NL9100347A - Integrated transformer circuit for ID or credit card - is interrogated via contactless inductive coupling using capacitor to form tuned circuit - Google Patents

Abstract

The integrated circuit (1) mounted in the card has active components (2) connected to a capacitor (5) in parallel with a spiral multi-turn flat primary winding (3) on the surface of the chip. A very thin transformer core (4) passes through the centre of the primary (3) and through the printed circuit one turn secondary winding (6). The primary winding and capacitor form a tuned circuit which determines the operating frequency of the inductive link between the card and a card reading machine. The secondary winding (6) is connected to a flat conductive loop (7) which forms an antenna as it runs around the perimeter of the card.

Description

Extract

The invention relates to a transformer which is part of an antenna configuration in an electronic contactless identification * or Integrated Circuit (IC) card, for example according to the ISO-7816 standard, the transformer secondary coil being part of the integrated circuit in the map.

The core material of the transformer forms a closed loop, which is comprised by both the primary coil and the secondary coil. The integrated circuit has a hole at the center of the secondary coil through which the core material is applied.

Integrated transformer for a contactless identification card. Ing. J.H.L. Hogen Esch

The invention relates to a transformer that is part of an antenna configuration in an electronic contactless identification or Integrated Circuit (IC) card, for example according to the standard ISO-7816, in which the secondary coil of the transformer is part of the integrated circuit in the map.

Integrated Circuit (IC) cards, such as used as a card for financial transactions or as an identification card, according to the ISO-7816 standard, must meet certain requirements with regard to dimensions, flexibility and durability. These requirements will also apply to the contactless implementation of these cards. The standards for these cards are currently in preparation.

A method is known, inter alia, from "Proceedings of the Stanford Conference of Advanced Research in VLSI" 1987, pp 231-247 entitled "Power and Communication Techniques for Physically Isolated Integrated Circuits", in which a coil is contactless inductive coupling is established between an integrated circuit and an inductor coupled to a transceiver. Such a system is also described in Carroll's US patent 4,857,893. The disadvantage of this method is that only little energy can be transferred in this way and that a very precise coupling between the coil on the integrated circuit and the inductor of the transceiver is necessary due to the small size of the integrated circuit. In the present invention, the coil integrated in the integrated circuit is part of a transformer and thus is not directly coupled to the transceiver inductor. To enable information transfer with cards that function without a battery also at a relatively large distance (> 50 cm), the energy consumption of the electronic circuit in the card must not only be very low, but also high demands are placed on the antenna in the map. The antenna in such a card is usually a tuned circuit consisting of an antenna coil with a large number of turns and a capacitor connected in parallel. This antenna not only serves to exchange information with the transmitter / receiver, but also to convert energy from the transmitter field into the energy required for the electronic circuit in the card to function. The aim is to have the information transfer between the card and the sender / receiver take place over the greatest possible distance. This distance is largely determined by the height of the voltage generated by the antenna in the transmission field. Applicant's patent application 9100176 discloses an antenna configuration for contactless identification tags. This antenna configuration consists of an antenna coil with a very limited number of turns, a transformer that transforms the voltage across the antenna coil upwards and a capacitor connected over the transformer's secondary coil, which forms a tuned resonant circuit with the antenna coil via the transformer . The integrated electronic circuit in the contactless identification label is connected across the capacitor and thus also across the transformer's secondary coil. This antenna configuration has the advantage that the large antenna coil can be made extremely thin and flexible, because: it is composed of only a very limited number of turns. In order to use such an antenna configuration in a contactless identification or IC card with dimensions and mechanical properties in accordance with the ISO-7816 standard, the entire antenna configuration must be extremely flat and flexible. In order to allow the greatest possible distance between the card and the transceiver for a given transmit field of the transceiver, the transformer must have a high coupling factor and a large parallel inductance. These conditions can be met by providing the transformer with core material with a high magnetic permeability and by increasing the self-inductance of, in particular, the secondary coil, by assembling this coil from a large number of turns, integrating a transformer with a secondary coil with. such a large number of turns in a card that meets the ISO-7816 standard in terms of dimensions and mechanical properties is difficult to achieve. To meet the thickness and flexibility requirements, it is not possible to use a conventional transformer with copper wire coils wrapped around a core. Such a construction is too thick and not flexible enough.

