RAPID: An Efficient and Accurate Ratio-Based Analytical Proxy for Interconnect Delay

Iterative physical-design optimization requires accurate timing feedback at proxy-timer speed. Conventional interconnect models expose an accuracy–efficiency tradeoff: Elmore delay is fast but loses waveform-shape information, whereas higher-order methods improve fidelity at the cost of more expensive distribution or waveform evaluation. We introduce RAPID, a ratio-based analytical proxy that moves Elmore delay toward higher-order timing fidelity through a positive, slew-aware delay-ratio correction. RAPID derives the correction from Wilson–Hilferty asymptotics of a moment-matched Gamma response and extends it to finite input transitions through normalized-slew dilution. The resulting ratio is computed by an Elmore-isomorphic linear-time traversal and used to calibrate interconnect delay and slew within a nonlinear delay model (NLDM)-compatible effective-load flow. On TAU benchmarks, RAPID achieves average R² = 0.9905 and end-to-end report_timing speedups of 9.84× over PrimeTime and 32.70× over OpenSTA. Without retuning, it reaches average R² = 0.9949 and mean absolute error (MAE) = 0.526 ps on unseen industrial ARM designs at Elmore-level runtime. In the evaluated repair flow, RAPID improves sign-off worst negative slack (WNS) and total negative slack (TNS) by up to 22.28% and 15.44%, respectively.