Soft Read Threshold Selection for Error Correction and Compression
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Solution Overview
Problem
Conventional error correction in memory devices, such as NAND flash memory, relies on hard bit reads which have limited error correction capabilities, and soft bit reads, while improving correction, can reduce data compressibility.
Innovation Solution
Implementing Soft Bit Read (SBR) thresholds that balance error correction capability with data compressibility by adjusting voltage levels for multiple reads, using a cost function that considers mutual information, compression ratio, and error correction strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft bit reads are performed at multiple threshold voltages to improve error correction capability, then error correction capability is improved, but data compressibility deteriorates
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the SBR thresholds based on the hard read result. When the hard read result is uncertain (close to the threshold), the SBR thresholds are adjusted to gather more reliable soft information. This selective adjustment of voltage parameters improves error correction only when necessary, preserving data compressibility for cases where hard reads are sufficient.
2Reliability
If multiple soft bit read thresholds are used to increase reliability, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements partial action by performing soft bit reads selectively rather than universally. The controller determines whether SBR is necessary based on the hard read result's proximity to the threshold. Only when the hard read is uncertain does the system perform additional soft bit reads, reducing overall operational complexity while maintaining reliability for critical cases.
Solution Approach 2:
The patent applies dynamics by making the read operation adaptive. The decision to perform soft bit reads and the selection of SBR thresholds are dynamic, changing based on the actual hard read outcome. This dynamic approach optimizes the balance between reliability and complexity by adjusting the read strategy in real-time according to data conditions.
Data Source
AI summary
A method for selecting Soft Bit Read (SBR) thresholds in a memory device, includes setting, by a controller, a range of SBR thresholds around a Hard Read Position (HRP) for the memory device. The controller calculates mutual information for each set of SBR thresholds within the range of SBR thresholds. The controller calculates a theoretical compression ratio for each set of SBR thresholds in the range of SBR thresholds. The controller selects SBR thresholds from the range of SBR thresholds that provide a balance of the mutual information and the theoretical compression ratio.