Xilinx Virtex-5 RocketIO GTP User Manual page 241

R
Next, using simulated measurements on the same transition modeled in HFSS, the time-
domain performance of this transition can be measured by doing a TDR on the
S-parameter results from the earlier frequency domain analysis.
In
the SMT pad without the ground plane cleared from underneath. The blue curve shows
that clearing out the ground plane removes much of the excess capacitance. This
improvement can be quantified using
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
0
Uncleared Planes
-20
-40
-60
0
Figure 13-7: Return Loss Comparison Between 0402 Pad Structures
0
-20
-40
-60
1E8
Figure 13-8: Return Loss Comparison Between 0402 Pad Structures on Log
Figure 13-9 and Figure 13-10, the red curve with the large capacitive dip corresponds to
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2 4
Frequency, GHz
+40dB/Decade RL Slope Shows a
Good Fit to Lumped Capacitance
1E9
Frequency, Hz
(Frequency) Scale
Equation 13-1 and
SMT Pads
Cleared Planes
6 8
UG196_c13_07_051406
1E10
UG196_c13_08_051406
Equation 13-2.
10
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