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TUSB1046-DCI: DisplayPort Signaling Questions

ReedKacz
Intellectual 2701 points
Part Number: TUSB1046-DCI

Hi TI Experts,

My customer is working on a display port layout and has a few questions for the signals:

1. How many mils is acceptable for intra-pair length matching? I have seen 2 to 5 mils in some of our documentation.

2. Can you help guide me on how closely matched inter-pair lengths need to be? Is there a calculator that could be used?

3. Do the signals on the USB-C side of the TUSB1046 need to have the same length matching rules as above for DisplayPort?

4. If one of the ML DisplayPort parts has an intra-pair length difference of 2 mils, then does the output of the TUSB1046 need to maintain length matching so that the sum of betore and after the TUSB1046 does not exceed your answer from question 1 above?

Thanks!

Reed

  • 0
    TI__Guru**** 154671 points

    Reed

    I will use this DisplayPort design guide as a reference for the intra- and inter- pair skew.

    1425.Texas Instruments DisplayPort Design Guide.pdf

    Since the TUSB1046 is a redriver, it does not provide skew compensation at its input. So the total skew should include both the skew at its input and output.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 85 points

    Hi David - 

    Thank you for following up on this!  We were referencing that TI design guide when we first jotted down these questions. I believe the answer your provided answers questions 3 and 4.  The design guide clearly mentions <5mil for intra-pair routing which answers question 1, but we are still a bit confused on question 2.   

    Question 2 - is there a strict inter-pair length matching requirement?   The TI document that is listed provides an inter-pair skew number of 2UI where each UI is 370ps for this type of DisplayPort.  Is there a way to translate this to a trace length number?

    -Shane

  • +1 in reply to electronshepherd
    TI__Guru**** 154671 points

    Shane

    The DisplayPort inter-pair skew requirement follows the data rate. The 370ps assumes the data rate is 2.7G.

    Assuming FR4 board material, you can assume typical FR4 propagation delay is 150ps/in for Microstrip and 180ps/in for Stripline. So with 740ps inter-pair skew, this translates to 5in skew for Microstrip and 4in skew for Stripline. 

    Please note even though the DisplayPort can tolerate a large inter-pair skew, I would still design the board to minimize the skew as much as possible.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 85 points

    Hi David -

    Thank you for clarifying this.   We were trying to match the inter-pair lengths within a couple of mil and were having a very difficult time.  Knowing that we have some headroom on that requirement is very useful.

    Thanks again!
    -Shane