The present invention relates to the wireless charging of electronic devices with rechargeable batteries or other means of storing electrical energy.

Modern portable electronic devices such as smartphones, tablets, wearables etc. typically require charging regularly e.g. on a daily basis. Many people own several of these devices and accordingly own many corresponding chargers (i.e. power adapters) to charge the battery of each device. While there have been efforts to standardise the connectors that are used on such devices such as the

near-ubiquitous micro Universal Serial Bus (micro-USB) connector or the

Lightning® connector used by Apple®, users are still typically required to own several chargers.

These chargers are usually constructed such that alternating current (AC) mains voltage (e.g. 120 or 240 V) is converted to low voltage, direct current (DC) via a transformer and rectifier and then provided to a charging circuit in the

corresponding portable device. This typically means that each charger has a mains plug housing the transformer and rectifier and a length of cable extending from the plug with a connector at the end that can be inserted into the portable device. With people typically owning multiple devices, this leads to having an undesirable number of trailing cables which are often aesthetically displeasing, become tangled and are prone to being damaged.

In order to overcome these issues, some modern portable devices are provided with inductive or "wireless" charging functionality. Wireless charging typically involves using an alternating magnetic field established by an antenna (typically a coil antenna) within a charging station or "pad" which is inductively coupled with a corresponding antenna (typically also a coil antenna) inside the portable device.

The portable device uses the power from the induced electrical current to charge its battery in the manner described above.

However while there have been many advances in this area, there are now conflicting standards that have been adopted by different manufacturers. One wireless charging standard known as Rezence® has been developed by the Alliance for Wireless Power (A4WP). Rezence® uses a field that varies with a frequency of 6.78 MHz. Another wireless charging standard known as Qi™ - owned by the Wireless Power Consortium (WPC) - has been adopted by Nokia®, Samsung®, Huawei®, and Sony® and uses a fields that vary with a frequency between 80 and 300 kHz. The Applicant has also appreciated that power may be harnessed from using the hardware provided for near-field communication (NFC) between devices, which typically uses fields at 13.56 MHz. The existence of competing standards hampers the adoption and acceptance of this technology and means that its full potential is not realised.

When viewed from a first aspect, the present invention provides an electronic device comprising:

an antenna;

an energy store;

a frequency detection section arranged to determine if an induced frequency of an electric current induced in said antenna corresponds to one of a plurality of predetermined frequencies and, if so, to charge said energy store using said induced electric current.

The invention extends to a method of operating an electronic device comprising an antenna and an energy store, the method comprising determining if an induced frequency of an electric current induced in said antenna corresponds to one of a plurality of predetermined frequencies and, if so, charging said energy store using said induced electric current.

Thus it will be appreciated by those skilled in the art that in accordance with the present invention an electronic device can detect when it is placed in the vicinity of a charging pad supporting one of a plurality of different wireless charging standards which have different induction frequencies. This advantageously allows such a device to be charged using a number of different wireless charging stations, offering greater convenience for the user and less concern regarding interoperability with peripheral chargers for the manufacturer. Adding a separate antenna for each charging standard would increase the cost and size of devices. However this is not required in accordance with the present invention as the same antenna can be used for multiple wireless charging standards. This allows embodiments of the invention to be provided with just a single antenna. Particularly advantageous embodiments of the invention can provide a "seamless" experience for users, whereby a user can place the portable device on any wireless charging station supporting one of the standards in order to charge the battery of the device without needing to worry about whether it is the right "kind" of station for their particular device or being required to make any changes to the settings of their device.

Furthermore, by detecting a characteristic frequency of a specific wireless charging standard at the physical layer, such an electronic device does not need to initialise or utilise any higher stack layers (e.g. the network layer or the application layer) if a particular wireless charging standard is not supported, providing a saving in both power consumption and computational requirements. These determinations can be made based on frequency alone and thus the device of the present invention does not require any protocol-specific messages or communications in order to begin charging.

In a set of embodiments, one of the plurality of frequencies is approximately 6.78 MHz - this allows the device to support the known Rezence® charging frequency.

In a set of embodiments, one of the plurality of frequencies is approximately 13.56 MHz - this allows the device to support charging at a frequency commonly used for near-field communication (NFC).

