Xilinx Virtex-5 RocketIO GTP User Manual page 234

Chapter 12: 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
even mode impedance (Z
Figure 12-1
A good PCB manufacturer understands controlled impedance and allows fine adjustments
for line widths to produce a Z
parameters necessary for the specific PCB layout. Some parameters can be calculated or
234
) of 60Ω or below is desired.
0E
through Figure 12-4 show example cross sections of differential structures.
w
h
d=2h+t
h
Figure 12-1: Differential Edge-Coupled Centered Stripline
h
orthogonal lines
w
h
d=3h+2t
h
Figure 12-2: Differential Edge-Coupled Offset Stripline
h
t
d=4h+2t
h
Figure 12-3: Centered Broadside-Coupled Stripline
t
w
h
Figure 12-4: Differential Microstrip
of 50Ω. The PCB manufacturer also provides the
0O
www.xilinx.com
of 50Ω. To clarify, with Z
0O
s w
t
UG196_c12_01_051406
s w
t
U G19 6_c 12 _02 _05 14 06
w
2h
t
UG196_c12_03_051406
s w Er = 1
Er
UG196_c12_04_051406
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
R
at 50Ω, an
0O
Er
t
Er
Er