Using Boolean Tests to Improve Detection of Transistor Stuck-Open Faults in CMOS Digital Logic Circuits

Currently transistor stuck-open (TSOP) faults in CMOS digital logic circuits are detected by two pattern tests consisting of an initialization pattern to set the output of a faulty gate followed by a pattern that detects a stuck-at fault. Some TSOP faults may not be detected by such two-pattern tests. One reason for this is that appropriate initialization patterns cannot be obtained using Boolean (steady state) analysis of the circuit. For some of these faults, required initialization may be possible using hazards (glitches) [10][13]. However, insuring that a test using hazard-based initialization actually detects the target fault requires accurate transient analysis of the circuit under test such as by SPICE. In this work we propose methods to augment test generation procedures to detect TSOP faults using traditional steady state Boolean analysis (called Boolean tests in this work). We also investigate the cause for the non-existence of test patterns for the faults not detected in benchmark circuits. In many such cases we found that the non-existence of test patterns is due to redundant gates that can be replaced by a constant 1 or 0. We present results on larger ISCAS-89 benchmark circuits to illustrate the effectiveness of the proposed methods to generate tests to detect TSOP faults and the results of analysis for the non-existence of tests for the remaining faults undetected by Boolean tests.