NAND Read Threshold Clustering for Storage Compression

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Solution Overview

Problem

In NAND flash devices, the optimal set of read thresholds changes over time due to programming and temperature effects, requiring storage for later use, which consumes significant memory, and existing compression or quantization methods introduce errors.

Innovation Solution

The method involves representing read thresholds as points in a multi-dimensional space and using weighted K-means clustering to minimize errors by associating new threshold sets with pre-defined clusters, reducing storage volume and error rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If read thresholds are stored for later use, then reliability is improved, but storage volume increases

Engineering Contradiction:
Improveread threshold reliabilityVSAvoidstorage volume
Core Design Contradiction:
ReliabilityVSVolume of stationary object

Solution Approach 1:

The patent segments the read threshold data by clustering similar threshold values into groups. Instead of storing all possible threshold values, the system identifies representative threshold sets from historical data and stores only these clustered representatives, significantly reducing storage volume while maintaining reliability for threshold retrieval.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The patent creates a compressed representation of read thresholds by copying only the essential characteristic data (clustered threshold values) rather than storing complete threshold tables. This copying approach retains the necessary information for reliable reads while dramatically reducing the storage footprint.

Inventive Principle:
Principle #26Copying

2Volume of stationary object

If compression or quantization of read thresholds is performed, then storage volume is reduced, but measurement precision deteriorates

Engineering Contradiction:
Improvestorage volumeVSAvoidread threshold precision
Core Design Contradiction:
Volume of stationary objectVSMeasurement precision

Solution Approach 1:

The patent applies local quality by analyzing and clustering read thresholds in a multi-dimensional space where different dimensions represent different threshold values. The clustering algorithm identifies local patterns and representative points that capture the essential characteristics of threshold data, preserving precision through intelligent selection of representative values rather than uniform quantization.

Inventive Principle:
Principle #3Local quality

Solution Approach 2:

The patent performs preliminary action by pre-clustering historical read threshold data into representative groups before actual read operations. This preliminary organization of data into clustered representations allows for efficient retrieval and reduces storage requirements while maintaining the precision needed for accurate reads, as the clustering is performed in advance on historical data.

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentUS11790984B1Clustering for read thresholds history table compression in NAND storage systems
Publication Date: 2023.10.17 KIOXIA CORP
  • US11790984B1 patent drawing
  • US11790984B1 patent drawing
  • US11790984B1 patent drawing

AI summary

A flash memory system may include a flash memory and a circuit for performing operations on the flash memory. The circuit may be configured to obtain reference voltages from one or more read samples, and a plurality of sets of reference voltages. The circuit may be configured to obtain a plurality of distances, each being a distance between a point corresponding to the obtained reference voltages and a point corresponding to a respective set of reference voltages. The circuit may be configured to determine a first set of reference voltages such that a distance between the point corresponding to the obtained reference voltages and a point corresponding to the first set of reference voltage is a minimum distance of the plurality of distances. The circuit may be configured to perform read operations on locations of the flash memory with the first set of reference voltages.