Abstract-Various X-filling methods have been proposed for reducing the shift and/or capture power in scan testing. The main drawback of these methods is that X-filling for low power leads to lower defect coverage than random-fill. We propose a unified low-power and defect-aware X-filling method for scan testing. The proposed method reduces shift power under constraints on the peak power during response capture, and the power reduction is comparable to that for the Fill-Adjacent X-filling method. At the same time, this approach provides high defect coverage, which approaches and in many cases is higher than that for random-fill, without increasing the pattern count. The advantages of the proposed method are demonstrated with simulation results for the largest ISCAS and the IWLS benchmark circuits.

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Abstract-Multi-detect (N-detect) testing suffers from the drawback that its test length grows linearly with N. We present a new method to generate compact test sets that provide high defect coverage. The proposed technique makes judicious use of a new pattern-quality metric based on the concept of output deviations. We select the most effective patterns from a large N-detect pattern repository, and guarantee a small test set as well as complete stuck-at coverage. Simulation results for benchmark circuits show that with a compact, 1-detect stuck-at test set, the proposed method provides considerably higher transition-fault coverage and coverage ramp-up compared to another recently-published method. Moreover, in all cases, the proposed method either outperforms or is as effective as the competing approach in terms of bridging-fault coverage and the surrogate BCE+ metric. In many cases, higher transition-fault coverage is obtained than much larger N-detect test sets for several values of N. Finally, our results provide the insight that, instead of using N-detect testing with as large N as possible, it is more efficient to combine the output deviations metric with multi-detect testing to get highquality, compact test sets.

Abstract-The main disadvantage of LFSR-based compression is that it should be usually combined with a constrained ATPG process, and, as a result, it cannot be effectively applied to IP cores of unknown structure. In this paper, a new LFSR-based compression approach that overcomes this problem is proposed. The proposed method allows each LFSR seed to encode as many slices as possible. For achieving this, a special purpose slice, called stop-slice, that indicates the end of a seed's usage is encoded as the last slice of each seed. Thus, the seeds include by construction the information of where they should stop and, for that reason, we call them self-stoppable. A stop-slice generation procedure is proposed that exploits the inherent test set characteristics and generates stop slices which impose minimum compression overhead. Moreover, the architecture for implementing the proposed technique requires negligible additional hardware overhead compared to the standard LFSR-based architecture. The proposed technique is also accompanied by a seed calculation algorithm that tries to minimize the number of calculated seeds.

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