LDPC Decoder Soft-Data Caching for Faster NAND Flash Decoding

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Solution Overview

Problem

As the number of memory bits and stacked layers in 3D NAND flash memory devices increase, the complexity of errors during read operations grows, leading to longer decoding times and weaker error-correction capabilities for LDPC hard-decision decoding.

Innovation Solution

A decoder is provided that includes a cache module for caching soft data related to a codeword to be decoded and a flip-indication module that uses this soft data to determine the number of parity checks not satisfied by bits in the codeword during hard-decision decoding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the number of memory bits and stacked layers in 3D NAND flash memory devices increases, then storage capacity is improved, but decoding time increases and error-correction capability deteriorates

Engineering Contradiction:

Improvestorage capacityVSAvoiderror-correction capability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary action by performing soft-decision decoding first to obtain soft data before hard-decision decoding. The soft data, which contains reliability information about each bit, is cached and used to guide the subsequent hard-decision flipping process. This preliminary soft-decision analysis enables the hard-decision decoder to make more informed flipping decisions, thereby maintaining error-correction capability even as storage capacity increases.

Inventive Principle:

Principle #10Preliminary action

2Quantity of substance

If the number of memory bits and stacked layers in 3D NAND flash memory devices increases, then storage capacity is improved, but decoding time increases

Engineering Contradiction:

Improvestorage capacityVSAvoiddecoding time

Core Design Contradiction:

Quantity of substanceVSLoss of time

Solution Approach 1:

The patent performs soft-decision decoding as a preliminary step before hard-decision decoding. The soft data obtained from this preliminary step is cached and used to guide the hard-decision process, reducing the number of flipping iterations needed and thereby reducing overall decoding time despite increased storage capacity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the soft data (which contains bit reliability information) to guide the hard-decision flipping process. The flip-indication module uses the cached soft data to determine which bits to flip during hard-decision decoding, creating a feedback loop that optimizes the decoding process and reduces iteration count.

Inventive Principle:

Principle #23Feedback

3Reliability

If soft data is used to assist flip decision in hard-decision decoding, then error-correction capability is improved, but device complexity increases

Engineering Contradiction:

Improveerror-correction capabilityVSAvoiddecoder complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts only the necessary soft data (reliability information) from the soft-decision decoding process and caches it for use in hard-decision decoding. Rather than processing all soft data through the entire decoding pipeline, the system extracts and stores only the relevant information needed to guide flipping decisions, thereby limiting the increase in device complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a cache module as an intermediary between soft-decision decoding and hard-decision decoding. This cache stores the soft data and makes it available to the flip-indication module, serving as a mediator that enables the integration of soft and hard decision processes without requiring direct complex interaction between all components.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Productivity

If soft data is cached and used in hard-decision decoding, then throughput is improved, but power consumption increases

Engineering Contradiction:

ImprovethroughputVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent performs soft-decision decoding and caches the soft data in advance before hard-decision decoding. This preliminary action enables faster hard-decision processing by providing pre-computed reliability information, thereby improving throughput. The caching mechanism allows the hard-decision decoder to quickly access soft data without re-computing it, reducing overall processing time and power consumption.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS12308856B2Decoder, decoding method, memory controller, and memory system

Publication Date: 2025.05.20 YANGTZE MEMORY TECH CO LTD

AI summary

According to one aspect of the present disclosure, a decoder is provided. The decoder may include a cache module. The cache module may be configured to cache soft data related to a codeword to be decoded. The decoder may include a flip-indication module. The flip-indication module may be configured to obtain the soft data from the cache module. The flip-indication module may be configured to, when performing hard-decision decoding on the codeword to be decoded, determine, at least in a first flip iteration and with assistance of the soft data, a number of parity checks not satisfied by bits in the codeword to be decoded.