TLK10031 Datasheet, PDF (139/146 Pages) Texas Instruments – TLK10031 Single-Channel XAUI/10GBASE-KR Transceiver

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TLK10031
SLLSEL3A – JULY 2015 – REVISED AUGUST 2015
Surface-mount connector pads such as those used with the SFP/SFP+ module connectors are wider and
hence have characteristic impedance that is lower than the regular high-speed PCB traces. If the pads are
more than 2 times wider than the PCB traces, the pads’ impedance needs to be increased to minimize
impedance discontinuities. The easy way of increasing the pads’ impedance is to cut out the reference
plane immediately under those pads as shown in Figure 10-4 so as to have the pads refer to a reference
plane on lower layers while maintaining 100 Ω differential characteristic impedance.
Figure 10-4. Surface-mount Connector Pads
10.1.1.2 AC-coupling
A 0.1-uF series AC-coupling capacitor should be connected to each of the high-speed data path pins
INA[3:0]P/INA[3:0]N, HSRXAP/HSRXAN, OUTA[3:0]P/OUTA[3:0]N, and HSTXAP/HSTXAN. If the
TLK10031 high-speed side data path pins are connected to SFP/SFP+ optical modules with internal AC-
coupling capacitors, then no external capacitors should be used. Adding additional series capacitors may
severely impact the performance.
To avoid impedance discontinuities, it is strongly recommended where possible to make the transmission
line trace width closely match the AC-coupling capacitor pad size. Smaller capacitor packages such as
0201 make it easy to meet that condition.
10.1.2 TLK10031 Clocks: REFCLK, CLKOUT
10.1.2.1 General Information
The TLK10031 device requires a low-jitter reference clock to work. The reference clock can be provided
on the REFCLK0P/N or REFCLK1P/N pins. Both reference clock input pins have internal 100-Ω
differential terminations, so they do not need any external terminations. Both reference clock inputs must
be AC-coupled with preferably 0.1-µF capacitors. The two channels (A and B) can have same or different
reference clocks.
The TLK10031 serial receiver recovers clock and data from the incoming serial data. The recovered byte
clock is made available on the CLKOUTAP/N pins. The CLKOUTAP/N CML output pins must be AC-
coupled with 0.1-µF AC-coupling capacitors.
Copyright © 2015, Texas Instruments Incorporated
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