Tapless Standard Cell Power Gating Without a Third Ground Rail
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Solution Overview
Problem
Existing integrated circuit design methods for reducing leakage currents in MTCMOS circuits require additional silicon area and routing resources due to the need for a third rail (virtual ground rail) in standard cells, which increases silicon cost and reduces circuit density.
Innovation Solution
A tapless standard cell design using switch cells to provide power gating, where standard cells lack substrate connections within the cell, and instead rely on switch cells or tap cells for connections, allowing for context-sensitive rails that function as virtual or real ground rails, reducing the need for additional rails and routing resources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If power gating is implemented using conventional standard cells with a third virtual ground rail, then leakage current is reduced, but silicon area and routing resources are significantly consumed
Solution Approach 1:
The patent merges the virtual ground rail function into the existing power supply grid by utilizing the ground reference grid conductors to serve dual purposes: as true ground references and as virtual ground rails for power-gated logic cells. This eliminates the need for a separate third rail, thereby reducing silicon area while maintaining leakage current reduction benefits.
Solution Approach 2:
The ground reference grid conductors are designed to perform multiple functions: serving as true ground references for non-power-gated cells and as virtual ground rails for power-gated cells. This multi-functionality approach eliminates redundant routing resources and reduces overall silicon area consumption.
2Object-affected harmful factors
If power gating is implemented using conventional standard cells with a third virtual ground rail, then leakage current is reduced, but routing resources are significantly consumed
Solution Approach 1:
The patent combines the virtual ground routing function with the existing ground reference grid, eliminating the need for separate virtual ground routing resources. The same conductors that provide ground references are used to provide virtual ground connections to power-gated cells, thereby reducing routing complexity.
Solution Approach 2:
The ground reference grid conductors are designed to serve dual purposes: as true ground references and as virtual ground rails. This multi-functionality reduces the total number of routing resources required while maintaining the ability to reduce leakage current through power gating.
3Reliability
If tap connections are provided within each standard cell, then substrate connections are established, but standard cell area increases
Solution Approach 1:
The patent extracts the substrate connection function from individual standard cells and relocates it to external tap cells. This allows standard cells to be smaller since they no longer need internal tap connections, while substrate connections are still provided through the external tap cells that connect to the power supply or ground rail.
Solution Approach 2:
The tap cells serve multiple standard cells simultaneously, providing substrate connections to multiple cells without each cell needing its own internal tap. This shared approach reduces the total area consumed by tap connections across the circuit while maintaining reliable substrate connections.
Data Source
AI summary
A method and a structure provide a space efficient integrated circuit using standard cells and power gating by switch cells. The standard cells may be tapless, i.e., not provided a substrate connection to a power supply or ground rail by a tap within the cell. The substrate connection for these standard cells may be provided by the switch cells or by specialized tap cells. The tapless standard cells may include only a context-sensitive rail, which may be configured to be a virtual ground rail by a power gating connection to a switch cell or by a direct connection to a power supply or ground rail.