CN116266768A - Circuit assembly for near field radio communication - Google Patents

Abstract

A circuit assembly for near field radio communication, the circuit assembly having a radio communication unit (10) and a transmitting antenna (13) connected to the radio communication unit (10), and the circuit assembly having a detection unit (17), wherein the detection unit (17) is connected to the transmitting antenna (13) for directly intercepting an antenna voltage, and the circuit assembly is arranged for reducing a transmitting power of the transmitting antenna (13) in a detection phase, in which detection phase the presence of an object in the vicinity of the transmitting antenna (13) is detected by emitting a high frequency signal by means of the transmitting antenna (13) and measuring and analyzing the antenna voltage by means of the detection unit (17), and the circuit assembly is arranged for near field communication with the detected object with a larger transmitting power in an identification phase than in the detection phase for identifying whether the object is suitable for near field radio communication.

Description

Circuit assembly for near field radio communication

technical field

The invention relates to a circuit arrangement for near-field radio communication, which has a radio communication unit and a transmitting antenna, which is connected to the radio communication unit, and which has a detection unit.

Background technique

This type of circuit assembly is used to identify objects located in the vicinity of a wireless charging transmitter or a near field communication device, wherein the identification takes place by means of an NFC controller (near field communication, Nahfeldkommunikation="Near Field Communication") and a further microcontroller . The invention is not limited to devices for wireless energy transfer, but can be applied to all devices comprising near field communication means.

In the following, the terms transmitter and receiver are used not only for wireless energy transfer, but also for near field communication, although different circuit components are responsible for the wireless energy transfer and the near field communication. Furthermore, the technology used for energy transfer is very similar to that used for near-field communication. In order to be able to clearly and uniquely distinguish which method is referred to in the description, in the following, the terms WC transmitter and WC receiver are used for energy transmission (wireless charging, Wireless Charging), and NFC transmitter and NFC receiver are used for near field communication.

Wireless energy transmission between a sending device (WC transmitter) and a mobile receiving device (WC receiver) typically takes place via two coils coupled by an alternating magnetic field. The electrical energy is converted into magnetic energy by means of a coil in the WC transmitter, and this magnetic energy is then converted into electrical energy again in a second coil, which is located spatially close to the first coil. In this case, the field lines of the magnetic field generated by the first coil essentially traverse both coils. Since the coupling effect between the two coils is incomplete, part of the magnetic field also acts in the environment outside the two coils. If the induced voltage is used in the receiver coil to supply energy to a load, for example to charge a battery, a current flow is generated in the receiver coil which likewise induces a magnetic field which is identical to the field generated by the transmitter coil point in the opposite direction (transformer principle). Since the resulting magnetic field is now smaller, the magnetic field outside the coil assembly is also smaller. As a result, the magnetic field in and outside the coil assembly is high when the receiving coil is not initiating energy transfer.

In order to communicate between a WC receiver and a WC transmitter, the transmitter must first apply an alternating magnetic field according to the Qi standard, which is detected by the receiver and loaded differently. Due to the different time loads, the bit-by-bit information is transmitted to the WC transmitter and decoded there. Thus, the transmitter can determine whether a compatible device is located near the sending coil and can receive energy. In order to identify compatible devices brought close to the sending coil as quickly as possible, the WC transmitter cyclically generates a magnetic field for a determined time and attempts to decode the response. If no response can be received, the magnetic field is removed again and the process is repeated after a defined pause time. This query method for compatibility is specified in the Qi standard and is referred to there as a digital ping. The disadvantage of this method is that energy is cyclically consumed in order to interrogate the presence of the WC receiver and that a magnetic field is cyclically generated which also has appreciable strength outside the area of the transmitting coil and which can damage nearby human bodies due to the permanent load organize. Here, national and international standards set limit values that may be exceeded by the method.

In addition, however, devices that are sensitive to magnetic fields can also be damaged by the circulating energy supply, as can be the case, for example, in the case of credit cards, chip cards, magnetic stripe cards or the like.

