Contactless Smart Cards
There are currently three different standards for contactless smart cards based upon a broad classification of the range.

Table 9.4 Available standards for contactless smart cards
Standard Card type Approximate range
ISO/IEC 10536  Close-coupling  0–1 cm 
ISO/IEC 14443  Proximity-coupling  0–10 cm 
ISO/IEC 15693  Vicinity-coupling  0–1 m 

Most of the standard for close-coupling smart cards – ISO 10536 – had already been developed by between 1992 and 1995. Due to the high manufacturing costs of this type of card2 and the small advantages in comparison to contact smart cards,3 close-coupling systems were never successful on the market and today they are hardly ever used.

ISO/IEC 10536 – Close-Coupling Smart Cards
The ISO/IEC standard 10536 entitled ‘Identification cards – contactless integrated circuit(s) cards’ describes the structure and operating parameters of contactless close-coupling smart cards. ISO/IEC 10536 consists of the following four sections:

Part 1: Physical characteristics
Part 2: Dimensions and location of coupling areas
Part 3: Electronic signals and reset procedures
Part 4: Answer to reset and transmission protocols (still under preparation)

Part 1 – Physical Characteristics
The physical characteristics of close-coupling cards are defined in Part 1 of the standard. The specifications regarding mechanical dimensions are identical to those for contact smart cards.

Part 2 – Dimensions and Locations of Coupling Areas
Part 2 of the standard specifies the position and dimensions of the coupling elements. Both inductive (H1–H4) and capacitive coupling elements (E1–E4) are used. The arrangement of the coupling elements is selected so that a close-coupling card can be operated in an insertion reader in all four positions (Figure 9.9).

Part 3 – Electronic Signals and Reset Procedures
9.2.1.3.1 Power Supply
The power supply for close-coupling cards is derived from the four inductive coupling elements H1–H4. The inductive alternating field should have a frequency of 4.9152MHz. The coupling elements H1 and H2 are designed as coils, but have opposing directions of winding, so that if power is supplied to the coupling elements at the same time there must be a phase difference of 180◦ between the associated magnetic fields F1 and F2 (e.g. through a U-shaped core in the reader). The same applies for the coupling elements H3 and H4.

The readers must be designed such that power of 150 mW can be provided to the contactless card from any of the magnetic fields F1–F4. However, the card may not draw more than 200mW via all four fields together.

Data Transmission Card → Reader
Either inductive or capacitive coupling elements may be used for data transmission between card and reader. However, it is not possible to switch between the two types of coupling during communication.

Inductive. Load modulation with a subcarrier is used for the transmission of data via the coupling fields H1–H4. The subcarrier frequency is 307.2 kHz and the subcarrier is modulated using 180◦ PSK . The reader is designed such that a load change of 10% of the base load at one or more of the fields F1–F4 can be recognised as a load modulation signal. The specified minimum load change for a card is 1 mW.

Capacitive. In this procedure the coupling fields E1, E2 or E3, E4 are used as pairs. In both cases the paired coupling fields are controlled by a differential signal. The voltage difference Udiff = UE1 – UE2 should be measured such that a voltage level of at least 0.33 V is present at the reader coupling surfaces E1  and E2. Data transmission takes place using NRZ coding in the baseband (i.e. no subcarrier). The data rate after reset is 9600 bit/s; however, a higher data rate can be used during operation.

Data Transmission Reader → Card
The standard gives preference to the inductive method for data transmission to the card. The modulation procedure is a 90◦ PSK of the fields F1–F4 and the phase position of all fields is modulated synchronously. Depending upon the position of the card in the insertion reader, the phase relationships shown in Tables 9.5 and 9.6 are possible between the coupling fields during modulation.

Data transmission takes place using NRZ coding in the baseband (i.e. no subcarrier). The data rate after reset is 9600 bit/s; however, a higher data rate can be used during operation.

Part 4 – Answer to Reset and Transmission Protocols
This part of ISO 10536 describes the transmission protocol between reader and card. We will not describe Part 4 here because it is still under development by the standardisation committee in question, and may therefore be subject to change.

