Electronic device for and method of contactless transmission of data

FIELD OF THE INVENTION

The invention relates to an electronic device, in particular a smart card. Beyond this, the invention relates a system for contactless transmission of data. Furthermore, the invention relates to the use of an autotransformer. Moreover, the invention relates to a method of contactless transmission of data.

BACKGROUND OF THE INVENTION

So-called smart cards are used in many technical fields, like credit cards, or identification cards. Such a smart card is defined as any pocket-sized card with embedded integrated circuits which can process information. For the communication between a contactless smart card and a reader an antenna system is used. Such an antenna system uses the idea of a coreless transformer to transfer energy and is used to transfer data. The flow of data is bidirectional. So the card has to modulate the field coming from the reader to transfer the data back to the reader. Typical credit cards have a normalized size according ID-I of the ISO 7810 standard.

This ID-I refers to a given size of the credit card (smart card) and further corresponds to a given antenna size. In case smaller smart cards should be developed also the area available for the antenna is decreased possibly leading to a decreased modulation ability of the smart card.

OBJECT AND SUMMARY OF THE INVENTION

It may be an object of the invention to provide an electronic device for contactless transmission of data, a system for contactless transmission of data, a use of an autotransformer, and a method of contactless transmission of data, wherein the electronic device may be suitable to provide an improved capability for signal modulation. In order to achieve the object defined above, an electronic device for contactless transmission of data, a system for contactless transmission of data, a use of an autotransformer, and a method of contactless transmission of data according to the independent claims are provided.

According to an exemplary embodiment an electronic device for contactless transmission of data comprises an autotransformer.

According to an exemplary embodiment a system for contactless communication comprises an electronic device according to an exemplary embodiment and a reader unit, wherein the electronic device is adapted to modulate a communication signal transmitted by the reader unit. In particular, the reader unit or reader device may be adapted to receive the communication signal modulated by the electronic device.

According to an exemplary embodiment a use of an autotransformer in an electronic device for contactless transmission of data is provided. According to an exemplary embodiment a method of contactless transmission of data by an electronic device according to an exemplary embodiment is provided, wherein the method comprises sending communication data from a reader unit, and modulating the sent communication data by the electronic device. In particular, the communication may be received by the electronic device before they are modulated and/or the modulated communication data may be sent back to the reader unit.

The term "autotransformer" may particularly denote a transformer comprising a single winding, having at least three connection points or taps. The voltage source is applied to two taps and a load is connected to two taps one of which is usually a common connection that is also connected to the source. Each tap corresponds to a different source or load voltage. In an autotransformer a portion of the same winding effectively acts as part of both the primary and secondary winding.

The term "contactless transmission" may particularly denote a transmission of a signal, or analog or digital data from a sending unit to a receiving unit, wherein the sending unit and the receiving unit are not directly connected by a connection line, e.g. either an electrically conductive line or a connection line adapted to transmit light. Thus a contactless transmission may be performed by an electromagnetic wave of any suitable frequency, e.g. a radio wave, a microwave, or a wave of infrared light.

By providing an electronic device having an autotransformer included it may be possible to provide a device wherein the Eigenfrequency of the electronic device is determined by the inductivity of the whole winding but only a portion of the voltage induced into the electronic device, having an integrated circuit implemented, for example, may be useable by the electronic device. This may lead to the fact that the modulation is increased, since typically the modulation depends on the voltage or power usable for the electronic device. Thus, the

amplitude of the modulation may be increased since the modulation is performed according to the lesser voltage of the autotrans former, while the transmission back to the sending or reader unit is performed according to the whole voltage. Thus, it may be possible that an electronic device according to an embodiment may cancel the disadvantages of smaller magnetic loop antenna systems on the electronic device, i.e. it may be possible to increase the modulation amplitude by the same size or to hold the modulation amplitude when decreasing the size. It may be seen as a gist of an exemplary embodiment that only a part of a voltage induced into the electronic device may be used by an integrated circuit of the electronic device due to the use of an autotransformer. This smaller voltage influences a stronger modulation of the integrated circuit. This modulation itself may operate not only an active part of the autotransformer, i.e. the portion the integrated circuit is connected to, but the whole autotransformer. This use, i.e. the use of the autotransformer in the reverse direction, may increase the load modulation, which may be equal the Sideband levels, a reader unit may detect on the card. Further, it may not be necessary to redesign existing hardware. Next, further exemplary embodiments of the electronic device for contactless transmission of data are described. However, these embodiments also apply to the system for contactless transmission of data, the use of an autotransformer, and the method of contactless transmission of data.

According to another exemplary embodiment of the device the autotransformer comprises at least three connection points, wherein one connection point forms an open end.

