Considerations for improving the accuracy of large-signal GaAs MESFET models 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 communications equipment. The validity of each modeling approach is examined by comparing simulations to the fundamental and harmonic output power of a MESFET using load pull to represent typical amplifier load lines. Two effects which are believed to influence model accuracy are considered: 1) low-frequency dispersion in output conductance, and 2) modulation of the threshold voltage as a function of drain-source voltage. The results suggest that improved modeling of the modulation in threshold voltage with respect to drain-source voltage provides significantly more accurate predictions. In contrast, for these applications, when conventional approaches for adding low-frequency dispersion effects to the model were implemented, inaccurate predictions resulted.<
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