What is core aspect ratio?
From PDVerse PnR Interview Handbook, part of the pdVerse Mentor Guide
Short Answer
Aspect ratio is simply width divided by height of the core: AR = W / H. AR = 1 is a square core; AR = 2 means the core is twice as wide as it is tall. Two floorplans can have identical area but very different shapes — a 1000×1000 µm square and a 2000×500 µm rectangle have the same area (1,000,000 µm²) but wildly different aspect ratios, and that shape difference changes everything about routing and timing.
Technical Explanation
- Always state the convention explicitly (AR = width/height, per your project's definition) — some teams flip it, and a silent mismatch causes confusing floorplan reviews.
- ), which sides your I/O needs to reach, whether you have separate voltage areas that want to sit side by side, and where your dominant dataflow runs (a datapath that flows left-to-right wants a wide, short core, not a square one).
- A poorly chosen aspect ratio for the logic it contains forces longer average wire lengths, worse macro-to-macro channels, and awkward power ring proportions — so this isn't a cosmetic choice, it has real timing and congestion consequences downstream.
Visual Verification
Aspect Ratio is defined as Core Height / Core Width (or Width / Height by tool convention). Different aspect ratios with identical total area dramatically change wirelength distribution.
Formula Or Decision Rule
AR = core width [um] / core height [um].
What To Check
- Warning sign: A shape meets area but forces long critical paths or narrow macro channels.
- Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause.
- Correct: Compare equal-area alternatives with the same constraints and evaluation method.
Command Checks & Actions
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: Core aspect ratio is width divided by height. Equal-area rectangles can have different aspect ratios and very different routing and timing behaviour.
- 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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