Patent Application
20230118148
The present application claims priority from South Africa application ZA 2021/08015, filed Oct. 20, 2021, contents of which is hereby incorporated by reference into this application.
Wearable electronic devices are increasingly adopted. Conservation of battery power is a continuous challenge for designers of these devices. Capacitive sensing is often used in wearables to detect user proximity and touch in order to determine when and in which manner a device is worn, allowing control of power-hungry functions to better conserve battery power. For instance, for smart watches and fitness trackers, capacitive sensing may be used to determine when the device is worn sufficiently close to the skin of the user to enable optical sensing of the user's pulse rate. If the wear status is incorrectly determined it may cause a number of unwanted effects. These may include incorrect pulse measurements, wastage of battery power by the optical unit while trying to obtain an acceptable pulse reading and emission of light from the optical unit beyond the immediate vicinity of the smart watch or fitness tracker, which could be irritating to the user or to people close by, etc.
Another challenge facing designers of wearable devices such as smart watches and fitness trackers that use capacitive sensing is the close proximity of grounded structures. This may significantly increase the difficulty of using capacitive sensing to accurately detect proximity distance, user touch and press events. For example, due to the close vicinity of grounded structures, the use of self- or surface-capacitance to sense user proximity, as is commonly used in the art, may not work well, given that electric fields may couple directly and strongly from electrodes to the grounded structure, with little emanation of fields into the space around the electrode. The close vicinity of grounded structures in wearables may also limit the use of mutual- or projected-capacitance electrodes in a similar manner, with transmitter electrodes typically coupling strongly to grounded structures, which may leave little charge to be transferred to receiver electrodes.
In the case of mutual-capacitance measurements, compensation and electrode design could possibly be used to negate the effect of said grounded structures, for example by an increase in mutual-capacitance between electrodes. However, this may lead to a situation where little information on proximity distance can be gleaned from measurements, with only a definite touch by the user, for example by the user's arm, which can be detected. This may be non-ideal in the case of smart watches and fitness trackers, as wristbands tend to move a fair amount about the user's arm, and may be fastened from loosely to tightly, dependent on user preference, which may lead to a requirement for accurate detection of proximity distance as well as touch to correctly determine wear state.
Small wearable electronic devices are inherently space constrained. This may also limit the size or area of conductive ground structures that can be realized in these devices. As is known in the art of mutual-capacitance sensing, increasing the amount of local ground available to a mutual-capacitance circuit for coupling via electrical earth to the user may increase the change in mutual-capacitance the user can cause, leading to improved sensing/detection. Given said space constraints in small wearables, such an increase in local ground is often not an option. An alternative may be to increase the amount of mutual-capacitance through correct design of electrode layout and parameters. Unfortunately, this may lead to a design which sacrifices proximity detection to allow improved touch detection.
Wearable devices that utilize capacitive sensing also need to compensate for changes in ambient temperature, which may be quite abrupt as a user moves from one environment to another. Traditionally, this has been done through the use of capacitive sensing baselines and/or long-term averages (LTA). However, this approach may have limitations. For example, while in a wear detected state, it may not be possible to form an LTA for baseline adjustment with measurement data from an electrode used for said wear detection. One may make use of a second electrode which is not exposed to the user and apply a specific factor or weight to adjust the baseline using measurement data from said second electrode. But this may come at the cost of additional processing overheads and power consumption and may not be completely fool proof.
The present invention addresses the above problems and may allow the wear state of devices such as fitness trackers and smart watches, amongst others, to be determined with higher accuracy and robustness than what is possible with prior art solutions, fulfilling an unmet need currently experienced in the wearables technology space.
In an effort to clarify the disclosure of the present invention, the following summary is presented. This should not be construed as limiting to the claims of the invention as it is merely used to support clarity of disclosure. A large number of alternative embodiments may exist that fall within the spirit and scope of the present invention, as may be recognised by one skilled in the relevant arts. This summary is not intended to identify key or critical elements of the disclosed subject matter, nor is it intended to delineate the scope of the present invention or the claims. It is intended to present a number of concepts in a simplified form to assist with the overall disclosure of the present invention.
Herein, “or” is used to convey inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” may mean “A, B, or_both,” unless expressly indicated otherwise or indicated otherwise by context. In addition, “and” is used to convey both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, “A and B” may mean
“A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context.
