Design and Implementation of Decimation Filter for 13-bit Sigma-Delta ADC Based on FPGA


A 13 bit Sigma-Delta ADC for a signal band of 40K Hz is designed in MATLAB Simulink and then implemented using Xilinx system generator tool. The first order Sigma-Delta modulator is designed to work at a signal band of 40 KHz at an oversampling ratio (OSR) of 256 with a sampling frequency of 20.48 MHz. The proposed decimation filter design is consists of a second order Cascaded Integrator Comb filter (CIC) followed by two finite impulse response (FIR) filters. This architecture reduces the need for multiplication which is need very large area. This architecture implements a decimation ratio of 256 and allows a maximum resolution of 13 bits in the output of the filter. The decimation filter was designed and tested in Xilinx system generator tool which reduces the design cycle by directly generating efficient VHDL code. The results obtained show that the overall Sigma-Delta ADC is able to achieve an ENOB (Effective Number Of Bit) of 13.71 bits and SNR of 84.3 dB.