Studies On Extended Compatibilities Scan Tree Construction Based On Weighted Compatible Cliques

Up to now, digit systems are applied to every corner of our daily life. Integrated circuit serves as the most important part in all kinds of digit systems. In recent decades, with the rapid development of very large scale integration (VLSI) technique, the density of transistors increases dramatically, hence the testing is becoming a huge challenge. Full-scan testing is one of the most important designs for testability methodologies. However, it costs too much test application time. In order to solve this problem, lots of researches have been done in the world, but unfortunately with somewhat limitations.This thesis firstly introduces some basic definitions about testing and elaborates the main principles of scan testing. It also summarizes the current technologies about scan testing and points out their advantages and disadvantages as well as their applicability.Secondly, the structure of extended compatibilities scan tree is illustrated. This technique extends the compatibility of scan cells through employing logic NOT and XOR functions. It shifts the same data into the compatible scan cells so that the length of scan chain is largely reduced. Compared with other scan tree technologies, this method is superior in reducing the test application time, data volume and test power. However, in this structure, most of the scan cells collect in just several compatible cliques, which results in more scan outputs.In order to solve the problems of extended compatible scan tree, the thesis proposes two rules to reduce the scan outputs and an extended compatibility scan tree construction based on weighted compatible cliques. On the premises of not decreasing the fault coverage, the two rules reduce scan outputs efficiently and not increase the layers. The weighted algorithm averagely distributes all scan cells to the compatible cliques so as to reduce the layers and scan outputs. Experimental results show that the number of layers averagely reduces by 8.5% compared with that of previous extended compatible scan tree approach, and the number of scan outputs averagely decreases by 30.4%. It largely reduces the test application time and hardware overhead. In addition, this thesis further improves the weighted algorithm about how to select scan cells and how to get XOR cliques. Experimental results show that the number of layers declines by 8.7% using the improved one with the number of scan outputs decreases by 7.9%.The thesis employs the weighted algorithm which constructs less-layer and less-output extended compatibilities scan trees effectively so as to reduce the test application time and hardware overhead.