
