ISO/IEC 14443 – Proximity-Coupling Smart Cards
ISO/IEC standard 14443 entitled ‘Identification cards – Proximity integrated circuit(s) cards’ describes the operating method and operating parameters of contactless proximity-coupling smart cards. This means contactless smart cards with an approximate range of 7–15cm, like those used predominantly in the field of ticketing. The data carrier of these smart cards is normally a microprocessor and they often have additional contacts (see also Section 10.2.1).

The standard comprises the following parts:

Part 1: Physical characteristics.
Part 2: Radio frequency power and signal interface.
Part 3: Initialisation and anticollision (still in preparation).
Part 4: Transmission protocols (in preparation).

Part 1 – Physical Characteristics
Part 1 of the standard defines the mechanical properties of the smart cards. The dimensions correspond with the values specified in ISO/IEC 7810, i.e. 85.72 × 54.03 × 0.76 mm ± tolerances.

Furthermore, this part of the standard also includes notes on the testing of the dynamic bending stress and dynamic torsion stress, plus irradiation with UV, X-ray and electromagnetic radiation.

Part 2 – Radio Frequency Interference
The power supply of inductively coupled proximity cards (PICC ) is provided by the magnetic alternating field of a reader (PCD) at a transmission frequency of 13.56 MHz. To this end the card incorporates a large area antenna coil typically with 3–6 windings of wire (see Figures 2.11 and 2.12).

The magnetic field generated by the reader must be within the range 1.5A/m ≤ H ≤ 7.5A/m. Thus the interrogation field strength Hmin of a proximity-coupling smart card is automatically Hmin ≤ 1.5 A/m. This is the only way to ensure that a smart card with an interrogation field strength Hmin = 1.5 A/m can be read by a reader that generates a field strength of just 1.5 A/m (e.g. a portable, battery-operated reader with a correspondingly lower transmission power), at least at distance x = 0 from the transmission antenna (smart card in contact) (Berger, 1998).

If the field strength curve of a reader and the interrogation field strength of a proximity-coupling smart card are known, then the range of the system can be calculated. The field strength curve of a typical reader in accordance with ISO/IEC 14443 is shown in Figure 9.11 (see Section 4.1.1.1). In this case, a smart card interrogation field strength of 1.5 A/m results in a range of 10 cm.

Unfortunately it was not possible to agree to a common communication interface in the development of this standard. For this reason, two completely different procedures for the data transfer between reader and proximity-coupling smart card have found a place in ISO/IEC 14443 – Type A and Type B. A smart card only has to support one of the two communication procedures. A reader conforming to the standard, on the other hand, must be able to communicate equally well by both procedures, and thus support all smart cards. This means that the reader must switch between the two communication procedures (polling) periodically during ‘idle’ mode (‘wait for smart card’).

However, the reader may not switch between the two procedures during an existing communication relationship between reader and card.

Communication Interface – Type A
In type A cards 100% ASK modulation with modified Miller coding (Figure 9.12) is defined as the modulation procedure used for the transfer of data from reader to card. In order to guarantee a continuous power supply to the card the length of the blanking intervals is just 2–3 µs. The requirements of the transient response and transient characteristics of the RF signal generated by the reader in the blanking intervals are described in detail in the standard. A load modulation procedure with subcarrier is used for data transfer from the smart card to the reader. The subcarrier frequency fH = 847 kHz (13.56 MHz/16). The modulation of the subcarrier is performed by on/off keying of the subcarrier using a Manchester coded data stream.

In both transfer directions the baud rate fBd = 106 kBit/s (13.56 MHz/128).

Communication Interface – Type B
In Type B cards 10% ASK modulation (Figure 9.14) is used as the modulation procedure for the data transfer from reader to card. A simple NRZ coding is used for bit coding. The transient response and transient characteristics of the RF signal in the 0/1 transitions are precisely defined in the standard and requirements of the quality of the transmission antenna can be derived from this (see Section 11.4.3).

For data transfer from the smart card to the reader load modulation with a subcarrier is also used for the Type B card. The subcarrier frequency fH = 847 kHz (13.56 MHz/16). The subcarrier is modulated by 180◦ phase shift keying (BPSK) of the subcarrier using the NRZ coded data stream.

