A power efficient 8-bit successive approximation register(SAR) A/D for the vital sign monitoring of a wireless body sensor network(WBSN) is presented.A charge redistribution architecture is employed.The prototype A/D is fabricated in 0.18μm CMOS.The A/D achieves 7.5ENOB with sampling rate varying from 64 kHz to 1.5 MHz. The power consumption varies from 10.8 to 225.7μW.