Xilinx Virtex-5 RocketIO GTP User Manual page 240

Chapter 13: Design of Transitions
3D field solver analysis or measurement along with several board iterations to get the
desired performance.
The 2D field solver example shows that close to 50Ω can be achieved if the ground plane
under the pad footprint is cleared out. A 3D field solver is then used to verify this result to
a greater degree of accuracy.
Figure 13-6
Using frequency domain analysis within HFSS, there is a 20 dB (10x) improvement in
return loss using this technique. The approximately -40 dB/decade slope in
shows good fit to the frequency response of a lumped capacitor.
240
- L = 241 nH/m
- C = 89 pF/m
- Zo = 52Ω
Figure 13-5: Transition Optimization
Figure 13-6: Ansoft HFSS Model of Pad Clear-Out
shows the ground plane cleared away exactly as it was for the 2D simulation.
www.xilinx.com
28 Mil Pad
Z
Virtex-5 RocketIO GTP Transceiver User Guide
UG196_c13_05_051406
Y
X
UG196_c13_06_051406
Figure 13-8
UG196 (v1.3) May 25, 2007
R