Flash Memory Reference Voltage Estimation for ECC Failure Recovery
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Solution Overview
Problem
Flash memory devices experience increased error rates due to changes in threshold voltage distributions over time, caused by physical changes such as aging and repeated cycles, leading to unreliable data reading and decoding.
Innovation Solution
A method and system for estimating and updating reference voltages and log-likelihood ratios (LLRs) to improve data reading and decoding accuracy, involving multiple read operations and dynamic LLR updating to adapt to changing threshold voltage distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed reference voltages are used for reading memory sectors, then the read operation is simple and fast, but error rates increase over time due to threshold voltage drift from aging and repeated cycles
Solution Approach 1:
The patent implements dynamic reference voltage adjustment by estimating threshold voltage distributions from read data and updating reference voltages accordingly. Instead of using fixed reference voltages, the system continuously adapts them to match the changing threshold voltage distributions caused by aging and repeated program/erase cycles, thereby maintaining reliable data reading throughout the device lifetime
Solution Approach 2:
The system employs feedback mechanisms where read data is analyzed to estimate threshold voltage distributions, which then feed back into updating the reference voltages. This closed-loop approach allows the system to automatically compensate for threshold voltage drift without external intervention, improving long-term reliability while keeping the complexity manageable through automated adaptation
2Reliability
If multiple read operations with updated reference voltages are performed, then error rates are reduced, but the reading time and processing overhead increase
Solution Approach 1:
The patent applies partial updating of reference voltages by estimating threshold voltage distributions only from selected read data rather than processing all read operations. This selective approach provides sufficient adaptation to reduce error rates while avoiding the time penalty of processing every single read operation, achieving a balance between reliability improvement and time efficiency
Solution Approach 2:
The system performs preliminary estimation of threshold voltage distributions from read data before executing the actual read operation with updated reference voltages. This preparatory step allows the system to pre-calculate the necessary voltage adjustments, reducing the time overhead during critical data retrieval operations while still achieving improved decoding accuracy
Data Source
AI summary
Embodiments provide a method for reading a target memory sector of a memory. The method comprises, based on read data corresponding to a plurality of memory sectors of the memory, estimating first one or more reference voltages and, using the first one or more reference voltages, performing a first read operation on the target memory sector. The method further comprises determining an error correcting code (ECC) decoding failure of the first read operation and, in response to determining the ECC decoding failure of the first read operation and based on read data corresponding to the target memory sector, updating the estimate of the first one or more reference voltages to generate second one or more reference voltages. The method also comprises using the second one or more reference voltages, performing a second read operation on the target memory sector.