Xilinx Virtex-4 RocketIO User Manual

Also see for Virtex-4 RocketIO: Configuration user guide User guide

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Xilinx Virtex-4 RocketIO User Manual Manual pdf 248 page image

248 www.xilinx.com Virtex-4 RocketIO MGT User GuideUG076 (v4.1) November 2, 2008Chapter 11: Design of Transitions RThe 2D field solver example shows that close to 50Ω can be achieved if the ground planeunder the pad footprint is cleared out. A 3D field solver is then used to verify this result toa greater degree of accuracy.Figure 11-6 shows the ground plane cleared away exactly as it was for the 2D simulation.Using frequency domain analysis within HFSS, Figure 11-7 shows a 21 dB (11x)improvement in return loss using this technique. The approximately +20 dB/decade slopein Figure 11-8 shows good fit to the frequency response of a lumped capacitor.Figure 11-6: Ansoft HFSS Model of Capacitor with a Pad Clear-OutFigure 11-7: Return Loss Comparison Between 0402 Pad StructuresUG072_c3_16_030106ZYX0-20-40-600 2 4 6Frequency, GHz8Cleared PlanesUncleared Planes10dB(S(3,3))dB(S(1,1))UG072_c3_17_102805