Mixed-level sequential test generation using a nine-valued relaxation algorithm

A powerful automatic test generation system which uses a novel nine-valued relaxation algorithm is presented. This algorithm, which brings together the relaxation technique from circuit simulation and a nine-valued algebra from sequential circuit test generation, is applied to the strongly connected DC coupling components so that for every possible choice of node values a stable state could be achieved through relaxation. Circuits which use bidirectional transistors and depend on the transistor strengths for correct operation are properly handled by this algorithm. A method called DC path sensitization is used to detect the stuck-at, stuck-on, stuck-open and bridging faults for CMOS transistors. The algorithm has been implemented in C++ and preliminary results are very promising. The algorithm can easily be extended to different circuit models and other technologies, or be incorporated into a higher level test generation system.<>