Area efficient floating-point FFT butterfly architectures based on multi-operand adders

Hardware implementation of the fast Fourier transform (FFT) function consists of multiple consecutive arithmetic operations over complex numbers. Applying floating-point arithmetic to FFT coprocessors leads to a wider dynamic range and allows the coprocessor to collaborate with general purpose processors via the standard floating-point arithmetic. This offloads compute-intensive tasks from the primary processor and overcomes floating-point concerns such as scaling and overflow/underflow detection. The downside, however, is that floating-point units are slower than the fixed-point counterparts. One of the popular ways to improve the speed of floating-point FFT units is to merge the arithmetic operations inside the butterfly units of a FFT architecture. This leads to a butterfly architecture based on multi-operand adders. Butterfly units are designed, in two of the most recent works, using three-operand and four-operand adders. However, the work reported here by the present authors goes further and a butterfly architecture based on a five-operand adder is proposed. Simulation results demonstrate that the proposed butterfly architecture is 50% smaller than the fastest previous work with about 17% latency overhead. Compared with the smallest previous work, the proposed design is 47% smaller and 8% faster.