Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1999-03-29
2004-08-17
Horabik, Michael (Department: 2635)
Communications: electrical
Selective
Interrogation response
C340S010510, C340S010400, C340S010340, C340S572400, C340S572100, C340S010500
Reexamination Certificate
active
06778070
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a remote transmission apparatus for portable objects such as cards, tickets, labels, etc. connected by inductive coupling to a fixed station such as a card or label reader or interrogator.
The invention has applications in all areas where data are to be exchanged by induction without physical contact between a portable object and a fixed station, in particular in the field of identifying items or objects, for example in controlling access to IT services, or card-payment tolls.
BACKGROUND ART
Techniques are known in the field of data exchange without physical contact for producing one- or two-way systems in which data are exchanged by induction between portable objects and a fixed station.
“Fixed station” is understood to mean any relatively large-size interrogator, reader or any type of receiver that contains its own power-supply means that are usually standard electrical equipment.
“Portable object” is understood to mean any chip-card, label or any type of small-size transponder that uses a very restrictive independent power source to send data to the fixed station. The portable objects are usually small, being the size of a credit card, for example. The portable object may be active, i.e. containing its own power source such as a battery or cell, or passive, i.e. remotely powered. A remotely powered portable object draws its power from the fixed station by means of inductive coupling which, in these systems, is achieved by means of coil-type antennas in conductor circuits. Consequently the portable object is no longer powered when it leaves the electromagnetic field of the fixed station, i.e. as soon as nominal coupling conditions are no longer present.
A standard system for exchanging data by inductive coupling is shown in FIG.
1
. The data exchange system generally comprises a fixed station
1
and one or more portable objects
10
. The fixed station
1
comprises a set of electronic circuits
2
, coupled to two antenna coils
3
and
4
. One of the antenna coils (coil
4
) emits an alternating magnetic field which is used to send data intended for the portable object
10
. A second antenna coil
3
collects a signal induced by the secondary emission caused by the current induced in the antenna of the portable object.
In the embodiment shown in
FIG. 1
the fixed station comprises two antennas, one for receiving and one for transmitting messages. It is, however, possible to use the same antenna to fulfil these two functions.
Portable object
10
comprises a set of electronic circuits
11
connected to the terminals of an antenna coil
12
. In the embodiment shown in
FIG. 1
a capacitor
13
is connected in parallel to the terminals of antenna
12
to form a resonant circuit.
A fixed station usually emits a powerful alternating magnetic field in a volume of space chosen for the application. As described by Lenz's law, the portable object interacts with this magnetic field via its antenna by emitting a secondary magnetic field that is a function of the impedance of the circuits connected to the antenna. In return, the secondary field induces a voltage that is detectable in the antenna of the fixed station.
This type of data exchange method is described, for example in the patent U.S. Pat. No. 3,299,424. This patent particularly describes a data exchange system in which the portable object is remotely powered and comprises a single antenna coil. In this patent the means for transmitting the data from the portable object to the fixed station consists of an impedor connected in series with a circuit breaker, the resulting assembly being connected to the terminals of the antenna. The impedance of the circuits connected to the antenna coil is thus modulated, as is the secondary magnetic field and consequently the associated voltage induced in the antenna of the fixed station.
This patent also describes the use of a capacitor combined with the antenna coil of the portable object in order to obtain a parallel inductance-capacitance resonant circuit designed to increase the voltage on the terminals of the antenna by creating an overvoltage relative to the electromotive force (e.m.f.) in the coil and increasing the effect induced in return in the coil antenna of the fixed station due to the presence of the portable object.
However, the means used in this patent to recover the remote power supply are closely related to the data transfer means which, in this system, consist of a diode tunnel.
Other more recent documents such as the patents U.S. Pat. No. 4,196,418 and FR-A-2 623 311 describe remotely powered portable objects in which the power supply is collected by the portable object from the induced voltage available on the terminals of the antenna of the portable object. This voltage, which is an alternating voltage on the terminals of the antenna, is transformed into a DC voltage by a rectifier that consists, in these systems, of a twin-diode voltage doubler connected to one of the terminals of the antenna, the other terminal of the antenna being connected to the mid-point of two storage capacitors that collect the rectified voltage.
Another patent, EP-0 204 542, describes a system that comprises means for rectifying the voltage achieved using two diodes, the mid-point of the antenna coil being connected to the zero point of the assembly.
In other systems the rectifying means are achieved using a four-diode bridge, namely a Graetz bridge, or MOS transistors wired as diodes (i.e. transistors whose gate is connected to their drain). These rectifying means are particularly described in documents U.S. Pat. No. 5,479,172 and WO-96 38805.
Patent WO 97/05504 describes a data exchange system that comprises a voltage-trebling rectifier together with a modulation function that acts on the antenna of the portable object; the antenna itself is connected in parallel to a capacitor to form a resonant circuit.
The systems described in patents U.S. Pat. No. 4,196,418 and FR-2 623 311 (described above) also comprise a stabilization function of the rectified voltage added to the remote power supply function described above. This stabilization function of the rectified voltage is achieved using a simple electronic component, namely a Zener diode. The electromotive force induced in the antenna coil of the portable object is proportional to the mutual coupling coefficient between the coil and that of the antenna of the fixed station. This coupling coefficient may vary over a wide range of values that reflect the required operating flexibility without physical contact. The voltage available on the terminals of the portable object is determined by the electromotive force, the internal impedance of the antenna and the load connected to it. The non-linear voltage-current characteristics of a Zener diode make it capable of simply stabilizing the rectified voltage.
The rectified voltage stabilizing function may also be performed using an electronic arrangement comprising a reference voltage, a differential amplifier and a controlled resistor, for example a transistor. This electronic arrangement, normally known as a shunt regulator, adapts the load connected to a voltage generator with a non-negligible internal impedance so that the voltage output by the generator is at a given value; the voltage generator may, for example, be an antenna connected to a rectifier.
Numerous documents describe a shunt regulator applied to a remote data exchange system. Examples of these documents are patents U.S. Pat. Nos. 5,302,954, 5,479,172 and EP-A2-0 706 151.
In remote data exchange systems it is possible to regulate voltage using a series regulator that supplies on output a regulated voltage with a given value converted from a non-regulated voltage of a higher value applied to its input. However, this type of regulator has the drawback of not controlling the voltage applied on input; this voltage may therefore be high. In a portable object in which all the electronic circuits may be integrated in a single electronic chip, voltage strength requirements apply t
Brown Vernal
Commissariat a l'Energie Atomique
Hayes & Soloway P.C.
Horabik Michael
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