Patent Application
20240235274
This application claims the priority benefit of European patent application number 23305014, filed on Jan. 5, 2023, entitled “NFC device configured for wireless power transfer,” which application is hereby incorporated herein by reference to the maximum extent allowable by law.
The present disclosure relates generally to electronic devices incorporating a near-field communication (NFC) circuit, more commonly called NFC devices. The present disclosure more particularly relates to an NFC device and method for wireless power transfer, for example to detect a foreign object during power transfer and/or to control the power transfer.
Wireless power transfer (WPT), or wireless power transmission, is used for various applications. One technique of wireless power transfer uses inductive coupling between a power transmitter and a power receiver, for example a resonant inductive coupling. For example, a transmitter, connected to a power source, converts electrical current into an alternating electromagnetic field through a first induction coil, and sends it to a power receiver. The power receiver comprises a second induction coil electromagnetically coupled to the first induction coil, and the electromagnetic field formed by the first induction coil induces an alternating current (AC) in the second induction coil. The induced alternating current may directly drive (supply) a load, or may drive a load with a direct current (DC) voltage generated by a rectifier in the power receiver. According to a resonant inductive coupling technique, each of the power transmitter and the power receiver comprises a resonant circuit (or oscillating circuit, or resonant tank), which may consist of a capacitor connected to the inductive coil, or a self-resonant coil, and the oscillating circuits of the power transmitter and the power receiver are tuned to resonate at the same resonant frequency.
In some applications, wireless communication is used between the power transmitter and the power receiver, for example to initialize the power transfer, to adjust the supplied power level during the power transmission, or to stop the power transfer. For example, Near-Field Communication (NFC) technology may be used for the wireless communication.
Near-Field communication technology typically uses a radiofrequency electromagnetic field, also called “carrier field”, typically at 13.56 MHz, generated by a first NFC device to detect and communicate with a second NFC device within range. Depending on the application, for a communication, one of the first and second NFC devices operates in so-called reader mode (NFC transmitter, or NFC transceiver), while the other of the first and second NFC devices operates in so-called card mode (NFC receiver), or both the first and second NFC devices communicate in peer-to-peer (P2P) mode.
In some particular applications, the carrier field may also be used to wirelessly supply a load of the second NFC device acting as a power receiver, when the second NFC device (NFC receiver) is adapted to NFC power transfer (“NFC charging”). In these applications, the first NFC device (NFC transmitter) acts as a power transmitter. The antenna of each of the first and second NFC devices is then adapted to manage both communications and charging. NFC charging is for example discussed in the NFC Forum Wireless Charging Specifications (WLC Specifications).
In other applications, NFC is used only for wireless communication, and not for charging, for example in applications in which the power to be transferred is relatively high. The antenna of each of the first and second NFC devices is used only for communications, and the power transmitter and power receiver each have an antenna for power transfer. For example, the first NFC device (NFC transmitter) is coupled to, or included in, the wireless power transmitter, and the second NFC device (NFC receiver) is coupled to, or included in, the wireless power receiver. In the following disclosure, this may also be designated as “NFC charging”.
A particular application of wireless power transmission using NFC for wireless communications is the so-called “Ki Cordless Kitchen standard” (“Ki standard”) developed by the Wireless Power Consortium (WPC), which is dedicated to the wireless transmission of power to cordless kitchen appliances, such as rice cookers, toaster, blenders, coffee makers, kettles, fryers and more. For example, in a wireless power transmission to a kitchen appliance, the first NFC device is coupled to, or included in, the wireless power transmitter, such as a kitchen hob, and the second NFC device is coupled to, or included in, the kitchen appliance, acting as a wireless power receiver.
A difficulty with wireless power transfer is that a foreign object (FO) of an electrically-conductive material may inadvertently be placed or fall within the field of the power transmitter during the power transfer (charging), for example between the power transmitter and the power receiver. This is a concern because the alternating electromagnetic field generated by the power transmitter can induce eddy currents in the electrically-conductive material that is exposed to the field, and the eddy currents may cause this material to heat up. Therefore, it is desired to detect the presence of a foreign object within range of the power transmitter so that the foreign object can be removed, and/or the wireless power transfer can be aborted or the level of transferred power be reduced, for efficient power deliver and safety of operation.
In the application of NFC charging, it is desired that the NFC transmitter can detect the presence of a foreign object, in particular during wireless power transfer. More generally, it is desired that the NFC transmitter can control the wireless power transfer.
