DE102021133464A1 - Circuit arrangement for near-field radio communication - Google Patents

Abstract

Circuit arrangement for near-field radio communication with a radio communication unit (10) and a transmitting antenna (13), which is connected to the radio communication unit (10), and with a detection unit (17), the detection unit (17) being connected to the transmitting antenna (13) for direct tap of the antenna voltage and the circuit arrangement for reducing the transmission power of the transmission antenna (13) in a detection phase, in which a detection of the presence of an object in the vicinity of the transmission antenna (13) by transmission of a high-frequency signal with the transmission antenna (13) and measurement and Evaluation of the antenna voltage with the detection unit (17) takes place, and is set up for near-field communication with a detected object in a detection phase with a higher transmission power than in the detection phase to detect whether the object is suitable for near-field radio communication.

Description

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

Such circuit arrangements are used to detect objects that are in the vicinity of a wireless charging transmitter or a near-field communication device, with the detection using an NFC controller (near field communication = "Near Field Communication") and an additional microcontroller. The invention is not limited to devices for wireless energy transmission, but can be used for all devices that contain a near-field communication device.

In the following, the terms transmitter and receiver are used both for wireless energy transmission and for near-field communication, although different circuit parts are responsible for this. In addition, the technologies for energy transmission and communication are very similar. In order to be able to clearly distinguish which method is meant in the description, the terms toilet transmitter and toilet receiver for energy transmission (wireless charging) and NFC transmitter and NFC receiver for near-field communication are used below.

The wireless transmission of energy between a transmitter (toilet transmitter) and a mobile receiver (toilet receiver) typically takes place via two coils coupled via an alternating magnetic field. The electrical energy is converted into magnetic energy in the WC transmitter with the help of a coil, and the magnetic energy is then converted back into electrical energy in a second coil located close to the first coil. The field lines of the magnetic field generated by the first coil essentially run through both coils. Since the coupling effect between the two coils is not complete, part of the magnetic field also acts in the area outside the two coils. In the event that in the receiver coil the induced voltage is used to power a load, e.g. B. to charge a battery, a current flow is created in the receiver coil, which also causes a magnetic field that opposes the field generated by the transmitter coil (transformer principle). Because the resulting magnetic field has now become smaller, the magnetic field outside the coil arrangement is also smaller. As a result, the magnetic field in the coil assembly and outside is higher when the receiving coil is not initiating energy transport.

For communication between the toilet receiver and toilet transmitter, the transmitter must first create an alternating magnetic field according to the Qi standard, which is detected by the receiver and subjected to different loads. Due to the different time loads, information is transmitted bit by bit to the WC transmitter and decoded there. This allows the transmitter to determine whether a compatible device is in the vicinity of the transmitting coil and can receive energy. In order to identify a compatible device that is brought close to the transmitter coil as quickly as possible, the WC transmitter cyclically generates a magnetic field for a specific time and attempts to decode a response. If no response could be received, the magnetic field is reduced again and the process is repeated after a defined pause time. This query procedure for compatibility is specified in the Qi standard and is referred to there as digital ping. The disadvantage of this method is that energy is consumed cyclically in order to query the presence of a toilet receiver, and that a magnetic field is generated cyclically, which also has considerable strength outside the transmission coil area and, due to the permanent exposure, may possibly damage nearby human beings tissue damage. National and international standards stipulate a limit value that could be exceeded using this method.

Furthermore, devices that are sensitive to magnetic fields could also be damaged by the cyclical energy supply, e.g. This could be the case, for example, with credit cards, chip cards, magnetic stripe cards or the like.

Another method is the detection of an object brought close to the transmitter coil by capacitive or inductive or optical proximity sensors. In this case, the cyclic energy supply only begins after it has been detected that an object is in the vicinity of the transmitter coil. The Qi specification also makes a proposal to use resonant frequency detuning to detect a nearby device. This method is referred to there as analog ping and applies a short high frequency signal to the transmitter coil at the resonant frequency of the transmitter coil without a low power receiver. If there is no object that detunes the resonance frequency in the vicinity of the transmitter coil, the voltage on the transmitter coil has its nominal value for the resonance frequency. If the resonant frequency is detuned by magnetic material, as is always the case with a Qi receiver, the voltage on the transmitter coil also has a different value, what detected by a microcontroller. Only then does the phase of the digital ping take place. The measurement by the test signal is energetically so low that the receiver is not woken up and does not start with the load modulation of the transmission signal. Since this analog ping or the proximity sensors do not detect whether the device in question is a compatible energy-receiving device or a foreign object, there is still a risk that the object will be damaged by the cyclical energy delivery of the subsequent digital ping. Furthermore, limit values for the permissible magnetic field could also be exceeded in this case.

