DRAM PRAC Gap Counting for Accurate Targeted Refresh
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Solution Overview
Problem
Existing semiconductor memory devices, particularly DRAM, face challenges in maintaining the integrity of stored information due to information decay over time, exacerbated by certain operation patterns such as row hammering, which leads to inaccurate PRAC counting during targeted refresh operations.
Innovation Solution
Implementing PRAC gap counting by updating and preserving access counts during the gap between targeted refresh operations using an access count update logic circuit, which compares and adjusts the PRAC values at the end of a refresh set to account for activations that occurred during this gap, ensuring accurate counting and potential adjustments to alert thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If targeted refresh operations are performed based on PRAC counting, then data integrity is improved, but access count accuracy deteriorates due to gaps between refresh operations
Solution Approach 1:
The patent applies preliminary action by locking the PRAC value at the beginning of a targeted refresh set before any access operations occur during the refresh gap. This pre-locking ensures that subsequent accesses during the refresh operations do not interfere with the counting accuracy, as the baseline value is already secured. The locked value serves as a reference point for later comparison to determine genuine access counts that occurred outside the refresh operations.
Solution Approach 2:
The patent implements feedback by comparing the locked PRAC value with the current PRAC value after the targeted refresh set completes. This comparison provides feedback about the number of accesses that occurred during the gap period. The difference between the two values indicates the actual access count, which feeds back into the refresh management system to adjust future refresh operations and alert thresholds accordingly.
2Measurement precision
If PRAC counting is performed continuously, then access accuracy is improved, but device complexity increases due to additional logic circuits
Solution Approach 1:
The patent applies segmentation by dividing the PRAC counting process into distinct phases: a locked phase during targeted refresh operations where the PRAC value is held constant, and an update phase where the PRAC value is incremented based on actual accesses. This segmentation allows the system to maintain accurate counts without requiring continuous complex monitoring, as the counter is simplified during the locked phase and only actively updated during the gap period.
Solution Approach 2:
The patent implements dynamics by making the PRAC counter behavior adaptive based on the operational state. The counter transitions between locked and unlocked states dynamically - locked during targeted refresh sets and unlocked during gap periods. This dynamic behavior allows the same hardware circuit to serve multiple functions: accurate counting during gaps and stable reference maintenance during refresh operations, reducing the need for separate dedicated circuits.
Data Source
AI summary
A memory device performs a set of targeted refresh operations based on an aggressor address. The last targeted refresh operation in the set is a reset targeted refresh operation. The memory device sets a per-row access count (PRAC) value based on the number of access operations which have occurred in the gap between the first targeted refresh operation in the set and the reset targeted refresh operation. For example, when the first targeted refresh operation is performed on an address, the PRAC value is locked in an aggressor register. As part of the reset targeted refresh operation, the current PRAC value is read out and compared to the stored PRAC value. The difference between those values is written as the new PRAC value.