Proximity sensor and antenna

Abstract

To provide a proximity detector capable of discriminating between objects with different permittivity.SOLUTION: A capacitive proximity sensor with a stacked electrode structure configured to allow an inner electrode to be partially screened by an upper electrode. Self-capacitance of a selected electrode is measured while other electrodes are held to ground or to a shield potential. The proximity sensor thus estimates a value of dielectric permittivity of an approaching body.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a proximity sensor that detects the approach of a user's body parts, eliminating the undesirable effects of water droplets or other similar contamination. An embodiment of the present invention relates to a connected portable device, such as a mobile phone, tablet or laptop, that is equipped with a proximity sensor of the present invention, thereby being able to reliably detect the approach of a user. A particular, but not exclusive, embodiment is a connected portable device that adapts its radio emission power taking into account the proximity of the user, in order to limit exposure to RF energy. Another particular application of the present invention is in wearable devices, such as smart watches, sports watches, earplugs, etc., where a proximity sensor is advantageously used as an input device. [Background technology]

[0002] In many applications it is important to detect if a body part is in close proximity to a device. In the special case of connected portable devices such as mobile phones, tablets or laptops, this information is useful for several important functions such as limiting the absorbed dose of RF energy, limiting power consumption by switching off the display when the phone is held up to the ear, or activating special functions.

[0003] Another important function of proximity sensors is to disable the touchscreen on mobile phones when the user holds the phone close to their ear - otherwise, users might accidentally hang up a call or trigger unwanted actions by touching the screen with their cheek or fingers.

[0004] There is an increasing need for miniaturized proximity sensors in wearable devices such as smart watches, sports watches, wireless earphones, etc. Space in wearable devices is very limited and traditional switch buttons are undesirable. Proximity sensors are used as described above and as input devices, for example to increase or decrease playback volume, reject or accept an incoming call, initiate Bluetooth pairing, and other useful functions. The device according to the present invention can also be used as a true proximity sensor in wearable devices, for example to detect whether an earplug is inserted in the user's ear.

[0005] Avoiding false positives is just as important as the ability to sense proximity. Many proximity sensors used in mobile phones rely on an electrode's capacitance changing in response to the proximity of a body part. The technology is attractive because the sensors are simple conductive electrodes and can be easily integrated on a printed circuit board. However, traditional capacitive systems can cause false positives because they cannot distinguish between a large object at a distance and a smaller object at a closer distance. They also cannot distinguish between the proximity of a human body part, such as a user's hand or head, and an inanimate object, such as a table top.

[0006] Other proximity sensing technologies are available, for example based on optical sensing, but drawbacks of these systems include power consumption, cost of the required components, integration into mobile devices, and the inability to distinguish between different objects.

[0007] US Patent No. 5,399,633 in the applicant's name describes a capacitive sensor that is read using a charge amplifier connected to a floating variable reference voltage, and describes the use of such a sensor in a touch-sensitive display.

[0008] Capacitive proximity sensors determine the presence of both conductive and dielectric objects within their detection volume. The effect of a dielectric object on the measured capacitance depends on its size, distance from the sensor, and the polarizability of the material, the latter being expressed as the material's relative permittivity ε (also simply called the dielectric constant or relative permittivity of the material). r For the purposes of this disclosure, a conductive object can be considered to be a dielectric object with a very high dielectric constant. Technically, a proximity sensor determines that an object is approaching when the measured capacitance is above a given threshold. However, this can occur at different distances depending on the size and dielectric constant of the approaching object, and conventional sensors are unable to distinguish between these factors. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] European Patent Registration No. 2876407 Summary of the Invention [Problem to be solved by the invention]

[0010] The present disclosure proposes a proximity detector that has the ability to distinguish between objects with different dielectric constants, such that the proximity of objects with different properties can trigger different actions, and the proximity threshold can be adjusted to be less dependent on the dielectric constant. [Means for solving the problem]

