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DS90UB954-Q1: FPDlink III - How to measure the eye diagram of the Backchannel

Vicent Climent14
Intellectual 360 points
Part Number: DS90UB954-Q1

Dear Ti Members,

In order to do some validation of our design, we are trying to measure the eye diagram of the FPDlink III back-channel but we have been unable until now.

What we have tried was to measure on RIN+ and RIN- pins, but the signal is all mixed with the forward channel data. We have tried to disable the forward channel on the 954 by setting the register 0x20 to 0x30 but the result was the same. 

  • How can we isolate the BC to perform this measurement?
  • Shall we measure the BC in the RIN pins or should we use the CMLOUT pins instead?

More over, in the datasheet there is a specification for the amplitude of the signal but there I has not able to find any for the eye width, is there any?

Thanks for your support.

Vicent Climent.

  • 0
    TI__Mastermind 37220 points

    Hi Vincent,

    I don't think we can measure the back channel eye diagram with both serializer and deserializer connected. The CMLOUT is filtered out the back channel; therefore, you are only getting the forward channel. If you want to measure the back channel eye diagram, you can disable the forward channel, and connect the deserializer to a scope. This will allow you to monitor the back channel. It will be very slow rate.

    Aaron

  • 0 in reply to Aaron Heng
    Intellectual 360 points

    Hello Aaron,

    Thx for your answer.

    Just to double check, we have already disabled the forward channel by changing the register 0x20 to the value 0x30 and tried to measure the back-channel on RIN+ and RIN- pins. This was not successful.

    If I understood correctly, you are suggesting to do the same but in addition we should disconnect the 953 from the 954, is that correct?

    We are trying to get this measurement from your datasheet. 

  • 0 in reply to Vicent Climent14
    TI__Mastermind 37220 points

    Hi Vicent,

    Yes. You need to disconnect the serializer side and connect the scope to the deserializer side in order to capture the eye of the back channel. You will also need to disable the forward channel as well.

    Aaron

  • 0 in reply to Aaron Heng
    Intellectual 360 points

    Hi Aaron,

    I was able to test is as you suggested and it worked for us.

    Thx for your support.

    Vicent