Another method is to detect objects brought into the vicinity of the transmitting coil by means of capacitive or inductive or optical proximity sensors. In this case, the cyclic energy supply does not start until an object has been detected in the vicinity of the transmitting coil. The Qi specification also proposes the use of offsets in resonant frequency to identify nearby devices. This method is referred to there as analog ping and supplies the sending coil with a short high-frequency signal at the resonance frequency of the sending coil without a receiver and with low energy. If there is no object in the vicinity of the sending coil that detunes the resonance frequency, the voltage across the sending coil has its nominal value for the resonance frequency. If the resonance frequency is detuned by the magnetic material (which is always the case in the case of Qi receivers), the voltage on the sending coil also has a different value, which is detected by the microcontroller. Then comes the digital ping stage. The energy of the measurement with the test signal is so low that the receiver is not woken up and the load modulation of the transmitted signal is not started. Since the analog ping or the proximity sensor does not detect whether this is a compatible device for receiving energy or a foreign object, there is also the risk that the object will be damaged by the cyclic energy supply of the subsequent digital ping. Furthermore, limit values for permissible magnetic fields may also be exceeded in this case.

Since near-field communication is increasingly required in addition to energy transfer between charging stations and mobile devices, object recognition can be combined with elements of near-field communication. In particular, antennas for near-field communication can be used here. Known object recognition methods first check whether an object is recognized, then check whether this is a compatible card with near field communication, such as a credit card or an access control card, and only check the compatibility of energy transmission (digital Ping). This ensures that the near field communication card is not damaged by the energy pulse. In addition, however, due to the continuous interrogation of the object, there is the disadvantage that national or international limit values for magnetic fields are exceeded. Especially in China, very low limit values apply to interference emissions in electric vehicles.

Another approach for object recognition exploits the ability to measure near-field antenna misalignment with objects located nearby. Due to the proximity of the capacitively active or inductively active material to the NFC antenna, the NFC antenna is detuned in its electrical properties, wherein this detuning contributes to a different voltage at the NFC transmitting antenna compared to an untuned antenna.

Near-field communication with passive NFC receivers, ie NFC receivers that do not have their own current supply (for example, via a battery), takes place by the NFC controller emitting a high-frequency signal of the operating frequency via its transmit amplifier, And the receiver circuit loads the receiving antenna bit by bit or offsets the resonant frequency bit by bit, wherein the loading or offset on the transmitting antenna of the NFC circuit can be measured as a voltage change by means of a reaction. If the NFC receiver is far away from the NFC transmitting antenna, eg 3 cm, the change is relatively small. On the other hand, an NFC receiver located directly on the transmitting antenna leads to relatively large voltage fluctuations on the transmitting antenna. A typical NFC transmitting circuit does not detect voltage fluctuations directly on the antenna, but instead detects the voltage on the output of a power amplifier, or directs the voltage back onto the circuit after a first filter. At this point, the voltage fluctuations are smaller than those directly at the antenna. Therefore, the transmit amplifier must release relatively high power in order to still be able to detect fluctuations on the first filter. In order to keep voltage fluctuations within a defined range, the NFC transmitter can regulate the power of the high-frequency radiation radiated by the transmitting antenna, which means that the power is increased to a maximum value in the absence of an NFC receiver in order to guarantee a maximum Receivers can still be identified on possible pitches. In order for the NFC receiver to be detected with the shortest possible time delay when approaching the transmitting antenna, the transmitter must always re-send the high-frequency signal at short intervals, for example several times per second, in order to detect whether the receiver is nearby. Due to the high energy and short distances of the test signals, environmental loads are generated by magnetic and electromagnetic fields which may exceed legally prescribed limit values.

