New Approach to VLSI Buffer Modeling, Considering Overshooting Effect

Abstract

In this brief, we use the alpha power law model for MOS devices to reach a more accurate modeling of CMOS buffers in very deep submicrometer technologies. We derive alpha model parameters of a CMOS buffer for 90-, 65-, and 45-nm technologies using HSPICE simulations. By analytical efforts we find the output resistance of a minimum-size buffer and compare it with those extracted from HSPICE simulations. We propose a new model for the output resistance of a given-size buffer in any technology, which demonstrates 3% error on average as opposed to the conventional model. Also a new buffer resistance is proposed analytically and numerically to calculate the crosstalk for interconnect analysis applications. In addition, we propose a model for the transfer function zero generated by the gate-drain capacitances of MOS transistors, which cause the overshooting effect, and develop an accurate expression for modeling this phenomenon. As the final point, together with the input-to-output capacitance, the equivalent output resistors present a simple and accurate macromodel for the CMOS buffer.