Appendix E: Serial Backplane System Design; Transmission Lines; Connector To Pcb Launch - Xilinx RocketIO X User Manual

R
Serial Backplane System Design
Additional PCB design guidelines are required to meet the demands of the RocketIO X
transceiver for operation above 3.125 Gb/s. Backplane system design guidelines can be
divided into three separate components. One component is directed toward the launch
from the package onto the line card or switch card PCB. A second component is focused on
the launch from the backplane connector onto either the line card or the backplane. A third
component covers the transmission lines that link the backplane connectors to each other
as well as the RocketIO X transceiver package.

Transmission Lines

The line card or switch card can be designed using microstrip or stripline technology.
When using microstrip lines, care must be taken to assure that a clean path exists from the
package to the backplane connector. Microstrip lines are ideal from the standpoint that
they eliminate the need for a via to internal signal layers. Unfortunately, microstrip lines
are not normally conducive to the design of high-density backplane systems.
Careful consideration should be given to the size of transmission line structures. Both the
line card and the backplane should avoid the use of minimal width transmission lines.
Note:
dielectric losses.

Connector to PCB Launch

Care must be taken in choosing the appropriate connector solution for the given data rate
of operation. Traditional connector technology relies on the use of large plated through
hole (PTH) vias to provide a robust mechanical mating interface between the backplane
and line card. High-density backplane applications require the use of multiple signal
routing layers, resulting in via stubs of varying depths. Optimizing via effects is therefore
the key to maximizing overall backplane transmission distance.
RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004
A transmission line width of no less than 8 mil is recommended to minimize skin effect and
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Appendix E
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