Flash Memory Read Control Using Threshold Voltage Distributions
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Solution Overview
Problem
The challenge of accurately reading data from flash memory due to changes in threshold voltage distribution caused by factors like read, write, and retention disturbances, leading to incorrect data retrieval.
Innovation Solution
A method and memory controller that adjust control gate voltages based on threshold voltage distributions to perform multiple read operations, using error correction techniques to determine optimal voltages for accurate data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If original control gate voltage settings are used for read operations, then the read operation can be performed with simple voltage control, but the threshold voltage distribution changes due to disturbances cause incorrect data retrieval
Solution Approach 1:
The patent applies preliminary action by performing a read disturbance compensation operation before the actual read operation. The controller first applies a compensation voltage to counteract the threshold voltage shift caused by read disturbance, then performs the read operation. This ensures accurate data retrieval without requiring complex real-time voltage adjustments during the read process.
Solution Approach 2:
The patent implements feedback by monitoring the threshold voltage distribution changes and adjusting the control gate voltage accordingly. The controller detects the threshold voltage shift caused by disturbances and dynamically adjusts the read voltage to compensate for these changes, ensuring accurate data retrieval despite varying memory cell states.
2Measurement precision
If threshold voltage distribution changes are compensated by adjusting control gate voltages, then data retrieval accuracy is improved, but the read operation process becomes more complex
Solution Approach 1:
The patent performs threshold voltage compensation in advance by applying a compensation voltage before the actual read operation. This preliminary action pre-adjusts the memory cell threshold voltages to counteract expected disturbances, simplifying the main read operation while maintaining high accuracy.
Solution Approach 2:
The patent changes the voltage parameter by introducing a compensation voltage that is added to or subtracted from the original control gate voltage. This parameter adjustment compensates for threshold voltage shifts without requiring complete redesign of the voltage control mechanism, balancing accuracy and complexity.
3Reliability
If multiple read operations are performed to compensate for threshold voltage changes, then bit error rate is reduced, but the reading time increases
Solution Approach 1:
The patent performs compensation operations before the main read operation to prevent errors rather than correcting them afterward. By pre-adjusting threshold voltages and applying compensation voltages in advance, the system reduces bit error rates in a single read operation rather than requiring multiple retry operations.
Solution Approach 2:
The patent skips the need for multiple iterative read operations by implementing a one-time compensation mechanism before reading. The compensation voltage is applied once to counteract threshold voltage shifts, allowing the system to rush through the read operation in a single pass without repeated attempts, thus reducing total reading time.
Data Source
AI summary
A method for reading data stored in a flash memory. The flash memory comprises a plurality of memory cells and each memory cell has a particular threshold voltage. The method includes: obtaining a first threshold voltage distribution representing threshold voltages of a first group of the memory cells; obtaining a second threshold voltage distribution representing threshold voltages of a second group of the memory cells, wherein the second threshold voltage distribution is different from the first threshold voltage distribution, and the first group of the memory cells comprises at least a part of the second group of the memory cells; and controlling the flash memory to perform at least one read operation upon the first group of the memory cells according to the second threshold voltage distribution.