Lumped Element Behavioural High Voltage MOS Model

Abstract

High voltage MOS transistors usually have a drift zone in the drain region. The conductivity of this drift zone is strongly dependent on the flowing current and gate voltage. Thus it has generally to be modelled with a variable resistance representing the effects on the current. The goal of this work is to show a phenomenological macro model including AC modelling. The model is restricted to a lumped element sub-circuit, which can be processed by a standard Spice simulator. A drain resistance can be described by a behavioural source and a resistance in series. The source could be a current or voltage source controlled by drain current and gate voltage. The example discussed in this paper describes a sub-circuit containing a current source with a resistor in series as well as a model of the voltage dependent gate to drain capacitance. One of the most important goals of development was a fast convergence of the transient simulation. This was achieved by a restriction of the mathematical formula for the current function. The model is tested by means of a ring oscillator. The results have been satisfactory for DC, AC as well as transient analysis