Reducing Scan Shifts Using Configurations of Compatible and Folding Scan Trees

In this paper, a new method for reducing scan shifts is presented. Scan design is one of the most popular designs for test method for sequential circuits. However, for circuits with many flip-flops, it requires a long test application time and high test-data volume. Our new scan method utilizes two configurations of scan chains, a folding scan tree and a fully compatible scan tree to alleviate these problems. It is observed that uncompacted test patterns typically contain a large fraction of don't care values. This property is exploited in the fully compatible scan tree to reduce scan shifts without degrading fault coverage. Then, a folding scan tree is configured to further reduce the length of scan chain and scan shifts. Experimental results on benchmark circuits show that this scan method can significantly reduce scan shifts. Hiroyuki Yotsuyanagi received his B.E., M.E. and Ph.D degrees from Osaka University, in 1993, 1995 and 1998, respectively. In 1998 he joined the Department of Electrical and Electronic Engineering, the University of Tokushima, where he is currently an Associate Professor. His research interest includes test synthesis for sequential circuits and current testing for CMOS ICs. He is a member of the IEICE and the IEEE. Toshimasa Kuchii received B.E., M.E., and Ph.D. degrees in Electrical and Electronic Engineering from the University of Tokushima in 1994, 1996, and 1999, respectively. He is currently a DFT engineer at Sharp Corporation. His research interests are DFT methodologies for SoC devices, PLL jitter testing, and DFT for image sensor devices. Shigeki Nishikawa received B.E. in the Department of Information and Behavioral Sciences from Hiroshima University in 1980. He is currently a manager of LSI test engineering department at Sharp Corporation. His research interests are DFT, DFM and the total solution of testing technologies in the CAE tools. Masaki Hashizume received his B.E. and M.E. degrees in electrical engineering from the Univ. of Tokushima and Dr.E. degree from Kyoto Univ., in 1978, 1980 and 1993, respectively. He is currently a Professor of the Department of Electrical and Electronic Engineering, Faculty of Engineering, the Univ. of Tokushima. His research interests are logic synthesis and supply current testing of logic circuits. Kozo Kinoshita received B.E., M.E., and Ph.D. in Communication Engineering from Osaka University in 1959, 1961, and 1964, respectively. From 1964 to 1966 he was an Assistant Professor and from 1967 to 1977, an Associate Professor of Electronic Engineering at Osaka University, Osaka, Japan. From 1978 to 1989, he was a Professor in the Department of Information and Behavioral Sciences, Hiroshima University, Hiroshima, Japan. From 1989 to 2000, he again joined Osaka University as a Professor in the Department of Applied Physics, and is enumerates professor of Osaka University. Since April 2000, he has been a professor at Faculty of Informatics, Osaka Gakuin University, and is the Dean of Informatics. His fields of interest are test generation, fault diagnosis, memory testing, current testing, crosstalk testing, compact testing and testable design for logic circuits. He organized a series of Asian Test Symposium and was the Group Chair of Asian and Pacific Activities in Test Technology Technical Council of IEEE Computer Society until 2002. Prof. Kinoshita is IEEE Life Fellow, IEICE Fellow and a member of the Institute of Information Processing of Japan. He was a member of the editorial board of JETTA until 2000.