Multiple stuck-at fault testability of self-testing checkers

As a feasibility study on offline testing of VLSI systems with concurrent error checking capability, the multiple fault testability is evaluated for self-testing checkers. New offline testing schema called codeword testing and noncodeword testing are introduced, in which all codewords and a small number of noncodewords are used as test inputs and the checker outputs are observed to decide if the circuit under test is faulty or not. It is proved that all the multiple stuck-at faults in tree-structured two-rail code checkers are detected with codeword testing followed by noncodeword testing. It is shown by simulation experiments that codeword testing can detect more than 99% of all possible double and triple faults in existing self-testing checkers for two-rail codes, Berger codes, and k-out-of-2k codes. The simulation experiments also show that all of the double and triple faults that elude the codeword testing are detected by noncodeword testing in which a small number of noncodewords are needed.<>