NAND Flash Pre-Soft-Decoding Voltage Tracking
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Solution Overview
Problem
Existing NAND flash devices face challenges in accurately determining optimal read reference voltages, leading to errors in soft decoding due to the accumulation of stresses and limited accuracy in charge injection, which affects the reliability of data retrieval.
Innovation Solution
The method involves obtaining multiple soft read samples using different reference voltages, generating soft information, and dynamically adjusting sampling ranges to centralize optimal read positions, thereby improving the estimation of optimal read threshold voltages and reducing errors in soft decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If soft sampling is performed multiple times with different read thresholds to generate soft information, then the reliability of soft decoding is improved, but the time and number of read operations increase
Solution Approach 1:
The patent performs preliminary soft sampling operations to generate soft information before the actual decoding process. By obtaining multiple soft read samples with different reference voltages in advance and generating soft information (such as likelihood values or confidence metrics) beforehand, the system prepares decoded data that can be more efficiently processed during the actual decoding stage, reducing the need for repeated read operations.
Solution Approach 2:
The patent uses feedback from the soft sampling results to dynamically adjust read thresholds and reference voltages. The soft information generated from initial read operations is fed back into the system to refine subsequent read operations, allowing the decoder to adapt to actual channel conditions and improve decoding reliability without requiring a fixed large number of read operations.
2Measurement precision
If read reference voltages are adjusted to improve accuracy of data retrieval, then the precision of read operations is improved, but the complexity of voltage control increases
Solution Approach 1:
The patent implements dynamic adjustment of read reference voltages based on feedback from soft sampling operations. Instead of using fixed voltage levels, the system continuously adapts reference voltages to match actual storage conditions and channel characteristics. This dynamic approach allows the system to maintain high read accuracy while using a relatively simple voltage control mechanism that responds to real-time conditions rather than requiring complex pre-calibration.
Solution Approach 2:
The patent changes read reference voltage parameters based on soft information from multiple read samples. By analyzing the distribution of soft read values and adjusting reference voltage parameters accordingly, the system optimizes the separation between logic states (0 and 1) to improve detection accuracy. This parameter adaptation allows accurate data retrieval without requiring overly complex voltage control hardware.
3Measurement precision
If multiple soft read samples are obtained with different reference voltages, then the accuracy of soft information is improved, but the number of read operations increases
Solution Approach 1:
The patent performs a limited number of soft read sampling operations with different reference voltages to generate sufficient soft information for accurate decoding. Rather than exhaustively sampling all possible voltage levels, the system performs a partial set of readings that provides adequate statistical information about the channel conditions. This partial action approach achieves the necessary accuracy for reliable decoding without the excessive overhead of comprehensive sampling.
Data Source
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 a first soft read sample by performing a first read operation on a location of the flash memory with a first reference voltage. The circuit may be configured to determine a second reference voltage based on the first soft read sample. The circuit may be configured to obtain a second soft read sample by performing a second read operation on the location of the flash memory with the second reference voltage. The circuit may be configured to generate soft information based on the first and second soft read samples. The circuit may be configured to decode a result of a third read operation on the location of the flash memory based on the soft information.