Research And Design Of Low Speed And High Precision Sigma-Delta Modulator

With the rapid development of science and technology,digital signal processing technology is becoming more and more mature.The accuracy of the analog-to-digital converter becomes a bottleneck in signal processing.Sigma-Delta ADC is an ADC that has received more and more attention in the high-precision field.As the core part of Sigma-Delta ADC,SigmaDelta modulator determines the accuracy,power consumption and other performance of ADC to a large extent.It is widely used in high-precision sensors,precise instruments,high-quality audio and other fields because it can achieve high accuracy that other ADCs cannot achieve.This paper has carried on the research and the design corresponding to the high-precision modulator used in the low frequency domain.Through the study of the principle and structure of the modulator,a fourth-order single-loop topology structure combining feedforward and feedback is designed;the transfer function is derived for the structure,the coefficients of the linear model are calculated.The Sigma-Delta modulator was modeled and simulated using MATLAB Simulink tool;simulation considers possible non-ideal factors in actual circuit design,and provides logical support and theoretical guidance for subsequent circuit design;simulation results show that the input signal bandwidth is 1k Hz and the oversampling rate is512.Under this condition,the signal-to-noise distortion ratio reached 119.5d B.Based on the results of Simulink modeling,a 0.25?m standard CMOS process was used on the Candence IC design platform to design the circuit level of the modulator and complete the layout drawing.The overall circuit adopts a fully differential structure,which effectively reduces even harmonics and common mode noise;the first-stage integrator uses chopping modulation technology to reduce low-frequency noise;The circuit design of switch capacitor integrator,clock generating circuit and comparator is completed;The simulation results show that when the sampling frequency is 1MHz,the input sine wave amplitude is 1V,and the frequency is 793 Hz,the signal-to-noise ratio of the modulator reaches 104.2d B,and the corresponding effective number of bits is 17.01 bits,which meets the expected high precision requirements.