Flash Memory Readout Using Bit Distribution and Voltage Compensation
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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
1Reliability
If original control gate voltage settings are used for reading flash memory cells, then the read operation is simple and fast, but the data retrieval accuracy deteriorates due to threshold voltage distribution changes from program/erase cycles and retention time
Solution Approach 1:
The patent applies preliminary action by performing a read disturbance compensation operation before the actual read operation. The controller first reads the data using original control gate voltages, then performs a compensation read with adjusted control gate voltages to correct for threshold voltage shifts caused by program/erase cycles and retention time. This preliminary compensation ensures accurate data retrieval without requiring complex real-time adjustments during the main read operation.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting control gate voltage levels based on the program/erase cycle count and retention time. The controller modifies the control gate voltage parameters to compensate for threshold voltage distribution changes in the flash memory cells. This allows the system to maintain high data retrieval accuracy by adapting the voltage parameters to the current state of the memory cells, rather than using fixed original voltage settings.
2Reliability
If multiple read operations with different control gate voltage settings are performed to track threshold voltage distribution, then data accuracy improves, but the read time increases
Solution Approach 1:
The patent uses preliminary action by performing the threshold voltage tracking and control gate voltage adjustment in advance, before the actual data read operation. The controller executes a compensation read operation first to determine the appropriate control gate voltage settings, then uses these pre-determined voltages for the main data read. This eliminates the need for multiple iterative reads during data retrieval, thus maintaining high accuracy while minimizing time loss.
Solution Approach 2:
The patent applies continuity of useful action by making the threshold voltage tracking an ongoing background process that continuously updates the control gate voltage settings based on program/erase cycle count and retention time. This continuous tracking ensures that the voltage parameters are always optimized for current memory cell conditions, allowing rapid accurate reads without requiring repeated measurement and adjustment cycles during each data access operation.
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.