An algorithm for zero-skew clock tree routing with buffer insertion

We study the problem of multi-stage zero skew clock tree construction for minimizing clock phase delay and wire-length. In existing approaches clock buffers are inserted only after the clock tree is constructed. The novelty of this paper lies in simultaneously performing clock tree routing and buffer insertion. We propose a clustering-based algorithm which uses shortest delay as the cost function. We show that the feasible positions for clock tree nodes and buffers can be generalized from diagonal segments (merging segments) to rectangles (merging blocks). Buffers are large components and must be placed pairwise disjointly. We also show that the problem of finding legal positions for buffers such that no buffers overlap can be formulated as a shortest path problem on graphs, and can be solved by the Bellman-Ford algorithm. By making use of the spacial properties of the graphs, we further speedup the Bellman-Ford algorithm. The experimental results show that our algorithm greatly outperforms the approach of inserting buffers after clock routing.