Sensor device and method for capacitive touch detection

Abstract

A sensor device (1) for capacitive touch detection has a first potential connection (14, 15) for connection to a first reference potential and a second potential connection (14, 15) for connection to a second reference potential, and an analog-to-digital converter (9) and a sensor electrode (6) which can be linked to at least one first potential connection (14, 15), or can be switched to a high impedance state. The sensor device has a reference capacitor (7, 7 '), the first connection of which can be linked via the sensor device (1) to at least one second potential connection (14, 15) or to the input (17) of the analog-to-digital converter (9), and a resistor arrangement (12, 27) for linking the sensor electrode (6) to the first connection of the reference capacitor (7, 7'). The sensor device (1) has a matching capacitor (8, 8 ') which can be connected or disconnected in parallel to the reference capacitor (7, 7').

Description

[0001] The present invention relates to a sensor device for capacitive touch detection, which has at least one first potential connection terminal (for connecting the sensor device to a first electrical reference potential respectively) and at least one second potential connection terminal (for connecting the sensor device to a second electrical reference potential respectively), an analog-to-digital converter, and a sensor electrode (designed to be touched by a user and linkable to the at least one first potential connection terminal through a first switching element of the sensor device, or switched to a high-impedance state), a reference capacitor (which has a first connection terminal that can be linked to the at least one second potential connection terminal or the input terminal of the analog-to-digital converter through a second switching element of the sensor device); and a resistor component for linking the sensor electrode to the first connection terminal of the reference capacitor. The present invention also relates to an input device for a motor vehicle that utilizes such a sensor device to capture user input, and to a hand detection device for a motor vehicle steering wheel that employs such a sensor device. The present invention also relates to a method for capacitive touch detection.

[0002] Document US9,823,798B2 describes a capacitive sensor system that includes a capacitive sensor device having a sensor electrode including a first capacitor, a first power supply voltage, and a first switch that can be operated to couple the sensor electrode to the first power supply voltage in a first mode and to an analog-to-digital converter in a second mode. A second switch can be operated to couple a second capacitor to a second power supply voltage in a first mode and to an open circuit in a second mode. A resistance element is provided that includes a first connection terminal and a second connection terminal, the first connection terminal being connected between the first capacitor and the first switch, and the second connection terminal being connected between the second capacitor and the second switch.

[0003] Document DE102019129802 A1 describes a capacitive sensor device having a sensor electrode, a control and evaluation device with a first connection contact and a second connection contact, a first connection line and a second connection line. The sensor electrode has a first electrode connection and a second electrode connection, and the first electrode connection terminal of the sensor electrode is linked to the first connection contact via the first connection line, and the second electrode connection terminal is linked to the second connection contact via the second connection line. The sensor device has a reference capacitor that is electrically linked to the first connection line, wherein the sensor electrode is electrically linked to the first connection contact via a resistor or can be electrically linked to the first connection contact, and wherein the reference capacitor is electrically linked to the first connection line between the first connection contact and the resistor on one hand and to a reference potential on the other hand.

[0004] Since the capacitance of the sensor electrode relative to ground changes depending on whether the sensor electrode is touched by a user, a touch-related voltage is established on the second capacitor, and the voltage of the second capacitor can be read out by an analog-to-digital converter. Based on this, it is possible to detect the situation where the sensor electrode is touched or approached (which also affects the capacitance). Such a sensor system can be used, for example, for capacitive detection of user input, especially for applications inside a motor vehicle, such as when detecting the actuation of a touch-sensitive operating panel or operating element.

[0005] If the two capacitances are not very different from each other, the accuracy of the voltage measurement is higher. Therefore, the measurement range for the capacitance of the sensor electrode to be measured is limited, within which accurate measurement and thus reliable detection can be achieved. For example, in different applications, the capacitance of the sensor electrode may vary because, for example, sensor electrodes of different sizes are used. In addition, the capacitance of the sensor electrode changes according to the ambient temperature.

[0006] The object of the present invention is to improve the reliability of touch detection for a larger measurement range and / or different measurement ranges when using a capacitive measurement principle.

[0007] This object is achieved by the respective subject matter of the independent claims. The dependent claims relate to advantageous improvements and preferred embodiments.

[0008] The present invention is based on the idea that, in addition to the reference capacitor mentioned at the beginning, a matching capacitor is provided, which can be connected to the reference capacitor in a parallel circuit or removed from this parallel circuit.

[0009] According to one aspect of the present invention, a sensor device for capacitive touch detection is proposed. The sensor device has at least one first potential connection terminal (for connecting the sensor device to a first electrical reference potential respectively) and at least one second potential connection terminal (for connecting the sensor device to a second electrical reference potential different from the first electrical reference potential respectively). The sensor device has an analog-to-digital converter (AD converter) and a sensor electrode, which is designed, in particular arranged, to be touchable by a user. The sensor electrode can be linked to the at least one first potential connection terminal or switched to a high-impedance state through a first switching element of the sensor device. The sensor device has a reference capacitor and a resistance component. The first connection terminal of the reference capacitor can be linked to the at least one second potential connection terminal or to the input of the analog-to-digital converter through a second switching element of the sensor device, and the resistance component is used to link the sensor electrode to the first connection terminal of the reference capacitor.

