Dynamic Read Voltage Adjustment for Nonvolatile Memory Cells
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Solution Overview
Problem
Non-volatile memory systems, such as EEPROM and flash memory, face errors due to thermal effects and capacitive coupling, which alter the threshold voltage distribution of memory cells, leading to data reading errors that Error Correction Codes (ECC) cannot always correct.
Innovation Solution
A system and method to measure and adjust the threshold voltage distribution of non-volatile memory cells, allowing for dynamic adjustment of read compare voltages to account for drift in the distribution, ensuring accurate data retrieval by performing multiple sensing operations and updating read compare voltages based on determined threshold voltage distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed read compare voltages are used, then device complexity is reduced, but data reading accuracy deteriorates due to threshold voltage distribution drift
Solution Approach 1:
The patent implements dynamic adjustment of read compare voltages based on measured threshold voltage distribution characteristics. Instead of using fixed read compare voltages, the system continuously adapts the read compare voltage levels to match the actual threshold voltage distribution of the memory cells, thereby maintaining high reading accuracy despite drift caused by thermal effects and capacitive coupling
Solution Approach 2:
The system performs multiple sensing operations to measure the threshold voltage distribution of memory cells, uses this measurement feedback to determine optimal read compare voltage levels, and applies these adjusted voltages in subsequent read operations. This closed-loop feedback mechanism ensures that read operations adapt to changing threshold voltage distributions, resolving the contradiction between reading accuracy and operational complexity
2Measurement precision
If multiple sensing operations are performed to measure threshold voltage distribution, then data reading accuracy is improved, but operation time increases
Solution Approach 1:
The patent performs multiple sensing operations to accurately characterize the threshold voltage distribution, using this information to determine optimal read compare voltage levels. By performing the measurement operations once to establish the distribution characteristics, the system achieves improved reading accuracy for subsequent operations without excessive time penalty, as the measurement data can be reused
Solution Approach 2:
The system performs sensing operations in advance to measure and characterize the threshold voltage distribution before performing actual data read operations. This preliminary characterization allows the system to pre-determine the optimal read compare voltage levels, so that when data reading is required, the system can immediately use the pre-calculated voltage levels without performing additional measurements, thereby reducing the time loss for actual data access
Data Source
AI summary
A system and methods to find the threshold voltage distribution across a set of nonvolatile memory cells, such that embodiments may incorporate this distribution information into calculations that may change the read compare voltages used to read the memory cells, while ensuring adequate separation in read voltage between different data states at which the memory cells may be read.