NVM Controller On-Chip Valley Search Read Level Adjustment
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Solution Overview
Problem
Existing storage devices face challenges in correcting errors in severely deteriorated memory cells, leading to unreliable read operations due to the limitations of error correction codes (ECC) and the need for alternative sensing methods during read retry operations.
Innovation Solution
A controller and storage device system that includes a buffer memory and an ECC circuit, which performs error correction and initiates an on-chip valley search operation when ECC fails, using detection information to adjust the read level and optimize data retrieval by updating offset information in tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction code (ECC) is used to correct errors in memory cells, then data reliability is improved, but it becomes ineffective when memory cells are severely deteriorated
Solution Approach 1:
The patent implements a dynamic read retry mechanism that adapts the read level based on the deterioration state of memory cells. When ECC fails to correct errors, the system dynamically adjusts the read level by applying offset information derived from valley search operations, enabling effective reading from severely deteriorated cells that static ECC cannot handle
Solution Approach 2:
The patent changes the read level parameter by applying offset information to the default read level. This parameter adjustment is based on valley search detection information that identifies the optimal read level for deteriorated memory cells, allowing the system to adapt to varying memory cell conditions beyond what fixed ECC can achieve
2Reliability
If a read retry operation is performed using a sensing method different from normal read operation, then data retrieval from deteriorated cells is improved, but device complexity increases
Solution Approach 1:
The patent performs preliminary valley search operations to detect the optimal read level before attempting to read data from potentially deteriorated memory cells. This preliminary detection of offset information enables subsequent read retry operations to use the correct adjusted read level, improving reliability while managing complexity through pre-characterization
Solution Approach 2:
The patent introduces offset information as an intermediary parameter that mediates between the default read level and the actual optimal read level for deteriorated cells. This intermediary enables the system to bridge the gap between normal reading operations and the specialized valley search method, simplifying the overall control logic
3Measurement precision
If offset information is updated based on valley search detection information, then read level accuracy is improved, but loss of time occurs during the valley search operation
Solution Approach 1:
The patent performs valley search operations in advance to pre-determine offset information that characterizes the memory cell deterioration. This preliminary characterization allows subsequent read operations to use the pre-computed offset without repeating the time-consuming valley search, achieving a balance between accuracy and time loss
Solution Approach 2:
The patent applies partial valley search by performing the detection operation selectively - only when ECC failure indicates severe deterioration. This partial application of the time-consuming valley search method minimizes overall time loss while maintaining read level accuracy when needed
Data Source
AI summary
A controller including: control pins for providing control signals to a nonvolatile memory; a buffer memory configured to store first to third tables; and an error correction code (ECC) circuit configured to correct an error in first data read from the nonvolatile memory according to a first read command, wherein the first table stores first offset information, the second table stores second offset information, and the third table stores third offset information, wherein the third offset information corresponds to a history read level and is determined by the first and second offset information, and when the error of the first data is uncorrectable, an on-chip valley search operation is performed by the nonvolatile memory according to a second read command, detection information of the on-chip valley search operation is received according to a specific command, and the second offset information which corresponds to the detection information is generated.