A novel digital baseband processor of an UHF RFID tag was presented based on the ISO/IEC18000-6 type C standard. In order to enhance the signal-noise ratio in the return link , spread spectrum technique was used in addition to the FM0 encoding/Miller subcarrier modulation. The tag supports all the 11 mandatory commands required by the 6C standard as well as the implementation of probabilistic/ slotted anti-collision scheme and read/write operation to EEPROM. Low power techniques were adopted to reduce the instantaneous power and average power. The chip was designed and fabricated using 0.18μm 6 metal layersCMOS technology. From the measurement result , the overall power consumption is about 16μW at the minimum voltage of 1.04 V , and the chip area is of 0.5 mm2.