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mohamed.shfat

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12-14-2016 10:55 AM

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Registered:
10-16-2016

FFT v 9.0 output makes no sense !

Hello

Please i want to ask very important thing and i really need a help . I have been trying to debug the FFT core v9.0 on vivado since two months approximately , but i'm still stuck with it . The FFT core gives me nothing at the output , it's just gives a peaks on the first and the last points of the frame (0.N-1) , but in other points i have nothing , it looks like there is no frequency in my input signal or something like that !

The picture below shows the results that i'm getting from each XADC and the FFT core , i'm really stuck here i couldn't understand what's the exact problem or what's wrong here so i can fix it to make the core works .

The sampling frequency of my XADC is about 1MSPS while i tried all possible frequencies for the input signal starts from 10 Khz up to 480 Khz which is the maximum freq i can use , FFT points are 1024 and i tried both scaled and unscaled design , and its in real time mode with natural order output . And the results are same for all cases above .

Please if anyone knows the problem and what's going on here i would really appreciate the help .

Note that this is not a simulation results , it's a really results taken by the ILA debugging core .

3 Replies

muzaffer

Teacher

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12-14-2016 11:44 AM

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Registered:
03-31-2012

@mohamed.shfat your description of your problem is not very clear. Can you capture the XADC output and run FFT on it and compare the results with a simulation of your logic and or the ILA captured data? It seems your waveform is zoomed-out. You can zoom in and see what values you have other than the peaks. Also how do you compute the magnitude of the FFT output ? Verify you are computing it correctly.

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mohamed.shfat

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12-14-2016 11:00 PM

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Registered:
10-16-2016

@muzaffer Sir , in this design the ILA debugging core is capturing the data from both XADC and the FFT and display it , i'm also extracting the data out in excel file and i'm using the values to see my output clearly on matlab , but it still makes no sense ! Just one peak at the first point N=0.

I'm computing the magnitude by square both the real and the imaginary parts of the output , summing them , and take their square root on the FPGA . the results above which are ( FFT output (MAG) ) are the output of this processing .

I'm just wondering why does the core can't give a logical results for the spectrum !

muzaffer

Teacher

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12-15-2016 08:01 AM

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Registered:
03-31-2012

@mohamed.shfat You should data you capture from XADC and simulate it with your design. It's difficult to debug why hardware is not working if you don't have a working simulation. After you have a working simulation, you can check the input/output handshake signalling of the FFT block to see if it is behaving the same way.

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