US 2012/0214411 A1 discloses a system and a method for detecting the presence of an NFC tag by applying a magnetic field and by acting on the magnetic field by a receiving coil of the NFC tag to detect a field change. If a change in the magnetic field has been detected, an inquiry is made via communication with higher power. There, no identification is provided for objects that do not correspond to NFC tags.

US 9,281,706 B2 describes a wireless charging system for devices which are adapted for near field communication (NFC) and which may be damaged by charging energy. In order to protect such NFC tags, the presence and capabilities of NFC tags located nearby are queried by communication with the tag, and the high transmit energy is used for wireless charging only when it has been confirmed by the receiver that the high transmit energy is suitable .

EP 3 664 253 A1 discloses a device and a method for wireless power transfer for inductive charging of devices eg according to the Qi standard. In order to detect the NFC receiver, an additional NFC read unit is present in the charging device, so that object detection does not have to be carried out solely by detecting the resonance shift of the charging signal of the Qi transmitting coil.

US 2021/0376882 A1 discloses a device and a method for wireless inductive charging of devices, in which first the presence of the device in the vicinity of the transmitting coil is queried by means of a digital ping. If the NFC tag has been detected, the maximum permissible charging power is coordinated in the identification phase and the configuration phase in order to prevent overloading of the NFC tag during wireless charging.

Contents of the invention

The object of the present invention is to provide an improved circuit assembly which not only limits the output power but also ensures identification at low output powers.

This object is achieved by means of a circuit arrangement having the features of claim 1 . Advantageous embodiments are described in the dependent claims.

It is proposed that the detection unit is connected to the transmitting antenna for the direct interception of the antenna voltage and that the circuit subassembly is provided for reducing the transmission power of the transmitting antenna in a detection phase in which a high-frequency signal is emitted by means of the transmitting antenna and The presence of an object in the vicinity of the transmitting antenna is detected by means of the detection unit, which measures and evaluates the antenna voltage, and the circuit assembly is provided for near-field communication with the detected object in the identification phase with a higher transmission power than in the detection phase , used to identify whether an object is suitable for near-field radio communication.

For detection, the higher voltage at the transmitting antenna is tapped directly, and the power upstream of the matching circuit of the transmitting antenna is not tapped (for example as a current and/or voltage value). Interrogation can thus be carried out with significantly reduced power during detection in order to still obtain a signal that can be evaluated.

In addition, the circuit assembly can be designed to measure and evaluate the signal of the transmitting antenna by means of a radio communication unit attached to the transmitting antenna. After the detection phase, further communications and adjustments are thus carried out, as is conventionally done with a radio communication unit, wherein possibly higher power can then be used than in the detection phase. This may depend on whether a sensitive object has been detected in the vicinity of the transmitting coil.

In addition to routing the voltage at the first filter back into the NFC transmitting circuit, it is also possible to route the significantly higher signal directly at the transmitting antenna to the input of a further microcontroller or to realize the detection unit and the function of the radio communication unit on separate inputs of the microcontroller.

A microcontroller within the meaning of the present invention is understood to be any suitable signal data processing unit which is programmable or hardcoded. This also includes Field-Programmable-Gate-Array FPGAs, microprocessors and the like.

The radio communication unit can have a transmit signal amplifier, a subsequent filter and a subsequent adaptation circuit, which is connected to the transmit antenna. In such a configuration, the radio communication unit can be configured to measure and evaluate the signal voltage at the input of the matching circuit at the connection between the filter and the matching circuit. The detection unit therefore uses the higher voltage of the transmitting antenna, while the radio communication unit intercepts and evaluates the power at the input of the matching circuit. This has the advantage that, during charging operation, detuning of the transmitting antenna is avoided by operating the detection unit directly using this higher voltage.

The detection unit can be configured to detect an object from the measured voltage change at the transmitting antenna. It is advantageous here if the detection unit has a peak detector for measuring the voltage peak of the signal voltage at the transmitting antenna. This enables a simple construction and a simple and reliable evaluation of the antenna power.

