Flash Memory Read Voltage Selection 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 caused by program/erase cycles and data retention, leading to incorrect threshold voltage settings and unsuccessful codeword error corrections.
Innovation Solution
A memory controller is designed with a control logic circuit, receiving circuit, data processing circuit, and storage unit to determine electric charge distribution parameters and utilize a look-up table to find a target gate voltage combination, enabling faster and more accurate data reading by adapting to changes in charge distributions without individually testing each voltage combination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional reading methods with fixed gate voltage combinations are used, then the reading process is simple, but the data reading accuracy deteriorates due to charge distribution changes from program/erase cycles and retention time
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing multiple gate voltage combinations and their corresponding electric charge distribution parameters in a look-up table before actual data reading operations. When reading data, the controller determines the current charge distribution state and directly retrieves the appropriate voltage combination from the pre-prepared table, avoiding real-time complex calculations and enabling accurate reading despite charge distribution changes from program/erase cycles and retention time effects
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting gate voltage combinations based on the determined electric charge distribution state of memory units. Instead of using fixed voltage values, the system selects from multiple pre-calculated voltage combinations that correspond to different charge distribution scenarios, allowing the reading operation to adapt to changing memory unit states caused by program/erase cycles and data retention, thereby maintaining high reading accuracy
2Measurement precision
If multiple gate voltage combinations are tested individually to find the correct one, then the reading accuracy is improved, but the reading time increases significantly
Solution Approach 1:
The patent eliminates time-consuming individual testing by pre-calculating all necessary gate voltage combinations and their corresponding electric charge distribution parameters before operation. The look-up table stores these pre-computed values, allowing the controller to directly retrieve the appropriate voltage combination based on the current charge distribution state, achieving both high reading accuracy and fast reading speed without sequential testing
Solution Approach 2:
The patent applies beforehand cushioning by pre-preparing a comprehensive look-up table that contains all possible gate voltage combinations and their corresponding charge distribution parameters. This pre-computation cushions against the time loss that would otherwise occur during actual reading operations, ensuring that regardless of the memory unit's charge distribution state, the correct voltage combination is immediately available for instant retrieval
3Productivity
If the original threshold voltage setting is used, then the reading operation is fast, but the error correction fails due to threshold voltage distribution changes
Solution Approach 1:
The patent implements feedback by determining the actual electric charge distribution state of memory units before reading operations and using this information to select the appropriate gate voltage combination from the look-up table. This feedback mechanism ensures that the threshold voltage settings are continuously adapted to the current memory unit state, maintaining both high reading speed and high error correction success rate by preventing mismatches between fixed voltage settings and changing charge distributions
Solution Approach 2:
The patent applies preliminary action by pre-calculating multiple gate voltage combinations corresponding to different electric charge distribution states and storing them in a look-up table. Instead of using a single original threshold voltage setting that becomes outdated, the system has all necessary voltage combinations prepared in advance, allowing immediate selection of the correct setting based on the current charge distribution state, thus maintaining both speed and reliability
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.