An LNS-based Low-power/Small-area FFT Processor for OFDM Systems

A low-power/small-area 128-point FFT processor is designed, which is based on logarithmic number system (LNS) and some design techniques to minimize both hardware complexity and arithmetic error. The complex-number multiplications and additions/subtractions for FFT computation are implemented with LNS adders and look-up table (LUT) rather than using conventional two's complement multipliers and adders. Our design reduces the gate counts by 21% and the memory size by 16% when compared to the conventional two's complement implementation. Also, the estimated power consumption is reduced by about 18%. The LNS-based FFT processor synthesized with 0.35 CMOS standard cell library has 39,910 gates and 2,880 bits memory. It can compute a 128-point FIT in 2.13 with 60 MHz@2.5V, and has the average SQNR of 40.7 dB.