ECC Decoding Retry Using Flip Read Voltages in Nonvolatile Memory
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Solution Overview
Problem
Nonvolatile memory devices face errors due to distorted threshold voltage distributions caused by factors like charge leakage and program disturbances, leading to incorrect data readouts and reduced reliability.
Innovation Solution
A method of error correction code (ECC) decoding that involves reading normal data, performing initial ECC decoding, and if failed, inverting error candidate bits in the flip range to generate corrected read data using flip read voltages, and retrying ECC decoding to enhance error correction capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If normal read voltages are used for reading data from nonvolatile memory device, then the read operation is simple and fast, but errors occur due to distorted threshold voltage distributions causing incorrect data readouts
Solution Approach 1:
The patent applies preliminary action by performing ECC decoding before final data output. The system reads data multiple times with different read voltages (normal read voltages and flipped read voltages) and performs ECC decoding in advance to identify and correct errors before the data is considered final, thereby improving reliability without significantly increasing operational complexity
Solution Approach 2:
The patent changes the read voltage parameter dynamically. When ECC decoding fails with normal read voltages, the system flips the read voltages (changes the voltage parameter) and re-reads the data. This parameter change allows the system to correct errors caused by threshold voltage distortion while maintaining a relatively simple decoding process
2Reliability
If ECC decoding is performed with normal read data only, then the decoding process is simple, but error correction capability is insufficient when threshold voltage distortion occurs
Solution Approach 1:
The patent applies partial action by performing additional read operations and ECC decoding only when necessary. The system first attempts ECC decoding with normal read data, and only when that fails does it perform the excessive action of reading with flipped voltages and performing additional ECC decoding. This approach improves error correction capability while minimizing time loss by avoiding unnecessary additional operations
Solution Approach 2:
The patent uses feedback from the ECC decoding result to determine whether additional read operations are needed. The ECC decoder provides feedback about decoding success or failure, and based on this feedback, the system decides whether to perform additional reads with flipped voltages. This feedback mechanism improves error correction capability while controlling time loss through conditional execution
3Reliability
If flip read voltages are used to correct errors, then error correction capability is enhanced, but the read operation becomes more complex with additional voltage switching
Solution Approach 1:
The patent applies preliminary action by preparing and testing normal read voltages first, and only switching to flipped read voltages when necessary. The system performs ECC decoding with normal voltages as a preliminary step, and only when that fails does it proceed to the more complex operation of using flipped voltages, thereby maintaining ease of operation for the common case while enabling enhanced error correction when needed
Solution Approach 2:
The patent changes the read voltage parameter from normal to flipped state only when error correction is needed. The system maintains simple normal read operations as the default, and switches to the more complex flipped voltage parameter only when ECC decoding fails, thus preserving ease of operation for typical cases while enabling enhanced error correction capability when required
Data Source
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AI summary
In a method of error correction code (ECC) decoding, normal read data are read from a nonvolatile memory device based on normal read voltages, and a first ECC decoding is performed with respect to the normal read data. When the first ECC decoding results in failure, flip read data are read from the nonvolatile memory device based on flip read voltages corresponding to a flip range of a threshold voltage. Corrected read data are generated based on the flip read data by inverting error candidate bits included in the flip range among bits of the normal read data, and a second ECC decoding is performed with respect to the corrected read voltage. Error correction capability may be enhanced by retrying ECC decoding based on the corrected read data when ECC decoding based on the normal read data results in failure.