Wire-sizing optimization with inductance consideration using transmission-line model

Because of the inaccuracy of the Elmore delay model and its inability to handle inductance, it is necessary to use a more accurate delay model in wire-sizing optimization. This paper presents continuous wire-sizing optimization by using a three pole based delay model. Our work is focused on exponential wire shape f(x) = ae^-bx, i.e., we determine a and b such that either delay or area is minimized. Fringing capacitance and inductance, which have been neglected in previous work on wire sizing, are taken into consideration in the delay model. Expressions involved in calculating all three poles are derived with the help of the Picard-Carson method. Since these expressions are all analytical, the delay calculation is very efficient. In our experiments, the delay model is found to be far more accurate than the Elmore delay model. We also observe that in determining the optimal shape that minimizes delay, the Elmore delay model performs as well as our delay model. However, in determining the optimal shape that minimizes area subject to a delay bound, the Elmore delay model performs much worse than our delay model.