New C∞ Functions for Drain–Source Voltage Clamping in Transistor Modeling

Smoothly clamping the drain-source voltage to its saturated value is a common technique used in compact modeling of transistors, such as MOSFETs, JFETs, and HEMTs. The most widely used approach, based on the power function, is not C
^∞
. This article proposes general formulas to construct C
^∞
clamping functions. Specifically, a new square root form is proposed, which is better than the existing methods and other forms in terms of derivatives and computational efficiency. The new clamping function is verified in the PSP model. It improves both the Gummel symmetry and the harmonic balance simulation.