Flash Memory Reference Voltage Updating for Read Error Control
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Solution Overview
Problem
Non-volatile data storage devices, such as flash memory devices, face accuracy issues in reading stored data due to variations in programmed states caused by factors like data retention and program disturb conditions, leading to errors when using fixed reference voltages over time.
Innovation Solution
The system updates a set of reference voltages based on a comparison of error counts, selecting or replacing reference voltages to reduce read errors, conditioned on a target number of error correction code pages read and the difference in mean error counts since the last update, thereby maintaining data accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference voltages are updated frequently to reduce read errors, then data reading accuracy is improved, but processing resources and time are increased
Solution Approach 1:
The system implements periodic updating of reference voltages based on read error counts. Instead of continuous updating, the controller periodically evaluates whether updates are needed by comparing error counts against thresholds, and only updates when necessary. This periodic approach maintains data reading accuracy while minimizing unnecessary processing time and resource consumption.
Solution Approach 2:
The system uses feedback from read error counts to dynamically control reference voltage updates. The controller monitors error counts during data reading operations and uses this feedback to determine when updates should occur. This feedback mechanism ensures updates happen only when actually needed, optimizing the balance between accuracy and processing efficiency.
2Measurement precision
If reference voltages are updated based on error counts, then data reading accuracy is improved, but device complexity is increased
Solution Approach 1:
The system implements dynamic reference voltage updating where the update behavior adapts based on monitored error counts. The controller dynamically adjusts whether to update reference voltages by comparing current error counts against stored thresholds. This dynamic approach improves reading accuracy while keeping the control logic manageable through adaptive rather than static decision-making.
3Reliability
If reference voltages are updated to reduce errors, then reliability is improved, but productivity is reduced due to processing overhead
Solution Approach 1:
The system applies partial updating of reference voltages by only updating when error counts exceed specific thresholds. Rather than continuously updating or updating all reference voltages, the controller performs selective updates based on actual error conditions. This partial action approach maintains data storage reliability while minimizing the processing overhead that would otherwise reduce productivity.
Data Source
AI summary
In a data storage device that includes a non-volatile memory, a method includes determining that a current error correction code page count (CEC) is at least as large as a target error correction code page count (TEC). The CEC is a page count of error correction code (ECC) pages of data read from the memory during a time period from a previous time to a particular time using a set of reference voltages. In response to the CEC being at least as large as the TEC, the method includes updating a subset of the set of reference voltages conditioned upon a difference between a current mean error count (CMEC) and a previous mean error count being at least as large as a target mean delta error. The CMEC is based on a count of read errors associated with the ECC pages read during the time period.