ADLINK aTCA-N700 - Manual (Page 31)

aTCA-RN720 User's Guide
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6 Data Path: Ports and Retimers
6.1 Overview
The retimers used on the board are essential to improve the 10Gbps SFI signal quality. According
to SFF 8431 specification, the SFI signal may not reach from a front blade to an RTM SFP+ port
or vice versa, at viable quality after traversing a Zone 3 connector and several vias on the lossy
PCB. The retimer along with equalization features compensates such losses and reflections. The
retimer used on the board is quad retimerGN2405A from Gennum. Shown in Figure 6-1are the
six retimers and the QSFP/SFP+ ports which are connected to the corresponding switch ports on
the front blade via the Zone 3 connector(s). A single GN2405A covers dual SFI+ RX/TX paths in
an asymmetric way. It is asymmetric in a sense that the path characteristic from the front blade
(via Zone 3 connector) to the retimer input and the one from the QSFP/SFP+ RX to the retimer
input are significantly different. So each one of the path should be configured differently, meaning
different adjustment may be applied for the different path characteristics for all the devices.
Figure 6-1 QSFP/SFP+ and Data Path