NAND Memory Read Voltage Search Using Inflection Point Tuning
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Solution Overview
Problem
The accuracy of data reading in NAND type memories is affected by the variation of stored charges over time and temperature, leading to increased read errors that conventional error correction methods struggle to address efficiently.
Innovation Solution
A method involving M first adjustments and N second adjustments of read voltages to determine a target valley bottom voltage, where M and N are positive integers greater than 1, reducing the number of cyclic iterations and improving read accuracy by identifying an inflection point voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional error correction methods are used to address read errors, then data reading accuracy is maintained, but the method cannot efficiently handle increased read errors caused by charge variation over time and temperature
Solution Approach 1:
The patent implements dynamic read voltage adjustment by performing multiple adjustments (M first adjustments with first step, and N second adjustments with second step) on the read voltage based on detected inflection points. This dynamic adaptation allows the system to optimize read voltage in real-time according to charge variations, thereby maintaining high reading accuracy while adapting to different usage conditions and temperature changes.
2Measurement precision
If read voltage is adjusted frequently to maintain accuracy, then read error reduction is achieved, but the complexity of the read operation increases
Solution Approach 1:
The patent segments the read voltage adjustment process into two distinct phases: M first adjustments with a larger first step for coarse tuning, and N second adjustments with a smaller second step for fine tuning. This segmentation allows the system to efficiently search for the optimal read voltage by first making larger adjustments to reach the vicinity of the inflection point, then making smaller adjustments to precisely locate it, thereby balancing accuracy with operational complexity.
3Productivity
If the number of cyclic iterations is reduced, then processing speed is improved, but the precision of determining optimal read voltage may be compromised
Solution Approach 1:
The patent performs preliminary action by first identifying inflection points through M first adjustments before proceeding to the N second adjustments for precise optimal voltage determination. This preliminary identification of inflection points provides a starting point that reduces the number of subsequent iterations needed, thereby maintaining precision while improving processing speed. The inflection point serves as a guide that narrows down the search space for the optimal read voltage.
Data Source
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AI summary
Examples of the present application disclose a memory device, a memory system, a memory controller, and an operation method. The memory device comprises: a memory cell array comprising a plurality of memory cells, wherein a preset number of the memory cells form a code word; and a peripheral circuit coupled with the memory cell array and configured to: perform M first adjustments on a target read voltage of at least one code word with a first step, and acquire M first results corresponding to M read voltages obtained after the M first adjustments respectively; take the minimum first result in the M first results as an inflection point value, wherein a read voltage corresponding to the inflection point value is an inflection point voltage; perform N second adjustments on the inflection point voltage with a second step, and acquire N first results corresponding to N read voltages obtained after the N second adjustments respectively, wherein the second step is less than the first step; and determine a target valley bottom voltage according to the acquired N first results, wherein M and N are both positive integers greater than 1.