An Improved VLSI Test Economics Analysis System - Laboratory for ...

4.2.1 Fault CoverageFault coverage is a function of test length as discussion in Section 2.6. Now, we try to ndparameter of this function.0.90.80.7Fault Coverage (FC)0.60.50.40.30.20.10−0.10 20 40 60 80 100 120 140 160 180 200Test Vector Length (V)Figure 4.1: Experimental and approximated result of fault coverage.In our experiment, ISCAS'89 benchmark circuits are applied to a sequential ATPG, called"HITEC". The fault coverage of each test length is obtained, as shown in Figure 4.1. Then,equationFC(V )=1, e , fcV(4.1)is used to t the experimental results. This tting curve is also shown in the same gure.Least square tting algorithm are adopted to evaluate fc of the function. Because we generallyuse only high fault coverage results, our tting process eliminates those data which faultcoverage fewer than 0.7. All experimental and evaluated results are included in Appendix B,and summarized in Table 4.2.Moreover, we consider that scan is added into the circuits. ISCAS'89 SCAN circuits areapplied to a combinational ATPG tool, called "ATALANTA". Because scan test need shift44