Digital Signal Processing Reference
In-Depth Information
the loss terms, equations (4-65) and (4-66) still apply, but we start from the lossy
coupled line equations [Paul, 1994]:
v
(z)
i
(z)
0
v
(z)
d
dx
0
−
Z
=
(4-85)
−
Y
i
(z)
Z
=
R
+
jω
L
(4-86)
Y
=
G
+
jω
C
(4-87)
In essence, we calculate the eigenvectors
T
v
and
T
i
from the product (
R
+
jω
L
)(
G
+
jω
C
) for the lossy case. Recalling from our example that we calcu-
lated
T
v
and
T
i
from the product
LC
, we realize that it is equivalent to using
(
R
+
jω
L
)(
G
+
jω
C
) with
R
=
G
=
0.
4.5 CROSSTALK MINIMIZATION
Since all of the major components in an interconnect system (i.e., PCB, packages,
connectors) can have enough crosstalk to harm system performance, we present
some crosstalk reduction guidelines in this section. Because it is often not pos-
sible to reduce crosstalk without affecting system cost, we include discussion of
trade-offs along with reduction techniques in Table 4-4. In particular, we note
that in cost-sensitive applications such as desktop personal computers, adding
layers in the printed circuit board represents significant added cost to the system.
Another technique that sometimes finds use is the placement of
guard traces
between signals. These are connected to the ground return layers using plated
via holes in the board. This technique requires careful attention to the design to
provide the desired crosstalk benefit. Inductance of the traces will tend to create
a potential difference at points that are a significant distance from the ground
vias. When this occurs, the guard traces can radiate the coupled energy, thereby
s
w
M1: Signal
h
Dielectric (
e
r
)
M2: Ground
M3: Signal
M4: Signal
M5:
V
CC
M6: Signal
Figure 4-31
PCB layer stackup for Example 4-6.
Search WWH ::
Custom Search