Configuring multiple scan chains for minimum test time

To reduce the high test time for serial scan designs, the use of multiple scan chains has been proposed. In this paper we consider the problem of optimally constructing multiple scan chains so as to minimize overall test time. Rather than follow the traditional practice of using equal length chains, we allow the chains to be of different lengths, and show that this can lead to lower test times. The main idea in our approach is to assign those scan elements that are more frequently accessed to shorter scan chains. Given a design with N scan elements, and given that k scan chains are to be used for applying tests, we present an algorithm of complexity 0(kN) for configuring the chains such that the overall test application time is minimized. By analyzing a range of circuit topologies, we demonstrate test time reductions as large as 40% over equal length chain configurations. References [1] K.-T. Cheng and V.D. Agrawal. A partial scan method for sequential circuits with feedback. IEEE Trans. on Computers, 39(4):544-548, April 1990. [2] R. Gupta, R. Gupta, and M. A. Breuer. The BALLAST methodology for structured partial scan design. IEEE Trans. on Computers, 39(4):538-543, April 1990. [3] P.P. Fasang et al. Automated design for testability of semicustom integrated circuits. In Proc., Int'l Test Conf., pages 558-564, November 1985. [4] S. Bhawmik and P. Palchaudhuri. DFT Expert: Designing testable VLSI circuits. IEEE Design & Test, pages 819, October 1989. [5] S.P.Morley and R.A.Marlett. Selectable length partial scan: a method to reduce vector length. In Proc. Int'l Test Conf ., pages 385-392, November 1991. [6] R.Gupta. Advanced Serial Scan Design for Testability. Ph.D. thesis, Univ. of Southern California, Dept. of Electrical Engg., 1991. CEng. Technical Report 91-10. [7] M. Abramovici, M. A. Breuer, and A. D. Friedman. Digital Systems Testing and Testable Design. Computer Science Press, New York, N.Y., 1990. [8] S. Narayanan, R. Gupta, and M.A. Breuer. Optimal configuring of multiple scan chains. Accepted for publication in IEEE Trans. on Computers . [9] F. Cormen, C. E. Leiserson, and R. L. Rivest. Introduction to Algorithms. The MIT Press, Cambridge, Massachusetts, 1990.