Flash Read Parameter Estimation for Decode Failure Recovery
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Solution Overview
Problem
Existing solid state storage devices face challenges in error recovery due to insufficient information from single-read operations, leading to inefficiencies in decoding and increased bit error rates, particularly in flash memory systems where hard information is not sufficient for data recovery.
Innovation Solution
The method involves processing multiple read values to determine read parameters such as log likelihood ratios (LLRs) and center read reference voltages, using signal counts from regions to customize read parameters for improved error correction, thereby enhancing decoding accuracy and reducing bit error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If single-read operations are used for data retrieval, then read speed is maintained, but decoding accuracy deteriorates due to insufficient information
Solution Approach 1:
The system performs preliminary multiple read operations to gather sufficient information before decoding attempts. By reading the same data multiple times in advance and collecting soft information (probabilistic data about bit values), the system ensures adequate information is available for accurate decoding, thereby resolving the contradiction between maintaining read speed and improving decoding accuracy.
2Measurement precision
If multiple read operations are performed to gather more information, then decoding accuracy improves, but read latency increases
Solution Approach 1:
The system performs a limited number of read operations (exactly three reads) rather than continuing indefinitely. This partial action approach gathers sufficient soft information for accurate decoding while preventing excessive latency. The method balances the need for multiple reads with time constraints by establishing a predetermined read count that provides adequate information without unnecessary delays.
3Device complexity
If hard decision decoding is used for simplicity, then device complexity is reduced, but error recovery capability deteriorates
Solution Approach 1:
The system changes the parameter of decoding by incorporating soft information (probabilistic bit values) into the decoding process. Instead of using only hard decisions (definite 0 or 1 values), the decoder utilizes confidence levels and probability data from multiple read operations. This parameter change enhances error recovery capability by providing the decoder with more nuanced information about bit reliability, thereby improving reliability without significantly increasing complexity.
4Device complexity
If default read parameters are used for all operations, then device complexity is reduced, but measurement precision deteriorates due to varying channel conditions
Solution Approach 1:
The system dynamically adjusts read parameters such as reference voltages based on actual channel conditions observed during multiple read operations. Instead of using fixed default parameters for all operations, the system adapts parameters in response to varying conditions like noise levels and signal quality. This dynamic adjustment improves read accuracy by optimizing parameters for each specific read operation while maintaining manageable complexity through systematic adaptation rules.
Data Source
AI summary
Read parameter estimation techniques are provided that obtain information from multiple read operations to customize read parameters for data recovery. One method comprises performing the following steps, in response to a decoding failure of a page of a memory or a codeword of the memory: obtaining at least three read values of the page or codeword; and processing the at least three read values to determine read parameters comprising: (i) a log likelihood ratio, and/or (ii) a center read reference voltage, wherein the determination is based on a signal count of a number of bits falling in particular regions of multiple regions of the memory and wherein the determined read parameters are used for a decoding of the page or codeword following the decoding failure and/or a subsequent read operation following a successful decoding of the page or codeword.