1500 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: REGULAR PAPERS, VOL. 54, NO. 7, JULY 2007 An Ultra-Low-Power Long Range Battery/Passive RFID Tag for UHF and Microwave Bands With a Current Consumption of 700 nA at 1.5 V Vijay Pillai, Member, IEEE, Harley Heinrich, David Dieska, Pavel V. Nikitin, Member, IEEE, Rene Martinez, and K. V. Seshagiri Rao, Senior Member, IEEE Abstract—We present for the first time, a fully integrated bat- tery powered RFID integrated circuit (IC) for operation at ultra- high frequency (UHF) and microwave bands. The battery pow- ered RFID IC can also work as a passive RFID tag without a bat- tery or when the battery has died (i.e., voltage has dropped below 1.3 V); this novel dual passive and battery operation allays one of the major drawbacks of currently available active tags, namely that the tag cannot be used once the battery has died. When pow- ered by a battery, the current consumption is 700 nA at 1.5 V (400 nA if internal signals are not brought out on testpads). This ultra-low-power consumption permits the use of a very small ca- pacity battery of 100 mA hr for lifetimes exceeding ten years; as a result a battery tag that is very close to a passive tag both in form factor and cost is made possible. The chip is built on a 1- m dig- ital CMOS process with dual poly layers, EEPROM and Schottky diodes. The RF threshold power at 2.45 GHz is -19 dBm which is the lowest ever reported threshold power for RFID tags and has a range exceeding 3.5 m under FCC unlicensed operation at the 2.4-GHz microwave band. The low threshold is achieved with ar- chitectural choices and low-power circuit design techniques. At 915 MHz, based on the experimentally measured tag impedance (92-j837) and the threshold spec of the tag (200 mV), the theoretical minimum range is 24 m. The tag initially is in a “low-power” mode to conserve power and when issued the appropriate command, it operates in “full-power” mode. The chip has on-chip voltage reg- ulators, clock and data recovery circuits, EEPROM and a digital state machine that implements the ISO 18000-4 B protocol in the “full-power” mode. We provide detailed explanation of the clock recovery circuits and the implementation of the binary sort algo- rithm, which includes a pseudorandom number generator. Other than the antenna board and a battery, no external components are used. Index Terms—18000–4B, active, battery, International Stan- dards Organization (ISO), microwave, passive, RFID, Schottky diode, tag, ultra-high frequency (UHF), ultra-low power. I. INTRODUCTION T HERE has been an exponential growth in RFID deploy- ment for various industries such as automated toll collec- tion for bridges, automated data collection and tracking of arti- cles on conveyor belts, anti-theft protection for high value mer- chandise and automatic billing at point of sale counters. One of the main advantages of RFID is the ability to communicate at a Manuscript received June 15, 2005; revised January 17, 2007. This paper was recommended by Associated Editor A. Wang. V. Pillai, H. Heinrich, P. V. Nikitin, R. Martinez, and K. V. S Rao are with the Intermec Technologies, Everett, WA 98275 USA (e-mail Vijay.pillai@intermec. com). D. Dieska is with the ASICOLOGY Inc., Longwood, FL 32752-0996 USA (e-mail d.dieska@ieee.org). Digital Object Identifier 10.1109/TCSI.2007.897768 distance—this nonproximity based reading of transponders will make RFID the “next generation bar code” if the cost of the tag can be brought down. Nonproximity based reading also enables RFID tags to be used as access cards (for identification to enter into a restricted area), contact-less sensors (for pressure, tem- perature) etc. As of today, RFID tags operate in several bands—high-fre- quency (HF) (13.56 MHz), ultra-high-frequency (UHF) (860–915 MHz), and microwave bands (2.4 GHz). Transpon- ders that operate at 125 kHz [1] and 13.56 MHz [2] have been widely deployed for a number of years. The main disadvantage of them is limited range typically (less than 2 m). Passive transponders that operate in the UHF band have ranges of 7.5–9 m [3], [4], and transponders that operate in the microwave band have ranges under 2 m. Karthaus et al. [4] reports a low-power RFID chip for UHF with very low power consumption which is obtained by the combination of pulsewidth modulation on the forward link (base-station to tag) with low RF-off times (no excess voltage droop on the on-chip power capacitor) and phase-shift keying (PSK) on the return link (tag to base-station) greatly facilitates working of the tag at large ranges. A high level description of a passive RFID chip that implements the EPC Class 0 protocol is provided in Glidden et al. [5]. De Vita et al. [6] provides a design criteria for the front-end of passive RFID tags. Nakamoto et al. details an RFID tag using ferroelectric memory [7]. Much work has been done on using CMOS front-ends and CMOS technology for RFID [8]–[12]. While the range for passive RFID tags at UHF and microwave is adequate for many applications, there are applications that re- quire greater range. For greater range, an active transponder is required. The disadvantage of an active transponder is that it requires a battery and as a result the transponder will have a fi- nite lifetime. Furthermore the battery should have a small form factor so that it can be seamlessly used in the assembly process for large volume production. The requirement of long lifetimes (usually in excess of 10 years) and the small form factor neces- sitates a battery of very small capacity- this translates to low power consumption on the active transponder for it to work throughout the full life of the tag. This paper presents an ultra-low-power active tag that has a lifetime in excess of 10 years with a tiny 100-mA h battery (for comparison an AA battery capacity is 2100 mA h). The long lifetime of the battery tag makes it highly attractive for appli- cations where a large range is required while at the same time adding very little cost from the use of a small battery. Further- more when the battery dies, the tag will continue to work as a 1549-8328/$25.00 © 2007 IEEE