RFID and Contactless Smart Card Applications

Contents ACKNOWLEDGEMENTS. FOREWORD. PREFACE. INTRODUCTION. Part One: Review and supplementary information. 1 Review. 1.1 The Elements of a Contactless Device. 1.2 General Operating Principles of the “Base Station–Transponder” Pair. 1.3 Before We Continue . . . Conventional Notation. 2 The Transponder: Supplementary Information. 2.1 Ready-made Products. 2.2 Specification or Choice of the Transponder Integrated Circuit. 2.3 The Transponder Antenna. 3 The Base Station: Supplementary Information. 3.1 The Base Station Antenna. 3.2 Review and Supplementary Technical Information. 3.3 Structure of the Driver Stage of the Base Station Antenna. 3.4 The Downlink. 3.5 Summary of the Principal Formulae of Chapters 2 and 3. Part Two: Applications and implementation. 4 Design and Implementation of a “Contactless” Application. 4.1 Specifying an Application. 4.2 Specifying the Requirements. 4.3 Specifying the Near Environment of the Application. 4.4 How to Approach an Application. 4.5 Choice of the Operating Frequency. 4.6 Overview of the Frequencies Used in RFID. 4.7 Choosing the Right Frequency. Part Three: Examples. 5 Examples at 125kHz. 5.1 The Usual Constants and Parameters of Applications Operating at 125 kHz. 5.2 Example. 6 Examples at 13.56MHz. 6.1 The Usual Constants and Parameters of Applications Operating at 13.56 kHz. 6.2 ISO 14 443 “Proximity” Applications (Approximately 10 cm). 6.3 “Vicinity” Applications (Approximately 70 cm) of the ISO 15 693 or 18 000 Type and Long-range Applications for Vicinity Cards or Item Management. 6.4 Applications and Conformity with Standards. Part Four: Antennae and their technology. 7 The Transponder Antenna and its Technology. 7.1 The Range of Technologies. 7.2 The Geometrical Shapes of the Windings. 8 The Base Station Antenna and Its Technology. 8.1 Shape, Size and Technology of the Base Station Antenna. Part Five: The electronics involved. 9 Electronic Systems of the Base Station. 9.1 Standard Base Station Circuits. 9.2 Advanced Base Station Circuits. 9.3 The Output Stage Transmission Part. 9.4 Driving the Antenna. 9.5 The Demodulators. 9.6 The Common Reception/Transmission Part. Part Six: Tools and Measurement Methods. 10 Development Aids and Tools. 10.1 Simulation of the System Performance. 10.2 Development Aid Tools. 11 Measurement Methods for Contactless Systems. 11.1 The Principal Parameters to be Measured for a Transponder. 11.2 Transponder Measurement Methods and Set-ups. 11.3 Measuring Complete Systems. 11.4 Conclusions. 11.5 The Future. Appendix A. A.1 Duality of Series and Parallel RLC Circuits. A.2 Useful Addresses and Information. INDEX.

1 Review Before going into the details, let us briefly review how the components of an RFID system are organized and how they operate. Figures 1.1a and 1.1b show the structure of a system of this kind. Base station Transponder Energy Microprocessor Host Interface Interface Memory Logic RF Data Base station Data_in Encoder Modu- Transponder lator Data communication Contactless interface Data_out Energy Power supply Decoder Demo- Data dulator Access control EEPROM Figure 1.1a Block diagram of a contactless system Note: for more detailed information, you should refer to the author’s very compre- hensive book on the subject, published previously by Dunod. RFID and Contactless Smart Card Applications D. Paret  2005 John Wiley & Sons, Ltd 4 1 REVIEW Magnetic field lines Energy Coil axis Transponder Data Antenna Figure 1.1b Operating principle of a “base station–transponder” system 1.1 The Elements of a Contactless Device 1.1.1 The transponder Let us start with the transponder, which uses a remote memory (ROM, PROM, E2PROM, etc.) to store data for the application in question, and which also controls communication and contains the part used for the RF link. 1.1.2 The air interface The air forms the communication medium. The electromagnetic RF waves carry the data. The air also plays a part in the (magnetic) coupling between the antennae of the transponder and the base station. 1.1.3 The base station The base station comprises an analogue part used for receiving and transmitting RF signals, the circuits controlling the protocol for communication with the transponder, the communication management (management of possible collisions, authentication, cryptography, etc.) and finally an interface for dialogue with the host system. 1.2 OPERATING PRINCIPLES OF THE ‘‘BASE STATION–TRANSPONDER’’ PAIR 5 1.1.4 The host system Finally, to complete this brief survey, we have the host system, providing the higher level control of the application. Now that the general picture is in place, let us examine each of these elements in more detail. 1.2 General Operating Principles of the ‘‘Base Station–Transponder’’ Pair For applications in which the remote element – the transponder – has no on-board power supply and therefore operates with a remote power supply, Figures 1.2a to 1.2c provide a summary of the physical principles of the three main stages of operation of a “base station–transponder” system. 1.2.1 Transfer, energy supply and remote power supply An alternating electrical signal at radio frequency, called the “carrier”, creates a mag- netic field, by means of the winding forming the base station antenna, to remotely induce a voltage in the antenna of the transponder; this voltage is rectified and filtered to provide a local power supply for the transponder (see Figure 1.2a). lt lb Energy Ub Ut Figure 1.2a Energy transfer phase 1.2.2 Data transfer from the base station to the transponder: the ‘‘uplink’’ In order to transmit commands and data to the transponder, the carrier is modulated with a binary stream based on specific bit codings (see Figure 1.2b). 6 1 REVIEW Data Demodulator lt l lb Energy Ut Ub Data Figure 1.2b Uplink phase 1.2.3 Data transfer from the transponder to the base station: the ‘‘downlink’’ The transponder can communicate with the base station by means of a modulation carried out by varying the load that it represents in the field (see Figure 1.2c). Demodulator lt lb VZ1 Data Energy Ut Ub Data VZ2 (VZ2 < VZ1) Figure 1.2c Downlink phase 1.2 OPERATING PRINCIPLES OF THE ‘‘BASE STATION–TRANSPONDER’’ PAIR 7 To explain the operation of the “base station–transponder” pair more simply, I shall look inside most of its constituent parts and try to explain the general principles as clearly as possible, breaking the process down into two main sections, namely, the transfer of energy on the one hand and the operation of the uplink and downlink on the other. 1.2.4 Energy transfer The transponder can only operate if it is supplied with power. In the present case, this is done by the remote power supply principle, which will be described in detail in this section. Figure 1.3 shows how the energy transfer is carried out by means of an alternating magnetic field H (t) produced by the flow of an alternating current I (t) in the antenna of the base station, according to the general equation H = NI , where N represents the number of turns per metre of the antenna carrying the current I . The strength of the magnetic field H is expressed in amperes per metre (A/m). Magnetic field lines Energy Antenna axis Transponder Data Antenna Figure 1.3 Energy transfer In the medium in which this magnetic field develops, there is a corresponding associated induction B(t) having the general form B(t) = µ H (t), where µ represents the magnetic permeability of the medium(s) through which the field passes. This magnetic permeability is expressed by µ = µ0 µr , 8 1 REVIEW where µ0 represents the permeability of the air (µ0 = 4π × 10−7 henrys/metre) and µr is the relative permeability of the medium concerned (water, metal, etc.). The value of the magnetic induction B is expressed in teslas (T).