Isolation Cell Test Circuit for Stuck-at Fault Detection
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Solution Overview
Problem
Integrated circuits with multiple power domains face challenges in avoiding indeterminate signal states when signals propagate from an unpowered domain to a powered domain, leading to potential improper operation or faults such as stuck-at 1 errors, which existing isolation cells may not adequately address.
Innovation Solution
The implementation of a test circuit and method that includes isolation cells and power-on-reset (POR) circuits, allowing for the detection of missing or wrongly connected isolation cells and stuck-at 1 faults by configuring selection circuits to provide test signals and functional signals to isolation cells, and using observation elements to measure voltages during different functional modes and test modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation cells are used to prevent indeterminate signal states when signals propagate from unpowered to powered domains, then signal reliability is improved, but device complexity increases due to additional isolation circuitry
Solution Approach 1:
The isolation cell is configured to automatically enable itself when detecting that its input signal originates from an unpowered domain, eliminating the need for external control logic. The cell monitors power domain states and autonomously activates isolation functionality, thereby improving signal reliability while minimizing additional complexity.
Solution Approach 2:
The isolation cell acts as an intermediary component inserted between the unpowered domain output and the powered domain input. It mediates signal transmission by conditionally blocking or passing signals based on power domain states, ensuring reliable operation while maintaining a simple structural insertion rather than complex control systems.
2Reliability
If traditional isolation cells are implemented, then indeterminate states are avoided, but stuck-at 1 faults cannot be detected
Solution Approach 1:
A test mode is implemented that performs preliminary fault detection before normal operation. The test circuit applies specific test patterns to isolation cells and monitors their responses to detect stuck-at 1 faults in advance, ensuring that only functional isolation cells are used during actual operation, thus maintaining reliability while enabling fault detection.
Solution Approach 2:
The isolation cell includes dynamic test functionality that can switch between normal operation mode and test mode. In test mode, the cell's internal logic is activated to respond to test patterns, allowing detection of stuck-at 1 faults. This dynamic behavior enables the same hardware to serve both isolation functions and self-diagnosis without permanent complexity additions.
3Reliability
If isolation cells are always enabled to prevent indeterminate states, then signal integrity is maintained, but power consumption increases
Solution Approach 1:
The isolation cell is enabled periodically or conditionally rather than continuously. It activates only when a signal transition is detected or when power domain state changes occur, maintaining signal integrity during critical moments while remaining inactive during stable periods, thereby reducing overall power consumption while preserving signal reliability.
Solution Approach 2:
The isolation functionality is applied locally and selectively only to specific signal paths that require isolation based on their power domain origins. Not all signals receive isolation treatment, but only those identified as potentially problematic, optimizing the balance between signal integrity maintenance and power consumption reduction.
Data Source
AI summary
A circuit includes: a first power domain including: an isolation cell, a first selection circuit having inputs for receiving a first functional signal and a first test signal and an output for controlling the isolation cell, and a second selection circuit having inputs for receiving a second functional signal and a second test signal and an output coupled to a signal input of the isolation cell; a second power domain including: a first circuit having an input coupled to a signal output of the isolation cell, a first observation element coupled to the signal output of the isolation cell, and a second observation element coupled to an output of the first circuit; where, when in test mode, the first selection circuit controls the isolation cell based on the first test signal, and the second selection circuit provides the second test signal to the signal input of the isolation cell.