Large-signal relaxation-time model for HEMTs and MESFETs

A nonquasistatic charge-conserving spline-based model has been implemented in the EEsof harmonic-balance simulator. The model uses a relaxation-time approximation to describe the intrinsic charging dynamics of unipolar transistors under arbitrary excitation. By describing the variation of instantaneous charges as a relaxation toward the time-varying steady-state target set by terminal bias, nonquasistatic behavior is accurately represented. Small-signal measurements are used to calculate the steady-state charges, currents, and time constants used in the simulation. Because these parameters are represented by bivariate splines, the characteristics of diverse transistors, including HEMTs (high electron mobility transistors) and MESFETs, have been accurately modeled. On-wafer large-signal measurements of HEMTs closely match simulation results.<>