EFFECTS OF REDUNDANCY ON FAUL DF TECTION AND DIAGNOSIS IN COMBINATIONAL LOGIC CIRCUITS

摘要

Most fault detection and diagnosis systems in use today operate under the single-fault assumption, namely that the circuits will be tested often enough so that any single fault can be detected and corrected before another fault occurs. This reasoning fails when the circuit under test contains redundancy because of the undetectable faults which redundancy implies. While an undetectable fault will not affect the logical operation of the circuit, it was demonstrated by Friedman that the presence of an undetectable fault can cause other faults (the second-generation faults) to behave differently than in the normal case or even to become undetectable. The result of this fact is that a fault which cannot be detected and therefore is not corrected, may cause tests for other faults to become invalid. To prevent this, Friedman recommended the removal of 'certain kinds of redundancy.' (Author)