Clock Tree Construction based on Arrival Time Constraints

Abstract

There are striking differences between constructing clock trees based on dynamic implied skew constraints and based on static arrival time constraints. Dynamic implied skew constraints allow the full timing margins to be utilized, but the constraints are required to be updated (with high time complexity). In contrast, static arrival time constraints are decoupled and are not required to be updated. Therefore, the constraints can be obtained in constant time, which facilitates the exploration of various tree topologies. On the other hand, arrival time constraints do not allow the full timing margins to be utilized. Consequently, there is a tradeoff between topology exploration and timing margin utilization. In this paper, the advantages of static arrival time constraints are leveraged to construct clock trees with useful skew while exploring various tree topologies. Moreover, the constraints are specified and respecified throughout the synthesis process reduce the cost of the constructed clock trees. It is experimentally demonstrated that the proposed approach results in clock trees with 16% lower average capacitive cost compared with clock trees constructed based on dynamic implied skew constraints.