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5882 Discussions

FFT IP not behaving as expected.

Sean2
Beginner
383 Views

I'm trying to use the FFT IP on Quartus Prime Pro 18.1 to do an inverse fft. When I input an fft of a signal I created in Matlab that has a frequency of 23, I do not get the expected output signal. When taking the fft, with Matlab, of the output signal, I get a frequency of 86.

Before I input the signal to the inverse FFT IP, I make sure to convert the signal to Radix-4 digit reverse order with the Matlab code provided in the FFT IP data sheet.

I tried doing an fftshift and inverse fftshift on both the input and the output to see if one was shifted, and this not fix the issue.  

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5 Replies
SengKok_L_Intel
Moderator
343 Views

Is the input data compliance with the single floating-point format? Does it work well with FFT before proceeding with iFFT? How about if change the input order to natural?


Sean2
Beginner
334 Views

The input data is in single floating-point format. When I change the input setting of the IP to natural input and input the signal in it's normal order, I get a very noisy output that is not at the desired frequency. When I use this natural input setting and input the data in radix-4 digit reverse order, I get a frequency spike at 86 instead of 23.

Sean2
Beginner
329 Views

When I use a testbench with just an FFT IP instead of an inverse FFT, I get the expected output of a spike at 23 after using Matlab code on the output to rearrange the radix-4 digit reverse order. However, when I hook up the FFT IP to the inverse FFT IP through Avalon streaming, the fft produces a different output. 

SengKok_L_Intel
Moderator
283 Views

Do you able to get the expected result if running in the RTL simulation?


SengKok_L_Intel
Moderator
224 Views

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