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AR# 34171

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


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

How is this implemented in the FFTv7.0 IP?


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.


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 01/05/2015
Status Active
Type Design Advisory
  • Fast Fourier Transform
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