Figure 10-1: Differential Edge-Coupled Centered Stripline - Xilinx Virtex-4 RocketIO User Manual

Chapter 10: PCB Materials and Traces
The same W/S ratio also must be less than 0.8, otherwise strong coupling between the
traces requires narrower, lossier traces for a Z
used, coupling can be kept at moderate levels by designing for a Z
the even-mode impedance (Z
Figure 10-1
Obtain dielectric material properties from the PCB manufacturer. Then, using either an
equation or simulation tool (preferred), compute the line widths required for the
242
) less than 60Ω.
0E
through Figure 10-4 show example cross sections of differential structures.
w
h
d=2h+t
h

Figure 10-1: Differential Edge-Coupled Centered Stripline

h
orthogonal lines
w
h
d=3h+2t
h
Figure 10-2: Differential Edge-Coupled Offset Stripline
h
t
d=4h+2t
h
Figure 10-3: Centered Broadside-Coupled Stripline
t
w
h
Figure 10-4: Differential Microstrip
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of 50Ω. If an impedance-checking tool is
0O
0O
s w
t
UG072_c3_23_102805
s w
t
U G07 2_ c3_ 24_ 10 2 8 05
w
2h
t
UG072_c3_25_102005
s w Er = 1
Er
UG072_c3_26_102005
Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
R
of 50Ω , while keeping
Er
t
Er
Er