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2007 | Buch

Design and Optimization of Passive UHF RFID Systems

verfasst von: Jari-Pascal Curty, Michel Declercq, Catherine Dehollain, Norbert Joehl

Verlag: Springer US


Über dieses Buch

Radio Frequency IDentification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is a small object that can be attached to

or incorporated into a product, animal or person. An RFID tag contains an antenna to enable it to receive and respond to Radio-Frequency (RF) queries from an RFID reader or interrogator. Passive tags require no internal power source, whereas active tags require a power source.

As of today (2006), the concepts of ubiquitous computing and ambient intelligence are becoming widespread. In order for these to become a reality, a number of key technologies are required. In brief, these technologies need to be sensitive, responsive, interconnected, contextualised, transparent and intelligent. RFID, and in particular passive RFID tags, are such a technology. In order to deliver the necessary characteristics that could lead to ambient intelligence, however, there are some challenges that need to be addressed.

Remote powering of the tags is probably the most important challenge. Issues concerning the antenna-tag interface and the rectifier design, that allow the RF signal to be converted to Direct Current (DC) are top priorities. Secondly, the communication link and the reader should be optimized. The RF signal that contains the tag data suffers from a power of four decay with the distance between tag and reader. As a result, both the reader sensitivity and the tag backscattered power efficiency have to be maximized. Long-range powering, as well as sufficient communication quality, are the guidelines of this work.

This work proposes a linear two-port model for an N-stage modified-Greinacher full wave rectifier. It predicts the overall conversion efficiency at low power levels where the diodes are operating near their threshold voltage. The output electrical behavior of the rectifier is calculated as a function of the received power and the antenna parameters. Moreover, the two-port parameter values are computed for particular input voltages and output currents for the complete N-stage rectifier circuit, using only the measured I-V and C-V characteristics of a single diode.

Also presented in this work is an experimental procedure to measure how the impedance modulation at the tag side affects the signal at the reader. The method allows the tag designer to efficiently predict the effect of a modulator design at the system level and gives a useful instrument to choose the most appropriate impedances.

Finally, the design of a fully-integrated, remotely powered and addressable RFID tag working at 2.45GHz is described. The achieved operating range at a 4W Effective Isotropically Radiated Power (EIRP) reader transmit power is at most 12 m. The Integrated Circuit (IC) is implemented in a 0.5 um silicon-on-sapphire technology. A state-of-the-art rectifier design is embedded to supply energy to the transponder. Inductive matching and a folded-dipole antenna are key elements for achieving this performance.


1. Introduction
2. Wireless Power Transmission
This chapter presents the history of Wireless Power Transmission (WPT) from Tesla to the rectenna. The basic rectifier, its building blocks and the full-wave modified Greinacher rectifier are then described [4]. The antenna and its issues for WPT illustrate the basic trade-offs that occur. Finally, a numerical example of WPT concludes this chapter.
3. Analysis of the Modified-Greinacher Rectifier
As described in chapter 2, the use of low threshold voltage and low reverse current diodes and capacitors makes it possible to obtain a relatively high output voltage (1–2 V) given a sinusoidal input signal of about 200 mV. These values depend on the received power, the DC output current delivered to the load, and the impedance matching quality between the antenna and the rectifier’s input. It is the purpose of this chapter to discuss all these issues in order to predict the performance of a modified-Greinacher full-wave rectifier in a given process technology [4].
4. Introduction to RFID
This chapter describes shortly the different types of RFID technologies available today. The issue of standardization is discussed for UHF and microwave frequencies. A section reports the power and frequency regulations around the world. The physical principles at UHF and microwave frequencies are presented for the passive case only. An overview of the environmental impacts is given and the data integrity issue is discussed.
5. Backscattering architecture and choice of modulation type
The input impedance of an RF transponder is mainly influenced by the rectifier. As seen in chapter 3, it is possible to compute the impedance coming from the rectifier. To enable the communication from the tag to the reader there are two backscattering modulation choices: Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK). A thorough comparison of these two modulation types in the light of the backscattering issue is presented in this chapter.
6. Backscattering modulation analysis
In this chapter, we analyze the backscattering phenomenon from a quantitative point of view. The theoretical background is described first. As a second step, a practical approach to quantify the effect of the tag loading at the reader side is derived. The impact on the RFID system and more particularly on the reader architecture is also studied. Finally, a graphical interpretation of the complex transformations that occur as well as the impact on the wireless power transmission issue conclude this chapter.
7. RFID Tag design
This chapter takes advantage of the previous one to define the specifications at the system level of an RFID tag. The operational principle as well as the communication protocol chosen in the hereafter developed system are presented. The different building blocks and their design issues in tight of low power consumption are described. Finally, the chapter concludes with the antenna choice and the experimental results [5].
8. High frequency interrogator architecture and analysis
This chapter presents the UHF reader architecture that was used for the RFID system development. The distortion due to the direct coupling between transmitting and receiving antennas (or port-to-port isolation in a circulator-based architecture) is analyzed in detail. The phase noise impact is studied. The noise figure as well as the gain distribution is presented. Finally we conclude with the obtained results and possible improvements.
9. Conclusion
Design and Optimization of Passive UHF RFID Systems
verfasst von
Jari-Pascal Curty
Michel Declercq
Catherine Dehollain
Norbert Joehl
Springer US
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