选择关键的常规扫描触发器进行置换是采用部分增强型扫描时延测试方法的核心问题.通过定义常规扫描触发器和未检测跳变时延故障的相关度的概念及其计算方法,提出一种触发器选择方法.首先找到被测电路中采用捕获加载方法不可测,但采用增强型扫描可测的跳变时延故障;然后依据常规扫描触发器与这些故障的相关度把少量关键的常规扫描触发器替换成为增强型扫描单元,从而有效地提高电路中跳变时延故障被检测的概率.实验结果表明,采用文中方法在可以接受的硬件开销下能有效地提高被测电路中的跳变时延故障覆盖率.
A key issue brought by partial enhanced-scan delay testing is how to select the critical normal-scan flip-flops to be replaced with enhanced-scan cells.We present a flip-flop selection method based on the defined relative measure between a normal-scan cell and the undetected transition delay faults,by which a small number of selected normal-scan cells can be replaced with enhanced-scan cells to improve the probability of detecting transition delay faults effectively.Experimental results demonstrated that the proposed method can improve transition delay fault coverage with acceptable hardware overhead.