Timing Metrics for VLSI Interconnects



Primary Contact

Kanak Agarwal <kba@us.ibm.com>

We have developed new and simple metrics for the slew rate of an RC circuit based on the first two circuit moments.  Metrics focusing on 50% delay of RC circuits have been proposed recently that greatly improve the accuracy of the traditional Elmore delay. However, these models have not been applied to the determination of transition or slew rates (e.g., 10-90%). We show that existing approaches to 50% delay modeling do not translate well to slew rate modeling. We develop two new slew metrics, S2M (slew with 2 moments) and scaled S2M, that provide high accuracy with the advantage of simple closed form expressions. 

We have developed an approach to model interconnect delay under process variability for timing analysis and physical design optimization. The technique allows for closed-form computation of interconnect delay probability density functions (PDFs) given variations in relevant process parameters such as linewidth, metal thickness, and dielectric thickness.  We express the resistance and capacitance of a line as a linear function of random variables and then use these to compute circuit moments. Finally, these variability-aware moments are used in known closed-form delay and slew metrics to compute interconnect delay PDFs.  The proposed methodology is found to agree well with SPICE based Monte Carlo simulations.


Simple Metrics for Slew Rate of RC Circuits Based on Two Circuit Moments

Kanak Agarwal, Dennis Sylvester, David Blaauw, “Simple Metrics for Slew Rate of RC Circuits Based on Two Circuit Moments,” ACM/IEEE Design Automation Conference (DAC), June 2003, pg. 950-953 ©IEEE