A novel CMOS temperature sensor embedded in apassive UHF RFID tag is presented. The sensor consistsof a temperature-to-current converter, twocurrent-starved ring oscillators and two digital counters.High power consumption band-gap voltage referencesand traditional ADCs are not used for low power design.Post-layout simulation show that the power consumptionis 0.64uW with a supply voltage of 0.8V at roomtemperature (27°C􀀀), and the conversion rate is up to 1kHz. The average temperature resolution is 0.2°C􀀀/LSBfrom -40°C􀀀~120°C􀀀. The sensor is implemented in CMOS0.18um and the core occupies an area of 0.09 mm2.