This paper introduces a hierarchical-fault-diagnosis algorithm as an aid to
testing analog and mixed signal circuits. The diagnosis approach is based
on that introduced by Wey and others and makes use of the self-test algorit
h, and the component-connection model. The main extension to these techniqu
es is the use of a hierarchical approach whereby blocks of circuitry are gr
ouped together leading to a reduction in matrix size, so making even large
scale circuits diagnosable. Other improvements from this approach include a
novel test-point selection procedure and the fact that hard faults can als
o be diagnosed, provided they lie completely within a hierarchical block.
The overall algorithm is described and the results from example circuits sh
ow good functionality of the diagnosis algorithm. Fault masking and sensiti
vity to the simulation/measurement resolution of test point values are exam
ined and are highlighted as future activities to further improve the approa
ch.