The present invention teaches that differential mutual-capacitance measurements may be used in a wearable device, for example a smart watch, fitness tracker, earbuds, earphones, headphones, health-monitor devices or others, or in a mobile device such as a smart phone, to negate the close vicinity of grounded structures, and through a sufficient amount of mutual-capacitance may allow accurate determination of user proximity distance from the wearable or mobile device as well as detection of touch and press events. To clarify, a wearable device embodiment of the invention may, for example have a ground conductor between capacitive sensing electrodes and a battery of said device. Due to the use of differential mutual-capacitance measurements as taught by the current invention, said ground conductor, for example a ground plate, may be in close vicinity to the capacitive sensing electrodes used for said differential measurements without preventing accurate detection of user proximity, touch and press events. In other words, the ground conductor may be within a sensing range of said electrodes. The location of the ground plate, or other grounded structures, between said electrodes and the battery may allow the latter to move without adversely affecting said detection of user proximity, touch and press events, for example. This may assist to accurately determine wear status which may be used to control functionality of said wearable device accordingly, or to determine when a mobile device is placed against a user's ear, for example. The use of differential mutual-capacitance measurements for wear detection in electronic devices may allow mutual-capacitance between electrodes to be increased significantly without compromising on proximity detection. This provides a clear benefit in small battery-operated systems which, due to space constraints, may be limited in the amount of increase in local ground area to improve coupling to the user via electrical earth and thereby mutual-capacitance sensing/detection.
To clarify the above, the present invention teaches that the problem of limited coupling between local ground and electrical earth may be solved by increasing the capacitance between receiver electrodes and local ground, and possibly also the capacitance between transmitter electrodes and local ground. The negative effect of these increases in capacitive coupling between electrodes and local ground on mutual-capacitance sensing may be countered by an increase in the values of mutual-capacitance between receiver and transmitter electrodes. Due to the use of differential mutual-capacitance sensing, such increases in mutual-capacitance may be done without losing the ability to discern user proximity events from user touch or press events. The present invention further teaches that the one-or-other compensation or cancellation method and/or apparatus may be used before, during or after said differential mutual-capacitance sensing to negate any detrimental effects of the increase in mutual-capacitance on sensing resolution, stability, repeatability, or temperature response.
According to another exemplary embodiment of the present invention, a matrix of mutual-capacitance electrodes comprising a plurality of at least two transmitter electrodes and a single central receiver electrode, e.g., may be used with differentially driven measurements to determine wear status of a wearable electronic device, for example a smart watch, fitness tracker, earbuds, earphones, headphones, health-monitor devices or others, or to detect when a mobile device, for example a smart phone, is in close proximity to a user. The matrix may be used in a manner which allows detection of signal saturation or degradation on specific differentially driven channels and identification of differentially driven channels which allows accurate detection of wear status or mobile device status, wherein a differentially driven channel may comprise at least two transmitter electrodes and a single receiver electrode, or more receiver electrodes. Allocation of differentially driven channels to said matrix may be performed dynamically as the wearable device moves on the wearer, or said mobile device moves closer to or further from a user, to allow continuous accurate detection of wear state or mobile device position.
Such a matrix of mutual-capacitance electrodes embodying the present invention may also be realized in an opposing layout format, wherein transmitter electrodes driven with opposing phases during differential capacitive sensing may be located directly opposite each other on two sides of a substrate, for example on opposite sides of a printed circuit board (PCB). One or more receiver electrodes may be located on each side of said substrate. As a specific example, the present invention may be embodied in a matrix using a two-layer PCB, with a single receiver electrode located on both the top and bottom layer, and centrally to a plurality of transmitter electrodes, with each transmitter electrode on said top layer opposed by another transmitter electrode of equal dimensions on the bottom layer. During sensing, the transmitter electrodes of a specific opposing pair may be driven with different phases, for example they may be driven with signals differing one-hundred-and-eighty degrees in phase.
