NAND Memory Read-Voltage Prediction for Accurate Data Retrieval
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Solution Overview
Problem
The accuracy of reading data from NAND type memory cells is affected by the variation of stored charges over time and repeated read operations, leading to inaccuracies in data retrieval.
Innovation Solution
A memory device and system that utilize a peripheral circuit to determine a target valley bottom voltage by analyzing the number of flipped bits at different read voltages, employing a mapping function and iterative adjustments to refine the read voltage, ensuring accurate data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed read voltages are used for reading data from memory cells, then the read operation is simple and fast, but the reading accuracy deteriorates due to charge variation over time and repeated reads
Solution Approach 1:
The system performs preliminary read operations at different voltages to acquire first results before determining the final target valley bottom voltage. This preliminary action allows the system to predict the optimal read voltage based on actual memory cell responses, thereby improving reading accuracy while managing complexity through structured pre-processing
Solution Approach 2:
The system uses the first results from preliminary reads as feedback to adjust and determine the target valley bottom voltage. This feedback mechanism enables the system to adapt to charge variations in memory cells over time and across different read operations, maintaining high reading accuracy without requiring complex external calibration equipment
2Measurement precision
If the read voltage is adjusted frequently to maintain accuracy, then reading precision improves, but the operation time increases
Solution Approach 1:
The system performs a limited number of preliminary read operations (excessive action) to gather sufficient data for accurate valley bottom voltage prediction, rather than continuously adjusting voltages during every read operation. This partial adjustment approach maintains precision while minimizing time loss by avoiding excessive voltage tuning
Solution Approach 2:
The valley bottom voltage is determined in advance through preliminary reads and prediction algorithms, so that once determined, the same target read voltage can be reused for subsequent reads. This preliminary determination reduces the need for frequent adjustments, thereby improving precision without proportionally increasing operation time
Data Source
AI summary
Examples of the present application disclose a memory device. The memory device includes: a memory cell array comprising memory cells that store a plurality of memory bits, the plurality of memory bits corresponding to a plurality of orders of read voltages, and a preset number of the memory cells forming a code word; and a peripheral circuit coupled with the memory cell array and configured to: acquire a first result of at least one code word corresponding to a target read voltage of a target order; acquire a predicted valley bottom voltage of the target order according to the first result of the at least one code word corresponding to the target read voltage of the target order and a level in which the target order is located; and determine a target valley bottom voltage of the target order based on the predicted valley bottom voltage of the target order.