Multiple time constant modeling of dispersion dynamics in hetero field-effect transistors

A new approach to the modeling of frequency dispersion effects encountered in the drain current characteristics of state-of-the-art hetero field-effect transistors is presented. The empirical, equivalent-circuit based model is dedicated to efficient microwave circuit design and allows for the inclusion of individual dispersion effects, taking into account their respective time constants. The proposed topology allows for small- and large-signal analysis in both the time and frequency domains. Parameter extraction and verification of the model is carried out using pulsed-I-V and dc measurements as well as microwave frequency S-parameter characterization of both a GaAs pseudomorphic high electron mobility transistor (pHEMT) and an InP pHEMT technology. Finally, the model is employed in the design and realization of a GaAs pHEMT traveling-wave monolithic microwave integrated circuit. Simulation results are compared to measurements with a focus on figures of merit which are affected by frequency dispersion