III–V FET high frequency model with drift and depletion charges

A formulation and implementation of the III-V FET nonlinear charge model decomposed into a combination of univariate voltage depletion charges and a bivariate mixed voltage-current dependent “drift” charge is presented. The concept is based on the principles used in well-established BJT models where depletion and diffusion charges are modeled separately. Analogous to the diffusion charge in BJT models, the drift charge represents the mobile carriers in the channel of the FET. The total charge depends on the depletion capacitances, drain current, and transit time, which links the FET charge model directly to the physical operation of the device. A measurement-based prototype model is demonstrated for a GaAs pHEMT using artificial neural networks to define the analytical constitutive relations of the depletion and drift charges.