TEST SEQUENCES TO ACHIEVE HIGH DEFECT COVERAGE FOR SYNCHRONOUS SEQUENTIAL-CIRCUITS

Test sets that detect each stuck-at fault n>1 times (called n-detectio n stuck-at test sets) were shown to be effective in achieving high def ect coverages. In addition, a pseudofunctional fault model defined bef ore was shown to result in test sets having similar defect coverages, Previous studies of n-detection stuck-at test sets and pseudofunctiona l test sets were for combinational circuits, In this paper, we study n -detection stuck-at test sequences and pseudofunctional test sequences for synchronous sequential circuits, Considering stuck-at faults, we propose five definitions of the number of detections achieved by a tes t sequence. These definitions lead to five different definitions of n- detection struck- at test sequences; We discuss the effects of these d efinitions on fault-simulation and test-generation procedures and pres ent experimental results for benchmark circuits to evaluate their rela tive effectiveness, The experimental results indicate the usefulness o f the simplest definition in generating test sequences that achieve im proved defect coverages. We also describe a pseudofunctional fault mod el that extends previous definitions. We describe fault-simulation and test-generation methods for this model and give experimental data to evaluate its effectiveness. The results indicate that this model too c an be used to generate test sequences with improved defect coverage. I ts advantages and disadvantages compared to the n-detection stuck-at m odel are also considered.