Including inductance in static timing analysis

Abstract

In this paper analytical expressions are derived for effective load capacitances of RLC interconnects to accurately estimate both the propagation delay and transition time at the output of a CMOS gate. The new effective capacitance calculation technique poses no extra complexity as compared to the RC based approaches but can accommodate inductance. These new expressions are derived based on a generalized driving point admittance. The generalized driving point admittance takes inductance into consideration and hence accounts for the inductive shielding that in some cases can even exceed the resistive shielding in current technologies. Another improvement in the new effective capacitance calculation method is the utilization of a more general waveform shape that accounts for the non-monotonic behavior due to inductance effects. It is shown throughout the paper that two effective capacitances are required for accurate estimation of the propagation delay and rise time with an RLC interconnect load. Simulation results show that the error in propagation delays and rise times when neglecting inductance can be over 60% as compared to an RLC model in realistic interconnects. On the other hand, simulations show that the propagation delay and rise time maximum errors associated with the proposed approach are less than 10% as compared to SPICE.