Improving the effectiveness of XOR-based decompressors through horizontal/vertical move of stimulus fragments

While test stimulus compression helps reduce test time and data volume, and thus alleviates test costs, the delivery of certain test vectors may not be possible, leading to test quality degradation. Whether a test vector is encodable in the presence of a decompressor strongly hinges on the distribution of its care bits. Utilization of stimulus manipulation techniques improves test pattern encodability as the distribution of care bits can be judiciously controlled. The desired test vector is delivered by resolving the stimulus conflicts that would have otherwise lead to pattern unencodability. Stimulus manipulation in the form of horizontal move of stimulus fragments has been shown to improve fan-out decompressors. In this work, we propose manipulation techniques in the form of horizontal or vertical move of stimulus fragments in order to improve XOR-based decompressors. Improvement in test pattern encodability reflects into savings in test costs and/or increase in test quality. The hardware and algorithmic support for each solution are also elaborated on, demonstrating the practicality of the proposed manipulation techniques.