Intermittent and Transient Fault Diagnosis on Sparse Code Signatures

Failure diagnosis of field returns typically requires high quality test stimuli and assumes that tests can be repeated. For intermittent faults with fault activation conditions depending on the physical environment, the repetition of tests cannot ensure that the behavior in the field is also observed during diagnosis, causing field returns diagnosed as no-trouble-found. In safety critical applications, self-checking circuits, which provide concurrent error detection, are frequently used. To diagnose intermittent and transient faulty behavior in such circuits, we use the stored encoded circuit outputs in case of a failure (called signatures) for later analysis in diagnosis. For the first time, a diagnosis algorithm is presented that is capable of performing the classification of intermittent or transient faults using only the very limited amount of functional stimuli and signatures observed during operation and stored on chip. The experimental results demonstrate that even with these harsh limitations it is possible to distinguish intermittent from transient faulty behavior. This is essential to determine whether a circuit in which failures have been observed should be subject to later physical failure analysis, since intermittent faulty behavior has been diagnosed. In case of transient faulty behavior, it may still be operated reliably.