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Performance-Driven Analog Placement Considering Monotonic Current Paths

This research presents a novel performance-driven approach to analog circuit placement, focusing on the impact of layout-induced parasitics. By employing symmetry islands and considering monotonic current paths, the proposed algorithms aim to enhance analog circuit performance through strategic placement of devices. The study includes a case analysis involving folded-cascode operational amplifiers, detailing generation methods using slicing trees and constraints to mitigate routing-induced parasitics. The paper reports experimental results that demonstrate the effectiveness of the proposed methodology.

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Performance-Driven Analog Placement Considering Monotonic Current Paths

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  1. Performance-driven Analog Placement Considering Monotonic Current Paths P. Wu, M. Lin, Y. Chen, B. Chou, T. Chen, T. Ho and B. Liu Department of CS, NCKU, Tainan, Taiwan ICCAD 2012

  2. Outline • Introduction • A Case Study • Generation of Symmetry Islands using Slicing Trees • Consideration of Monotonic Current Paths in Slicing Trees • The Proposed Algorithms • Experimental Results • Conclusions

  3. Introduction • The performance of analog circuits is very sensitive to the impact of layout-induced parasitics. • As a result, analog devices must be symmetrically and proximally placed for both parasitic matching and parasitic reduction. • The routing-induced parasitics on the current/signal paths usually have the greatest impact on analog circuit performance.

  4. Introduction

  5. Introduction

  6. A Case Study • Two placement topologies of the folded-cascode Op-Amp. Without considering monotonic current paths Considering monotonic current paths

  7. A Case Study

  8. Generation of Symmetry Islands using Slicing Trees • Slicing Tree Floorplan Non-skewed slicing tree Skewed slicing tree

  9. Symmetry-Island-Feasible Slicing Trees

  10. Symmetry-Island-Feasible Slicing Trees • To satisfy the feasible condition, the representative module of self-symmetry module must be on the left boundary of the right-half plane.

  11. Hierarchical Slicing Trees

  12. Topological Monotonic-Current-Path Constraint • Given a current path among three modules, Mi -> Mj -> Mk, the following topological monotonic-current path constraints must be satisfied. • If Mi is north to Mj, Mk must not be north to Mj. • If Mi is south to Mj, Mk must not be south to Mj. • If Mi is east to Mj, Mk must not be east to Mj. • If Mi is west to Mj, Mk must not be west to Mj.

  13. Topological Monotonic-Current-Path Constraint

  14. Geometrical Monotonic-Current-Path Constraint

  15. Geometrical Monotonic-Current-Path Constraint

  16. The Proposed Algorithms • Use Defer to explore the solution space under symmetry-island and monotonic-current-path consideration. • In the beginning of the algorithm, each symmetry island and non-symmetry module is represented by a leaf node in the hierarchical slicing tree. • Construct an initial hierarchical slicing tree by adjusting the order of the leaf nodes such that the topological current-path constraint is satisfied.

  17. Multiple Placement Generation • After enumerative packing, fix the geometrical current-path constraint violation by module positioning for each packing solution. • After a point is selected, start the back-tracing step to obtain the corresponding slicing tree and the placement. • It is possible to generate multiple placements by choosing several points in the shape curve of the root node.

  18. Experimental Results

  19. Experimental Results

  20. Experimental Results

  21. Conclusions • This paper introduced the current-path constraints in analog placement. • They proposed a novel performance-driven analog placement flow based on the deterministic algorithm to explore the solution space under symmetry-island and monotonic-current-path constraints.

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