2D Scan Chain Diagnosis Using Orthogonal Shift Patterns
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Solution Overview
Problem
Conventional scan chain diagnosis methods, especially in two-dimensional architectures, face challenges in accurately identifying faulty scan cells due to un-modeled fault behaviors and require additional hardware or increased silicon area, which is not feasible in all scenarios.
Innovation Solution
A method involving shifting test patterns in orthogonal and pseudo-diagonal directions within scan chains to generate chain test results, allowing for the identification of good and faulty scan chains, and pinpointing faulty scan cell candidates without the need for extra hardware, by leveraging the circular shifting capability of scan cells coupled across multiple chains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two-dimensional scan architecture is used to improve chain diagnosis resolution, then diagnostic accuracy is improved, but the number of input/output scan channels and silicon area increase
Solution Approach 1:
The patent applies two-dimensional scan architecture where scan cells are arranged in a 2D grid rather than a single linear chain. This allows test patterns to be shifted in multiple directions (horizontal, vertical, diagonal) to activate and propagate faults through different paths, significantly improving diagnostic resolution by enabling more comprehensive fault coverage with the same number of scan cells.
Solution Approach 2:
Each scan cell in the 2D architecture serves multiple functions: it can receive test patterns from multiple directions, propagate faults along multiple paths, and be observed from different chain exits. This multi-functionality allows the same hardware resources to achieve higher diagnostic capability without proportional increases in silicon area.
2Measurement precision
If two-dimensional scan architecture is used to improve chain diagnosis resolution, then diagnostic accuracy is improved, but the number of input/output scan channels increases
Solution Approach 1:
By transitioning from 1D to 2D scan architecture, the system gains additional spatial dimensions for test pattern propagation. This allows faults to be activated and observed through multiple directional paths (horizontal, vertical, diagonal shifts) without requiring a proportional increase in the number of external I/O channels, as the 2D arrangement internally routes signals through multiple paths.
Solution Approach 2:
The patent employs dynamic control of scan chain directions, where the same physical scan channels can be reconfigured to shift patterns in different directions (horizontal, vertical, diagonal) based on test requirements. This dynamic reconfiguration allows a limited number of I/O channels to effectively control a larger 2D scan cell array, reducing the need for additional channels.
3Device complexity
If conventional diagnosis methods are used for un-modeled faults, then diagnostic accuracy degrades, but no additional hardware is required
Solution Approach 1:
The 2D scan architecture provides multiple propagation paths through horizontal, vertical, and diagonal directions. When a fault occurs, especially an un-modeled fault with intermittent behavior, the fault effect can be propagated through alternative paths that may reveal the defect. This multi-directional approach increases the probability of detecting and localizing un-modeled faults without requiring additional hardware beyond the 2D scan structure.
Solution Approach 2:
The patent implements iterative diagnosis procedures where test patterns are shifted in multiple directions, results are analyzed, and subsequent test patterns are designed based on previous results. This feedback loop allows the system to progressively narrow down faulty scan cell candidates by eliminating good cells based on their behavior across different shift directions, improving diagnostic accuracy for un-modeled faults through intelligent algorithmic approaches.
Data Source
AI summary
A test pattern is shifted into scan chains in a circuit in a first direction. The scan cells on each of the scan chains are further coupled to corresponding scan cells on two other scan chains in the scan chains such that data bits stored in the scan cells can be shifted circularly in a second direction orthogonal to the first direction based on a control signal. The loaded test pattern is then shifted in the second direction for a number of clock cycles equal to the number of the scan chains. The test pattern is then shifted in the first direction out of the scan chains to generate a chain test result. Faulty scan cell candidates on faulty scan chains may be determined based on part of the chain test result for one of good scan chains.