A recursive technique for computing delays in series-parallel MOS transistor circuits

An efficient recursive technique for computing the Elmore delay in series-parallel resistance-capacitance (RC) networks is presented. The time complexity of the algorithm is on the order of the number of resistors times the number of nodes to which the delay has to be computed. In this respect it is superior to other known methods, particularly to that of P.K. Chan Karplus. Although that algorithm is more general, the present method should be attractive given the fact that many VLSI MOS circuits are based on design styles which are restricted to series-parallel transistor networks, which, in particular, exclude bridges. A special type of series-parallel RC circuit occurs in interconnection networks driven by multiple sources. A variation on the first algorithm, which is especially useful in a hierarchical simulator, is presented for computing the Elmore delay in such networks