The frequency detection section could be implemented in any of a number of ways that are known in the art per se. In some embodiments the frequency detection section comprises a counter arranged to compare a number of cycles (e.g. rising or falling edges) of the induced current in a given time period to a plurality of predetermined values corresponding to the plurality of predetermined frequencies. This allows the relevant frequency to be readily determined using a relatively small number of components that do not use much power - without needing to use a central processing unit for example. In an advantageous set of embodiments the device comprises a resonant circuit including the antenna and tuneable to at least first and second resonant frequencies and is arranged to:

tune said resonant circuit to the first resonant frequency if the induced frequency corresponds to the first resonant frequency;

tune said resonant circuit to the second resonant frequency if the induced frequency corresponds to the second resonant frequency. As the skilled person will appreciate, tuning the resonant circuit to an appropriate frequency allows the efficient transfer of energy from the charging station via the antenna to the energy store.

When viewed from a second aspect the invention provides an electronic device comprising:

an antenna;

an energy store;

a resonant circuit including said antenna and tuneable to at least first and second resonant frequencies;

a frequency detection section arranged to determine whether an induced frequency of an electric current induced in said antenna corresponds to one of the first and second resonant frequencies;

wherein the device is arranged to:

tune said resonant circuit to the first resonant frequency if the induced frequency corresponds to the first resonant frequency;

tune said resonant circuit to the second resonant frequency if the induced frequency corresponds to the second resonant frequency; and

charge said energy store using said induced electric current. This aspect of the invention extends to a method of operating an electronic device comprising an antenna, an energy store and a resonant circuit including said antenna and tuneable to at least first and second resonant frequencies, the method comprising:

determining if an induced frequency of an electric current induced in said antenna corresponds to one of a plurality of predetermined frequencies; tuning said resonant circuit to the first resonant frequency if the induced frequency corresponds to the first resonant frequency;

tuning said resonant circuit to the second resonant frequency if the induced frequency corresponds to the second resonant frequency; and

charging said energy store using said induced electric current.

The resonant circuit could be could be implemented in any of a number of ways. In a set of embodiments the resonant circuit comprises a capacitor. The capacitor could be a variable capacitor to allow the resonant circuit to be tuned. One or more additional components could be changed to provide the necessary tuning. In a set of embodiments however the resonant circuit comprises first and second capacitors and a switching arrangement to switch between a first and second capacitance to tune the resonant circuit to the first and second resonant frequencies respectively. The switching arrangement could switch between the first and second capacitors or could switch one of them into or out of a circuit to provide the different

capacitances.

Additionally or alternatively the tuning of the resonant circuit could be achieved partly or fully by changing the antenna. Whilst it was explained above that it is advantageous to be able to use a single antenna to support multiple charging standards in accordance with the invention, the Applicant also recognises that in some circumstances it would be desirable to use a change in the antenna to provide tuning. This could be achieved, for example, by switching part of the antenna in or out depending on the required resonant frequency. As a portion, possibly a major portion, would be common to both frequencies, at least some of the benefit of a single antenna may thus still be realised.

Where reference is made to first and second resonant frequencies, this should not be taken as limiting; three or more frequencies could be supported within the scope of the invention.

Preferably at least part of the electronic device comprises an integrated circuit device. The antenna could be provided on the integrated circuit but typically it is provided separately. ln a set of embodiments a power supply circuit is provided between the antenna and the energy store. This would typically include a rectifier section and a regulator section. The electronic device could be a portable device such as a smartphone, tablet, smart watch, laptop, wireless speaker etc.

The energy store would typically be a rechargeable battery but this is not essential. It could for example comprise a supercapacitor or any other form of electrical energy storage.

Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figs. 1A and 1 B show, for reference purposes only, a typical device that supports wireless charging and a wireless charging station;

Fig. 2 illustrates, for reference purposes only, the operation of wireless charging; and

Fig. 3 shows a block diagram of an electronic device with automatic frequency selection in accordance with an embodiment of the present invention.

Figs. 1 A and 1 B show a typical device that supports wireless charging and a wireless charging station. Shown in Fig. 1A is a top-down view of a smartphone 2 that has wireless charging functionality which has been placed on a compatible wireless charging pad 4. The wireless charging pad 4 is connected to a mains outlet 6 via a plug 8 which is connected to the charging pad 4 by a length of cable 10.

