Memory System Read-Retry Voltage Control for Multi-Bit Cells
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Solution Overview
Problem
Existing memory systems face challenges in accurately reading data from multi-bit memory cells due to variations in threshold voltages, leading to read errors and inefficiencies in data retrieval.
Innovation Solution
A memory system and control method that utilize a test read voltage and a read retry table to determine voltage offset values, adjusting read voltages based on threshold voltage counts and expected counts to improve data read accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed read voltage is used for reading data from multi-bit memory cells, then the device complexity is reduced, but the measurement precision of threshold voltage detection deteriorates leading to read errors
Solution Approach 1:
The patent implements dynamic read voltage adjustment by introducing a read retry voltage generation mechanism that adapts the read voltage based on detected threshold voltage distributions. The memory controller dynamically selects from multiple read retry voltages (e.g., Vr1, Vr2, Vr3) depending on the detected data state distribution, transforming the static read voltage into a dynamic parameter that adapts to actual memory cell conditions, thereby resolving the contradiction between simplicity and precision.
Solution Approach 2:
The patent changes the read voltage parameter from a fixed value to a variable that can take multiple discrete values (default read voltage and multiple read retry voltages). By establishing a mapping between detected threshold voltage counts and appropriate read retry voltages, the system adjusts the read voltage parameter to match the actual threshold voltage distribution of memory cells, improving detection precision without significantly increasing system complexity.
2Measurement precision
If read retry operations with multiple voltage levels are implemented, then the measurement precision of data state detection is improved, but the loss of time for read operations increases
Solution Approach 1:
The patent performs preliminary detection of threshold voltage counts before executing the actual data reading operation. By first counting how many memory cells have threshold voltages below or above a reference voltage, the system can predict the appropriate read retry voltage to use, avoiding unnecessary trial-and-error read operations and reducing the overall time penalty of implementing multiple voltage levels.
Solution Approach 2:
The patent implements a feedback mechanism where the detected threshold voltage count information is fed back to select the appropriate read retry voltage. This feedback loop allows the system to adaptively choose the optimal read voltage based on actual memory cell conditions, improving detection accuracy while minimizing the time penalty by avoiding exhaustive search through all possible voltage levels.
3Reliability
If the read voltage is adjusted based on threshold voltage distribution, then the reliability of data reading is improved, but the device complexity increases due to additional voltage control circuitry
Solution Approach 1:
The patent designs the read retry voltage generation mechanism to serve multiple functions: it detects threshold voltage distributions, determines appropriate correction voltages, and executes adaptive reading operations. By making the memory controller multi-functional, the patent avoids adding separate dedicated circuits for each function, thereby improving reading reliability while minimizing the increase in overall device complexity.
Solution Approach 2:
The patent introduces a read retry table as an intermediary data structure that stores the mapping between threshold voltage count ranges and corresponding read retry voltages. This intermediary component simplifies the control logic by pre-establishing the relationship between detection results and corrective actions, reducing the complexity of real-time voltage selection while maintaining high reading reliability.
Data Source
AI summary
An example memory system includes a memory device and a memory controller. The memory device includes memory cells each configured to be in one of data states. The memory controller is configured to: perform a read operation using a test read voltage corresponding to a selected data state among the data states; acquire a count of memory cells each having a threshold voltage that satisfies a preset condition including: the threshold voltage being less than or equal to the test read voltage, or the threshold voltage being greater than or equal to the test read voltage; determine a difference between the count and an expected count; and acquire at least one read retry voltage according to the difference, a mapping relationship, and a read retry table, wherein the mapping relationship includes a correspondence between an expected voltage offset value and the difference.