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Altera_Forum

Honored Contributor I

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02-03-2015
02:14 PM

946 Views

FFT_verification

Hi !

When I run FFT and IFFT tool in megawizard, the results are not logical. For example firstly I run the FFT tool with the megawizard tb (input: natural order, output : digit reversed order) then I use the FFT output txt files for the input files of IFFT ( input : digit reversed order output: natural order) the result of IFFT dont match with the input of FFT . What could be the problem ? P.S = I use single precision floating point representation for the 16-FFT tool. Thanks allLink Copied

4 Replies

Altera_Forum

Honored Contributor I

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02-05-2015
02:41 PM

39 Views

Altera_Forum

Honored Contributor I

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02-05-2015
03:18 PM

39 Views

I used the output of FFT for the input of IFFT.I mean I modified the tb for IFFT.

By the way I found the solution ;) When you check in binary for floating point it is hard to find what is wrong. When I converted to decimals in Matlab I saw that the output multiplied with the FFT size. For example if you use 8-IFFT the outputs are 8 time greater than the outputs had used to be. You should normalize them by IFFT size ;) Thanks anyway for your reply
Altera_Forum

Honored Contributor I

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06-02-2015
02:25 AM

39 Views

Hi ferdiskaras,

I guess I have the same problem you went through. I have implemented a VARIABLE STREAMING (N=8), SINGLE-FLOAT-POINT FFT/IFFT. These are my results: input (natural order): (8 0 0 0 8 0 0 0) FFT output (Digit-reverse order): [16 16 0 0 16 16 0 0] /* the same as [16 0 16 0 16 0 16 0 ] Natural order */ input(Digit-reverse order): [16 16 0 0 16 16 0 0] IFFT output (natural order): (64 0 0 0 64 0 0 0) How did you normalize it? Where did you make de division by N? In your hardware or in your software? Is there a way to set FFT core to output data already normalized? Thanks
Altera_Forum

Honored Contributor I

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06-30-2015
05:13 AM

39 Views

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