In this paper, power optimization of two high performance ΔΣ modulators for portable measurement applications is presented. One modulator is a single-loop single-bit topology which achieves an 89.8dB peak SNDR and consumes 20μW with a 1.5V supply. Here, a new power efficient current mirror Class-AB OTA is introduced to reduce the power. The other modulator adopts both multi-bit technique and switched-opamp (SO) technique to realize the ultra-low power target. Its total power consumption is only 9μW at a 1.8V supply, and the peak SNDR reaches 80.5dB. Especially, a new fully-clocked SO is proposed in this modulator to achieve a 50% power saving and double Figure-of-Merit (FOM) over the traditional type. Besides, to realize a zero-optimization coefficient of 1/100 and improve the performance, a novel resonator idea applicable to SO technique is adopted with 75% power and 70% area reduction. Both modulators are fabricated in a low cost 0.35μm CMOS process with a bandwidth of 1 kHz. The measured results show high FOM of the designed modulators.