Unknown-tolerance analysis and test-quality control for test response compaction using space compactors

M.C.-T. Chao, Kwang-Ting Cheng, Seongmoon Wang, S. Chakradhar, Wen-Long Wei
2006 Proceedings - Design Automation Conference  
pattern-dependent circuitry and [4] requires a special ATPG to sup-For a space compactor, degradation of fault detection capability caused port its compaction scheme. Besides, they may mask some known by the masking effects from unknown values is much more serious scan-out responses in addition to unknowns. than that caused by error masking (i.e. aliasing). In this paper, we The selective compactors proposed in [5] and [6] select only the first propose a mathematical framework to estimate the
more » ... k to estimate the percentage scan-out responses with faulty values for observation and hence avoid of observable responses under unknown-induced masking for a space the masking effect due to unknowns. All other responses are discompactor. We further develop a prediction scheme which can cor-carded. However, an important assumption of structural testing is relate the percentage of observable responses with the modeled-fault that the patterns for the target modeled faults could detect many uncoverage and with a n-detection metric for a given test set. As a re-modeled faults as well. Therefore, discarding a majority of scan-out sult, the quality of a space compactor can be measured directly based responses would degrade the overall test quality. on its test quality, instead of based on indirect metrics such as the Another class of response compactors, called space compactors, number of tolerated unknowns or the aliasing probability. With the allow unknown values feeding to the compactor but use an XOR maprediction scheme above, we propose a construction flow for space trix to reduce the probability that a response is masked by the uncompactors to achieve the desired level of test quality while maxi-known values [8] [9]. The methods proposed in [10] and [11] furmizing the compaction ratio. ther use storage elements along with an XOR matrix to improve the compaction ratio and unknown tolerance. The methods proposed in Categories and Subject Descriptors [8], [9], [10] and [11] can guarantee some degree of error detection B.8.1 [Hardware]: Reliability, Testing, and Fault-Tolerance in the presence of one unknown. However, for high-ratio response compaction, a large number of responses will be processed by the General Terms space compactor, and hence the probability that more than one un-Design known concurrently appears at the inputs of the compactor is high. For such a multiple-unknown situation, some responses may become Keywords unobservable due to the masking of unknowns. Different configu-Test response compaction, design for test rations of a space compactor may result in different percentages of responses being observable. The method proposed in [12] analyzes
doi:10.1109/dac.2006.229401 fatcat:czhdjiiz4zdvpmcqgtaf7tviru