Flash Memory Readout Using Bit Distribution Voltage Tracking
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Solution Overview
Problem
Flash memory systems face challenges in accurately reading data due to changes in threshold voltage distribution caused by factors like increased program/erase cycles and retention time, leading to incorrect data retrieval and uncorrectable errors.
Innovation Solution
A method and memory controller that utilize binary digit distribution characteristics of bit sequences to adaptively track and adjust control gate voltages, ensuring accurate data reading by performing multiple read operations with different voltage settings and employing error correction mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If original control gate voltage settings are used for reading data from flash memory cells, then the reading process is simple and fast, but data accuracy deteriorates due to threshold voltage distribution changes caused by program/erase cycles and retention time
Solution Approach 1:
The patent applies preliminary action by performing a test read operation before the actual data read to detect threshold voltage distribution changes. The controller reads test data, compares it with expected values, and adjusts control gate voltages in advance based on detected errors. This preliminary detection and adjustment ensures that subsequent data reads use optimized voltage settings, resolving the contradiction between simple reading processes and data accuracy.
2Reliability
If multiple read operations with different control gate voltage settings are performed to improve data accuracy, then reading reliability improves, but reading time increases
Solution Approach 1:
The patent performs voltage adjustment and test reads in advance before actual data retrieval. By detecting threshold voltage distribution changes and optimizing control gate voltages beforehand, the system ensures that subsequent data reads require minimal additional operations. This preliminary action reduces the time penalty of multiple read operations while maintaining high reading reliability.
Solution Approach 2:
The patent implements feedback by reading test data, comparing it with expected values, and using the detected errors to adjust control gate voltages. This closed-loop feedback mechanism optimizes voltage settings based on actual memory cell behavior, improving reading reliability while minimizing the number of retry operations needed, thus reducing overall reading time.
3Measurement precision
If control gate voltages are adjusted to track threshold voltage distribution changes, then data retrieval accuracy improves, but the control mechanism becomes more complex
Solution Approach 1:
The patent uses feedback by reading test data, comparing it with expected values, and adjusting control gate voltages based on detected errors. This feedback loop continuously optimizes voltage settings to track threshold voltage distribution changes, improving data retrieval accuracy while keeping the control mechanism manageable through automated error detection and correction.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting control gate voltage levels based on detected threshold voltage distribution shifts. Instead of using fixed voltage settings, the system modifies voltage parameters in response to memory cell degradation, thereby maintaining high data retrieval accuracy despite increasing control complexity.
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.