Hierarchical B*-Tree Analog IC Placement
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Solution Overview
Problem
Existing analog IC placement tools face challenges in efficiently searching for optimal placements that satisfy symmetry constraints, leading to large solution spaces and increased processing times, especially for large ICs with multiple symmetry groups.
Innovation Solution
A placement tool generates a hierarchical B*-tree representation of the IC, allowing for iterative perturbations and cost function evaluations to select optimal placements, with the use of ASF-B*-trees and HB*-trees to ensure symmetry islands and proximity groups are placed efficiently, reducing the search space and processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional placement tools process each device module independently to satisfy symmetry constraints, then placement accuracy is improved, but processing time increases significantly
Solution Approach 1:
The patent segments the placement problem by introducing a hierarchical structure where symmetry groups are identified and processed as unified units. Device modules are organized into symmetry groups based on their symmetry relationships, allowing the placement tool to handle groups collectively rather than individual devices, thus reducing processing time while maintaining placement accuracy.
Solution Approach 2:
The patent applies preliminary action by pre-identifying and organizing device modules into symmetry groups before the actual placement process. The placement tool determines symmetry groups in advance based on symmetry constraints, creating a structured representation that guides subsequent placement operations and reduces computational complexity during optimization.
2Manufacturing precision
If the placement tool searches the entire solution space to find optimal placements, then placement quality is improved, but the search space becomes too large and computation becomes infeasible
Solution Approach 1:
The patent segments the solution space by introducing hierarchical levels: individual device modules, symmetry groups, and higher-level structural units. This segmentation allows the placement tool to perform localized optimization within each symmetry group while maintaining global consistency, effectively reducing the search space from the entire IC layout to manageable sub-regions.
Solution Approach 2:
The patent adds a hierarchical dimension to the placement search space. Instead of searching only in the two-dimensional physical layout space, the tool operates in a three-dimensional space that includes hierarchical level, symmetry group membership, and physical position. This dimensional expansion enables more efficient search strategies by constraining the search at each hierarchical level.
3Reliability
If symmetry constraints are strictly enforced for all device modules, then circuit performance is improved, but placement flexibility decreases and routing becomes more difficult
Solution Approach 1:
The patent applies local quality by differentiating the treatment of device modules based on their symmetry group membership and individual characteristics. While symmetry constraints are enforced within identified symmetry groups, the placement tool maintains flexibility for devices outside these groups or for specific devices within groups where symmetry may be relaxed. This localized application of constraints optimizes circuit performance for critical symmetric pairs while preserving overall placement flexibility.
Data Source
AI summary
A placement tool generates an optimal placement for a plurality of device modules within an analog integrated circuit (IC) subject to device matching, symmetry, and proximity constraints by first defining a multiple-level hierarchy of constraint groups, wherein each constraint group consists of elements that are subject to one of the placement constraints. Each element of each constraint group consists of either of one of the device modules or another one of the constraint groups residing at a lower level of the hierarchy. The tool then generates a hierarchical B*-tree representation of a trial placement for the IC including a separate node representing each constraint group of the hierarchy and a separate node for each of device module not included in any of the constraint groups. Each node representing a constraint group defines relative positions within the IC of each the device modules or lower level constraint groups forming the constraint group that are consistent with the placement constraint on the constraint group. The placement tool iteratively perturbs the hierarchical B*-tree to generate a sequence of trial placements for the IC design and then evaluates a cost function for each trial placement to select a best one of the trial placements as the optimal trial placement.