Qualitative Analysis of MOS Circuits

Abstract With the push towards submicron technology, transistor models have become increasingly complex. The number of components in integrated circuits has forced designers' efforts and skills towards higher levels of design. This has created a gap between design expertise and the performance demands increasingly imposed by the technology. To alleviate this problem, software tools must be developed that provide the designer with expert advice on circuit performance and design. This requires a theory that links the intuitions of an expert circuit analyst with the corresponding principles of formal theory (i.e., algebra, calculus, feedback analysis, network theory, and electrodynamics), and that makes each underlying assumption explicit. Temporal qualitative analysis is a technique for analyzing the qualitative large signal behavior of MOS circuits that straddle the line between the digital and analog domains. Temporal qualitative analysis is based on the following four components: First, a qualitative representation is composed of a set of open regions separated by boundaries. These boundaries are chosen at the appropriate level of detail for the analysis. This concept is used in modeling time, space, circuit state variables, and device operating regions. Second, constraints between circuit state variables are established by circuit theory. At a finer time scale, the designer's intuition of electrodynamics is used to impose a causal relationship among these constraints. Third, large signal behavior is modeled by transition analysis, using continuity and theorems of calculus to determine how quantities pass between regions over time. Finally, feedback analysis uses knowledge about the structure of equations and the properties of structure classes to resolve ambiguities.