One embodiment provides a NFC device configured for wireless power transfer, the NFC device comprising:
In an embodiment, the microcontroller unit is adapted to:
One embodiment provides a method for controlling wireless power transfer using a NFC device having a frontend circuit coupled to a microcontroller unit, the controlling method comprising:
In an embodiment, the method is implemented during a wireless power transfer between the NFC device and an NFC receiver, for example continuously during the wireless power transfer.
In an embodiment, the method comprises a first detection method implemented by the microcontroller unit, the first detection method comprising, after or during the step of processing the digital signal:
In an embodiment, the first detection method is adapted to detect whether an electrically-conductive foreign object is within the field of the NFC device, the impedance change is, for example, an impedance rise, and the detection threshold is a first detection threshold.
In an embodiment, the first detection method is adapted to detect whether a power receiver, or an electrically-conductive foreign object, is removed from the field of the NFC device, the impedance change is, for example, an impedance drop, and the detection threshold is a second detection threshold.
In an embodiment, determining if the impedance change is greater or equal to the detection threshold comprises:
In a particular embodiment, the average reference value corresponds to a previous average value obtained by a previous averaging, the current averaging being separated from the previous averaging by a transition period.
In an embodiment, the method comprises a second detection method implemented by the microcontroller unit, the second detection method being for example adapted to detect whether a wireless power transfer stop signal is sent to the NFC device, the second detection method comprising:
The following embodiments can be applied to an NFC device and/or to a method for controlling wireless power transfer using an NFC device.
In an embodiment, the analog-to-digital converter is an n-bit analog-to-digital converter, for example where n is equal to at least 10.
In an embodiment, the microcontroller unit further comprises a computer program processor or processing unit adapted to process the digital signal.
In an embodiment, the analog-to-digital converter is coupled to a first pin of the frontend circuit adapted to output the amplitude analog signal and/or a second pin of the frontend circuit adapted to output the phase analog signal.
In an embodiment, the analog signal is an electrical signal.
One embodiment provides a wireless power transmission system comprising:
In an embodiment, the wireless power transmission system further comprises a wireless power receiver including:
In an embodiment, the NFC receiver is also configured to manage NFC charging, and is connected to a load of the wireless power receiver, for example via a load controller.
In an embodiment, the wireless power transmission system further comprises a user interface coupled to the microcontroller unit of the NFC transmitter, the user interface being adapted to send a warning signal to a user, for example if the impedance change corresponds to the presence of an electrically-conductive foreign object in the field of the NFC transmitter.
The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:
Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.
For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the NFC communication protocols and the usual electronic devices or circuits implementing these protocols have not been described, these protocols being well-known by the one skilled in the art and being compatible with the described embodiments. Similarly, NFC charging, for example according to the NFC Forum Wireless Charging Specification, and the usual electronic devices or circuits adapted to NFC charging, have not been described, the described embodiments being compatible with known NFC charging techniques.
Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.
In the following disclosure, unless indicated otherwise, when reference is made to absolute positional qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or to relative positional qualifiers, such as the terms “above”, “below”, “higher”, “lower”, etc., or to qualifiers of orientation, such as “horizontal”, “vertical”, etc., reference is made to the orientation shown in the figures.
Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.
In the following disclosure, when reference is made to a “power transmitter” or a “transmitter”, it designates a wireless power transmitter. Similarly, when reference is made to a “power receiver” or a “receiver”, it designates a wireless power receiver, and when reference is made to a “power transmission system”, it designates a wireless power transmission system.
In the following disclosure, when reference is made to an “NFC device”, it designates an electronic device incorporating one or several near-field communication (NFC) circuits. The near-field communication circuits each have various elements or electronic circuits for generating or detecting a radiofrequency signal using an NFC antenna, and/or modulation or demodulation circuits. Each NFC antenna may comprise, or be part of, an oscillating circuit.
The NFC device 110 comprises:
Alternatively, the analog-to-digital converter 114 is not included in the microcontroller unit 113, and is connected, for example coupled, to the microcontroller unit 113.
The computer program is for example stored in a memory of the microcontroller unit (not represented), such as a FLASH memory and/or RAM (Random Access Memory).
The NFC device 110 may be referred as an “NFC transmitter”, and the antenna 111 as a “transmitter antenna”. The frontend circuit 112 may be referred as an “NFC frontend”. The microcontroller unit 113 may be referred as a “microcontroller”.
