Z-DFD: design-for-diagnosability based on the concept of Z-detection

We address the problem of design-for-diagnosability, i.e., improving the accuracy of fault diagnosis or reducing its complexity through the insertion of observation points. To perform design-for-diagnosability efficiently, we use a procedure developed earlier for computing the number of fault pairs, N_P, that are not guaranteed to be distinguished by a given test set. By using the concept of z -detection, N_P can be computed efficiently without enumerating fault pairs and without performing non-fault dropping fault simulation. We study the possibility of increasing the diagnosability of a circuit by inserting observation points so as to reduce N_P. Our results include the following. (1) We find experimentally the number of observation points that need to be inserted in order to achieve a close-to-minimum value for N_P. (2) We describe an efficient procedure for inserting a given number of observation points so as to reduce N_P. We present experimental results for benchmark circuits to demonstrate the accuracy of using N_P to guide a design-for-diagnosability process.