DenseChip

STA Mastery · All levels

Variation Signoff Dashboard: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Variation Signoff Dashboard.

Step-by-step analysis walkthrough

Use when you own Variation Signoff Dashboard in a timing war room.

  1. Open signoff scenario list — note worst WNS corner.

  2. report_timing -max/-min on failing group.

  3. Trace launch and capture clocks on critical path.

  4. Check exceptions and generated clocks on path.

  5. Break down cell vs net delay.

  6. Compare implementation vs signoff view if delta suspicious.

  7. Assign owner: RTL, synth, PD, CTS, SI.

  8. Propose ECO with hold/SI check plan.

  9. Run regression matrix.

  10. Update closure dashboard and memo.

Artifacts to collect

  • signoff dashboard screenshot, weekly WNS trend, closure memo

  • SDC file

  • SPEF tag

  • MMMC scenario list

  • ECO ticket

Decision memo template

diagram
STA DECISION MEMO — Variation Signoff Dashboard
corner/mode:
WNS/TNS:
hypothesis:
ECO:
regression:
owners: STA lead, program management

Reference visuals

Weekly WNS trend

diagram
WNS TREND (all signoff scenarios)

 0ps |           ___----
-50ps |      ____/
-100ps| ____/
      +-----------------> week
      w1   w2   w3   w4

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

Variation signoff tracks closure across the full derate matrix and flags corners where margin is consumed by policy not implementation.

Metric: WNS/TNS across derate corners, hold/setup closure rate, margin trend

Practice this lesson