MXPA99003464A - Data-transmission circuit with a station and a response circuit - Google Patents

Abstract

The invention concerns a data-transmission circuit with a station (1) and a response circuit (2), the station comprising a primary coil (4) with a signal generator (3) for generating a magnetic alternating field at a carrier frequency, and an amplitude demodulator (6). The response circuit (2) comprises a secondary coil (7) and an amplitude modulator (13) for influencing the load on the secondary coil. The amplitude modulator (13) is designed such that the magnetic alternating field can be modulated by a data signal.

Description

CIRCUIT OF TRANSMISSION OF DATA WITH A STATION AND WITH A CIRCUIT OF RESPONSE FIELD OF THE INVENTION The invention relates to a data transmission circuit with a station and with a response circuit, the station presenting a primary coil with a signal generator to produce an alternating magnetic field with a carrier frequency, as well as a amplitude demodulator, the response circuit having a secondary coil as well as an amplitude modulator to influence the secondary coil load and the amplitude modulator being configured in such a way that the alternating magnetic field can be modulated with a signal of data.

BACKGROUND OF THE INVENTION Data transmission circuits of this type are used in particular in SPR (Simultaneous) systems Powering and Reading) with inductive transmission of energy and data. This type of SPR systems are also used in applications with contactless chip cards. In operation, the signal generator of the station produces a periodic signal for the primary coil, on the basis of which an inductive alternating field is formed in its zone, or well, an alternating magnetic field, which acts in the area around the primary coil as a so-called "near field". In contrast to an electromagnetic wave that starts from the primary coil, the purely inductive action of the signal that starts from the primary coil is in the near field of the primary coil. In the area of this near field, a response circuit can be introduced, which obtains its operation energy particularly from the alternating magnetic field. For this, the response circuit is equipped with a secondary coil, in which the alternating magnetic field is induced. The alternating voltage that is induced in said place is rectified in the response circuit, filtered and fed to a data signal generating block. This is so connected to an amplitude modulator arranged in particular in the area of the secondary coil, that the modulator, depending on a data signal generated by the data signal generation block, can modify the coil load. high school. For this, in the state of the art, the amplitude modulator must be configured as a variable resistive load, the resistance load of the secondary coil being modified accordingly according to the data signal. A modification of this type of resistance load of the secondary coil has the consequence that the electrical properties of the primary coil on the side of the station, since there is an inductive coupling between the primary and secondary coils. The coupling factor of this inductive coupling is usually between one and five percent. In the aforementioned manner, the alternating magnetic field can be modulated with the data signal of the response circuit, if this is in the area close to the primary coil. On the side of the primary coil, the amplitude demodulator explores the voltage that is modified by the data signal, which falls on the primary coil, and reconstructs the data signal from the above. With the data transmission circuit of this type, power can be reliably supplied to the response circuits, further ensuring that a data signal emitted by the response circuit can be read on the side of the station. However, by practically applying data transmission circuits of this type, it has been observed that, in particular in the case of series production thereof, situations often arise in which the data signal modulated by the response circuit according to the alternating magnetic field, can not be rebuilt on the side of the station. The foregoing, especially in the case of application of the transmission circuit of this type in vehicle locks in vehicles, led to the user of a vehicle, despite being authorized, can not use it. British Patent GB-A-2 232 851 shows a loosely coupled transformer, through which energy is supplied to a measuring circuit, for example, in a movable part of a vehicle. The transformer is charged by the measurement electronics through a switch, namely with a frequency, whose integral multiple is the power supply frequency. This periodic load is modulated in terms of its phase, when the level of a binary data signal is modified, the data signal being transmitted by the measurement circuit. The modulated signal is transmitted again to the primary side of the transformer and, to obtain the data, it is demodulated by multiplication with a periodic signal.

