Totally self-checking checker modules revisited

In this paper, conventional gate-level circuit compositions of the totally self-checking two-rail checker unit and the 2-of-4 checker unit are revisited. With respect to the former (latter), when the two input code words compared is not complementary (if two 1's are not present in the four input rails) and in the presence of an internal stuck-at fault, the checker is no more fault secure. In both the cases, the checker ceases to be totally self-checking. Given this, we suggest suitable cell based designs to overcome the above drawbacks. Hence, this work presents a new insight into combinational checker circuits.