Feedback-guided design made all 20 amplifier layouts clean and smaller
CASCoDe: A Closed-Loop Agentic Framework for Analog Sizing and Layout Co-Design · arXiv:2611.11710
In plain words
Analog circuit designers must choose transistor sizes and arrange and connect the devices on a chip. CASCoDe is a computer framework that tries those choices, checks each layout, and uses the results to decide what to change next, including earlier sizing choices.
On 20 amplifiers, its layouts passed physical-rule and circuit-connection checks for all 20. They also used less routed area than layouts from APPlace, though the full comparison changed sizing as well as layout.
The research
A layout can meet its design rules yet lose circuit performance after wires and device placement are accounted for.
CASCoDe's results show that feeding those effects back into sizing and layout decisions can produce smaller, passing designs on the tested amplifiers, changing what an automated flow can achieve in this setting.
CASCoDe uses an AI agent and post-layout feedback to revise analog circuit sizing and layout, then checks whether the resulting designs meet performance and physical requirements.
The researchers compared CASCoDe with three layout flows on 20 SKY130 amplifiers, using the same performance reference and a requirement that each circuit metric retain at least 80% of its pre-layout value.
CASCoDe's layouts passed physical-rule and circuit-connection checks on all 20 circuits, compared with 15 for APPlace, none for MAGICAL, and one for ALIGN.
Its routed area was 59–85% lower than APPlace's across the circuits, averaging 71% lower. Because the end-to-end flows used different sizing candidates, a second comparison held sizing fixed; CASCoDe still had smaller area than APPlace across all three stage classes.
The comparisons cover 20 amplifiers made with the SKY130 process, and the component-removal tests cover only five selected circuits. The checks and testbenches do not measure every concern addressed in hand-crafted layout, including reliability or shielding sensitive wires.
What the evidence shows
- Feedback guides design changes
CASCoDe is a closed-loop framework for analog circuit sizing and layout. Its agent uses physical and electrical feedback to revise transistor sizes, device arrangements, floorplans, and routing.
This addresses a coordination gap in the flows described by the paper: layout results could be evaluated, but often could not guide targeted changes to earlier sizing or structural layout decisions.
- Every circuit passed checks
CASCoDe produced clean layouts for all 20 circuits, while APPlace produced clean layouts for 15. This comparison shows that CASCoDe more consistently met the physical-rule and circuit-connection checks under the tested flows.
- Smaller area end to end
Across the end-to-end comparison, CASCoDe's routed area averaged 71% lower than APPlace's. Since the flows used different sizing candidates, this result describes the combined sizing-and-layout process, not layout alone.
- The layout difference remains
When the researchers held sizing constant, CASCoDe still produced smaller layouts than APPlace across all three stage classes. This shows sizing differences alone do not account for the area advantage in this comparison, which tested the layout flows only at CASCoDe's final sizing.
- Components matter in selected cases
On five selected circuits, versions without CASCoDe's structured actions or tree search used more area and time than the full framework. The agent-alone version finished only three cases, none with a clean design-rule check.
These component tests suggest those parts helped on the selected circuits, but do not extend the main 20-circuit result to every setting.
Deep
- Original paper authors
- Ziming Wei, Bingyang Liu, David Z. Pan
- Submitted to arXiv
- License
- arXiv non-exclusive