The development of very large scale integrated circuit (VLSI) process technology has resulted in more and more integrated circuits with mixed analog/digital circuitry. The technological improvements in digital VLSI circuits make it important to reduce the cost of the analog to digital (A/D) converter, which is the main part in the analog circuits. The oversampling sigma delta (ΣΔ) A/D converter is a high-resolution and low-cost A/D converter. Oversampling and noise shaping can improve the signal-to-noise ratio (SNR) in baseband to provide high resolution. The characteristics of theΣΔ modulator with different structures were analyzed to develop high performance A/D. Simulation results were obtained using MATLAB and Pspice, and several modulator circuits with switched-capacitor were designed. The oversampling A/D converters are suitable for high-resolution and low bandwidth signal processing, such as the processing of voice and video information.