Design Of 14-bit Single-loop Sigma-delta Modulator

With the continuous development of digital communication technology and wireless sensor network,people are demanding more and more on analog-to-digital converters.High-speed,high-precision and low power consumption have become the important research trends in the field of data converters.In all types of ADC architectures,sigma-delta ADC achieves high accuracy with a trade-off of speed accuracy and noise shaping.The sigma-delta ADC is almost synonymous with the high-precision ADC.Discrete-Time sigma-delta modulators provide a good trade-off between speed,accuracy bandwidth,and power consumption,in addition to their insensitivity to matching of analog devices.So that it gets favor of many ADC developers in the field of audio application and in recent years has ushered in biological and industrial field.In this paper,a modulator part of a high-precision ADC for audio signal,biological signal and industrial signal sensor is studied and designed.The baseband frequency is 200 kHz and the precision is 14 bits.In this paper,the current research situation of analog-to-digital converter is introduced firstly,then the basic principle of ADC and the main performance index of sigma-delta ADC are introduced,and the four kinds of sigma-delta modulator are analyzed and compared.On this basis,the structure adopted in this design--second order single loop structure was determined.The second-order sigma-delta modulator is then modeled using the Matlab/Simulink tool,taking into account the main non-ideal factors such as clock jitter,switching thermal noise,op amp nonlinearities,etc.As a system-level,the feasibility of the system and the correctness of the model are verified.On the basis of behavioral modeling,in order to make the model and circuit design converge better and save the simulation time,this design also uses Verilog-A to model each module,and the simulation result is easy to carry out and the circuit design result to be compared.The design of the ADC circuit is simulated by TSMC 0.18?m process,the transistor-level circuit design of the modulator is presented,including two-phase non-overlapping clock,bootstrap switch,two-stage operational amplifier,switched capacitor integrator,comparator and feedback DAC,etc.Complete the layout design and post-simulation.The simulation results show that the second-order modulator can achieve the accuracy of 13.72 bit under the sinusoidal input signal of 1 V and 115.967 kHz,lack of accuracy compared to 14-bit precision index.Finally,based on the requirements of 14 bit precision index,the circuit is improved,the third-order sigma-delta modulator is designed and the behavior level simulation,circuit design and pre-simulation are completed.The results of the previous simulation show that the third-order modulator achieves 15.8 bits when the other main indicators are satisfied,under the sinusoidal input signal of 1 V and 115.967 kHz,leaving enough margin for the final 14-bit requirement.