Rail Power Density Aware Cell Placement for IR Drop Mitigation
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Solution Overview
Problem
Conventional solutions for mitigating IR drop in integrated circuits, such as cell downsizing and adding power staples, fail to address the robust constraint-based mathematical representation of operating behavior, leading to timing pushout and IR drop vulnerability in other areas.
Innovation Solution
The method involves reorganizing standard cell placement within bounding box regions of an integrated circuit to normalize power density across supply rails, distributing current consumption more evenly and reducing current spikes, without the need for cell downsizing or buffering areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cell downsizing is used to mitigate IR drop, then IR drop is reduced in some areas, but timing pushout occurs in other areas
Solution Approach 1:
The patent applies local quality by evaluating and optimizing power density at specific location-level granularities within the integrated circuit. Instead of uniform cell downsizing, the method identifies specific high-power-density regions and redistributes cells locally to balance power consumption, thereby mitigating IR drop in critical areas without causing timing pushout in other regions.
Solution Approach 2:
The patent changes the parameter of cell placement configuration to optimize power density distribution. By using an objective function that evaluates power density metrics and iteratively adjusting cell positions, the method transforms the placement parameters to achieve balanced power consumption across the circuit, resolving the contradiction between IR drop mitigation and timing preservation.
2Reliability
If power staples are added to reduce resistance, then IR drop is mitigated, but device complexity increases
Solution Approach 1:
The patent extracts the power mitigation function from physical structural modifications (power staples) and implements it through computational optimization of cell placement. Instead of adding physical power staples to the circuit, the method uses an objective function to evaluate and redistribute power density through cell repositioning, thereby achieving IR drop mitigation without increasing device complexity.
3Reliability
If cell padding with buffer areas is implemented, then IR drop is reduced, but area utilization decreases
Solution Approach 1:
The patent applies dynamics by making the placement configuration adaptable and iterative. Instead of static buffer areas, the method uses an objective function that dynamically evaluates power density and iteratively adjusts cell positions to achieve balanced power distribution. This dynamic approach mitigates IR drop without requiring fixed buffer zones, thereby maintaining area utilization.
4Productivity
If conventional placement techniques are used, then placement speed is maintained, but power density normalization is insufficient
Solution Approach 1:
The patent implements feedback by using an objective function that continuously evaluates power density metrics during the placement process. The objective function provides feedback on the current power distribution state, and the placement algorithm iteratively adjusts cell positions based on this feedback to achieve power density normalization, thereby resolving the contradiction between placement speed and power normalization effectiveness.
Data Source
AI summary
To ensure proper operation (e.g., speed and/or function) of standard cells fabricated within an integrated circuit a minimum potential difference between the high and low power supply rails needs to be maintained. IR drop refers to a reduction in the potential difference between the power supply rails and is caused when the switching activity of cells that share a power supply rail is greater than can be provided at a particular time. Before fabrication, placement of the cells is reorganized within bounding box regions. Power density across the power rails within each bounding box is normalized based on spatial and temporal power density characteristics of each cell. The reorganization is IR aware and has minimal impact on timing and IR drop is mitigated because distributing current consumption between the supply rails reduces current spikes and IR drops.