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!

AR# 34171

FFTv7.0 - How to implement the 1/N scaling that is typically included in the IDFT equation

Description

The equation for IDFT typically has a 1/N scaling factor. 

How is this implemented in the FFTv7.0 IP?

Solution

The FFT IP does not automatically include this 1/N scaling factor. 

In order to implement the 1/N scaling, an appropriate scaling schedule must be used.  

The correct scaling schedule depends on whether a Radix-4 or Radix-2 butterfly is used.  

For Radix-4, a scaling schedule of all '3' (scaling by a factor of 4 in each stage) should be used.  

For Radix-2, the scaling schedule depends on whether the IFFT point size is a power of 4 or not.  

If the point size is a power of 4, a scaling schedule of all '2' (scaling by a factor of 3 in each stage) should be used.

Examples:

nfft = 256 : scaling schedule = 2222, binary = 10101010

nfft = 512 : scaling schedule = 12222, binary = 0110101010

nfft = 1024 : scaling schedule = 22222, binary = 1010101010

nfft = 2048 : scaling schedule = 122222 binary = 011010101010

Pages 3 and 12 of the datasheet contain documentation related to this topic.

AR# 34171
Date Created 01/19/2010
Last Updated 01/05/2015
Status Active
Type Design Advisory
IP
  • Fast Fourier Transform