When using differentially driven capacitive measurements to determine wear state of a wearable electronic device, situations may arise where the various electrodes of a specific differentially driven channel is located at exactly the same distance from a user. Alternatively, electrode-to-user distances for the various electrodes in a differentially driven channel may differ, but the capacitive coupling areas for said electrodes may be such as to compensate for the difference in electrode-to-user distances. In either case the differential output signal may be zero or near zero. If the wearable device is located at a sufficient distance from said user to qualify as a non-wear case, the zero or near zero value of the differential output should not pose a problem. However, if the wearable device is sufficiently close to the user that the wear status should be set to worn, the zero or near zero differential output may cause erroneous state identification or operation. The present invention teaches that this problem may be solved by connecting a discrete, known value capacitor between one of the transmitter electrodes and the receiver electrode of a differentially driven capacitive channel. If the wearable device is sufficiently far away from the user to qualify as a non-wear case, connection of said discrete capacitor may cause a large change in differential output. On the other hand, if the wearable device is located in close proximity to the user, and therefore couples strongly with the user, connection of said discrete capacitor may not cause a significant change in differential output, dependent on the amount of said coupling and the value of the discrete capacitor. In this manner a wearable device may discern between a worn and non-worn case where differential output is zero or near zero. The discrete capacitor may be any off-chip or integrated capacitor of a value as required by design parameters. For example, it may be an on-chip calibration capacitor, or other capacitors integrated into a circuit used for capacitive sensing or other purposes.
In yet another exemplary embodiment of the present invention, two consecutive measurements may be performed to detect when a wearable electronic device, or another device, is touching or in close proximity to a user. A first measurement of the two measurements may be characterised by driving a first transmitter electrode high first during a first phase, with said first transmitter electrode being part of a plurality of transmitter electrodes used in a differentially driven channel. A second transmitter electrode of said plurality is held low during said first phase. This may be followed by a second phase of said first measurement where a second transmitter electrode of said plurality is driven high, while said first transmitter electrode is held low, and thereafter repeating the first and second phases until the end of the first measurement. A second consecutive measurement may be characterised by said second transmitter electrode being driven high first during a first phase of the second measurement and said first transmitter electrode held low, whereafter said first transmitter may be driven high during a second phase of the second measurement and said second transmitter electrode held low, followed by a repetition of the first and second phases until the end of the second measurement. According to the present invention, by comparing the output of the first measurement with that of the second measurement, a wearable device, for example a fitness tracker, smart watch, earbuds, earphones, headphones, health-monitor devices or others, or a mobile device such as a smart phone, may be able to detect a user touch and/or proximity event with high accuracy, which may be used to determine wear status or whether the mobile device is on- or off-ear, for example. Such an embodiment may also advantageously negate changes in capacitive sensing output due to temperature, or other environmental changes. This may allow capacitive sensing without the need to use a baseline or long-term average value against which to test possible events.
According to the present invention, by using embodiments as disclosed herein, a wearable electronic device, or another device, for example a smart watch, fitness tracker, earbuds, earphones, headphones, health-monitor devices or others, may obtain differential capacitive output signals with a positive or negative polarity for a specific user touch or proximity event, dependent on the sensing electrodes used in a matrix of mutual-capacitance sensing electrodes. This may be used to discern specific wear cases for the wearable electronic device, which may allow improved wearable functionality and performance.
In another embodiment of the present invention, a wearable electronic device may utilize the same electrode structures used for differentially driven capacitive sensing, or another dedicated conductive structure, to also perform inductive sensing. Said dedicated conductive structure may be a coil structure, as is known in the art. The inductive sensing results may be used in a number of ways by the wearable electronic device, for example by a smart watch, fitness tracker, earbuds, earphones, headphones, health-monitor devices or others. Or it may be used by a mobile electronic device, for example a smart phone. It may be used to detect the proximity of conductive surfaces, for example a metal table, which may be used by said wearable device during determination of wear status, as an example. Or it may be used to measure or monitor magnetic fields incident on said electrode structures or said dedicated conductive structure, wherein said measurement or monitoring results may be used to facilitate further functionality of the wearable electronic device. As another example, inductance measurements via said electrode structures or dedicated conductive structure may be used to detect user activation of a user interface element, for example, a push-button. The inductance measurements may be based on charge transfer methods and circuits. The same circuit may be used to perform the capacitive measurements and said inductance measurements. For example, said same circuit may use a single measurement circuit for both capacitive measurements and for inductance measurements. As a further, more detailed example, said single measurement circuit may be a charge transfer measurement circuit. Said same circuit may also comprise an integrated circuit, using one or more dies.
