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alexboin
Observer
Observer
6,430 Views
Registered: ‎08-19-2012

Verify fft Core in sysGen

Hi friends,

I want to test xilinx fft core7.1,but i can not get the right answer even for simplest signals,

I attach an image,Tell me if you can guess my mistake.

xilinxfft.jpg
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8 Replies
bwiec
Xilinx Employee
Xilinx Employee
6,413 Views
Registered: ‎08-02-2011

How are you concluding that it is incorrect? What is the expected response?

 

How are you configuring the FFT? What is your simulink system period (set in the SysGen token)? What data type/rate are you setting in the gateway in for your data?

www.xilinx.com
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alexboin
Observer
Observer
6,408 Views
Registered: ‎08-19-2012

I attached my matlab simulink file.

My input signal is just a sine wave,so i have only one frequency(but i find diffrent values in fft result)

the configuration is 8k point pipelined fft with 64MGHz Simulation frequency,13 bti phase factor width,unscaled,and natural order.

gateway_in data type is fixed point 14 bit with 13 binary point.

thanks for your answer.

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bwiec
Xilinx Employee
Xilinx Employee
6,362 Views
Registered: ‎08-02-2011

You forgot to attach your model.

www.xilinx.com
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alexboin
Observer
Observer
6,354 Views
Registered: ‎08-19-2012

 
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bwiec
Xilinx Employee
Xilinx Employee
6,339 Views
Registered: ‎08-02-2011

First, your FFT is only 512 long. Thus, looking at your 8K deep ROM with 1 period of a sine wave in it, keep in mind that you are only sending in 1/16 of a period for each FFT.

 

Secondly, you need to use xk_index (and rdy) to qualify your data. If you look at the image below, you see only one spike per FFT frame.

 

fft.png

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bwiec
Xilinx Employee
Xilinx Employee
6,336 Views
Registered: ‎08-02-2011

If you change the FFT to 8k and run the sim a bit longer (and zoom in!), you will see what I suspect is more of the result you are looking for:

 

fft2.png

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alexboin
Observer
Observer
6,326 Views
Registered: ‎08-19-2012

Thanks for your answer my friend.

I can't see ur images,and i want to know what exactly tells me checking the value & its index?

also my result is sth like image below.

i visited http://myfpgablog.blogspot.com/2010/07/fft-results-from-matlab-fft-bit.html 

but i could not verify my result yet,because i can't run the 

Bit Accurate C model presented there

?

thanks

FFt.jpg
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bwiec
Xilinx Employee
Xilinx Employee
6,322 Views
Registered: ‎08-02-2011

You are just about there. Now just zoom in on one full period of the ramp in the x-direction and zoom in on the data a bunch in the y-direction. I've attached the picture this time so you can download it.

www.xilinx.com
fft2.png