A GA-Based Method for High-Quality X-Filling to Reduce Launch Switching Activity in At-speed Scan Testing

Power-aware X-filling is a preferable approach to avoiding IR-drop-induced yield loss in at-speed scan testing. However, the quality of previous X-filling methods for reducing launch switching activity may be unsatisfactory, due to low effect (insufficient and global-only reduction) and/or low scalability (long CPU time). This paper addresses this quality problem with a novel, GA (Genetic Algorithm) based X-filling method, called GA-fill. Its goals are (1) to achieve both effectiveness and scalability in a more balanced manner, and (2) to make the reduction effect of launch switching activity more concentrated on critical areas that have higher impact on IR-drop-induced yield loss. Evaluation experiments are being conducted on benchmark and industrial circuits, and initial results have demonstrated the usefulness of GA-fill.2009 15th IEEE Pacific Rim International Symposium on Dependable Computing, 16-18 November 2009, Shanghai, Chin

Inserting Test Points to Control Peak Power During Scan Testing

This paper presents a procedure for inserting test points at the outputs of scan elements of a full-scan circuit in such a manner that the peak power during scan testing is kept below a specified limit while maintaining the original fault coverage. If the power in a clock cycle during scan testing excee& a specified limit (which depen& on the peak power the chip has been designed to supply), a "peak power violation" is said to occur. Given a set of vectors, simulation is used to identify the cycles in which peak power violations occur (called "violating cycles"). For each violating cycle, the reduction in power caused by a control-O and control-1 test point at each scan element is determined by simulation. The optimization problem then is to select as few test points as possible to eliminate all violating cycles. We present a heuristic procedure for minimizing the number of test points using integer linear programming techniques. The test points are activated and deactivated in a manner such that there is neither any loss in fault coverage nor peak power violations in the capture cycle. Experimental results indicate that the proposed procedure is very effective in controlling peak power during scan testing using a small number of test points