The invention aims to eliminate the said drawback. By incorporating the transformer's secondary coil into the integrated circuit for the card, it is possible to construct a coil with a large number of turns on a very small area, just a few mm2. At the center of the coil, the integrated circuit has a hole for the core material of the transformer.

Figure 1 schematically shows a possible embodiment of the antenna configuration and the integrated circuit. The following components can be distinguished in figure 1: the integrated circuit (1), in which the electronic circuit (2) is shown hatched; the secondary coil of the transformer (3), which is part of the integrated circuit and is composed of a large number of windings; - the core material (4) of the transformer, which forms a closed loop through the primary and secondary coils of the transformer; - the capacitor (5), which is connected across the secondary coil and which forms a tuned circuit together with the secondary coil, the primary coil, the antenna coil and the core material; - the primary coil (6) of the transformer, which is composed of one or only a few turns; - the antenna coil (7), which is composed of one or only a few turns and which is (are) arranged along the edge of the card.

Figure 2 shows the underside of the integrated circuit, with some of the carrier material being etched or otherwise removed to prevent shorting winding around the core material. The core material may be ferrite or amorphous magnetic material. If ferrite is used, it can be in the form of two U-shaped segments or in the form of a round or square pot core, which encompasses the entire integrated circuit. The latter has the additional advantage that the integrated circuit is immediately protected against external influences. Amorphous magnetic material can be used in the form of a wire which is wound through the hole in the integrated circuit around this integrated circuit and one or several primary winding (s). In order to prevent the mono-crystal conductive support material on which the integrated circuit is built from acting as a short circuit winding, this material will have to be removed locally from the hole in the integrated circuit to the outside. This can be done, for example, by etching away this material, as shown in figure 2. The secondary coil, mounted on the integrated circuit, can, as shown in figure 1, be arranged next to the other electronic components in this circuit. However, it is also possible to arrange this secondary coil on top of the other electronic components, saving space and using a smaller circuit. A great advantage of the construction of the transformer according to this invention is further that no connections in the form of bonds using gold or aluminum wire from the chip or the integrated circuit to a second carrier are required, which makes a relatively inexpensive construction. to realise. However, this is only possible if the capacitor (5) can be integrated sufficiently accurately and reproducibly into the integrated circuit, or if provision is made for precisely adjusting the value of this capacitor afterwards, for example by laser trimming or electronically. .

Claims (5)

Integrated transformer for a contactless identification or integrated circuit card, characterized in that the secondary coil of this transformer forms part of the integrated circuit and is arranged around a hole in the integrated circuit and the core material of this transformer forms a closed loop through both the primary coil and the secondary coil of the. transformer is included. Integrated transformer for a contactless identification or integrated circuit card according to claim 1, characterized in that the core material of the transformer consists of two, through the hole in the integrated circuit and around one or several primary winding (s), clamped U-shaped ferrite parts. Integrated transformer for a contactless identification or integrated circuit card according to claim 1, characterized in that the core material of the transformer consists of two, through the hole in the integrated circuit and around one or several primary winding (s), round or rectangular ferrite pot core clamped together. Integrated transformer for a contactless identification or integrated circuit card according to claim 1, characterized in that the core material of the transformer consists of amorphous magnetic material, which in the form of a wire passes through the hole in the integrated circuit, round the integrated circuit and one or several primary winding (s) is wound. Integrated transformer for a contactless identification or integrated circuit card according to one or more of the preceding claims, characterized in that the conductive monocrystalline carrier material of the integrated circuit locally from the hole, intended for: the core material, up to has been removed from the outer edge of the integrated circuit to prevent a short-circuit winding around the transformer's core material, which would result in strong attenuation.