LS1043A, XFI, AC coupling Capacitance query

[logeshs]

Hi,

In our System, we are connecting LS1043A with another LS1043A in other board via backplane using XFI/SGMII (2.5G) interface. SGMII(2.5G) has the AC coupling Capacitance range, but for XFI we dont get that AC coupling capacitance range.

Also in SGMII (2.5G) AC coupling caps are recommended near transmitting end, for XFI shall we use the same caps (that is near the transmitting end)? Please suggest.

Thanks

[r8070z]

Have a great day,

XFI as SGMII also assumes AC caps. The hi-speed  channel characteristics is board and layout dependent. It is impossible quantify the actual channel loss introduced during board design, layout and fabrication of all end product systems. Designers should always perform board level simulation and also use other appropriate tool (for example, NXP’s SerDes Validation Tool). You can find more details about XFI design in white paper "Considerations for High Speed PCB Track Design in 10Gb/s Serial Data Transmission"

https://www.smtnet.com/library/files/upload/Considerations-for-High-Speed-PCB-Track-Design.pdf

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[logeshs]

Hi,

Thanks for your reply.

1. We are connecting two LS1043A using XFI via backplane connector(without XFP) as shown in the below image. Kindly let me know what should be the maximum trace length that XFI can be routed (i.e., end to end, transmitting LS1043A to Receiving LS1043A)? The document which is shared explained along with XFP module, In our case we are not using XFP module and we are connecting directly using XFI interface.

2. Please find the attached image below for our block diagram of XFI implementation. Please reply to the query mention in the image. Is AC capacitors must?

Thanks.

[r8070z]

The LS1043A XFI is interface to an XFP module that can be plugged into a system with an XFP connector. I did not see any NXP document or reference design where XFI is used as a backplane interface. The XFP connector and the potential long PCB trace will degrade the 10-Gb/s electrical signal. As I can see in such applications, the distance between the chip and the XFP module can be up to 10 inches.  You will get 2 connectors so I think 10 inch is valuable estimation. Without capacitors you have to check carefully for the LS1043A serdes DC specifications (maximal input/output DC current and so on). I do not see that in the data sheet, so I prefer using  capacitor (same as in XFP module) but on the transmit sides.

[logeshs]

Hi,

Thanks for your reply.

In our system we are using two identical main boards (each mounted with LS1043A processor) connected via backplane. One board will be Active and other is used for redundant purpose. The communication between two main boards is performed using LS1043A XFI interface connected directly by running XFI in backplane (without XFP module) . As per current placement scenario in our board the maximum trace length of XFI is around 16 inch (i.e., end to end, from transmitting LS1043A to receiving LS1043A). But from LS1043 datasheet we understand that the allowable link budget is ~ 10dB. Kindly please provide the link budget using XFI alone which runs through backplane (without considering XFP module, and we are using ExaMax High speed backplane connector in our implementation). 

So We would also look to remove AC coupling capacitance to increase the link budget.

1. Could you please confirm do we need the AC coupling capacitance between two LS1043A.

2. I also request you to confirm what should be the maximum length that XFI can be routed as per our implementation?

3. Is there any SW setting to increase the link budget (any appnote, guidelines)

We would like to get expert advice on this.

Thanks

[r8070z]

I suggest you get IEEE 802.3ap-2007 documentation. They claim in the manual that LS1043A supports it. It specifies 10GBASE-KR features related to the backplane Ethernet. Due to that the length can be up to 1 m (~39 inches) including 2 connectors.

[logeshs]

As We are connecting LS1043A against another LS1043A, I believe AC coupling cap are not required. Suppose We are connected Two LS1043A via XFI interface, is AC caps must between them?

Also suggest me the maximum length the XFI interface lines can be routed?