Fig. 1 B shows a perspective view of the same smartphone 2 and charging pad 4. Once placed on the charging pad 4, the battery (not shown) within the smartphone 2 is inductively charged using a varying magnetic field established by the charging pad 4 (illustrated by the set of arrows 12). This process is described in greater detail with reference to Fig. 2 below.

Fig. 2 illustrates the wireless charging operation carried out by the smartphone 2 and charging pad 4 of Fig. 1. The smartphone 2 comprises an inductive receiver coil antenna 16, a receiver circuit 20 and a battery 24. Similarly, the charging pad 4 comprises a matching inductive transmitter coil antenna 18 and a transmitter circuit 22. Typically, these coil antennae 16, 18 are formed as a loop antenna and arranged in a spiral or rectangular shape.

The transmitter coil antenna 18 within the charging pad 4 is connected to a transmitter circuit 22 that takes AC mains voltage from a wall socket 6 via the plug 8 and cable 10 and increases its frequency to a predetermined value specified in accordance with the wireless charging protocol to which the device 2 and pad 4 are designed. This high frequency current is passed through the inductive coil antenna 18 which produces a time-varying magnetic field 12. The time-varying magnetic flux lines that make up the field 12 are then "cut" by the receiver coil antenna 16, which induces a current in the receiver coil antenna 16. In other words, when brought into close proximity with one another, the transmitter coil antenna 18 within the charging pad 4 is inductively coupled to the receiver coil antenna 16.

The induced current in the receiver coil antenna 16 is then passed to a receiver circuit 20 which shifts the voltage to the correct value and converts the AC current to DC so as to be suitable for charging the battery 24.

Fig. 3 shows a block diagram of an electronic device in the form of a smartphone 102 with automatic frequency selection in accordance with an embodiment of the present invention. The device 102 comprises an antenna 116, a power supply module 120, a battery 124 and a frequency detection module 136. The power supply module 120 comprises a tuning circuit 126 and a power control module 128.

The antenna 1 16 is connected to the tuning circuit 126 via an electrical interface 134 so that together they form a resonant circuit. The tuning circuit 126 comprises a variable capacitance e.g. by means of a variable capacitor or a pair of different capacitors that can be switched e.g. using transistors. This allows the resonant frequency of the resonant circuit to be altered. For example it might be selectably operated at either 6.78 MHz or 13.56 MHz for use with Rezence® or for harnessing energy from an NFC field as desired. The power control module 128, which is in turn connected to the battery 124, performs rectification and regulation of the current induced in the antenna 1 16 to provide a stable low voltage DC supply to the battery 124 in order to charge it. The power control module 128 may also contain standard battery management features such as state of charge monitoring, full charge cut-off etc. The frequency detection module 136 comprises a counter which counts edges, peaks or the like in the current induced in the antenna 116 and compares the count value with a number of stored values on a periodic basis. By counting the number of cycles (e.g. rising or falling edges) of the induced current that occur in a given amount of time, can be readily determined whether the frequency corresponds to a predetermined value.

In use the device 102 is placed on a charging station which induces a periodically varying current in the antenna 1 16 as previously described with reference to Figs. 1 and 2. The frequency detection module 136 counts cycles as described and thus determines whether the frequency of the induced current corresponds for example to the Rezence® charging protocol or to a frequency typical of an NFC field.

The frequency detection module 136 passes a signal back to the tuning circuit 126 to determine which capacitor to switch into the circuit in order to match the resonant frequency of the resonant circuit to the frequency detected. Once the resonant frequency of the resonant circuit matches the induced current from the charging station, the energy is transferred efficiently to the battery 124 via the power control module 128. The transmitter (not shown) and receiver coil antennae 116 may also be used to send and/or receive control or data signals between the smartphone 102 and the charging pad. This may for example be implemented using near-field

communication (NFC), particularly where the charging protocol uses a frequency at or near an NFC frequency. These signals might include the smartphone 102 notifying the charging pad that it supports a particular wireless charging protocol such as Rezence® or that it supports NFC functionality.

Thus it will be seen that an electronic device that can automatically detect a characteristic frequency of a plurality of wireless charging standards and tune an antenna accordingly has been described herein. Although particular embodiments have been described in detail, it will be appreciated by those skilled in the art that many variations and modifications are possible using the principles of the invention set out herein.