Hierarchical physical defect reasoning in digital circuits

We propose a hierarchical physical defect-oriented approach for fault diagnosis in combinational digital circuits. We present the circuit as a network of modules. As modules we consider either library components (e.g. complex gates) of digital circuits or arbitrary subcircuits. The higher level fault diagnosis is carried out in two phases. In the first phase, faulty modules are located by cause–effect analysis using high-level faulty module dictionary. The size of the dictionary depends linearly on the number of modules in the circuit. In the second phase, the set of suspected faulty modules is pruned by reasoning of the defective behaviour. At the lower level, the physical defects are directly located in suspected faulty modules using defect libraries of the modules or by effect–cause reasoning inside the module. The proposed approach to fault diagnosis helps to cope with the growing complexities of digital circuits. The experimental results show high module-level diagnostic resolution of the proposed approach.