Threshold-voltage swap

Threshold-voltage swap. A multi-Vt (threshold-voltage) library carries each cell in several flavours. A lower threshold makes the cell faster (less delay) but leaks far more current. The path here is built entirely of high-Vt (HVT) cells and misses setup.

Click a cell's Vt to cycle HVT -> SVT -> LVT. Each step down cuts that cell's delay but multiplies its leakage (HVT 1x, SVT 3x, LVT 9x). Close the setup path (slack at or above zero) while keeping total leakage under the budget.

Swapping every cell to the fastest LVT meets timing but busts the leakage budget, so the move is selective: swap the largest-delay cells first (they buy the most speed per unit leakage), and only as far down in Vt as needed. Reach positive slack at the least leakage, then Submit swaps.