HK1153310B - Electronic devices with capacitive proximity sensors - Google Patents

Description

Electronic device with capacitive proximity sensor

Priority of the present application claims priority from U.S. provisional patent application No.61/226,683 filed on 7/17/2009 and U.S. patent application No.12/632,695 filed on 12/7/2009, the entire contents of which are incorporated herein by reference.

Technical Field

The present invention relates generally to antennas, and more particularly to antennas for electronic devices.

Background

Electronic devices such as portable computers and handheld electronic devices are becoming increasingly popular. Devices such as these typically have wireless communication capabilities. For example, the electronic device may use long-range wireless communication circuitry, such as cellular telephone circuitry, to communicate using cellular telephone bands at 850MHz, 900MHz, 1800MHz, and 1900MHz (e.g., the main global system for mobile communications or GSM cellular telephone bands). Long range wireless communications circuitry may also be used to handle the 2100MHz band and other bands. The electronic device may use a short-range wireless communication link to handle communications with nearby devices. For example, the electronic device may use signals at 2.4GHz and 5GHz(IEEE 802.11) frequency band (sometimes referred to as local area network band) and at 2.4GHzFrequency bands to communicate.

There may be difficulties in successfully incorporating antennas into electronic devices. Some electronic devices are manufactured with a small form factor, thereby limiting the space for the antenna. In many electronic devices, electronic components located near the antenna act as a possible source of electromagnetic interference. Antenna operation may also be blocked by conductive structures. This may make it difficult to implement an antenna in an electronic device that contains conductive housing walls or other conductive structures that may block radio frequency signals. Regulatory bodies may impose limits on the rf transmit power. These limitations pose challenges when operating electronic device antennas at elevated power levels.

Accordingly, it would be desirable to provide improved antennas for wireless electronic devices.

Disclosure of Invention

Electronic devices such as tablet computers or other portable devices may have a conductive housing. A portion of the conductive housing in each device may serve as an antenna ground for the antenna. The antenna may be fed with a positive antenna feed terminal coupled to the antenna resonating element and a ground antenna feed terminal coupled to the conductive housing.

The antenna resonating element may be mounted proximate an antenna window in the conductive housing. To ensure that the desired maximum output power limit of the radio frequency signal is met when an external object, such as a human body, is in the vicinity of the antenna window, the electronic device may be provided with a capacitive proximity sensor. The proximity sensor may have a capacitive proximity sensor electrode interposed between the antenna resonating element and the antenna window. During operation, a proximity sensor may detect when an external object, such as a part of a user's body, comes within a given distance of the proximity sensor and antenna. When these conditions are detected, circuitry in the electronic device may reduce the maximum transmit output power through the antenna.

The capacitive proximity sensor electrode may have first and second conductive layers separated by a dielectric layer. The first and second conductive layers may be coupled to respective first and second inputs of a signal detector, such as a capacitive-to-digital converter (c/d converter), using first and second inductors, respectively.

The capacitive proximity sensor electrode may act as a parasitic antenna resonating element for the antenna that helps reduce radio frequency signal hot spots (hotspots). A capacitor may be used to connect the capacitive proximity sensor electrode to the conductive housing.

Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.

Drawings

FIG. 1 is a front perspective view of an illustrative electronic device having an antenna and a proximity sensor in accordance with an embodiment of the present invention.

FIG. 2 is a rear perspective view of an illustrative electronic device having an antenna and a proximity sensor in accordance with an embodiment of the present invention.

FIG. 3 is a schematic diagram of an illustrative electronic device having an antenna and proximity sensor configuration in accordance with an embodiment of the present invention.

FIG. 4 is a side cross-sectional view of an illustrative electronic device having an antenna and a proximity sensor in accordance with an embodiment of the present invention.

FIG. 5 is a diagram of an illustrative electronic device having an antenna and wireless circuitry that may reduce the amount of power transmitted through the antenna when a proximity sensor detects that an external object is within a given range of the antenna and the electronic device in accordance with an embodiment of the present invention.

Fig. 6 is a perspective view of an illustrative antenna having an antenna resonating element and a proximity sensor electrode that functions as a parasitic antenna resonating element that overlaps (overlaps) a dielectric antenna window in accordance with an embodiment of the present invention.

Fig. 7 is a graph illustrating how the presence of a parasitic antenna resonating element may help reduce radio frequency signal hotspots and thus near-field radiated hotspots generated by an antenna in an electronic device, according to an embodiment of the present invention.

Fig. 8 is a top view of a parasitic antenna resonating element, such as a capacitive proximity sensor electrode, that has been coupled through a capacitor to a portion of a conductive device housing that serves as an antenna ground in accordance with an embodiment of the present invention.

FIG. 9 is a diagram illustrating how a proximity sensor may have capacitor electrodes for detecting the presence of an external object, such as a portion of a user's body, in accordance with an embodiment of the present invention.

Figure 10 is a diagram illustrating how a capacitive proximity sensor may have a two-layer capacitive sensor with a shield electrode and a sensor electrode monitored by a capacitive-to-digital converter in accordance with an embodiment of the present invention.

Figure 11 is a perspective view of an illustrative two-layer capacitive proximity sensor electrode structure in accordance with one embodiment of the present invention.

Figure 12 is a perspective view of an elongated two-layer capacitive proximity sensor electrode in accordance with one embodiment of the present invention.

Detailed Description

The electronic device may be provided with wireless communication circuitry. The wireless communication circuitry may be used to support wireless communications in one or more wireless communication bands. For example, the wireless communication circuitry may transmit and receive signals in the cellular telephone frequency band.

To meet consumer demand for small form factor wireless devices, manufacturers are continually striving to reduce the size of the components used in these devices while providing enhanced functionality. Particularly in configurations where electronic devices are used to transmit and receive radio frequency signals in cellular telephone bands and other communication bands having relatively wide bandwidths, meeting desired antenna performance standards in compact devices can be challenging. High transmit power and wide antenna bandwidth may be desirable to ensure adequate signal strength during communication, but these properties may present challenges for controlling the transmitted radiation level.

It is often impractical to completely shield a user of an electronic device from transmitted radio frequency signals. For example, conventional cellular telephone handsets typically transmit a signal near the user's head during a telephone call. Government regulations limit the power of radio frequency signals. At the same time, wireless operators require that user equipment used in their networks be able to generate a certain minimum radio frequency power to ensure satisfactory operation of the equipment.

