Decoupling Capacitor Placement via Hypergraph Connectivity
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Solution Overview
Problem
The existing methods for placing decoupling capacitors (dcaps) in integrated circuit design are not optimal, as they are typically inserted before circuit element placement, limiting the ability to achieve ideal placement and impacting timing results, and lack flexibility in considering the logic layout.
Innovation Solution
A method that involves receiving a description of the integrated circuit design with logic cones, associating candidate dcap regions with functional cells, identifying overlaps, and inserting dcaps in regions with higher insertion rates, using a hypergraph to determine the best location for dcap placement, allowing for more accurate and flexible dcap placement proximate critical logic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If decoupling capacitors are inserted before circuit element placement using fixed grid methods, then the placement process is simplified and automated, but the decoupling effectiveness is reduced due to suboptimal placement locations
Solution Approach 1:
The patent performs preliminary identification of candidate dcap regions and associates them with functional cells before final placement decisions are made. This allows the placement process to be guided by pre-analyzed optimal locations rather than random grid insertion, improving decoupling effectiveness while maintaining automation.
Solution Approach 2:
The patent assigns different dcap insertion rates to different logic cones based on their specific noise characteristics and functional requirements. This localized approach allows critical areas to receive higher dcap density while less critical areas use lower density, optimizing overall decoupling effectiveness rather than using a uniform grid approach.
2Ease of manufacture
If decoupling capacitors are placed uniformly across the chip, then the manufacturing process is simplified, but the timing results deteriorate due to inability to target critical logic areas
Solution Approach 1:
The patent implements non-uniform dcap distribution by assigning different insertion rates to different logic cones. Critical logic areas identified through hypergraph analysis receive higher dcap insertion rates, while non-critical areas use lower rates, thereby optimizing timing precision without significantly complicating the manufacturing process.
Solution Approach 2:
The patent uses hypergraph connectivity analysis to identify critical logic areas and their noise susceptibility. This feedback information guides the dcap placement strategy, allowing the system to automatically adjust dcap insertion rates based on the specific timing and noise characteristics of each logic cone.
3Reliability
If decoupling capacitors are inserted at all candidate regions, then noise coverage is maximized, but the device complexity and area increase
Solution Approach 1:
The patent applies dcap insertion selectively rather than uniformly across all candidate regions. By using different insertion rates (some regions may have 0% insertion, others up to 100%), the system achieves adequate noise control in critical areas while avoiding unnecessary capacitors in non-critical areas, thereby reducing overall device complexity.
Solution Approach 2:
The patent changes the insertion rate parameter for different logic cones based on their noise susceptibility and criticality. This parameter variation allows the system to adapt dcap density to local requirements, achieving effective noise control where needed while minimizing overall capacitor count and device complexity.
Data Source
AI summary
Decoupling capacitors (dcaps) are placed in an IC design by assigning different dcap utilization rates to logic cones, applying the rates to corresponding dcap regions surrounding cells in the cones, identifying any overlap of regions from different logic cones, and inserting a dcap at the overlapping region having the highest dcap utilization rate. The best location for the dcap is computed using a hypergraph wherein the cells are edges and the regions are nodes. Any node that is dominated by another node is removed and its edge is extended to the dominating node. The dcap is inserted in the region having the most edges (the edges can be weighted). The process is repeated iteratively, updating the hypergraph by removing nodes connected to dcap location, and inserting the next dcap at a region corresponding to the node which then has the greatest number of connected edges.