Xilinx Virtex-4 RocketIO User Manual page 260

Chapter 12: Guidelines and Examples
Table 12-1: Model-Derived Loss for Differential Vias of Various Dimensions (Continued)
Board Stub Via
Thickness Length Diameter
(mils) (mils) (mils)
16
0
12
16
125 28
12
16
95
12
10
0
8
10
50 11
8
10
39
8
To understand how to use
Example 1:
For a targeted BER at a data rate of 4.25 Gb/s, assume that an IL of less than 10 dB is
required. The channel is from a motherboard to a daughter card using a very clean
mezzanine connector with no appreciable loss. Assume a 100 mil thick motherboard and a
50 mil thick daughtercard with 0.4 dB/inch at 2.125 Ghz and 12-inch maximum routes for
4.8 dB of channel loss. Using the 125 mil long vias from the table, if no or short stubs are
allowed, then a 16 mil diameter/35 mil pitch via has –0.164 IL @ 2 GHz. Therefore, the via
pitch can simply be increased to 40 mils, and/or a 12 mil diameter via can be used to keep
the via IL below –0.1 dB. A –0.1 dB IL is presumed to be an acceptably low-loss for a
transition so as to have no noticeable effect on overall channel performance.
Example 2:
This example assumes a 6 Gb/s application and the choice of using either an expensive
connector with a 200 fF launch or a less expensive connector with a 400 fF launch. A board
260
Via Excess
RL @1GHz
Pitch Capac.
(dB)
(mils) (fF)
35 494 -22.2
50 33 -45.6
35 208 -29.7
50 163 -31.8
35 614 -20.3
50 177 -31.1
35 334 -25.6
50 12 -54.5
35 868 -17.3
50 392 -24.2
35 548 -21.3
50 265 -27.6
25 250 -28.1
35 67 -39.6
25 183 -30.8
35 22 -49.1
25 326 -25.8
35 131 -33.7
25 253 -28.0
35 67 -39.6
25 379 -24.5
35 201 -30.0
25 319 -26.0
35 158 -32.1
Table 12-1, three examples are given below:
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IL @1GHz IL @2GHz IL @3GHz
(dB) (dB) (dB)
-0.026 -0.105 -0.242
0.000 0.000 -0.001
-0.005 -0.019 -0.042
-0.003 -0.011 -0.026
-0.041 -0.164 -0.381
-0.003 -0.013 -0.030
-0.012 -0.048 -0.109
0.000 0.000 0.000
-0.082 -0.335 -0.796
-0.017 -0.066 -0.151
-0.032 -0.130 -0.300
-0.008 -0.030 -0.068
-0.007 -0.027 -0.061
0.000 -0.002 -0.004
-0.004 -0.014 -0.033
0.000 0.000 0.000
-0.011 -0.046 -0.104
-0.002 -0.007 -0.017
-0.007 -0.027 -0.062
0.000 -0.002 -0.004
-0.015 -0.062 -0.141
-0.004 -0.017 -0.039
-0.011 -0.044 -0.099
-0.003 -0.011 -0.024
Virtex-4 RocketIO MGT User Guide
UG076 (v4.1) November 2, 2008
R
IL @4GHz IL @5GHz
(dB) (dB)
-0.436 -0.709
-0.002 -0.003
-0.074 -0.118
-0.046 -0.072
-0.695 -1.154
-0.054 -0.085
-0.194 -0.310
0.000 0.000
-1.519 -2.721
-0.270 -0.434
-0.543 -0.890
-0.121 -0.193
-0.108 -0.172
-0.008 -0.012
-0.058 -0.091
-0.001 -0.001
-0.185 -0.295
-0.029 -0.047
-0.110 -0.176
-0.008 -0.012
-0.251 -0.403
-0.069 -0.110
-0.176 -0.282
-0.043 -0.067