The Design Of Sigma-Delta Modulator Based On Mash Structure

With the development of electronic technology, analog to digital converterincreasingly requires high precision in the field of communications and other audiofield, the conventional Nyquist analog to digital converters has been unable to meetthe requirement of high precision of the analog to digital converter, so thedevelopment of high resolution arouses great concern.Sigma-Delta analog to digital converter in the resolution and circuitimplementation are excellent against traditional Nyquist ADC, because Sigma-Deltaanalog to digital converter has two advanced technology, one is the oversamplingtechnology and another is noise shaping technology. These two techniques can notonly be compatible with modern CMOS technology, but also reduce the complexityof analog circuits in high resolution ADC design. The method of speed to accuracyimproves the signal to noise ratio and reduces the noise inside the modulator.Therefore in the audio, electronic measurement and voice communication, Sigma-Delta analog to digital converter can be widely applied.This paper researched the principle of Sigma-Delta modulator and analysisedthe nonideal factors (MOS nonlinearity, clock jitter, switched capacitor noise andcomponent mismatch) that affect the performance of modulator. It accomplishedbehavioral modeling of Sigma-Delta modulator with fourth-order cascade structureand designed integrator module, clock module, quantizer module and digital offsetmodule of behavioral model. This paper designed the circuit of Sigma-Deltamodulator with fourth-order cascade structure when simulation of behavioral scalemeets the design requirement. The circuit of MASH structure is simulated by use of0.5μm CMOS process in the conditions that the rate is256,the frequency of input signal is20KHz and supply voltage is5V. Finally, it got SNRfor103.5dB and resolution for16bits, which meets the design objectives.