An algorithm for calculating correlation coefficients between Elmore interconnect delays

As process technologies move into nanoscales, variabilities of circuit parameters increase, and as a result, statistical timing analysis computing distribution of the critical delay of a circuit is receiving a great deal of attention. For these statistical approaches, the correlations between random variables are important to the accuracy of analysis. Since interconnect delays dominates in recent technology, their correlations are of primary concern in statistical timing analysis. In this paper, we propose an efficient algorithm for calculating correlation coefficients between Elmore delays of interconnects under the assumption of Gaussian distributions. Our algorithm yields correlation coefficients with less than 2% errors to those obtained by Monte-Carlo simulations. Moreover, the correlation coefficients are compared with 50% SPICE delays calculated by Monte-Carlo simulations.