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A novel structure of VCO-based quantizer for CT ΣΔ modulator is presented which can significantly improve the VCO linearity. Compared to the traditional methods, the proposed structure uses only one VCO in the system and it also maintains the intrinsic Dynamic Element Matching (DEM) function of the VCO-based quantizer. A first order CT ΣΔ modulator with the proposed quantizer is designed and simulated in a 65nm CMOS process. The DAC of the ΣΔ modulator is optimized, which can also save half of the DAC cells. The performance of the modulator can reach 69/67 dB SNR/SNDR and a dynamic range of 78 dB with a bandwidth of 10MHz at 1V supply voltage.