Semiconductor Operational Cell Placement for IR Drop Reduction
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Solution Overview
Problem
In low-voltage, high-current semiconductor designs, significant power loss occurs due to IR drop caused by resistive losses in active portions of the semiconductor device, particularly in localized areas where operational cells switch simultaneously, leading to increased timing delays and power consumption.
Innovation Solution
A method for initially placing and re-placing operational cells within a semiconductor physical layout, which involves determining timing data, switching activity, and power grid switch locations to derive a cost function, optimizing cell placement to minimize IR drop by relocating cells with high IR drop values caused by simultaneous switching, and iteratively refining the placement to reduce overall IR drop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If operational cells are placed in a semiconductor physical layout, then the device can function with required operational capability, but localized IR drop occurs due to simultaneous switching causing power loss and timing delays
Solution Approach 1:
The patent applies local quality by making the placement optimization local rather than global. It identifies specific regions with high simultaneous switching activity and high IR drop, then selectively relocates operational cells in those localized areas. This approach optimizes power and timing performance where needed without requiring complete re-placement of all cells, thus resolving the contradiction between maintaining timing constraints and reducing energy loss.
Solution Approach 2:
The patent performs preliminary identification of operational cells with high simultaneous switching activity and high IR drop before final placement optimization. By pre-calculating switching activity metrics and identifying problematic regions in advance, the method prepares placement strategies that proactively prevent severe IR drop and timing violations, rather than reacting to problems after placement.
2Loss of energy
If operational cells are relocated to reduce IR drop, then power loss is reduced, but device complexity and placement optimization difficulty increase
Solution Approach 1:
The patent segments the placement optimization problem into manageable parts by dividing the semiconductor device into regions based on simultaneous switching activity and IR drop characteristics. It processes and optimizes placement in these segmented regions independently rather than attempting to optimize the entire device globally, thus reducing computational complexity while still achieving power loss reduction through targeted cell relocation.
Solution Approach 2:
The patent changes parameters such as switching activity thresholds and IR drop thresholds to control the optimization process. By adjusting these parameters, the method can control which operational cells are selected for relocation and to which target locations, providing a systematic way to manage placement complexity while achieving the desired reduction in power loss.
3Loss of energy
If more operational cells are relocated for optimization, then IR drop and power consumption decrease, but manufacturing and design time increase
Solution Approach 1:
The patent applies partial action by selectively relocating only those operational cells that meet specific criteria (high simultaneous switching activity and high IR drop) rather than relocating all cells. This partial optimization approach achieves sufficient reduction in power consumption and timing violations without incurring the excessive time cost of optimizing every cell, thus resolving the contradiction between energy loss reduction and time loss.
Data Source
AI summary
There is provided a method of placing a plurality of operational cells of a semiconductor device within a semiconductor layout, comprising determining timing data for each of the plurality of operational cells, determining switching activity from RTL or design constraints for each of the plurality of operational cells, determining power grid switch locations relative to each of the plurality of operational cells, deriving a cost function based upon the determined timing data, determined switching activity from RTL/design constraints and determined relative power grid switch locations and initially placing the plurality of operational cells according to the derived cost function.