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TMDS181: Compliance Testing, Voff Measurements

Kyle Simons
Prodigy 50 points
Part Number: TMDS181


Hi all.  Curious if anyone has run into this similar issue failing Voff compliance test measurements on the data lines using the TMDS181 with the Keysight DSAV164A.  For other video sources with no TMDS181, this test passes fine with readings ~0mV.  The limit is -10mV <= value <= 10mV.  However, when using the TMDS181 eval board and also on our own design, we are getting readings ~15mV on D0+.  Voff Clock +, Clock -, and D0- pass but ~6-9mV.  I tried power savings mode in I2C mode but that did not seem to have any impact.  Maybe there are other tricks to bring this down closer to 0mV?

  • 0
    TI__Guru**** 180881 points

    Hi,

    Refer to the test procedure, are you powering down TMDS181 and make sure HPD_SNK is driven low?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 50 points

    Thank you David for the quick reply.    We are testing in standby mode.  Appears to be item 9 in your list.  

    We noticed with no source video, we were in the ~200mV range.  Once we removed the EDID board per the manual (FlexEDID board), it brought it down the measurements I previously mentioned.  It makes note if video cannot be disabled, disconnect the FlexEDID board.   We can try powering off, I suspect it passes, but seems we need to pass in standby mode too.

    Edit:  Clarification, when I say no source video, we removed the HDMI cable from the input of the TMDS181 evaluation board.  I do not fully understand why removing the EDID board would bring it down from ~200mV range to ~14mV.

  • 0 in reply to Kyle Simons
    TI__Guru**** 180881 points

    Hi,

    I am sorry for the late reply as I was out of office last week. I tested Voff on the TMDS181EVM and am able to get to get passing result on the CLK and D0 lane. 

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/138/TMDS181_5F00_EVM_5F00_VOFF_5F00_CLK_5F00_D0.mht

    The EVM is set up in the I2C mode with all the registers bit in default state except the SIG_EN bit, which I changed from '0' to '1'. I then remove the HDMI cable from the input side and did the Voff measurement.

    Thanks
    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 50 points

    No worries, appreciate your help!   That information helps.  Let us try a few more things with the TMDS181 eval module.