Symcell II - A Second-generation Symbolic Standard Cell System

Abstract

Timberwolf placement and routing, the use of over-the-cell routing, an expanded library of compound cells and the introduction of techniques for controlling clock line current density have combined to allow the SYMCELL symbolic standard cell system to produce combined high density and high speed results in a technology-insensitive methodology.Densities achieved are significantly higher than with comparable systems, and channel heights are close to row heights. I. INfRODUCTIONThe SYMCELL symbolic standard cell system was introduced two years ago as a new standard cell system that combined the advantages of symbolic layout with those of cell-based design[l]. This approach is notable for employing a cell library that is symbolic, so that cells are compacted with a virtual grid compactor and pitchmatcher for a chosen technology at the time of constructing a particular design [2,3]. This approach provides for technology insensitivity, ease of library cell creation and high cell performance.The TimberWolf[4] cell placement and global routing tool has now been integrated into the SYMCELL system and a technique for over-the-cell routing via incorporation of integral cell feedthroughs has been introduced. These enhancements were made to achieve high layout density and quality in a fully automated manner. Additional