Input/Output Buffer Information Specification (IBIS) behavioral models are widely used for circuit-level signal integrity (SI) analysis due to its fast simulation speed and good accuracy. This work presents a tool to generate models of circuits specified by IBIS models. The model generation tool estimates poles, rise time and fall time of a circuit specified by IBIS models. The method consists of two steps; first regression analysis is performed on IBIS data with Weibull distribution function (WCDF) as the regression function. Based on the estimated parameter values, rise time and fall time values are obtained. The second step involves matching moments of WCDF to circuit moments and obtaining the estimated poles of the system. The method is generic and is scalable in nanometer CMOS. CMOS inverters have been used to demonstrate the methodology.