UPGRADE YOUR BROWSER

We have detected your current browser version is not the latest one. Xilinx.com uses the latest web technologies to bring you the best online experience possible. Please upgrade to a Xilinx.com supported browser:Chrome, Firefox, Internet Explorer 11, Safari. Thank you!

cancel
Showing results for 
Search instead for 
Did you mean: 
Highlighted
Visitor swain168
Visitor
8,461 Views
Registered: ‎11-18-2008

Why the output of my FFT_IFFT model is incorrect?

Jump to solution

 input signal is cos(2*pi/192)(real component) and sin(2*pi/192)(image component)

Simple time is 3,

Simulink system period is 1s,

Down sampling rate is 3,

FFT bolck is FFT v4_1

 

Message Edited by swain168 on 07-22-2009 05:55 AM
0 Kudos
1 Solution

Accepted Solutions
Observer aarunya
Observer
5,372 Views
Registered: ‎04-13-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

um hi,

 

i have actually switched updated my xilinx sofware ISE 11 to get Virtex6 support.

in that i have used the FFT v7.0. i have made a few corrections and both FFT ant IFFT have started working

1. i was using the run time configurable transform length.

      -the nfft_we should be high for only one clock cycle during which the transform length Nfft is being configured. if Nfft_we is tied to high, it keeps on trying to configure the block and hence the processing never starts.

      -the input data to the FFT block has to be sent with one clock delay after the dynamic transform length is set.

2. though, the dynamic transform length is being used, the transform length that can be chosen in block parameters from the drop down list has to be set at the maximum that u may be using. the dynamic length can be for setting any size smaller than the transform length in the block parameters only.

 

with these 2 modifications, the FFT started to work.

 

3. for the IFFT, i have noticed that the output of FFT seems to saturate the IFFT and hence was not giving me results. so i did the 1/N scaling after the FFT and havethen passed the data to IFFT. due to this scaling, the IFFT also started working

 

Aarunya

13 Replies
Visitor swain168
Visitor
8,463 Views
Registered: ‎11-18-2008

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution
 The output  of 1024 point FFT
FFT_OUT.JPG
0 Kudos
Visitor swain168
Visitor
8,453 Views
Registered: ‎11-18-2008

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

The output of 1024 points IFFT

 

Could you help me ?

IFFT_out.bmp
0 Kudos
Observer pjayav
Observer
7,826 Views
Registered: ‎11-11-2009

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

hi,

     me too having the same problem. Did u got solution for your problem. If so, please share with me

 

Thanks & regards

selvam

0 Kudos
Observer aarunya
Observer
7,611 Views
Registered: ‎04-13-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

I am having that problem too.

I have also noticed that my FFT output from Matlab and output from Sysgen do not match properly. 

 

aarunya 

0 Kudos
Adventurer
Adventurer
7,604 Views
Registered: ‎08-20-2007

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

Can you post your model as MDL file? It is too hard to analyze without knowledge of all block parameters.

0 Kudos
Xilinx Employee
Xilinx Employee
7,592 Views
Registered: ‎11-28-2007

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

If you are asking about IFFT, please take a look at this blog: http://myfpgablog.blogspot.com/2009/11/ifft-in-system-generator.html

 


aarunya wrote:

I am having that problem too.

I have also noticed that my FFT output from Matlab and output from Sysgen do not match properly. 

 

aarunya 


 

 

Cheers,
Jim
0 Kudos
Observer aarunya
Observer
7,566 Views
Registered: ‎04-13-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

thank you syoma. The FFT is solved. but my IFFT is not solved.

I'll look into the blog which Jim is refering to and if i can't solve, I'll get back.

thank you.

0 Kudos
Observer aarunya
Observer
7,565 Views
Registered: ‎04-13-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

Thank you Jim.

I'll check that

0 Kudos
Visitor farshade
Visitor
7,536 Views
Registered: ‎12-20-2009

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

@aarunya wrote:

thank you syoma. The FFT is solved. but my IFFT is not solved.

I'll look into the blog which Jim is refering to and if i can't solve, I'll get back.

thank you.


Can you please tell me how you solved the mismatching outputs for FFT between MATLAB and SysGen?

I appreciate if you attach the working .mdl file.

Thanks a lot.

0 Kudos
Observer aarunya
Observer
5,373 Views
Registered: ‎04-13-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

um hi,

 

i have actually switched updated my xilinx sofware ISE 11 to get Virtex6 support.

in that i have used the FFT v7.0. i have made a few corrections and both FFT ant IFFT have started working

1. i was using the run time configurable transform length.

      -the nfft_we should be high for only one clock cycle during which the transform length Nfft is being configured. if Nfft_we is tied to high, it keeps on trying to configure the block and hence the processing never starts.

      -the input data to the FFT block has to be sent with one clock delay after the dynamic transform length is set.

2. though, the dynamic transform length is being used, the transform length that can be chosen in block parameters from the drop down list has to be set at the maximum that u may be using. the dynamic length can be for setting any size smaller than the transform length in the block parameters only.

 

with these 2 modifications, the FFT started to work.

 

3. for the IFFT, i have noticed that the output of FFT seems to saturate the IFFT and hence was not giving me results. so i did the 1/N scaling after the FFT and havethen passed the data to IFFT. due to this scaling, the IFFT also started working

 

Aarunya

Newbie akilan
Newbie
4,318 Views
Registered: ‎04-15-2010

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

Thanks a lot for the solution

0 Kudos
Visitor king1
Visitor
3,705 Views
Registered: ‎12-10-2011

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

Hi Aarunya,

Can you please mail me the solution for FFT_IFFT model. I require it urgently. My email id is vikrantmahajan.iitkgp@gmail.com. 

Thanx in advance.

 

 

0 Kudos
Xilinx Employee
Xilinx Employee
3,698 Views
Registered: ‎11-28-2007

Re: Why the output of my FFT_IFFT model is incorrect?

Jump to solution

Check http://forums.xilinx.com/t5/DSP-Tools/FFT-IFFT-famous-problem/m-p/193978#M4856

 


@king1 wrote:

Hi Aarunya,

Can you please mail me the solution for FFT_IFFT model. I require it urgently. My email id is vikrantmahajan.iitkgp@gmail.com. 

Thanx in advance.

 

 




Cheers,
Jim
Tags (1)
0 Kudos