FFT

[vince31500]

Hello,
I have a question about fft in fpga.
I working with simulink to perform xilinx fft V4_1.
I don't understand how it works.

I have a 10000 point sinusoidal input on which I want to perform a 1024 point fft.
I firstly put the start always equal to one; I obtain the output a screenshot of which I joined to this post (output1.jpg)
As you can see, the fft doesn't begin immediatly, I don't understand why. (I join the "busy parameter" : busy.jpg)

Furthermore, I don't understand why the peaks are positioned like that. I thought each one represented the frequency of my sinusoidal input but I tried to verify and it seems I'm not right.
Have you please some explanation ?

[chrisar]

The output is as expected.

An FFT performs a transform on the same number of samples as the point size of the FFT.

For example, in your case you are using a 1024pt FFT.  This means that for ever 1024 data samples, you will receive a result.

Some other things to keep in mind are that there is an initial delay in processing, which is why you do not see an output before about 2000 samples.  Then you will see consistently a new block (1024 outputs samples) every 1024 clock cycles.

For more information, I would recommend reading the FFT Datasheet, or opening a case with the Xilinx Technical Support.

[surendraadapa9]

Hi,

how can i perfom 1024 point fft............that means how can i give 1024 samples as a input.......pls help me.....

Thanks
surendra