[0011] According to the present invention, these objectives are achieved by the subject matter of the appended claims, in particular by a capacitive proximity sensor for detecting the presence of a conductive or dielectric object in a detection area adjacent to a mobile device, the sensor having a layered structure with a first electrode on a first layer facing the detection area and an inner electrode on a second layer, the first electrode having a plurality of openings by which the first electrode partially shields the inner electrode to allow partial capacitive coupling between the inner electrode and the conductive and / or dielectric object in the detection area, the capacitive proximity sensor further comprising a first electrode arranged to measure the capacitance of one of the electrodes. or a plurality of capacitance reading units and a shield control unit configured to generate a shield potential that tracks the capacitance of the electrode whose capacitance is measured by the capacitance reading unit, and the capacitive proximity sensor includes a readout circuit configured to measure a first capacitance of either the first electrode or the internal electrode by applying a shield potential to the other electrode, and to measure a second capacitance of either the first electrode or the internal electrode by holding the other electrode at a fixed potential, and to determine the dielectric constant of an object within the detection region based on the first capacitance and the second capacitance.

[0012] The fixed potential used in measuring the second capacitance may be ground potential, although in practice the absolute value of this potential is not relevant.

[0013] The dependent claims relate to important but not essential useful features of the invention such as the determination of the distance to an object in the detection field based on said first and second capacitances, or a digital interface for transmitting the distance, permittivity or binary proximity values ​​to a host system, where these data are transmitted as multi-bit binary variables over a suitable bus, preferably a serial bus such as I2C to reduce the number of interconnects.

[0014] The sensor of the present invention is provided with an interrupt request terminal by which it can request the attention of the host system (microcontroller) upon detection of proximity.

[0015] In the capacitive proximity sensor as claimed in claim 1, the openings are arranged in the form of a regular lattice of holes or stripes.

[0016] The electrodes of the sensor according to the invention can be obtained in many ways, a particularly convenient realization being by etching the copper of a multilayer printed circuit. The same circuit can also comprise the electronic elements of the sensor in an integrated circuit.

[0017] As a technical finding, the present invention offers the advantage that it can be easily integrated into portable electronic devices and provides a wealth of information in a small package. These electrodes are readily available with standard PCD manufacturing techniques and do not take up much space. The permittivity measurement and, optionally, the distance measurement, are useful for identifying false approaches. The unit can also be used to realize very sensitive input devices that respond to finger touch without moving parts and are not easily tripped by false events, contamination or water.

[0018] Importantly, the proximity detector operates at low frequencies and is less sensitive to radio frequency signals. One or all can be capacitively coupled to a radio circuit to double as an antenna. The radio circuit can be a transmitter and / or receiver, or most preferably a digital two-way radio interface such as a Bluetooth interface, a WiFi interface, a cellular interface, etc. The electrodes can have the structure of a planar antenna without altering their effectiveness as a proximity sensor. A decoupling inductor can be used to block radio frequency signals at the input of the proximity sensor.

[0019] As will become clearer in the following disclosure, the proximity detector according to the invention uses a different configuration of electric field, which arises when the first electrode and the inner electrode are at the same potential or, alternatively, when one of them is held at a fixed potential. In the former case, the electric field is close to that of a simple planar electrode and spreads away from the detector. In the latter case, the electric field is stronger in the space between the electrodes and decays rapidly with distance from the detector. In the following, it will be shown that the invention uses this difference to estimate the permittivity of the approaching object, or even the distance, and transmits this estimated quantity, encoded in a digital variable, to the host system via a suitable data bus. [Brief description of the drawings]