In many jurisdictions, Specific Absorption Rate (SAR) standards are adopted, which impose maximum energy absorption limits on handset manufacturers. These standards place limits on the amount of radiation that can be emitted at any particular point within a given distance of the antenna. Of particular concern is radiation limitation at a distance of about 1-20mm from the device, where a body part of the user is likely to be close to the antenna.

Satisfactory antenna performance and regulatory compliance may be ensured by using antennas that do not exhibit local "hot spots" where the emitted radiation exceeds the desired power level. Proximity sensors may also be used to detect when external objects such as the user's body are in the vicinity of the antenna. When the presence of a foreign object is detected, the transmit power level may be reduced.

The hot spots can be minimized by proper antenna design. If desired, a parasitic antenna resonating element may be placed near the device antenna to help smooth the near-field emission radiation pattern. The electromagnetic shielding arrangement may also be implemented with ferrite tape (ferrite tape) or other high permeability material.

Any suitable electronic device may have an antenna and a proximity sensor using these configurations. By way of example, the antenna and proximity sensor may be formed in an electronic device such as a desktop computer, a portable computer (such as a laptop computer and a tablet computer), a handheld electronic device (such as a cellular telephone), and the like. With one suitable configuration, which is sometimes described herein as an example, antennas and proximity sensors are formed in a relatively compact electronic device in which interior space may be at a premium. These compact devices may be portable electronic devices.

Portable electronic devices that may have antennas and proximity sensors include laptop computers and small portable computers such as ultra-portable computers, netbook computers, and tablet computers. The portable electronic device may also be a slightly smaller device. Examples of smaller portable electronic devices that may have an antenna include cellular telephones, wrist-watch devices, pendant devices, headset and earpiece devices, and other wearable and miniature devices.

Space in portable electronic devices is at a premium and the housings of these devices are sometimes constructed of conductive materials that block antenna signals. An arrangement in which the antenna structure and proximity sensor are formed behind the antenna window may help address these challenges. An antenna window may be formed in the conductive housing wall by forming a dielectric antenna window structure from an opening in the conductive housing wall. If desired, a slot-based antenna window may be formed in the conductive housing wall. In slot-based antenna windows, the window area is defined by a pattern of window slots. Arrangements using dielectric antenna windows are sometimes described herein as examples.

The antenna resonating element may be formed below the antenna window. Portions of the conductive housing or other conductive structures may serve as antenna grounds. The antenna may be fed with a positive antenna feed terminal coupled to the antenna resonating element and with a ground antenna feed terminal coupled to the conductive housing. During operation, radio frequency signals for the antenna may pass through the antenna window. The parasitic antenna resonating element and the ferrite strip may help reduce near-field hot spots.

Proximity-based antenna power control circuitry may be used to reduce near-field electromagnetic radiation intensity upon detection of the presence of an external object in the vicinity of the antenna. The proximity-based antenna power control circuit may be based on a capacitive proximity sensor. Sensor electrodes for a capacitive proximity sensor may be located near the antenna. If desired, the conductive structure, such as the sensor electrode, may be used as part of both the capacitive sensor and the parasitic antenna resonating element. With this type of arrangement, the sensor electrodes can be used to reduce near-field radiation hotspots, while being part of the capacitor electrodes of the proximity detector used to detect the presence of nearby external objects.

Antenna and proximity sensor structures having configurations such as these may be mounted on any suitable exposed portion of the portable electronic device. For example, the antenna and proximity sensor may be disposed on a front or top surface of the device. In a tablet computer, cellular telephone, or other device in which all or a substantial portion of the front surface of the device is occupied by a conductive structure such as a touch screen display, it may be desirable to form at least a portion of the antenna window on the back surface of the device. Other configurations are possible (e.g., antennas and proximity sensors mounted in more localized locations, on the device side walls, etc.). By way of example, it is sometimes described herein to use an antenna mounting location where at least a portion of a dielectric antenna window is formed in a conductive housing rear surface, but in general, any suitable antenna mounting location may be used in an electronic device, if desired.

Fig. 1 shows an illustrative portable device that may include an antenna and a proximity sensor. As shown in fig. 1, device 10 may be a relatively thin device, such as a tablet computer. The device 10 may have a display such as the display 50 mounted on its front (upper) surface. The housing 12 may have a curved portion forming an edge of the device 10 and a relatively flat portion forming a rear surface of the device 10 (as an example). An antenna window, such as antenna window 58, may be formed in housing 12. An antenna structure for the device 10 may be formed adjacent the antenna window 58.

Device 10 may have user input and output devices such as buttons 59. The display 50 may be a touch screen display for collecting user touch input. The surface of the display 50 may be covered with a dielectric element such as a flat cover glass member. The central portion of the display 50 (shown as region 56 in fig. 1) may be an active area that is sensitive to touch input. The outer perimeter area of the display 50, such as area 54, may be an inactive (inactive) area without touch sensor electrodes. A layer of material, such as opaque ink, may be placed on the bottom surface of the peripheral region 54 of the display 50 (e.g., on the bottom surface of the cover glass). This layer may be transparent to radio frequency signals. The conductive touch sensor electrodes in area 56 may tend to block radio frequency signals. However, the radio frequency signal may pass through the cover glass and opaque ink in the inactive display area 54 (as an example). In the opposite direction, radio frequency signals may pass through the antenna window 58. The low frequency electromagnetic field also passes through the window 58 and thus the capacitance measurement of the proximity sensor can be made through the antenna window 58.

The housing 12 may be formed of one or more structures. For example, the housing 12 may include an inner frame and a flat housing wall mounted to the frame. The housing 12 may also be formed from a single piece of material such as an aluminum casting or an aluminum machined block. Arrangements using both methods may also be used if desired.

The housing 12 may be formed of any suitable material, including plastic, wood, glass, ceramic, metal, or other suitable material, or a combination of materials. In some cases, portions of the housing 12 may be formed of a dielectric or other low conductivity material so as not to interfere with the operation of conductive antenna elements located near the housing 12. In other cases, the housing 12 may be formed from a metal element. One advantage of forming the housing 12 from metal or other structurally sound conductive material is that it may improve the aesthetics of the device and may help improve durability and portability.

