Refresh Address Generator Lookup Table Segmentation
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Solution Overview
Problem
As volatile memory devices shrink, their refresh characteristics degrade, leading to increased size of lookup tables needed to store addresses of weak cells that require frequent refresh, which in turn increases the chip size.
Innovation Solution
A refresh address generator circuit with a lookup table that divides addresses into groups based on data retention time, with more frequently accessed addresses stored in separate portions and accessed in order from lowest to highest retention time, minimizing the size of the lookup table by reducing redundant arrangements of frequently refreshed cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If volatile memory devices are made smaller, then device size is reduced, but refresh characteristics degrade leading to increased lookup table size
Solution Approach 1:
The lookup table is segmented into multiple portions, each storing addresses of weak cells with different data retention times. This segmentation allows the system to organize and manage weak cell addresses more efficiently, reducing the overall lookup table size while maintaining proper refresh coverage for all weak cells.
Solution Approach 2:
Different portions of the lookup table are allocated based on local characteristics of weak cells - specifically their data retention times. Addresses with shorter retention times are placed in portions that are accessed more frequently, while addresses with longer retention times are placed in portions accessed less frequently. This local quality differentiation optimizes the lookup table structure and reduces its size.
2Reliability
If weak cells are refreshed more frequently, then data retention is improved, but access time increases
Solution Approach 1:
The lookup table is divided into multiple portions corresponding to different data retention time categories. This segmentation enables the refresh operation to access only the relevant portion for the current refresh cycle, rather than scanning the entire lookup table, thereby reducing access time while maintaining proper refresh frequency for each weak cell group.
Solution Approach 2:
The refresh operation implements periodic access to different portions of the lookup table based on data retention time requirements. Portions with shorter retention times are accessed more frequently in a periodic manner, ensuring these weak cells receive timely refreshes while optimizing the overall refresh schedule to minimize access time.
Data Source
AI summary
A refresh address generator may include a lookup table including a first portion storing a first group of addresses associated with a first data retention time, and a second portion storing a second group of addresses associated with a second data retention time different from the first data retention time, wherein the addresses of the first portion are more frequently accessed than the addresses of the second portion to refresh the memory cells corresponding to the addresses. Systems and methods may also implement such refresh address generation.