Digital Signal Processing - IP and Algorithms

[yasirmahmoodqureshi]

I am usinf FFT IP core V6.0. When I took the FFT of following data  points

1.1     2.2      3.3     4.4    1.1     2.2     3.3       4.4  

  in floating point format using the transform length of eight, i get the following Result

22     0       -4.4000 - 4.4000i      0          -4.4000           0            -4.4000 + 4.4000i        0  

whereas MATLAB gives the following Result

22     0       -4.4000 + 4.4000i      0          -4.4000           0            -4.4000 - 4.4000i        0  

The problem is that the signs of imaginary part is inverted. I have check it in both fixed point and floating formats, but problem remains the same, the signs of the imaginary parts are inverted, when we compare the results of MATLAB with that of FFT core.

Regards

Yaasir

[ywu]

Can you attach your model or testbench?

Cheers,

Jim

[tremois]

Hi,

I think you've done an IFFT instead of an FFT.

Check the 'fwd_inv' input; it must be set to 0 for  inverse transform and 1 forforward transform

Olivier

[vytautas]

Hello.

FFT datasheet includes waveforms how initialization should be done. This is the first step. Second, you need to add 3 clocks delay between every input. How do you read output?

[yasirmahmoodqureshi · Accepted solution]

thanks everyone, got it right

actually there was some mistake with my initializations

thanks again

Regards

Yasir

[mofa77]

i use the fft ipcore to compute fft and ifft 

but both the result are fft data

i have set the fwd_inv both 0 and 1

the result is fft result

can you tell me some reason

thank you 

[technovlsi]

@ vytautas sir, i have set the clk frq 250 Mhz. .then how do i insert 3 clk cycle delay in testbenvh. plz help.

[vinodlk123]

hello sir,

when im simulating fft core  7.1, im getting unexpected results....

i am not able to understand where i'v done wrong ...

i'v added some simulation results...

if u can plz provide the correct code or help me to get correct output...

thank you...

[bwiec]

For completeness, refer to this thread:

http://forums.xilinx.com/t5/Digital-Signal-Processing-IP-and/FFT-CORE-INCORRECT-RESULTS/m-p/207813#M...