This paper describes a method of test data compression for a given test set using statistical encoding. In order to maximize the effectiveness of statistical encoding, the method first converts some specified input values in the test set to unspecified ones without losing fault coverage, and then reassigns appropriate logic values to the unspecified inputs. Experimental results for ISCAS-89 benchmark circuits show that the proposed method can on the average reduce the test data volume to less than 25% of that required for the original test set.

If a test set for more complex faults than stuck-at faults is generated, higher defect coverage would be obtained. Such a test set, however, would have a large number of test vectors, and hence the test costs would go up. In this paper we propose a method to detect bridge defects with a test set initially generated for stuck-at faults in a full scan sequential circuit. The proposed method doesn't add new test vectors to the test set but modifies test vectors. Therefore there are no negative impacts on test data volume and test application time. The initial fault coverage for stuck-at faults of the test set is guaranteed with modified test vectors. In this paper we focus on detecting as many as possible non-feedback AND-type, OR-type and 4-way bridging faults, respectively. Experimental results show that the proposed method increases the defect coverage.