This paper presents a new analytic approximation to the general diode equation with the presence of a series resistance. Using exact first-and second-order derivatives and a modified Newton-Raphson formula, a concise analytic approximate solution is derived for the diode equation with the significant improvement on the accuracy and computation efficiency, thus it is very useful for users to implement the diode model and the inversion charge models in other advanced MOSFET compact models such as ACM, EKV and BSIM5 into the circuit simulators, e.g., SPICE for circuit simulation and analysis. (c) 2006 Elsevier Ltd. All rights reserved.