Memory Distortion Estimation for ECC Decoding

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Solution Overview

Problem

Memory devices, such as Flash and DRAM, face distortion issues due to electrical field coupling, Back Pattern Dependency, and threshold voltage drift, which affect the accuracy of data retrieval from analog memory cells.

Innovation Solution

A method that encodes data using Error Correction Codes (ECC) and estimates distortion in memory cells, computing error correction metrics to improve ECC decoding performance by adjusting decision thresholds and using feedback to refine the decoding process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If multi-level cells are used to increase storage density, then storage capacity is improved, but distortion from electrical field coupling and threshold voltage drift increases

Engineering Contradiction:

Improvestorage densityVSAvoiddata retrieval accuracy

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies preliminary distortion estimation before ECC decoding by analyzing patterns from previously read pages. The system predicts distortion values for current data based on historical distortion patterns from adjacent memory cells, allowing the distortion compensation to be performed in advance of the actual decoding operation

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using distortion information from previously decoded pages to improve the decoding of current pages. The system continuously updates distortion estimates based on feedback from the decoding process, creating a closed-loop system where past performance informs future accuracy

Inventive Principle:

Principle #23Feedback

2Reliability

If distortion estimation and feedback mechanisms are added to improve ECC performance, then data retrieval accuracy is improved, but system complexity increases

Engineering Contradiction:

ImproveECC decoding accuracyVSAvoidprocessing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies partial action by estimating distortion only for memory cells that are likely to exhibit significant distortion based on their location and programming history. Rather than calculating distortion for every cell in the array, the system selectively applies distortion estimation to cells where it will have the greatest impact on decoding accuracy

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The system performs preliminary distortion estimation using stored pattern information before the actual ECC decoding process, preparing compensation values in advance to simplify the main decoding operation and reduce real-time computational complexity

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8156403B2Combined distortion estimation and error correction coding for memory devices

Publication Date: 2012.04.10 APPLE INC

AI summary

A method for operating a memory device (24) includes encoding data using an Error Correction Code (ECC) and storing the encoded data as first analog values in respective analog memory cells (32) of the memory device. After storing the encoded data, second analog values are read from the respective memory cells of the memory device in which the encoded data were stored. At least some of the second analog values differ from the respective first analog values. A distortion that is present in the second analog values is estimated. Error correction metrics are computed with respect to the second analog values responsively to the estimated distortion. The second analog values are processed using the error correction metrics in an ECC decoding process, so as to reconstruct the data.