Analytical bias dependent noise model for InP HEMT's

Abstract

A practical device model for both high frequency small signal and noise behavior of InP-HEMT's depending on both gate and drain voltage has been developed. The model is based on the two-piece linear approximation using charge control and saturation velocity models. Combining large signal model and analytical expressions for the noise source parameter P, R, and C, an analytical bias-dependent noise model can be obtained. For implementation into high frequency simulation software, the exact calculated bias dependence was mathematically fitted by elementary functions. It could be shown that lowest noise is observed when the drain current for maximum gain is reduced to a third while the drain voltage is reduced to the start of the saturation region V/sub ds/=0.6 V. Modeling scaling effects of the noise behavior shows that lowest noise is observed for a gate width of 1/spl times/40 /spl mu/m. Multi-finger layouts are preferable for gate widths above 70 /spl mu/m. Furthermore it is shown, that the optimum width of each finger decreases with the number of fingers. >