On using implied values in EDT-based test compression

On-chip test compression has quickly established itself as one of the mainstream design-for-test (DFT) methodologies. It assumes that a tester delivers test patterns in a compressed form, and on-chip decompressors expand them into actual data loaded into scan chains. This paper presents a new and comprehensive method to boost performance of sequential test compression and ATPG operations. The approach is primarily aimed at reducing CPU time associated with generating and compressing test patterns. It prevents ATPG from assigning specified values to many inputs in order to cut down a time-consuming backtracking process needed to resolve conflicts leading to compression aborts. The proposed scheme efficiently combines test compression constraints with ATPG. Experimental results obtained for industrial designs illustrate feasibility of the proposed scheme and are reported herein.