Interconnect

$$ % 6.1 Interconnect notation (no equations, just variables) \text{Wire geometry: } (w,\,s,\,t,\,h,\,l) \newline\quad\text{with top metals: low }R\text{ for power/clock; lower metals: dense routing} $$

Interconnect modelling

Wires are distributed RC with per unit length parameters, with L- $\pi$ models by cascading segments

• Resistance → cross section
• Capacitance → charge that must fill before the far end moves
• Inductance → rate change inertia

$$ % 6.2 Distributed RC approximations \text{Distributed line } \rightarrow \text{cascade of } N \text{ small }(R/N,\,C/N)\text{ segments}\quad\Rightarrow\quad\text{L-, }\pi\text{-, or T-models for timing/energy estimates} $$

Interconnect impact

• For distributed TC lines, practical delay (flight time) can be well estimated as $\frac{RC}{2}$ using true wire resistance, more detailed reviews relate to $\ln 2$ scaling of effective $RR$ and input slew results

$$ t_{\text{wire}} \approx \frac{R\,C}{2}\quad\text{(distributed RC; good estimate for practical use)} $$