A bridging fault model where undetectable faults imply logic redundancy

Abstract

We define a robust fault model as a model where the existence of an undetectable fault implies the existence of logic redundancy, or more generally, a suboptimality in the synthesis of the circuit. The stuck-at fault model is robust, but other fault models such as certain bridging fault models are not. A robust fault model provides a mechanism to synthesize circuits in which all the target faults are detectable and 100% fault coverage is achievable. The ability to achieve 100% fault coverage, or understand why it is not achievable, is important since the requirement to achieve high test quality translates into a requirement to achieve complete fault coverage for target faults, regardless of the metrics used to measure test quality. We discuss a robust bridging fault model and its use as part of a test generation process for a non-robust bridging fault model (a non-robust bridging fault model may have to be used in order to capture the behavior of bridging defects). We also present experimental results related to the robust bridging fault model.