Design of a Noise Transfer Function for Single-loop 4th-order Sigma Delta Modulators

In order to solve high-order single-loop structure Sigma Delta modulator SNR contradiction with input dynamic range, Butterworth filter and the Chebyshev type Ⅱ filter are used to dedign a Noise Transfer Function for single-loop 4th-order Sigma Delta Modulators, so that to obtain a higher signal to noise ratio of the system also has a good input dynamic range. The simulation results show that the system has reached the peak signal to noise ratio 131.9dB. While the noise transfer function parameters are mapped into the model parameters of FFFB structure, and normalized amplitude of -3dB input was selected for simulink simulation.We got 128.7dB of SNR from the simultation, which indicated that the dynamic range of the system is of good performace. The method mentioned in this breif can also be extended to higher order, multi-bit quantizer and other oversampling rate Sigma Delta modulator design.