Flash Memory Read Threshold Adaptation for Charge Distribution Drift
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Solution Overview
Problem
Flash memories face challenges in accurately reading data due to disturbances in electric charge distributions caused by program/erase cycles and data retention, leading to incorrect threshold voltage settings and unsuccessful codeword error corrections.
Innovation Solution
A memory controller with a control logic circuit, receiving circuit, and data processing circuit that selects an initial gate voltage combination, performs codeword error correction, and determines an electric charge distribution parameter, using a look-up table to find a target gate voltage combination for accurate data reading, thereby reducing the need for individual testing of voltage combinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional fixed threshold voltage settings are used for reading flash memory, then the reading process is simple and fast, but the accuracy of data retrieval deteriorates due to charge distribution changes from program/erase cycles and retention
Solution Approach 1:
The system performs preliminary actions by determining electric charge distribution parameters and selecting optimized gate voltage combinations before the actual data reading operation. The control logic circuit determines threshold voltage distribution parameters and selects gate voltage combinations in advance, so when data needs to be read, the appropriate voltage settings are already prepared, improving accuracy without adding complexity to the reading process itself
Solution Approach 2:
The system implements feedback by using determined electric charge distribution parameters to adjust and select gate voltage combinations. The control logic circuit continuously monitors charge distribution changes and provides feedback by selecting appropriate gate voltage combinations from a codebook, creating a closed-loop system that adapts to memory state changes while maintaining reading simplicity
2Measurement precision
If individual testing of voltage combinations is performed to find optimal settings, then reading accuracy improves, but the time required for data retrieval increases significantly
Solution Approach 1:
The system pre-determines electric charge distribution parameters and pre-selects optimized gate voltage combinations before actual data reading operations. By performing voltage combination selection in advance based on charge distribution analysis, the system avoids time-consuming individual testing during data retrieval, thus improving accuracy without sacrificing speed
Solution Approach 2:
The system changes parameters by determining electric charge distribution parameters and using these to select from multiple pre-defined gate voltage combinations. Instead of individually testing voltages, the system changes to a parameter-based selection approach where the control logic circuit determines charge distribution characteristics and maps these to appropriate voltage combinations from a codebook, significantly reducing retrieval time
3Reliability
If adaptive tracking of electric charge distributions is implemented, then uncorrectable errors are reduced, but the complexity of the memory controller increases
Solution Approach 1:
The control logic circuit implements feedback by determining electric charge distribution parameters and using this information to select optimized gate voltage combinations. This closed-loop approach continuously adapts to charge distribution changes, reducing uncorrectable errors while maintaining controller complexity at acceptable levels through efficient algorithms and pre-computed voltage combinations
Solution Approach 2:
The control logic circuit acts as an intermediary between the flash memory and the host system, performing adaptive charge distribution analysis and gate voltage selection. This intermediary function handles the complexity of adaptive tracking internally, presenting a simple interface to the host while improving reliability through sophisticated charge distribution monitoring and voltage combination selection
Data Source
AI summary
An exemplary method for reading data stored in a flash memory includes: selecting an initial gate voltage combination from a plurality of predetermined gate voltage combination options; controlling a plurality of memory units in the flash memory according to the initial gate voltage combination, and reading a plurality of bit sequences; performing a codeword error correction upon the plurality of bit sequences, and determining if the codeword error correction successful; if the codeword error correction is not successful, determining an electric charge distribution parameter; determining a target gate voltage combination corresponding to the electric charge distribution parameter by using a look-up table; and controlling the plurality of memory units to read a plurality of updated bit sequences according to the target gate voltage combination.