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TMDS361B - Clock detect feature and compliance testing

Kawai
Guru 19785 points
Other Parts Discussed in Thread: TMDS361B

Hi Team,

I had posted the following topic in the past, however, could you please let me ask you again about the clock detection function and  HDMI compliance testing ?

TMDS361B - HDMI Compliance Testing
http://e2e.ti.com/support/interface/digital_interface/f/130/t/300191.aspx

[Question1]
I believe that the reason why TMDS361B cannot pass HDMI compliance test by clock detect feature ENABLED is because there is no 50ohm pull-up to VCC when there is NO input clock. The device would not be able to satisfy the requirement of TMDS termination voltage; TMDS pin voltage = AVCC+/-10mV.

First of all, is my recognition correct ?

[Question2]
If my recognition of Question1 is correct, I thought that by adding 1kohm resistors to each TMDS+/- would pull-up each TMDS pin voltage to VCC. Do you think the following schematic would be able to pass the HDMI compliance test  enabling clock detect feature ?
Can you recommend these pull up resistors ?

I am grateful for your help.

Best Regards,
Kawai

  • 0
    TI__Guru* 76130 points

    Hello Kawai,

    First of all, your assumptions seems to indicate the the device has some kind of problems passing compliance test, the TMDS361B has no issues passing the "tmds voltage termination" compliance test when you apply a valid clock input or when you disable the clock detect feature.

    That being said, your assumption 1 is correct.

    For your question 2: the termination required is 50ohm on each TMDS line.

    Regards.

  • 0 in reply to Elias Villegas M.
    Guru 19785 points

    Hi Elias-san,

    Thanks for your comment.

    >For your question 2: the termination required is 50ohm on each TMDS line.

    Could you please tell me specifically ? I am not much familiar to the requirements of the compliance test.
    Does the TMDS input must be always terminated to VCC with 50ohm ?

    Japanese customers conducts the compliance test  with the actual condition of the system usage, i.e. if the system is used with clock detect feature enabled, compliance test must be done with the clock detect feature enabled,  likewise, if the feature is disabled in their system, the test should be done with the feature disabled.

    I understand there is description about the clock detection in the datasheet that you must disable this feature to pass the compliance test. Customer developed the system with the feature disabled (to pass compliance test), however, they had a noise issue using the feature disabled.

    The HDMI Receiver detected clock signal even they did not apply any signal to the input. They see noise on the output which is leading to false detection.

    We are looking for a solution which could pass the compliance test and clear the noise issue.

    Thanks and Best Regards,
    Kawai