Group delay as an estimate of delay in logic

Wire routing by optimizing channel assignment within large apertures, " in Proc. Abstract-It is an accepted practice in signal delay estimation to model MOS digital circuits as RC circuits. In most cases Elmore's delay definition is applied. This paper has several objectives. First, it shows that Elmore's definition is exactly equivalent to the group delay of the network at zero frequency. Second, it presents a computationally efficient noniterative method to calculate this delay for networks with any linear elements and arbitrary topology. Third, it shows that in RC networks, under certain conditions, the Elmore delay and the 50% unit step response delay are related by a constant which is largely independent of the element values and topology. Finally, it presents an efficient method to obtain sensitivities of the delay with respect to any element in the network. These last two properties make design for specified delays feasible and computationally efficient.