In both transmission directions the baud rate fBd = 106 kBit/s (13.56 MHz/128).

Part 3 – Initialisation and Anticollision
If a proximity-coupling smart card enters the interrogation field of a reader, then a communication relationship must first of all be built up between reader and smart card, taking into consideration the fact that there may be more than one smart card within the interrogation zone of this reader and that the reader may already be in communication with another card. This part of the standard therefore first describes the structure of the protocol frames from the basic elements defined in Part 2 – data bit, start-of-frame and end-of-frame marks – and the anticollision procedure used for the selection of an individual card. Since the different modulation procedure for Type A and Type B also requires a different frame structure and anticollision procedure, the divide between the two types A and B is reflected in Part 3 of the standard.

Type A Card
As soon as a Type A smart card enters the interrogation zone of a reader and sufficient supply voltage is available, the card’s microprocessor begins to operate. After the performance of some initialisation routines – if the card is a dual interface card these include checking whether the card is in contactless or contact mode – the card is put into so-called IDLE mode. At this point the reader can exchange data with another smart card in the interrogation zone. However, smart cards in the IDLE state may never react to the reader’s data transmission to another smart card (‘any command’) so that an existing communication is not interrupted.

If, when the card is in IDLE mode, it receives a valid REQA command (Request-A), then an ATQA block (answer to request) is sent back to the reader in response (Figure 9.16). In order to ensure that data destined for another card in the interrogation field of the reader is not falsely interpreted as a REQA command, this command is made up of only 7 data bits (Figure 9.17). The ATQA block sent back, on the other hand, consists of 2 bytes and is returned in a standard frame.

After the card has responded to the REQA command it is put into the READY state. The reader has now recognised that at least one card is in the interrogation field and begins the anticollision algorithm by transmitting a SELECT command. The anticollision procedure used here is a dynamic binary search tree algorithm.4 A bit-oriented frame is used for the transfer of the search criterion and the card’s response, so that the transmission direction between reader and card can be reversed after a desired number of bits have been sent. The NVB (number of valid bits) parameter of the SELECT command specifies the current length of the search criterion.

The length of a single serial number is 4 bytes. If a serial number is detected by the anticollision algorithm, then the reader finally sends the full serial number (NVB = 40 h) in the SELECT command, in order to select the card in question. The card with the detected serial number confirms this command by an SAK (SELECT-Acknowledge) and is thereby put into ACTIVE state, the selected state. A peculiarity, however, is that not all cards possess a 4-byte serial number (single size). The standard also permits serial numbers of 7 bytes (double size) and even 10 bytes (triple size). If the selected card has a double or triple size serial number, this will be signalled to the reader in the card’s SAK, by a set cascade bit (b3 = 1), with the card remaining in the READY state. This results in the anticollision algorithm being restarted in the reader so that it can detect the second part of the serial number. In a triple size serial number the anticollision algorithm must even be run a third time. To signal to the card which part of the serial number is to be detected by the algorithm that has been initiated, the SELECT command differentiates between three cascade levels (CL1, CL2, CL3) (Figure 9.19). However, the process of detecting a serial number always begins with cascade level 1. In order to rule out the possibility of fragments of a longer serial number corresponding by coincidence with a shorter serial number, so-called cascade tags (CT = 88 h) are inserted at a predetermined position in the double or triple size numbers. This value may therefore never occur at the corresponding byte positions in the shorter serial numbers.

Precise timing between a reader’s command and the smart card’s response should also be ensured. The standard prescribes a synchronous behaviour of the smart card, which means that the response may only be transmitted at defined moments in a fixed time grid For the response to a REQA, WakeUp or SELECT command N = 9. For all other commands

(e.g. application commands) N must be greater than or equal to 9 (N = 9,10,11,12,…).
Type B Cards
If a Type B smart card is brought within the interrogation field of a reader, the smart card, after the performance of a few initialisation routines, is initially put into IDLE mode and waits to receive a valid REQB (REQUEST-B) command (Figure 9.20).

