Independence Fault Collapsing

This paper introduces independence fault collapsing. Faults are grouped into independent fault subsets such that each subset has some faults that cannot be covered by the tests derived for any other subset. Using these fault subsets, optimally compact tests can be found. For an equivalence or dominance collapsed fault set an independence graph is generated using structural and functional independences. Each fault is represented as a node and an undirected edge between two nodes indicates independence of the corresponding faults; two independent faults cannot be detected by the same vector. A “similarity-based” collapsing procedure reduces the graph to a fullyconnected graph, whose nodes specify concurrently-testable (possibly testable by a common vector) fault targets for the ATPG. For the four-bit ALU (74181) circuit, our procedure produced 12 independent fault subsets. Each fault set produced one vector thus giving the smallest possible test set.