Parallel-Coupled Flash CAM Cell for High Matching Accuracy
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Solution Overview
Problem
Existing Content Addressable Memory (CAM) designs face challenges in achieving high matching accuracy and are not suitable for long search word designs, particularly in NOR flash in-memory searching systems, due to the limited on/off ratio of emerging nonvolatile memories.
Innovation Solution
A Content Addressable Memory (CAM) cell and device utilizing parallel-coupled flash memory cells, where data storage is based on combinations of threshold voltages, and an operation method that applies search voltages to generate match addresses through sensing amplifiers and decoders, enhancing matching accuracy and suitability for long search words.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If emerging nonvolatile memories (NVMs) are used to construct compact CAM cells, then memory density is improved, but matching accuracy deteriorates due to small on/off ratio
Solution Approach 1:
The patent divides the storage of a single data bit into multiple parallel-coupled flash memory cells (e.g., two cells), where each cell stores a portion of the data. This segmentation allows the system to achieve high memory density while maintaining sufficient on/off ratio for accurate matching by distributing the storage function across multiple cells with individual threshold voltages.
Solution Approach 2:
The patent utilizes different threshold voltages (e.g., first threshold voltage and second threshold voltage) for the parallel-coupled flash memory cells to represent different data states. By changing the threshold voltage parameter, the system achieves high matching accuracy even with small on/off ratio, as the threshold voltage differences provide clear discrimination between data states.
2Device complexity
If single level cell (SLC) NVM is used, then device complexity is reduced, but matching accuracy deteriorates for long search word design
Solution Approach 1:
The patent segments the data storage into multiple parallel-coupled flash memory cells, each contributing to the overall matching accuracy. This segmentation enables long search word design by distributing the matching function across multiple cells, where each cell's threshold voltage contributes to the cumulative matching accuracy without significantly increasing overall device complexity.
Solution Approach 2:
The patent creates a composite memory structure by combining multiple flash memory cells with different threshold voltages in parallel. This composite approach leverages the different threshold voltage characteristics of the cells to achieve high matching accuracy for long search words while maintaining manageable device complexity through a standardized parallel coupling architecture.
3Measurement precision
If parallel-coupled flash memory cells with different threshold voltages are used, then matching accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple flash memory cells with different threshold voltages into a single parallel-coupled unit that functions as one CAM cell. This merging approach achieves high matching accuracy by combining the threshold voltage information from multiple cells while keeping the device complexity manageable through a unified parallel structure that shares common control and readout circuits.
Data Source
AI summary
The application provides a Content Addressable Memory (CAM) cell, a CAM memory device and an operation method thereof. The CAM cell includes: a plurality of parallel-coupled flash memory cells: wherein a storage data of the CAM cell is based on a combination of a plurality of threshold voltages of the parallel-coupled flash memory cells.