Hardware Reference
In-Depth Information
Fig. 6.12
Type-1 and Type-2 NPSF
of fault models are particularly indicated when dealing with high density DRAMs,
due to the reduced memory cell capacitance.
In general two types of neighborhood patterns are considered: Type-1 including
four deleted neighborhood cells, and Type-2 including eight deleted neighborhood
cells (
Suk et al.
1979
)
. The type-2 model is more complex and allows to model
diagonal coupling effects in the memory matrix. Figure
6.12
shows the two types of
neighborhood.
Three types of NPSF have been considered in the literature:
1.
Active NPSF (ANPSF) (
Suk et al.
1980
), also called dynamic NPSF (
Saluja
et al.
1985
) where the base cell changes its value based on a change in the pattern
of the deleted neighborhood. In particular, a cell of the deleted neighborhood has
a transition while the rest of the neighborhood including the base cell has a given
pattern. For example <x
d
1
x
d
2
x
d
3
x
d
4
x
5
;
w
d0
x
1
= x
5
=
>,wherex
i
2 f
0; 1
g
,
denotes a generic FP belonging to the ANPSF FFM.
2.
Passive NPSF (
Suk et al.
1980
): a certain neighborhood pattern prevents the base
cell to change.
3.
Static NPSF (
Saluja et al.
1985
): the base cell is forced into a particular state
when the deleted neighborhood contains a particular pattern. This differs from
the ANPSF as no transition is required to excite the fault.
6.4.6
Multiple Faults
It may happen that the effects of two FFMs link together. If the faults share the
same aggressor cell and/or the same victim cell, the FFMs are said to be
linked
.
As an example let's consider the CF
ds
denoted by the following two FPs:
FP
1
D
<
0
a
0
v
;
w
1
=1
v
=
>,and
FP
2
D
<0
a
1
v
;
w
1
=0
v
=
>.
