IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS, VOL. 17, NO. 12, DECEMBER 2009 1719 Improved Pervasive Sensing With RFID: An Ultra-Low Power Baseband Processor for UHF Tags Andrea Ricci, Member, IEEE, Matteo Grisanti, Ilaria De Munari, and Paolo Ciampolini Abstract—Recently, radio frequency identification (RFID) sys- tems 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 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. Exploiting ultra-low power tag circuitry would provide sensing sections with higher energy, thus improving measurement performance. In this paper, the design of a novel circuit is presented, which implements the baseband processor of a UHF-RFID tag in compliance with the ISO 18000-6B protocol. Regardless of protocol selection issues, several power saving strategies are devised, both at the system and circuit levels, suitable for passive transponder implementation. Near-threshold operation has been exploited to attain ultra-low power consumption while keeping fair performance. A set of standard cells has been designed, suitable for the power-limited specific application. The proposed solution has been successfully checked by means of a physical implementation on CMOS 0.18 m technology. Test chips have been characterized in terms of voltage and frequency operating range and power consumption figure has been extensively analyzed. Measurement results fully support the selected design approach: the baseband processor dissipates only 440 nW average power when operated at 800 kHz and 0.6 V. This extremely-low power consumption enables high-performance ubiquitous computing. Index Terms—Baseband processor, ISO 18000-6B, low-power design, passive tag, radio frequency identification (RFID), stan- dard cell, ultra-low voltage, VLSI digital systems. I. INTRODUCTION R ADIO FREQUENCY identification (RFID) systems are gaining increasing popularity in several fields (manufacturing, logistics, transportation, etc.) where unique identification and tracking of items is a major concern. RFID tags represent a cost-effective solution for many problems in the full automation of supply chains and are candidate to the Manuscript received June 17, 2008; revised August 23, 2008. First published March 24, 2009; current version published November 18, 2009. This work was supported in part by Regione Emilia-Romagna (Italy), PRRIITT Misura 3.4 Azione, through TECAL Laboratories. This paper was presented in part at the 2007 International Symposium on Circuits and Systems (ISCAS), New Orleans, LA, May 27–30, 2007. The authors are with the Department of Information Engineering, Univer- sity of Parma, Parma 43100 Italy (e-mail: andrea.ricci@unipr.it; ilaria.demu- nari@unipr.it; paolo.ciampolini@unipr.it; matteo.grisanti@nemo.unipr.it). Digital Object Identifier 10.1109/TVLSI.2008.2006617 replacement of widespread optical barcode technologies, over- coming some of its inherent limitations (such as the reader–tag maximum distance). However, RFID promises go well beyond the mere replacement of barcode functionalities. Research on ubiquitous and pervasive computing aims at the creation of “active spaces,” integrating distributed computational infra- structure into the physical surroundings. RFID transponders may play a major role in the noninvasive environment moni- toring: the tag chip may embed local computing power, data storage, sensors, and communication devices, thus acting as “intelligent,” yet cheap, network nodes. In particular, transpon- ders operating in the UHF band, featuring large read ranges (up to several meters) can be profitably exploited. Aiming at mass market penetration, cost figures in the order of few cents per tag should be achieved; in order to meet such a stringent constraint, a cheap fabrication process is needed. For most applications, this rules out active transponders (which in- clude a power source, i.e., an expensive battery) and makes the choice of passive tag almost mandatory. A high-performance passive RFID tag just consists of a tiny IC chip, a flexible printed antenna, and an adhesive label substrate for application to items [1]. Power needed to operate the tag circuitry is obtained by harvesting energy from the field irradiated by the reader during the communication. At large read distance, this severely limits the amount of available power. Hence, effective low-power operating strategies are to be implemented, to preserve large communication range and circuit functionalities. Although a tag chip includes an analog RF front-end and a memory as well, the largest power fraction is usually required by the baseband processor [2]. Moreover, as we know, the power consumption of analog circuit and electri- cally erasable programmable read-only memory (EEPROM) is very difficult to reduce. Hence, exploiting an ultra-low power baseband processor would provide sensing section with higher energy, thus improving measurement performance. At present, most RFID systems operate in the ISM13.56 MHz band [1], [3]. Although reliable and suitable for many appli- cations, such systems (which exploit near-field communication between the tag and the reader) are substantially limited in the achievable read range. Alternative systems exploiting higher frequencies, such as the 868/915 MHz [4]–[11] and 2.4 GHz ISM bands [12], [13], are under active development. UHF sys- tems allow the reader-to-tag coupling by means of radiated en- ergy in the far field, and hence, may feature much larger read ranges. Moreover, a larger bandwidth is available, which, in turn, may be exploited to attain higher data rates. Several studies have been done on complete RFID chip, using proprietary communication protocols between tag and reader. Kocer et al. [4] reports a wireless telemetry device that just re- covers power and a reference clock from a 450 MHz incident 1063-8210/$26.00 © 2009 IEEE