The term "open end" may particularly denote that one end or tap of the autotransformer is not connected to a further element of the integrated circuit. In particular, this may correspond to the fact that the open end is not connected to ground. By using an autotransformer having an open end it may not be necessary to redesign existing hardware in order to ensure a sufficient load modulation even for a small electronic device, e.g. an electronic device smaller than the ID-I standard of the ISO 7180, e.g. a smart card having only half of the corresponding size. This may be ensured by just using the open turn antenna topology. By using such a topology it may in particular possible to provide an antenna, wherein the resonance frequency is determined by the sum of all windings, while the voltage in the integrated circuit of the smart card is only determined by the number of windings in the active part of the autotransformer or card antenna.

According to another exemplary embodiment of the device the electronic device is a contactless transponder. In particular, the contactless transponder may be formed by a smart

- A - card or an RFID tag or RFID label. For example, the contactless transponder may be a passive RFID tag or a passive smart card.

According to another exemplary embodiment of the device the autotransformer forms an antenna of the electronic device. In particular, the antenna may be a loop antenna. By using the autotransformer as an antenna of the electronic device an efficient way to manufacture a passive electronic device, e.g. a passive smart card, may be provided. In particular, the autotransformer may be an efficient way to split the antenna in two parts, one "active part" which is conducted to both sides of an integrated circuit or electronic module of the electronic device. The second part is a passive one. This passive part is connected on one side to the integrated circuit or chip module and open on the other side. These two parts may work as one Antenna. This may influence the communication between the electronic device, e.g. smart card, and a reader unit in such a way that only the active part of the antenna with reactions on both parts, i.e. of the whole antenna system, may to be handled With such an antenna topology only a part of the whole induced voltage may be used by the integrated circuit. This smaller voltage influences a stronger modulation of the integrated circuit. This modulation itself may operate not only an active part of the antenna, i.e. the portion the integrated circuit is connected to, but the whole antenna. This use, i.e. the use of the autotransformer in the reverse direction, may increase the load modulation, which may be equal the Sideband levels, a reader unit may detect on the card. According to another exemplary embodiment of the device the autotransformer is adapted to provide a fixed transformation ratio.

In particular, the term "transformation ratio" may denote a ratio between a primary voltage and a secondary voltage, which may correspond to the number of windings of the primary side and the number of windings on the secondary side. In case of an autotransformer the ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. Thus, a fixed transformation ratio may mean that only three connection points are present and no switching between different voltages on the secondary side is possible.

According to another exemplary embodiment the device further comprises an electronic circuit comprising a first contact terminal and a second contact terminal, wherein one connection point of the autotransformer is fixedly connected to the first contact terminal, and wherein another connection point of the autotransformer is fixedly connected to the

second contact terminal. In particular, a third contact point forms an open end, i.e. is not connected to any contact terminal.

The term "fixedly connected" may particularly denote the fact that the two parts are fixed to each other in a way the connection is not easily disconnected again, i.e. fixedly connected does not include a connection by a switching element or by a plug or clip. Thus, it may in particular the case that the autotransformer is not switchable, has a fixed inductivity, and a fixed voltage ratio. This may be a substantial difference to electronic devices like smart cards using a switchable antenna topology in order to change the Eigenfrequency or resonant frequency of the smart card. Embodiments of the above described open turn antenna topology may be used for all applications concerning to ISO/IEC 14443 and MasterCard - standard that need smaller antenna systems than ID-I, e.g. payment solutions.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. Fig. 1 schematically illustrates a system for contactless communication according to an exemplary embodiment.

Fig. 2 schematically illustrates a detail of a smart card using an autotransformer. Fig. 3 schematically illustrates some Sideband levels for smart cards samples using an autotransformer. Fig. 4 schematically illustrates some Sideband levels over fieldstrenght for some of the smart cards of Fig.3.

DESCRIPTION OF EMBODIMENTS

The illustration in the drawing is schematically. In different drawings, similar or identical elements are provided with similar or identical reference signs.

Fig. 1 schematically shows a system for contactless communication 100 according to an exemplary embodiment. The system 100 comprises a reader unit or reader 101 and a smart card 102, which may be a passive smart card like a credit card. The reader unit 101 is only indicated by a reader antenna 113. The smart card 102 comprises a card antenna 103, and an integrated circuit or chip module 104. The card antenna 103 is formed by an autotransformer having exactly three connection points. The card antenna has two parts, namely a passive part 110 which is formed by an open end 105, i.e. a first one of the connection points, and a second connection point 117, which is connected to the integrated circuit 104. Furthermore, the card antenna 103 comprises an active part 108, which is formed by the second connection point 117 and a third connection point 119 which are both contacted to the integrated circuit 104. By using an autotransformer as the card antenna only a part of the whole induced voltage is used for the chip, namely the voltage corresponding to the number of windings between the second connection point 117 and the third connection point 119. Thus, the whole induced voltage PCD is divided between the two parts of the card antenna (active and passive) according to their respective windings. The smaller voltage PICC induced into the active part 108 influences a stronger modulation of the integrated circuit. This modulation itself operates not only the active part 108 of the card antenna, but the whole card antenna. This use, i.e. the use of the card antenna formed by an autotransformer in the reverse direction, may increase the load modulation, which may be equal the Sideband levels, the reader unit 101 may detect on the smart card 102.

