This paper proposes a new per-test fault diagnosis method based on the X-fault model. The X-fault model can represent all possible faulty behaviors of a physical defect or defects in a gate and/or on its fanout branches by assigning different X symbols assigned to the fanout branches. A partial symbolic fault simulation method is proposed for the X-fault model. Then, a novel technique is proposed for extracting more diagnostic information by analyzing matching details between observed and simulated responses. Furthermore, a unique method is proposed to score the results of fault diagnosis. Experimental results on benchmark circuits demonstrate the superiority of the proposed method over conventional per-test fault diagnosis based on the stuck-at fault model.
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