Fitted Elmore delay: a simple and accurate interconnect delay model

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In this paper, we present a new interconnect delay model called fitted Elmore delay (FED). FED is generated by approximating Hspice delay data using a curve fitting technique. The functional form used in curve fitting is derived based on the Elmore delay model. Thus, our model has all the advantages of the Elmore delay model. It has a closed form expression as simple as the Elmore delay model and is extremely efficient to compute. Interconnect optimization with respect to design parameters can also be done as easily as in the Elmore delay model. In fact, most previous algorithms and programs based on the Elmore delay model can use our model without much change. Most importantly, FED is significantly more accurate than the Elmore delay model. The maximum error in delay estimation is at most 2% for our model, compared to 8.5% for the scaled Elmore delay model. The average error is less than 0.8%. We also show that FED can be more than 10 times more accurate than the Elmore delay model when applied to wire sizing.