The detection unit can be configured to measure the positive half-wave and the negative half-wave of the signal voltage at the transmitting antenna. This is done, for example, by means of two diodes connected in different flow directions or by means of a rectifier (for example a bridge rectifier). It is conceivable to attach a diode in each case to the positive connection and to the negative connection of the transmitting antenna in the direction of flow, and to supply the two signals separately from one another to the corresponding analog-to-digital converter.

In addition, a voltage-limiting component can be provided for protecting subsequent components, such as in particular an analog-to-digital converter, against overvoltage. This can be achieved, for example, by means of Zener diodes.

In addition, a current-limiting resistor, which can optionally be bridged by a transistor, can be inserted in the supply line for the transmit amplifier. Thus, for example, the radio communication unit can have a transmit signal amplifier, which is connected to a limiting resistor that can be added, wherein the circuit assembly is provided to reduce the transmit power by switching on the limiting resistor.

An additional energy charging unit can be provided, which is connected to the transmitting antenna or a separate charging coil assembly and is configured to transmit energy wirelessly to the receiver. Thus, for example, an NFC communication unit and a Qi charging unit can be implemented side by side in the circuit assembly. It is conceivable here that the circuit assembly is provided for radio communication with an object detected in the detection phase when it was determined in the identification phase that the object is not provided for near-field communication. Coordination of the charging process with the energy charging unit can thus take place, for example, according to the Qi standard, when no NFC-enabled device is detected.

Recognition of objects can now proceed in one embodiment as follows:

First, the current limiting resistor is not bridged by the transistor. The NFC transmission circuit generates its high frequencies as usual with maximum power, however, this maximum power is limited by the resistance in the supply line for the transmission amplifier. The transmit signal is placed at the input of the analog-to-digital converter of the microcontroller by directly tapping off the transmit antenna, where it is digitized and further processed in the microcontroller. If an object made of capacitively or inductively relevant material approaches the transmitting antenna, this can be detected by a voltage change at the transmitting antenna and can be evaluated by the microcontroller. Induction-relevant materials are, for example, ferromagnetic materials, such as iron or metal surfaces, which generate eddy currents or resonant circuits in NFC receivers. Capacitance-related materials are, for example, plastic or the human body.

After the detection of an object approaching the transmitting coil, a query is made as to whether the object is a device for near-field radio, for example an NFC device or an RFID card. To do this, the transistor bridges the current limiting resistor, and the NFC circuit now tries to independently establish communication with the item. If this is not possible after a corresponding time, the system goes back into the low power state, ie the transistor is switched off and the current limiting resistor is activated again, and the circuit tries to detect the subsequent change in the antenna voltage.

The reduction of output power can also be realized by other methods, for example, an attenuation element that can be connected can be arranged between the output terminal of the transmission amplifier and the subsequent filter and/or between the filter and the matching circuit, and the attenuation element can Activated in situations where less output power is required.

If the NFC transmitter is built into the device enabling wireless charging of mobile devices and has identified an item that is not an NFC device and is not an RFID card, an attempt can be made to communicate with the receiving device for wireless energy transfer by means of a digital ping. Since it is clear that the item is not a near-field communication device, the item is also immune to damage by the digital Ping's magnetic field. If the device is identified as a compatible device for wireless energy transfer by corresponding communication, the energy transfer phase then begins.

Another possibility is to recognize an approaching item as an NFC device, but it is known from the transmitted data that this is an NFC device inside the wireless energy receiver. In this case energy transfer is also initiated, but damage to the NFC receiver by digital ping or energy transfer is excluded, since such a device is necessarily designed for energy transfer and therefore the NFC receiver must be structurally protected . For identification as an NFC device within a wireless energy receiver, data from a standard can be used or a comparison of the pattern of the received data with a set of characteristic patterns, which are stored in the memory of the microcontroller, can be used .

