Read Voltage Search Unit for Nonvolatile Memory
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Solution Overview
Problem
In nonvolatile memory devices, especially multi-level cell (MLC) systems, the threshold voltage distribution can shift due to various factors, leading to read voltage misalignment, which affects data retention and read performance, and existing solutions are inefficient in quickly adapting to these changes.
Innovation Solution
A data storage device with a memory controller that includes an ECC circuit and a read voltage search unit, which calculates and adjusts the read voltage based on fail bit information to predict the moving direction and level of the read voltage, optimizing read performance by reducing the time taken to search for the optimal read voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a multi-level cell (MLC) is used to increase storage capacity, then the capacity is improved, but the threshold voltage distribution shifts leading to read voltage misalignment
Solution Approach 1:
The patent implements a feedback mechanism where the memory controller performs read operations, detects fail bits indicating threshold voltage shifts, and uses this information to dynamically adjust read voltages. The ECC circuit provides feedback about read errors, which triggers voltage search and adjustment operations to realign the read voltage with the shifted threshold voltage distribution, thereby maintaining measurement precision despite increased storage capacity.
Solution Approach 2:
The patent changes the read voltage parameter dynamically based on detected threshold voltage shifts. When fail bits indicate a shift in threshold voltage distribution, the memory controller performs a read voltage search to determine the optimal read voltage and adjusts the read voltage parameter accordingly. This allows the system to maintain accurate read operations in MLC configurations where threshold voltage shifts occur due to the increased storage capacity.
2Reliability
If traditional read voltage adjustment methods are used, then data retention is maintained, but the time to search for optimal read voltage is excessive
Solution Approach 1:
The patent performs preliminary actions by continuously monitoring fail bits during normal read operations and proactively adjusting read voltages before significant data retention issues occur. The system uses ECC information to detect early signs of threshold voltage shifts and initiates voltage search and adjustment operations in advance, reducing the overall time needed to maintain optimal read voltage alignment while ensuring data retention.
Solution Approach 2:
The patent applies partial action by performing read voltage searches and adjustments only for specific read units where fail bits indicate threshold voltage shifts, rather than globally adjusting all read voltages. This selective approach reduces the time required for voltage search and adjustment operations while maintaining data retention reliability in affected areas, avoiding unnecessary operations in read units that are still functioning correctly.
3Productivity
If the read voltage is adjusted frequently to track threshold voltage shifts, then read performance is improved, but the system complexity increases
Solution Approach 1:
The patent implements a self-service mechanism where the memory controller autonomously monitors fail bits, performs read voltage searches, and adjusts read voltages without external intervention. The ECC circuit automatically detects read errors and triggers voltage adjustment operations, and the system self-corrects threshold voltage misalignment issues using its own resources and information, reducing the need for complex external control mechanisms while maintaining high read performance.
Solution Approach 2:
The patent makes the memory controller multi-functional by combining error correction, fail bit detection, read voltage search, and voltage adjustment operations into a single integrated unit. Rather than requiring separate dedicated circuits for each function, the memory controller performs multiple functions using the same hardware resources, reducing overall system complexity while enabling frequent read voltage adjustments to maintain high read performance.
Data Source
AI summary
A data storage device according to example embodiments of inventive concepts includes a nonvolatile memory and a memory controller. In the nonvolatile memory, one read unit is configured to store a plurality of codewords. If a fail occurs in one or more codewords stored in the nonvolatile memory, the memory controller may search a read voltage of the nonvolatile memory using a correctable codeword. The data storage device according to example embodiments may predict an optimum read voltage level without performing a valley search operation.