Hardware Reference
In-Depth Information
For a SLAT test pattern t , the evidence will provide maximum
t
and
t
D
t
D
0 as this fault explains all the errors and there is no single stuck-at fault with
a higher number of predictions.
The evidence of a fault f and a test set T is
e.f; T /
D
.
T
;
T
;
T
/; with
T
D
X
t 2T
t
;
D
X
t 2T
T
t
; and
D
X
t 2T
T
t
Again, if the real culprit is indeed the stuck-at fault f ,weget
T
D
T
D
0 and
T
will be maximum.
While processing pattern after pattern, t
1
;:::;t
i
, the knowledge base is con-
structed by the evidences e.f; T
i
/; T
i
Df
t
1
;:::;t
i
g
for all the stuck-at faults f .
If a fault is not observable under a certain pattern, no value change takes place and
this fault is not considered within this iteration. If the DUD gives the correct output
under a pattern t , only
T
is increased for faults which are observable under this pat-
tern and hence lead to a misprediction. In this way, candidates can be excluded using
passing patterns, too. The maximum achievable diagnostic resolution is bounded by
the size of the equivalence classes of the faults in the knowledge base.
If the fault in the DUD is not always active due to nondeterministic behav-
ior or some unknown activation mechanism, the measure still provides consistent
evidences.
For instance, let f
0
be a slow to rise transition fault. For some patterns t ,
fault f
0
will appear as a stuck-at 0 fault, for others it is not observable. In this
case, e.f; t/
D
.
t
;
t
;
t
/ provides
t
Q
t
for all the other evidences
e. f;t/
D
.
Q
t
;
Q
t
;
Q
t
/. As a consequence, we have
T
Q
T
for all evidences
e. f;T/and the evidence e.f; T / still contributes information for locating the fault.
However, the value
T
will not be zero anymore and can be used for ranking fault
candidates.
Now we define
t
D
min
f
t
;
t
g
and
T
D
t 2T
t
.
Under the single fault assumption, let f be a stuck-at fault which models at least
a part of the DUD behavior for some patterns under some conditions. If the condi-
tions are satisfied for a pattern t
2
T , the set of failing outputs of
FM(f)
corresponds
to the fails of the DUD and there is no misprediction (
t
D
0/.Otherwise,the
failing outputs of
FM(f)
and DUD are disjoint (
t
D
0/. Hence, all
t
and also
corresponding conditional stuck-at is not a single fault candidate. When assuming
multiple faults, we observe that mutual fault masking is rather rare, and ranking the
stuck-at fault according to the size of
T
provides a good heuristic.