In the example represented in
The NFC transmitter 110 comprises, for example, at least a microchip or electronic circuit capable of near field communications.
In the example represented in
The transmitter antenna 111 may comprise one or more inductive coils or elements, for example in the form of a patch antenna or a microstrip antenna. The at least one inductive coil or element is, for example, connected to, or comprised in, an oscillating circuit (not represented).
The frontend circuit 112 is adapted to perform operations for generating and receiving radiofrequency signals by means of the transmitter antenna 111. The frontend circuit 112 for example comprises:
The frontend circuit 112 may be connected or coupled to, or may include, an impedance matching circuit (not represented), which in turn is connected or coupled to the transmitter antenna 111. The frontend circuit 112 may also comprise other circuits (not represented), which are standard circuits well known to those skilled in the art.
The frontend circuit 112 may be referred as an “NFC reader”.
The microcontroller 113 is connected or coupled to the frontend circuit 112, for example using a digital connection and an analog connection. The microcontroller 113 is for example configured to implement a wireless control protocol and to transmit an instruction signal to the frontend circuit 112. In return, the frontend circuit 112 may send a confirmation signal to the microcontroller 113. This is represented in
The analog-to-digital converter 114 may be connected to one or several dedicated pins of the frontend circuit 112, for example a first pin adapted to output an analog amplitude signal (AM) and/or a second pin adapted to output an analog phase signal (PH). For example, each of the first and second pins can be configured to route an amplitude or phase signal from the receiver to the pin. The one or several dedicated pins can be for example one or several Test Analog Digital (TAD) pins.
The analog amplitude and/or the phase signal (AM/PH) is sent by the frontend circuit 112 to the analog-to-digital converter 114 after an internal extraction of the amplitude and/or phase signal. This is represented in
As represented in
The power receiver 120 comprises:
In alternative embodiments, the power receiver 120 could additionally or alternatively comprise a different type of load.
The NFC receiver device 122 may be referred as an “NFC receiver”.
The receiver antenna 121 may comprise one or more inductive coils or elements, for example in the form of a patch antenna or a microstrip antenna. The at least one inductive coil or element is, for example, connected to, or comprised in, an oscillating circuit (not represented).
The NFC receiver 122 is for example configured to manage Near-Field communications. For example, the NFC receiver 122 comprises demodulating and/or modulating circuits configured to demodulate and/or modulate a radiofrequency signal in order to receive data from, and/or send data to, the NFC transmitter 110, using NFC communication protocols.
For example, the NFC receiver 122 is, or comprises, a microchip or electronic circuit capable of near field communications.
In the example of
The NFC receiver 122 may be connected or coupled to, or may include, an impedance matching circuit (not represented), which in turn is connected or coupled to the receiver antenna 121.
In the example represented in
Although not shown in
When power is wirelessly transferred to the power receiver 120, the microcontroller 113 for example monitors the analog amplitude and/or phase signal sent by the frontend circuit 112 in order to indirectly detect if there is an impedance change within the field of the NFC transmitter 110. A detected impedance change may be due to various events.
An impedance change may be due to the arrival of an electrically-conductive foreign object 10 within the field (within range) of the NFC transmitter 110. The foreign object may be positioned between the power transmitter 101 and the power receiver 120, or in another place within range of the power receiver 120, as shown in
If an electrically-conductive foreign object 10 is located within the field of the NFC transmitter 110, a coupling may occur between the foreign object 10 and the antenna 111 of the NFC transmitter 110. This coupling may modify the impedance of the oscillating circuit of the NFC transmitter 110, which results in a variation of the amplitude and/or phase of a signal across the terminals of this oscillating circuit, typically an electrical signal. The amplitude and/or phase of the electrical signal is output by the frontend 112 circuit, which sends it to the microcontroller 113. The microcontroller 113 is configured to detect an amplitude and/or phase variation of the electrical signal.
An impedance change may also be due to a removal of the power receiver 120 from the field of the NFC transmitter 110. The detection of such a removal is similar to that of the foreign object detection.
An impedance change detected by the microcontroller 113 may also be due to a signal sent by the power receiver 120, for example the NFC receiver 122 of the power receiver, to request that the power transfer is stopped or that the power level of the power transfer is changed. The detection of such a signal sent by the power receiver is explained in detail hereafter.
