How does a power domain differ from a voltage area?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
A power domain is a logical concept — it says which electrical rules (supply, isolation, retention) apply to a group of cells. A voltage area is the physical fence — it says where on the floorplan those cells are actually allowed to sit. They're related but not synonyms: you can define a power domain in UPF and still get the physical implementation wrong if the voltage area's shape, alignment, or utilization doesn't actually support it.
Technical Explanation
- The floorplan has to carry the domain's full intent physically: correct supplies routed in, isolation and level-shifter cells placed at the right boundary, retention cells where required, switch-cell corridors reserved, and boundary/guard cells inserted.
- Also check the mundane stuff — utilization headroom inside the voltage area, grid alignment, and whether every macro assigned to that domain is actually compatible with living inside that physical region.
Visual Verification
Voltage areas group standard cells operating at distinct supply voltages into dedicated physical floorplan regions, guarded by isolation and level-shifter cells at domain boundaries.
Formula Or Decision Rule
Decision rule: every domain cell must have a legal physical region and access to the supplies and interface cells it needs.
What To Check
- Warning sign: The logical domain exists but its voltage area is missing, too small, or creates unusable slivers.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Correct the region and associated physical-cell plan, then rerun multivoltage and floorplan checks.
Command Checks & Actions
- create_voltage_area -power_domains <domain_list> -region <region_list> -name <voltage_area>: creates a physical region for one or more power domains
report_design-floorplan: reports the floorplan state understood by the tool
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.
Healthy, Suspicious & Hard-stop Results
- Healthy: A power domain describes logical power intent; a voltage area is the physical region where its cells may be placed. They are related but not interchangeable.
- Hard stop: required legality or physical feasibility is missing or unexplained.
Common Mistake
The Trap: Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change.
What The Interviewer Is Testing
” to measurable physical evidence and an owned correction.
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