Multilevel tree fusion for robust clock networks

Abstract

Recent improvements in clock-tree and mesh-based topologies maintain a healthy competition between the two. Trees require much smaller capacitance, but meshes are naturally robust against process variation and can accommodate late design changes. Cross-link insertion has been advocated to make trees more robust, but is limited in practice to short distances. In this work we develop a novel non-tree topology that fuses several clock trees to create large-scale redundancy in a clock network. Empirical validation shows that our novel clock-network structure incrementally enhances robustness to satisfy given variation constraints. Our implementation called Contango3.0 produces robust clock networks even for challenging skew limits, without parallel buffering used by other implementations. It also offers a fine trade-off between power and robustness, increasing the capacitance of the initial tree by less than 60%, which results in 2.3× greater power efficiency than mesh structures.