Understanding Hierarchical Design

Abstract

With the exponential improvement in integrated circuit technology comes the problem Of how to design systems containing millions of devices. This thesis presents a new look at hierarchical design based on the Caltech structured design methodology. The hierarchy is separated into two parts: leaf cells, containing no instances of other cells, and composition cells, containing only instances of other cells. A leaf cell can be implemented in many different representations. A representation consists of a set of leaf cells and a composition rule that builds correct higher level cells. The separated hierarchy is suitable for mathematical analysis by the use of Curry's theory of combinators. In this form, a hierarchy is represented by a mathematical operator that produces a digital system from the leaf cells. The question of hierarchical equivalence is examined. Three sample composition rules, or algorithms, are presented as examples. The SLAP system provides a geometry composition rule that produces the mask description of a system given the geometries of the leaf cells. In analogy to TYPEing in a programming language, two representations that enforce a certain design style are discussed. The first TYPE system guarantees signal integrity. The second TYPE system guarantees mutual exclusion between the sources on a bus.