The transmission of a REQB command immediately initiates the anticollision algorithm in Type B cards. The procedure used here is a dynamic slotted ALOHA procedure,5 in which the number of slots can be dynamically changed by the reader. The number of slots currently available is encoded in a parameter of the REQB command. In order to facilitate a preselection during the selection of a card, the REQB command has a further parameter, the application family identifier (AFI), which allows a certain application group to be entered as a search criterion (Table 9.10).

After a card has received a valid REQB command it checks whether the application group preselected in the parameter AFI is present in the applications stored on the card. If so, the parameter M of the REQB command is evaluated to detect the number of slots available for anticollision (Table 9.11). If the number of available slots is greater than one, a random-check generator in the card is used to determine the number of the slot in which the card wishes to transmit its response to the reader. In order to guarantee the synchronisation of the cards with the slots, the reader transmits its own slot marker at the beginning of each slot. The card waits until the slot marker of the previously determined slot is received (Ready Requested State) and responds to the REQB command by sending an ATQB (Answer To Request B).

A short time after the transmission of a slot marker (Figure 9.23) the reader can determine whether a smart card has begun to transmit an ATQB within the current slot. If not, the current slot can simply be interrupted by the transmission of the next slot marker in order to save time.

The request response ATQB sent by the smart card provides the reader with a range of information about important parameters of the smart card (see Figure 9.22). In order to be able to select the card, the ATQB first of all contains a 4-byte serial number. In contrast to Type A cards, the serial number of a Type B card is not necessarily permanently linked to the microchip, but may even consist of a random number, which is newly determined after every power-on reset (PUPI, pseudo unique PICC identifier). Parameters of the contactless interface are encoded within the ‘Protocol Info’ parameter, for example the maximum possible baud rate of the smart card, the maximum frame size,6 or information on alternative protocols. The ‘Application Data’ parameter can, moreover, include information on several applications available on the card (multi-application card).

As soon as the reader has received the ATQB of at least one smart card without errors the card can be selected. This takes place by means of the first application command transmitted by the reader. The structure of this command corresponds with that of a standard frame (Figure 9.24), but it is extended by additional information in a special prefix, the ATTRIB prefix (Figure 9.25).

The ATTRIB prefix itself is made up of the (previously determined) serial number (PUPI) of the card to be selected and a parameter byte. The parameter byte contains important information on the possible communication parameters of the reader, such as the smart card’s minimum waiting time between a reader’s command and the smart card’s response, or the necessary waiting time between the switching on of the subcarrier system in the load modulator and the first data bit sent by the card.

Part 4 – Transmission Protocols
After a communication relationship has been established between a reader and a proximity-coupling smart card, commands for reading, writing and the processing of data can be sent to the card. This part of the standard describes the structure of the data protocol that this necessitates and the processing of transmission errors, so that data can be transferred between the communication participants without errors.

In the Type A card, additional information for the configuration of the protocol to different card and reader properties (e.g. possible baud rates, maximum size of the data blocks, etc.) must be transferred. In Type B cards this information has already been transferred during the anticollision process (ATQB, ATTRIB), so in the case of this card type, the protocol can be commenced immediately.

Protocol Activation in Type A Cards
The selection of a Type A card in the anticollision loop is confirmed by the card by the transmission of a SAK (select acknowledge). The SAK contains information about whether a protocol in accordance with ISO/IEC 14443-4 has been implemented in this card, or whether the card has a proprietary protocol (e.g. MIFARE).

If a protocol in accordance with ISO/IEC 14443-4 is available in the card, the reader demands the card’s ATS (answer to select) by transmitting a RATS command (request for answer to select, Figure 9.26). The RATS command contains two parameters that are important for the subsequent communication: FSDI and CID.

FSDI (frame size device integer) defines the maximum number of bytes that may be sent from the card to the reader in one block. Possible values for this are 16, 24, 32, …128 and 256 bytes.

Furthermore, the smart card is allocated a CID (card identifier). Using the CID, it is possible for a reader to maintain several Type A cards in a selected state at the same time and to address an individual card selectively via its CID.

The ATS (answer to select) sent by the card in response to the RATS command corresponds to the function of the ATR (answer to reset) of a contact smart card and describes important protocol parameters of the smart card’s operating system, so that the data transmission between card and reader can be optimised in relation to the properties of the implemented application.

