Storage Device Shift Level Determiner for Read Voltage Adaptation
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Solution Overview
Problem
Current storage devices face challenges in maintaining effective read performance, particularly when read operations fail, due to variations in threshold voltage distributions across memory cells, leading to data retrieval errors.
Innovation Solution
The implementation of a storage device with a memory cell array, a read operator, a shift level determiner, and a read operation controller that calculates a shift value to determine a shift level for threshold voltage distributions, allowing for a soft read operation using multiple soft read voltages to improve read performance and error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single read voltage is used for reading memory cells, then the device complexity is low, but the read performance deteriorates when threshold voltage distributions shift
Solution Approach 1:
The patent implements dynamic read voltage selection based on detected shift levels. The read operation controller selects from multiple read voltages (first read voltage, second read voltage, third read voltage) depending on the threshold voltage distribution state, making the read voltage adaptive rather than fixed. This resolves the contradiction by allowing the system to maintain low complexity under normal conditions while improving reliability when shifts occur.
Solution Approach 2:
The patent changes the read voltage parameter based on the detected shift level. When a shift is detected, the system transitions from using a first read voltage to using a second or third read voltage with different characteristics. This parameter adaptation allows the system to maintain high read performance across varying threshold voltage distributions without permanently increasing device complexity.
2Measurement precision
If multiple soft read voltages are applied to read memory cells, then the measurement precision of threshold voltage distribution improves, but the use of energy increases
Solution Approach 1:
The patent segments the read operation into distinct phases based on shift level detection. Instead of continuously applying multiple soft read voltages, the system first detects the shift level and then applies only the necessary read voltage for that specific condition. This segmentation reduces energy consumption while maintaining measurement precision by using multiple voltages only when and where needed.
Solution Approach 2:
The patent applies partial action by using multiple read voltages only partially - specifically, only when shift levels are detected that require such precision. For normal operating conditions, a single read voltage suffices, reducing energy consumption. The excessive precision of multiple voltages is applied only when necessary to maintain measurement accuracy.
3Loss of information
If read operations are performed without considering shift levels, then the productivity is high, but the loss of information increases due to read failures
Solution Approach 1:
The patent performs preliminary detection of shift levels before executing the main read operation. The read operation controller first determines the shift level based on threshold voltage distribution characteristics, then selects the appropriate read voltage accordingly. This preliminary action prevents information loss by ensuring the correct read voltage is used, while maintaining productivity by avoiding unnecessary retry operations.
Solution Approach 2:
The patent implements feedback by using the detected shift level information to adjust the read voltage selection. The system continuously monitors threshold voltage distributions and adjusts read operations based on this feedback, ensuring high data retrieval accuracy. The feedback mechanism maintains productivity by preventing read failures rather than requiring corrective retries.
Data Source
AI summary
A memory device includes a memory cell array, a read operator, a shift level determiner, and a read operation controller. The read operator applies a read voltage to a selected word line coupled to selected memory cells and reads the selected memory cells in response to an evaluation signal. The shift level determiner calculates a shift value indicating a difference between a number of memory cells read as on-cells and a reference number, and determines a shift level of a threshold voltage distribution for the selected memory cells. The soft read table storage stores soft read set parameters. The read operation controller determines a plurality of soft read voltages based on the shift level and the soft read set parameters and controls the read operator in response to the evaluation signal.