SSD Controller Read Voltage Adjustment via Bit Error Feedback
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Solution Overview
Problem
Storage devices with nonvolatile memory, such as SSDs, face delays in response to read commands due to repeated retry operations caused by unsuitable read voltages leading to data errors, which are corrected through iterative adjustments of the read voltage.
Innovation Solution
A storage device with a controller that adjusts the read voltage based on the difference between the measured and expected bit numbers during data read operations, utilizing retry read tables and second correction values to optimize read voltage settings, thereby reducing the number of retry operations and improving data accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the storage device repeats retry read operations while changing the read voltage to correct errors, then data accuracy is improved, but the response time to read commands increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal read voltage values in a lookup table based on program voltage conditions before actual read operations occur. When a read command is received, the controller directly retrieves the pre-determined optimal read voltage corresponding to the measured program voltage, eliminating the need for iterative retry operations and voltage adjustments during the read process itself.
Solution Approach 2:
The patent implements feedback by measuring the actual program voltage applied to memory cells during write operations and using this measured value to dynamically select the appropriate read voltage from a lookup table. The system continuously monitors program voltage variations and adjusts read voltage selection accordingly, creating a closed-loop control mechanism that adapts to changing conditions while maintaining optimal read performance.
2Device complexity
If the storage device uses a fixed read voltage for data read operations, then the device complexity is reduced, but data read accuracy deteriorates due to threshold voltage variation
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the read voltage parameter based on measured program voltage conditions. Instead of using a fixed read voltage, the system varies the read voltage selection according to the actual program voltage applied during write operations. This is achieved by storing multiple read voltage values in a lookup table and selecting the appropriate one based on program voltage measurements, thereby adapting to threshold voltage variations without requiring complex real-time voltage generation circuitry.
Solution Approach 2:
The patent introduces an intermediary lookup table that mediates between the program voltage measurement and the read voltage application. The lookup table stores pre-calculated optimal read voltage values corresponding to different program voltage conditions. This intermediary structure simplifies the control logic by replacing complex real-time voltage adjustment mechanisms with a straightforward table-lookup operation, maintaining low device complexity while improving data read accuracy.
Data Source
AI summary
According to one embodiment, a storage device includes a nonvolatile memory and a controller. The controller is configured to read data from the nonvolatile memory by applying a read voltage to the nonvolatile memory. The controller is configured to correct the read voltage based on a difference between a measured value of a bit number obtained when the data is read from the nonvolatile memory by applying the read voltage to the nonvolatile memory and an expected value of the bit number.