Individually, the (optional) parameters listed in Table 9.12 can be contained in the ATS.

Immediately after receiving the ATS, the reader can still initiate the changeover of the transmission baud rates by sending out a special PPS command (protocol parameter selection). Based upon an initial baud rate of 106 Kbit/s, the baud rates in both transmission directions can be increased independently of one another by a factor of 2, 4 or 8 if the smart card has signalled the support of higher baud rates in the optional parameters DS and DR in the ATS.

  Protocol
The protocol described in ISO/IEC 14443-4 supports the transmission of application data (APDU = application data unit) between the reader and the smart card. The transmitted APDU can contain any desired data, such as command and response. The structure of this protocol is based heavily upon the protocol T = 1 (ISO/IEC 7816-3) that we know from contact smart cards, in order to keep the integration of this protocol into smart card operating systems that are already available, in particular dual interface smart cards, as simple as possible. The protocol defined in ISO/IEC 14443-4 is therefore often called T = CL.

The entire data transmission to an ISO/IEC 14443 card can also be represented in accordance with the OSI layer model, as Figure 9.27 shows. In this model, every layer independently takes on specific tasks and is thus transparent to the level above it. Layer 1, the physical layer, describes the transmission medium and the coding of the data at byte level. ISO/IEC 14443-2 provides two equivalent procedures here, Type A and Type B. Layer 2, the transport layer, controls the transmission of data between reader and smart card. Layer 2 automatically looks after the correct addressing of the data blocks (CID), the sequential transmission of excessively sized data blocks (chaining), the monitoring of the time procedure (FWT, WTX), and the handling of transmission errors. Layer 7, the application layer, contains the application data, i.e. the command to the smart card or the response to a command. In contactless smart cards the data structures used in the application layer are generally fully identical to those used in contact smart cards. This procedure is very worthwhile for dual interface smart cards in particular, because it means that the application layer is independent of the communications interface that is currently being used (contact, contactless). Layers 3–6 are used in complex networks for the determination and forwarding of data packets. In smart cards these layers of the OSI layer model are not used.

After the smart card has been activated (e.g. Type A after the transmission of the ATS and possibly a PPS) it waits for the first command from the reader. The sequence that now follows always corresponds with the master–slave principle, with the reader as master and the card as slave. The reader always sends a command to the smart card first, which executes the command and sends a response back to the reader. This pattern may never be broken; a smart card thus cannot initiate any communication with the reader.

The basic structure of a data block (frame) from the transport layer is shown in Figure 9.28. We differentiate between three types of blocks according to the method of functioning:

Iblock (information block): Transmission of data from the application layer (APDU)
Rblock (recovery block): Handling of transmission errors
Sblock (supervisory block): Higher control of the protocol
The blocks are differentiated by different coding of the PCB (protocol control byte), as shown in Figure 9.29.

The optional CID (card identifier) is used for addressing an individual smart card in the interrogation zone of the reader. Thus, several smart cards can be activated at the same time and addressed selectively using their CID. The NAD byte (node address) was introduced in order to ensure compatibility between ISO/IEC 14443-5 and ISO/IEC 7816-3 (T = 1). The use of this byte is therefore not further defined in ISO/IEC 14443.

In the case of an I block, the information field (INF) serves as a container for the data of the application layer (APDU). The content is transmitted entirely transparently. This means that the content of the protocol is forwarded directly without analysis or evaluation.

Finally, a 16-bit CRC is appended as an EDC (error detection code) for error control.

ISO/IEC 15693 – Vicinity-Coupling Smart Cards
The ISO/IEC standard 15693 entitled ‘Identification cards – contactless integrated circuit(s) cards – Vicinity Cards’ describes the method of functioning and operating parameters of contactless vicinity-coupling smart cards. These are smart cards with a range of up to 1 m, like those used in access control systems. The data carriers used in these smart cards are predominantly cheap memory modules with simple state machines (see Section 10.1.2.1).