Fig. 2 schematically illustrates a detail of the smart card 102 of Fig. 1 using an autotransformer as the card antenna 103. The card antenna 103 is formed by a loop antenna having an open end 105. The use of an open end may be advantageous since it may be possible to save a via or bridge, since no turns of the loop antenna have to be bridged. The passive part 110 of the loop antenna is indicated by the area surrounded by the dashed line 211 and is formed between the open end 105 and the second connection point 117. The active part 108 is indicated by the area between the pointed line 212 and the dashed line 211 and is formed between the second connection point 117 and the third connection point 119 both of which are fixedly connected to the integrated circuit 104, i.e. no switching is possible between different turning ratios of the autotransformer built by the card antenna 103. According to Fig.

2 the active part 108 comprises more than one full loop, so that a bridge 213 or a via is necessary. However, the active part 108 may be formed by less than a complete loop leading to the fact that no via or bridge is necessary to connect the second connection point 117 to the integrated circuit 104. In general the number of active and passive turns may depend on the thickness of the used wires or printed lines, its accuracy of winding, e.g. gaps between the wires, and the area the wires enclose. These parameters are also responsible for the resonance frequency of the smart card, which includes the card antenna or autotransformer and the integrated circuit connected thereto. In most cases the single wires are lying directly on each other, i.e. each turn is directly adjacent to the next turn, so that the single turns touch each other. This may be an important production matter, since this possibly influences the resonance frequency dramatically.

Fig. 3 schematically illustrates some Sideband levels for smart cards samples using an autotransformer. In particular, Fig. 3a shows Sideband levels for ten antennas connected to a first type of smart cards, the so-called P5CD009, wherein the antennas having half the size of an typical antenna of an ID-I card. The first nine antennas are different with respect to the winding ratio and further the tenth one is a common loop antenna, i.e. an antenna not formed by an autotransformer. The first antenna 301 of which the result is shown in Fig. 3a has a winding ratio of 4 to 12, a size of 77 mm to 19 mm, and a wire diameter of 0.14 mm. The winding ratio is defined by the number of winding or turns of the active part to the number of turns in the passive part. The second antenna 302 of which the result is shown in Fig. 3 a has a winding ratio of 4 to 13, a size of 76 mm to 18 mm, and a wire diameter of 0.14 mm. The third antenna 303 of which the result is shown in Fig. 3a has a winding ratio of 4 to 13, a size of 77 mm to 19 mm, and a wire diameter of 0.14 mm. The fourth antenna 304 of which the result is shown in Fig. 3a has a winding ratio of 4 to 14, a size of 76 mm to 18 mm, and a wire diameter of 0.14 mm. The fifth antenna 305 of which the result is shown in Fig. 3a has a winding ratio of 4 to 9, a size of 78 mm to 20 mm, and a wire diameter of 0.1 mm. The sixth antenna 306 of which the result is shown in Fig. 3 a has a winding ratio of 4 to 10, a size of 77 mm to 19 mm, and a wire diameter of 0.1 mm. The seventh antenna 307 of which the result is shown in Fig. 3a has a winding ratio of 4 to 11 , a size of 77 mm to 19 mm, and a wire diameter of 0.1 mm. The eighth antenna 308 of which the result is shown in Fig. 3a has a winding ratio of 4 to 11 , a size of 77 mm to 19 mm, and a wire diameter of 0.1 mm. The ninth antenna 309 of which the result is shown in Fig. 3a has a winding ratio of 4 to 12, a size of

77 mm to 19 mm, and a wire diameter of 0.1 mm. The tenth antenna 310 of which the result is shown in Fig. 3a is a common loop antenna.

As can be seen from Fig. 3a all nine antennas which are formed by an autotransformer result in a Sideband level above a threshold level of 5 mV, while the Sideband level corresponding to the common loop antenna 310 is below this threshold level.

