Dynamic LLR Estimation in NAND Flash Soft Decoding
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Solution Overview
Problem
NAND flash memory devices face errors due to stress conditions such as NAND noise and interference during programming and read operations, leading to challenges in accurately decoding read outputs and maintaining endurance and resilience.
Innovation Solution
A method and system for decoding flash memory read operations by estimating slope information based on soft decoding errors, generating estimated soft information, and using this information to improve decoding efficiency, particularly under dynamic stress conditions, through techniques like dynamic LLR estimation and error vector analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hard decoding is used for NAND flash memory read operations, then the decoding process is simple and fast, but the error correction capability is insufficient under stress conditions
Solution Approach 1:
The patent introduces soft information (LLR values) as an intermediary between the read operation and the decoding process. Instead of directly decoding hard binary values, the system first generates soft information that represents the reliability of each bit, then uses this soft information to guide the decoding process. This intermediary layer enables more sophisticated error correction while maintaining a manageable system architecture.
Solution Approach 2:
The patent performs preliminary estimation of slope information and generation of soft information before the actual decoding operation. By pre-processing the read data to extract reliability information and estimate channel characteristics, the system prepares optimal decoding parameters in advance, which improves error correction capability without significantly increasing the complexity of the main decoding process.
2Adaptability or versatility
If static LLR estimation is used, then the decoding process is straightforward, but it cannot adapt to dynamic stress conditions during read operations
Solution Approach 1:
The patent implements dynamic LLR estimation by continuously updating slope information based on soft decoding errors observed during read operations. Instead of using fixed static parameters, the system adapts its estimation process in real-time according to the actual stress conditions and error patterns encountered, making the decoding process resilient to varying operational environments.
Solution Approach 2:
The patent employs feedback mechanisms where soft decoding errors are fed back into the slope information estimation process. The system monitors decoding performance and uses this feedback to refine and update the LLR estimation parameters, creating a closed-loop system that automatically adapts to changing stress conditions without manual intervention.
3Reliability
If multiple read operations are performed to improve accuracy, then the error correction improves, but the read time and energy consumption increase
Solution Approach 1:
The patent maintains continuous useful action by performing slope information estimation and soft information generation during the first read operation itself, rather than requiring separate preparation steps. The system extracts and processes reliability information concurrently with the read operation, ensuring that the full read time contributes to both data retrieval and error correction preparation, thereby avoiding additional time penalties.
Data Source
AI summary
A flash memory system may include a flash memory and a circuit for performing operations of the flash memory. The circuit may be configured to estimate slope information of a plurality of threshold voltage samples based on soft decoding errors in connection with a first read operation on the flash memory. The circuit may be further configured to generate estimated soft information based on the estimated slope information. The circuit may be further configured to decode a result of a second read operation on the flash memory based on the estimated soft information.