This paper presents in details the architecture and most of RF front-end building blocks of a fully integrated passive radio frequency identification (RFID) transponder operating at UHF 902MHz to 928MHz. A novel architecture for the transponder IC and a new low power on-off keying (OOK) demodulator are proposed in this paper. For realizing the system, a low power CMOS full-wave rectifier achieving a power conversion efficiency of 31.9% has been integrated in this transponder. Simulation results show that the global input power of front-end circuits is only about 21μ in order to drive a load of 1.8μA at the rectifier output and the power consumption of the proposed demodulator is less than 0.4μ. The transponder is fabricated in a 0.18μm mixed-mode CMOS technology and has the area of 0.70 mm2.