[0020] Embodiments of the invention are disclosed herein and illustrated in the drawings. [Figure 1] FIG. 1 is a highly simplified conceptual diagram of a detector according to the present invention and a host system (digital processor) connected thereto; [Diagram 2] Schematic diagram of a possible implementation of the invention in a mobile phone with the detector integrated on a printed circuit board, also showing some dielectric or conductive objects in the detection area. [Diagram 3] FIG. 1 is a schematic diagram of a possible implementation of the sensing electrodes used according to the invention on a printed circuit board; [Figure 4] FIG. 2 is an idealized schematic diagram of electrostatic induction between a detector according to the invention in a first measurement mode and two objects at different distances within the detection region; [Diagram 5] Another idealized schematic of electrostatic induction between a detector and the same object as in FIG. 4 in the second measurement mode. [Figure 6] A graphical representation of one possible method for measuring the dielectric constant. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Figure 1 illustrates a simplified circuit of a capacitive proximity sensor that can be used within the scope of the present invention. The sensor comprises an electronic circuit 80, preferably an integrated circuit, that reads the capacitance of at least two electrodes. This example illustrates two electrodes: a first electrode 25 (also called the "outer electrode") connected to a first capacitive input 31 of the integrated circuit, and an inner electrode 20 connected to a second capacitive input 32 of the same integrated circuit. This first electrode is layered on top of the inner electrode 25, partially shielding it from a sensing area 90 above the first electrode. The first electrode 25 has a series of openings that allow partial capacitive coupling between the inner electrode 25 and the charges in the sensing area.

[0022] This electrode stack 29 is completed by, optionally, an active shield electrode 23 below the inner electrode connected to a shield control terminal of circuit 80, and preferably a passive screen 27 below the active shield 23.

[0023] The example illustrated in Figure 1 is a single channel sensor. The integrated circuit 80 is configured to read a single stack of electrodes 29. However, this is not a limitation of the invention. The circuit 80 can be configured to read multiple stacks of electrodes without departing from the scope of the present disclosure.

[0024] The first electrode 25 is connected to a first capacitance input of the circuit 80 and to a capacitance measurement circuit 53, e.g. a capacitance-to-voltage converter, which generates a signal related to the self-capacitance of the first electrode 25. Several circuits can be used to achieve this. In a possible implementation, the capacitance measurement unit applies a variable voltage to the electrode and measures the corresponding charge by a current integration circuit, so that the capacitance is given by the ratio between the charge and the voltage change.

[0025] The capacitance of the first electrode 25 is subject to change by the approach of a dielectric object, and this change in capacitance is used to detect the approach of such an object. However, the change induced by the approach is much smaller than the sum of the intrinsic capacitance of the electrode and the capacitance of the connection lines connecting the electrode to the measurement circuit. Preferably, the circuit includes an offset subtraction circuit 50 configurable by the processor 65 to subtract any reference value from the output of the capacitance measurement circuit. The resulting value is then converted to a suitable digital representation by an A / D converter 55 and forwarded to the digital processor 65 for further refinement.

[0026] Advantageously, the input terminal 32 of the inner electrode can be set in a shield mode where it is connected to a shield control unit 51, or in a ground mode where it is connected to a fixed potential that is the ground reference. This shield control unit 51 generates a shield potential that closely follows the potential of the capacitance input being measured at a given moment. In this way, the electrode in shield mode does not participate in the measured capacitance.

[0027] This shield potential is often understood to be a variable potential that tracks the variable voltage of the active input terminal. These two potentials should be the same, at least within the frequency band in which the measurements are made. For example, no constant voltage offset is involved.

[0028] In the example shown here, both the first input 31 and the second input 32 can be set to a measurement mode, a shield mode or a ground state, as indicated by switches S1, S2, and the inner electrode is connected to its own capacitance measurement circuit 53 and offset compensation unit 50 configuration, while a multiplexer 54 is used to pass either one of the capacitance signals to the ADC 55. However, this is not strictly necessary.

[0029] The capacitive proximity IC 80 has terminals for communication with a host system 100, which may be a microcontroller. They include a digital bus 37, for example an I2C bus, for transmitting desired digital variables, and a proximity binary output 36 for signaling the approach of an object into the detection field.

[0030] 2 is a schematic diagram of a capacitive proximity sensor in a mobile device 40. The mobile device 40 is embodied here as a smartphone with a touch-sensitive display, speaker 110, and microphone 105, although these are not required features. The device 40 can be a tablet, a laptop, a wearable device such as a smart watch or training watch, a Bluetooth speaker, earphones, a network device such as a router or Wi-Fi access point, or any type of portable electronic device that requires recognition of physical proximity. This disclosure will simply refer to a "smartphone" for the sake of brevity, but it should be understood that this is not a limiting feature of the present invention.

