How do you solve/fix IR drop issues (at placement, ECO stage)?

o   Fixing IR drop involves 1) strengthening the Power Distribution Network (PDN) to reduce its resistance or  2) reducing the current drawn by the logic.

o   During Placement/Floorplan (Preventative)

o   Robust PDN Design: Plan a dense power grid using wide straps/rings on low-resistance metal layers with ample vias

o   Macro Placement: Place high-power macros near power sources or ensure they have strong connections to the power grid.

o   Cell Placement: Avoid clustering high-power or high-switching activity cells in one area. Use density controls.

o   During Post-Route Optimization / ECO Stage:

o   Strengthen PDN:

§  Add/Widen Power Straps: Introduce more power/ground stripes in areas with high voltage drop or increase the width of existing straps.

§  Add Power Vias: Increase the number of vias connecting different layers of the power grid, at connections to cell rails, to reduce vertical resistance.

o   Add Decap Cells (Primarily for Dynamic IR):

o   Reduce Current Draw:

§  Cell Downsizing: Replace high-power cells in the violating region with smaller drive-strength equivalents, if no timing violations.

§  VT Swapping (Higher Vt): Swap cells to higher-Vt to reduce leakage current (helps static IR) and slightly reduce peak dynamic current (helps dynamic IR), If no timing issues.

o   Spread High-Activity Cells: If dynamic IR drop is caused by simultaneously switching cells clustered together, try spreading these cells apart during ECO placement