Design Of Discrete Time Sigma Delta Modulator

Because of the performance of laser in the optical communication changed with temperature,Analog to Digital Converter of high resolution is needed to monitor the temperature of laser constantly.?? ADC has adopted the technology of oversampling,noise modulation and down-sampling digital decimation filtering,so it can realize analog to digital conversion of high resolution.Besides,?? ADC is an ADC of easy-integrated,superior overall performance and a low requirement for analog device matching,thus ?? ADC has been developing rapidly in recent years.Based on the requirement of laser monitoring system for ADC's high resolution,a 14bits Discrete Time?? modulator is designed in this thesis.Firstly,the principle of Discrete Time ?? Modulator is analyzed deeply.And first order,second order and even more order ?? Modulator is researched.According to the requirement of performance index,a third order and one bit Discrete Time ?? Modulator with CIFF(Cascade-of-Intergrators FeedForward)is designed.The tools of Toolbox is utilized to set up behavioral modeling for Discrete Time EA Modulator by the software of Simulink.And some non-idealities including clock jitter,sampling-switch noise,and input equivalent noise,limited-gain,limited-bandwidth,slew rate of the operational amplifier are analyzed and simulated by Simulink so that the general scope of operational amplifier's limited-gain,limited-bandwidth and slew rate can be ensured.The circuits are designed with TSMC 0.18?m CMOS process in the software of Spectre after the behavioral modeling is well designed and simulated.Switched capacitor integrator is applied in this paper which meets the requirement of Discrete Time ?? Modulator.One bit is adopted on quantizer Because of natural linearity.The result of the simulation shows that the design satisfies the requirement and the system works well.At last,the layout of Discrete Time ?? Modulator are designed in TSMC 0.18?m CMOS process.The area of layout is 680×445?m2.The power supply is 3.3V,and the clock frequency is 2MHz.With a 3.66211kHz,1.1 V input signal,the simulation results show that ENOB is 15.66 bits.The power of the whole modulator is 1.8mW,and all of the design specifications are fully met.