Linearity metrics of pre-matched AlGaN/GaN RF transistor: multi-tone simulation and measurement analysis

Abstract

The present work provides a comprehensive analysis of non-linear distortions using Unequally Spaced Multi-Tone (USMT) signals under realistic modulated operating conditions. The investigation focused on USMT stimuli with 2, 4, and 6 tones, with the objective to assess large-signal performance of a pre-matched GaN HEMT device at 29 GHz manufactured by United Monolithic Semiconductors. Experimental measurements were conducted on-wafer and compared with nonlinear Harmonic Balance simulations, incorporating electromagnetic models for passive elements and the manufacturer’s design kit for active components. Furthermore, continuous-wave load-pull simulations were conducted to assess the optimal load impedance for maximum power-added efficiency (PAE). The findings indicate that increasing the number of tones results in a substantial decrease in drain current density due to trapping effects, along with a concomitant degradation in PAE. A corresponding reduction in adjacent channel power ratio (ACPR) was also observed, and an analytical relationship between ACPR and the number of tones was derived. The strong agreement between simulated and measured ACPR values serves to confirm the accuracy of the modelling approach and to validate the reliability of the measurement setup.