Abstract: A second-order low-power Sigma-Delta modulator used in the temperature compensated crystal oscillator (TCXO) has been designed using CSMC 0.35 μm mixed process.To reduce the effects of 1/f noise in low-frequency temperature signal bandwidth and the offset on the accuracy of the modulator, the chopper technique was applied to move the 1/f noise and offset out of the useful signal bandwidth.Simulation results using Cadence Spectre and Matlab indicate that the modulator achieves an SNR of 93.6 dB, an accuracy of 15.26 bits, and a static power dissipation of less than 80 μW under 3 V supply, meeting the low-power and 14-bit accuracy requirements of the TCXO system to the modulator.