Controller Erasure Status Detection Using Dual Read Voltages
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Solution Overview
Problem
Data storage devices face challenges in accurately determining whether memory cells are erased, leading to instability in the flash translation layer (FTL) due to incomplete erase operations and environmental disturbances.
Innovation Solution
A data storage device with a nonvolatile memory device and a controller that applies a first read voltage and, if necessary, a second read voltage to determine the erasure status of memory cells, using the lowest levels of read voltages within a set, and performs error correction operations to ensure accurate determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single read voltage is used to determine erasure status, then the operation is simple and fast, but the determination accuracy is insufficient leading to FTL instability
Solution Approach 1:
The patent segments the read voltage set into multiple distinct read voltages (first read voltage and second read voltage) to perform separate reads. By dividing the determination process into multiple stages with different voltages, the system achieves higher accuracy in erasure status detection while managing complexity through structured segmentation of the read operations.
Solution Approach 2:
The patent applies partial action by selectively performing a second read operation only when the first read indicates an indeterminate erasure status. This approach avoids always performing excessive reads while ensuring accuracy is maintained when needed, balancing operation complexity with determination precision.
2Measurement precision
If multiple read voltages are applied to determine erasure status, then determination accuracy improves, but power consumption and operation time increase
Solution Approach 1:
The patent implements partial action by applying the second read voltage only when necessary - specifically when the first read result indicates an indeterminate erasure status. This conditional approach ensures high determination accuracy while minimizing unnecessary power consumption from redundant read operations.
Solution Approach 2:
The system uses feedback from the first read operation to determine whether a second read is necessary. The controller analyzes the first read result and only initiates additional read operations when the feedback indicates ambiguity in erasure status, thereby optimizing power consumption based on actual determination needs.
3Reliability
If error correction operations are performed, then data accuracy improves, but operation time and processing complexity increase
Solution Approach 1:
The patent applies partial action by performing error correction operations only when the read results indicate potential errors or indeterminate erasure status. Normal operations proceed without correction, minimizing time loss while maintaining high data accuracy when needed.
Solution Approach 2:
The system uses feedback from read operations to determine whether error correction is necessary. The controller monitors read results and selectively initiates error correction only when feedback indicates data integrity issues, thereby balancing reliability with operation time efficiency.
Data Source
AI summary
A data storage device includes a nonvolatile memory device including a plurality of memory cells; and a controller suitable for determining whether the memory cells are erased or not, wherein, when it is determined, based on first data read as a read voltage set including a first read voltage is applied to the memory cells, that the memory cells are not erased, the controller determines whether the memory cells are erased or not based on second data read as the read voltage set in which the first read voltage is replaced with a second read voltage is applied to the memory cells, and wherein the first and second read voltages are read voltages of lowest levels among read voltages included in the read voltage set.