LDPC Read Recovery Using RAIN-Derived Soft Bits
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Solution Overview
Problem
Conventional read retry algorithms in memory sub-systems require significant resources and often necessitate a RAIN recovery operation to correct errors, which can impact performance and reduce user-available NAND capacity.
Innovation Solution
The implementation of an improved decoder capability using a RAIN drop associated with a failed translation unit (TU), calculated through an XOR operation with a raw read, to generate a third soft bit for the 1H3S decoding algorithm, thereby increasing the likelihood of TU recovery without needing a RAIN recovery operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read retry algorithms are used with RAIN recovery operation, then error correction capability is improved, but machine cycles and memory space are consumed
Solution Approach 1:
The patent performs an XOR operation between the RAIN drop and the raw read data to generate a third soft bit before the LDPC decoding process. This preliminary action prepares additional error correction information in advance, enabling the decoder to recover more errors without requiring a full RAIN recovery operation, thus reducing machine cycle consumption.
Solution Approach 2:
The patent modifies the input parameters to the LDPC decoder by generating an enhanced soft bit vector that includes three soft bits per data bit instead of the conventional two. This parameter change (adding the third soft bit derived from RAIN drop) improves the decoder's error correction capability, allowing successful recovery without invoking the resource-intensive RAIN recovery operation.
2Reliability
If RAIN recovery operation is performed, then failed TU recovery is achieved, but user-available NAND capacity is reduced
Solution Approach 1:
The patent applies partial action by using only the RAIN drop (a portion of the RAIN parity information) to generate the third soft bit, rather than performing a complete RAIN recovery operation that would require reading and processing all parity data. This partial use of RAIN information provides sufficient error correction capability for many cases while avoiding the full overhead of RAIN recovery.
3Reliability
If improved decoding with third soft bit is performed, then TU recovery likelihood is increased, but decoding complexity increases
Solution Approach 1:
The patent introduces the RAIN drop as an intermediary element that bridges the raw read data and the LDPC decoding process. By XORing the RAIN drop with the raw read to generate the third soft bit, it creates an intermediate representation that enhances decoding capability without requiring complex modifications to the underlying LDPC decoder architecture.
Data Source
AI summary
A sign bit of a low-density parity-check (LDPC) codeword associated with a translation unit (TU) can be generated by performing an XOR operation on a RAIN drop corresponding to the TU and a raw read of the TU. The LDPC codeword can include a hard bit and three soft bits that include the sign bit. The LDPC codeword can be decoded using the hard bit and the three soft bits. A read recovery operation can be performed on the TU using the decoded LDPC codeword.