(Even More) Useful Skew : Teklatech Adapts Useful Skew Concepts To Close Dynamic IR

Zero clock skew is not a necessary thing. As long as timing can be closed, clock skew is immaterial. This kind of thinking is what gave birth to the concept of useful skew. The use of useful skew in contemporary design is mostly restricted to timing closure. In this method, the arrival of clock edges at the launch and sink registers of critical paths are changed to increase the effective clock period available to the critical path. Since different registers have different clock latencies, one side-effect of this optimization is that all your registers don't transition at once.

But is there a benefit from having all your registers transition at different times? Enter Dynamic IR (stage left). When a large number of transitions occur in a very short period of time (right after the active clock edge, for example), the power network is not in a position to supply such a large amount of current in such a short space of time. Result: large and localized instantaneous drops.

Teklatech's FloorDirector uses useful skew concepts to spread out the register transitions by playing around with the clock edges and thus reduces the dynamic IR drop problem without affecting timing. Elegant, huh?

Tags : ASIC, VLSI