Processor and method for performing a fast fourier transform and/or an inverse fast fourier transform of a complex input signal

A method for performing a Fast Fourier Transform (FFT) and/or an Inverse Fast Fourier Transform (IFFT) of a complex input signal having a real component and an imaginary component, the method comprising:

• applying the complex input signal to a first stage and when a Fast Fourier Transform procedure is to be applied passing the input signal to a second stage, and when an Inverse Fast Fourier Transform procedure is to be applied swapping the real and imaginary components of the complex input signal before passing the signal to a second stage;
• applying in a second stage a first portion of the signal output from the first stage to a radix-4 butterfly element;
• applying in the second stage a second portion of the signal output from the first stage to a second radix-4 butterfly element;
• performing a butterfly operation in each of the first and second radix-4 butterfly elements on the respective portions of the signal to generate in each of the butterfly elements a processed output signal;
• applying the processed output signal from the first butterfly element to a first input to a third stage, the third stage being arranged to switch between a first operating mode and a second operating mode, the second operating mode being for processing a complex conjugate symmetrical input signal;
• applying the processed output signal from the second butterfly element to a second input to the third stage;
• applying an output signal from the third stage derived from the first output from the first butterfly element to a first input to one or more of a plurality of processing units in a fourth stage, one or more of said processing units comprising a radix-2 pipelined Fast Fourier Transform (FFT) processor;
• and
• applying an output signal from the third stage derived from the first output from the second butterfly element to a second input to one or more of the plurality of processing units;
• processing in the fourth stage the processed output signals received from the first and second butterfly elements according to a Fast Fourier Transform (FFT) processing procedure to produce a processed output signal;
• applying the processed output signal to a fifth stage arranged for switching with the third stage between the first operating mode and the second operating mode;
• applying the signal output from the fifth stage to a sixth stage,
• passing the signal output from the fifth stage to an output of the sixth stage if a Fast Fourier Transform procedure is performed and swapping the real and imaginary component of the complex signal output from the fifth stage before passing the signal to an output of the sixth stage if an Inverse Fast Fourier Transform is performed to produce an output signal.