SAW and CMOS RFID transponder-based wireless systems and their applications

Today, there exists a huge market pull towards radio frequency identification (RFID) and/or wireless sensing for high-volume applications as well as for professional applications based on the use of passive, i.e. batteryless, low-cost transponders (tags, labels). In order to arrive at smaller transponder dimensions, higher transceiver-to-transponder interdistances, and more flexible, i.e. application-dependent antenna designs, higher than LF/HF-carrier frequencies are required. Two of the most interesting key technologies for these mass-market applications are, respectivly, the SAW technology and the CMOS technology both of which being able to provide single-chip passive transponders. CMOS has taken the lead in the high-volume markets. Here, the development trends for RFID transponders go towards bi-or even triple-frequent operation at the 13 MHz, 900 MHz, and 2.4 GHz bands, and towards the integration of sensor and energy harvesting functionalities. SAW RFID techniques are going to find their markets in lower volume, professional application markets. SAW RFID transponders are radiation hard, and they can operate in harsh environments and at temperatures higher than 400 °C. The present work explains the system architectures of passive RFID sensing systems and reviews the state-of-the-art of SAW transponders as well as of CMOS transponders for such applications. Furthermore the advantages and shortcomings of both SAW and passive CMOS transponders, as well as future trends will be discussed.