Research And Design Of CMOS Sigma-delta Modulator For Audio Code

The Sigma-Delta A/D converter has been widely used in the digital audio signal processing system because of its high accuracy,high linearity,easy integration,low cost and anti aliasing effect.Based on the analysis of the basic theory of Sigma-Delta modulator and compared different modulator structure,the relationship between modulator structure order number,sampling rate,and the SNR was mastered.then preset sigma-delta modulator system index.And using the Simulink tool makes the behavioral simulation of the two order and three order single-loop Sigma-Delta modulator,verifies the feasibility and correctness of the modulator circuit,then a type of audio modulator was designed.The modulator adopts two-order single loop structure,including the switch capacitor integrator,a comparator,a DAC,bandgap,non overlapping clock circuit.in order to improve the stability of power supply circuit module,the way of curvature compensation is used to design the bandgap circuit.The reference circuit based on the exponential characteristic of sub-threshold voltage of MOS transistors to compensate the high order temperature of the emitter voltage of the PNP transistor,and then a reference source of low temperature coefficient is obtained.Based on the SMIC 0.35 um of CMOS technique,the whole circuit is simulated,the simulation results analyzed by spectrum shows that under the condition that the supply voltage is 3.3V,oversampling ratio is 64,the effective number of the Sigma-Delta modulator is more than 12 bits,and the performance of the modulator is up to the design requirements.