OBJECTIVES AND ADVANTAGES OF THE INVENTION The objective of the invention is to provide a data transmission circuit of the aforementioned type, which always works reliably. In accordance with the invention, said objective is achieved when the response circuit additionally has a phase modulator to influence the electrical properties of the secondary coil, the amplitude modulator and / or the phase modulator being configured in such a way that they can be controlled by at least one modulation signal. The object of the invention is based on the fundamental knowledge for the same that, in particular in the case of a series production of a response circuit, due to manufacturing tolerances, the primary circuit may be untuned with respect to the coil primary and secondary circuit, with respect to the secondary coil. In certain coupling factors, in particular in those dependent on the distance between the secondary and primary coils, this leads to the fact that the reception voltage in the primary coil is no longer modulated according to a purely amplitude modulation. Rather, the reception voltage in the primary coil, under certain conditions, is modulated according to a phase modulation. Since only one amplitude demodulator is provided on the station side, it can no longer demodulate the phase-modulated signal, which is expressed as a so-called zero point in the demodulation of the received signal. By configuring the response circuit according to the main claim 1, it is achieved that the alternating magnetic field can be subjected to both an amplitude modulation and a phase modulation.

By activating or deactivating the amplitude modulator and / or the phase modulator appropriately, it is possible to achieve that both modulations are out of phase, for example, with respect to the modulation signal, by 90 °. When both modulations are subsequently carried out in an adequate manner in terms of intensity, so that in relation to the amplitude they generate approximately equal sidebands, then, with an adequate phase shift of the amplitude and phase modulation, an elimination of a lateral band of modulation. In this way, with respect to the amplitude modulation, independently of the manufacturing tolerances and variable distances of the response circuit and the station, so-called "modulation zero points" are avoided. In addition, both an amplitude modulator and, according to claim 2, a phase modulator can demodulate the signal at any time, since the modulation according to the invention of the alternating magnetic field leads only to phase differences of the received data signal. , which do not disturb in the case of a data signal encoded in a desired manner. In accordance with the fundamental idea of the invention, it is sufficient when the phase modulation and the amplitude modulation are performed in such a way on the side of the response circuit, that a sideband of the amplifier is weakened. alternating magnetic field with respect to the other lateral band. Simply by this measure the advantage according to the invention is achieved, according to which, on the part of the station, only one phase demodulator is sufficient to demodulate the data signal modulated with the carrier signal. In accordance with the invention, the amplitude modulator is configured as a resistor that can be connected in parallel to the secondary coil. The phase modulator according to the invention can be configured as a capacitor which can be connected in parallel to the secondary coil, the capacitor having the function of a phase-shifting capacitor. In one embodiment of the response circuit, the invention is provided with an intermediate modulation device for modulating the data signal with an auxiliary carrier signal, the frequency of which is, in particular, different from the frequency of the carrier signal, or alternatively, of the alternating magnetic field. The auxiliary carrier signal can be obtained advantageously from the carrier signal, namely by applying a frequency divider in a cycle bypass device. The system cycle then indirectly serves to control the phase and / or amplitude modulator. However, the auxiliary carrier signal can be generated in another way.

