IR drop: definition · Chip Field Guide

Beginner

The push of electricity (the voltage) that gets lost along a chip’s thin power wires, like water pressure dropping along a long pipe.

Novice

The voltage lost across the resistance of the power wiring: $\text{drop} = \text{current} \times \text{resistance}$ ( $V = IR$ , hence “IR”). Cells far from the supply or in busy areas get less than the full supply voltage, and lower voltage makes them slower.

Expert

Static IR drop uses each cell’s average current and is a pure resistance problem. Dynamic IR drop follows current over time as many cells switch together, so capacitance and package inductance matter too. Both are budgeted against the supply voltage the timing analysis assumes.