Delay bounded buffered tree construction for timing driven floorplanning

Abstract

As devices and lines shrink into the deep submicron range, the propagation delay of signals can be effectively improved by repowering the signals using intermediate buffers placed within the routing trees. Almost no existing timing driven floorplanning and placement approaches consider the option of buffer 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 buffered trees are used to estimate wire delay during floorplanning. 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 buffered trees (DBB-tree) and propose an efficient algorithm to construct a DBB spanning tree for use during floorplanning. Experimental results show that the algorithm is very effective. Using buffer insertion at the floorplanning stage yields significantly better solutions in terms of both chip area and total wire length.