3D CAM Cell Architecture for High-Speed Search
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Solution Overview
Problem
Content-addressable memory (CAM) architectures achieve high search speeds but come at the cost of increased power consumption and required die area, posing challenges in efficient design and operation.
Innovation Solution
A three-dimensional (3D) CAM cell architecture is developed, featuring multiple tiers of semiconductor dies with a bit storage cell and a bit comparison cell, utilizing 3D connections to perform XOR operations without affecting transistor functionality, enabling efficient CAM searches per clock cycle with reduced power consumption and die area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If CAM architecture is used to achieve high search speeds, then search speed is improved, but power consumption increases
Solution Approach 1:
The patent transitions from a conventional two-dimensional CAM cell layout to a three-dimensional stacked architecture. Multiple CAM cells are vertically stacked across different semiconductor dies, with bit storage cells on one die and bit comparison cells on another die connected via through-silicon vias (TSVs). This vertical stacking enables higher density and improved power efficiency while maintaining high search speeds, as the 3D structure reduces the number of transistors required per search operation compared to planar designs.
2Speed
If CAM architecture is used to achieve high search speeds, then search speed is improved, but die area increases
Solution Approach 1:
The patent employs a three-dimensional stacked architecture where multiple CAM cells are arranged vertically across different semiconductor dies. Bit storage cells are fabricated on a first die while bit comparison cells are fabricated on a second die, connected through TSVs. This vertical integration dramatically increases storage density per unit die area, allowing high-capacity CAM structures without proportionally increasing the footprint of individual dies.
Solution Approach 2:
The CAM cell is segmented into separate functional components distributed across different dies: bit storage cells on one die and bit comparison cells on another die. This segmentation allows each die to be optimized for its specific function and enables parallel processing of multiple search operations, improving overall search speed while reducing the area required on any single die.
3Device complexity
If 3D connections are used to couple die tiers, then integration density is improved, but transistor functionality may be affected
Solution Approach 1:
The patent uses through-silicon vias (TSVs) as intermediary connection structures to couple the bit storage cell die and bit comparison cell die. These TSVs provide reliable electrical connections between the stacked dies while being carefully designed to minimize their impact on transistor functionality. The TSVs are positioned and dimensioned to avoid interfering with the active transistor regions, thus maintaining device reliability while achieving high integration density through the 3D stacked architecture.
Data Source
AI summary
A content-addressable memory (CAM) storage element includes bit storage cell bit comparison cells. The bit storage cell is arranged on a first die tier and includes at least one transistor, one or two bit lines, and a storage node. The bit comparison cell is arranged on a second die tier and has a match line, complementary search lines, and at least three transistors. The complementary search lines are decoupled from the bit line(s). A 3D connection couples the storage node to one of the transistors of the second die tier. The CAM cell performs at least one CAM search per clock cycle using at least four transistors per search, including the at least one transistor of the bit storage cell and the at least three transistors of the bit comparison cell, and to output results of the at least one CAM search on the match line.