Research And Design Of Second-order Sigma-Delta Modulator

Conventional Nyquist Analog-to-digital converters require precise analog circuits.In contrast,oversampling converters use oversampling technique,make the quantization noise power small in baseband(especially when F_S is much larger than F_B),increase the SNR in baseband and achieve the more ENOB.It can be implemented using simple and high-tolerance analog circuits.Moreover,sampling at high frequency eliminates the need for abrupt cut-off anti-aliasing filter.In addition to the oversampling,noise shaping technique is used in sigma-delta ADC to increase the SNR further.In sigma-delta ADC,the analog signal conversion can be implemented using simple and high-tolerance analog circuits,such as swith-capacitor integrator,one-bit comparator,and having a precision that is usually less than the resolution of the conventional converter.The digital signal conversion circuit can be implemented using digital filter.With the advanced VLSI and CMOS technique,sigma-delta ADC have been widely used for high resolution Analog-to-digital converters.In this thesis,according to the study and understanding to the principle of oversampling sigma-delta modulator,a design flow from system to circuits were described,including the considering the influence of different non-ideal factors and selecting the system parameter.In the circuits design flow,after calculating,simulation and analysis, circuits design of fully differential OP,comparator, two phase clock generator and bandgap voltage reference circuits in sigma-delta modulator were completed with system parameter and CSMS 0.6um DMDP spice model.And implemented a 16-bit second-order sigma-delta modulator with 256KHz samplig clock,256 OSR, 500Hz bandwidth and 99.3dB SNDR.