A 700-nA voltage regulator, consisting of a self-biased mutuallycompensated voltage reference, a low dropout(LDO) voltage regulation circuit and a power-on-reset (POR) circuit, has been applied to a passive UHF RFID tag IC and fabricated in a commercial 0.18?µm CMOS technology. The temperature coefficients of the voltage reference and the output voltage are only 9 and 43?ppm/?C, respectively. A POR signal with 150-ns-width pulse is also generated for the digital processing part in the tag IC.