Hierarchical Composition of VLSI Circuits

Abstract

A transistor level representation for VLSI circuits is presented. This representation is simple but general, technology independent, hierarchical, and maintains connectivity, circuit schematic information, and the information for mask geometry. A transistor level cell is represented as the interconnection of devices along with their types, sizes and placement, and the cell's typed ports. Connection is represented explicitly by shared connection points. The ports describe the interface between this cell and other cells. This representation, together with a set of synthesis and analysis rules, enforces the description of strictly legal designs. The synthesis rules ensure that each structure is correct by construction. The analysis rules check for geometrical design rule violations which cannot, by their nature, be enforced by construction. A file of technology dependent information indicates how to implement each transistor type, interconnect type and connection point type, as well as how structure types may interact. Cells described in this representation may be composed hierarchically to form larger cells. Given a valid composition, the topology, geometry and connectivity of the composite structure is guaranteed to be legal. A working system supporting this hierarchical representation is also described. This system currently supports design rules for nMOS and cMOS/bulk, and has produced chip descriptions that have been both fabricated and tested.

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