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AR# 30293

LogiCORE Fast Fourier Transform (FFT) - When I look at my output, why does the output of my inverse FFT appear to be time reversed?

Description

Keywords: FFT Compiler, xFFT, IFFT, inverted, backwards, Radix 4, Radix 2, v5.0

When I look at my output, why does the output of my inverse FFT appear to be time reversed?

Solution

A forward FFT will appear as a time reversed inverse transform, due to a known property of the FFT algorithm. Double check that the direction of the FFT is set properly. FWD_INV = 1 will be a forward transform, and FWD_INV = 0 will result in an inverse transform.

NOTE: you must pulse or tie fft_inv_we High in order to change the direction to be an inverse transform.

Please see (Xilinx Answer 29209) for a detailed list of LogiCORE Fast Fourier Transform (FFT) Release Notes and Known Issues.

AR# 30293
Date Created 02/15/2008
Last Updated 02/14/2008
Status Active
Type General Article