With one suitable arrangement, the housing 12 may be formed from a metal such as aluminum. The portion of the housing 12 located near the antenna window 58 may serve as an antenna ground. The antenna window 58 may be formed from a dielectric material, such as Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), a PC/ABS blend, or other plastic (as examples). The window 58 may be attached to the housing 12 using an adhesive, fasteners, or other suitable attachment mechanism. To ensure the aesthetic appearance of the device 10, it may be desirable for the window 58 to be formed such that the outer surface of the window 58 conforms to the edge profile exhibited by the housing 12 in the remainder of the device 10. For example, if the housing 12 has a straight edge 12A and a flat bottom surface, the window 58 may be formed with a right angle bend and vertical sidewalls. If the housing 12 has a curved edge 12A, the window 58 may have a similarly curved surface.

Fig. 2 is a rear perspective view of the device 10 of fig. 1, showing how the device 10 may have a relatively flat rear surface 12B, and showing how the shape of the antenna window 58 may be rectangular with a curved portion that matches the shape of the curved housing edge 12A.

Fig. 3 shows a schematic diagram of the device 10, illustrating how the device 10 may include one or more antennas 26 and transceiver circuitry in communication with the antennas 26. The electronic device 10 of fig. 3 may be a portable computer such as a laptop computer, a portable tablet computer, a mobile phone with media player capabilities, a handheld computer, a remote control, a game console, a Global Positioning System (GPS) device, a desktop computer, a combination of such devices, or any other suitable electronic device.

As shown in fig. 3, the electronic device 10 may include storage and processing circuitry 16. Storage and processing circuitry 16 may include one or more different types of storage devices, such as hard drive storage, non-volatile memory (e.g., flash memory or other electrically programmable read-only memory), volatile memory (e.g., static or dynamic random access memory), and so forth. Processing circuitry in storage and processing circuitry 16 may be used to control the operation of device 10. The processing circuitry 16 may be based on a processor such as a microprocessor and other suitable integrated circuits. With one suitable arrangement, the storage and processing circuitry 16 may be used to run software on the device 10, such as internet browsing applications, Voice Over Internet Protocol (VOIP) telephone call applications, electronic mail applications, media playing applications, operating system functions, control functions for controlling radio frequency power amplifiers and other radio frequency transceiver circuitry, and so forth. The storage and processing circuitry 16 may be used to implement appropriate communication protocols. Communication protocols that may be implemented using storage and processing circuitry 16 include Internet protocols, cellular telephone protocols, wireless local area network protocols (e.g., IEEE802.11 protocols-sometimes referred to as IEEE802.11 protocols) For use in itIts protocol for short-range wireless communication links (such asProtocol), etc.

Input-output circuitry 14 may be used to allow data to be provided to device 10 and to allow data to be provided from device 10 to external devices. Input-output devices 18, such as touch screens and other user input interfaces, are examples of input-output circuitry 14. The input and output devices 18 may also include user input and output devices such as buttons, joysticks, click wheels (click wheels), scroll wheels, touch pads, keypads, keyboards, microphones, cameras, and the like. A user may provide commands through these user input devices to control the operation of device 10. Display and audio devices such as Liquid Crystal Display (LCD) screens, Light Emitting Diodes (LEDs), Organic Light Emitting Diodes (OLEDs), and other components that present visual information and status data may be included in device 18. The display and audio components in the input-output device 18 may also include audio devices such as speakers and other devices for creating sound. If desired, the input-output devices 18 may include audio-visual interface devices, such as jacks and other connectors for external headphones and monitors.

Wireless communications circuitry 20 may include Radio Frequency (RF) transceiver circuitry 23 formed from one or more integrated circuits, power amplifier circuitry, low noise input amplifiers, passive RF components, one or more antennas, and other circuitry for processing RF wireless signals. Wireless signals may also be transmitted using light (e.g., using infrared communication).

The wireless communication circuitry 20 may include radio-frequency transceiver circuitry for handling multiple radio-frequency communication bands. For example, circuitry 20 may include transceiver circuitry 22 that handles 2.4GHz and 5GHz frequency bands for WiFi (IEEE 802.11) communications, as well as 2.4GHz Bluetooth communication frequency bands. The circuitry 20 may also include cellular telephone transceiver circuitry 24 for handling wireless communications in cellular telephone bands, such as the GSM band and 2100MHz data band (as examples) at 850MHz, 900MHz, 1800MHz, and 1900 MHz. The wireless communication circuitry 20 may include circuitry for other short-range and long-range wireless links, if desired. For example, the wireless communication circuitry 20 may include a Global Positioning System (GPS) receiver device, radio circuitry for receiving radio and television signals, paging circuitry, and the like. In WiFi and Bluetooth links, as well as other short-range wireless links, wireless signals are typically used to transmit data over distances of tens or hundreds of feet. In cellular telephone links and other long range links, wireless signals are typically used to transmit data over distances of thousands of feet or miles.

The wireless communication circuit 20 may include an antenna 26, such as an antenna located near the antenna window 58 of fig. 1 and 2. The antennas 26 may be single-band antennas, each covering a particular desired communication band, or may be multi-band antennas. Multi-band antennas may be used, for example, to cover multiple cellular telephone communication bands. If desired, the dual-band antenna may be used to cover two WiFi bands (e.g., 2.4GHz and 5 GHz). Different types of antennas may be used for different frequency bands and combinations of frequency bands. For example, it may be desirable to form a dual-band antenna for forming a local wireless link antenna, a multi-band antenna for handling cellular telephone communication bands, and a single-band antenna for forming a global positioning system antenna (as examples).

The transmission line path 44 may be used to transmit radio frequency signals between the transceivers 22 and 24 and the antenna 26. Radio frequency transceivers such as radio frequency transceivers 22 and 24 may be implemented with one or more integrated circuits and associated components (e.g., switching circuits, matching network components such as discrete inductors, capacitors, and resistors, and integrated circuit filter networks, etc.). These devices may be mounted on any suitable mounting structure. With one suitable arrangement, the transceiver integrated circuit may be mounted on a printed circuit board. Path 44 may be used to interconnect transceiver integrated circuits and other components on a printed circuit board with an antenna structure in device 10. Path 44 may include any suitable conductive path through which radio frequency signals may be transmitted, including transmission line path structures such as coaxial cables, microstrip transmission lines, and the like.

The antenna 26 may generally be formed using any suitable antenna type. Examples of suitable antenna types for antenna 26 include antennas having resonating elements formed from patch (patch) antenna structures, inverted-F antenna structures, closed and open slot antenna structures, loop antenna structures, monopoles, dipoles, planar inverted-F antenna structures, hybrids of these designs, and so forth. With one suitable arrangement (which is sometimes described herein as an example), a portion of the housing 12 (e.g., a portion of the housing 12 near the antenna window 58) may form a ground structure for the antenna associated with the window 58.

