Research And Design Of Continuous Time Sigma Delta Modulator For Wireless Communication

The signals that can be captured by people in nature are all analog signals,while the signals that computers can process are all digital signals.As a bridge connecting the analog and digital worlds,analog-to-digital converters(ADCs)have always been a hot research topic in academic and industrial institutions at home and abroad.With the country’s emphasis on the microelectronics industry,the speed of the rise of wireless communication technology and chip technology can be described as rapid progress.The internal receiver systems in the field of wireless communication also require increasingly high performance indicators for ADC,and the high-precision and broadband continuous time Sigma Delta ADC perfectly meets the requirements of wireless communication.Therefore,designing a continuous time Sigma Delta ADC that combines accuracy and bandwidth is of great significance.The traditional continuous time Sigma Delta ADC has always been known for its wide bandwidth.Compared to the discrete time Sigma Delta ADC,it has a slight disadvantage in accuracy.This article addresses this issue and improves its accuracy,making it have a broader application prospect in the field of wireless communication.The main work and innovations of this article are as follows:(1)Study several common modulator architectures and compare their advantages and disadvantages,design the single loop feedback architecture used in this article,and then conduct theoretical analysis to design its parameters.Finally,through Matlab Simulink modeling and simulation verification,obtain the specific coefficients of the system function H(s)to guide the transistor level circuit design in the subsequent text.(2)We have studied and designed a single loop third-order feedback continuous time Sigma Delta modulator.This article mainly starts with improving its signal-to-noise ratio(SNR)by bridging feedback resistors between the subsequent two integrators,which can move the DC zero of the system’s noise transfer function(NTF)away,thereby significantly improving its signal-to-noise ratio(SNR)and improving the modulator accuracy;Simultaneously,a dynamic latch comparator is used as the quantizer,effectively reducing the static power consumption of the circuit.In addition,a bandgap reference voltage source was studied and improved.This article aims to reduce its temperature drift and improve its power suppression ratio,using NMOS transistor subthreshold current to compensate for the higher-order term of the transistor VBE to reduce the temperature coefficient;At the same time,a pre stabilized circuit is added to power the reference source circuit,effectively improving the power suppression ratio.(3)Based on the SMIC 180 nm CMOS process environment,the layout design of the Sigma Delta modulator and bandgap reference voltage source designed in this paper was carried out and simulated using Cadence Spectre software.The results show that under the input signal bandwidth of 2MHz and power supply voltage of 1.8V,the modulator has 13.6effective bits and a power consumption of approximately 4.1m W;The bandgap reference voltage source has a temperature drift of 3.05ppm/℃ within the range of-40～140 ℃,and a power suppression ratio of-105 d B within 1k Hz.