Since near-field communication is increasingly required in addition to energy transfer between the charging station and the mobile device, object recognition can be combined with the elements of near-field communication. In particular, the antenna for near-field communication can be used here. A well-known method of object detection first checks whether an object is detected, then checks whether it is a compatible card with near-field communication, e.g. B. credit card or access card, and only when it is certain that it is not such a card, the compatibility of the energy transmission is checked (digital ping). This ensures that a near-field communications card will not be destroyed by a pulse of energy. However, the disadvantage of exceeding national or international limit values for the magnetic field still exists due to the ongoing query for an object. In China in particular, there is a very low limit value for interference emissions within electric vehicles.

Another method for object detection uses the property that a detuning of the near-field antenna is measured by a nearby object. When a capacitively or inductively effective material approaches the NFC antenna, its electrical properties are detuned, with the detuning resulting in a voltage at the NFC transmitting antenna that is different than that of the antenna that is not detuned.

Near-field communication to passive NFC receivers, i.e. an NFC receiver without its own power supply, e.g. B. by a battery, happens because the NFC controller emits a high-frequency signal of the working frequency via its transmitter amplifier and the receiver circuit loads the receiving antenna bit by bit or detunes the resonant frequency bit by bit, with these loads or detunings on the transmitting antenna of the NFC circuit are measurable as voltage changes due to the feedback. If the NFC receiver is far away from the NFC transmitter antenna, e.g. B. 3 cm, the changes are relatively small. On the other hand, an NFC receiver that is located directly on the transmitting antenna causes greater voltage fluctuations at the transmitting antenna. Typical NFC transmission circuits do not detect the voltage fluctuations directly at the antenna, but rather the voltage at the output of the power amplifier or the voltage is fed back to the circuit after the first filter. At this point, the voltage fluctuations are even lower than directly at the antenna. Therefore, the transmission amplifier must deliver a relatively high power so that the fluctuations can still be detected at the first filter. In order to keep the voltage fluctuations within a defined range, the NFC transmitter can regulate the power of the radio frequency radiated from the transmitting antenna, which means that in the absence of an NFC receiver, the power is increased to a maximum to ensure that a receiver in can still be recognized from the furthest possible distance. In order for an NFC receiver to be recognized with as little time delay as possible when approaching the transmitting antenna, the transmitter must be at a short distance, e.g. B. several times per second, repeatedly emit high-frequency signals to detect whether a receiver is nearby. Due to the high energy and the short distances between the test signals, there is environmental pollution from magnetic and electromagnetic fields that could exceed the legally specified limit values.

U.S. 2012/0214411 A1 discloses a system and a method for detecting the presence of an NFC tag by applying a magnetic field and detecting a field change by loading the magnetic field through the receiving coil of an NFC tag. If a change in the magnetic field is detected, a query is made by communicating at a higher power. There is no provision for recognizing an object that does not correspond to an NFC tag.

US 9,281,706 B2 describes a wireless charging system for devices that are suitable for near field communication (NFC) and could be damaged by the charging energy. To protect such NFC tags, the presence and properties of nearby NFC tags are queried by communicating with the tags and high transmission energy is only used for wireless charging if the receiver has confirmed suitability for the high transmission energy.

EP 3 664 253 A1 discloses a device and method for wireless power transmission for the inductive charging of devices, for example according to the Qi standard. For detecting NFC receivers An additional NFC reading unit is also available in the charger, so that the object does not have to be detected solely by recognizing a resonance shift in the charging signal of the Qi transmitter coil.

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

It is the object of the present invention to provide an improved circuit arrangement which both limits the output power and also ensures detection in the event of a low output power.

The object is achieved with the circuit arrangement having the features of claim 1. Advantageous embodiments are described in the dependent claims.

It is proposed that the detection unit be connected to the transmitting antenna for direct pick-up of the antenna voltage and the circuit arrangement for reducing the transmission power of the transmitting antenna in a detection phase in which a detection of the presence of an object in the vicinity of the transmitting antenna by emitting a high-frequency signal with the transmitting antenna and the antenna voltage is measured and evaluated with the detection unit, and is set up for near-field communication with a detected object in a detection phase with a higher transmission power than in the detection phase to determine whether the object is suitable for near-field radio communication.

