Value Override Circuits for Automatic Test Pattern Generation
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Solution Overview
Problem
The presence of unknown values in digital circuit designs during automatic test pattern generation testing increases testing runtime, pattern count, and costs, while also causing false paths, fault aliasing, and unpredictable logic behavior.
Innovation Solution
The method involves inserting value override circuits into identified paths within the circuit design that contribute to unknown values. These value override circuits, such as dedicated wrapper cells or custom logic circuits, are configured to provide output values of zero or one, reducing unknown values during testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard testing methods are used without value override circuits, then the circuit design can be tested with minimal modifications, but unknown values increase testing runtime and pattern count
Solution Approach 1:
Value override circuits are inserted into identified paths before testing to preemptively eliminate unknown values. The circuits are configured with control signals that force unknown values to known values (0 or 1) before they can propagate through the circuit, thereby reducing testing runtime without requiring extensive test pattern modifications
Solution Approach 2:
Value override circuits act as intermediary elements inserted between circuit components that generate unknown values and the rest of the circuit. These intermediary circuits capture and override the unknown values, preventing them from affecting test results while allowing the original circuit functionality to remain intact
2Reliability
If value override circuits are inserted into identified paths, then unknown values are reduced, but device complexity increases
Solution Approach 1:
The circuit design is segmented by identifying specific paths that generate unknown values. Value override circuits are inserted only in these identified paths rather than throughout the entire circuit, allowing targeted elimination of unknown values while minimizing the addition of complex circuitry to the overall design
Solution Approach 2:
Value override circuits are applied locally only to specific paths where unknown values are generated, rather than uniformly across the entire circuit. This localized application reduces the overall increase in device complexity while maintaining testing accuracy by addressing only the problematic areas
3Productivity
If value override circuits are used to reduce unknown values, then testing pattern count decreases, but additional control logic is required
Solution Approach 1:
Value override circuits are designed with multi-functionality, serving both as test aids for reducing unknown values and as potential functional elements in the circuit. The control logic for these circuits can be integrated with existing test control infrastructure, reducing the need for entirely separate control systems and minimizing additional complexity
Data Source
AI summary
Systems and techniques directed at reducing unknown values in automatic test pattern generation testing are disclosed. Various paths through a circuit design that generate an unknown value (e.g., not a value of zero or a value of one) during automatic test pattern generation testing are identified. A value override circuit may be inserted into paths identified as providing an unknown value. The value override circuit may be programmed to provide an output of a value of zero or a value of one during automatic test pattern generation testing. The insertion of value override circuits within a circuit design may reduce unknown values in automatic test pattern generation testing of the circuit design. The reduction of unknown values generated during automatic test pattern generation testing of a circuit design saves time and, thus, money.