Dynamic Read Voltage Grouping for Memory Reliability
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Solution Overview
Problem
Existing memory systems face challenges in maintaining data reliability and processing capability due to time differences in write operations, which affect the optimal read voltage values and increase error bits.
Innovation Solution
The memory system dynamically adjusts the configuration of cell unit groups by moving the boundary position between groups based on time differences in write operations, allowing for optimal read voltage settings and reducing error bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the memory system uses a fixed read voltage for all cell units, then the device complexity is reduced, but the data reliability deteriorates due to time differences in write operations causing threshold voltage shifts
Solution Approach 1:
The memory controller divides cell units into multiple groups (first group and second group) based on write operation timing. Each group is assigned a different read voltage correction amount, allowing differentiated voltage control for cells written at different times. This segmentation resolves the contradiction by enabling reliability improvement through group-specific voltage adjustment without requiring individually complex control for each cell unit.
Solution Approach 2:
The system changes the read voltage parameter dynamically based on the write operation time difference. When the time difference exceeds a reference value, the system switches from using a first read voltage correction amount to a second read voltage correction amount. This parameter change approach allows the system to adapt to threshold voltage shifts caused by time differences, improving data reliability while maintaining relatively simple control logic.
2Reliability
If the memory system applies error correction processes frequently, then the data reliability is improved, but the processing capability deteriorates due to increased time consumption
Solution Approach 1:
The system performs preliminary classification of cell units into different groups based on write operation timing before read operations occur. By pre-organizing cell units according to their write time characteristics, the system can apply appropriate read voltage correction amounts without requiring frequent error correction processes. This preliminary action reduces the need for subsequent error correction, thereby improving processing capability while maintaining data reliability.
3Measurement precision
If the memory system uses a single correction amount for all cell units, then the device complexity is reduced, but the measurement precision deteriorates in detecting actual data due to threshold voltage variations
Solution Approach 1:
The system applies different read voltage correction amounts to different groups of cell units based on their specific write operation timing characteristics. Instead of using a uniform correction amount, the system tailors the correction amount to each group's local characteristics (write time differences). This local quality approach improves measurement precision by matching correction amounts to actual threshold voltage variations in each group, while keeping device complexity manageable through group-based rather than individual-based control.
Data Source
AI summary
According to one embodiment, a memory system includes a memory chip and a memory controller. A first cell unit and a second cell unit are classified into a first group. A third cell unit is classified into a second group. The memory controller is configured to use a first correction amount of a read voltage when data of the first group is read and to use a second correction amount of the read voltage when data of the second group is read. When a time difference from a write operation of the first cell unit to the write operation of the second cell unit exceeds a reference value, the memory controller is configured to change a boundary position between the first group and the second group to between the first cell unit and the second cell unit, and to classify the second cell unit into the second group.