According to the invention, the result of the modulation of the data signal and the auxiliary carrier signal are subsequently modulated with the alternating magnetic field. In this way, a particularly simple configuration of the amplitude demodulator results, since the result of the modulation can be demodulated in a particularly simple manner. The response circuit can have a phase-shifting device, which can be configured in such a way that from the cycle of the system at least one first control cycle and at least one second control cycle are generated, respectively deprecated by each other. a certain amount. The phase-shifting device is equipped, in particular, with at least one frequency divider. In this way, without a noteworthy work, control cycles are generated that are out of phase by exactly 90 °, from the oscillation of the carrier signal of the alternating magnetic field, which can be used directly to control the amplitude modulator and the of phase. These out-of-phase oscillations, derived from the carrier signal, can be used as auxiliary carrier signals, according to which the data signal is modulated. The amplitude demodulator has, on the input side, in particular, a bandpass filter whose center frequency is essentially equal to the sum or the difference of the frequencies of the carrier signal and the auxiliary signal. A particularly simple configuration of the data transmission circuit according to the invention results when the response circuit and / or the station are configured in such a way that they can process digital signals. This type of circuit can be configured in a particularly simple way with the usual digital circuit technology. The invention also relates to a response circuit, which is intended in particular for use in a transponder or a chip card, the response circuit of a secondary coil being provided, as well as an amplitude modulator to influence the resistance load of the secondary coil. The amplitude modulator is configured in such a way that an external alternating magnetic field can be modulated with a data signal generated, in particular, by the response circuit, when it is in the vicinity of that primary coil generating the alternating magnetic field. In accordance with the invention, the response circuit additionally has a phase modulator for influencing the electrical properties of the secondary coil, the modulator of amplitude and / or the phase modulator in such a way that they can be controlled by an activation signal. The response circuit can be developed in particular according to one of claims 3 to 13, whereby advantageous embodiments of the response circuit according to the invention are obtained. The invention also relates to a method for modulating an external alternating magnetic field of a station, with a modulation signal generated by a response circuit based on a data signal. According to the invention, the modulation is carried out in such a way that a lateral band of the alternating magnetic field modulated is generated with greater intensity than the other. In this way, the signal strength of the alternating magnetic field modulation is concentrated in a sideband channel and the zero points of modulation are eliminated. From the sub-claims 16 to 21 there are advantageous embodiments of the method according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in more detail in the drawing, with the help of an exemplary embodiment. Figure 1 shows a schematic diagram of a data transmission circuit in accordance with the invention, with a station and a response circuit. Figure 2, a block for generating a data signal of the response circuit of Figure 1. Figure 3, a vector diagram of the modulation of an alternating magnetic field of the data transmission circuit of Figure 1. Figure 4, a vector diagram of the modulation of an alternating magnetic field of the data transmission circuit of Figure 1, at a time t = 0. Figure 5, a vector diagram of the modulation of an alternating magnetic field of the transmission circuit of data of Figure 1, at a time t = 90 °. And Figure 6, a vector diagram of the modulation of an alternating magnetic field of the data transmission circuit of Figure 1, at a time t >; 90 °.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a data transmission circuit according to the invention, with a station 1 and with a response circuit 2. Station 1 has a signal generator 3, which, in a primary circuit , generates an alternating voltage signal with a carrier frequency O. The alternating voltage signal generated by the signal generator 3 is fed to the primary coil 4, being provided in the current circuit between the signal generator 3 and primary coil 4, an oscillatory circuit capacitor 5a, as well as a damping resistance 5b. The station 1 also has a demodulator connected in parallel to the primary coil 4. The demodulator 6 is not shown in detail in this figure, it can be carried out both as an amplitude demodulator and also as a phase demodulator. The response circuit 2 has a secondary coil 7, which, in the operation of the data transmission circuit according to the invention, is brought to the vicinity of the primary coil 4. The secondary coil 7 forms with a capacitor of oscillatory circuit 9 a secondary circuit. The oscillatory circuit capacitor 9 gives the secondary circuit a suitable resonance frequency. The part of the response circuit 2 which is connected to the secondary coil 7, as well as to the oscillatory circuit capacitor 9, is essentially divided into a power supply component and a modulation component of the carrier signal. The power supply component has a rectifier 8 for this purpose, which, at its output, is provided with a filter capacitor 10. Furthermore, the power supply component has a voltage regulator in the form of a Zener diode 11. In the mode shown 2 of the response circuit, the rectifier 8 is configured as a bridge rectifier with four diodes. The modulation component of the carrier signal essentially consists of a data signal generation block 12, an amplitude modulator 13, as well as a phase modulator 14. The amplitude modulator 13 is connected in parallel to the secondary coil 7. , so that it can be loaded with additional resistance. Correspondingly, the phase modulator 14 has a capacitor that can be connected in parallel to the secondary coil 7, so that its capacitive load can be modified. The amplitude modulator 13 and the phase modulator 14 can be realized both as linear modulators and also as non-linear modulators. In the embodiment shown, the amplitude modulator is embodied as a series connection of an ohmic resistor and an electrically operable switch. The phase modulator 14, correspondingly, is configured as a series connection of a capacitor and an electrically operable switch. The amplitude modulator 13 and the phase modulator 14, respectively through a connection line 15, or 16, are connected to the generation block of a data signal 12, namely, in such a way that its switches they can be operated according to instructions of the generation block of a data signal 12.