[0031] The mobile device 40 has a printed circuit board 26 with electronic components soldered to it. Among them is an integrated circuit capacitive proximity sensor 80 soldered onto the PCB 26. The electrode stack 29 is integrated onto the PCB and connected to the integrated circuit 80 by conductive tracks within the PCB, not necessarily in close proximity to it. This greatly simplifies the circuit layout.

[0032] Figure 3 illustrates a cross section of the stack-up 29. The vertical scale in this figure has been expanded for clarity. The first electrode 25, connected to the first capacitance input 31, is a conductive pattern etched into one layer of the PCB, completely covering the layers below 20, 23. The bottom layer of the stack-up has a ground plane 27, but can also have variable voltage paths if the layout requires it.

[0033] The internal electrode 20, which is connected to the second capacitance input 32 of the integrated circuit 80, is on a layer below the layer of the first electrode 25 and can be a solid area of ​​copper. Preferably, the internal electrode 20 is completely covered by the first electrode 25. The first electrode 25 is not completely shielded from the sensing area 90 because it has an opening 45 to allow some capacitive coupling. In other words, the first electrode 25 partially shields the second electrode 20 from the sensing area 90 by virtue of its opening 45.

[0034] The arrangement, number and shape of these openings 45 are not critical and are defined as those that will leave a reasonable degree of coupling. As a rule of thumb, the area ratio of the solid part of the electrode 25 to the openings is close to 1, but can deviate significantly from this.

[0035] The laminate 29 has an active shield electrode 23 connected to a shield terminal 34 of a capacitance circuit 80 on a layer of the PCB below the layer of the internal electrodes 20 and above the layer of the passive screen layer 27. In the drawings, the electrodes 25, 20, 23, 27 are shown on immediately adjacent layers of the printed circuit board, but this is not a requirement. It is also not necessary that the first electrode 25 be on the top layer of the PCB.

[0036] 4 and 5 show a simplified illustration of two objects 220, 230 in the detection area 90 facing the electrodes 25 and 20. The electrodes are separated from the detection area 90 by an enclosure 75 of the mobile device, e.g., a display panel, which has a negligible or fixed effect on capacitive coupling that can be ignored or subtracted out. The objects 220, 230 are different distances from the electrodes, are different sizes, and their dielectric constants can be different.

[0037] 4, the inner electrode 20 is in a shield mode and the first electrode 25 is in a measurement mode, in which the ADC of the sensor's integrated circuit 80 measures the first capacitance C1 of the first electrode 25. In this configuration, the inner electrode 20 can be considered to be at an equipotential with the first electrode 25.

[0038] In Fig. 5 the inner electrode 20 is in ground mode and fixed at a constant potential, in this configuration the ADC of the sensor's integrated circuit 80 measures the second capacitance C2 of the first electrode 25. It can be seen (even though these figures are only simplified drawings) that the electric field in the two configurations is different, i.e. in Fig. 4 the electric field is comparable to that of a flat electrode, whereas in Fig. 5 the electric field is confined to the space between the first and inner electrodes and does not reach far from these electrodes.

[0039] The invention stems from the observation that both objects 230 and 220 contribute to changing the value of C1, even though object 230 is much closer to the sensing electrode 25. On the other hand, in this configuration object 220 has less effect on the value of C2, since the electric field becomes very small very quickly when moving away from the sensing electrode. Therefore, from the values ​​of C1 and C2, it is possible to determine an estimate of the dielectric constant of the approaching object.

