The Design Of Sigma-Delta Modulator Based On Audio Application

For audio ADC, a16bit, high speed, high-precision consumption sigma-deltamodulator is designed in this paper. Compared with the Nyquist frequency ADC,lower precision of analog component and matching property is required in sigma-delta ADC. Therefore, the sigma-delta ADC has a lot of advantages in accuracy andimplementation. The development status quo and the theory of sigma-delta ADC areintroduced in detail in this article, and a full differential structure of sigma-deltaADC is presented. After analysis, the feedforward structure is employed in thissigma-delta ADC due to its low requirement of output swing of the integrator, whichreduces the complexity of the op-amp and the harmonic distortion of the filter.The full differential sigma-delta modulator mainly includes high-speedsumming circuit, high-speed comparator,1bit quantizer and digital-to-analogconverter (DAC) feedback loop. In this paper, the complete design procedure ofsigma-delta modulator is presented. First of all, the behavioral modeling of Sigma-Delta is established. The influences of KT/C noise, clock jitter noise and the op-amp’s inherent non-ideal factors are analyzed. The integrator output swing and theoptimal coefficients are obtained by simulation; hence, the whole design time isreduced. Secondly, the design of circuit level of Sigma-Delta modulator is completedbased on the module of behavior level，wherein the key part is the design ofintegrator and the op-amplifier. Due to high requirement of the integrator at inputterminal, the design of sigma-delta modulator must be strictly followed the results ofbehavior to prevent oscillations or output overload which appear in integrator.However, the performance requirement of other integrators which located inmodulator loop is lower. Finally, based on the circuit design in0.5μm CMOSprocess, the layout of sigma-delta modulator is drawn with Virtuso and verified byCalibre，and DFT is also done by Matlab.The sampling frequency of sigma-delta modulator is10.24MHz; OSR is256 within the20KHz signal bandwidth. The maximum SNR of Sigma-Delta modulator103.5dB is obtained by the simulation of modulator circuit by Spectre, under the0.5um CMOS process. And the accuracy of Sigma-Delta modulator is reached to16bit. The design of modulator which has high performance and high resolution isrealized, so it meets the expectant design requirements.