A low power and variable-length FFT processor design for flexible MIMO OFDM systems

In this paper, we present a low power and variable-length design of fast Fourier transform (FFT) processor for flexible MIMO-OFDM applications. In this work, mixed-radix-2/4/8 algorithm and new continuous-flow method are applied to achieve variable-length of 1K/2K/4K/8K points and in-order output. Furthermore, ping-pong cache memory architecture and optimized data scaling strategy are also applied to reduce main memory accesses up to 50% and achieve higher SQNR requirements of 16/64-QAM signals for multi-standards. A test chip of the proposed FFT processor has been designed and fabricated using CMOS 0.18 mum 1P6M process with the core area of 4.96 mm². Our proposed processor can perform four independent data sequences of 2048-point FFT within 205.2 mus at operating clock rate of 20 MHz. The power consumption of calculating single 8192-point FFT sequence is only 20.88 mW at operating clock rate of 10 MHz.