For the detection, the higher voltage at the transmitting antenna is tapped directly and not the power upstream of a matching circuit of the transmitting antenna (e.g. as current and/or voltage value). In this way, the interrogation during detection can be carried out with significantly reduced power, in order to still obtain an analyzable signal.

In addition, the circuit arrangement for measuring and evaluating the signal of the transmitting antenna can be designed with the radio communication unit connected to the transmitting antenna. This means that further communication and regulation after the detection phase takes place as is conventional with the radio communication unit, in which case a higher power than in the detection phase can then be used if necessary. This can depend on whether or not a sensitive object was detected near the transmitter coil.

In addition to feeding back the voltage at the first filter in the NFC transmission circuit, the signal can also be routed directly to the transmission antenna, which is much higher, to an input of another microcontroller or to a separate input of the microcontroller that implements the functionality of the detection unit and radio communication unit.

A microcontroller within the meaning of the present invention is understood to be any suitable signal data processing unit that is programmable or hard-coded. This also includes field programmable gate arrays, FPGAs, microprocessors and the like.

The radio communication unit may have a transmission signal amplifier, a subsequent filter and a subsequent matching circuit connected to the transmission antenna. In such a configuration, the radio communication unit can be set up 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 thus accesses the higher voltage of the transmitting antenna, while the radio communication unit taps off and evaluates the power at the input of the matching circuit. This has the advantage that detuning of the transmitting antenna is avoided during charging operation due to the operation of the detection unit that uses it directly.

The detection unit can be set up to detect objects from a measured voltage change at the transmitting antenna. It is advantageous here if the detection unit has a peak value detector for measuring voltage peak values of the signal voltage at the transmitting antenna. This enables a simple structure and a simple and reliable evaluation of the antenna performance.

The detection unit can be set up to measure positive and negative half-waves of the signal voltage at the transmitting antenna. This can be achieved, for example, with the help of two diodes that are connected in different forward directions, or with a rectifier (e.g. bridge rectifier). It is conceivable to connect a diode in the forward direction to the positive and negative connection of the transmitting antenna and to feed both signals separately from one another to a respective analog-to-digital converter.

In addition, voltage-limiting components can be used to protect the downstream structures Elements, such as analog-to-digital converters in particular, must be provided against overvoltage. This can e.g. B. with Zener diodes.

Furthermore, a current-limiting resistor can be inserted into the supply line for the transmission amplifier, which can be bridged by a transistor if necessary. So e.g. B. the radio communication unit have a transmission signal amplifier, which is connected to an interposable current-limiting resistor, wherein the circuit arrangement is set up to reduce the transmission power by switching on the current-limiting resistor.

An additional energy charging unit can be provided, which is connected to the transmission antenna or a separate charging coil arrangement and is set up for the wireless transmission of energy to a receiver. In this way, for example, an NFC communication unit and a Qi charging unit can be implemented next to one another in the circuit arrangement. It is conceivable that the circuit arrangement is set up for radio communication with an object detected in the detection phase if it was determined in the detection phase that the object is not set up for near-field communication. This allows the charging process to be coordinated with the energy charging unit, for example according to the Qi standard, if no NFC-enabled device has been detected.

• Zuerst wird der Strombegrenzungswiderstand nicht vom Transistor überbrückt. Der NFC-Sendeschaltkreis erzeugt wie üblich seine Hochfrequenz mit der maximalen Leistung, die jedoch durch den Widerstand in der Versorgungsleitung für den Sendeverstärker begrenzt ist. Über den Abgriff direkt von der Sendeantenne wird das Sendesignal auf Analog-Digital-Wandlereingänge des Mikrocontrollers gelegt, dort digitalisiert und im Mikrocontroller weiterverarbeitet. Sobald sich ein Gegenstand aus kapazitiv oder induktiv relevantem Material der Sendeantenne nähert, ist dies über die Spannungsänderung an der Sendeantenne erkennbar und vom Mikrocontroller auswertbar. Induktiv relevante Materialien sind z. B. ferromagnetische Stoffe wie Eisen oder Metallflächen, die Wirbelströme erzeugen oder Resonanzschaltkreise in einem NFC-Receiver. Kapazitiv relevante Materialien sind beispielsweise Kunststoffe oder der menschliche Körper.