[0040] FIG. 6 is a graph showing the values ​​of C1 and C2 for two objects with a first dielectric constant (circles) and a second dielectric constant (crosses) higher than the first at random distances from the sensing electrode (superimposition of noise is unavoidable). The units of the C1 and C2 axes are arbitrary and different, as dictated by the different variation ranges of C1 and C2. The dielectric constant cannot be estimated from the value of either C1 or C2 alone, but can be calculated by ε r Based on knowing the combination of C1 and C2, assuming the difference between them is not lost in noise, a division line 250 can be found and by observing which side of the division line the C1 and C2 measurements lie, it is possible to tell whether an object has a first dielectric constant or a second dielectric constant.

[0041] The digital processor 65 of the capacitive sensor is therefore configured or programmed to determine the dielectric constant based on the values ​​of C1 and C2 measured as described above. The graphical method described in this example is just one of many possibilities for achieving this result.

[0042] In an embodiment, the value of the dielectric constant is estimated based on the ratio between C1 and C2. In general, the value of the dielectric constant is estimated from the value of a suitable mathematical function of C1 and C2 that can be calculated by the digital processor 65. A suitable mathematical function can be predetermined experimentally and empirically with reasonable effort in testing and simulation. Similarly, for each possible combination of C1 and C2, ∈ r The most likely values ​​of C can be pre-calculated or predetermined by measurement and stored in a double-entry look-up table that a digital processor can address using the measured values ​​of C1 and C2. The size of this look-up table can be managed by using a transformation of variables, by quantizing the values ​​of C1 and C2, or by other known techniques.

[0043] In an extension of the invention, processor 65 can be programmed to estimate the distance to an approaching object rather than, or in addition to, the dielectric constant.

[0044] It will be appreciated that the roles of the first electrode 25 and the inner electrode 20 can be swapped without departing from the invention. The capacitive sensor can use the capacitance of the inner electrode measured while the first electrode is held at the shield potential in place of C1, and the capacitance of the inner electrode measured while the first electrode is held at a fixed potential in place of C2.

[0045] Returning to the diagram of FIG. 1, the processor 65 determines if an object is approaching the detection area 90 by observing the capacitance of the sense electrodes and uses C1 and C2 as disclosed to calculate a digital value representing the permittivity of the approaching object. This may be the result of a suitable portion of software running on the processor 65. The integrated circuit 80 may provide a digital output 36 to signal that an object is approaching the detection area. This triggers an action in the host system 100. The estimated permittivity value and possibly the estimated distance value may be associated with predefined registers for readout by the host system via the bus 37. The present application relates to the invention described in the claims, but may also include the following configurations as other aspects. 1. 1. A capacitive proximity sensor for detecting the presence of a conductive or dielectric object within a detection area adjacent to a portable device, comprising: The sensor has a laminated structure with a first electrode on a first layer facing the detection area and an internal electrode on a second layer, the first electrode having a plurality of openings that allow partial capacitive coupling between the internal electrode and conductive and / or dielectric objects in the detection area so as to partially shield the internal electrode; the capacitive proximity sensor comprising one or more capacitance reading units configured to determine the capacitance of one of the electrodes; and a shield control unit configured to generate a shield potential that tracks the potential of the electrode whose capacitance is measured by the capacitance reading unit; The capacitive proximity sensor is provided with a readout circuit configured to determine a first capacitance of either the first electrode or the internal electrode by applying a shield potential to the other electrode, and to determine a second capacitance of either the first electrode or the internal electrode by holding the other electrode at a fixed potential, and to determine a dielectric constant of an object within the detection region based on the first capacitance and the second capacitance. 2. 2. The capacitive proximity sensor of claim 1, wherein the readout circuit is configured to determine a distance between the capacitive proximity sensor and an object within a detection region based on the first capacitance and the second capacitance. 3. 2. A capacitive proximity sensor as described in claim 1, wherein the openings are arranged in the form of a regular lattice of holes or stripes. 4. 2. The capacitive proximity sensor according to claim 1, wherein the fixed potential is ground potential. 5. A data transmission interface for communication with a host system, the data transmission interface comprising: a logical proximity signal indicating that an object is within the detection region; a proximity value encoding a distance between the capacitive proximity sensor and an object within a detection field as a binary variable, the distance being determined from the first capacitance and the second capacitance; A permittivity value that encodes the permittivity of an object within the detection region as a binary variable; 2. The capacitive proximity sensor according to claim 1, configured to transmit one or more of the following: 6. 6. The capacitive proximity sensor according to claim 5, wherein the data transmission interface is a serial bus, for example an I2C bus. 7. 6. A capacitive proximity sensor as described in claim 5, having an interrupt request output which is issued when an object is detected within the detection area. 8. 8. The capacitive proximity sensor according to any one of 1 to 7 above, wherein the first electrode and the internal electrode are formed by etching a conductive layer of a multi-layer printed circuit board. 9. 9. A capacitive proximity sensor as claimed in claim 8, wherein the first electrode and / or the inner electrode are capacitively coupled to a radio circuit to provide an antenna for the radio circuit. [Explanation of symbols]

