This paper presents a novel impedance matching approach for passive UHF RFID transponder ICs,which are compatible with the ISO/IEC 18000-6B standard and operate in the 915MHz ISM band. The passive UHF RFID transponder with complex impedances is powered by received RF energy. The approach uses the parasitic inductance of the antenna to implement ASK modulation by adjusting the capacitive reactance of the matching network, which changes with the backscatter circuit. The impedance matching achieves maximum power transfer between the reader, antenna, and transponder. The transponder IC,whose operating distance is more than 4m with the impedance matching approach,is fabricated using a Chartered 0.35μm two-poly four-metal CMOS process that supports Schottky diodes and EEPROM.
