Unit-Distance Code Mapping for Memory Page Error Rate Discrepancy
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Solution Overview
Problem
Memory devices experience an error rate discrepancy between pages due to non-uniform voltage drifts across different voltage threshold regions, leading to increased read bit error rates over time.
Innovation Solution
Implementing a unit-distance code that maps read voltages to pages in a way that minimizes the range of average read voltage drifts across pages, thereby reducing the error rate discrepancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coding schemes are used for memory cells, then the memory device can store and retrieve data, but error rate discrepancy between pages increases due to non-uniform voltage drifts
Solution Approach 1:
The patent applies local quality by assigning different code words from the unit-distance code to different pages based on their specific voltage drift characteristics. Each page receives a code word optimized for its local error rate conditions, rather than using a uniform coding scheme across all pages. This localized optimization reduces error rate discrepancy between pages while maintaining manageable coding complexity.
Solution Approach 2:
The patent changes the coding parameter by using a unit-distance code (such as Gray code) instead of conventional binary coding. This parameter change ensures that adjacent code words differ by only one bit, which minimizes the impact of voltage drifts and reduces bit error rates. The unit-distance code property directly addresses the error rate discrepancy problem by making the coding scheme more robust to voltage variations.
2Productivity
If read voltages are applied to memory cells over time, then data can be read from the memory device, but voltage drifts cause increased bit error rates
Solution Approach 1:
The patent applies preliminary action by pre-mapping read voltages to code words using a unit-distance code before actual read operations occur. This pre-establishment of the voltage-to-code mapping ensures that even as voltage drifts occur over time, the code structure maintains its error-resistant properties. The preliminary coding arrangement prepares the system to handle voltage variations without compromising read efficiency or increasing bit error rates.
Solution Approach 2:
The patent implements feedback by monitoring voltage drifts and adjusting the code word assignments or read voltage levels accordingly. The system uses the known unit-distance code structure to detect and correct errors that arise from voltage drifts, feeding this information back into the read operation to maintain low bit error rates. This feedback mechanism allows the system to adapt to changing voltage conditions while preserving read efficiency.
3Adaptability or versatility
If different pages have different average read voltage drifts, then the memory device can operate with multiple pages, but error rate discrepancy between pages increases
Solution Approach 1:
The patent applies local quality by assigning different code words from the unit-distance code to different pages based on their specific voltage drift characteristics. Each page receives a code word optimized for its local error rate conditions, rather than using a uniform coding scheme across all pages. This localized optimization reduces error rate discrepancy between pages while maintaining manageable coding complexity.
Solution Approach 2:
The patent applies universality by using a single unit-distance code structure that can serve multiple pages with different voltage drift characteristics. The unit-distance code provides a universal framework that adapts to each page's specific conditions through appropriate code word selection, enabling multi-page operation while maintaining error rate uniformity across all pages.
Data Source
AI summary
Methods, systems, and devices for coding to decrease error rate discrepancy between pages are described. For example, to identify a unit-distance code for operating a memory device, voltage drifts of a set of read voltages after a duration may be identified and each of the read voltages may be mapped to one of a set of pages of the memory cell using various possible unit-distance codes. Thus, for each unit-distance code the set of pages may be associated with respective subsets of the set of read voltages. Then, for each unit-distance code a set of average read voltage drifts corresponding to one of the set of pages may be identified. The memory device may be operated using a unit-distance code associated with a smaller range of the set of average read voltage drifts than ranges of sets of average read voltage drifts associated with other unit-distance codes.