Abstract: A Sigma-Delta modulator applied in the audio and sensor is proposed in this paper.The proposed modulator is implemented in the single loop forth order one bit CRFF structure.A fully differential switch capacitor circuit is used to reduce the even order distortions and the noises from substrate and power,and chopping is applied to reduce the offset and the 1/f noise,to improved the precision and reduce the power consumption.The whole circuit is based on the Global foundries 0.18 μm CMOS technology with a supply voltage of 1.8 V,an OSR of 128,and a sampling frequency of 5.12 MHz.Simulation results show that SNR of the modulator can reach 100.2 dB,while the power dissipation is merely 380 μW.

Key words: audio;sensor;Sigma-Delta modulator;oversampling