Functional broadside tests were developed to avoid overtesting of delay faults. The tests achieve this goal by creating functional operation conditions during their functional capture cycles. To increase the achievable fault coverage, close-to-functional scan-based tests are allowed to deviate from functional operation conditions. This article suggests that a more comprehensive functional broadside test set can be obtained by replacing target faults that cannot be detected with faults that have similar (but not identical) detection conditions. A more comprehensive functional broadside test set has the advantage that it still maintains functional operation conditions. It covers the test holes created when target faults cannot be detected by detecting similar faults. The article considers the case where the target faults are transition faults. When a standard transition fault, with an extra delay of a single clock cycle, cannot be detected, an unspecified transition fault is used instead. An unspecified transition fault captures the behaviors of transition faults with different extra delays. When this fault cannot be detected, a stuck-at fault is used instead. A stuck-at fault has some of the detection conditions of a transition fault. Multicycle functional broadside tests are used to allow unspecified transition faults to be detected. As a by-product,more »
Covering Undetected Transition Fault Sites with Optimistic Unspecified Transition Faults under Multicycle Tests
When a transition fault test set leaves undetected transition faults because of logic redundancies, test constraints, or the existence of hard-to-detect faults, it leaves transition fault sites uncovered. For the case where multicycle tests are used, this paper explores the possibility of covering the sites of undetected transition faults by using tests for what are referred to as optimistic unspecified transition faults. For this discussion, a standard transition fault is associated with an extra delay of a single clock cycle. An unspecified transition fault captures in a single fault the behaviors of transition faults of different durations. Because faults with different durations may be detectable or undetectable independently by a multicycle test, an unspecified transition fault may be detected even if the standard transition fault at the same site is undetectable. This effect is enhanced with optimistic unspecified transition faults. The paper describes an iterative test compaction procedure for multicycle tests that supplements the set of standard transition faults with optimistic unspecified transition faults to cover the sites of undetected standard transition faults.
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- European Test Symposium
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- National Science Foundation
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