If the microcontroller 113 detects an impedance change within the field of the NFC transmitter 110, depending on the event, then the microcontroller 113 is for example configured to send a control signal (CTRL) to the frontend circuit 112, for example to stop the power transfer and/or to change the level of the transferred power, and/or the microcontroller 113 is for example configured to send a warning signal to a user interface 130, for example to warn a user to remove a foreign object.
The user interface 130 is coupled to the microcontroller 113, and may be included in, or connected to, the NFC transmitter 110, the power transmitter 101, or the power receiver 120. For example, the user interface 130 comprises a light source and/or a sound emitter or any other signal emitter adapted to warn a user.
Examples of methods adapted to detect a variation of the amplitude and/or phase of the analog signal, and thus, an impedance change in the field of the NFC transmitter 110, are described hereafter. For example, these detection methods are implemented in a computer program, for example executed by the computer program processor or processing unit 115. The computer program is, for example, stored in a memory of the microcontroller 113.
For example, in order to be considered as being due to a foreign object arrival, the change duration tfod,resp of the impedance change stage 213 has to be more than a minimal change duration tfod,resp,min, and/or the voltage drop 214, or the impedance rise, has to be greater than, or equal to, a first detection threshold, for example equal to a voltage drop, or impedance rise, of about 10%. For example, the detection method may validate a foreign object presence if the voltage drop or impedance rise is greater or equal to the first detection threshold and lasts at least the minimal change duration tfod,resp,min.
By monitoring the voltage amplitude, the microcontroller 113 is for example configured to detect the impedance rise, for example after the transition period 212. If the event is the arrival of an electrically-conductive foreign object 10, the microcontroller 113 is then for example configured to send a control signal to the frontend circuit 112, for example to stop the power transfer or limit the level of the transferred power, and/or the microcontroller 113 is configured to send a warning signal to the user interface 130 to warn a user to remove the foreign object. For example, the microcontroller 113 sends a control and/or warning signal if the first detection threshold is crossed and if the minimal change duration tfod,resp,min is respected.
For example, the transition duration tS,imp-transition of the transition period is about 50 ms. For example, the minimal change duration tfod,resp,min is equal to about 1.4 ms. For example, the change duration tfod,resp is comprised between 1.4 ms and 110 ms, for example equal to about 50 ms.
For example, in order to be considered as being due to the removal of the power receiver, the change duration tfod,resp of the impedance change stage 223 has to be more than a minimal change duration tfod,resp,min, and/or the voltage rise 224, or the impedance drop, has to be greater than, or equal to, a second detection threshold, for example equal to a voltage rise, or impedance drop, of about 10%. For example, the detection method may validate the removal of the power receiver if the voltage rise or impedance drop is greater or equal to the second detection threshold and lasts at least the minimal change duration tfod,resp,min.
By monitoring the voltage amplitude, the microcontroller 113 is for example capable of detecting the impedance drop, for example after the transition period 222. If the event is the removal of the power receiver 120, the microcontroller 113 is for example configured to send a control signal to the frontend circuit 112 to stop the power transfer or to limit the level of transfer power. For example, the microcontroller 113 is configured to send a signal if the second detection threshold is crossed and if the minimal change duration tfod,resp,min is respected.
For example, the transition duration tS,imp-transition of the transition period is about 50 ms. For example, the minimal change duration tfod,resp,min is equal to about 1.4 ms. For example, the change duration tfod,resp is comprised between 1.4 ms and 110 ms, for example equal to about 50 ms.
An example of a first detection method will now be described, with reference to
At least during power transfer, the analog amplitude (and/or the phase) signal is for example continuously sent by the frontend circuit 112 to the analog-to-digital converter 114, which transforms the analog signal into a digital signal. The amplitude (and/or the phase) signal is for example in the form of an analog voltage level. The digital signal is for example processed by the computer program processor or processing unit 115.
The computer program processor or processing unit 115 is for example configured to perform a first averaging of the digital signal during an averaging period, which is preferably comprised between 4 and 10 ms, for example equal to 8 ms, in order to generate a first average value, which can be used as an average reference value.
Then, the computer program processor or processing unit 115 is for example configured to perform a second averaging of the digital signal, during the same averaging period, after the first averaging, the first and second averaging being separated by a waiting period, which is preferably chosen to be close to the transition duration tS,imp-transition. For example, the waiting period has a duration of between 40 and 60 ms, for example equal to around 50 ms. The second averaging generates a second average value, which is compared, for example by the computer program processor or processing unit 115, to the average reference value, in order to determine if there is a variation, for example a variation greater than, or equal to, a (first or second) detection threshold, and for example if the variation is a drop or a rise.
