Adaptive Read Voltage Adjustment in NAND Flash Memory
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Solution Overview
Problem
In NAND flash memory systems, changes in the distribution of electric charge in floating gates can lead to reading errors due to variations in threshold voltage, making it challenging to maintain optimal read voltages for accurate data retrieval.
Innovation Solution
A memory system that includes a nonvolatile memory and a controller, which calculates a second read voltage based on the threshold voltage distribution deviation between representative and other memory cells, allowing for adaptive read voltage adjustment to reduce reading errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If threshold voltage tracking operations are performed frequently to maintain accurate read voltages, then reading accuracy is improved, but system performance and throughput deteriorate due to increased operation frequency
Solution Approach 1:
The patent applies partial action by performing threshold voltage tracking selectively rather than continuously. The controller determines whether tracking is needed based on specific conditions (read error detection, program/erase operations, wear level thresholds) and only executes tracking operations when necessary. This reduces the frequency of tracking operations while maintaining reading accuracy when actually needed.
Solution Approach 2:
The patent changes the parameter of tracking operation frequency dynamically based on memory block wear level. When wear level exceeds a threshold, tracking is performed more frequently; when wear level is low, tracking is performed less frequently. This adaptive parameter adjustment optimizes the balance between reading accuracy and system performance throughout the memory's lifecycle.
2Reliability
If adaptive read voltage adjustment is implemented to reduce reading errors, then reading reliability is improved, but device complexity increases due to additional control logic
Solution Approach 1:
The patent implements self-service by enabling the memory system to automatically adjust read voltages based on its own state. The controller monitors read errors, program/erase operations, and wear levels, then autonomously determines when and how to perform threshold voltage tracking without external intervention. This self-managing approach improves reliability while keeping the control logic integrated and manageable within the existing controller architecture.
Data Source
AI summary
According to one embodiment, a controller searches a threshold voltage distribution of first memory cells corresponding to a first processing unit that is one processing unit among a plurality of processing units, and acquires a first read voltage. The controller calculates a second read voltage that is a read voltage for second memory cells corresponding to a second processing unit based on the acquired first read voltage and a first relation. The controller reads data from third memory cells included in the second memory cells by using the calculated second read voltage.