Logic restructuring

Logic restructuring. A path can be slow because of the shape of the logic, not the strength of the cells. A deep chain of gates adds one gate delay per level, and a late-arriving signal buried deep in it then passes through many more gates on its way to the output. Restructuring rebuilds the same function with a better shape, so it changes no cell sizes and no thresholds.

Two levers set the delay. Balance the tree so it is shallow: combining the early signals first keeps the depth low. And put the latest-arriving signal closest to the output, so it sees the fewest gates after it.

These signals combine through 2-input gates, and each gate's output is ready at the later of its two inputs plus one gate delay. Signal s5 arrives late, so keep it for the final gate. Click two nodes to combine them, build the tree down to one output at or under the required time, then Submit tree.