LiB: a CMOS cell compiler

An automatic layout generation system, called LiB, for the small-scale integrated (SSI) cells used in CMOS VLSI design, is presented. LiB takes a transistor-level circuit schematic in SPICE format and outputs a mask layout in CIF. The layout style is a modification of that proposed by T. Uehara, and W. M. van Cleemput (IEEE Trans. Comput., vol.C-30, no.5, p.305-12, 1981). An optimal transistor chaining algorithm has been developed to derive a transistor placement with a minimum number of diffusion separations. To meet the cell height constraint, large transistors are folded into multiple columns algorithmically. The whole cell is divided into five routing regions. Two are on the diffusion island and the others are rectilinear-shaped routing channels. A graph-theoretic method for selecting nets (subnets) for routing on the diffusion island is proposed. A global routing algorithm has been developed to assign the remaining nets to the three rectilinear channels. For the detailed routing SILK, a simulated evolution router, is employed. LiB can be used as a cell library builder or as a subsystem of a random logic module generator. Users can alternate LiB's layout using a symbolic editor.<
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