In one exemplary embodiment, the detection of objects can proceed as follows:

• First, the current limiting resistor is not bypassed by the transistor. As usual, the NFC transmitter circuit generates its high-frequency with the maximum power, which is, however, limited by the resistance in the supply line for the transmitter amplifier. Via the tap directly from the transmitting antenna, the transmission signal is applied to the analog-to-digital converter inputs of the microcontroller, where it is digitized and further processed in the microcontroller. As soon as an object made of capacitively or inductively relevant material approaches the transmitting antenna, this can be recognized by the voltage change on the transmitting antenna and evaluated by the microcontroller. Inductively relevant materials are e.g. B. ferromagnetic materials such as iron or metal surfaces that generate eddy currents or resonant circuits in an NFC receiver. Capacitively relevant materials are, for example, plastics or the human body.

After it has been recognized that an object has approached the transmitter coil, the query is made as to whether this object is a device for near-field radio, e.g. B. an NFC device or an RFID card. To do this, the transistor bridges the current-limiting resistor and the NFC circuit now independently attempts to establish communication with the object. If this is not possible after a certain amount of time, the system goes back into the low-power state, i. H. the transistor opens and the current-limiting resistor is active again, and the circuit attempts to detect the next change in antenna voltage.

The reduction in output power can also be achieved using other methods, e.g. B. can be arranged between the transmission amplifier output and the subsequent filter and / or the filter and the matching circuit, a switchable attenuator, which can be activated in the case of the required lower output power.

If the NFC transmitter is installed in a device that enables wireless charging of mobile devices and an object that is not an NFC device and not an RFID card is detected, then a digital ping can be attempted with a receiving device to communicate for wireless energy transfer. Since it is already clear that the item is not a near-field communication device, the item cannot be destroyed by the magnetic field of the digital ping either. If the device identifies itself as a compatible device for the wireless power transfer through appropriate communication, the power transfer phase then begins.

Another possibility is that the approached object identifies itself as an NFC device, but the transmitted data shows that it is an NFC device within a wireless energy receiver. In this case, the energy transfer also begins, but the NFC receiver cannot be damaged by the digital ping or the energy transfer, since such a device is designed for the energy transfer and the NFC receiver must therefore be structurally protected. Data from a standard or the comparison of patterns of the received data with a set of characteristic patterns stored in the memory of the microcontroller can be used for identification as an NFC device within a wireless energy receiver.

However, if an NFC device or an RFID card without the possibility of energy transfer was detected, the communication is continued with the current-limiting resistor bridged and the data exchange is used for its actual purpose, e.g. B. the transfer of the vehicle start authorization used. Only when this transfer z. B. cancels by removing the authorization card, the system goes back to the low-power detection of an object.

• 1 - Prinzip der Nahfeldkommunikation mit einem passiven Empfänger;
• 2 - Übertragungskurve ohne und mit Objekt in der Nähe;
• 3 - Schaltbild mit einer Low-Power-Objekterkennung;
• 4a - Elektromagnetische Emissionen einer herkömmlichen Schaltung;
• 4b - Elektromagnetische Emissionen der erfindungsgemäßen Low-Power-Erkennung.

The invention is explained in more detail below using exemplary embodiments with the accompanying drawings. Show it:

• 1 - Principle of near-field communication with a passive receiver;
• 2 - Transmission curve with and without an object nearby;
• 3 - Circuit diagram with a low-power object detection;
• 4a - Electromagnetic emissions of a conventional circuit;
• 4b - Electromagnetic emissions from the low-power detection according to the invention.

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 transmission unit 10, which includes a transmission amplifier 18 for the transmission frequency, which is supplied by a supply voltage U _T . There is a filter 11 at the push-pull output TX and TX' of this unit, which cuts away all unwanted frequency components outside the useful frequency. Behind this is a matching circuit 12 for the transmitting antenna 13, which is typically designed as a loop antenna. The reaction is typically picked up at the output of the filter 11 and fed back to the transmission unit 10 via the lines RX and RX', where the evaluation takes place. The output voltage at the transmission amplifier 18 is typically around 5 Vpp, while the voltage at the transmission antenna 13 is 40 Vpp, for example, since the matching circuit 12 consists of capacitors and, together with the transmission coil, forms an oscillating circuit that is designed so that its resonant frequency corresponds to the transmission frequency . The magnetic field generated by the current flow of the transmitting antenna 13 (e.g. loop antenna) is used for the transmission of energy and information. The electromagnetic field plays a subordinate role in this area.

The receiving antenna 20 of the NFC receiver 2 is located near the transmitting antenna 13. It is coupled to the transmitting antenna 13 via the alternating magnetic field and therefore induces a voltage that causes a current to flow in the NFC receiver 2. The electronics 22 in the NFC receiver 2 are supplied with energy via a rectifier 21, with which the NFC receiver 2 is ready to work.

