Fault simulation methods based on efficient reconvergent fan-out stem fault detection

Abstract

A line in a combinational circuit is classified into three types: a primary output, an input of a gate, and a stem. More precisely, a stem is either non-reconvergent fan-out or reconvergent fan-out. We use the fault simulation method based on the topology analysis of a circuit. During the topological fault simulation, a fault at a non-reconvergent fan-out stem is detected by searching the fan-outs of the stem, while the fault at the reconvergent fan-out stem cannot be detected. For the fault detection at the reconvergent fan-out stem, it is necessary to propagate the fault until the detection is determined. It is desirable to reduce the number of gates to be activated in propagating fault for the detection of the reconvergent fan-out stem. In this thesis, we propose two efficient fault detection methods for different circumstances. One is a primary output oriented fault detection method which is useful when test patterns are incrementally given one by one. The other is a fault detection method which is useful when a lot of test patterns are deposited at once. Both of them especially concentrate on the effective fault detection of the reconvergent fan-out stem to reduce the number of gates to be activated. Faults are detected in sequence from the primary outputs to the primary inputs. In the first method, the fault detection is traced with respect to each primary output with a single test pattern. This method is called primary output oriented fault detection, which is the firstly proposed parallel scheme for the fault simulation. The fault detection with respect to each primary output is performed in parellel. The event driven tracing is used during the fault propagation. The fault at a reconvergent fan-out stem can be detected without propagating the fault through all the propagation region, because the fault detection is determined independently with respect to each primary output. The region where the fault should be propagated is dynamically changed during t...