CONSIDERATIONS FOR IMPROVING THE ACCURACY OF LARGE-SIGNAL GAAS-MESFETMODELS TO PREDICT POWER-AMPLIFIER CIRCUIT PERFORMANCE

Several approaches to large-signal GaAs MESFET modeling are considered as they apply to the design of high-efficiency portable communication s equipment. The validity of each modeling approach is examined by com paring simulations to the measured fundamental and harmonic output pow er of a MESFET using load pull to represent typical amplifier load lin es. Two effects which are believed to influence model accuracy are con sidered: 1) low-frequency dispersion in output conductance, and 2) mod ulation of the threshold voltage as a function of drain-source voltage . The results suggest that improved modeling of the modulation in thre shold voltage with respect to drain-source voltage provides significan tly more accurate predictions. In contrast, for these applications, wh en conventional approaches for adding low-frequency dispersion effects to the model were implemented, inaccurate predictions resulted.