Furthermore, the NFC receiver 2 has an additional element 23, which is connected bit by bit to the receiving antenna 20 (also referred to as a receiving coil) via an electronic switch 24, thereby loading it. Due to the different loads, there is a reaction on the transmitting antenna 13. There, the bit pattern applied by the NFC receiver 2 appears as a voltage change at the transmitting antenna 13. The further the NFC receiver 2 is from the transmitting antenna 13, the smaller the reaction and the smaller is the communication signal. So that the strength of the feedback signal is within a certain range, the transmission amplifier 18 can change its power, for example. The advantage of this is that only a small amount of power is required for communication with nearby NFC receivers 2 .

In the diagram in 2 it is shown that the circuit arrangement from 1 can be used not only for communication with an NFC Receiver 2, but also for detecting changes in the resonant circuit when the transmitter coil is approached by objects that change the resonance properties. These can be objects, for example, whose dielectricity or permeability differs from the ambient air. Here, too, the resonant frequency of the overall system changes, which is reflected in a changed voltage at the transmitting antenna 13 and thus also in the changed voltage behind the filter 11, where the feedback is tapped and fed to the evaluation electronics.

If there is no object in the vicinity of the transmitting antenna 13, then the voltage U1 of the resonant frequency f _R at the transmitting antenna 13 is in a defined range with a lower (Gu) and an upper (Go) limit. Resonance curve 1 applies in this case. The upper limit can also be infinity because this is not relevant for object detection. Approaches an object of the transmitting antenna 13, z. B. a card made of plastic, the resonance properties change due to the changed dielectricity, which is shown in the changed curve 2, and the voltage drops below the lower limit Gu. Thus the object was recognized.

The situation is similar with ferromagnetic or conductive material in the vicinity of the transmitting antenna 13, or with the introduction of an NFC receiver 2 with an oscillating circuit consisting of the receiving antenna 20 designed as a loop with a capacitance connected in parallel.

The voltage at the transmitting antenna 13 is shown in each case. The voltage at the tap RX/RX` occurs before the resonant circuit and is therefore significantly lower. Since the output power of the transmitter (NFC transmitter 1) can be changed, a high level is required to detect objects Output power chosen so that the difference in the feedback is as large as possible. However, it is also possible to transmit with lower powers, but then the limit values described above, which describe a range for the normal case without an object in the vicinity of the transmitting antenna 13, also change.

3 reveals an improved circuit arrangement. Here there is another signal tap directly on the transmitting antenna 13 for the detection of objects.

The signal can be routed to an analog input of a microcontroller 17 via a peak detector formed from two diodes 16 . Two diodes 16 are therefore advantageous in order to be able to evaluate the peaks of both half-waves of the antenna voltage of the transmitting antenna 13. In this way, receivers can also be detected that only change the feedback for one half-wave.

The signal routing from the diodes 16 to the analog input is high-impedance, so that the transmission signal is loaded as little as possible both during object recognition and during communication with the NFC receiver 2, which would impair communication. Since the transmission antenna 13 is tuned to the resonant frequency by the matching circuit, the voltages at the transmission antenna 13 are significantly higher than at the tap behind the filter 11, which is used to measure the feedback for the transmission circuit. This is particularly relevant when the transmitter circuit performs low-power object detection. If the communication with the NFC receiver 2 runs at higher power, voltages of 40Vpp or more can occur at the transmitting antenna 13 . In order to protect the analog input against these voltages, voltage-limiting protective components, e.g. As zener diodes are used.

The second change from conventional circuitry can be a current limiting resistor 14 in the supply line for the power amplifier, i. H. be the transmission amplifier 18. This can be connected to a switch 15, e.g. B. be realized with a transistor bridged.

In the object detection phase, the transmitter chip tries to detect a change in the voltage at the tapping point with the highest possible transmission power. Since the current-limiting resistor is not bypassed at this stage, the output power remains severely limited, with the result that the transmitter circuitry does not detect a possible object. The evaluation of the voltage is taken over by the external microcontroller 17 in this phase. If this detects an object by evaluating the voltage at the transmitting antenna 13, it switches the transmitting circuit from detection mode to communication mode and at the same time switches on the transistor (switch 15) so that the output power is no longer limited.

From this point on, complete near-field communication control is taken over by the transmit circuitry; H. the microcontroller only evaluates the analog signal from the antenna again when communication with the NFC receiver 2, e.g. B. canceled by removing the NFC receiver 2.

