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DS280DF810EVM: Low EYE amplitude problem

Xavier Lamarche
Prodigy 10 points
Part Number: DS280DF810EVM

I have DS280DF810EVM. When I use it to generate PRBS and check the eye on a DCA I only have an amplitude of 395mV. That is really low. I'm using Sigcon. I have try different setting for the ''transmitter FIR/VOD settings'' I can lower the signal but can't go over 395mV at 25 Gbps. If I lower the data rate, I have little more amplitude, but still low.

  • +1
    TI__Mastermind 19135 points

    Hi,

    I believe that this green signal for DCA channel 2 is signal-ended. Looking at your picture the amplitude p-p is around 500mV for this signal. Thus, the differential amplitude would be around 1Vpp. That's not small at all.

    Regards,

    Rodrigo Natal

  • 0 in reply to Rodrigo Natal
    Prodigy 10 points

    Hi Rodrigo,

    I only have 375mV like I said before, not 500mV. How I can get 500mV?

    Thanks 

    Xavier 

  • 0 in reply to Xavier Lamarche
    TI__Mastermind 19135 points

    Not correct Xavier. You have 500mVpp. The DCA scope measurement type you selected is not the peak-to-peak amplitude measurement. When the scope measured this "Amplitude" parameter via Eye Mask mode it is applying a histogram to the 1 and 0 levels. Thus, the resulting amplitude would be closer to the average of the inner eye height and the outer amplitude peak-to-peak. When you are transmitting 25G data the higher frequency component will be attenuated more compared to the low frequency component. That is why the inner eye height is smaller than the outer amplitude peak-to-peak.

    To observe the true voltage output you should use a lower frequency pattern like 8T (i.e. eight 1s and eight 0s.) .

    The amplitude value you are observing should be more than sufficient to comply with industry standard specs.

    Thanks,

    Rodrigo