DYNAMIC MODELS FOR SUBSTRATE COUPLING IN MIXED-MODE SYSTEMS

摘要

In modern monolithic integrated circuits, substrate coupling is a major concern in mixed-mode systems design. Noise injected into the common substrate by fast switching digital blocks may affect the correct functioning or performance of the overall system. Verification of such systems implies the availability of accurate and simulation-efficient substrate coupling models. For frequencies up to a few gigahertz pure resistive models are considered sufficient, but increasing frequencies of operation imply that capacitive coupling analysis also becomes mandatory. In this paper, we motivate the use of dynamic resistive-capacitive (RC) models of substrate coupling as a natural extension to the standard purely resistive models. We propose an extraction methodology that starts from information about the process parameters and the contact layout of the circuit, and leads to a contact-to-contact RC element model. The underlying algorithm is based upon a Finite Difference discretization of the substrate, leading to a large tridimen-sional mesh which is solved by means of a fast Multigrid algorithm. The proposed model is trivially incorporated into circuit simulation tools. Comparisons are also made to a model obtained using standard model order reduction algorithms and it is shown to be of similar accuracy. The formulation proposed can accurately model substrate coupling effects for frequencies up to several tens of gigahertz.