Fig. 4 shows a cross-sectional view of the device 10 near the antenna window 58. As shown in fig. 4, antenna 26 may have an antenna resonating element 68 (e.g., a patch antenna resonating element, a single-arm inverted-F antenna structure, a two-arm inverted-F antenna structure, or other suitable multiple-or single-arm inverted-F antenna structures, closed and open slot antenna structures, loop antenna structures, monopoles, dipoles, planar inverted-F antenna structures, hybrids of these designs, etc.). The housing 12 may act as an antenna ground for the antenna 26.

Antenna 26 may also have a parasitic antenna resonating element formed from one or more conductive structures, such as structure 66. The structure 66 may include, for example, a capacitive proximity sensor electrode. If desired, a layer of ferrite material, such as ferrite tape 74, may be placed between the antenna resonating element 68 and the window 58 to help reduce the near-field signal strength without unduly attenuating the far-field signal. In the example of fig. 4, ferrite strips 74 have been placed under the structure 66.

As shown in fig. 4, antenna 26 may be fed with a positive antenna feed terminal (such as positive antenna feed terminal 76) coupled to antenna resonating element 68 and a ground antenna feed terminal (such as ground antenna feed terminal 78) coupled to housing 12.

Antenna resonating element 68 may be positioned near dielectric antenna window 58, as shown in fig. 4, so that radio frequency signals may be transmitted through window 58 (e.g., in directions 72 and 71). Radio frequency signals may also be transmitted through a transparent display cover member such as cover glass 60. The display 50 may have an active area, such as area 56, in which the cover glass 60 has conductive structures, such as a display panel module 64, underneath it. Structures in display panel 64 such as touch sensor electrodes and active display pixel circuitry may be conductive and may therefore attenuate radio frequency signals. However, in region 54, display 50 may be inactive (i.e., panel 64 may not be present). Opaque ink, such as ink 62, may be formed on the bottom surface of transparent cover glass 60 in region 54 to prevent antenna resonating element 68 from being seen. The ink 62 in the area 54 and the dielectric material of the cover member 60 may be sufficiently transparent to radio frequency signals so that the radio frequency signals may be transmitted through the structures in the direction 70.

Any suitable conductive material may be used to form the antenna structure of antenna 26. With one suitable arrangement, the conductive structures for both antenna resonating element 68 and parasitic antenna resonating element 66 may be formed from conductive traces on a dielectric support. The conductive traces may be formed of copper or other metals (as an example) to help ensure low loss and good performance at radio frequencies. The dielectric support for these structures may be a printed circuit board or a plastic part. Plastic support structures may also be used to support the printed circuit board. In general, printed circuit boards may be rigid or flexible. Rigid printed circuit boards may be formed from epoxy (e.g., FR4) or other dielectric substrates. Flexible printed circuit boards ("flex circuits") may be formed from flexible polymer sheets, such as polyimide sheets or other flexible dielectrics. When the antenna structure is formed from a flexible circuit substrate, the flexible circuit may be bent to form a curved surface (e.g., to accommodate bending of the plastic support structure), if desired. For rigid substrate arrangements, printed circuit boards are typically flat.

Structures such as conductive structure 66 may provide multiple functions. For example, because structure 66 is adjacent to antenna resonating element 68, structure 66 affects the electromagnetic behavior of antenna 26 and thus may function as a parasitic antenna resonating element. Also, if desired, the conductive structure 66 may serve as a sensor electrode for a proximity sensor.

Transceiver circuitry 23 may be mounted to printed circuit board 79 and may be connected to wires in transmission line 44 via connector 81 and traces in printed circuit board 79. Transmission line 44 may have a positive conductor and a ground conductor and may be used to convey radio frequency antenna signals between transceiver 23 and feed terminals 76 and 78 of antenna 26.

The device 10 and antenna window 58 may have any suitable dimensions. For example, the lateral dimension of the device 10 may be about 10-50 cm. The thickness of the device 10 may be greater than 2cm, less than 1.5cm, or less than 0.5 cm.

In a thin device configuration, the elimination of the conductive housing portion immediately adjacent antenna resonating element 68 helps to ensure that antenna 26 exhibits satisfactory efficiency and bandwidth (e.g., for supporting communication in a broadband remote antenna band such as a cellular telephone communication band).

Fig. 5 shows a circuit diagram that illustrates how the proximity sensor signal can be used to control the amount of power transmitted by the antenna 26. As shown in fig. 5, the device 10 may include storage and processing circuitry 16 (see, e.g., fig. 3). Device 10 may also include a proximity sensor such as proximity sensor 80. The proximity sensor 80 may be implemented using any suitable type of proximity sensor technology (e.g., capacitive, optical, etc.). One advantage of capacitive proximity sensing techniques is that they may be relatively insensitive to changes in the reflectivity of the external object 87.

As shown in the example of fig. 5, proximity sensor 80 may include a capacitor electrode formed from a conductive element, such as conductive element 66 (fig. 4). If desired, conductive element 66 may serve as a parasitic antenna resonating element for antenna 26.

The proximity sensor 80 may be mounted in the housing 12 in the vicinity of the antenna 26 (as shown in fig. 4) to ensure that the signal from the proximity sensor 80 indicates the presence of an external object 87 in the vicinity of the antenna 26 (e.g., within a distance D of the antenna 26 and/or the device 10).

The output signal from the proximity sensor 80 may be communicated to the storage and processing circuitry 16 using path 86. The signal from the proximity sensor 80 may be an analog or digital signal that provides proximity data to the storage and processing circuitry 16. The proximity data may be Boolean data representing that the object 87 is or is not within a given predetermined distance of the antenna 26 or may be continuous data representing the current estimated distance value of D.

