Virtex-5 RocketIO GTP Transceiver User Guide
243
UG196 (v1.3) May 25, 2007
Differential Vias
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.
shows a Ground-Signal-Signal-Ground (GSSG) type differential via. Ground
vias are connected to each ground plane in the stackup, while signal layers only contain
pads for the entry and exit layers.
Figure 13-11:
840 fF Excess Capacitance with Ground Plane Intact
Figure 13-12:
57 fF Excess Capacitance with Ground Plane Intact
550
500
450
400
350
300
0.55
0.60
0.65
0.70
0.80
0.90
0.95
1.00
0.85
0.75
Time, ns
m1
VtdrPlaneNotCleared, mV
VtdrPlaneCleared, mV
UG196_c13_11_051406
m2
550
500
450
400
350
300
0.55
0.60
0.65
0.70
0.80
0.90
0.95
1.00
0.85
0.75
Time, ns
m1
VtdrPlaneNotCleared, mV
VtdrPlaneCleared, mV
UG196_c13_12_051406
m2