Hybrid test schemes comprising on-chip test compression and logic built-in self-test are expected to play a pivotal role in the design of new integrated circuits and delivering high quality tests. As architectural differences between these two paradigms are gradually blurring, and both schemes efficiently share test logic, they become more vulnerable to unknown (X) states whose sources vary from uninitialized memory elements to unwrapped-for-test analog modules. Typically, X values degrade test results, and thus test response compaction schemes must be duly protected. This article presents maXpress-an X-tolerant tunable compactor deploying a new scan chain selection mechanism capable of completely masking X states, as required by many in-system or one-directional streaming test applications, within redefinable groups of scan chains and designated scan shift cycles. The proposed scheme is also supporting separate observation scan chains that, in contrast to conventional scan, capture faulty effects every shift cycle, while their content is gradually shifted into a compactor shared with the remaining chains. In addition to a new layout-friendly architecture, the article proposes algorithms to automate maXpress control settings based on scan chain selection rules deployed to suppress X states. Experimental results obtained for industrial designs show feasibility and efficiency of the proposed scheme altogether with actual impact of X-masking on a resultant test coverage and test pattern counts.

中文翻译：

---

X-Tolerant Compactor maXpress 用于带观察扫描的系统内测试应用


包括片上测试压缩和逻辑内置自测试的混合测试方案预计将在新型集成电路的设计和提供高质量测试中发挥关键作用。随着这两种范式之间的架构差异逐渐模糊，并且两种方案有效地共享测试逻辑，它们变得更容易受到未知（X）状态的影响，这些状态的来源从未初始化的内存元素到未包装的测试模拟模块。通常，X 值会降低测试结果，因此必须适当保护测试响应压缩方案。本文介绍了 maXpress - 一种 X 容错可调压缩器，它部署了一种新的扫描链选择机制，能够根据许多系统内或单向流测试应用程序的要求，在可重新定义的扫描链组和指定的扫描移位内完全屏蔽 X 状态循环。所提出的方案还支持单独的观察扫描链，与传统扫描相比，该扫描链在每个移位周期捕获错误效应，而其内容逐渐转移到与其余链共享的压缩器中。除了新的布局友好架构之外，本文还提出了基于扫描链选择规则来自动化 maXpress 控制设置的算法，以抑制 X 状态。工业设计获得的实验结果表明了所提出方案的可行性和效率，以及 X 掩蔽对最终测试覆盖率和测试模式计数的实际影响。