Storage and processing circuitry 16 may be coupled to transceiver circuitry 23 and power amplifier circuitry 82. Dashed line 83 shows how a received radio frequency signal may be transmitted from antenna 26 to transceiver circuitry 23. During data transfer operations, control lines 84 may be used to transmit control signals from storage and processing circuit 16 to transceiver circuit 23 and power amplifier circuit 82 to adjust the output power in real time. For example, when data is being transmitted, transceiver 23 and associated output amplifier 82 may be instructed to increase or decrease the power level of the radio frequency signal being provided to antenna 26 over transmission line 44 to ensure that regulatory limits on electromagnetic radiation emissions are met. For example, if the proximity sensor 80 does not detect the presence of the external object 87, power may be provided at a relatively high (unrestricted) level. However, if the proximity sensor 80 determines that the user's leg or other body part or other external object 87 is in close proximity to the antenna 26 (e.g., within 20mm or less, within 15mm or less, within 10mm or less, etc.), the storage and processing circuitry may respond accordingly, instructing the transceiver circuitry 23 and/or the power amplifier 82 to transmit a radio frequency signal through the antenna 26 at a reduced power.

Fig. 6 shows a perspective view of an exemplary antenna 26. As shown in fig. 6, antenna resonating element 68 may include one or more conductive traces, such as conductive trace 96. In the example of fig. 6, antenna resonating element 68 has an inverted-F structure. With this structure, antenna resonating element 68 may have a dielectric substrate, such as a rigid or flexible printed circuit board 90, on which a conductive pattern, such as conductive trace 94, has been formed. Conductive trace 94 may have a main resonant element arm 92, a shorting branch (e.g., a path coupled to antenna feed terminal 78 of fig. 4) such as branch 96 that shorts arm 92 to ground, and a branch 98 that couples positive antenna feed terminal 76. If desired, the arm 92 may have different shapes (e.g., multiple branches) to support operation in a desired communication band having a desired bandwidth. The trace pattern for antenna resonating element 68 shown in fig. 6 is merely illustrative. In general, any suitable type of antenna resonating element pattern may be used for antenna resonating element 68, if desired.

Antenna resonating element 68 may be mounted to overlap antenna window 58 and underlie inactive region 54 of display 50 (fig. 4). Conductive structure 66 may be interposed between antenna resonating element 68 and window 58.

During operation of antenna 26, the electromagnetic field generated by antenna resonating element 68 may induce a current in conductive housing 12, such as current 95 near window 58. The relative shapes and sizes of the components of the antenna 26 may cause undesirable current crowding if not careful. This, in turn, can lead to undesirable hot spots in the near field radiation pattern of the antenna 26 as the induced currents re-radiate electromagnetic energy through the antenna window 58.

Fig. 7 shows a graph illustrating how an antenna signal may exhibit undesirable hot spots. In the graph of fig. 7, the power associated with a near-field transmitted radio frequency signal (e.g., a signal of antenna 26 that has been transmitted through antenna window 58 in direction 72 or 71) is shown as a function of position (e.g., position along the inner edge of antenna window 58). The solid line 120 corresponds to a possible near-field radiation pattern without a suitable antenna structure to reduce hot spots in the current 95 and associated hot spots in the transmitted radio frequency signal power. The dashed line 122 illustrates how hot zones may be minimized or eliminated by including suitable hot zone reduction structures. The dashed line 122 reflects a reduced spatial concentration of the rf signal power because the dashed line 122 is smoother than the solid line 120 and exhibits a lower peak power. The smooth radiation characteristic facilitates the antenna 26 to transmit a desired amount of signal power when communicating with a remote base station without exceeding regulatory limits on the transmitted radiation level.

The near field radiation pattern smoothing structure may include structures such as parasitic antenna resonating element 66. The ferrite strip 74 may also help reduce hot zone and/or near field signal strength while enabling the desired far field antenna efficiency criteria to be met. Proximity sensor based conditioning may be used in conjunction with these techniques, if desired.

Parasitic antenna resonating element 66 may be formed from one or more conductive structures. For example, parasitic antenna resonating element 66 may be formed from a rectangular (patch) structure, a straight or curved elongated structure, a structure with a groove, a structure with a curve, other suitable shapes, and combinations of these shapes. Some or all of these structures may be used as capacitive proximity sensor electrodes.

Fig. 8 is a top view of parasitic antenna resonating element 66, which is formed from a substantially rectangular conductive member (e.g., a rectangular patch). The patch may have lateral dimensions LP and WP. Any suitable size may be used for dimensions LP and WP, if desired. By way of example, LP may be about 40mm (e.g., 10-70mm) and WP may be about 15mm (e.g., about 5-25 mm). The outline of the antenna window 58 may also be rectangular and may have any suitable dimensions. For example, the profile of the antenna window 58 may have lateral dimensions L and W. With one suitable arrangement, L may be about 80mm (e.g., 50-110mm) and W may be about 15mm (e.g., about 5-25 mm).

Capacitor 124 may be coupled between housing 12 (e.g., antenna ground) and parasitic antenna resonating element 66 using capacitor terminals 126 and 128. The capacitance of capacitor 124 may be selected to provide sufficient coupling between terminal 126 and terminal 128, and thus between housing 12 and element 66, at the operating frequency of antenna 26 (e.g., at 850-. For example, the capacitance of a capacitor, such as capacitor 124, may be about 1-5pF (i.e., less than 100 pF).

The parasitic antenna resonating element 66 may be used as part of a capacitive proximity sensor. With this type of arrangement, element 66 can be used to transmit and receive radio frequency signals (e.g., at signal frequencies of 850MHz and above), while serving as a capacitor electrode at lower frequencies (e.g., at frequencies of about 200-250kHz, at frequencies below 1MHz, or at other suitable frequencies). At these lower frequencies, the circuit of proximity sensor 80 (FIG. 5) may detect a change in capacitance when an external object approaches the capacitor electrodes.

Fig. 9 shows a schematic capacitive proximity sensor arrangement that may be used for the proximity sensor 80 of fig. 5. As shown in fig. 9, the proximity sensor 80 may include control circuitry, such as a signal generator 130 and a signal detector 132. Conductive element 66 may serve as an electrode for proximity sensor 80. The signal generator 130 may be a voltage source that generates an Alternating Current (AC) signal at a frequency of about 200-250kHz (as an example), for example. The signal detector 132 may be a current meter or other suitable measurement circuitry for monitoring a signal associated with the capacitor electrode 66.

During operation, signal detector 132 may monitor a capacitance associated with electrode 66. When a user's leg or other external object 87 comes within range of the electrode 66, the presence of the external object will cause a change in capacitance that can be detected by the signal detector 132. The signal detector 132 may provide an output signal on line 134 that is indicative of the presence or absence of a foreign object 87 in the vicinity of the electrode 66. The signal, which may be provided in analog or digital form, may be a boolean value having a first logical value (e.g., a logical 0) when no external object 87 is detected and a second logical value (e.g., a logical 1) when an external object 87 is detected.

