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AD9633/HSC-ADC-EVALCZ Visual Analog comparison to Oscope not matching

I'm comparing data captured by the oscope and by the ad9633/evalcz combo using Visual Analog default data capture and I'm not understanding the difference.

vs Visual Analog Graph:

It doesn't quite look like it's reversed, and it's supposed to be FIFO so it should be left to right.  I'm also seeing a small spike artifact on the top of the downward slope in both images.  If I reverse the data from the DAQ, then the spike is at the top of the leading edge, not falling edge.

What am I missing or not understanding?

Thanks,

Mark.

  • Hi Mark,

    Thank you for your interest in AD9633. You make an interesting observation.

    Where on the board are you taking the oscilloscope measurement?

    Was the VisualAnalog capture performed with the oscilloscope probes in place?

    Thank you.

    Doug

  • Hi Doug,  

    Thanks for some help, I'm pretty confused.

    The oscilloscope picture is taken using the same cable from the function generator going into (channel D of) the AD9633 eval board.  So it's a physical disconnect and reconnect to the other instrument.  It's 100% repeatable and I've performed the swap and the sampling many times.  I've tested multiple channels on the oscilloscope and on the eval board with no change in behavior.

  • Hi Mark,

    Thank you for the additional information.

    The reason I asked the questions in my previous post is that we do not know what the ADC "sees" right at its pins, during your test. The square wave from your signal generator passes through an RF balun on its way to the ADC, on the evaluation board. This balun should do a decent job of doing the single-ended to differential conversion of your square-wave, but again we do not know what the ADC "sees" right at its pins.

    Is your oscilloscope input impedance set to Hi-Z, or 50Ohms? Another thing to try is to try switching the input impedance from Hi-Z to 50Ohms, to see if/how that affects the waveform you see. The evaluation board is designed to present a load of about 50Ohms as seen by the signal source at the board connector. Does changing the input impedance of your oscilloscope change the waveform that you observe?

    Also, if you try looking at the signal close to the ADC input pins on the board, you will see spikes from "kickback", from the ADC inputs. This is normal on converters that have a switched-capacitor input and does not cause a problem.

    Thank you.

    Doug