STA Mastery · All levels
Derate Policy & Approval: Comparison Matrix
Comparison Matrix for Derate Policy & Approval.
Comparison matrix
OCV, AOCV, and POCV differ in pessimism and approval burden.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | safe | slow closure | risk-averse |
| Balanced | practical | needs discipline | production |
| Aggressive | fast | regression risk | tapeout crunch |
| RTL change | structural | long loop | architectural |
+------------------+----------------+----------------+----------------+When to choose each approach
Match approach to schedule and silicon risk
Interview traps
One-size ECO playbook
Ignoring hold
Evidence comparison
STA EVIDENCE MATRIX — Derate Policy & Approval
+-------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-------------------+------------------------+--------------------------+-------------------------+
| report_timing | critical path slack | root cause class | cell vs net split |
| clock report | clock reachability | path delay | fix generated_clock |
| SDC diff | constraint change | physical delay | re-run all scenarios |
| SPEF tag compare | parasitic view | constraint quality | isolate view mismatch |
| MMMC dashboard | worst scenario | single-path fix | assign path group owner |
+-------------------+------------------------+--------------------------+-------------------------+STA deep dive
Variation policy is negotiated margin, not a tool checkbox.
Concept diagram
VARIATION STACK
nominal delay + OCV/AOCV/POCV margin = signoff delayMetric graph
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
Derating policy is a contractual margin between implementation and signoff; changes need documented approval and regression.
Metric: approved derate set, waiver count, signoff pessimism budget