DS125BR800 Datasheet, PDF (44/59 Pages) Texas Instruments – Low-Power 12.5-Gbps 8-Channel Repeater With Input Equalization and Output De-Emphasis

DS125BR800
SNLS426E – AUGUST 2012 – REVISED JANUARY 2015
9 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The DS125BR800 is a high performance circuit capable of delivering excellent performance. Careful attention
must be paid to the details associated with high-speed design as well as providing a clean power supply. Refer
to Layout Guidelines and the LVDS Owner's Manual, SNLA187, for more detailed information on high speed
design tips to address signal integrity design issues.
9.2 Typical Application
System Board
Root Complex
8
TX
Connector
8
RX
DS125BR800
8
RX
DS125BR800
Connector
8
TX
BoTarardce
ASIC
or
PCIe EP
Figure 9. Typical Application
9.2.1 Design Requirements
As with any high speed design, there are many factors which influence the overall performance. Below are a list
of critical areas for consideration and study during design.
• Use 100 Ω impedance traces. Generally these are very loosely coupled to ease routing length differences.
• Place AC-coupling capacitors near to the receiver end of each channel segment to minimize reflections.
• The maximum body size for AC-coupling capacitors is 0402.
• Back-drill connector vias and signal vias to minimize stub length.
• Use Reference plane vias to ensure a low inductance path for the return current.
9.2.2 Detailed Design Procedure
The DS125BR800 is designed to be placed at a location where the input CTLE can help to compensate for a
portion of the overall channel attenuation. In order to optimize performance, the repeater requires tuning to
extend the reach of the cable or trace length while also recovering a solid eye opening. To tune the repeater, the
settings mentioned in Table 2 and Table 3 (for Pin Mode) are recommended as a default starting point for most
applications. Once these settings are configured, additional tuning of the EQ and, to a lesser extent, VOD may
be required to optimize the repeater performance for each specific application environment. Examples of the
repeater performance as a generic high speed datapath repeater are illustrated in the performance curves in the
next section.
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