Flash Memory Read Threshold Search for Joint Soft Decoding
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Solution Overview
Problem
High resolution read attempts in flash memory devices are time-consuming due to the need for multiple read attempts around proximate read thresholds, which are affected by aging effects and changes in threshold voltage distribution over time, leading to inefficiencies in finding desired read thresholds and generating reliability metrics for soft decoding.
Innovation Solution
Implementing a joint digital signal processing (DSP) and error correction code (ECC) operation that performs multiple read attempts using multiple read thresholds to determine reliability metrics, allowing for high resolution soft sampling and reducing the overhead in producing decoder inputs by characterizing the statistical distribution of flash memory cells and adjusting read thresholds accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple read attempts are performed around proximate read thresholds to achieve high resolution metrics, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent combines the read threshold search process and soft decoding process into a single joint operation. Instead of performing threshold search first and then separately performing soft decoding with multiple high-resolution read attempts, the system performs both operations simultaneously using the same read attempts, thereby reducing the total number of read operations required while maintaining measurement precision.
Solution Approach 2:
The patent performs a limited number of read attempts at high resolution that suffice for both threshold determination and soft decoding purposes. Rather than exhaustively searching all possible thresholds and then performing separate soft decoding, the system performs a targeted set of read attempts that provide sufficient information for both functions, reducing overall time consumption.
2Reliability
If separate DSP operation for threshold search and separate soft sampling are performed, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent merges the DSP threshold search operation and the soft sampling operation into a single integrated process. The same read attempts used for threshold search are also utilized for generating soft decoding inputs, eliminating the need for separate operational stages and reducing overall system complexity while maintaining reliability.
Solution Approach 2:
The read attempts are designed to serve multiple functions simultaneously: they are used for both determining the optimal read threshold and for generating the soft information required for decoding. This multi-functionality reduces the number of separate operations needed and simplifies the overall read process.
3Measurement precision
If additional read attempts are performed after threshold finding for soft sampling, then measurement precision is improved, but productivity decreases
Solution Approach 1:
The patent combines threshold search and soft sampling into a single operation, so that the read attempts performed for threshold determination are simultaneously used for generating soft information. This eliminates the need for additional separate read attempts after threshold finding, thereby improving productivity while maintaining the precision required for soft decoding.
Solution Approach 2:
The system maintains continuous useful action by ensuring that each read attempt serves dual purposes: contributing to threshold determination and simultaneously providing data for soft decoding. This continuous multi-purpose action eliminates idle or redundant read operations, improving overall reading efficiency.
Data Source
AI summary
A flash memory controller, a computer readable medium and a method. The method may include performing, by a flash memory controller, multiple read attempts of a group of flash memory cells, using multiple read thresholds, to provide multiple read results; determining, by the flash memory controller and based upon the multiple read results, a reliability metric of each of the multiple read results; and error correction decoding the multiple read results based upon reliability metrics associated with the multiple read results.