DS125BR820 Datasheet, PDF (42/62 Pages) Texas Instruments – Low-Power 12.5 Gbps 8-Channel Linear Repeater

DS125BR820
SNLS491B – JULY 2014 – REVISED FEBRUARY 2015
Typical Applications (continued)
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Pattern
Generator
V_OD = 1.0 Vp-p,
DE = -6 dB
PRBS15
TL1
Lossy Channel
IN DS125BR820 OUT
TL2
Lossy Channel
Figure 10. Test Setup Connections Diagram
Scope
BW = 60 GHz
8.2.1.1 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.
8.2.1.2 Detailed Design Procedure
The DS125BR820 is designed to be placed at an offset location with respect to 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 11 (for Pin
Mode) and Table 12 (for SMBus Modes) 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.
8.2.1.3 Application Performance Plots
Time (20.83 ps/DIV)
No Repeater Used
TJ (1.0E-12) = 21.6 ps
Figure 11. TL = 5 Inch 5–Mil FR4 Trace,
No Repeater, 8 Gbps
Time (20.83 ps/DIV)
DS125BR820 Settings: EQA = Level 2, VODA = Level 6
TJ (1.0E-12) = 13.6 ps
Figure 12. TL = 5 Inch 5–Mil FR4 Trace,
DS125BR820 CHA_0, 8 Gbps
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