Memory Subsystem Controller Voltage Distribution Read Levels
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Solution Overview
Problem
Memory devices face increased bit error rates due to temporal voltage shift caused by slow charge loss, which affects the accuracy of read operations in non-volatile memory systems like NAND devices.
Innovation Solution
A memory sub-system controller determines read level values by measuring voltage distribution parameters for each block, using a mapping table to identify suitable read levels that mitigate temporal voltage shift, allowing for efficient read operations by storing and retrieving distribution voltages less frequently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If read level values are determined dynamically for each read operation to mitigate temporal voltage shift, then data retrieval accuracy is improved, but the number of operations and overhead increases
Solution Approach 1:
The system performs preliminary measurement of voltage distribution parameters and determines read level values in advance, storing them for later use. This preliminary action eliminates the need to perform measurements and determinations during every read operation, thereby reducing the number of operations while maintaining data retrieval accuracy through adaptive read levels
Solution Approach 2:
The system determines voltage distribution parameters and read level values specifically for each block based on its local characteristics, rather than using global parameters for the entire memory device. This block-level local quality approach ensures accurate compensation for temporal voltage shift in each block while avoiding unnecessary operations in blocks that don't require it
2Reliability
If voltage distribution parameters are measured for each block to adapt to temporal voltage shift, then error rates are reduced, but device complexity increases
Solution Approach 1:
The system introduces voltage distribution parameters as intermediary measurements that characterize the temporal voltage shift in each block. These parameters serve as mediators between the physical voltage shift phenomenon and the read level adjustment mechanism, simplifying the control complexity by providing a single measurable quantity that captures the essential behavior of voltage drift over time
Solution Approach 2:
The system changes the parameter used for read level determination from fixed threshold voltages to dynamic voltage distribution parameters that adapt to temporal voltage shift. By monitoring changes in these parameters over time, the system can adjust read levels to compensate for voltage drift, thereby reducing error rates while maintaining manageable device complexity through parameter-based control
Data Source
AI summary
A method can include receiving a request to read data from a memory cell of a memory device coupled with the processing device, determining a voltage distribution parameter value associated with the memory cell, determining a set of read levels associated with the voltage distribution parameter value, wherein each read level in the determined set of read levels corresponds to a respective voltage distribution of the memory cell, and reading, using the determined set of read levels, data from the memory cell. The voltage distribution parameter value can be determined by identifying a particular voltage distribution of the memory cell by sampling the memory cell at a plurality of voltage levels, and determining the voltage distribution parameter value based on the particular voltage distribution. The voltage distribution parameter value can be a voltage value that is included in the particular voltage distribution.