NAND Flash Soft Decoding Using Extrinsic Page Information
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Solution Overview
Problem
Flash memory devices, such as NAND flash memory, experience errors due to noise and interference during programming and read operations, leading to inaccuracies in stored information bits, which existing error correction codes struggle to address effectively, especially under high stress conditions.
Innovation Solution
A soft decoder system that performs error correction by utilizing extrinsic page information from adjacent pages in a memory block, allowing for secondary decoding processes and log-likelihood ratio (LLR) allocation to improve decoding accuracy without additional latency, by modifying voltage thresholds and allocating LLRs based on page information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hard decoding is used, then decoding speed is fast, but error correction capability is insufficient under high noise conditions
Solution Approach 1:
The patent changes the parameter of decoding input from hard decisions (0/1) to soft decisions (log-likelihood ratios with continuous values). This allows the decoder to utilize magnitude information from read operations to improve error correction capability while maintaining computational efficiency through modified BCH decoding algorithms that process soft information without requiring complex iterative processes.
2Reliability
If additional read operations are performed to gather extrinsic page information, then decoding capability is improved, but latency increases
Solution Approach 1:
The patent performs preliminary action by reading all pages in a row during the initial read operation and storing extrinsic page information in buffers before the decoding process. This allows the decoder to access extrinsic information without requiring additional read operations, thereby improving decoding capability while maintaining low latency.
Solution Approach 2:
The patent introduces buffer memory as an intermediary to store extrinsic page information read from adjacent pages. This intermediary allows the decoder to access additional information without performing additional NAND reads, effectively decoupling the read operation from the decoding operation and reducing latency while improving capability.
3Reliability
If voltage thresholds are modified for soft sampling, then decoding reliability is improved, but read operation complexity increases
Solution Approach 1:
The patent segments the voltage threshold modification process into discrete steps: first reading with initial thresholds, then modifying thresholds based on extrinsic information, and finally performing soft sampling with adjusted thresholds. This segmentation allows systematic improvement of decoding reliability while managing complexity through structured processing.
Data Source
AI summary
Aspects of this technical solution can include selecting a plurality of memory locations at a memory device, the memory locations corresponding to a first page including a first plurality of bits and a second page including a second plurality of bits, modifying, based on the first plurality of bits and the second plurality of bits, a first voltage threshold corresponding to an estimated read voltage for the first plurality of bits, allocating, to a voltage range bounded by the first voltage threshold, a log-likelihood ratio (LLR), and decoding, based on the LLR corresponding to the voltage range, the first plurality of bits.