2 2 RELATED WORKS AND OVERVIEW OF DBB - TREE ALGORITHMour

abstract As devices and lines shrink into the deep submicron range, the propagation delay of signals can be eeectively improved by repowering the signals using intermediate buuers placed within the routing trees. Almost no existing timing driven oorplan-ning and placement approaches consider the option of buuer insertion. As such, they may exclude solutions, particularly early in the design process, with smaller overall area and better routability. In this paper, we propose a new methodology in which buuered trees are used to estimate wire delay during oorplanning and placement. Instead of treating delay as one of the objectives, as done by the majority of previous work, we formulate the problem in terms of Delay Bounded Buuered Trees (DBB-tree). The DBB formulation is as follows: Given a net and delay bounds on critical sinks, construct a tree with intermediate buuers inserted to minimize both the total wiring length and the number of buuers while satisfying the given delay bounds. Based on the Elmore delay model, we propose an eecient algorithm to construct a DBB spanning tree for use during oorplanning and placement. Experimental results show that the algorithm is very eeective. Using buuer insertion at the oorplanning and placement stage yields signiicantly better solutions in terms of both chip area and total wire length.