Flash Memory Read Threshold Selection
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Solution Overview
Problem
Flash memory systems face errors during read operations due to changes in threshold voltage distribution, which existing methods fail to accurately address by setting fixed read thresholds, leading to inefficiencies in error correction and data retrieval.
Innovation Solution
A method is introduced to dynamically select and adjust read thresholds based on error correction decoding scores and threshold voltage distributions, using multiple read attempts and calculations to optimize threshold settings, thereby reducing errors and improving data reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed read thresholds are used in flash memory read operations, then the read operation is simple and fast, but read errors increase due to threshold voltage distribution changes
Solution Approach 1:
The patent implements dynamic read threshold selection by evaluating multiple candidate thresholds and selecting the optimal one based on real-time voltage distribution characteristics. Instead of using a fixed threshold, the system dynamically adjusts the read threshold to match changing voltage distributions, thereby maintaining high read accuracy while managing complexity through structured evaluation procedures
Solution Approach 2:
The patent changes the read threshold parameter based on observed voltage distribution characteristics. By monitoring threshold voltage shifts and adjusting the read threshold parameter accordingly, the system adapts to distribution changes and maintains optimal read performance without requiring complete system redesign
2Reliability
If multiple read attempts are performed with different threshold candidates, then read accuracy improves, but read time increases
Solution Approach 1:
The patent performs preliminary evaluation of multiple threshold candidates using test reads before committing to the final read operation. By pre-assessing candidate thresholds and selecting the optimal one in advance, the system ensures high read accuracy while minimizing the time penalty through efficient preliminary screening rather than exhaustive testing
Solution Approach 2:
The patent performs a limited number of read attempts with different threshold candidates rather than exhaustive testing of all possible thresholds. By performing partial action (selective sampling of candidate thresholds), the system achieves sufficient accuracy improvement without incurring excessive time costs from complete enumeration
Data Source
AI summary
A system, method and computer readable medium for performing a first read attempt of multiple codeword portions while using a first read threshold candidate to provide multiple first read results, wherein the multiple codeword portions are stored in multiple flash memory cells; calculating a first read threshold candidate error correction decoding based score; wherein the calculating comprises error correction decoding of the multiple first read results; performing a second read attempt of the multiple codeword portions while using a second read threshold candidate to provide multiple second read results; calculating a second read threshold candidate error correction decoding based score; wherein the calculating comprises error correction decoding of the multiple second read results; and selecting a first read threshold out of the first and second read threshold candidates based on a relationship between the first and second read threshold candidate error correction decoding based scores.