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Visitor
Visitor
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Registered: ‎07-10-2017

FFT Testbench unexpected output

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Hi all,

 

I'm running the testbench supplied by Vivado and am having some trouble understanding the output.

 

Here's both of the input and the output.

 

fft_input_vs_output.PNG

 

My question is, I don't see m_axis_data_tdata showing what I expect to be the fourier transform of the input signal. 

Here is what I expect the output to look like when I run it on matlab, where the top is the input signal and the bottom the fourier transform.

 

correct fft output matlab.png

 

I know that in order to see the correct FFT waveform you need to take the absolute value, so I saved the input/output data points to a textfile so I could run it in matlab. Here's the results with the input unchanged on the top and the absolute value of the output on the bottom.

 

Screen Shot 2017-07-26 at 12.03.36 PM.png

 

The results still don't match what I expect, as I don't see the correct FFT output at any point. I've also tried saving the imaginary and real parts of the output separately, and then taking the magnitude that way and graphing but it still did not work.

 

Any ideas of how to get the correct output? As the testbench is essentially running a series of FFTs and IFFTs on the same input signal and the signal appears to get recreated correctly, it seems like the core is working as it should, but I just don't see how to view the output of the FFT in the m_axis_data_tdata field.

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Visitor
Visitor
2,324 Views
Registered: ‎07-10-2017

Re: FFT Testbench unexpected output

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Solved, had to make sure that I was doing natural order output. 

View solution in original post

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Visitor
Visitor
2,325 Views
Registered: ‎07-10-2017

Re: FFT Testbench unexpected output

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Solved, had to make sure that I was doing natural order output. 

View solution in original post

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Observer
Observer
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Registered: ‎03-17-2018

Re: FFT Testbench unexpected output

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I am implementing fft .

I want to check fft output  via logic analyzer as it working fine or not, I am not getting idea how to use logic analyzer to check my fft output.

2 nd 

I  implemented adc, echo server, ram etc can  please help me  put all  component in right manner for proper fft interfacing.

  

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