A sigma-delta modulator designed as part of a complete GSM (enhanced data rate for GSM evolution) transceiver is described. High-resolution wide-band analog-to-digital converters enable the receiver to rely on digital processing, rather than analog filtering, to extract the desired signal from blocking channels. High linearity and High SNR are the most stringent requirements for the converters in this wireless application. In this paper a second-order modulator with feed forward structure in order to cover bandwidth correspond to GSM telecommunication standards is designed and simulated. In this modulator, low distortion structure and according to the relevant standard bandwidth is used. In order to provide minimum GSM standard requirement parameters, a second – order modulator is used and by an oversampling rate of 120 and bandwidth of 200 KHZ, SNR, 98 dB and the accuracy of 15.5 bits is achieved. Also its circuit structure by using capacitance switch method with 0.13 micron technology and 1.8 volt power supply has been implemented. پرونده مقاله