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TMDS181: How to leverage EQ and de/pre-emphasis to enhance signal integrity?

Gabriel Xu
Intellectual 2145 points
Part Number: TMDS181

Hi teams

An application issue has been reported from my customer and I need your help to figure it out what I should do next.

Customer is used TMDS181 in TV side as a source device for HDMI2.0 out. But the eye diagram is not good enough to past the standard so far.

Inside the TV the cable(trace) length between the signal source and TMDS181 is about 180mm. The distant between TMDS181 and connector is about 75mm.

The first diagram I showed below is capture in TV connector without output cable.

The second diagram is the output signal after 3m cable.

Below is my question:

If we found the signal is bad in output, what the major procedure to debug the signal integrity issue?

Do we have any guideline about how to configure the EQ and emphasis parameter?

  • 0
    TI__Guru**** 177301 points
    Gabriel

    Do you have the full test report?

    Is the first eye diagram the output of TMDS181 and second eye diagram the output of TMDS181+3m cable?

    Would you please send me the schematic and layout of their design?

    Thanks
    David
  • 0 in reply to David (ASIC) Liu
    TI__Intellectual 2145 points

    Hi David

    Yes you are right.

    The first diagram is output side signal without cable and another one is with 3M signal.

    Below is few PCB layout snapshot from customer.

    Customer also said that they have try different EQ parameter and the eye diagram didn't change.

    Several questions:

    1. After we modified EQ parameter are we need to write 1 to 0xAh[2]APPLY_RXTX_CHANGES to make this configuration apply?
    2. Should we enable or disable DIS_HDMI2_SWG function in such situation? (We are using HDMI2.0 out)
    3. Should we enhance the output data swing or decrease it? It determine by what?

  • 0 in reply to Gabriel Xu
    TI__Guru**** 177301 points

    Gabriel

    It looks like the eye mask they are using is the eye mask at TP2_EQ as defined by the HDMI spec.

    For TP2_EQ, the worst cable and equalizer has already been added to the output of TMDS181, so I don't know why they would add a 3m cable in addition to the worst cable emulator and expect the eye to pass.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    TI__Guru**** 177301 points

    Gabriel

    Please have the customer refer to the HDMI CTS spec for the HDMI electrical compliance test setup and requirement.

    For VSWING, please adjust VSADJ external resistor first as this will change both the clock and data swing. You can then write to 0x0Ch register to change data and clock separately.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    TI__Intellectual 2145 points

    HI David

    The issue seems to lead by the customer un-proper measure method.

    It has been fixed now.

    Thanks.