GENAC: An Automatic Cell Synthesis Tool

We present a solution to the layout problem of cell synthesis, which achieves multiple optimization objectives. In particular, we propose a new hierarchical method for fast and optimal placement of the transistors in a cell. The method minimizes the number of diffusion breaks, and allows a further pursuit of a secondary optimization objective, such as routing channel density. For cells with non-uniform transistor widths, the transistors are folded in such a way as to optimize a cost function which is a good approximation to the area of the final (compacted) layout of the cell. We also analyze the characteristic nature of routing in cell generation problem, and design an algorithm for doing routing over the transistors; such routing reduces the routing channel density in the central region of the cell. The routing in the central region is completed by a new channel router at, or near, the channel density. The algorithms are implemented in a system call GENAC. The input to GENAC is a transistor net list, describing the connectivity as well as the size and type of each transistor. The output is a synthesized layout of the cell in symbolic language.