A 256-point Analog Discrete-Time FFT

In support of future multi-carrier waveforms, this paper presents the design and simulation of a differential complex-valued 256-point analog discrete-time Fast Fourier Transform (FFT). A four-stage radix-4 decimation-in-time architecture was used, allowing the structure to be scaled to FFT sizes with thousands of points. Being high speed and having a large bin count makes this FFT a practical front end receiver component for waveforms that rely on the FFT, such as Orthogonal Frequency Division Multiplexing (OFDM) and future 5G waveforms like cyclic prefix OFDM (CP-OFDM). The FFT architecture was simulated using IBM's 32nm Silicon-on-Insulator (SOI) process, and the results are compared to other published analog discrete-time FFTs.