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DP83848-EP IBIS glitch on PHY outputs

user4354969
Intellectual 370 points

Dear Ross,

In the frame of our development studies, we have carried out some IBIS simulations with the IBIS model of the PHY DP83848 you have sent.

We have an issue with the falling edge of the PHY outputs.

In all our simulations, we observe an glitch on the falling front of PHY outputs, like depicted in the screenshot bellow :

 

 

We are puzzled with this unexpected behavior.

Is there something wrong with the IBIS Model or with our studies ? I guess this glitch is not present on the real part, but we don't have samples to test here.

 

Thank you in advance for your support,

 

Best regards,

 

PGC

  • 0
    TI__Guru 62930 points
    PGC,
    Presumably you are referring to the RXD drivers?
    This looks like a reflection. Do you have series termination on these lines? The reference schematics have 33ohm series resistors.
    Someone from the ethernet team may have additional comments.
    Regards,
    Wade
  • 0 in reply to Wade Vonbergen
    Intellectual 370 points

    Dear Wade,

    Thank you for your answer.

    I am referring to the RXD drivers of the PHY.

    We have performed the study with different serial resistor terminations, and we observed a similar behavior with 31, 68 and 100 Ohm resistors.

    Moreover, we have tested with different PCB track lengths, and this did not shift the glitch. Therefore, we did not interpret this as a reflection.

    I don't know it your Ethernet team has already encountered this kind of artifact ?

    Best regards,

    P-G C.

  • 0 in reply to user4354969
    TI__Mastermind 23675 points

    Hi PGC,

    I do not see the same waveform you see unfortunately.

    Here is what i see:

    Kind regards,

    Ross

  • 0 in reply to Ross Pimentel
    Intellectual 370 points

    Dear Ross,

    Thank you for these simulations. In order to understand the difference we observed, we have re-done our simulations from the bare PHY pad to the whole setup, with PCB and input MAC receiver pads.
    It appears that the issue is caused by the pad of the specific ASIC connected to the other side of the line (it does not appear with other kind of pads). We have been hable to solve it with filtering resistors.

    Thank you for your support !

    Best regards,

    P-G C.