Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 241
UG196 (v1.3) May 25, 2007
SMT Pads
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 Figure 13-9 and Figure 13-10, the red curve with the large capacitive dip corresponds to
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 Equation 13-1 and Equation 13-2.
Figure 13-7: Return Loss Comparison Between 0402 Pad Structures
Figure 13-8: Return Loss Comparison Between 0402 Pad Structures on Log
(Frequency) Scale
0
-20
-40
-60
024 6
Frequency, GHz
8
Cleared Planes
Uncleared Planes
10
dB(S(3,3)) dB(S(1,1))
UG196_c13_07_051406
0
-20
-40
-60
1E8 1E9
Frequency, Hz
+40dB/Decade RL Slope Shows a
Good Fit to Lumped Capacitance
1E10
dB(S(3,3)) dB(S(1,1))
UG196_c13_08_051406

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English