The output signal on line 134 may also have a level that continuously changes in response to different detected changes in capacitance. With this type of arrangement, the proximity sensor 80 can estimate the value of the distance D by which the electrode 66 is separated from the external object 87. When the object 87 is close, the proximity detector will generate a relatively high value on output line 134. When the object 87 is far away, the proximity detector will generate a relatively low value on output line 134. The signal on output line 134 may be an analog signal (e.g., an analog voltage) or a digital value.

The output signal on line 134 may be fully processed (e.g., to represent the value of D) or may be a raw signal (e.g., a signal representing the detected capacitance value from electrode 66). The raw signal may be further processed using storage and processing circuitry 16. Other arrangements may be used, if desired. For example, other signal sources may be used, other signal detection schemes may be used, a combination of analog and digital signals may be utilized to provide a signal output, and so forth.

The sensor electrodes 66 may be formed from any suitable conductive structure capable of detecting a change in capacitance due to the presence of an external object, such as a human body part. The shape of the electrode 66 may have a straight side, a curved side, a mixture of straight and curved sides, or other suitable shape when viewed from above. For example, the electrode 66 may have a rectangular profile. The dimensions of electrode 66 may be such that the profile of electrode 66 fits within the profile of dielectric antenna window 58, as shown in fig. 8. In cross section, the thickness of the electrode 66 may be less than 1mm, less than 0.5mm, less than 0.2mm, less than 0.1mm, or any other suitable thickness. Substrates such as rigid and flexible printed circuit board substrates may be used to form the electrodes 66. The electrode 66 may also be formed from a metal foil or other conductive material.

The electrode 66 may be formed from a single layer of conductive material or two or more layers of conductive material. For example, the electrodes 66 may be formed from a flexible circuit substrate or other printed circuit board substrate having an upper conductive layer and a lower conductive layer. The upper and lower conductive layers may be, for example, rectangular conductive traces formed on a flexible circuit or rigid printed circuit board substrate. These conductive traces may be formed from a metal such as copper.

With this type of two-layer arrangement, one electrode layer may serve as the sensor electrode layer, while the other electrode layer may serve as the active shield layer. Fig. 10 shows a schematic arrangement of this type.

As shown in fig. 10, the sensor electrode 66 may have an upper layer 66A and a lower layer 66B. The lower layer 66B may be a sensor electrode layer (sometimes referred to as a sensor electrode). The upper layer 66A may be a movable shield layer (sometimes referred to as an AC shield or AC shield).

Fig. 10 illustrates the capacitance associated with a capacitive sensor structure using two layers of sensor electrodes. The conductive layer in the sensor electrode 66 may be coupled to a signal detector 132. In the example of fig. 10, the signal detector 132 includes a capacitance-to-digital converter (CDC)136 connected to the electrode layers 66A and 66B through respective inductors L2 and L1, respectively. The inductors L1 and L2 may have inductance values of approximately 220-390nH (e.g., 390nH), or other suitable values that enable the inductors L1 and L2 to function as radio frequency chokes (i.e., radio frequency choke inductors). Radio frequency signals transmitted by antenna resonating element 68 may be electromagnetically coupled into the conductive structures of sensor electrodes 66. When the inductance values of L1 and L2 are properly selected, these radio frequency signals experience relatively high impedance and do not pass to the capacitance-to-digital converter 136. While the radio frequency signal from antenna resonating element 68 is blocked by inductors L1 and L2 (which act as radio frequency chokes), low frequency signals, such as Alternating Current (AC) excitation signals in the kHz range provided to sensor electrodes 66 by source 130 (fig. 9), may pass from sensor electrodes 66 to the capacitive-to-digital converter via inductors L1 and L2. This is because the impedance of inductors L1 and L2 is proportional to frequency.

The capacitive-to-digital converter 136 may be implemented using any suitable capacitive touch sensor control circuitry. With one suitable arrangement, the capacitance-to-digital converter 136 may be implemented using an AD714 programmable capacitance-to-digital converter integrated circuit (available from Analog Devices of Norwood, Mass.). The capacitance-to-digital converter 136 converts the capacitive input signal on its input to a digital capacitance value on its output.

During operation, the measured capacitance C2 between the conductive electrode layers 66A and 66B may be minimized by driving signals onto the conductors 66A and 66B in parallel. This helps to improve sensor performance. There is typically a fixed capacitance C1 of about 150pF or less between sensor electrode 66A and housing 12. Capacitance C1 is caused by the electromagnetic field within housing 12 and is not responsive to changes in the position of external object 87 relative to electrode 66. Fringing electric fields outside of the housing 12 cause a capacitance CA between the conductive layer 66B and the housing 12. A variable capacitance CAX appears between the external object 87 and the conductive layer 66B. The magnitude of the capacitance CAX depends on the distance between the external object 87 and the electrode layer 66B. When the external object 87 is not present, the value of CAX is minimal. As object 87 approaches layer 66B, the value of CAX increases. A relatively large CAX value occurs when object 87 is near layer 66B (i.e., when object 87 is less than 2cm from layer 66B or some other suitable distance). Capacitance-to-digital converter 136 may measure a capacitance CAX (which is in parallel with capacitance CA) and may generate a corresponding digital capacitance value. The storage and processing circuitry 16 (fig. 3) may receive the digital capacitance values that have been measured by the capacitance-to-digital converter 136 and may calculate a corresponding distance value representing the distance of the external object from the sensor electrode 66.

When an external object 87 is proximate to the sensor electrode 66 (e.g., when the user places the device 10 over the user's knee such that the antenna resonating element 68 and other structures in the antenna 26 are proximate to the user's leg), the capacitive-to-digital converter (CDC)136 may output a correspondingly high capacitance value. The storage and processing circuitry 16 may analyze the capacitance signal from the capacitance-to-digital converter 136 and may take appropriate action.

