How to reduce size of a signature-based diagnostic dictionary used for testing of connections

The paper presents a novel method for size reduction of a signature-based diagnostic dictionary that is used in testing of static and delay faults in connections by means of specific Interconnect BIST (IBIST) structure. The IBIST has a form of a ring register R-LFSR which feedback lines constitute connections under test. The previous studies of the authors assumed implementation of a single 2n-bit R-LFSR structure for testing and diagnosis of faults occurring in buses with the width n ≤ 32 bits. As size of the diagnostic dictionary rapidly grows in pace with both the number of connections under test and increase of the fault-multiplicity, it was a significant drawback that hindered examination of very wide buses. This study proposes how to solve this problem by splitting the n-bit bus into b fragments with the width of k bits each. Every fragment is tested by an independent R-LFSR register with its length of 2 k bits. The study assumes faults with the maximum fault-multiplicity r_max = 3 for each k-bit fragment of the bus, where the faults present combinations of stuck-at 0/1, AND /OR shorts of two or three lines and delay faults. The proposed approach has made it possible to significantly reduce size of the signature-based diagnostic dictionary that is necessary to locate and identify the mentioned faults. It was achieved by substantial reduction of the number of signature entries covered by the dictionary as well as by shortening the length of the signatures by b times. Moreover, the newly developed method enables to locate and identify substantial part of faults for the entire bus with the width of n, where the multiplicity of faults can be even as high as b r_max.