Memory Controller Read Bias Selection for Distorted Threshold Distributions
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Solution Overview
Problem
Current memory systems face challenges in efficiently detecting optimal read bias, leading to errors and reduced reliability due to distorted threshold voltage distributions in multi-level cell nonvolatile memory devices.
Innovation Solution
A controller system that includes a mean-bias manager, reliability interval manager, and read bias manager to estimate and select optimal mean bias voltages, determine confidence intervals, and decide target read voltages for accurate data reading, thereby improving read operation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read bias detection methods are used, then the read operation can be performed, but errors occur and reliability is reduced due to distorted threshold voltage distributions
Solution Approach 1:
The system performs preliminary detection of threshold voltage distribution shifts before executing the actual read operation. By estimating the shift amount and applying compensation in advance, the system determines an optimal read bias that accounts for distribution distortion, thereby improving read reliability without requiring complex real-time adjustments during the read operation itself.
2Reliability
If the controller implements complex bias detection and adjustment mechanisms, then read reliability improves, but device complexity increases
Solution Approach 1:
The controller implements a feedback mechanism where the detected threshold voltage distribution shift is used to adjust the read bias voltage. The system continuously monitors the voltage distribution, estimates shifts, and compensates by adjusting the read bias accordingly. This closed-loop feedback approach improves reliability while maintaining relatively simple device architecture by using software-based compensation rather than complex hardware modifications.
Data Source
AI summary
An operating method of controller includes estimating, by a mean-bias manager, candidates of a mean bias voltage based on source read voltages corresponding to respective program states; determining, by a reliability interval manager, whether the candidates of the mean bias voltage are within confidence intervals respectively corresponding to the program states; selecting, by the reliability interval manager, the candidates of the mean bias voltage when the candidates of the mean bias voltage are within confidence intervals, respectively; deciding, by a read bias manager, target read voltages based on selected mean bias voltages or the selected candidates of the mean bias voltage; and reading, by a processor, target data according to the target read voltages.