Row Refresh Circuit Using Hot and Cold Tables for Row Hammering
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Solution Overview
Problem
The increasing integration of memory devices leads to a coupling effect between word lines, causing data loss due to the 'row hammering' phenomenon, where frequently enabled word lines disturb adjacent memory cells, and existing methods to address this issue result in excessive overhead.
Innovation Solution
A circuit and method utilizing a cold table and hot table to efficiently select rows for refresh, where rows are ranked based on usage, with hot rows being refreshed first and ranks adjusted to optimize the selection process, reducing overhead and data loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a method of counting the number of enabled times of every row is used to find rows that have been enabled several times, then the row hammering phenomenon can be prevented, but the overhead is excessively increased
Solution Approach 1:
The patent segments the monitoring of row enabled times into two distinct data structures: a cold table for rows that have been enabled a small number of times (up to a first threshold) and a hot table for rows that have been enabled a large number of times (exceeding the first threshold). This segmentation allows the system to apply different management strategies to different categories of rows, reducing the overall overhead compared to uniformly monitoring all rows.
Solution Approach 2:
The patent changes the parameter of how row enabled times are stored and managed by introducing a threshold-based classification system. Rows are transitioned between cold and hot tables based on whether their enabled time count exceeds the threshold, allowing the system to optimize memory usage and access patterns based on the actual distribution of row activity.
2Productivity
If the distance between word lines is reduced to increase the degree of integration, then memory integration is improved, but the coupling effect between adjacent word lines is increased
Solution Approach 1:
The patent applies preliminary action by proactively identifying rows that are likely to be affected by row hammering (adjacent to frequently enabled rows) and pre-loading them into the cold table for monitoring. This allows the system to prepare refresh operations in advance before actual data corruption occurs, mitigating the harmful coupling effect without requiring physical separation of word lines.
Data Source
AI summary
A circuit for selecting a row of memory cells of a memory device to be refreshed may include: a cold table suitable for storing as a cold row a row selected as a hammered row when the row selected as the hammered row is neither one of cold rows stored in the cold table nor one of hot rows stored in a hot table; and the hot table suitable for storing, as a hot row, the row selected as the hammered row when the row selected as the hammered row is one of the cold rows stored in the cold table.