If, however, an NFC device or an RFID card without energy transfer capability is detected, communication via the bridged current-limiting resistor continues and the data exchange is used for its real purpose, for example the transmission of a vehicle start authorization. Only when the transmission is interrupted, for example by removal of the authorization card, does the system return to the low-power identification of the object.

Description of drawings

In the following, the invention is explained in more detail on the basis of exemplary embodiments with the aid of the accompanying drawings. The accompanying drawings show:

Figure 1 shows the principle of near-field communication with a passive receiver;

Figure 2 shows the transmission curves in the case where there is no object in the vicinity and in the case where there is an object in the vicinity;

Figure 3 shows a circuit diagram with low power object recognition;

Figure 4a shows the electromagnetic emission of a conventional circuit;

Figure 4b shows electromagnetic emissions for low power identification according to the present invention.

Detailed ways

FIG. 1 shows the principle of near field communication between an NFC transmitter 1 and a passive NFC receiver 2 . The NFC transmitter 1 has a transmitter unit 10 which contains a transmitter amplifier 18 for the transmission frequency, which is supplied by a supply voltage _UT . At the push-pull outputs TX and TX' of the unit is located a filter 11 which cuts off all undesired frequency components other than the useful frequency. A matching circuit 12 for a transmitting antenna 13 , which is typically designed as a loop antenna, is located downstream of this filter. The reaction is typically performed at the output of the filter 11 and is conducted via the lines RX and RX′ back to the transmitting unit 10 where it is evaluated. The output voltage at the transmit amplifier 18 is typically about 5 Vpp, while the voltage at the transmit antenna 13 is, for example, 40 Vpp, since the matching circuit 12 is formed by capacitors and together with the transmit coil forms a resonant circuit which is designed such that the resonant circuit The resonant frequency corresponds to the transmission frequency. The magnetic field generated by the current flow of the transmitting antenna 13 , for example a loop antenna, is used for energy transmission and information transmission. This electromagnetic field has a secondary role in the field.

The receiving antenna 20 of the NFC receiver 2 is located close to the transmitting antenna 13 . The receiving antenna is coupled to the transmitting antenna 13 via an alternating magnetic field and thus induces a voltage which causes a current to flow in the NFC receiver 2 . The electronics 22 in the NFC receiver 2 are powered via the rectifier 21 , so that the NFC receiver 2 is ready to work.

In addition, the NFC receiver 2 has an additional element 23 which is connected bit by bit in parallel to the receiving antenna 20 (also referred to as receiving coil) via an electronic switch 24 and thus loads it. Due to the different loads, there is a reaction to the transmit antenna 13 . At this transmitting antenna, the bit pattern imposed by the NFC receiver 2 appears as a voltage change on the transmitting antenna 13 . The farther the NFC receiver 2 is from the transmitting antenna 13, the smaller the reaction and the smaller the communication signal. In order to bring the strength of the reaction signal into a defined range, for example transmit amplifier 18 can vary its power. This has the advantage that only low power is required for communication when the NFC receiver 2 is nearby.

It is shown in the graph in Fig. 2 that the circuit assembly in Fig. 1 can be used not only to communicate with the NFC receiver 2, but also to detect changes in the resonant tank when an item changing the resonant properties approaches the sending coil. This can be, for example, objects which have a different dielectric or magnetic permeability than the ambient air. Here too, the resonant frequency of the entire system changes, which is reflected in the changed voltage at the transmitting antenna 13 and thus also in the changed voltage downstream of the filter 11 at which the reaction is intercepted and provided For analysis processing electronics.

If no objects are present in the vicinity of transmitting antenna 13 , voltage U1 at resonance frequency f _R at transmitting antenna 13 lies in a defined range with a lower limit (Gu) and an upper limit (Go). Resonant curve 1 is suitable for this case. The upper limit can also be infinite, since this upper limit is not important for object recognition. If an object, such as a card made of plastic, approaches the transmitting antenna 13, the resonance behavior changes due to the changed dielectric, which is shown in the changed curve 2, and the voltage drops below the lower limit Gu . Therefore, the object has been recognized.

