DS125BR820 Datasheet, PDF (47/62 Pages) Texas Instruments – Low-Power 12.5 Gbps 8-Channel Linear Repeater

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DS125BR820
SNLS491B – JULY 2014 – REVISED FEBRUARY 2015
Typical Applications (continued)
8.2.2.2 Detailed Design Procedure
In front port applications, it is important to ensure that the placement of the DS125BR820 corresponds with the
direction of the data flow, since the device is unidirectional. For egress applications, the DS125BR820 should be
placed close to the connector cage, and for ingress applications, the DS125BR820 should be placed closer to
the switch ASIC. Once the DS125BR820 placement is decided on the signal path, the repeater must be tuned.
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 in order to
meet the link training requirements for 40G-CR4 and eye mask requirements for 40G-SR4/LR4.
An example of a test configuration used to evaluate the DS125BR820 in this application can be seen in
Figure 34. For more information about DS125BR820 front port applications, please refer to application note
SNLA226:
Agilent DCAx
Scope with
86108B PTB
Molex zQSFP+^TM
Host Compliance Board
(HCB)
2x1 Stacked
QSFP+
DS125BR820
QSFP+ Test Board
DS125BR820
Huber+Suhner
2x8 MXP
connector
~1 inch
FR4
~1 inch
FR4
9 inch
cable
FR4 Trace: 5inch to 15inch
9 inch
cable
10G Transmitter Test Board
Huber+Suhner
1x8 MXP
connector
~4 inch
10G
Transmitter
with FIR
Figure 34. 10 GbE Transmitter with DS125BR820 QSFP+ Test Board
8.2.2.3 Application Performance Plots
Time (16.16 ps/DIV)
DS125BR820 Settings: EQA = Level 2, VODA = Level 6
Figure 35. nPPI Eye Mask Performance with 5 Inch 4-Mil
FR4 Input Trace, Test Pattern = PRBS-9, 10.3125 Gbps
Time (16.16 ps/DIV)
DS125BR820 Settings: EQA = Level 2, VODA = Level 6
Figure 36. nPPI Jitter Performance with 5 Inch 4-Mil FR4
Input Trace, Test Pattern = PRBS-9, 10.3125 Gbps
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