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Webench Interface Designer - DS125RT410 simulation bug

Kawai
Guru 19775 points
Other Parts Discussed in Thread: DS125RT410

Hello Team,

I found a bug when simulating DS125RT410. From the simulation result the device seems to be able to equalize -60dB insertion loss at 6.25Gbps. Could you please confirm the simulation ?

Best Regards,

Kawai

  • 0
    TI__Mastermind 29655 points
    Hi Kawai-san,

    Based on my understanding of our IBIS-AMI model, you are partially correct. In a realistic scenario, the CDR would be unable to recover the clock from the incoming data to acquire lock. This is due to significant attenuation, particularly at bits that transition at the Nyquist frequency. Therefore, with a real part, when the CDR is unable to lock, then the retimer output is muted. Therefore, I do not expect the retimer to produce the clean eye. I actually would expect the output waveform to be muted.

    However, after reviewing the DS1xxDF410/DS1xxRT410 model documentation, it looks like the model performs the CTLE + DFE optimization, but ultimately, the output will make some kind of slicing decision to declare each bit as either a "1" or "0", regardless of whether the CDR would actually achieve lock in a realistic scenario. This is not necessarily a bug in Webench Interface Designer as this is a limitation of IBIS-AMI models in general.

    When using the IBIS-AMI retimer model, it is often more important to look at the output directly after the CTLE + DFE than the Tx output of the retimer. It is important to ensure that the equalized eye that the CDR sees internally is as open as possible.

    Thanks,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19775 points
    Hi Michael-san,

    Thank you for taking your time giving me your comment. I was just wondering because I had never seen such clean eye when evaluating with the cable/trace with huge insertion loss, using DF410 devices.

    I understood that it is not a bug for the simulation due to the slicing function in the IBIS model. However, this result may be confusing for the user that they may think this device could be used in their condition. I believe their is no document which explains in detail about the Webench Interface Designer. It may be helpful for the user to have such information.

    Thanks and Best Regards,
    Kawai