Two-Graph Approach to Temperature Dependent Skew Scheduling

Temperature is one of the major sources of delay variability which may cause timing violations. In this paper, a novel design method of temperature dependent intentional skew is proposed in order to improve the performances (clock frequency, operating temperature range, etc.) of a sequential circuit under the temperature dependent delay variability. Our approach is based on a constraint graph which consists of two subgraphs and edges for bridging these two subgraphs. One subgraph is for representing constraints at a specified low-end operating temperature, another subgraph is for constraints at a high-end temperature, and bridging edges constrain the relation between the amounts of skew at the low-end and high-end temperatures reflecting the characteristics of the temperature dependency of intentional skews. Our approach can handle the mixture of various types of temperature dependent delays of both signal propagation delays in a combinatorial circuit and clock propagation delays for intentional skews.