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DS90UB926Q-Q1: 925EVM with 926EVM eye pattern question

AJ Cheng
Genius 3615 points
Part Number: DS90UB926Q-Q1

Hello Sir

I used the 925EVM with the 926EVM pclk 85M to measure the TP2 and TP3 (CMLOUT) signals.

The signals obtained did not meet the datasheet specifications. Is there any thing that we ignored? Thanks for kindly help~

TP2

TP3

  • 0
    TI__Genius 12866 points
    Could you tell us a little more information on your setup?
    When you measuring at TP2, did you remove the deserializer?
    Are you using STP cable or coax?
  • 0 in reply to Charley Cai
    TI__Guru** 103215 points
    AJ,

    Any more feedback on this issue? Otherwise we could like to close the thread if the issue got resolved

    Best Regards,
    Casey
  • 0 in reply to Charley Cai
    Genius 3615 points

    Dear Charley and Casey.

    We used the 925EVM with the 926EVM to test performance and using the coax cable.

    Test the eye diagram on the CMLOUT pin of the UB926. The result of using a long cable and a short cable is the same for a coax cable.

    The 60MHz PCLK is Pass. But the 78MHz is Fail. Please refer to the eye diagram below. Is there any way to solve it?

    In addition, we use adaptive EQ better than manual adjustment of EQ. Thanks for kindly.

    60MHz eye diagram is pass

    78MHz eye diagram is Fail

    PCLK Waveform

    2: 925 PCLK

    3: 926 PCLK

    4: 926 R0(data)

     PCLK = 60Mhz

     PCLK = 78Mhz

  • 0 in reply to AJ Cheng
    TI__Guru** 103215 points

    Hello AJ, 

    First of all, 926 does not support coax configuration, only STP. Second, the signals measured appear to have significant common mode conversion which is indicative of skew between the P/N signals in the high speed length. That tells me there is something wrong with the interconnect. Also, not exactly sure how you are testing coax configuration with 926 since the EVM does not have a coax connector?

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    Genius 3615 points

    Dear Casey.

    Good day.

    Please refer to the following test environment. In the case of 78MHz, the eye diagram Fail. But the output image is OK.

    Please let us know where the problem is. Thank for kindly help~

  • 0 in reply to AJ Cheng
    TI__Guru** 103215 points
    I suspect the issue with the high speed probe you are using although it is hard to see in the picture how it is connected. Are you using some sort of breakout connector to attach it to the CMLOUT SMA connectors? What is the breakout device? Is it possible that it is introducing skew between the P/N of the probe? Because the scope waveform clearly shows the signs of common mode conversion but I don't see an issue in the connection between the two FPD EVMs

    Best Regards,
    Casey