The block for generating a data signal 12, through a carrier signal line 17, is directly connected to the secondary coil 7. Finally, the block for generating a data signal 12 also has power supply connections 18. , or, 19, with which it is linked to the power supply component of the response circuit 2. Figure 2 shows the generation block of a data signal 12 of the response circuit 1 in greater detail. The block for generating a data signal 12 has a cycle preparation device 23, which, through the carrier signal line 17, is connected to the secondary coil 7. A cycle connection device 23 is connected to the frequency divider 24, which includes, in addition, a phase shifting device not shown in this figure. The frequency divider 24 generates two signals of the same frequency, out of phase with each other, which are emitted through a first output line 25 and a second output line 26. The first signal generated by the frequency divider 24 is transmitted through the first output line 25 to a first auxiliary bearer modulator 27. The second signal generated by the frequency divider 24 is transmitted through the second output line 26 to the second auxiliary bearer modulator 28. To transmit the signals from the first auxiliary carrier modulator 27 and the second carrier modulator 28, these are connected to the junction lines 15, or 16 mentioned above. The first auxiliary bearer modulator 27 and the second auxiliary bearer modulator 28 further receive a data signal from a logical and storage device 29 additionally provided in the block for generating a data signal 12. The logical and storage device 29 , like all other components of the generation block of a data signal 12, receives its operation energy from the power supply connections 18 and 19. The first auxiliary carrier modulator 27 and the second auxiliary bearer modulator 28 are configured in such a way, that the signals generated by the frequency divider 24 can be modulated with the data signal of the logical and storage device 29. In operation, the data transmission circuit according to the invention behaves as follows . The signal generator 3 in station 1 generates a high frequency alternating voltage signal, which is fed to the primary coil 4. Due to a series resonance, the oscillatory circuit capacitor 5a leads to an increase in the voltage in the primary coil 4. The damping resistance 5b deals with the necessary bandwidth. The primary coil 4 connected to the two connections of the signal generator 3 is therefore charged with the alternating voltage signal generated by the signal generator 3, with a carrier frequency O. Thus, an inductive alternating magnetic field is formed in the area of the primary coil 4. , which in the area around the primary coil 4 acts as a so-called near field. Thus, the intensity of the alternating magnetic field changes with the carrier frequency O. In the operation of the data transmission circuit according to the invention, the response circuit 2 is introduced in the area of the near field of the primary coil 4, know in such a way, that the secondary coil 7 of the response circuit 2 is in the direct environment of the primary coil 4. Thus, the alternating magnetic field induces in the secondary coil an alternating voltage with a frequency that agrees with the carrier frequency O. This alternating voltage is scanned by the power supply component of the response circuit 2 and rectified. For this, the rectifier 8 is connected to the two outputs of the secondary coil 7. At the output of the rectifier 8, due to the action of the filter capacitor 10, a filtered direct voltage appears, whose magnitude is limited by the Zener diode 11. , namely, to a value that is required for the operation of the generation block of a data signal 12. The filtered and limited output voltage of the power supply component is applied through the power supply connections 18 and 19 to the generation block of a data signal 12. Next, the generation block of a data signal 12 goes into an active state, in which it explores through the signal line carrier 17 the voltage induced in the secondary coil 7. The cycle bypass device 20 shown in Figure 2 is derived from the alternating voltage induced in the secondary coil 7, one system cycle and carries it to the frequency divider 21. In the frequency divider 21 there is provided a phase shifting device not shown in this figure, which from the system cycle generates a first auxiliary carrier signal as well as a second auxiliary carrier signal of the same frequency as the first, which with respect to this one it is out of phase by 90 °. In the auxiliary carrier modulators 24, 25 shown in Figure 2, the data signal stored in the storage and logic block 26 is modulated with the auxiliary carrier signals, to obtain a signal modulated in its phase and a signal modulated in its amplitude. This is fed through the connection line 15 to the amplitude modulator 13, while the phase modulated signal is fed through the connection line 16 to the phase modulator 14.