The standard is made up of the following parts:

Part 1: Physical characteristics
Part 2: Air interface and initialization
Part 3: Anti-collision and transmission protocol
9.2.3.1 Part 1 – Physical Characteristics
Part 1 of the standard defines the mechanical properties of proximity-coupling smart cards. The dimensions of the smart card correspond with those specified in ISO/IEC 7810, i.e. 85.72 × 54.03 ×

0.76 mm ± tolerances.
Furthermore, this part of the standard includes additional notes for the testing of the dynamic bending stress and the dynamic torsion stress, plus irradiation with UV, X-ray and electromagnetic radiation.

Part 2 – Air Interface and Initialization
The power supply of the inductively coupled vicinity card (VICC ) is provided by the magnetic alternating field of a reader (PCD) at a transmission frequency of 13.56 MHz. The vicinity card incorporates a large area antenna coil for this purpose, typically with 3–6 windings of wire (see Figures 2.11 and 2.12).

The magnetic field to be generated by the reader must lie within the limit values 115 mA/m ≤ H ≤ 7.5 A/m. Thus, it is automatically the case for the interrogation field strength Hmin ofa proximity-coupling smart card that Hmin ≤ 115 mA/m.

Data Transfer Reader → Card
Both 10% ASK and 100% ASK modulation are used for the data transfer from a reader to a vicinity smart card (see Section 6.2.1). Regardless of the selected modulation index, moreover, one of two different coding procedures can be selected: a ‘1 of 256’ code or a ‘1 of 4’ code.

A vicinity smart card must, in principle, support both modulation and coding procedures. However, not all combinations are equally practical. For example, 10% ASK modulation in combination with ‘1 of 256’ coding should be given preference in ‘long-distance mode’. The lower field strength of the modulation sidebands in comparison to the field strength of the (13.56 MHz) carrier signal in this combination permits the full exploitation of the permissible magnetic field strength for the power supply of the card (see FCC 15 Part 3: the permissible magnetic field strength of the modulation side bands lies 50 dB below the maximum field strength of the carrier signal of 42 dBµA/m here). By contrast, 100% ASK modulation in combination with ‘1 of 4’ coding in readers can be used with reduced range or even shielded readers (‘tunnel’ readers on conveyor belts).

‘1 of 256’ Coding
This coding procedure is a pulse position modulation (PPM ) procedure. This means that the value of the digit to be transferred is unambiguously defined in the value range 0–255 by the time position of a modulation pulse (Figure 9.30). Therefore, 8 bits (1 byte) can be transferred at the same time in one step. The total transmission time for a byte is 4.833 ms. This corresponds with 512 time slots of 9.44 µs. A modulation pulse can only take place at an uneven time slot (counting begins at zero). The value n of a transferred digit can easily be determined from the pulse position:

Pulse position = (2 · n)+ 1 (9.1)

The data rate resulting from the transmission period of a byte (4.833 ms) is 165 Kbit/s.

The beginning and end of a data transmission are identified by defined frame signals – startof-frame (SOF) and end-of-frame (EOF). The coding of the SOF and EOF signals selected in the standard is such that these digits cannot occur during a transmission of useful data (Figure 9.31). The unambiguity of the frame signals is thus always ensured.

The SOF signal in ‘1 of 256’ coding consists of two 9.44-µs-long modulation pulses separated by a time slot of 56.65 µs(9.44 µs × 4, Figure 9.32). The EOF signal consists of a single modulation pulse lasting 9.44 µs, which is sent at an even time slot in order to ensure its clear differentiation from a data byte (Figure 9.33).

‘1 of 4’ Coding
In this coding too, the time position of a modulation pulse determines the value of a digit. Two bits are transmitted simultaneously in a single step; the value of the digit to be transferred thus lies in the value range 0–3. The total transmission time for a byte is 75.52 µs, which corresponds with eight time slots of 9.44 µs. A modulation pulse can only be transmitted at an uneven time slot (counting begins at zero). The value n of a transmitted figure can easily be determined from the pulse position:
Pulse position = (2 · n) + 1 (9.2)
The data rate resulting from the time taken to transmit a byte (75.52 µs) is 26.48 Kbit/s.

In ‘1 of 4’ coding the SOF signal is made up of two modulation pulses lasting 9.44 µs separated by an interval of 37.76 µs (Figure 9.34). The first digit of the useful data begins after an additional pause of 18.88 µs after the second modulation pulse of the SOF signal (Figure 9.35).

