cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
swain168
Visitor
Visitor
9,270 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
aarunya
Observer
Observer
6,181 Views
Registered: ‎04-13-2010

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

View solution in original post

13 Replies
swain168
Visitor
Visitor
9,272 Views
Registered: ‎11-18-2008
 The output  of 1024 point FFT
FFT_OUT.JPG
0 Kudos
swain168
Visitor
Visitor
9,262 Views
Registered: ‎11-18-2008

The output of 1024 points IFFT

 

Could you help me ?

IFFT_out.bmp
0 Kudos
pjayav
Observer
Observer
8,635 Views
Registered: ‎11-11-2009

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
aarunya
Observer
Observer
8,420 Views
Registered: ‎04-13-2010

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
syoma
Adventurer
Adventurer
8,413 Views
Registered: ‎08-20-2007

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

0 Kudos
ywu
Xilinx Employee
Xilinx Employee
8,401 Views
Registered: ‎11-28-2007

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
aarunya
Observer
Observer
8,375 Views
Registered: ‎04-13-2010

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
aarunya
Observer
Observer
8,374 Views
Registered: ‎04-13-2010

Thank you Jim.

I'll check that

0 Kudos
farshade
Visitor
Visitor
8,345 Views
Registered: ‎12-20-2009

@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
aarunya
Observer
Observer
6,182 Views
Registered: ‎04-13-2010

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

View solution in original post

akilan
Newbie
Newbie
5,127 Views
Registered: ‎04-15-2010

Thanks a lot for the solution

0 Kudos
king1
Visitor
Visitor
4,514 Views
Registered: ‎12-10-2011

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
ywu
Xilinx Employee
Xilinx Employee
4,507 Views
Registered: ‎11-28-2007

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