For example, if the storage and processing circuitry 16 concludes that the external object 87 is more than 2cm (or other suitable distance) from the antenna resonating element 68 and other such antenna structures in the device 10, the transceiver circuitry 23 may be allowed to transmit the radio frequency antenna signal at any desired power, including the maximum available transmit power of the device 10. However, if the storage and processing circuitry 16 concludes that the external object 87 is in the vicinity of the antenna 26, the storage and processing circuitry 16 may limit the amount of allowable transmit power from the transceiver 23. In this way, storage and processing circuitry 16 may use the external object proximity information to determine how much of the radio frequency output power level to use in operating transceiver circuitry 23. When an external object, such as a user's body, is brought into close proximity to the device 10 and antenna 26, the maximum transmit power may be reduced to ensure compliance with regulatory limits. When there are no external objects in the vicinity of device 10 and antenna 26, the proximity-based transmit power limit may be removed and a greater radio frequency output power may be used.

Fig. 11 and 12 show schematic structures that can be used for the double layer sensor electrode. As shown in fig. 11, the capacitive sensor electrode 66 may have conductive layers 66A and 66B formed of conductive traces on opposite sides of a dielectric substrate 138. The outline of layers 66A and 66B may be rectangular (as shown in FIG. 11) or may have other suitable shapes. Capacitor 124 (fig. 8) may be connected to layer 66A (as an example) at terminal 128. The dielectric substrate 138 may be plastic, epoxy (e.g., fiberglass filled epoxy such as FR4, or other rigid printed circuit board dielectric), or a flexible polymer sheet (e.g., a polyimide layer for a flexible circuit). Conductive layers 66A and 66B may be formed by physical vapor deposition, electroplating, screen printing, or any other suitable layer formation technique. The thickness of layers 66A and 66B may be less than 0.1mm, less than 0.05mm, less than 0.01mm, and so forth. The dielectric base layer 138 may have a thickness of less than 1mm, less than 0.5mm, less than 0.1mm, less than 0.05mm, and so on.

In the schematic layout of fig. 11, the sensor electrodes 66 have a generally rectangular outline. If desired, the sensor electrodes 66 may have a non-rectangular shape. As shown in fig. 12, for example, the sensor electrode 66 may be an elongated shape having one or more bends. In fig. 12, the sensor electrode 66 has three layers: conductive layer 66A, dielectric layer 138, and conductive layer 66B. The electrode 66 may have more or fewer layers, if desired. Layers 66A and 66B may be metal layers or other suitable layers of conductive material, as described in connection with fig. 11. Layer 138 may be a printed circuit board substrate, such as a rigid printed circuit board or a flexible circuit substrate. For the dielectric substrate layer 138 of fig. 11, a typical thickness that can be used for the substrate 138 is less than 1 mm. For example, the thickness of the dielectric layer 138 may be less than 0.5mm, less than 0.1mm, less than 0.05mm, and so forth.

The layouts of fig. 11 and 12 are merely schematic. Any suitable sensor electrode may be used, if desired. The sensor electrodes 66 may be, for example, elongated in shape, have a straight edge, have a curved edge, or the like. Both single layer arrangements and multilayer arrangements may be used. As described in connection with fig. 6-8, sensor electrodes 66 may function as parasitic antenna resonating elements for reducing radio frequency hot spots in the electromagnetic radiation emitted by device 10. This may help ensure that the device 10 meets regulatory restrictions on the radio frequency signal transmission power, particularly through lower portions of the device 10 that may come into contact with external objects such as a human body.

According to an embodiment, there is provided an electronic apparatus including: a housing; an antenna window in the housing; an antenna resonating element mounted in the housing to cause radio frequency signals to be transmitted through the antenna window; and a capacitive proximity sensor electrode located between the antenna resonating element and the antenna window.

According to another embodiment, the capacitive proximity sensor comprises: a dielectric layer, and first and second conductive layers on opposite sides of the dielectric layer.

According to another embodiment, the dielectric layer comprises a polymer flexible sheet.

According to a further embodiment, the first and second conductive layers comprise a metallic cuboid.

According to another embodiment, the dielectric layer comprises a rigid printed circuit board substrate.

According to another embodiment, the housing comprises a conductive housing, the electronic device further comprising a capacitor connected between the first conductive layer and the conductive housing.

According to another embodiment, the conductive housing comprises a metal housing, the electronic device further comprising: a positive antenna feed terminal connected to the antenna resonating element, a ground antenna feed terminal connected to the metal housing, and a capacitor connected between the metal housing and the capacitive proximity sensor electrode, wherein the capacitive proximity sensor electrode functions as a parasitic antenna resonating element.

According to another embodiment, the electronic device has a front surface and a back surface, the electronic device further includes a display on the front surface of the electronic device, and the display has an inactive region through which radio frequency signals are transmitted from the antenna resonating element.

According to a further embodiment, the electronic device further comprises a ferrite strip located between the capacitive proximity sensor electrode and the antenna window.

According to another embodiment, the electronic device further comprises: a capacitive-to-digital converter having a first input and a second input, and a first radio frequency choke inductor and a second radio frequency choke inductor coupled between the capacitive proximity sensor electrode and the capacitive-to-digital converter.

According to another embodiment, the capacitive proximity sensor electrode comprises: a dielectric layer; and a first conductive layer and a second conductive layer on opposite sides of the dielectric layer, the first conductive layer being connected to the first input terminal through the first radio frequency choke inductor, the second conductive layer being connected to the second input terminal through the second radio frequency choke inductor.

According to another embodiment, the electronic device further includes a display having a display panel circuit covered by a transparent dielectric cover member, and the antenna resonating element emits a radio frequency signal that passes through the transparent dielectric cover member and not through the display panel circuit.

According to an embodiment, there is provided a tablet computer including: a conductive housing; a dielectric antenna window in the conductive housing; radio frequency transceiver circuitry; an antenna with which the radio-frequency transceiver circuitry transmits radio-frequency signals in at least one cellular telephone frequency band, wherein the antenna comprises an antenna ground formed by at least a portion of the conductive housing and an antenna resonating element mounted proximate the dielectric antenna window; and a capacitive proximity sensor electrode mounted between the antenna resonating element and the dielectric antenna window.

According to another embodiment, the tablet computer further comprises a capacitive digitizer coupled to the capacitive proximity sensor electrode.

According to another embodiment, the capacitive proximity sensor includes a first conductive layer and a second conductive layer separated by a dielectric layer.

According to another embodiment, the tablet computer further comprises a pair of inductors coupled between the capacitive proximity sensor electrodes and the capacitive digitizer.

According to another embodiment, the tablet computer further comprises a capacitor having a first terminal connected to the conductive housing and a second terminal connected to the capacitive proximity sensor electrode, and the capacitive proximity sensor electrode acts as a parasitic antenna resonating element for the antenna.

