XStat: Statistical X-Filling Algorithm for Peak Capture Power Reduction in Scan Tests

Excessive power dissipation can cause high voltage droop on the power grid, leading to timing failures. Since test power dissipation is typically higher than functional power, test peak power minimization becomes very important in order to avoid test induced timing failures. Test cubes for large designs are usually dominated by don't care bits, making X-leveraging algorithms promising for test power reduction. In this paper, we show that X-bit statistics can be used to reorder test vectors on scan based architectures realized using toggle-masking flip flops. Based on this, the paper also presents an algorithm namely balanced X-filling that when applied to ITC'99 circuits, reduced the peak capture power by 7.4% on the average and 40.3% in the best case. Additionally XStat improved the running time for Test Vector Ordering and X-filling phases compared to the best known techniques.