Memory Controller Read Voltage Iteration for Data Reliability
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Solution Overview
Problem
The reliability of data read operations in semiconductor memory systems is compromised due to changes in threshold voltage distributions during repeated program/erase cycles, making it difficult to set an optimal read voltage, which leads to increased error bits and reduced data accuracy.
Innovation Solution
A method is introduced where the memory system performs ECC decoding on initial data, re-reads data at varying voltages, and iteratively adjusts the read voltage until the number of error bits is below a threshold, using both hard and soft decoding techniques to determine the optimal read voltage for reliable data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the read voltage is set using conventional methods (read-retry table, gradient analysis, or threshold voltage analysis), then the read operation can be performed, but the reliability of data read deteriorates due to changes in threshold voltage distribution during program/erase cycles
Solution Approach 1:
The patent implements a feedback mechanism where the controller performs ECC decoding on read data, counts error bits, and uses this information to adjust the read voltage for subsequent read operations. This closed-loop feedback allows the system to adapt to threshold voltage changes and minimize error bits, directly improving data read reliability without requiring complex manual voltage tuning
Solution Approach 2:
The patent dynamically changes the read voltage parameter based on the number of error bits detected during ECC decoding. When error bits are detected, the controller adjusts the read voltage to a different level and retries the read operation. This parameter adjustment adapts the system to changing threshold voltage distributions, resolving the contradiction between maintaining simple operation and ensuring high reliability
2Reliability
If the number of read operations increases to handle threshold voltage changes, then data reliability improves, but the time required for data retrieval increases
Solution Approach 1:
The feedback mechanism allows the system to perform read operations only as many times as necessary. By detecting error bits and adjusting voltage accordingly, the system can often achieve reliable data retrieval in a single or few read attempts, avoiding unnecessary repeated reads and minimizing time loss while maintaining high accuracy
Solution Approach 2:
The patent applies partial action by performing ECC decoding and error bit counting only when necessary (when errors are detected), rather than always performing multiple read operations. This selective approach maintains reliability when needed while avoiding time consumption during successful single-attempt reads
Data Source
AI summary
Second data is generated by re-reading first data using a second read voltage when a first ECC decoding to first data using a first read voltage fails. Third data is generated by performing a second ECC decoding to the second data. An error-bit-number, which is a number of bits different between the second data and the third data, is obtained when the second ECC decoding fails. The process is repeated by changing the second read voltage until the error-bit-number is smaller than a predetermined threshold value. A third ECC decoding is performed to an optimal data that is the second data read using the second read voltage, with which the error-bit-number is smaller than the predetermined threshold value.