Ring generators - new devices for embedded test applications

This paper presents a novel methodology of designing generators and compactors of test data. The essence of the proposed approach is to use a set of transformations, which alters the structure of the conventional linear feedback shift registers (LFSRs) while preserving the transition function of the original circuits. It is shown that after applying the transition function preserving transformations in a certain order, the resultant circuits feature a significantly reduced the number of levels of XOR logic, minimized internal fanouts, and simplified circuit layout and routing, as compared to previous schemes based on external feedback LFSRs, internal feedback LFSRs, and cellular automata, all implementing the same characteristic polynomial. Consequently, the proposed devices can operate at higher speeds than those of conventional solutions and become highly modular structures.