As signal speeds increase and gate delays decrease for high-perform ance digital integrated circuits, the gate delay m odeling problem becom es increasingly m ore difficult.With scaling, increasing interconnect resistances and decreasing gateoutput im pedances m ake it m ore difficult to em pirically characteriz e gate-delay m odels.Moreover, the single-input-switching assum ption for the em pirical m odels is incom patible with the inevitable sim ultaneous switching for todays high-speed logic paths.In this paper a new em pirical gate delay m odel is proposed.Instead of building the em pirical equations in term s of capacitance loading and input-signal transition tim e, the m odels are generated in term s of param eters which com bine the benefits of em pirically derived k -factor m odels and switch-resistor m odels to efficiently: 1) handle capacitance shielding due to m etal interconnect resistance, 2) m odel the RC interconnect delay, and 3) provide tighter bounds for sim ultaneous switching.

With finer line widths and faster switching speeds, the resistance of on-chip metal interconnect is having a dominant impact on the timing behavior of logic gates. Specifically, the gates are switching faster and the interconnect delays are getting longer due to scaling. This results in a trend in which the RC interconnect delay is beginning to comprise a larger portion of the overall logic stage delay. This shift in relative delay dominance from the gate to the RC interconnect is increased by resistance shielding. That is, as the gate "resistance" gets smaller and the metal resistance gets larger, the gate no longer "sees" the total net capacitance and the gate delay may be significantly less than expected. This trend complicates the timing analysis of digital circuits, which relies upon simple, empirical gate delay equations for efficiency. In this paper, we develop an analytical expression for the "effective load capacitance" of a pc interconnect. In addition, when there is significant shielding, the response waveforms at the gate output may have a large exponential tail. We show that this waveform tail can strongly influence the delay of the RC interconnect. Therefore, we propose an extension of the effective capacitance equation that captures the complete waveform response accurately, with a two-piece gate-output-waveform approximation.>