The 4a and 4b show the frequency spectrum of the radiated energy from the transmitting antenna 13. This spectrum is measured with a measuring antenna from a distance, e.g. B. 3m, from the measurement object. The magnetic field, which is relevant for near-field communication and no longer plays a role at the distance from the measuring antenna, is also not measured. Rather, the energy of the electromagnetic field is measured, which can cause interference in other devices. However, the electromagnetic field is also generated from an alternating magnetic field.

In 4a , which shows the spectrum of the typical circuit, the proportion of radiated energy (transmission energy) is high at the useful frequency of 13.56 MHz. It is in the range of the relevant limit value (E-field), which means that it is not possible to guarantee compliance with the limit value. The limit value (E-field) is plotted in the example by the Chinese standard GB/T-18387-2017 over the frequency range from 150 kHz to 30 MHz as an electric field in dbµV/m. The transmission energy emitted by the conventional circuit examined as an example is also plotted with its electric field in dBµV/m over the specified frequency range (resolution bandwidth RBW = 9 kHz, horizontal maximum peak).

4b shows the spectrum of modification with power limitation. It can be seen here that the power of the electromagnetic field (transmission energy) radiated by the circuit arrangement according to the invention is far below the limit value (E field), in this case approx. 25 dB below, which means that compliance with the limit value can be guaranteed. In particular, this is a decisive advantage for markets in which the limit value for this operating state is significantly lower than in average markets.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US20120214411A1 [0011]
• US 9281706 B2 [0012]
• EP 3664253 A1 [0013]
• US20210376882A1 [0014]

Claims (12)

Circuit arrangement for near-field radio communication with a radio communication unit (10) and a transmission antenna (13), which is connected to the radio communication unit (10), and with a detection unit (17), characterized in that the detection unit (17) with the transmission antenna (13 ) is connected for direct tapping of the antenna voltage and the circuit arrangement for reducing the transmission power of the transmission antenna (13) in a detection phase in which a detection of the presence of an object in the vicinity of the transmission antenna (13) by emitting a high-frequency signal with the transmission antenna (13) and the antenna voltage is measured and evaluated with the detection unit (17), and is set up for near-field communication with a detected object in a detection phase with a higher transmission power than in the detection phase to determine whether the object is suitable for near-field radio communication. Circuit arrangement according to claim 1 , characterized in that the circuit arrangement for measuring and evaluating the signal of the transmitting antenna (13) is formed with the radio communication unit (10) connected to the transmitting antenna (13). Circuit arrangement according to claim 2 , characterized in that the radio communication unit (10) has a transmission signal amplifier (18), a subsequent filter (11) and a subsequent matching circuit (12) which is connected to the transmission antenna (13), the radio communication unit (10) being used for measuring and Evaluation of the signal voltage at the input of the matching circuit (12) is set up at the connection between the filter (11) and the matching circuit (12). Circuit arrangement according to one of the preceding claims, characterized in that the detection unit (17) is set up to detect objects from a measured voltage change at the transmitting antenna (13). Circuit arrangement according to one of the preceding claims, characterized in that the radio communication unit (10) has a transmission signal amplifier (18) which can be selectively switchably connected to a current-limiting resistor (14), the circuit arrangement for reducing the transmission power by effectively connecting the current-limiting resistor (14) is set up with the transmission signal amplifier. Circuit arrangement according to claim 5 , characterized in that the current-limiting resistor (14) can be bridged by a controllable switch (15), in particular a transistor. Circuit arrangement according to one of the preceding claims, characterized in that the detection unit (17) is designed as a separate microcontroller. Circuit arrangement according to one of the preceding claims, characterized in that the detection unit (17) has a peak value detector for measuring voltage peak values of the signal voltage at the transmitting antenna (13). Circuit arrangement according to one of the preceding claims, characterized in that the detection unit (17) is set up to measure positive and negative half-waves of the signal voltage at the transmitting antenna (13). Circuit arrangement according to one of the preceding claims, characterized in that the transmitting antenna (13) is connected to the detection unit (17) with at least one voltage-limiting component, in particular diodes. Circuit arrangement according to one of the preceding claims, characterized by an energy charging unit which is connected to the transmitting antenna (13) or to a separate charging coil arrangement and is set up for the wireless transmission of energy to a receiver. Circuit arrangement according to claim 11 , characterized in that the energy charging unit is set up for radio communication with an object detected in the detection phase with the energy charging unit if it was determined in the detection phase that the object is not set up for near-field communication.

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