Memory Controller Voltage Calibration for Inter-Cell Interference
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Solution Overview
Problem
Existing memory systems face challenges in accurately reading data due to inter-cell interference effects, which can lead to read errors and reduced operation reliability, especially as data ages and threshold voltages shift over time.
Innovation Solution
The memory system employs a controller that executes multiple reading operations, including normal, first calibrating, and second calibrating readings, using shift tables to adjust voltages based on inter-cell interference effects, and groups word lines by threshold levels to optimize reading voltages and reduce the number of operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple reading operations (normal, first calibrating, second calibrating) are executed to suppress read errors, then reliability is improved, but the number of operations increases and reading speed decreases
Solution Approach 1:
The patent applies preliminary action by performing calibration reading operations before the normal reading operation. The controller executes first calibrating reading and second calibrating reading to adjust voltages based on inter-cell interference effects, thereby preparing the reading conditions in advance. This allows the subsequent normal reading to be performed with optimized voltages, reducing the need for multiple retry operations and improving overall reading efficiency while maintaining high reliability.
2Measurement precision
If calibration reading operations are performed to adjust voltages for inter-cell interference, then measurement precision is improved, but the time required for reading increases
Solution Approach 1:
The patent segments the calibration process into two distinct stages: first calibrating reading that adjusts voltages based on first inter-cell interference effects, and second calibrating reading that further adjusts voltages based on second inter-cell interference effects. This segmentation allows each calibration stage to focus on specific interference patterns, making the calibration process more efficient and targeted, thereby reducing the total time required while achieving high measurement precision.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting reading voltages based on detected inter-cell interference effects. The controller modifies voltage parameters during first and second calibrating reading operations to compensate for threshold voltage shifts caused by inter-cell interference. This adaptive parameter adjustment ensures accurate data reading even as interference conditions change, maintaining measurement precision without requiring excessive time.
3Reliability
If shift tables are used to adjust voltages based on inter-cell interference effects, then reliability is improved, but device complexity increases
Solution Approach 1:
The shift table is pre-populated with voltage adjustment values corresponding to different inter-cell interference conditions before normal operation. During calibration reading, the controller detects the interference level and directly retrieves the appropriate voltage adjustment from the pre-computed shift table, rather than calculating adjustments in real-time. This preliminary preparation of the shift table simplifies the controller's real-time processing requirements while maintaining high reliability through accurate voltage compensation.
Data Source
AI summary
According to one embodiment, a memory system includes a semiconductor memory and a controller. The semiconductor memory is configured to execute a first to third read operations. In the first read operation, a first voltage is applied to a selected word line. In the second read operation, a second voltage different from the first voltage and a third voltage are applied to the selected word line. In the third read operation, a fourth voltage different from the first to third voltages and a fifth voltage are applied to the selected word line. An absolute value of a difference between the second voltage and the fourth voltage is different from an absolute value of a difference between the third voltage and the fifth voltage.