Forum Discussion

JWall40's avatar
JWall40
Icon for New Contributor rankNew Contributor
5 years ago

FFT IP Core - Input and output number format?

I am unsure what data format I should use for the FFT IP core input and what data format it will output I can only find a few references to this topic in the user guide: “Imaginary input data, whic...
CheepinC_altera's avatar
CheepinC_altera
Icon for Regular Contributor rankRegular Contributor
5 years ago

Hi Jack,

Thanks for your update. By merely looking at the FFT output, it is rather difficult for me to tell if they are expected without a reference for comparison. Just to check with you on the following:

  1. What is your expected output from the FFT?
  2. Just wonder if you have had a chance to run a Modelsim simulation for comparison?
  3. One thing that you can try is to connect the output of the FFT to an iFFT to see if you can recover back similar shape of input waveform to FFT.

Please let me know if there is any concern. Thank you.

  • JWall40's avatar
    JWall40
    Icon for New Contributor rankNew Contributor
    5 years ago

    Hi Chee,

    1. Given that my input is a sine wave of 1KHz, with a DC offset, sampled at approximately 83KHz, I would expect the real output of the FFT to look like this:

    2. I have tried to run a modelsim simulation but I am yet to successful simulate the FFT IP Core, I get errors when loading the simulation and the FFT outputs never even change state

    3. This would be very interesting but my data out of the ADC is fixed point and ifft only supports floating point data. I cannot seem to find a way of using my fixed point ADC data in a floating point FFT system?

    Kind regards

    Jack