Incremental Memory Refresh for Nonvolatile Storage
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Solution Overview
Problem
Nonvolatile memory systems face challenges in maintaining accurate charge levels over time due to charge decay, especially after repeated programming and erase operations, which can lead to incorrect data reading and storage issues.
Innovation Solution
A wear-leveling module and control module system that distributes write operations across multiple memory blocks, tracks erase operations, and performs incremental refreshing to counteract charge decay by adjusting charge levels based on usage data, ensuring data integrity and preventing charge levels from shifting out of programmed states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charge storage cells are periodically refreshed by reading and rewriting all values, then charge level accuracy is maintained, but memory operation time and energy consumption increase significantly
Solution Approach 1:
The patent applies local quality by dividing the memory into multiple blocks and selectively refreshing only specific blocks based on their individual charge decay characteristics. Instead of uniformly refreshing all memory blocks, the system identifies and refreshes only those blocks whose charge levels have decayed beyond acceptable thresholds, thereby reducing overall refresh time and energy consumption while maintaining charge accuracy where needed.
Solution Approach 2:
The patent implements dynamics by making the refresh operation adaptive rather than static. The refresh interval and scope are dynamically adjusted based on monitored charge decay rates, usage patterns, and block-specific characteristics. This allows the system to optimize refresh operations in real-time, refreshing memory blocks only when necessary rather than following a fixed periodic schedule.
2Duration of action of stationary object
If wear-leveling distributes write operations across multiple memory blocks, then memory cell lifespan is extended, but charge decay varies differently across blocks making refresh timing more complex
Solution Approach 1:
The patent applies feedback by continuously monitoring charge decay in each memory block and using this information to control refresh operations. The system tracks charge levels and decay patterns across all blocks, and this feedback drives decisions about which blocks need refreshing and when. This closed-loop control simplifies the management of varied decay characteristics by automatically adapting refresh timing to actual block conditions rather than requiring complex predetermined schedules.
Solution Approach 2:
The patent implements preliminary action by proactively refreshing memory blocks before their charge levels decay to critical thresholds. The system monitors charge decay trends and performs refresh operations in advance, preventing data corruption rather than reacting to errors after they occur. This proactive approach simplifies error handling and maintains data integrity without requiring complex error correction mechanisms.
3Productivity
If incremental refreshing is performed based on usage data, then refresh operations are optimized, but additional tracking and control mechanisms are required
Solution Approach 1:
The patent applies universality by designing the control module to perform multiple functions: it manages wear-leveling, tracks charge decay, determines refresh timing, and executes refresh operations. By consolidating these functions into a single integrated control mechanism, the system avoids the overhead of separate tracking and control systems while still achieving optimized incremental refreshing based on usage data.
Data Source
AI summary
A method of operating a memory system, including charge storage cells arranged into blocks, includes receiving a read request from a host that designates a location to be read within a first block. The method includes, in response to the read request, making measurements on the location to be read and responding to the host based on the measurements. The method includes receiving a write request from the host that designates a location to be written within the first block. The method includes, in response to the write request, selectively erasing the first block and resetting a timer. The method includes, in response to either the timer exceeding a predetermined time, or the measurements being outside of a predetermined range, refreshing the first block and resetting the timer. Refreshing the first block comprises adjusting charge levels in the charge storage cells of the first block without erasing the first block.