The conclusion of the transmission is identified by the familiar frame end signal (EOF).

Data Transfer Card → Reader
Load modulation with a modulated subcarrier is used for the data transfer from a vicinity card to a reader. The ohmic or capacitive modulation resistor is switched on and off in time with the subcarrier frequency. The subcarrier itself is modulated in time with the Manchester coded data stream, using ASK or FSK modulation (Table 9.14). The modulation procedure is selected by the reader using a flag bit (control bit) in the header of the transmission protocol defined in Part 3 of the standard. Therefore, in this case too, both procedures must be supported by the smart card.

The data rate can also be switched between two values (Table 9.15). The reader selects the data rate by means of a flag bit (control bit) in the header of the transmission protocol, which means that, in this case too, the card must support both procedures.

ISO/IEC 10373 – Test Methods for Smart Cards
ISO 10373 provided a standard relating to the testing of cards with and without a chip. In addition to tests for the general quality characteristics, such as bending stiffness, resistance to chemicals, dynamic torsional stress, flammability, and dimensions of cards or the ultraviolet light resistance of the data carrier (since EEPROM memories lose their content when irradiated with UV light a special test has been developed to ensure nonsensitivity to this), specific test procedures have also been developed for the latest methods of data transmission or storage (magnetic strips, contact, contactless, optical). The individual test procedures for testing magnetic strips (ISO/IEC 7811), contact smart cards (ISO/IEC 7816) or contactless smart cards (ISO/IEC 14443, ISO/IEC 15693) were summarised in independent parts of the standard for the sake of providing an overview (Table 9.16).7

Part 4: Test Procedures for Close-Coupling Smart Cards
This part of the standard describes procedures for the functional testing of the physical interface of contactless close-coupling smart cards in accordance with ISO/IEC 10536. The test equipment consists of defined coils and capacitive coupling areas, which facilitate the evaluation of the power and data transmission between smart card and reader.

However, due to the secondary importance of close-coupling smart cards we will not investigate this procedure further at this point.

Part 6: Test Procedures for Proximity-Coupling Smart Cards
This part of the standard describes test procedures for the functional testing of the physical interface between contactless proximity-coupling smart cards and readers in accordance with ISO/IEC 14443-2, The test equipment consists of a calibration coil, a test set-up for the measurement of the load modulation (PCD assembly test) and a reference card (reference PICC). This equipment is defined in the standard.

Calibration Coil
To facilitate the measurement of the magnetic field strength generated by a reader without complicated and expensive measuring equipment, the standard first describes the layout of a calibration coil that permits the measurement of magnetic field strengths in the frequency range of 13.56 MHz with sufficient accuracy, even with a simple oscilloscope.

The calibration coil is based upon an industry-standard copper coated FR4 printed circuit board and smart card dimensions in accordance with ISO/IEC 7810 (72 × 42 × 0.76 mm). A conductor coil (i.e. a coil with one winding) with dimensions 72 × 42 mm is applied onto this base board using the normal procedure for the manufacture of printed circuits. The sensitivity of the calibration coil is 0.3 Vm/A. However, during the field strength measurement particular care should be taken to ensure that the calibration coil is only subjected to high-ohmic loads by the connected measuring device (sensing head of an oscilloscope), as every current flow in the calibration coil can falsify the measurement result.

If the measurement is performed using an oscilloscope, then the calibration coil is also suitable for the evaluation of the switching transitions of the ASK modulated signal from a reader. Ideally, a reader under test will also have a test mode, which can transmit the endless sequence 10101010 for the simpler representation of the signal on the oscilloscope.