The amplitude modulator 13 and the phase modulator 14 load the secondary coil 7 according to the signals that are supplied to them. Since there is a coupling between the primary coil 4 and the secondary coil 7, the loading of the secondary coil 7 by the phase modulator 14 and the amplitude modulator 13 affects the electrical properties of the secondary coil 4. In this way they modify the shape and size of the signal that results in the primary coil 4, which is recorded by the demodulator 6. With a suitable configuration of the demodulator 6 not shown in detail in this figure, the data signal can be reconstructed from of the alternating voltage modified in this way in the primary coil 4. Figures 3 to 6 show the operation of the modulation according to the invention of the carrier signal, with the auxiliary carrier signal, these diagrams being limited to the auxiliary carrier signals not affected, or, to the modulated phase and amplitude signals, to make the fundamental idea of the invention clearer. Figure 3 shows a vector scheme of a modulation of the auxiliary carrier signals with the carrier signal, as carried out through the amplitude modulator 13 and the phase modulator 14. The signal carrier is shown as a signal vector carrier 20, which rotates around the origin 0 with its carrier frequency O. The vectors of the modulated amplitude signal 21a (ax) and 21b (a2) are shown in rotation around the tip of the carrier signal vector 20, as well as the signal vectors of Modulated phase 22a (px) and 22b (p2). For both the amplitude modulation of the data signal and for the phase modulation of the carrier signal, respectively two vectors 21a, 21b, or 22a, 22b are shown, which respectively represent both spectral portions of the amplitude modulation. and the phase modulation. The auxiliary carrier signals, or the modulated phase and amplitude signals have a constant frequency?. The rotation speed? of the spectral portions with respect to the carrier signal agrees with the frequency of the auxiliary carrier signal, which is identical for all amplitude modulation and phase modulation vectors 21a, 21b, 22a, 22b. However, the vectors 21a and 22a of the amplitude modulation, or of the phase modulation, rotate in the opposite direction to the vectors 21b, or 22b of the amplitude modulation, or of the phase modulation. Figure 4 shows the vector diagram of Figure 3 at a time t = 0. The carrier signal vector 20 rotates with a carrier frequency O, while the amplitude modulation vectors a1, a2, as well as the Phase modulation vectors p17 p2 do not move. At time t = 0, amplitude modulation starts. Therefore, amplitude modulation vectors a1? a2 begin to rotate around the tip of the carrier signal vector 20 with the rotation speed α, rotating the spectral portion a.1 in the figure shown counterclockwise, while the other spectral portion a2 rotates in the meaning of them. Figure 5 shows the vector diagram of the modulation of the alternating magnetic field of the data transmission circuit at time t = 90 ° / ?. At that time, the spectral portions a17 to 2 of the amplitude modulation were moved from the vertical position shown in Figure 4 to the horizontal position, so that the spectral portion a2 of the amplitude modulation coincides with both spectral portions p? r p2 of the phase modulation, while the other spectral portion a of the amplitude modulation is opposite to the spectral portions a2 Pi P2- Just at this moment the spectral portions p17 p2 of the phase modulation are set in motion . The spectral portion px then begins to move with frequency? in the counterclockwise direction, while the other spectral portion p2 begins to move with frequency? in the sense of the same. As you can clearly see in this figure, if you have the same amplitude in the spectral portions a1 and p17 the spectral portion ax is canceled with the spectral portion px. The remaining spectral portions a2 and p2 of the phase modulation are reinforced. Figure 6 shows the vector diagram of the Figure 3 at the time t > 90 ° / ?. At that time, the spectral portions a1 # a2 of the amplitude modulation were moved from the position of Figure 5 at a certain angle. The spectral portions p17 p2 also moved a certain angle from the position in Figure 5. The angles in which the spectral portions moved from the position in Figure 5 to t a2, or, plf p2, are respectively in agreement with each other, because the spectral portions rotate respectively with the same frequency? around the tip of the carrier signal vector 20. As can be seen "particularly well in this figure, the spectral portion ax of the amplitude modulation and the spectral portion px of the phase modulation are canceled, while the spectral portions a2 amplitude modulation and p2 of the phase modulation are reinforced, thus, in the response circuit according to the invention, for example, phase modulation precedes amplitude modulation by 90 ° of the signal period of the frequency of the auxiliary carrier signal, however, it is also conceivable that the phase modulation thus goes 90 ° of the signal period of the frequency? of the auxiliary carrier signal delayed with respect to amplitude modulation. In the first case, the addresses of the vectors 21b and 22b always coincide, while the addresses of the vectors 21a and 22a are always opposite. For this reason, the zero points of the modulation are eliminated. If the vectors 2la and 22a have the same length, a total cancellation of one sideband results, so that the power of the signal of the modulation of the alternating magnetic field is concentrated in one sideband.

Claims (21)

NOVELTY OF THE INVENTION Having described the above invention, it is considered as a novelty, and therefore, the content of the following is claimed as property: CLAIMS

1. A data transmission circuit with a station and with a response circuit designed in particular for a chip card, the station having a primary coil with a signal generator for the generation of an alternating magnetic field with a carrier frequency, as well as an amplitude demodulator, the response circuit having a secondary coil as well as an amplitude modulator to influence the load of the secondary coil, the amplitude modulator being configured in such a way that the alternating magnetic field can be modulated with a data signal, characterized in that the response circuit has a phase modulator for influencing the electrical properties of the secondary coil, the amplitude modulator and / or the phase modulator respectively being controllable by means of at least one signal of modulation.

