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R
Differential Vias
The most common transition is the differential via where the signal pair must transition
from an upper stripline layer or top microstrip to a lower stripline layer or bottom
microstrip.
Figure 13-13
vias are connected to each ground plane in the stackup, while signal layers only contain
pads for the entry and exit layers.
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
550
500
450
400
350
300
0.55
0.60
0.65
Figure 13-11: 840 fF Excess Capacitance with Ground Plane Intact
550
500
450
400
350
300
0.55
0.60
0.65
Figure 13-12: 57 fF Excess Capacitance with Ground Plane Intact
shows a Ground-Signal-Signal-Ground (GSSG) type differential via. Ground
www.xilinx.com
m1
0.70
0.75
0.80
0.85
Time, ns
m1
m2
0.70
0.75
0.80
0.85
Time, ns
Differential Vias
m2
0.90
0.95
1.00
UG196_c13_11_051406
0.90
0.95
1.00
UG196_c13_12_051406
243
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