What is core aspect ratio?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Core aspect ratio is width divided by height. Equal-area rectangles can have different aspect ratios and very different routing and timing behaviour.
Technical Explanation
A square and a long rectangle can hold the same area, but paths, channels, and pin distances change. Use the project convention explicitly: AR = width / height. Relate the shape to macro dimensions, I/O sides, buses, voltage areas, and dominant dataflow.
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. • Suspicious: A shape meets area but forces long critical paths or narrow macro channels. • Hard stop: required legality or physical feasibility is missing or unexplained. Compare equal-area alternatives with the same constraints and evaluation method.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. A shape meets area but forces long critical paths or narrow macro channels.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “What is core aspect ratio?” to measurable physical evidence and an owned correction.
Practical Example
Symptom: A shape meets area but forces long critical paths or narrow macro channels. Corrective path: Compare equal-area alternatives with the same constraints and evaluation method.
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