ECC Codeword Shifting for NAND Open-Circuit Writes
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Solution Overview
Problem
Conventional techniques for handling open circuits in NAND flash memory and other non-volatile memory types increase the raw bit error rate (RBER) during writing, and complex circuitry is required to manage open circuits during read operations, impacting performance.
Innovation Solution
A defect management apparatus that shifts codeword bits to avoid open circuits during writing and punctures the parity portion to minimize the impact of open circuits, using an address indirection table and defect map to track and handle open circuit locations, thereby reducing RBER.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques are used to handle open circuits during write operations, then open circuits can be managed, but the raw bit error rate (RBER) increases
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different codeword portions. The message portion is protected with full ECC encoding while the parity portion is intentionally left vulnerable (punctured) to absorb open circuit defects. This localized differentiation allows the system to handle open circuits effectively while minimizing their impact on data integrity, thereby reducing RBER compared to uniform protection approaches.
Solution Approach 2:
The patent converts the harmful effect of open circuits into a beneficial outcome by deliberately placing them in the parity portion where they cause minimal damage. By puncturing the parity portion and allowing open circuits to concentrate there, the system transforms what would otherwise be random errors throughout the codeword into localized defects that the ECC can easily correct, thus reducing overall RBER.
2Reliability
If complex circuitry and mechanisms are used to handle open circuits during read operations, then RBER can be reduced, but performance is negatively impacted
Solution Approach 1:
The patent applies preliminary action by preparing the codeword structure before writing to memory. The ECC encoding is performed in advance with the understanding that the parity portion will be punctured. During read operations, the decoder simply needs to account for the known puncture pattern, which is a straightforward operation compared to complex defect detection and correction mechanisms. This advance preparation eliminates the need for complex real-time circuitry during read operations, maintaining high performance while achieving low RBER.
3Reliability
If codeword bits are shifted to avoid open circuits, then open circuits are concentrated in the least vulnerable location, but codeword structure is modified
Solution Approach 1:
The patent applies parameter changes by modifying the codeword structure parameters - specifically, by puncturing (removing) certain parity bits from the codeword. This changes the length and composition of the parity portion, creating a structure where open circuits can be absorbed without affecting the message portion. The ECC encoder is configured with these modified parameters, allowing the system to achieve reliable open circuit handling while maintaining a systematic and manageable codeword structure.
Data Source
AI summary
Systems, apparatuses and methods may provide for recording, if a non-volatile memory (NVM) location satisfies an open circuit condition, open circuit location information associated with the NVM location. Additionally, a shift of one or more bits may be conducting during a write of a codeword to the NVM location to avoid open circuit in the NVM location. Moreover, an end of a parity portion of the codeword may be punctured by an amount of the shift. In one example, the end of the parity portion includes a last circulant of the codeword.