[0046] 20 Internal electrode 21 Protective Ring 23 Shield 24 Protective Ring 25 First electrode 26 Printed Circuit Board 27 Ground plate 28 Dielectric Layer 29 Electrode stack 31 First Capacitive Input 32 Second Capacitive Input 34 Shield terminal 36 Proximity Signal 37 Digital Bus 40 Mobile Devices 41 Via 45 opening, hole 50 Offset correction section 51 Shield control circuit 53 Capacitance measurement circuit, capacitance reading unit 54 Multiplexer 55 Analog / Digital Converter 65 Digital processor, readout circuit 75 Glass 80 Capacitive proximity integrated circuits, proximity sensors 90 Detection Area 100 Host Systems 105 Microphone 110 Speakers 220 Object 230 Object 250 Dividing Line

Claims

1. 1. A capacitive proximity sensor for detecting the presence of a conductive or dielectric object within a detection area adjacent to a portable device, comprising: The sensor has a laminated structure with a first electrode on a first layer facing the detection area and an internal electrode on a second layer, the first electrode having a plurality of openings that allow partial capacitive coupling between the internal electrode and conductive and / or dielectric objects in the detection area so as to partially shield the internal electrode, the capacitive proximity sensor comprising one or more capacitance reading units configured to determine the capacitance of one of the electrodes; and a shield control unit configured to generate a shield potential that tracks the potential of the electrode whose capacitance is measured by the capacitance reading unit; The capacitive proximity sensor is provided with a readout circuit configured to determine a first capacitance of either the first electrode or the internal electrode by applying a shield potential to the other electrode, and to determine a second capacitance of either the first electrode or the internal electrode by holding the other electrode at a fixed potential, and to determine a dielectric constant of an object within the detection region based on the first capacitance and the second capacitance.

2. 2. The capacitive proximity sensor of claim 1, wherein the readout circuit is configured to determine a distance between the capacitive proximity sensor and an object within a detection region based on the first capacitance and the second capacitance.

3. 2. The capacitive proximity sensor of claim 1, wherein the openings are arranged in a regular grid of holes or stripes.

4. 2. The capacitive proximity sensor of claim 1, wherein the fixed potential is a ground potential.

5. A data transmission interface for communication with a host system, the data transmission interface comprising: a logical proximity signal indicating that an object is within the detection region; a proximity value encoding a distance between the capacitive proximity sensor and an object within a detection field as a binary variable, the distance being determined from the first capacitance and the second capacitance; A permittivity value that encodes the permittivity of an object within the detection region as a binary variable; 2. The capacitive proximity sensor of claim 1, configured to transmit one or more of:

6. The capacitive proximity sensor according to claim 5 , wherein the data transmission interface is a serial bus or an I2C bus.

7. 6. The capacitive proximity sensor of claim 5, further comprising an interrupt request output which is issued when an object is detected within the detection region.

8. 8. The capacitive proximity sensor according to claim 1, wherein the first electrode and the internal electrode are formed by etching a conductive layer of a multi-layer printed circuit board.

9. 9. The capacitive proximity sensor of claim 8, wherein the first electrode and / or the inner electrode are capacitively coupled to a radio circuit to provide an antenna for the radio circuit.

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