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DP83TG720EVM-MC: Facing issue in signal quality

Vivek Nandha
Prodigy 20 points
Part Number: DP83TG720EVM-MC


Hello TI Team,

 

We have purchased two “DP83TG720EVM-MC” media converter evaluation module to do 1000BaseT1 decoder. To do the decoding, we require proper amplitude signal as per 1000BaseT1 specification. However, we are facing issue in signal quality.

 

We are trying to capture waveform of Automotive ethernet from the output TE Matenet connector. We are using 4GHz Cable Assembly Coaxial BNC to SMA to probe the waveforms.

Currently We are using single DP83TG720EVM-MC board to capture Link synchronization part of Master of 1000BaseT1. But we are getting disturbed waveforms as shown in below image.

We can see in below image that the peak to peak of waveform is not reach to the it’s actual amplitude.

 

Very first, we have provided power supply to the DP83TG720EVM-MC board using micro USB, later on we have used 12V power adapter for power supply to the board.

But we got same result as shown in above image.

 

Please guide us to improve the quality of waveforms or let us know if we missed some steps to follow.

Also let us know to thing to consider during use of DP83TG720EVM-MC board.

  • 0
    TI__Expert 3595 points

    Hi Vivek,

    The signal you've captured actually matches the IEEE 802.3 standard. This is what we expect to see. :) Hope this helps!

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 20 points

    Hi Lysny,

    Thank you for your response.

    Yes, as you told PAM2 signal is as per IEEE802.3bp-2016 standards. But I suspect that PAM3 signal generated using below setup shown in diagram is not as per IEEE802.3bp. Could you please confirm this by looking at image-2?

    Now I have formed a complete network between two PC as show in bellow diagram.

     

                                                                                                      Image-1

    I can ping PC#1 from PC#2 and vice versa. So, I have captured signal during the data transmission.

    So, the signal should be PAM3 as per the IEEE802.3bp-2016 standard. But while looking at the signal it was not PAM3 signal as you can see in below image.

                                                                                                 Image-2

    Please guide us to improve the signal quality and get the proper PAM3 signal Or you can send image of PAM3 signal capture using TI board on your end.

    Thanks,

    Vivek

  • 0 in reply to Vivek Nandha
    TI__Expert 3595 points

    Hi Vivek,

    The PAM3 signal should be an amplitude modulated signal like the one shown above. Depending on where in the design you are measuring, the signal quality will not always match an ideal waveform, but the devices are designed to handle a tolerance. Are you having any issue with communication? Is there a specific part of that signal that is concerning you the most?

    Thanks,

    Lysny

  • 0 in reply to Lysny Woodahl
    Prodigy 20 points

    Hi Lysny,

     

    No, I was not facing any issue with communication. We are developing decoder for 1000BaseT1. For that we require signal on which we can apply the logic as per mentioned on IEEE802.3bp-2016 standard.

    In standard they have mentioned that initially PHY send PAM2 signal for Link synchronization and after Link synchronization is done, PHY sends SEND_T signal which is again PAM2 signal. Up to SEND_T, we are good with the signal. After that when actual data transmission starts between two PHY, at that time signal is PAM3.

    According to standard, PAM3 has +1, 0, -1 symbols in signal. And one symbol time period is 1.5ns(neno second). So when we look at output signal of the Automotive port, how can we identify the +1, 0, -1 symbol from below signal?

     

     

    In above Image, I have tried to identify +1, 0, -1 symbol as per standard. So is it correct? Or let me know if I did wrong.

  • 0 in reply to Vivek Nandha
    TI__Expert 3595 points

    Hi Vivek,

    PAM3 decoding is something out of the PHY support team's scope, but I will do some reading/research and see if I'm able to help you with this.

    Thanks,

    Lysny 

  • 0 in reply to Lysny Woodahl
    TI__Expert 3595 points

    HI Vivek,

    From the definition of PAM3, this looks correct to me

  • 0 in reply to Lysny Woodahl
    Prodigy 20 points

    Hi Lysny,

    Thank you for your response.

    We cannot see proper 3 level(1, 0, -1) of PAM3. But as you said the devices are handle to tolerate. So if this PAM3 signal seems correct then we need to apply some equalization process and correct the edges of signal. 

    Let see the equalization is helpful of not. I will let you know once equalization is done. 

    Thanks,

    Vivek