Controller Category Table for Nonvolatile Memory Read Voltage
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Solution Overview
Problem
Data storage devices using semiconductor memory devices often experience errors due to interference or wear from repeated erase/program operations, leading to failed read operations if not corrected.
Innovation Solution
A data storage device with a controller that includes a category table and a read voltage table, allowing for the determination of suitable read voltages based on logical block addresses to improve read operation success rates by adjusting read voltages according to the characteristics of the data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed read voltage is used for all memory cells, then the device complexity is low, but the read operation success rate decreases due to wear and interference variations
Solution Approach 1:
The patent segments the memory device into multiple categories based on wear and interference characteristics. The category table divides logical block addresses into different groups, and the read voltage table assigns specific read voltages to each category, allowing differentiated read operations for different memory regions.
Solution Approach 2:
The patent changes the read voltage parameter dynamically based on the memory cell category. Instead of using a fixed read voltage, the controller selects from multiple read voltages (e.g., first read voltage, second read voltage) depending on the wear and interference characteristics of the target memory region.
2Reliability
If read voltage is adjusted for each memory cell, then the read operation success rate improves, but the operation time increases due to voltage determination overhead
Solution Approach 1:
The patent performs preliminary classification of logical block addresses into categories and pre-assigns read voltages to each category before actual read operations. The category table and read voltage table are prepared in advance, allowing the controller to quickly determine the appropriate read voltage by simply looking up the category corresponding to the target LBA.
Solution Approach 2:
The patent creates lookup tables (category table and read voltage table) that store pre-computed mapping relationships between LBAs and read voltages. During read operations, the controller copies the relevant category and voltage information from these tables rather than performing complex real-time analysis, significantly reducing operation time.
3Measurement precision
If multiple read voltages are used for different memory regions, then measurement precision of data state improves, but the device complexity increases due to additional voltage control
Solution Approach 1:
The patent applies different read voltages to different local regions (memory blocks or pages) based on their specific wear and interference characteristics. Each memory region is assigned a appropriate read voltage from the read voltage table, allowing optimized data sensing for each local area while maintaining overall system manageability.
Solution Approach 2:
The patent introduces the category table and read voltage table as intermediary structures that mediate between the controller and the diverse memory regions. These tables serve as lookup mechanisms that simplify the voltage selection process, translating complex wear and interference characteristics into straightforward voltage selections.
Data Source
AI summary
A data storage device includes a nonvolatile memory device and a controller configured to control an operation of the nonvolatile memory device. The controller includes an RAM in which a category table that categories with respect to LBAs are defined and a read voltage table that read voltages with respect to the categories are set are stored and a controller configured to, when a read request and an LBA to be read are received from a host apparatus, determine a category corresponding to the LBA with reference to the category table and perform a read operation on a read-requested memory cell of the nonvolatile memory device by applying a read voltage corresponding to the determined category to the memory cell with reference to the read voltage table.