Two moment RC delay metric for performance optimization

Abstract

For performance optimization tasks such as floorplanning, placement, buffer insertion, wire sizing, and global routing, the Elmore RC delay metric remains popular due to its simple closed form expression, fast computation speed, and fidelity with respect to simulation. More accurate delay computation methods are typically either CPU intensive or difficult to implement. To bridge this gap between accuracy and simplicity, we propose the D2M RC delay metric, which is virtually as simple and fast as the Elmore metric but is significantly more accurate. The new metric is theoretically bounded above by the Elmore delay, yet it rarely is more than a few percent below the actual delay. Consequently, the metric behaves like the Elmore metric in that it generally overestimates delay, but with consistently less error. Further, the metric is extremely accurate at the far end of RC lines.