According to an embodiment, there is provided an electronic apparatus including: at least one conductive housing structure to which a ground antenna feed terminal is connected; an antenna window in the at least one conductive housing structure; an antenna resonating element formed from conductive traces on a flexible circuit, the antenna resonating element having a positive antenna feed terminal connected thereto; a radio frequency transceiver circuit coupled to the positive antenna feed terminal and the ground antenna feed terminal and transmitting radio frequency signals through the antenna window using the antenna resonating element; and a capacitive proximity sensor electrode interposed between the antenna resonating element and the antenna window.

According to another embodiment, the radio-frequency transceiver circuitry transmits the radio-frequency signal at an output power, and the electronic device further comprises: circuitry coupled to the capacitive proximity sensor electrode that limits the output power when an external object is detected within a given distance of the capacitive proximity sensor electrode.

According to another embodiment, the capacitive proximity sensor electrode comprises a first conductive layer and a second conductive layer coupled to the circuit by respective first and second inductors, and the circuit comprises a capacitive digitizer to perform a capacitance measurement on the capacitive proximity sensor electrode.

According to another embodiment, the capacitive proximity sensor electrode functions as a parasitic antenna resonating element, and the electronic device further comprises a capacitor connected between the conductive housing structure and the capacitive proximity sensor electrode.

According to another embodiment, the capacitive proximity sensor includes a first conductive layer and a second conductive layer separated by a dielectric substrate.

The foregoing merely illustrates the principles of the invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented alone or in any combination.

Claims (17)

1. An electronic device, comprising:

a housing;

an antenna window in the housing;

an antenna resonating element mounted in the housing proximate the antenna window to cause radio frequency signals to be transmitted through the antenna window;

a capacitive proximity sensor electrode located between the antenna resonating element and the antenna window;

a capacitive-to-digital converter having a first input terminal and a second input terminal; and

a first and second radio frequency choke inductor coupled between the capacitive proximity sensor electrode and the capacitive-to-digital converter.

2. The electronic device defined in claim 1 wherein the capacitive proximity sensor electrodes comprise:

a dielectric layer; and

a first conductive layer and a second conductive layer on opposite sides of the dielectric layer.

3. The electronic device defined in claim 2 wherein the dielectric layer comprises a polymer flexible sheet.

4. The electronic device of claim 3, wherein the first and second conductive layers comprise a metallic cuboid.

5. The electronic device defined in claim 2 wherein the housing comprises a conductive housing, the electronic device further comprising a capacitor connected between the first conductive layer and the conductive housing.

6. The electronic device defined in claim 5 wherein the conductive housing comprises a metal housing, the electronic device further comprising:

a positive antenna feed terminal connected to the antenna resonating element;

a ground antenna feed terminal connected to the metal housing; and

a capacitor connected between the metal housing and the capacitive proximity sensor electrode, wherein the capacitive proximity sensor electrode functions as a parasitic antenna resonating element.

7. The electronic device defined in claim 6 wherein the electronic device has a front surface and a back surface, the electronic device further comprising a display on the front surface of the electronic device wherein the display has an inactive region through which radio frequency signals are transmitted from the antenna resonating element.

8. The electronic device defined in claim 6 further comprising a ferrite strip between the capacitive proximity sensor electrodes and the antenna window.

9. The electronic device of claim 1, wherein the capacitive proximity sensor electrode comprises:

a dielectric layer; and

a first conductive layer and a second conductive layer on opposite sides of the dielectric layer, wherein the first conductive layer is connected to the first input terminal through the first radio frequency choke inductor and the second conductive layer is connected to the second input terminal through the second radio frequency choke inductor.

10. The electronic device defined in claim 9 further comprising a display having display panel circuitry covered by a transparent dielectric cover component, wherein the antenna resonating element emits radio-frequency signals that pass through the transparent dielectric cover component but not through the display panel circuitry.

11. A tablet computer, comprising:

a conductive housing;

a dielectric antenna window in the conductive housing;

radio frequency transceiver circuitry;

an antenna with which the radio-frequency transceiver circuitry transmits radio-frequency signals in at least one cellular telephone frequency band, wherein the antenna comprises an antenna ground formed by at least a portion of the conductive housing and an antenna resonating element mounted proximate the dielectric antenna window;

a capacitive proximity sensor electrode mounted between the antenna resonating element and the dielectric antenna window; and

a capacitive digitizer coupled to the capacitive proximity sensor electrode.

12. The tablet of claim 11 wherein the capacitive proximity sensor electrode comprises a first conductive layer and a second conductive layer separated by a dielectric layer.

13. The tablet computer of claim 12 further comprising a pair of inductors coupled between the capacitive proximity sensor electrodes and the capacitive digitizer.

14. The tablet computer of claim 11 further comprising a capacitor having a first terminal connected to the conductive housing and a second terminal connected to the capacitive proximity sensor electrode, wherein the capacitive proximity sensor electrode functions as a parasitic antenna resonating element for the antenna.

15. An electronic device, comprising:

at least one conductive housing structure to which a ground antenna feed terminal is connected;

an antenna window in the conductive housing structure;

an antenna resonating element formed from conductive traces on a flexible circuit proximate the antenna window, a positive antenna feed terminal connected to the antenna resonating element;

a radio frequency transceiver circuit coupled to the positive antenna feed terminal and the ground antenna feed terminal and transmitting radio frequency signals through the antenna window using the antenna resonating element;

a capacitive proximity sensor electrode between the antenna resonating element and the antenna window, wherein the radio frequency transceiver circuitry transmits the radio frequency signal at an output power; and

circuitry coupled to the capacitive proximity sensor electrode that limits the output power when an external object is detected within a given distance of the capacitive proximity sensor electrode.

16. The electronic device defined in claim 15 wherein the capacitive proximity sensor electrode comprises first and second conductive layers that are coupled to the circuitry coupled to the capacitive proximity sensor electrode through respective first and second inductors and wherein the circuitry coupled to the capacitive proximity sensor electrode comprises a capacitive-to-digital converter that measures capacitance of the capacitive proximity sensor electrode.

17. The electronic device defined in claim 15 wherein the capacitive proximity sensor electrode functions as a parasitic antenna resonating element, the electronic device further comprising a capacitor connected between the conductive housing structure and the capacitive proximity sensor electrode, wherein the capacitive proximity sensor electrode comprises first and second conductive layers separated by a dielectric substrate.