Hardware Reference
In-Depth Information
the primary output. However, all these vectors are not equivalent in terms of defect
detection. Several points can be discussed.
First, it should be noted that some vectors have larger ADIs than others. For
instance, the ADI associated to vector #6 is larger than the ADI associated to vector
#7. This means that vector #6 covers a larger range of detectable bridge resistance
value than vector #7, i.e. vector #6 is more efficient than vector #7 in terms of defect
detection domain.
The second point that should be noted is that some vectors have ADIs contained
in the ADI of another vector, whereas others have ADIs that cover different ranges.
For instance, the ADI associated to vector #2 is contained in the ADI associated
to vector #6, whereas the ADIs associated to vector #2 and #7 are fully disjoint.
Consequently regarding defect detection, it is completely useless to use both vectors
#2 and #6 while the use of both vectors #2 and #7 permits to cover a larger range
of detectable bridge resistance value. In other words, using several vectors may
permit to enlarge the defect detection domain but these vector have to be adequately
selected.
Finally, the last point that should be highlighted in the example of Table
2.4
is
that it exists a domain for the bridge resistance value that is not covered by any
vector: [R
4
C
;
1
]. Obviously, such a domain must not be considered from the point
of view of the optimization process.
All these points can be generalized and formalized by introducing the concepts
of '
Global-ADI
'and'
Covered-ADI
'.
Definition 2.1.
Given a circuit under test and the list of Analogue Detectability
Intervals ADI
V
associated to each possible input vector V for a considered defect,
the Global Analogue Detectability Interval G-ADI is given by the union of all ADIs:
G
ADI
D
[
ADI
V
The Global ADI represents the complete domain of the unpredictable parameter
for which the defect can be detected considering the given test technique. On the
example, the G-ADI represents the complete domain of the bridge resistance that
can be detected by the input vectors using the static voltage test technique. This
Global ADI is equal to G-ADI
D
Œ0; R
4
C
]. If the bridge resistance of the defect
falls into the G-ADI, then it exists at least one input vector able to detect the
defect.
In opposition, if the bridge resistance of the defect falls out of the G-ADI, there
is no input vector able to detect this defect. In that case, the defect can be deemed
as a
redundant defect
for the test technique under consideration. This concept of
redundancy must be carefully considered as it differs from the usual concept of re-
dundancy. The classical concept of a redundant fault refers to a fault that cannot be
excited and/or propagated for a given test technique. In case of a bridging defect,
two situations may arise. The first situation is similar to the classical concept used
for redundant faults: the defect cannot be excited and/or propagated whatever the
input vector, which means that the global-ADI is empty for this particular defect.
