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Code for fft/ifft DSPF28044 Fixed-point C28x

Ousama OSMAN

Prodigy 40 points

Other Parts Discussed in Thread: TMS320F28044

Hi,

I need some help regarding IFFT and FFt

Is there any library supplied by TI that contains IFFT (Inverse Fast Fourier Transform) functionality that can be used with the TMS320F28044 (Fixed point)?

I am using a fixed-point DSPF28044, and I want to do a ifft (Inverse Fast Fourier Transform)) for a table containing the amplitude and the phase shifted of the harmonics (3, 5, 7, 9, 11, 13) to retrieve the continuous signal. So I'm looking for a code in Fixed-point(IQ) that will make this transformation, could you help me please.

thanks a lot,

Ousama

over 11 years ago

0 Vishal_Coelho over 11 years ago

TI__Mastermind 20850 points

Hi Ousama,

We dont have the ifft routine in there at this point but you can use the forward FFT to calculate the IFFT

There are a couple of ways to do it:

1. let X(k) = fft(x(n))

then x(n) = conj(fft(conj(X(k))) so basically conjugate -> fft -> conjugate

see http://www.dsprelated.com/showmessage/25408/1.php

2. switch the real imag parts of the input, run the fft then switch re imag parts again

3. run the forward FFT then rearrange the output as follows

x(0), x(N-1), x(N-2),........x(1)

Basically keep the first output where it is and reverse the order of the rest.

This page shows the derivations for the first two methods:

http://www.embedded.com/design/embedded/4210789/DSP-Tricks--Computing-inverse-FFTs-using-the-forward-FFT

0 Ousama OSMAN over 11 years ago in reply to Vishal_Coelho

Prodigy 40 points

Hi Vishal,

Thank you for your ideas, I'll see the links and I hope I will succeed in finding a solution as soon as possible.

thank you very much

Best regards,

ousama