FFT IP Core: User Guide

ID 683374
Date 11/06/2017
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4.2. Implementing Scaling

To implement the scaling algorithm, follow these steps:
  1. Determine the length of the resulting full scale dynamic range storage register. To get the length, add the width of the data to the number of times the data is shifted. For example, for a 16-bit data, 256-point Quad Output FFT/IFFT with Max = –11 and Min = –3. The Max value indicates 11 shifts to the left, so the resulting full scaled data width is 16 + 11, or 27 bits.
  2. Map the output data to the appropriate location within the expanded dynamic range register based upon the exponent value. To continue the above example, the 16-bit output data [15..0] from the FFT/IFFT is mapped to [26..11] for an exponent of –11, to [25..10] for an exponent of –10, to [24..9] for an exponent of –9, and so on.
  3. Sign extend the data within the full scale register.