Content Addressable Memory with Concurrent Read and Search Operations
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Solution Overview
Problem
Conventional content addressable memory (CAM) devices are limited to one-dimensional searching and lack soft-error detection capabilities, as they cannot perform concurrent read and search operations, leading to inefficiencies and increased power consumption when attempting to implement soft-error scrubbing.
Innovation Solution
A CAM device with a 20-transistor ternary CAM cell configuration that enables two-dimensional searching along both row and column directions, allowing for concurrent read and search operations, and incorporating NFET stacks for match and read circuitry to facilitate soft-error detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional CAM devices perform search operations, then search capability is provided, but soft-error detection cannot be performed
Solution Approach 1:
The patent merges read and search operations into a single unified circuit structure. The same bit lines and sense amplifiers are used for both reading stored data and comparing search data, allowing both operations to occur concurrently without requiring separate dedicated circuits. This integration enables soft-error detection during search operations while maintaining full search functionality.
Solution Approach 2:
The patent makes the CAM cell and associated circuitry multi-functional by enabling the same hardware to perform both read and search/compare operations. The bit lines serve dual purposes: carrying search data during comparison and carrying stored data during read operations. This universality allows the system to maintain search capability while adding soft-error detection through concurrent read operations.
2Reliability
If additional DRAM cells are used for soft-error scrubbing, then soft-error detection capability is improved, but area overhead and power consumption increase
Solution Approach 1:
The patent eliminates the need for separate DRAM cells by merging the read function into the existing CAM structure. The same bit lines, word lines, and sense amplifiers used for search operations are also used for read operations, thereby providing soft-error detection capability without adding any extra storage cells or increasing area overhead.
Solution Approach 2:
The CAM cell serves its own read requirements through its existing search comparison circuitry. The sense amplifiers that detect match/mismatch conditions during search operations are also used to read the stored data values for error detection purposes. This self-service approach eliminates the need for dedicated read circuitry or additional storage elements.
3Reliability
If additional DRAM cells are used for soft-error scrubbing, then soft-error detection capability is improved, but power consumption increases
Solution Approach 1:
The patent combines read and search operations into the same physical circuit path, so that the power-consuming elements (bit lines, sense amplifiers, word lines) are shared between operations. When performing a search, the same circuits that would be used for reading are activated, thereby providing error detection capability without the additional power cost of separate dedicated read circuitry or DRAM cells.
Solution Approach 2:
The CAM cell's existing search circuitry serves the dual purpose of both search comparison and data reading for error detection. This eliminates the need for separate power-consuming read circuits or DRAM refresh operations, as the search comparison infrastructure is reused for both functions simultaneously.
4Adaptability or versatility
If conventional CAM performs only one-dimensional searching, then circuit simplicity is maintained, but two-dimensional search capability is limited
Solution Approach 1:
The patent makes the CAM circuit universal by enabling it to perform both traditional row-based search operations and column-based search operations. The same bit lines and sense amplifiers can be activated by either word lines (for row searches) or by column-select signals (for column searches). This multi-functionality provides two-dimensional search capability without requiring separate dedicated circuit paths for each search direction.
Solution Approach 2:
The patent introduces dynamic configurability to the CAM circuit, where the search direction (row or column) can be changed on-the-fly through control signals. The circuit can dynamically switch between operating modes: traditional CAM search mode activated by word lines, and 2D search mode activated by column-select signals. This dynamic behavior enables versatile search capability without permanently increasing circuit complexity.
Data Source
AI summary
A content addressable memory (CAM) device includes an array of memory cells arranged in rows and columns; compare circuitry configured to indicate match results of search data presented to each row of the array; and compare circuitry configured to indicate match results of search data presented to each column of the array, thereby resulting in a two-dimensional search capability of the array.