Flash Memory Read Offset Compensation for Charge Loss Drift
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Solution Overview
Problem
Flash memory devices experience read errors due to charge loss, which leads to inefficient read operations and increased error recovery times, as fixed read offsets fail to compensate for dynamically changing charge loss across blocks.
Innovation Solution
Implement a dynamic read offset compensation mechanism that adjusts the read voltage based on the number of memory cells in programmed states, using mapping tables to determine a tailored offset that is updated periodically to account for charge loss accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed read offset is used, then the read operation is simple and fast, but it cannot compensate for dynamically changing charge loss across blocks
Solution Approach 1:
The patent implements dynamic read offset compensation by adjusting the read offset value based on the actual charge loss state of each block. The system continuously monitors the number of memory cells in programmed states and updates the offset accordingly, transforming the fixed offset approach into a dynamic one that adapts to changing charge loss conditions across different blocks.
Solution Approach 2:
The patent changes the read offset parameter dynamically based on the charge loss state. By monitoring the number of memory cells in programmed states and using mapping tables to determine appropriate offset values, the system adjusts the read offset parameter to compensate for varying charge loss conditions, thereby improving read reliability without requiring complex hardware modifications.
2Reliability
If charge loss is not compensated, then the device structure remains simple, but read errors increase and error recovery times increase
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the read offset before read errors occur. The system monitors charge loss conditions and pre-adjusts the read offset based on the number of memory cells in programmed states, preventing read errors before they happen rather than recovering from them after occurrence, thereby reducing error recovery time.
Solution Approach 2:
The patent implements feedback mechanisms by continuously monitoring the number of memory cells in programmed states and using this information to adjust the read offset. This closed-loop feedback system ensures that the read offset is always optimized for the current charge loss condition, preventing read errors and reducing recovery time when issues arise.
3Measurement precision
If the read offset is updated frequently, then charge loss compensation accuracy improves, but the update frequency may interfere with normal read operations
Solution Approach 1:
The patent applies periodic action by updating the read offset at specific intervals or triggered by specific conditions (such as after programming operations or when charge loss thresholds are crossed). This periodic updating approach ensures accurate charge loss compensation while avoiding continuous interruptions to normal read operations, thereby maintaining productivity.
Solution Approach 2:
The system performs self-service by automatically monitoring and adjusting the read offset based on the actual charge loss state of the memory blocks. The monitoring and adjustment processes are integrated into the normal operation flow, allowing the system to maintain accurate compensation without requiring external intervention or significantly impacting read operation throughput.
Data Source
AI summary
A memory controller coupled to a memory device including an array of memory cells, each memory cell being set to one of 2N states corresponding to a piece of N-bits data, where N is an integer greater than 1, and the array of memory cells being partitioned into one or more units. The memory controller is coupled to the memory device and configured to, upon executing instructions, obtain, from the memory device, a number P of memory cells in a unit of the units that are in one or more programmed states of the 2N states; calculate, based on the number P, a compensated read voltage with an offset from a default read voltage; and provide, to the memory device, the compensated read voltage for a read operation performed on a selected memory cell of the memory cells in a unit of the units.