Flash Memory Readout Using Bit Distribution and Adaptive Voltages
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Solution Overview
Problem
Flash memory cells experience disturbances in threshold voltage distribution due to factors like increased program/erase cycles and retention time, leading to incorrect data retrieval when using original control gate voltage settings.
Innovation Solution
A method and memory controller that perform multiple read operations on flash memory cells using different control gate voltage settings to determine binary digit distribution characteristics, allowing for accurate data retrieval by adapting to changes in threshold voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If original control gate voltage settings are used for reading data, then read operation simplicity is maintained, but data accuracy deteriorates due to threshold voltage distribution changes
Solution Approach 1:
The patent applies preliminary action by performing a read disturbance operation before the actual read operation. This preliminary read operation detects changes in threshold voltage distribution and adjusts control gate voltage settings in advance, ensuring that the subsequent data read operation uses optimized voltage settings for accurate data retrieval despite P/E cycle-induced distribution shifts.
2Measurement precision
If multiple read operations with different voltage settings are performed, then data retrieval accuracy improves, but read access time increases
Solution Approach 1:
The patent applies partial action by performing only one additional read operation beyond the standard single read. This read disturbance operation uses a first control gate voltage setting to detect threshold voltage distribution changes, allowing the system to achieve improved data retrieval accuracy without requiring multiple excessive read operations, thus limiting time overhead to a single additional operation.
3Reliability
If control gate voltage settings are adjusted to track threshold voltage distribution, then uncorrectable errors are reduced, but operation complexity increases
Solution Approach 1:
The patent applies feedback by using the results of the read disturbance operation to adjust control gate voltage settings for subsequent data read operations. The system detects threshold voltage distribution changes through the first read operation and uses this feedback information to optimize voltage settings, thereby reducing uncorrectable errors while maintaining a relatively simple operational framework through automated voltage adjustment.
Data Source
AI summary
A method for reading data stored in a flash memory includes at least the following steps: controlling the flash memory to perform a plurality of read operations upon a plurality of memory cells included in the flash memory; obtaining a plurality of bit sequences read from the memory cells, respectively, wherein the read operations read bits of a predetermined bit order from the memory cells by utilizing different control gate voltage settings; and determining readout information of the memory cells according to binary digit distribution characteristics of the bit sequences.