ABSTRACT
CONTENTS 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 3.2 Survey on State-of-the-Art RFID Implementations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.3 RFID System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
3.3.1 EM Wave Propagation Basics and Tag Power Consumption . . . . . . . . . . . 62 3.3.2 Fabrication Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.3.3 Air Interface Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.4 Analog Front End and Antenna Design Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.4.1 Antenna Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 3.4.2 RF Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.4.3 Voltage Booster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.4.4 Device Safety Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.4.5 Voltage Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.4.6 ASK Demodulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.4.7 Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 3.4.8 Backscatter Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3.5 Digital Baseband Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 3.5.1 Low-Power Standard-Cell Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 3.5.2 Baseband-Processor Building Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.5.2.1 Solutions for ISO 18000-6B Implementation . . . . . . . . . . . . . . . . 82 3.5.2.2 Solutions for ISO 18000-6C Implementation . . . . . . . . . . . . . . . . 88
3.5.3 Integration with Sensing Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.6 Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Recently radio-frequency identification (RFID) systems have gained popularity in manufacturing units, inventory and logistics, as they represent an inexpensive and reliable solution for automatic identification. Moreover, RFID transponders are expected to become a key element in the ubiquitous computing scenario. Tags will likely be used to collect sensors data, enabling noninvasive environment monitoring. Low-cost passive ultra-high frequency (UHF) transponders are expected to play a major role in this context, due to extended read range capabilities. Within a passive tag, power harvested from the field irradiated by the reader during the communication should operate both digital control circuitry and potential sensing devices. Effective low-power operating strategies are to be implemented, to preserve large communication range and circuit functionalities. In this chapter, the state of the art in transponder design is examined. Insights for the design of a low-power tag, operating in the UHF band, are presented, in compliance with standard protocols (ISO 18000-6B and -6C), to support device interoperability. This chapter is concluded by identifying some open research issues in the realization of high-performance ubiquitous sensing transponders.
