Registers – Records – Conductive
Reexamination Certificate
2000-11-15
2003-03-18
Lee, Michael G. (Department: 2876)
Registers
Records
Conductive
C235S380000, C235S435000, C235S441000
Reexamination Certificate
active
06533178
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for a contactless transmission of data between a data transceiver and at least one portable data carrier.
Contactless identification systems with inductive transmission of energy and data from a data transceiver (COD—Card Operating Device) onto a portable data carrier via an alternating magnetic field are used, for example in the case of chip cards. Such a system is described by Klaus Finkenzeller in the book entitled “RFID-Handbuch” [RFID (radio frequency identification) manual], Carl Hanser Publishers Munich 1998, pages 183 to 205. Operating the chip cards with the data transceiver requires a given power to generate the alternating magnetic field.
The antenna for generating the alternating magnetic field is generally an arbitrarily shaped conductor loop. The conductor loop has an inductive reactance under the usual operating conditions. In the normal case, this inductive reactance is compensated through the use of a matching circuit composed of resistors, capacitors and coils, and the antenna is thereby tuned to a resonant frequency. Tuning to the resonant frequency means that the inductive reactance has a value equal to zero, and that essentially only the loss resistances remain as impedance.
It is necessary to match the antenna to resonance when the antenna and the power source are connected in the data transceiver via a cable of unknown length. In order to remain independent of the cable length, the antenna and the power source must be matched to the characteristic impedance of the line. The matching of the antenna to the characteristic impedance is described, for example, in U.S. Pat. No. 5,241,160.
Operation in resonance is usually also employed when the antenna is connected directly to the power source. This is the case, for example, whenever the antenna and the power source are mounted on the same printed circuit board.
When no portable data carrier is located in the alternating magnetic field, a maximum current flows in the case of tuning the antenna to resonance. This maximum current entails a maximum magnetic field.
Consequently, tuning to resonance also causes high losses in no-load operation. No-load operation is understood in the following as the operating state of the data transceiver in which no portable data carrier is located in the active field of the data transceiver. The active range of the data transceiver is that distance from the data carrier to the antenna at which the alternating magnetic field is still just sufficiently large to enable data to be exchanged with the portable data carrier.
The alternating magnetic field, which is generated by the current flowing through the antenna, is mostly much stronger than actually required, particularly in the case of data transceivers of short range (so-called closed coupling systems).
If a portable data carrier is located in the active field, the latter reacts on the antenna. This reaction or feedback can be seen in the occurrence of an additional impedance in the antenna circuit of the data transceiver. If the antenna is tuned to resonance, this reaction is a maximum, that is to say the additional impedance occurring in the antenna circuit effects a reduction in the antenna current, and thus simultaneously a reduction in the magnetic field. This reaction or feedback increases with an increasing coupling between the antenna and the portable data carrier. The coupling is generally larger for smaller distances between the antenna and the portable data carrier. In the most unfavorable case, as the antenna is approached, the portable data carrier can reduce the current through the latter because of the reaction to such an extent that an adequate power supply between the data transceiver and the data carrier is no longer possible.
In order to ensure operation of the data carrier in the active field of the data transceiver, it is therefore necessary, when the antenna is tuned to resonance, to maintain a correspondingly high current in the no-load operation. This ensures that, when a data carrier is in the active range, the magnetic field strength is still adequate, despite the reaction, to preserve an adequate power supply for the data carrier. This means that the current through the antenna is sufficiently strong when a data carrier is brought into the active field very high losses occur as a consequence of the high power for generating the alternating magnetic field in no-load operation.
The mode of operation described in the case of configuring the antenna for resonance is even more disadvantageous when the system is configured for a plurality of data carriers. The reaction or feedback of a plurality of data carriers to the antenna circuit is then multiplied in accordance with the number of the data carriers located in the active field. The power source providing the power for the data transceiver must therefore be even larger, which results in an increase of the required space and in high costs.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device for a contactless transmission of data which overcomes the above-mentioned disadvantages of the heretofore-known devices of this general type and which consumes only little power for generating an alternating magnetic field for a given active range.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for a contactless transmission of data between a data transceiver and at least one portable data carrier, including:
a data transceiver and a portable data carrier;
the data transceiver includes a transmitting device for producing a first signal of a given frequency; a receiving device for receiving a second signal of a given frequency; an impedance-transformed antenna connected to the transmitting device and to the receiving device; and a power supply connected to the transmitting device;
the portable data carrier includes a data carrier antenna for one of receiving and transmitting an induced signal; a circuit configuration connected to the data carrier antenna for processing the induced signal and for producing a signal to be transmitted to the impedance-transformed antenna of the data transceiver; the impedance-transformed antenna of the data transceiver having a total impedance composed of a reactance and an ohmic loss resistance, the reactance being not equal to zero when the portable data carrier is not inductively connected to the impedance-transformed antenna of the data transceiver.
In other words, according to the invention the antenna of the data transceiver is configured in terms of the total impedance, that is to say in a circuit which performs an impedance transformation, such that the reactance is non-vanishing when no portable data carrier is inductively connected to the antenna. In other words, this means that the antenna is not tuned to resonance if no portable medium is located in the active range of the data transceiver.
In this way, the introduction of a reactance into the antenna reduces the current which has to be maintained in the case of a no-load operation by comparison with the prior art. This entails lower low-load losses. For this reason, the power supply can be less powerful and/or of smaller dimensions. There is no need to provide an expensive cooling device. A further advantage is that, due to the reactance already present in no-load operation, upon the introduction of a data carrier, the reaction or feedback in relation to the data carrier on the antenna can be reduced, in other words it is used in an advantageous way. This has the consequence, for example, that the current reduction due to the introduction of the data carrier into the active field is substantially smaller than the current drop in the case of a data transceiver according to the prior art. It is thereby possible to avoid the problem that the current in the antenna can be cut off due to the introduction of a data carrier into the active field.
The reactance can be both, an inductive-type re
Gaul Lorenz
Häring Martin
Greenberg Laurence A.
Ho Lee Seung
Infineon - Technologies AG
Lee Michael G.
Locher Ralph E.
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