This paper presents a design of a switched-capacitor discrete time 1st order Delta-Sigma modulator used for a resolution of 8 bits Sigma-Delta analog to digital converter. For lower power consumption, the use of operational transconductance amplifier is necessary in order to provide wide output voltage swing and moderate DC gain. Simulation results showed that with 0.35um CMOS technology, 80 KHz signal bandwidth and oversampling rate of 64, the modulator achieved 49.25 dB Signal to Noise Ratio (SNR) and the power consumption was 5.5 mW under ±1.5V supply voltage .