Models for Bridging Defects Test and Diagnosis - Models in Hardware Testing - page 45

I 2 = 0

I 1 = 0

Gate c

Vn 1

n 3 = effect

Gate a Vth c

1

Gate e
O = effect

Rsh

0

Gate d

I 3 = 1

Gate b

Vth d

n 2

1

n 4

I 4 = 0

Vn 1

5 5

#2

Vth c

#6

0 0

R 1 C R 2 C

Rsh

Fig. 2.11 Different excitations ( Renovell et al. 1999 )

determined by the input vector. As an example, the vector #2 in Fig. 2.9 propagates
the effect through gate 'c' (with I 3 I 4 D l0), while the vector #3 in Fig. 2.12 prop-
agates the effect through both gates 'c' and 'd' (with I 3 I 4 D 11). Different logic
gates have different logic thresholds. The value of the critical resistance is therefore
different through gate 'c' and through gate 'd'.
A very important point for propagation concerns the re-convergence of effects.
Considering vector #2, the effect of the defect is propagated through a single gate
(gate 'c') implying no re-convergence: the ADI is equal to [0; R C ]. Considering now
vector #3 in Fig. 2.12 , the effect of the defect is propagated through two different
gates (gates 'c' and 'd'). The two effects re-converge on gate 'e'. According to the
unpredictable resistance value, a defect-free or a defective effect may be propagated,
as illustrated in Fig. 2.13 :
Between0andR 1 C , the two defective effects cancel each other producing a
defect-free value on the primary output.
Between R 1 C and R 3 C , a defective and defect-free effects re-converge producing
a defective value on the primary output.
Between R 3 C and infinity, the two defect-free effects obviously produce a defect-
free effect on the primary output.
The Analogue Detectability Interval corresponding to vector #3 is consequently
equal to [R 1 C ,R 3 C ]. This small example illustrates that the propagation of the ef-
fect has to be taken into account when defining the ADI.