A comparator speed enhancement technique for SAR ADC under near- and sub-threshold supply voltages has been introduced in this work. The proposed delayed cross-coupling comparator improves the comparator speed without degrading the noise performance. After post-layout simulation, the SAR ADC using this comparator technique has achieved 0.35V 8bit 12MS/s performance indicators in 65nm CMOS technology. The simulation results prove that the proposed delayed cross-coupling comparator effectively improves the speed in Near- and Sub-Threshold ADCs.