LDPC Decoding Feedback for Flash Memory Damaged Bits
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Solution Overview
Problem
Flash memory with damaged bit cells or bit lines can lead to errors in LDPC decoders, reducing decoding capability, as damaged bits consistently output '1', and identifying these positions requires significant storage for error correction.
Innovation Solution
An ECC decoding method and apparatus that temporarily stores codewords in a buffer and uses a decoding circuit to perform iterative decoding operations, utilizing feedback from successfully decoded codewords to modify and correct initially undecodable codewords by changing bit values or reliability information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If positions of damaged bits/bit lines are marked as erasure to prevent LDPC decoder from being misled, then decoding capability is improved, but storage space requirement increases significantly
Solution Approach 1:
The patent uses feedback from successfully decoded codewords to identify damaged bit positions, then applies this information to correct errors in undecodable codewords. The decoding result of one codeword feeds back into the correction process for another codeword, enabling error correction without requiring additional storage for damage position records.
Solution Approach 2:
The patent copies information from successfully decoded codewords (second codeword) to correct undecodable codewords (first codeword). By copying the decoded bit values from the second codeword to corresponding positions in the first codeword, the system corrects errors without needing to store separate damage position records.
2Ease of operation
If damaged bit cells output data '1' consistently, then memory operation simplicity is maintained, but information accuracy deteriorates
Solution Approach 1:
The system uses feedback from successfully decoded codewords to identify which bit positions are damaged. By comparing decoded results from the second codeword with the original first codeword, the system identifies damaged positions and corrects them, thereby recovering lost information while maintaining the simple 'output 1' behavior of damaged cells.
Solution Approach 2:
The patent converts the harmful effect of damaged bit cells (consistently outputting '1' and causing errors) into a beneficial effect. By using the decoded information from successfully decoded codewords, the system identifies and corrects the erroneous '1' outputs from damaged cells, transforming the error source into a correctable condition.
3Reliability
If iterative decoding with feedback is performed to correct errors in undecodable codewords, then decoding capability is improved, but processing time increases
Solution Approach 1:
The patent performs preliminary decoding on the second codeword first to obtain decoded information that will be used to correct the first codeword. By preparing the correction information in advance through the second codeword's decoding, the system reduces the overall processing time compared to attempting multiple failed decodings of the first codeword alone.
Solution Approach 2:
The system skips the time-consuming process of attempting multiple decoding iterations on the undecodable first codeword by instead using the decoded second codeword to directly provide correction information. This approach rushes through the correction process by leveraging already-decoded information rather than performing exhaustive search.
Data Source
AI summary
An error checking and correcting (ECC) decoding method and apparatus are provided. A decoding circuit decodes a codeword using (or without using) reference information, wherein when the decoding circuit fails to decode a first codeword, the decoding circuit decodes a second codeword to produce decoded data. The decoding circuit checks whether a change has occurred from each codeword bit of the second codeword to a corresponding bit of the decoded data. In accordance with a bit position of the changed corresponding bit, the decoding circuit correspondingly changes the first codeword to a modified codeword, and/or correspondingly changes the reference information to modified information. The decoding circuit performs the ECC decoding again on the modified codeword (or the first codeword) using (or without using) the modified information.