The situation is similar when ferromagnetic or electrically conductive materials are present in the vicinity of the transmitting antenna 13, or when an NFC receiver 2 is introduced with an oscillating circuit consisting of a receiving antenna 20 configured as a loop line with a capacitor connected in parallel .

The voltages at the transmitting antenna 13 are shown in each case. The voltage on tap RX/RX' appears before the resonant tank and is therefore much smaller. Since the output power of the transmitter (NFC transmitter 1 ) can be varied, a high output power is chosen for object detection so that the difference in reaction is also as large as possible. However, it is also possible to transmit with a lower power, however, the previously described limit values which describe the range for the normal situation in which no objects are present in the vicinity of the transmit antenna 13 then also change.

The improved circuit assembly can be seen in FIG. 3 . In this case, further signal taps are present directly on transmit antenna 13 for detecting objects.

In this case, the signal can be routed via a peak detector formed by two diodes 16 to an analog input of microcontroller 17 . Therefore, two diodes 16 are advantageous so that the peak values of the two half-waves of the antenna voltage of transmitting antenna 13 can be evaluated thereby. Thus, receivers that change reaction only for one half-wave can also be identified.

The signal routing from diode 16 to the analog input takes place in a high-ohmic manner in order to load the transmission signal as little as possible, which would impede communication, not only during object recognition but also during communication with NFC receiver 2 . Due to the matching of the transmitting antenna 13 to the resonance frequency by means of the matching loop, the voltage at the transmitting antenna 13 is much higher than the voltage at the tap after the filter 11 which is used to measure the reaction for the transmitting circuit. This is especially important when the transmitting circuit is performing object recognition at low power. If the communication with the NFC receiver 2 is operated at a higher power level, voltages of 40 Vpp or higher can occur at the transmitting antenna 13 . In order to protect the analog input from these voltages, voltage-limiting protective components, such as Zener diodes, can be used at the analog input.

A second change compared to the conventional circuit connection may be the current-limiting resistor 14 in the supply line for the power amplifier, ie transmit amplifier 18 . The current-limiting resistor can be bridged by means of a switch 15 which is realized, for example, by means of a transistor.

In the object detection phase, the transmitting chip attempts to detect the change in voltage at the tap point with the maximum possible transmission power. Since there is no bridging current-limiting resistor in this phase, the output power remains strongly limited, which prevents the sending circuit from recognizing possible objects. The evaluation of the voltage is taken over by the external microcontroller 17 in this phase. If an external microcontroller detects an object by evaluating the voltage on the transmitting antenna 13, the external microcontroller switches the transmitting circuit from the recognition mode into the communication mode and simultaneously switches on the transistor (switch 15) so that the output Power is no longer limited.

From this point in time, the complete control of the near-field communication is taken over by the transmitting circuit, ie the microcontroller only evaluates the analog signal of the antenna again if the communication with the NFC receiver 2 is interrupted, for example by removing the NFC receiver 2 .

4a and 4b show the frequency spectrum of the radiated energy of the transmitting antenna 13 . The spectrum is measured by means of a measuring antenna at a distance, for example 3 m, from the measuring object. The magnetic field is also not measured, which is relevant in the case of near-field communication but no longer plays a role in measuring the distance of the antenna. Instead, the energy of electromagnetic fields that can cause interference in other devices is measured. However, this electromagnetic field is also generated by an alternating magnetic field.

In FIG. 4 a , which shows the spectrum of a typical circuit, the proportion of radiated energy (transmitted energy) is high at a useful frequency of 13.56 MHz. This radiant energy is in the range of the limit value (E field) which is relevant for this, which makes it impossible to ensure compliance with this limit value. The limit value (E field) is plotted in this example as the electric field in dbμV/m by the Chinese standard GB/T-18387-2017 over the frequency range from 150 kHz to 30 MHz. The transmitted energy radiated by the conventional circuit studied as an example is likewise plotted with its electric field in db μV/m in the mentioned frequency range (resolution bandwidth (“Resolution Bandwidth”) RBW=9 kHz, horizontal maximum peak value (Horizontaler maximaler Peak)).

