Xilinx Virtex-5 RocketIO GTP

242 www.xilinx.com Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
Chapter 13: Design of Transitions
R
As shown from Figure 13-11 and Figure 13-12, clearing the ground plane under SMT pads
yields a significant improvement in the performance of an SMT pad transition. Excess
capacitance is reduced by 15x and return loss is improved by 20 dB.
Figure 13-9: TDR Results Comparing 0402 Pad Structures
Figure 13-10: TDR Results Comparing 0402 Pad Structures
0
100
200
300
400
500
600
0.0 0.5 1.0 1.5
Time, ns
2.0 2.5 3.0
VtdrPlaneCleared, mV
VtdrPlaneNotCleared, mV
UG196_c13_08_051406
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.000.55 1.05
350
400
450
500
300
550
Time, ns
VtdrPlaneNotCleared, mV
VtdrPlaneCleared, mV
UG196_c13_10_051406