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

Analog to Digital Converter(ADC)is a bridge between the analog world and the virtual digital world.With the continuous development of Internet of Things technology,how to achieve higher accuracy has become the core issue of ADC design.Sigma-Delta ADC is the preferred solution for high-precision ADCs,and Sigma-Delta modulator is the core module.This thesis aims to design a high-precision Sigma-Delta modulator with more than 18 bits in the 1 KHz bandwidth range,which can be applied to a variety of high-precision signal transmission scenarios.By analyzing the basic principles and main categories of Sigma-Delta modulators,combined with the expected indicators of this thesis,the fourth-order feedforward single-bit quantization structure is selected as the topology of the high-precision Sigma-Delta modulator in this paper.After that,the behavioral model of the modulator is established by MATLAB Simulink software,and various non-ideal factors that may occur in the circuit design of the modulator are analyzed.Finally,through behavioral simulation,the Signal to Noise Distortion Ratio(SNDR)of the non-ideal model of the high-precision Sigma-Delta modulator in this paper reaches 126.2 d B,and the effective number of bits reaches 20.67 bits.Under the SMIC 130 nm CMOS process,the circuit-level design of each module and the entire high-precision Sigma-Delta modulator system is completed in Cadence software with a 3.3 V power supply voltage.The modulator layout is drawn and post-simulated.In the circuit,the charge injection and clock feedthrough of the switch are reduced by the lower plate sampling technology.The chopper operational amplifier is analyzed and designed to reduce the influence of offset and flicker noise on the accuracy of the modulator.At the same time,a separate common mode level generation circuit is proposed to prevent the modulator system distortion caused by the fluctuation of the external power supply voltage.The matching degree is increased by symmetrical layout and unit component cascade on the layout to reduce the mismatch on the circuit.The simulation results show that under the input signal amplitude of 1.5 V and 1 KHz bandwidth,the typical SNDR of the modulator under different PVT reaches 119.4 d B,the effective number of bits reaches 19.54 bits,and the typical offset voltage is 2.5μV.The overall power consumption of the modulator is 1.68 m W,and the layout area is 0.72 mm~2.The modulator can work normally in the range of 10%power supply voltage fluctuation and-40～105°C external temperature variation.Compared with the related papers published in recent years,the high-precision Sigma-Delta modulator in this thesis has reached a high level in accuracy and comprehensiveness.