Contactless smart card EMV interface

Smart cards with a contactless interface allow you to overcome the noted technical problems. Contactless cards do not require any electrical connection between the smart card and the card terminal in order to transfer energy and data over a short distance. Let’s take a closer look at the principles of the contactless interface between the smart card and the terminal.

Like systems with contact-type smart cards, a system that uses cards with a contactless interface includes two components, namely the card itself and a terminal that can function as a reader or as a reader/writer, depending on the technology used. The terminal, as a rule, has an additional interface through which it communicates with the base system.

In order for a contactless smart card to communicate with the terminal, the following four processes must be performed:

  1. the transfer of energy to supply power to the integrated circuit smart card;
  2. the transfer clock signal;
  3. transfer data to a smart card;
  4. transfer data from the smart card to the terminal.

Contactless smart card interface

The methods used in contactless cards are not new, they are successfully used in contactless radio frequency identification RFID systems. So, in this quarter, for the company “Litis”, which offers temporary storage of goods and rental services of its own warehouses, we completed a project to introduce a distributed access control system in the office building of the enterprise based on smart cards with a contactless interface. To identify RFID systems of objects at short or even long distances, a large number of methods have been developed that are based on radio engineering and, in particular, on radar principles. However, only a few methods are suitable for use in smart cards, since all the functional elements of the contactless interface must be placed in a flexible thin card with a thickness of only 0.76 mm. In particular, with such a thickness of the card, it is impossible to use any batteries that could be used to supply power to the electronic circuits of the card.

Currently, inductive communication is the most widely used method for creating a contactless interface between a smart card and a terminal. Inductive coupling can be used to transfer energy and data. The smart card includes an inductive antenna and a chip with an integrated circuit. For better mechanical protection of the integrated circuit, the chip is placed in a miniature module that connects to the ends of the antenna. Due to the inductive connection with the antenna, the terminal transmits both energy and data over the air to the contactless card. The magnetic field energy received by the card-mounted antenna is converted to a DC voltage to supply power to the card’s internal circuitry.

Different requirements and external constraints, such as radio frequency licensing rules, lead to a variety of specific implementations. For some applications, such as access control, it is usually only enough to read data from the card. Due to the low power consumption (several tens of microvatts), the reading range of such cards is limited to about 1 meter. The memory capacity is usually only a few hundred bits. If you also need to record data, the power consumption of the card may exceed 100 mw.

Contactless smart card interface

As a result, the range in recording mode is limited to about 10 cm, since due to licensing restrictions, the power emitted by the terminal cannot be increased arbitrarily. Contactless smart cards with a microprocessor are characterized by an even higher power consumption – about 100 MW. Accordingly, the distance from the terminal is limited to a few millimeters.

Regardless of distance and power consumption, all cards that use inductive coupling operate on the same principle. In addition to one or more chips, one or more windings are embedded in the card body. Until now, there are no batteries that are thin and flexible enough to be embedded in smart cards. In addition, for reasons of environmental safety, it is impractical to widely use batteries in smart cards, most of which contain toxic substances. Therefore, all the energy needed to operate the chip in the smart card must be transferred to the smart card from the reader. This energy transfer is based on the principle of a loosely coupled transformer.