In another exemplary embodiment of the present invention, a wearable, or other, electronic device may perform both differentially driven capacitive sensing as well as another form of sensing to monitor another parameter, for example inductive sensing, using the same or different circuits and the same or different electrodes and/or conductive structures. Said device may utilize measured changes in said another parameter, for example measured changes in inductance, to determine when to perform differentially driven mutual-capacitance sensing for wear, or other, detection, wherein the differentially driven mutual-capacitance sensing may be performed with or without the use of a baseline or LTA. According to the present invention, this may reduce complexity during capacitive sensing. For example, a device may perform either self-inductance or mutual-inductance sensing using a charge-transfer based circuit and a coil-like structure or structures. Changes in measured inductance may need to cross a predetermined threshold or thresholds before said circuit may be used to perform differentially driven mutual-capacitance measurements with a plurality of electrodes, for example with a single receiver electrode and a plurality of transmitter electrodes, similar to that described elsewhere during the present disclosure. The differential capacitance sensing values thus obtained may then be used without a baseline or LTA to detect wear status of said device. As more specific examples, said changes in the another parameter, for example changes in measured inductance, may be caused by changes in a mechanical configuration of the one-or-other structure within said device due to a user interaction, input or another event. For instance, the change in said another parameter, for example changes in inductance, may be caused by a user pressing a push-button, or by a user unfolding a set of head-phones, or by a user removing a set of earbuds from a storage and/or charging case. The skilled reader will appreciate that a large number of applications may exist which embodies the directly preceding teachings.
The present invention further teaches that differentially driven capacitive sensing measurements as described herein may be used to determine, or to help determine, the angle between a wearable electronic device, for example a fitness tracker, smart watch, earbuds, earphones, headphones, health-monitor devices or others, or a mobile device such as a smart phone, and a body part of a user, for example his or her arm. Said differentially driven capacitive sensing measurements may be used with, for example, gyroscope or accelerometer measurements to accurately determine said angle. The determined angle may be used by circuitry in the wearable device, or by other remote circuitry in communication with the wearable device, to improve optical measurements of blood flow and blood oxygen levels, for example. Said improvement may be made through use of said angle to adjust or correct optical measurement values to compensate for errors introduced due to said angle, or to compensate for other errors.
The present invention may be embodied in a method for wear detection by a wearable electronic device comprising mutual-capacitance sensing circuitry as well as grounded structures that are located within a sensing range of mutual-capacitance sensing electrodes of said device, said electrodes comprising one or more receiver electrodes and a plurality of transmitter electrodes, and wherein the method comprises at least one of the following two groups of steps. Group A, comprising forming pairs of transmitter electrodes, and driving the two transmitter electrodes within a pair out of phase with each other; determining mutual capacitance values for combinations of said receiver electrode(s) and specific transmitter electrodes of said plurality of transmitter electrodes; subtraction of mutual capacitance values of specific ones of said combinations from each other to find a plurality of sensing channel output values; selection of one or more of said sensing channels output values and determination of a wear status of said device based on the selected values. Group B, comprising the step of increasing mutual capacitance between the receiver electrode(s) and specific transmitter electrodes to compensate for weak coupling between the grounded structures and a surrounding electrical earth.
The present invention teaches a wearable electronic device comprising mutual-capacitance sensing circuitry as well as grounded structures that are located within a sensing range of mutual-capacitance sensing electrodes of said device, wherein the electrodes comprise one or more receiver electrodes and a plurality of transmitter electrodes, wherein transmitter electrodes are paired in groups of two by the device to drive the transmitter electrodes within a pair out of phase with each other, wherein mutual capacitance values of combinations of the receiver electrode(s) and specific ones of the plurality of transmitter electrodes are measured by the device, with mutual capacitance values of specific ones of said combinations subtracted from each other by the device to determine a plurality of sensing channel output values, wherein one or more of said channel output values are selected and used by the device to determine a wear status of said wearable device.
An exemplary embodiment of the present invention may be found in a wearable electronic device with mutual-capacitance sensing circuitry and electrodes, said electrodes comprising one or more receiver electrodes and a plurality of transmitter electrodes, wherein the device pairs transmitter electrodes in groups of two to drive the transmitter electrodes with a pair out of phase with each other, wherein the device increases mutual capacitance of combinations of the receiver electrode(s) and specific ones of the plurality of transmitter electrodes to compensate for weak coupling between a surrounding electrical earth and grounded structures, said grounded structures located within a sensing range of the electrodes in said device, and wherein mutual capacitance values of said combinations are measured by the device, with mutual capacitance values of specific ones of said combinations subtracted from each other by the device to determine a plurality of sensing channel output values, wherein one or more of said channel output values are selected and used by the device to determine a wear status of said wearable device.
