The validity of the quasi-static GaAs FET model

Large-signal equivalent circuit FET models rely on the validity of the quasi-static assumption. That is to say that the element values are assumed to change instantaneously with their controlling voltages and that these voltage relationships do not vary with time. This assumption is used to construct microwave frequency models from elements whose nonlinearities have been established with respect to DC bias voltages. However, low frequency dispersion effects are known to degrade GaAs MESFET performance, and this compromises the accuracy achievable by this approach. The authors report on an investigation into the validity of GaAs MESFET models which are based on DC I-V characteristics and consider the effectiveness of simple linear correction factors. The use of a fast pulse technique is compared, which provides a direct measurement of the large-signal dynamic performance of the FET current generators.<>