Flash Memory Read Threshold Adjustment for Charge Distribution Shifts
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Solution Overview
Problem
Flash memories face challenges in accurately reading data due to disturbances in electric charge distributions, which can result from write, read, or retention disturbances, leading to incorrect threshold voltage settings and failed codeword error corrections.
Innovation Solution
A memory controller is designed to determine an electric charge distribution parameter by performing codeword error correction and using a look-up table to find a target gate voltage combination, thereby adapting to changes in charge distributions and ensuring accurate data reading without the need for individual testing of each gate voltage combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional fixed threshold voltage reading methods are used, then the reading process is simple and fast, but the accuracy deteriorates due to charge distribution changes from write/read/retention disturbances
Solution Approach 1:
The patent implements dynamic threshold voltage adjustment by determining an electric charge distribution parameter that reflects the actual charge state of the flash memory. Instead of using fixed predetermined threshold voltages, the system adaptively adjusts the threshold voltage based on the determined charge distribution parameter, allowing the reading process to respond to changes caused by write disturbances, read disturbances, and retention disturbances. This dynamic approach resolves the contradiction by maintaining reading accuracy through adaptation while managing complexity through systematic parameter determination.
Solution Approach 2:
The patent changes the threshold voltage parameter based on the determined electric charge distribution parameter. By modifying the threshold voltage to match the actual charge distribution state, the system compensates for disturbances and maintains accurate data reading. This parameter change approach allows the system to adapt to varying charge conditions without requiring complete redesign of the reading mechanism.
2Measurement precision
If individual testing of each gate voltage combination is performed, then the most accurate threshold can be found, but the time consumption and productivity are significantly reduced
Solution Approach 1:
The patent performs preliminary determination of the electric charge distribution parameter before the actual data reading operation. By establishing the charge distribution state in advance, the system can directly apply the corresponding threshold voltage without needing to test multiple combinations during the reading process. This preliminary action eliminates time-consuming iterative testing while ensuring accurate threshold voltage selection, thereby resolving the contradiction between precision and productivity.
Solution Approach 2:
The system uses feedback from the determined charge distribution parameter to directly set the threshold voltage. Instead of testing multiple gate voltage combinations and evaluating results iteratively, the feedback mechanism provides direct information about the optimal threshold voltage setting based on the current charge state. This feedback approach achieves high accuracy without the time penalty of exhaustive testing.
3Productivity
If predetermined control gate voltages are used for reading, then the reading operation is efficient, but it fails when charge distribution changes due to disturbances
Solution Approach 1:
The patent transforms the static predetermined gate voltage approach into a dynamic system that adjusts gate voltages based on the determined charge distribution parameter. By making the gate voltage selection adaptive rather than fixed, the system maintains both efficiency and reliability - the efficiency comes from direct parameter-based selection rather than iterative testing, while reliability is ensured by matching the gate voltage to the actual charge state.
Solution Approach 2:
The system changes the gate voltage parameter based on the determined charge distribution parameter to compensate for disturbances. When write disturbances, read disturbances, or retention disturbances alter the charge distribution, the system detects these changes and adjusts the gate voltage accordingly. This parameter adaptation maintains reading success rates while preserving operational efficiency through systematic rather than trial-based adjustment.
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.