Detectability of structural defects using octree encoding

Testing of analogue and M-S circuits using octree encoding in alternate measurements space has been shown effective to detect parametric failures. In this paper, the analysis of the viability to use octree encoding to detect catastrophic faults has been explored. In addition to the classical short and open defects, the class of controlling open faults causing unpredictable behaviour have been considered. In this category, fall some opens causing floating gate defects where the high impedance node gets a voltage imposed by the capacitive coupling of surrounding lines and possible leakage currents to the floating node. The method has been applied to a Biquad filter where a wide class of catastrophic defects (shorts, path opens and floating opens) have been injected. Parametric and catastrophic failures were detected using the same alternate test procedure achieving significant savings in test application time. The results show that with a simple octree based on two indirect measures detectability was guaranteed forall shorts, and path opens. A significant number of floating gate opens is also detectable. The floating gate defects escaping assured detection would be those in which the floating gate during test excitation produces voltages at the open gate(s) similar to the voltage of the non-defective circuit.