A Storage Based LBIST Scheme for Logic Diagnosis

When LBIST is used for test application in-field, and the presence of a defect is detected by the LBIST test set, it is advantageous if the same LBIST test set is used for diagnosis, either by itself or as part of a diagnostic test set. The goal of this paper is to develop an LBIST scheme for generating a test set that is useful for logic diagnosis. The proposed approach belongs to the class of storage-based LBIST approaches, and has the ability to produce additional (diagnostic) tests from the same type of stored test data entries used for fault detection. The main contributions of the paper are: (1) the derivation of targets for diagnostic tests that are suitable for LBIST, (2) the computation of stored test data for diagnosis to enhance the stored test data used for fault detection, and (3) a logic diagnosis process that is suitable for the LBIST approach. Experimental results for benchmark circuits and logic blocks of the OpenSPARC T1 microprocessor demonstrate the effectiveness of the proposed scheme in producing a diagnostic test set.