Abstract

This paper presents a non-linear p-HEMT model taking into account the non quasi-static currents and charges variations versus Vgs and Vds to predict accurate behaviour of the devices up to millimetric frequencies. The major refinement of this model concerns the introduction of voltage dependant 2 nd order frequency coeficients (1 st order non quasi-static terms) generally considered constant or partially variable in previous published models. The non quasi-static ehaviour of the transistor is modelled by time second derivatives of non-linear functions Ags(vgs,vds) and Ads(vgs,vds) integrated from linear 2 ndorder frequency coefficients. Classical method are used to extract non-linear elements from pulsed S-parameters and current measurement set-up [1]. Most of the voltage dependant coefficients (currents, charges and non-quasi-static terms) are precisely fitted with bicubic spline functions for very accurate description. This model has been implemented in commercial balance harmonic software. Ags and Ads tim second derivatives are generated partially in the non-linear part of the model (time first derivative considered as charge derivative) and partially with a linear sub-circuit (second derivative). This model would predict more accurate 2nd and 3 rd harmonics behaviour for applications at fundamental frequencies up to 20 GHz.