Figure 4b shows the spectrum of a modification with power limitation. It can be seen here that the power (transmitted energy) of the electromagnetic field radiated by the circuit assembly according to the invention is well below the limit value (E field), in this case approximately 25 dB below this, so that compliance with the limit value. In particular, this is of decisive advantage for markets in which the limit values for this operating state are still significantly lower than the general market.

Claims (12)

1. A circuit assembly for near-field radio communication, said circuit assembly having a radio communication unit (10) and a transmitting antenna (13), said transmitting antenna being connected to said radio communication unit (10), and said The circuit assembly has a detection unit (17), characterized in that, The detection unit (17) is connected to the transmission antenna (13) for directly intercepting the antenna voltage, and the circuit assembly is configured to reduce the transmission power of the transmission antenna (13) during the detection phase, during In the detection phase, the presence of objects in the vicinity of the transmitting antenna (13) is detected by emitting a high-frequency signal with the aid of the transmitting antenna (13) and measuring and evaluating the antenna voltage with the aid of the detection unit (17) , and the circuit assembly is configured for near-field communication with the detected object in the identification phase with a higher transmission power than in the detection phase, for identifying whether the object is suitable for near-field radio communication. 2. The circuit assembly as claimed in claim 1, characterized in that the circuit assembly is designed to measure and evaluate the transmission by means of a radio communication unit (10) attached to the transmission antenna (13). Signal from the antenna (13). 3. The circuit assembly according to claim 2, characterized in that the radio communication unit (10) has a transmit signal amplifier (18), a subsequent filter (11) and a subsequent matching circuit (12), the A matching circuit is connected to the transmitting antenna (13), wherein the radio communication unit (10) is configured to measure and evaluate the The signal voltage on the input terminal of the matching circuit (12). 4 . The circuit assembly as claimed in claim 1 , characterized in that the detection unit ( 17 ) is provided to detect an object from the measured voltage change at the transmitting antenna ( 13 ). 5 . 5. The circuit assembly as claimed in claim 1, characterized in that the radio communication unit (10) has a transmit signal amplifier (18), which can optionally be switched in a switchable manner It is connected to a current-limiting resistor (14), wherein the circuit assembly is configured to reduce the transmit power through an effective connection of the current-limiting resistor (14) to the transmit signal amplifier. 6. The circuit assembly as claimed in claim 5, characterized in that the limiting resistor (14) can be bridged by a controllable switch (15), in particular a transistor. 7. Circuit assembly according to any one of the preceding claims, characterized in that the detection unit (17) is implemented as a separate microcontroller. 8. The circuit assembly according to any one of the preceding claims, characterized in that the detection unit (17) has a peak detector for measuring the signal voltage on the transmitting antenna (13) the peak voltage. 9. The circuit assembly according to any one of the preceding claims, characterized in that the detection unit (17) is configured to measure the positive half-wave and negative half-wave of the signal voltage on the transmitting antenna (13) . 10. The circuit assembly according to any one of the preceding claims, characterized in that the transmitting antenna (13) is connected to the detection unit (17) by means of at least one pressure limiting component, in particular diode. 11. The circuit assembly according to any one of the preceding claims, characterized in that it is an energy charging unit, the energy charging unit is connected with the transmitting antenna (13) or a separate charging coil assembly, and is configured to charge energy transmitted wirelessly to the receiver. 12. The circuit assembly according to claim 11, characterized in that the energy charging unit is arranged to carry out radio communication with the object detected in the detection phase by means of the energy charging unit, if in the identification Phase has determined that the object is not configured for near field communication.

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