STA Mastery · All levels

Path Depth Sensitivity: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Path Depth Sensitivity.

Step-by-step analysis walkthrough

Use when you own Path Depth Sensitivity in a timing war room.

Open signoff scenario list — note worst WNS corner.
report_timing -max/-min on failing group.
Trace launch and capture clocks on critical path.
Check exceptions and generated clocks on path.
Break down cell vs net delay.
Compare implementation vs signoff view if delta suspicious.
Assign owner: RTL, synth, PD, CTS, SI.
Propose ECO with hold/SI check plan.
Run regression matrix.
Update closure dashboard and memo.

Artifacts to collect

path depth vs slack scatter, AOCV table dump, hold/setup split report
SDC file
SPEF tag
MMMC scenario list
ECO ticket

Decision memo template

diagram

STA DECISION MEMO — Path Depth Sensitivity
corner/mode:
WNS/TNS:
hypothesis:
ECO:
regression:
owners: STA owner, library owner

Reference visuals

Depth vs slack scatter

diagram

SLACK vs LOGIC DEPTH

slack
  + |     *  *  *
    |   *   *  *
  0 |--*--*-----*---  WNS
    | *
  - |*
    +----------------> depth (stages)

Short paths cluster left — hold risk zone.

STA deep dive

Variation policy is negotiated margin, not a tool checkbox.

Concept diagram

diagram

VARIATION STACK

nominal delay + OCV/AOCV/POCV margin = signoff delay

Metric graph

diagram

DERATE IMPACT ON WNS

OCV only     WNS -120ps
AOCV         WNS -45ps
POCV         WNS -60ps (policy dependent)

Reports and artifacts

derate table
AOCV depth report
POCV sigma
hold/setup split

Mini case study

Switched to AOCV without re-baselining hold — short paths failed min analysis.

Debug branches

Short paths for hold
Policy approval for derate changes

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

Key takeaways

State corner, mode, view, and database tag with every slack claim.
Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

Comparing STA runs with different SPEF or SDC tags.
Broad false_path to green-wash violations.
Setup-only ECO without hold check.

Principal STA review addendum

Short paths see different variation pessimism than long paths; depth-aware models prevent both optimism and excess margin.

Metric: short-path hold margin, long-path setup margin, depth bucket WNS

Practice this lesson