If the detected variation is greater or equal to the (first or second) detection threshold, and if the variation duration is greater or equal to the minimal change duration tfod,resp,min, then the microcontroller 113 is for example configured to send a control signal to the frontend circuit 112 and/or a warning signal to the user interface 130, depending on the detected event.
If the detected variation is below the (first or second) detection threshold, and/or if the variation duration is less than the minimal change duration tfod,resp,min, then the computer program processor or processing unit 115 is for example configured to perform a third averaging, after the waiting period, using the same averaging period, in order to generate a third average value, and the third average value is compared to the second average value. This process is for example repeated, with the current average value being compared with the previous average value, until an event is detected.
The graph 310 comprises a No Impedance Change stage 311 and an Impedance Change stage 312, which corresponds to a request signal to stop the wireless power transfer (WPT). It may be used by the power receiver to then request for another power level. The WPT stop signal 312 is for example sent by the power receiver, for example the NFC receiver 122 of the power receiver 120 of
For example, the WPT stop signal is generated by the NFC receiver 122 by periodically disconnecting and reconnecting the receiver antenna 121, or by periodically changing the impedance of the receiver antenna 121.
The WPT stop signal 312 is for example a square-wave signal comprising a plurality of elementary stop patterns 314 (also named “S patterns”), illustrated as short voltage drops from Vnic to Vic, corresponding to impedance rises, two voltage drops being separate by a voltage rise from Vic to Vnic. In
In order to be considered as an elementary stop pattern (S pattern), the duration (timp-change) during which the voltage is low (low pulse duration) is for example lower than a pulse duration threshold which is for example comprised between 0.8 and 1.2 ms, for example equal to about 1 ms, and the rise times (tWPT-r) and fall times (tWPT-f) of the voltage signal (signal transitions) are for example lower than a transition threshold, for example about 2.5 μs. In addition, the voltage drop, or the impedance rise, is for example greater than, or equal to, a third detection threshold, for example about 6 or 7%.
The graph 320 of
The graph 320 comprises a No Impedance Change stage 321 and an Impedance Change stage 322, which also corresponds to a request signal to stop the wireless power transfer (WPT). It may be used by the power receiver to then request for another power level. The level change request signal 322 is for example a square-wave signal comprising a plurality of elementary stop patterns 324, illustrated as short voltage rises from Vnic to Vic, corresponding to impedance drops, two voltage drops being separate by a voltage drop from Vic to Vnic. In
The request signal 322 is typically sent by the power receiver, for example the NFC receiver 122 of the power receiver 120 of
In order to be considered as an elementary stop pattern (S pattern), the duration during which the voltage is high (high pulse duration) is for example lower than a pulse duration threshold, for example comprised between 0.8 and 1.2 ms, for example equal to about 1 ms, and/or the rise times and fall times of the voltage signal (signal transitions) are lower than a transition threshold, for example about 2.5 μs. In addition, the impedance drop, or the voltage rise, is for example greater than, or equal to, a fourth detection threshold, for example about 6 or 7%.
An example of a second detection method will now be described with reference to
At least during power transfer, the phase (and/or the amplitude) of the analog signal is continuously sent by the frontend circuit 112 to the analog-to-digital converter 114, which is configured to sample the analog signal, for example the analog phase signal, for example every 250 μs. Graph 410 of
For example, the analog-to-digital converter 114 is a n-bit ADC, where n is for example equal to at least 12.
The first and second detection methods may be implemented simultaneously. Indeed, applying the first detection method to a WPT stop signal does not trigger a foreign object detection, because the frequency of 500 Hz corresponds to a duration of 2 ms for each S pattern, and the averaging period of the first detection method is greater than 2 ms, therefore, averaging the WPT stop signal would result in an average value of at most around half the magnitude of the voltage change, which for example does not exceed the foreign object detection threshold (third or fourth detection threshold).
In an embodiment, if a first S pattern of a WPT stop signal is detected by the second detection method, then the first detection method is inhibited at least for the duration of the WPT stop signal.
The method for detecting the power level change signal of
Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art.
Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23305014.5 | Jan 2023 | EP | regional |
