NARROW-BAND FIR FILTERING WITH FPGAS USING SIGMA-DELTA MODULATION ENCODING

This paper addresses the problem of implementing narrow-band FIR filte rs using FPGAs. Rather than employing a conventional multiply-accumula te unit to compute the inner-product, an alternative method based on r e-quantization of the input data stream using a sigma-delta modulator is presented. The re-quantization process preserves the dynamic range of the signal components contained in the bandwidth of the filter, whi le shifting the re-quantization noise to the spectral region to be rej ected by the filter. The reduced bit length representation of the re-q uantized input data samples removes the requirement for a full multipl ier in the filter hardware. This makes the method very attractive for realization using FPGA technology. The filtering technique is describe d and implementation results using a Xilinx XC4010FPGA are presented. A 200-tap filter implemented in a single FPGA achieves a computation r ate of 415 MOPS and has a memory bandwidth of 1.66 Gbytes/s. An extens ion of the method using a quadrature re-quantizer and filter is also p resented.