HF/UHF dual band RFID transponders for an information-driven public transportation system

Abstract

The limited communication range of HF radio frequency identification (RFID) smart cards does not allow to automatically assess the alighting point of passengers on public transportation. This work considers HF/UHF dual band RFID transponders for electronic ticketing in an information-driven public transportation system. The UHF RFID interface is intended to enable a remote detection of passengers inside a vehicle and thus to assess the alighting point of passengers. A review of the specific operating conditions for the UHF RFID link is given and associated privacy issues are addressed. We introduce a low-complexity approach to safeguard the privacy of passengers. Following a discussion of the architecture of appropriate HF/UHF dual band transponder ICs, the focus is set on questions of the circuit implementation. With regard to the progressing CMOS technology scaling, we can observe potential risks of overvoltage stress for the UHF RFID front-end at high input powers. Two RF voltage limiters that prevent overvoltages are presented. Experimental results of circuit prototypes in a 40 nm CMOS technology demonstrate the functionality of two UHF RFID front-ends that incorporate the RF voltage limiters.