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ADS8688EVM-PDK: confusion in FFT analysis page in GUI

Robin Liu
Intellectual 1940 points
Part Number: ADS8688EVM-PDK

Hello,

I'm Robin, AFAA from Shenzhen, China.

when I use the ADS8688EVM-PDK and GUI to test the dynamic performance, I find we must input the actual FI to get the correct result of SNR e.g. And all the items calculated based on the coherent FI. 

thus it may make some confusions.

1) If we input a fault value of actual FI, it still can get the SNR result, but obviously error. So what is that?

2) we must know the exact frequency of the input signal, so if I input an unknown signal, I can't get the SNR e.g. results from the GUI, is that right?

3)With these confusion, I learned the theory of coherent sample. But I concern that it is not friendly enough to our customer without the relevant knowledge background.

Further more, is that the EVM86xxEVM-PDK GUI solve the problem? I find it is not compatible with the ADS8688EVM-PDK, for the connection can't be recognized.

And is the EVM86xxEVM-PDK still supported?

  • 0
    TI__Mastermind 25020 points

    Hello Robin,

    Let me try to clear up the confusion.

    An input signal is used, the input frequency does not need to be known, the GUI will calculate the frequency of that input signal, this is the Actual FI. The dynamic performance measurements are based on this calculated frequency. These results are calucated using a 7-term Blackman-Harris window, thus the results are reliable.

    The Coherent FI the GUI shows is the frequency the GUI calculated to maintain coherency. In theory, when you intially input a signal, the GUI will show the Coherent FI, then the user is to change the input frequency to the shown Coherent FI initially given. But in real life applications, there are errors introduced, through equipment and such.

    If you or your customer would like to learn more about this topic, there is a Precision Lab on ADCs available: 4.3 Coherent Sampling and Filtering to IMprove SNR and THD

    Both GUIs should be similiar in this aspect. I will look into the connection/compatibily of the GUIs.

    Regards, Cynthia