**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!

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- Community Forums
- :
- Forums
- :
- Intellectual Property
- :
- DSP IP and Tools
- :
- Why the output of my FFT_IFFT model is incorrect?

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Mute
- Printer Friendly Page

Highlighted

swain168

Visitor

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

07-22-2009 05:42 AM - edited 07-22-2009 05:55 AM

8,461 Views

Registered:
11-18-2008

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

1 Solution

Accepted Solutions

aarunya

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

05-09-2010 06:41 PM

5,372 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

13 Replies

swain168

Visitor

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

07-22-2009 06:01 AM

8,463 Views

Registered:
11-18-2008

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

The output of 1024 point FFT

swain168

Visitor

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

07-22-2009 06:08 AM

8,453 Views

Registered:
11-18-2008

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

The output of 1024 points IFFT

Could you help me ?

pjayav

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

02-07-2010 07:45 PM

7,826 Views

Registered:
11-11-2009

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

hi,

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

Thanks & regards

selvam

aarunya

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

04-26-2010 08:37 PM

7,611 Views

Registered:
04-13-2010

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

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

syoma

Adventurer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

04-27-2010 01:39 AM

7,604 Views

Registered:
08-20-2007

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

ywu

Xilinx Employee

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

04-27-2010 08:17 PM

7,592 Views

Registered:
11-28-2007

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

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

Jim

aarunya

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

04-29-2010 08:14 PM

7,566 Views

Registered:
04-13-2010

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

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.

aarunya

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

04-29-2010 08:15 PM

7,565 Views

Registered:
04-13-2010

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

Thank you Jim.

I'll check that

farshade

Visitor

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

05-02-2010 09:48 PM

7,536 Views

Registered:
12-20-2009

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

@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.

aarunya

Observer

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

05-09-2010 06:41 PM

5,373 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

akilan

Newbie

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

05-18-2010 09:38 AM

4,318 Views

Registered:
04-15-2010

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

Thanks a lot for the solution

king1

Visitor

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

12-11-2011 08:15 PM - edited 12-11-2011 08:16 PM

3,705 Views

Registered:
12-10-2011

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

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.

ywu

Xilinx Employee

- Mark as New
- Bookmark
- Subscribe
- Mute
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Report Inappropriate Content

12-12-2011 04:30 AM

3,698 Views

Registered:
11-28-2007

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

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

Jim