Fault diagnosis assistant : Edward T. Purcell. IEEE Circuits Devices Mag., 47 (January 1988)

Abstract

This article describes a first implementation of a knowledge-based system for interactive support of test engineers in gate-level troubleshooting offaulty VLSZ chips, by offering advice on the next-best internal probe point for an electron-beam test probe system. The current OPS83 production system implementation of the fault diagnosis assistant (FDA) recommends an efficient sequence of probes at internal nodes that progressively localizes and identifies single stuck-at faults in combinational logic or combinational partitions within setlscan logic. Unlike the system-specific approaches implemented by most fault diagnosis expert systems, FDA implements the strategically correct (but more challenging) first-principles approach to fault diagnosis. This model-based diagnostic methodology is based primarily on using model knowledge of the system's structure (connectivity file) and function (normal, design-prescribed behavior) of the system's primitive components. The model-based approach has the potential to offer excellent fault coverage for large classes of custom design systems, although it can be difficult to implement because of the need to reason with accurate fault-free system simulation data. The prototype version of FDA has been exercised over several simulated examples of single stuck-at faults in simple test combinational circuits. This initial diagnostic capability is the foundation for future versions of FDA whose objectives will include coverage of multiple, nonclassical faults in sequential VLSI circuits.