Memory Controller Patrol Operation for Data Reliability
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Solution Overview
Problem
Existing memory systems face challenges in efficiently managing read operations and maintaining data reliability due to variations in threshold voltage of memory cell transistors over time, leading to increased error bits and potential data retention issues.
Innovation Solution
The memory system employs a patrol operation that includes tracking read and shift read to optimize read voltages, record correction values, and detect defects, thereby improving data reliability and reducing read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If patrol operation is executed for all word lines including both first group and second group, then data reliability is improved through comprehensive defect detection, but read latency increases due to additional read operations
Solution Approach 1:
The patent segments word lines into two groups: first group word lines undergo patrol operation (tracking read and shift read) while second group word lines are skipped. This segmentation allows the system to detect defects in critical areas without performing exhaustive reads on all word lines, thereby reducing overall read latency while maintaining data reliability through targeted inspection of the first group.
2Measurement precision
If tracking read and shift read are performed for all word lines, then optimal read voltages are determined accurately, but power consumption increases due to multiple read operations
Solution Approach 1:
The patent applies segmentation by limiting tracking read and shift read operations to only the first group of word lines. This selective approach enables accurate determination of optimal read voltages for the majority of data storage areas without incurring the power cost of performing the same operations on every single word line, thus achieving a balance between measurement precision and energy efficiency.
3Reliability
If patrol operation is executed frequently to detect defects early, then data integrity is maintained, but productivity decreases due to increased operation overhead
Solution Approach 1:
The patent segments the patrol operation scope to include only first group word lines, excluding second group word lines from routine patrol operations. This segmentation reduces the overhead of frequent defect detection operations while maintaining data integrity for the critical first group areas, thereby improving overall operation efficiency without significantly compromising reliability.
Data Source
AI summary
A memory system according to an embodiment includes a semiconductor memory, and a memory controller. The semiconductor memory comprises memory cells and word lines. Each of the word lines is connected to the memory cells. The memory controller executes a patrol operation including a read operation of the semiconductor memory. The word lines are classified into one of first and second groups. The memory controller executes patrol operations in which the word lines are respectively selected in a first patrol period and, in a second patrol period subsequent to the first patrol period, executes a patrol operation in which the word line included in the first group is selected and omits a patrol operation in which the word line included in the second group is selected.