The invention is further described by way of examples with reference to the accompanying drawings in which:
To further clarify the disclosure of the present invention, the following descriptions relating to the appended drawings are presented. These should not be construed as limiting to the claims of the invention and are merely used to support clarity of disclosure. A large number of other equivalent embodiments may be possible that still fall within the spirit and scope of the present invention, as may be recognised by one skilled in the relevant arts.
Herein, “or” is used to convey inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” may mean “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. In addition, “and” is used to convey both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, “A and B” may mean “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context.
The embodiment shown at 1.17 in
However, according to the present invention, the zero differential or near zero output shown at 1.10 should potentially not be used to declare a not-worn state, as a zero or near zero output may also be obtained when a wearable device is located in close proximity to a user 1.12 at a distance d2, as illustrated at 1.13 in
The method shown at 3.1 starts by detecting that a differential output is zero or near zero, as shown at 3.2. This may be followed by the step of connecting a discrete capacitor between one of the transmitter electrodes and the receiver electrode of the differentially driven capacitive sensing channel under consideration, as shown at 3.3. Next, the step of checking for a corresponding change in the differential output, and whether it is larger than a predetermined threshold, may be performed, as shown at 3.4. If it is found that said corresponding change did occur, it may be deduced that the device is not worn, as shown at 3.5. However, if no corresponding change in differential output is detected, or a corresponding change is detected, but it is less than or equal to said predetermined threshold, it may be deduced that the device is worn, as shown at 3.6. This may be based on the premise that when the device is worn in close proximity to the user, coupling between each transmitter and receiver pair in the differentially driven channel may be quite high due to the low impedance path via the user's skin, or another surface. Therefore, connection of another discrete capacitor across one pair should have little effect. Naturally, this may be dependent on the design parameters at hand, with the capacitance of said discrete capacitor relative to the effective capacitance between each electrode pair which should be considered.
In general, embodiments of the present invention may allow inherent compensation for temperature, or other environmental, changes. This is illustrated in exemplary manner by the typical charge transfer capacitive measurements shown at 5.1 in
According to the present invention the use of differentially driven capacitive sensing measurements in a wearable electronic device, as described herein, may allow accurate capacitive sensing and wear detect without the use of a baseline or long term average to identify user touch and proximity events. For example,
Wearable electronic devices are often removed by the wearer and placed on the one or other surface, for example a conductive surface or a surface with appreciable conductivity due to moisture content or other properties. When only capacitive sensing is used for wear detect, such surfaces may result in an erroneous detection result. The present invention teaches that this may potentially be solved through the use of additional inductance measurements.
According to the present invention, a method as depicted in exemplary manner at 9.1 by
As will be appreciated by those skilled in the art of capacitive sensing, step 9.2 may be detrimental to mutual-capacitance sensing sensitivity and/or resolution. Therefore, according to the present invention, step 9.3 may be performed, whereby mutual-capacitance values for each, or for some, of the receiver-transmitter electrode pairs may be increased to counter-act the effect of step 9.2 on sensing sensitivity and/or resolution. This may be followed by optional step 9.4 which may be used to compensate for the increased mutual-capacitance values during measurements. For example, step 9.4 may entail artificial subtraction of capacitance and/or charge values, or other values, during measurement and processing to compensate for said increases in mutual-capacitance. This may assist, as will be appreciated by skilled readers, to allow detection of small changes in measured capacitance.
Step 9.5 performs differentially driven capacitive sensing using mutual-capacitance values, similar to that described elsewhere in the current disclosure. Due to the use of differentially capacitive sensing, large mutual-capacitance values may be handled. In step 9.6 the results of said differential sensing are used for wear detect, similar to that described elsewhere in the current disclosure.
Sensing of another parameter, for example inductive sensing, may be used together with differential capacitive sensing to perform wear detection for an electronic device, according to the present invention. This may hold a number of advantages in terms of wear detection robustness, material detection and error rate.
Once said inductive sensing event is detected, for example once a change in a measured self- or mutual-inductance value crosses a predetermined threshold, the method may perform differentially driven capacitive sensing similar to that described elsewhere in the current disclosure. For example, differential capacitive sensing without the use of a baseline or LTA value, as per step 10.3, may be performed. Subsequently or concurrently, the wear status of the electronic device may be determined, as per step 10.4, for example using the differential capacitive sensing value or values only, or using these along with values from said inductive sensing. It is to be appreciated that in the directly preceding description of
A related six-channel differential capacitive sensing embodiment is depicted in exemplary manner at 11.8 and 11.9 in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021/08015 | Oct 2021 | ZA | national |
