Dummy Read Prevents Crowbar Current in SRAM Arrays
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Solution Overview
Problem
Simultaneous read and write operations in memory arrays, particularly in SRAM, can lead to crowbar currents due to meta-stable states in cross-coupled bitline keepers, causing damage and functional errors, with existing solutions being inefficient or impractical, such as preventing read operations or relying on expensive write buffers.
Innovation Solution
Implementing a dummy read operation on a second entry of the SRAM array when a simultaneous read and write collision is detected, using detection logic to suppress the read operation on the first entry and redirecting bitline discharge current to prevent crowbar currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If simultaneous read and write operations are allowed on the same memory entry to increase instruction throughput, then productivity is improved, but harmful crowbar currents are generated causing reliability degradation
Solution Approach 1:
The detection logic performs preliminary detection of read-write collision conditions before the actual read operation occurs. When a collision is detected, the system preemptively suppresses the read operation and performs a dummy read on a different entry, preventing the harmful crowbar current from occurring in the first place.
Solution Approach 2:
A dummy read operation on a second entry acts as an intermediary mechanism to redirect the bitline discharge current. Instead of allowing the current to create a harmful crowbar effect on the first entry, the dummy read provides an alternative path that safely dissipates the current through the second entry's bitlines.
2Reliability
If read operations are suppressed to prevent crowbar currents, then reliability is improved, but productivity is reduced due to fewer operations per cycle
Solution Approach 1:
The system creates a copy of the read operation by performing a dummy read on a second entry instead of suppressing the read operation entirely. This dummy read is a simplified version that maintains the necessary bitline discharge path while avoiding the harmful interaction with the write operation on the first entry.
Solution Approach 2:
The suppression and dummy read operations are applied locally to specific memory entries based on the collision detection. Only the first entry involved in the read-write collision is affected, while other entries in the memory array continue to operate normally, minimizing the overall impact on productivity.
3Reliability
If write buffers are used to prevent read-write collisions, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The memory array performs self-protection against read-write collisions using its own internal structure. The detection logic monitors the operational state of the array and automatically suppresses conflicting read operations, eliminating the need for external write buffers or complex arbitration mechanisms.
Solution Approach 2:
The functions of collision detection, read operation suppression, and dummy read execution are merged into a single integrated hazard management logic block. This unified approach consolidates multiple protective functions that would otherwise require separate circuits, reducing overall device complexity.
Data Source
AI summary
Systems and methods for detecting and suppressing crowbar currents in memory arrays. A dummy read is implemented to prevent crowbar currents in the case of simultaneous read-write collisions in a static random access memory (SRAM) array having cross-coupled bitline keepers. When a simultaneous read and write operation to a first entry of the memory array is detected, the read operation to the first entry is suppressed and a dummy read operation to a second entry of the memory array is performed. The write operation to the first entry is allowed to proceed undisturbed.