Fuse Circuit Test Mode Using Select Transistor Segmentation
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Solution Overview
Problem
It is challenging to test fuse circuits and individual fuses under programming conditions without actually programming them, as fuses are one-time programmable devices, making it difficult to assess their functionality and reliability before implementation.
Innovation Solution
A fuse circuit design that allows for a test mode where only one select transistor per fuse cell is made conductive during a programming test operation, reducing the programming current to a level that does not blow the fuse, enabling the testing of programming circuitry and voltage sources without altering the fuse state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If programming voltage is applied to test fuse circuits, then programming circuitry can be tested, but fuse may be blown due to sufficient current
Solution Approach 1:
The patent divides the programming current path into multiple parallel paths by using multiple select transistors. During testing, only one select transistor is activated at a time, segmenting the total programming current into smaller portions that flow through each individual fuse. This segmentation allows the programming voltage to be applied for testing while preventing any single fuse from experiencing the full current that would blow it.
Solution Approach 2:
The patent applies partial action by activating only a subset of select transistors (specifically one transistor per fuse cell) during testing operations, rather than activating all transistors simultaneously. This partial activation reduces the current through each fuse to a safe level for testing while still providing sufficient current to test the programming circuitry functionality.
2Reliability
If all select transistors are made conductive during programming test, then programming current is sufficient to test circuitry, but fuse will be programmed/blown
Solution Approach 1:
The patent segments the select transistor array into individual controllable transistors, where each transistor controls current to a specific fuse. During testing, only one transistor per fuse cell is activated, dividing the programming current into discrete, controlled segments that prevent fuse programming while enabling circuit testing.
Solution Approach 2:
The patent applies local quality by differentiating the state of individual select transistors within the same fuse cell. While all transistors exist in the circuit, only specific local transistors are activated during testing, creating a localized conduction path that tests circuit functionality without applying full programming current to the fuse.
3Reliability
If programming voltage source and bit line are tested under programming conditions, then programming circuitry functionality is verified, but fuse state is altered
Solution Approach 1:
The patent segments the current distribution so that during programming voltage source and bit line testing, the programming current is divided across multiple fuse cells through activated select transistors. This segmentation ensures that while the programming circuitry is tested under full programming conditions, no single fuse receives the full current necessary to alter its state.
Data Source
AI summary
During a program operation of a fuse cell of a fuse circuit, all of a group of select transistors of a fuse cell are made conductive to program the fuse cell. During a test operation of a fuse cell of the fuse circuit, less than all of the group of select transistors are made conductive so that current less than a programming current flows through the fuse cell.