Pin Accessibility-Driven Cell Layout Redesign and Placement Optimization

Abstract

The layout of standard cells is very dense these days, so some pins are hard to get access to. This is in particular true in complex cells with many pins (e.g. AOI) and in the layout where many of those cells are densely packed without much whitespace. We redesign those complex cells, so a library now contains both original cell and its new version with easier pin access; a systematic method is proposed to pick candidate cells for redesign and to dictate how redesign should be performed. We also introduce a measure of inaccessibility of pins in a cell, named IOC. Placement optimization is performed, which uses IOC to determine which cells should be replaced by its redesigned version and how whitespace should be redistributed. Experiments with 12 test circuits indicate that the number of routing errors (after the initial placement) is reduced by 82% on average, and the subsequent detailed routing takes 72% less runtime.