Explain OCV, AOCV, and POCV analysis techniques.

OCV (On-Chip Variation) accounts for variations in nominally identical structures. Traditional OCV applies flat derating (e.g., +/- 5%) to all cells. AOCV (Advanced OCV) uses depth and distance-based derating: variation decreases with more stages (statistical averaging) and distance (spatial correlation). Tables specify derates based on path depth. POCV (Parametric OCV) is most accurate: uses statistical timing with cell-specific sigma values, computes path variation using SRSS (square root of sum of squares), provides realistic pessimism reduction. Modern signoff requires AOCV or POCV for reasonable margins while maintaining guardband.