Measuring the Load Modulation
The precise and reproducible measurement of the load modulation signal of a proximity-coupling smart card at the antenna of a reader is very difficult due to the weak signal. In order to avoid the resulting problems, the standard defines a measuring bridge, which can be used to compensate the reader’s (or test transmitter’s) own strong signal. The measuring arrangement for this described in the standard consists of a field generator coil (transmission antenna) and two parallel sensor coils in phase opposition. The two sensor coils (‘reference coil’ and ‘sense coil’) are located on the front and back of the field generator coil, each at the same distance from it, and are connected in phase opposition to one another (Figures 9.36 and 9.37), so that the voltages induced in the coils cancel each other out fully. In the unloaded state, i.e. in the absence of a load from a smart card or another magnetically coupled circuit, the output voltage of this circuit arrangement therefore tends towards zero. A low residual voltage, which is always present between the two sensor coils as a result of tolerance-related asymmetries, can easily be compensated by the potentiometer.

The following procedure should be followed for the implementation of the measurement. The smart card to be tested is first placed on the measuring bridge in the centre of the sense coil. As a result of the current flowing through the smart card coil, a voltage us is induced in the neighbouring sense coil. This reduces the symmetry of the measurement arrangement, so that an offset voltage is set at the output of the measurement circuit. To prevent the falsification of the measurement by an undefined offset voltage, the symmetry of the measurement arrangement must be recreated with the measurement object in place by tuning the potentiometer. The potentiometer is correctly set when the output voltage of the measurement bridge reaches a minimum (→ 0).

After the measurement bridge has been adjusted, the reader connected to the field coil sends a REQUEST command to the smart card under test. Now, if the smart card begins to send a response to the reader by load modulation, the symmetry of the measuring bridge is disrupted in time with the switching frequency (this corresponds with the subcarrier frequency fs) as a result of the modulation resistor in the smart card being switched on and off. As a result, a subcarrier modulated RF voltage can be measured at the measurement output of the measuring bridge. This signal is sampled over several periods using a digital oscilloscope and then brought into the frequency range by a discrete Fourier transformation. The amplitudes of the two modulation sidebands fc ± fs that can be seen in the frequency range now serve as the quality criterion for the load modulator and should exceed the limit value defined in ISO/IEC 14443.

The layout of the required coils, a circuit to adapt the field coil to a 50  transmitter output stage, and the precise mechanical arrangement of the coils in the measuring arrangement are specified in the Annex to the standard, in order to facilitate its duplication in the laboratory (see Section 14.4).

Reference Card
As a further aid, the standard defines two different reference cards that can be used to test the power supply of a card in the field of the reader, the transient response and transient characteristics of the transmitter in the event of ASK modulation, and the demodulator in the reader’s receiver.

Power supply and modulation. With the aid of a defined reference card it is possible to test whether the magnetic field generated by the reader can provide sufficient energy for the operation of a contactless smart card. The principal circuit of such a reference card is shown in Figure 9.38. This consists primarily of a transponder resonant circuit with adjustable resonant frequency, a bridge rectifier, and a set of load resistors for the simulation of the data carrier.

To carry out the test, the reference card is brought within the interrogation zone of a reader (the spatial characteristics of the reader’s interrogation field are defined by the manufacturer of this device and should be known at the start of the measurement). The output voltage Umeas of the reference card is now measured at defined resonant frequencies (fres = 13–19MHz) and load resistances (910, 1800 ) of the reference card. The test has been passed if the voltage within the interrogation zone does not fall below a lower limit value of 3 V.

Load modulation. A second reference card can be used to provide a test procedure that makes it possible to test the adherence of the receiver in the reader to a minimum necessary sensitivity. The circuit of this test card largely corresponds with the circuit from Figure 9.38, but it has an additional load modulator.

To carry out the test, this reference card is brought into the interrogation zone of a reader, this interrogation zone being defined by the manufacturer. The reference card thus begins to transmit a continuous subcarrier signal (847 kHz in accordance with ISO/IEC 14443) by load modulation to the reader and this signal should be recognised by the reader within a defined interrogation zone. The reader under test ideally possesses a test mode for this purpose, in which the operator can be alerted to the detection of a continuous subcarrier signal.

Part 7: Test Procedure for Vicinity-Coupling Smart Cards
This part of the standard describes test procedures for the functional testing of the physical interface between contactless smart cards and readers in accordance with ISO/IEC 15693-2. The test equipment and testing procedure for this largely correspond with the testing equipment defined in Part 6. The only differences are the different subcarrier frequencies in the layout of the reference card (simulation of load modulation) and the different field strengths in operation.