Research And Design Of A16Bit Sigma-delta Modulator

ADC is a bridge to connect the analog world and digital world. It can convertanalog signals into digital signals, convenient for data storage, processing andtransmission. With the rapid development of electronics industry, the application ofADC is also very extensive. Sigma-Delta ADC is one of the many ADCs. Its principleand structure make its high-precision and low power consumption. It has a veryimportant position in the ADC market. Sigma-Delta ADC has two parts, analogmodulator and digital filter. The performance of the modulator determines theperformance of the Sigma-Delta ADC, so its design is crucial. In recent years,Sigma-Delta ADC’s development has been more and more mature. It has become apopular product for domestic and foreign componys to research and develop. How touse a simple structure to achieve high accuracy becomes the goal pursued by all.This article analyzed the principle of Sigma-Delta modulator in-depth, studied thetwo technical features of over-sampling and noise shaping. Over-sampling is tosample the analog signal with the frequency much higher than the Nyquist frequency,then into the quantizer. Over-sampling technique can reduce the noise in the signalband, and the noise spectrum can distribute much wider in the frequency domain. Thecircuit design requirements is relatively simple. In order to reduce the over-samplingratio, Sigma-Delta modulator also uses a feedback network. It has a unique noiseshaping technology. Quantization noise is shaped by a high pass filter, the remainingnoise in the signal band is very little. Even using1bit quantizer can achieve a highsignal to noise ratio with higher accuracy.The article also discussed the impact of non-ideal factors and noise in the circuitdesign, and listsed the theoretical formula in detail. It played a guiding role in theactual circuit design. This article accordanced strictly with the process of analog ICdesign. First, I determined the structure of the modulator by simulink modeling.Generally, Sigma-Delta modulator has two kinds of structure, single-loop and mash. One order and two orders single-loop modulator don’t have stability problems, butthree or high orders have this difficulty. Mash structure modulator can achieve highaccuracy, but it will involve a more complex nonlinear problems. This article hopes toadopt a relatively simple structure to achieve excellent performance goals. I choosetwo orders single-loop structure. Through PSD simulation, the results can get thedesired goals, and determine the overall parameters of the modulator.In the circuit design, the article analyzed the performance indicators of eachmodule in detail, and considered noise and nonlinear impact to the modulatoraccuracy. Finally determined the circuit structure of each module. For the importantmodule, such as amplifiers and switched-capacitor integrators, analyzed theadvantages and disadvantages of the various structures in detail. Be careful in theselection of the MOS transistor dimensions and capacitor size to ensure that eachmodule can achieve the desired requirements firstly. In the connection of the wholecircuit, paid attention to the control of the circuit timing, must be very clear to workstatus of each tense of the circuit. Through repeated simulation, the final digital signaloutput of the modulator is extracted, the matlab analysis and calculation results canachieve the desired goal. In order to ensure good performance, also analyzed themodulator in each corner. The results show that the modulator is stable. Thismodulator’s ENOB is16Bit, SNDR is100dB by charter0.35μm technology, and itspower consumption is below16mW. On this basis, the layout design, uses2P4Mprocess. The chip area is400μm×490μm. This Sigma-Delta modulator’s structure issimple. It has high effective accuracy and large dynamic range, the chip area is small.It has practical significance.