Figure 1: (a) The inaccurate distribution (in the middle position) might lead to the conclusion that the circuit is faulty when the fault signature value of locates in the fault-free range ( ). Here, the accurate distribution of a fault state is on the left side. (b) The traditional intellectual method depending on known samples investigation, leads to different estimated range of fault signature for the same fault . Moreover, there is no possibility to simply tell us which estimation is trustworthy.