Flash Memory Data Refresh via Time Estimation
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Solution Overview
Problem
Multi-value flash memory devices have a low data retention capability, especially when exposed to high temperatures or frequent writing, leading to data volatilization, which can cause issues in applications like car navigation systems where data refresh is necessary but often results in increased costs and inefficient timing.
Innovation Solution
An electronic device connected to a flash memory that temporarily stores data, estimates the passage of time since data was written, and refreshes the data when the estimated time exceeds a threshold, eliminating the need for a memory cell state detection circuit and allowing for timely data updates without circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is frequently refreshed in multi-value flash memory, then data retention is improved, but the life of the nonvolatile memory decreases due to increased writing frequency
Solution Approach 1:
The patent applies preliminary action by estimating the passage of time since data was written to the nonvolatile memory and proactively refreshing the data before significant degradation occurs. The update control means estimates time elapsed and triggers data refresh operations in advance, preventing data volatilization due to high temperature or prolonged storage without requiring frequent reactive rewriting. This reduces unnecessary write operations that would otherwise shorten memory life.
Solution Approach 2:
The patent utilizes parameter changes by monitoring and responding to environmental conditions (particularly temperature) and time parameters. The system adjusts its data refresh strategy based on estimated passage of time and detected temperature levels, triggering updates only when parameters indicate degradation risk. This selective approach based on parameter thresholds minimizes unnecessary writing operations while ensuring data integrity when actually needed.
2Reliability
If a circuit is provided to detect memory cell state and determine refresh timing, then data retention is improved, but manufacturing cost increases
Solution Approach 1:
The patent introduces an intermediary approach by using the controller unit as a mediator between the nonvolatile memory and the refresh operation. Instead of adding specialized detection circuits to the memory itself, the controller estimates passage of time and determines refresh timing based on this estimation and temperature detection. This intermediary control mechanism achieves reliable data retention without modifying the memory structure, avoiding increased manufacturing costs while maintaining data integrity.
Solution Approach 2:
The system applies self-service by using readily available components (controller unit with temperature sensor and passage of time estimation capability) to perform the function that would otherwise require specialized memory cell state detection circuits. The controller autonomously determines when refresh is needed based on time and temperature parameters, eliminating the need for additional expensive circuitry in the memory device itself.
3Ease of manufacture
If data is refreshed only when temperature exceeds threshold, then manufacturing cost is reduced, but data retention is insufficient because exposure time to high temperature is not considered
Solution Approach 1:
The patent combines preliminary action with environmental monitoring by estimating passage of time and using this estimation proactively to trigger refresh operations. The system doesn't wait for temperature to exceed a threshold; instead, it proactively refreshes data based on time elapsed since writing, which correlates with degradation risk. This preliminary refresh approach, combined with temperature awareness, ensures data retention without requiring complex real-time temperature-based decision circuits.
Solution Approach 2:
The system applies dynamics by making the refresh decision process adaptive and flexible. Rather than using a fixed temperature threshold, the controller dynamically determines refresh timing based on a combination of estimated passage of time and current temperature conditions. This dynamic approach allows the system to adjust refresh behavior to actual degradation risks, improving data retention while avoiding unnecessary operations that would increase manufacturing complexity.
Data Source
AI summary
A navigation device realizes such processing as map display and route guidance based on map data stored in a memory card. The data in the memory card tends to be volatilized with an increase in the frequency of reading of data. Therefore, the data that are highly frequently read out are held in a RAM so as to be read from the memory card at a decreased frequency. Further, the passage of time is calculated from the date and hour the data are recorded in the memory card, and the whole data in the memory card are refreshed every time when the passage of time exceeds a threshold value T1.