Furthermore, Fig. 3b shows Sideband levels for eight antennas connected to a second type of smart cards, the so-called Desfϊre 8, wherein the antennas having half the size of an typical antenna of an ID-I card. The first seven antennas are different with respect to the winding ratio while the eight one is a common loop antenna, i.e. an antenna not formed by an autotransformer. The first antenna 311 of which the result is shown in Fig. 3b has a winding ratio of 4 to 12, a size of 77 mm to 19 mm, and a wire diameter of 0.14 mm. The winding ratio is defined by the number of winding or turns of the active part to the number of turns in the passive part. The second antenna 312 of which the result is shown in Fig. 3b has a winding ratio of 4 to 13, a size of 76 mm to 18 mm, and a wire diameter of 0.14 mm. The third antenna 313 of which the result is shown in Fig. 3b has a winding ratio of 4 to 13, a size of

77 mm to 19 mm, and a wire diameter of 0.14 mm. The fourth antenna 314 of which the result is shown in Fig. 3b has a winding ratio of 4 to 14, a size of 76 mm to 18 mm, and a wire diameter of 0.14 mm. The fifth antenna 315 of which the result is shown in Fig. 3b has a winding ratio of 4 to 9, a size of 78 mm to 20 mm, and a wire diameter of 0.1 mm. The sixth antenna 316 of which the result is shown in Fig. 3b has a winding ratio of 4 to 10, a size of

77 mm to 19 mm, and a wire diameter of 0.1 mm. The seventh antenna 317 of which the result is shown in Fig. 3ba has a winding ratio of 4 to 11 , a size of 77 mm to 19 mm, and a wire diameter of 0.1 mm. The eighth antenna 320 is a common loop antenna. As can be seen from Fig. 3b all seven antennas which are formed by an autotransformer results in a Sideband level above a threshold level of 5 mV, while the Sideband level corresponding to the common loop antenna 318 is below this threshold level.

Fig. 4 schematically illustrates some Sideband levels over fieldstrength for some of the smart cards of Fig.3a. Furthermore, a new ISO limit is indicated in Fig. 4 corresponding to ISO/IEC 14443 and test standard ISO/IEC 10373-6. In particular, Fig. 4a shows the upper and lower Sideband levels for five antennas connected to the first type of smart cards of Fig. 3a, e.g. the first four smart cards as shown in Fig. 3a, and further the smart card connected to a common loop antenna.

In particular, the line 401 indicates the lower Sideband level (SBL) of the smart card corresponding to column 301 in Fig. 3a. The line 402 indicates the upper SBL of the smart card corresponding to column 301 in Fig. 3a. The line 403 indicates the lower SBL of the smart card corresponding to column 302 in Fig. 3a. The line 404 indicates the upper SBL of the smart card corresponding to column 302 in Fig. 3 a. The line 405 indicates the lower SBL of the smart card corresponding to column 303 in Fig. 3a. The line 406 indicates the upper SBL of the smart card corresponding to column 303 in Fig. 3a. The line 407 indicates the lower SBL of the smart card corresponding to column 304 in Fig. 3a. The line 408 indicates the upper SBL of the smart card corresponding to column 304 in Fig. 3a. The line 409 indicates the lower SBL of the smart card corresponding to column 310 in Fig. 3a, i.e. the common type loop antenna. The line 410 indicates the upper SBL of the smart card corresponding to column 310 in Fig. 3a. The line 430 corresponds to a new ISO limit

As can be seen from Fig. 4a the smart cards using an antenna topology or an autotransformer topology according to an exemplary embodiment show a higher SBL over all tested filedstrengths compared to the smart card using a common type antenna topology. In particular, also at low fϊeldstrength the smart cards using an antenna topology according to an exemplary embodiment have a SBL higher than the new ISO limit.

In particular, Fig. 4b shows the upper and lower SBL for five antennas connected to the second type of smart cards of Fig. 3, e.g. the first four smart cards as shown in Fig. 3b, and further the smart card connected to a common loop antenna.

In particular, the line 411 indicates the lower SBL of the smart card corresponding to column 311 in Fig. 3b. The line 412 indicates the upper SBL of the smart card corresponding to column 311 in Fig. 3b. The line 413 indicates the lower SBL of the smart card corresponding to column 312 in Fig. 3b. The line 414 indicates the upper SBL of the smart card corresponding to column 312 in Fig. 3b. The line 415 indicates the lower SBL of the smart card corresponding to column 313 in Fig. 3b. The line 416 indicates the upper SBL of the smart card corresponding to column 313 in Fig. 3b. The line 417 indicates the lower SBL of the smart card corresponding to column 314 in Fig. 3b. The line 418 indicates the upper SBL of the smart card corresponding to column 314 in Fig. 3b. The line 419 indicates the lower SBL of the smart card corresponding to column 320 in Fig. 3b, i.e. the common type loop antenna. The line 420 indicates the upper SBL of the smart card corresponding to column 320 in Fig. 3b. The line 430 corresponds to the new ISO limit.

As can be seen from Fig. 4b as well, the smart cards using an antenna topology or an autotransformer topology according to an exemplary embodiment show a higher SBL over all tested fieldstrengths compared to the smart card using a common type antenna topology. In particular, also at low fϊeldstrength the smart cards using an antenna topology according to an exemplary embodiment have a SBL higher than the new ISO limit.

Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.