Low Power And High Performance Sigma Delta Modulator For Audio Band

Sigma Delta ADC (Analog to Digital converters) consists of Sigma Deltamodulator and decimation filter, Realizing high resolution by adopting oversamplingtechnique、noise shaping and digital filtering technique. In the prerequisite for thehigh accuracy, Sigma Delta modulator require low matching processing device andlow design index of analog circuits, so it is widely used in the field of Digital audiosignal processing.The performance of the Sigma Delta modulator decides the high resolution ofthe whole Sigma Delta ADC. Reducing the noise of signal baseband by adoptingoversampling and noise shaping technology respectively by reducing the noise floorand pushing the quantization noise outside of the signal baseband, to improve theSNR of the Sigma Delta modulator, ensure the acquisition of high resolution.First of all, the paper describes the basic principle of Sigma Delta modulator,comparing and analyzing the advantage and disadvantage of different structures ofSigma Delta modulator. According to the design requirements of system performanceby Richard Schreier Toolbox, complete the design of structure、order、quantizer bitsand oversampling rate, then determine the modulator coefficients based on it.Secondly, by analyzing the non-ideal characteristics of Sigma Delta modulator,carrying through a analysis on the modeling and behavior simulation of three ordersingle loop single bit Sigma Delta modulator by simulink，optimizing the modulatorcoefficients, and the ideal and non ideal conditions are analyzed in the frequencydomain，the SNR are107dB and96dB, meet the performance index. Finally, basedon the Simulink non ideality modeling, acquire the requirements of analog circuits,complete the design of SC integrators、non overlapping clock circuit、 high speeddynamic latch comparator and bandgap circuits, simulate the whole system in the timedomain by Spectre，consistent with the behavioral level simulation waveform.The design for the audio input signal between20Hz and24KHz, adopting thestructure of Cascade of integrators feedback form which uses128oversampling rate，perform the frequency domain analysis from the time domain out of Spectre under theclock of6.144MHz, SNR achieves91.3dB,14.87bits high resolution and Spuriousfree dynamic range is92dB. The modulator is implemented in CSMC0.35μmstandard process，the capacitor is implemented by MIM structure of0.2pf as unit.Complete the layout design of the modulator，the whole area is1120μm*1120μm. Under the supply voltage of3.3V, the power dissipation is7.5mw, achieves the FOMis0.93for high resolution，low power Sigma Delta modulator.