Path Depth Sensitivity · sta

Part 6 · OCV, AOCV, POCV and Variation · All levels

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The effect of variation on a path depends on its depth. A simulation shows the averaging directly. Short paths, typical of hold, see a large relative spread; deep paths, typical of setup, a small one. Clock paths add variation of their own, partly cancelled by common path removal. The topic closes with a worked comparison of flat, depth-based and statistical analysis over twenty paths.

Lesson	After it you can...
Depth Versus Variation	Show the 1/sqrt(n) averaging with a simulation.
Short Paths Versus Long	Compare derate cost on hold and setup paths.
Clock Path Variation	Quantify skew uncertainty from variation.
Worked Comparison	Compare three methods on twenty paths.

Check yourself Which has a larger relative spread, a 1-stage path or a 16-stage path, if stages vary independently?

The 1-stage path: relative spread falls as one over the square root of the stage count, so the 16-stage path has a quarter of it.

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