High-Precision Audio Sigma-Delta D/A Converter Chip Design Research

DAC(Digital to Analog Convert,digital-to-analog converter)is an important part of the digital-analog mixing part,and has important applications in the field of digital audio.With the rapid development of audio technology,the accuracy requirements for DACs are getting higher and higher.Sigma-Delta oversampling digital-to-analog converter can realize higherprecision digital-to-analog conversion,so it has been more and more widely used.SigmaDelta DAC makes full use of digital signal processing technology,and implements the modulator and interpolation filter in the digital part,and its sampling frequency is much higher than the traditional Nyquist frequency.This article first describes its working principle from the perspective of digital-to-analog converter,and then analyzes the working principle of Sigma-Delta DAC in depth.The overall system is mainly composed of three modules: interpolation filtering,Sigma-Delta digital modulator and analog reconstruction stage.Among them,the interpolation filter adopts a four-stage cascaded structure,which is composed of two-stage half-band filters,CIC compensation filters and CIC filters,which achieves an oversampling rate of 128 times.Based on the analysis of the traditional half-band filter structure,the folding structure and tap coefficient CSD coding technology are adopted to greatly reduce the power consumption and hardware circuit consumption.In order to realize the high-precision digital bit stream output of the digital part,a multi-bit quantized cascade structure Sigma-Delta digital modulator is adopted.Each stage adopts an error feedback structure to achieve highprecision output by multi-stage cascade.Effectively reduce the complexity of the circuit.Considering that multi-bit quantization will bring about non-linear problems,a dynamic matching unit module is also designed,using DWA(Digital Weighted Average)technology to convert the mismatched noise of the modulator’s multi-bit output into white noise for lowpass filtering.The overall signal-to-noise ratio of the digital module has reached 131.2d B,and the effective number of bits is 21.5.The reconstruction filter is mainly composed of a switched-capacitor digital-to-analog converter and a low-pass filter.In the realization of the circuit structure of Sigma-Delta DAC,it is mainly optimized.The first is to optimize the structure of the interpolation filter,the power consumption is reduced by putting the interpolation stage after filter.In terms of the hardware structure of the SigmaDelta modulator,a 4-stage 4-bit quantized MASH structure is adopted,and each stage adopts an error feedback structure,and the multiplication operation is implemented by shifting.The quantizer of each stage are all realized by truncation,which can effectively reduce the area of the circuit.When the DWA algorithm circuit is realized,the 4-bit output of the modulator is converted into a thermometer code,which is realized by a cyclic shift.An improved switched capacitor DAC structure is used in the analog reconstruction section,which can effectively reduce the impact of reference source noise on the overall performance.The lowpass filter uses the second-order Chebyshev Sallen-Key structure to filter out high-frequency noise.This article carried out the modeling and circuit realization of the digital part and the analog part of the cascaded Sigma-Delta DAC.The system performance and feasibility are analyzed by Matlab modeling.The circuit functions are verified by Verilog simulation.