Staggered Self-Refresh Strategy for DRAM Peak Current Reduction
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Solution Overview
Problem
As memory density increases in semiconductor devices like DRAM, the peak self-refresh current exceeds maximum specified limits, causing array write-back issues and violating refresh timing budgets, especially when all memory banks refresh simultaneously.
Innovation Solution
Implementing a staggered refresh strategy across multiple refresh cycles by grouping memory banks into odd and even units, or into larger groups, and increasing the frequency of the self-refresh oscillator to reduce the number of banks refreshing simultaneously, thereby distributing the peak current demand over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all memory banks refresh simultaneously, then data integrity is maintained, but peak self-refresh current exceeds maximum specified limits
Solution Approach 1:
The patent divides memory banks into multiple groups (e.g., first group and second group) and staggers their refresh operations across different refresh cycles. This segmentation prevents all banks from refreshing simultaneously, thereby reducing the peak current demand while maintaining data integrity through systematic refresh coverage.
Solution Approach 2:
The patent implements periodic refresh cycles where different groups of memory banks are refreshed in alternating periods. By using periodic action with staggered timing, the system maintains continuous data integrity while distributing current demand over time, preventing peak current exceedance.
2Productivity
If all memory banks refresh simultaneously, then data is updated frequently, but refresh timing budget is violated
Solution Approach 1:
By segmenting memory banks into multiple groups with staggered refresh timing, the patent achieves frequent data updates without violating the refresh timing budget. The segmented approach allows overlapping refresh operations that fit within the total timing budget while maintaining high update frequency.
Solution Approach 2:
The patent performs preliminary grouping and scheduling of refresh operations, where banks are pre-assigned to different refresh cycles based on their group membership. This preliminary action ensures that data is updated frequently while the staggered timing automatically adjusts to fit within the refresh timing budget.
3Quantity of substance
If memory density increases, then storage capacity improves, but peak self-refresh current exceeds maximum specified limits
Solution Approach 1:
The patent applies segmentation to high-density memory configurations by dividing memory banks into groups that are refreshed in staggered cycles. This approach enables support for higher memory density without proportionally increasing peak current, as the current demand is distributed across multiple time periods rather than occurring simultaneously.
Data Source
AI summary
Devices and methods include organizing memory units of a memory device into a number of groups. The devices and methods also include self-refreshing each group of memory units on different corresponding sequential clock pulses of a self-refresh clock. Specifically, at least one of each group of memory units counts pulses of a self-refresh clock and invokes a self-refresh after every nth pulse of a cycle of pulses while not invoking a self-refresh on all other pulses of the cycle of pulses.