A tree-structured LFSR synthesis scheme for pseudo-exhaustive testing of VLSI circuits

This paper presents a new test architecture, called Tree-LFSR/SR, to more effectively generate pseudo-exhaustive test patterns for combinational VLSI circuits. Instead of using a single scan chain, the proposed test architecture routes a scan tree driven by the LFSR to generate all possible input patterns for each output cone. The new test architecture is able to take advantages of both signal sharing and signal reuse. The benefits are: (1) the hardware overhead can be greatly reduced by saving routing area and XOR circuits, and (2) the difficulty of test architecture synthesis can be eased by accelerating the searching process of appropriate residues. The Tree-LFSR/SR configuration is then extended, if necessary, by adding XOR networks to deal with more complex input-output relations. An efficient method to directly synthesize the XOR network is also included. Experimental results obtained by simulating combinational benchmark circuits are very encouraging