A calculating approach of sigma delta modulator with AC input

Conventional sigma delta A/D convertor was composed of sigma delta modulator and digital decimation filter. By anti-aliasing filter and sampling-holder circuit, the AC analog signal functioned as DC signal to guarantee the steady conversion precision. Based on the characters of sigma delta modulator, A/D conversion can be finished by only sigma delta modulator without any other accessory circuit. Considering the calculating data is a limit long in a practical application, the analog signal were obtained by calculating the output data stream of sigma delta modulator. Furthermore, the processing will be simpler to approximate the difference every two adjacent sampling point as same. The calculating approach decreased the error which brought by the anti-aliasing filter, sampling-holder and digital decimation filter. By omitting these accessories, the circuit is simply and easy be used in a practical application. A good result was given by data analysis for the processing method