A smooth and derivable large-signal model for microwave HEMT transistors

In this paper we present the Smoothed Piecewise Linear (SPWL) model as a useful tool for device modeling problems. The SPWL model is an extension of the well-known canonical piecewise linear model proposed by Chua, which substitutes the abrupt absolute value function for a smoothing function (the logarithm of hyperbolic cosine). This function makes the model derivable; moreover the smoothness of the global model can be controlled by means of a single smoothing parameter. The parameters of the model are adapted to fit the nonlinear function, while the smoothing parameter is selected according to derivative constraints. The proposed SPWL model is successfully applied to model a microwave HEMT transistor under optical illumination using real measurements.