Automatic dependency model generation using SPICE event driven simulation

Intelligent Automation, Incorporated, (IAI) with the U.S. Army Communications and Electronics Command, is developing a system called MIDIS (Microelectronic Display). MIDIS is comprised of two tools: one for designing built-in testing and diagnosis of printed circuit boards and one for automatically generating dependency models and performing testability and diagnosability analysis. This paper focuses on our method of generating dependency models using a SPICE simulator. We use two separate modules to perform this function. The first module is based on fault propagation analysis using an event-driven simulator. Each component in the SPICE netlist is replaced with a fault propagation model, which models both the component´s fault propagation properties and its failure modes. In turn, every component enters faults into the simulation and we record how the failure modes of all components propagate to each test point. The totality of these runs yields a dependency model for the system. The event-driven simulation is fast but gives only an approximate view of the true system dependencies. Once the analysis yields good results, we turn to the second module. Here, a full analog SPICE simulation is run for every failure of each component. The readings at each test point are compared to the nominal (no-fault) readings to determine whether a fault is detectable. This process is repeated for the individual failure modes of all components, yielding the full dependency model. Unfortunately, for complex circuits this can be very slow. Our two-tier structure greatly reduces the number of times the full SPICE analysis is required