Flash Memory Controller Soft Information Generation
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Solution Overview
Problem
Flash memory devices face increased read errors due to retention effects, where charge distribution shifts and widens over time, affecting the decoding capability, especially as the number of programming and erase cycles increases, and existing methods do not effectively provide reliability information per bit using a standard interface.
Innovation Solution
A method involving multiple read attempts using a hard information interface to generate reliability information for flash memory cells by estimating voltage differences and using mappings between read results and reliability values, allowing for the calculation of log likelihood ratios and selection of reference voltages that minimize flipping errors, even when exact read thresholds are unknown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple read attempts are performed to obtain reliability information, then decoding capability is improved, but read operation time increases
Solution Approach 1:
The patent performs multiple read attempts in advance to collect soft information (reliability data) before the actual decoding process. By gathering this reliability information beforehand through preliminary read operations, the system can perform more accurate decoding without requiring additional time during the critical read path, thus resolving the contradiction between improved decoding capability and increased read time.
2Reliability
If retention effects are compensated for through multiple reads, then read error rate decreases, but manufacturing complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where multiple read attempts provide reliability information that is fed back into the decoding process. This feedback loop allows the system to dynamically adjust decoding strategies based on actual read results, compensating for retention effects without requiring complex hardware modifications. The feedback-based approach achieves error compensation through software/algorithms rather than hardware complexity.
3Measurement precision
If soft information is generated alongside hard read results, then decoding accuracy is improved, but data processing complexity increases
Solution Approach 1:
The patent introduces soft information (reliability metrics) as an intermediary between the hard read results and the final decoded data. This intermediary layer provides additional context about the confidence level of each read result, enabling more accurate decoding decisions. The intermediary soft information acts as a bridge that enhances decoding accuracy without requiring fundamental changes to the read interface, thereby managing processing complexity through a structured intermediate representation.
Data Source
AI summary
A flash memory controller, a computer readable medium and a method for generating reliability information using a hard information interface, the method may include performing multiple read attempts, while using the hard information interface, of a plurality of flash memory cells to provide multiple read results; wherein each flash memory cell is read by providing a reference voltage to the flash memory cell; wherein a same reference voltage is provided during the multiple read attempts; and generating, for each flash memory cell, reliability information based upon multiple read results of the flash memory cell.