Memory Controller Read-Voltage Mapping for Threshold Drift Correction
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Solution Overview
Problem
Existing memory devices face challenges in accurately reading data due to variations in threshold voltage distributions caused by temperature changes and read disturbances, leading to read errors that conventional error correction methods struggle to address effectively.
Innovation Solution
Implementing a memory controller that utilizes a read retry table and error correction mechanisms, including hard bit decode, soft decode, and RAID-based data recovery, to identify optimal read voltages and correct errors through a combination of hard and soft decoding and redundant array techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional error correction methods are used, then the system structure remains simple, but read accuracy deteriorates due to threshold voltage variations and read disturbances
Solution Approach 1:
The patent performs preliminary actions by conducting multiple read operations at different read voltages before final error correction. The controller reads data at a first read voltage to obtain first read data, then at a second read voltage to obtain second read data, and uses these preliminary readings to determine the final corrected data. This preliminary action approach allows the system to adapt to threshold voltage variations and read disturbances before making the final correction decision.
Solution Approach 2:
The error correction process is segmented into multiple independent stages: first read operation at first read voltage, second read operation at second read voltage, comparison stage to determine discrepancy, and correction stage. By dividing the error correction into these segments, the system can handle different types of errors at different stages without requiring a completely complex unified correction mechanism.
2Reliability
If read voltage is fixed, then the control mechanism remains simple, but reliability deteriorates under temperature changes and read disturbances
Solution Approach 1:
The patent implements dynamic read voltage adjustment by performing read operations at multiple different read voltages (first read voltage and second read voltage) rather than using a fixed voltage. The controller dynamically selects and switches between different read voltages based on the detected threshold voltage variations and read disturbances, thereby maintaining reliable data retrieval under changing temperature and disturbance conditions.
Solution Approach 2:
The system uses feedback by comparing the first read data obtained at the first read voltage with the second read data obtained at the second read voltage. Based on this comparison and the detected discrepancies caused by threshold voltage variations, the controller determines the appropriate correction and adjusts subsequent read operations accordingly, creating a closed-loop feedback mechanism for maintaining reliability.
3Measurement precision
If multiple read voltages are used, then read accuracy improves through error correction, but processing time increases due to multiple read operations
Solution Approach 1:
The patent applies partial action by performing multiple read operations only when necessary - specifically when error correction is needed due to detected threshold voltage variations or read disturbances. The controller determines whether correction is required by comparing read data from different voltages, and only then performs the additional read operations and correction steps, rather than always performing full multi-voltage read sequences.
Data Source
AI summary
Examples of the present disclosure disclose a memory controller, a memory system, and a control method thereof. The memory controller is configured to: control a memory device to perform a read operation with a first read voltage corresponding to a first data state of a memory cell; obtain the first number of memory cells with a threshold voltage being less than or equal to the first read voltage, and obtain the second number of memory cells with a threshold voltage being greater than the first read voltage; determine a difference between the second number and the first number; and acquire a voltage offset value from a mapping table according to the difference.