Selective Word Line Refresh in DRAM Memory Devices
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Solution Overview
Problem
Conventional DRAM memory cell refreshing techniques are inefficient as they refresh all memory cells regardless of charge state, leading to unnecessary power consumption and performance impairment.
Innovation Solution
A semiconductor memory device with a word line enable signal generation unit that selectively refreshes memory cells based on whether data is stored, preventing unnecessary refresh operations by grouping word lines into sets and using a logic level signal to control refresh operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional refresh techniques are used to refresh all memory cells, then data integrity is maintained, but power consumption increases and performance deteriorates due to unnecessary refresh operations
Solution Approach 1:
The patent applies local quality by differentiating refresh operations based on the specific state of each word line. Instead of uniformly refreshing all memory cells, the system selectively applies refresh only to word lines that contain valid data, thereby localizing the refresh action to where it is actually needed and avoiding unnecessary power consumption in empty regions
Solution Approach 2:
The patent implements self-service through the word line enable signal generation unit that automatically detects whether data is stored in each word line and generates appropriate enable signals. The system serves itself by making autonomous decisions about which word lines require refresh based on their own state, eliminating the need for external control of each individual refresh operation
2Reliability
If conventional refresh techniques are used to refresh all memory cells, then data integrity is maintained, but refresh cycle time increases due to unnecessary refresh operations
Solution Approach 1:
The patent extracts unnecessary refresh operations from the overall refresh process by identifying and excluding word lines that do not contain valid data. The word line enable signal generation unit extracts the essential subset of word lines that require refresh, separating them from the complete set of all word lines, thereby reducing the total refresh cycle time while maintaining data integrity for actual data storage
3Productivity
If word lines are grouped into sets with enable signals, then refresh efficiency is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple control functions into a single word line enable signal generation unit that handles detection and control for multiple word lines simultaneously. By grouping word lines into sets and using collective enable signals, the system reduces the number of independent control circuits needed, achieving better refresh efficiency without proportionally increasing device complexity
Data Source
AI summary
A semiconductor memory device comprises a plurality of memory cells connected to a plurality of word lines grouped in word line sets. Each of the word line sets is connected to a word line enable signal generation unit which stores information indicating whether data has been written to any of the memory cells connected to the word line set. The word line enable signal generation unit controls refresh operations for memory cells connected to the word line set so that only word lines connected to memory cells that have been programmed are refreshed.