2. A data transmission circuit with a station and with a response circuit designed in particular for a chip card, the station having a primary coil with a signal generator for the generation of an alternating magnetic field as well as a demodulator, the response circuit having a secondary coil as well as an amplitude modulator for influencing the load of the secondary coil, the amplitude modulator being configured in such a way that the alternating magnetic field can be modulated with a data signal, characterized in that the response circuit has a phase modulator to have an influence on the electrical properties of the secondary coil, the amplitude modulator and / or the phase modulator respectively being controllable by means of at least one modulation signal, and in that the demodulator is configured as a phase demodulator.

3. A data transmission circuit according to claim 1 or claim 2, characterized in that the response circuit is configured in such a way that the amplitude modulator and / or the phase modulator can be controlled in such a way, that the phase modulation is out of phase with respect to the amplitude modulation.

4. A data transmission circuit in accordance with claim 3, characterized in that the response circuit is configured in such a way that the amplitude modulator and / or the phase modulator can be controlled in such a way that the phase modulation precedes, or is delayed by 90 ° with respect to the signal period of amplitude modulation.

5. A data transmission circuit according to claim 1, characterized in that the amplitude modulator is configured as a resistor that can be connected in parallel to the secondary coil.

6. A data transmission circuit according to claim 1, characterized in that the phase modulator is configured as a capacitor that can be connected in parallel to the secondary coil.

7. A data transmission circuit according to claim 1, characterized in that the response circuit has at least one intermediate modulation device for modulating the data signal with an auxiliary carrier signal.

8. A data transmission circuit according to claim one of the preceding claims, characterized in that the response circuit presents a cycle derivation device for the derivation of an auxiliary carrier signal from the alternating magnetic field.

9. A data transmission circuit in accordance with the claim in one of the preceding claims, characterized in that the response circuit has a phase-shifting device, which is configured in such a way that at least one first auxiliary carrier signal and at least one second auxiliary carrier signal respectively phase-shifted from each other can be generated from the system cycle. for a certain amount.

10. A data transmission circuit according to claim 1, characterized in that the phase shifting device has at least one frequency divider.

11. A data transmission circuit according to claim 1, characterized in that the demodulator has a bandpass filter at the input

12. A data transmission circuit in accordance with the claim in claim 10 as well as in accordance with claim 11, characterized in that the center frequency of the bandpass filter is essentially equal to the sum or difference of the carrier signal and the carrier signal frequencies. assistant.

13. A data transmission circuit according to claim 1, characterized in that the response circuit and / or the station are configured as circuits for the processing of digital signals.

14. A response circuit, in particular for use on a transponder or on a chip card, with a secondary coil, as well as with an amplitude modulator to influence the electrical properties of the secondary coil, being configured in such a way the amplitude modulator, that an external alternating magnetic field can be modulated with a data signal, characterized in that the response circuit has a phase modulator to influence the electrical properties of the secondary coil, the amplitude modulator being configured and / or the phase modulator respectively controllable by at least one modulation signal.

15. A method for modulating an external alternating magnetic field of a station with a modulation signal generated by a response circuit according to a data signal, characterized in that the modulation takes place in such a way that a sideband of the field alternating magnetic modulation is generated with greater intensity than the other.

16. A method according to claim 15, characterized in that the modulation of the alternating magnetic field is carried out both by amplitude modulation and by phase modulation.

17. A method according to claim 16, characterized in that the amplitude modulation is carried out in phase with respect to the phase modulation.

18. A method according to claim 17, characterized in that the offset is 90 °, namely, forward or backward.

19. A method according to claim 15, characterized in that the amplitude modulation is carried out with an amplitude modulator controlled by an amplitude modulation signal and because the phase modulation is carried out with an amplitude modulation signal. a phase modulator controlled by a phase modulation signal, the amplitude and / or phase modulation signals being generated respectively from a modulation of the data signal with respectively an auxiliary carrier signal.

20. A procedure in accordance with claimed in claim 19, characterized in that the auxiliary carrier signal or the auxiliary carrier signals are derived by frequency division from the alternating magnetic field.

21. A method according to claim 19 or claim 20, characterized in that the auxiliary carrier signals are generated in such a way that between them there is a phase shift of 90 ° in particular.