[0010] The switching element can in particular be controlled by at least one control unit of the sensor device. In particular, the at least one control unit can be configured to control the third switching element independently of the first and second switching elements. Conversely, the at least one control unit can control the first and second switching elements, for example, such that the first connection terminal of the reference capacitor and the detection electrode are simultaneously or substantially simultaneously linked to the at least one second potential connection terminal or the at least one first potential. Similarly, the at least one control unit can control the first and second switching elements such that the first connection terminal of the reference capacitor and the detection electrode are simultaneously or substantially simultaneously linked to the input of the AD converter or switched to a high-impedance state.

[0011] For example, the first electrical reference potential can correspond to the ground potential, and the second electrical reference potential can correspond to a non-zero reference potential, with the result that a non-zero, in particular positive, reference voltage is generated between the first and second reference potentials. However, the first electrical reference potential can also be non-zero, while the second electrical reference potential can correspond to the ground potential. The first electrical reference potential and the second electrical reference potential can also both be non-zero.

[0012] Each of the at least one first potential connection terminal is linked to the first electrical reference potential or can be linked to the first electrical reference potential, and each of the at least one second potential connection terminal is linked to the second electrical reference potential or can be linked to the second electrical reference potential. Thus, linking a sensor electrode, the first connection terminal of the reference capacitor or other connection terminals, etc. to the at least one first potential connection terminal can be understood as linking to one of the at least one first potential connection terminal. Linking a sensor electrode, the first connection terminal of the reference capacitor or other connection terminals, etc. to the at least one second potential connection terminal can be understood as linking to one of the at least one second potential connection terminal.

[0013] Terms such as "linked", "linked to", etc. include direct linking as well as indirect linking, and also include switchable linking and non-switchable linking. If a connection terminal, etc. can be switched or linked through a switching element, etc., this also includes direct linking and indirect linking. In this case, direct linking can be understood as: if necessary, except for the corresponding switching element, no other electrical or electronic components are arranged between the components to be linked; while indirect linking can be understood as: if necessary, except for the corresponding switching element, one or more other electrical or electronic components, such as resistors, capacitors, coils, etc., are arranged between the components to be linked.

[0014] In particular, each switching element can assume a closed state and an open state. The resistance of the corresponding switching element is lower in the closed state than in the open state. For example, the resistance in the closed state is nominally zero, while the resistance in the open state can be nominally infinite. If the first switching element is in the closed state, for example, the sensor electrode is connected to the at least one first potential connection terminal; and if the first switching element is in the open state, for example, the sensor electrode is switched to a high impedance state, and vice versa. If the second switching element is in the closed state, for example, the first connection terminal of the reference capacitor is connected to the at least one second potential connection terminal; and if the second switching element is in the open state, for example, the first connection terminal of the reference capacitor is connected to the input terminal of the AD converter, and vice versa. If the third switching element is in the closed state, for example, the matching capacitor is connected in parallel with the reference capacitor; and if the first switching element is in the open state, the matching capacitor is removed from the parallel circuit, for example, and vice versa.

[0015] The high impedance state of the sensor electrode, the first connection terminal of the reference capacitor, and any other possible connection terminals can be understood as a state in which there is no significant charge outflow from the sensor electrode, the first connection terminal of the reference capacitor, and any other possible connection terminals, and correspondingly, there is no significant charge inflow. For example, this can be achieved by disconnecting the corresponding connection terminal or connecting the corresponding connection terminal to a sufficiently large resistor. In individual cases, how large a resistor is sufficient depends on the measurement accuracy to be achieved. Since the voltage is to be measured by the AD converter, connecting to the input terminal of the AD converter corresponds in particular to switching to the high impedance state.

[0016] The reference capacitor and the matching capacitor each have a known capacitance, which is in particular independent of whether the sensor electrode is touched. First, it is assumed that the matching capacitor is removed from the parallel circuit with the reference capacitor. If, during the charging phase, the sensor electrode is connected to the first electrical reference potential via the at least one first potential connection terminal, and the first connection terminal of the reference capacitor is connected to the second electrical reference potential via the at least one second potential connection terminal, for example, the reference capacitor can be charged to the reference voltage, and the effective capacitor formed by the sensor electrode with respect to ground can be brought to 0 volts, or vice versa, depending on the interconnection of the second connection terminal of the reference capacitor. If, during the charge redistribution phase, the sensor electrode is subsequently switched to the high impedance state, and the first connection terminal of the reference capacitor is connected to the input terminal of the AD converter (which also corresponds to the high impedance state), the charge is distributed according to the current capacitance of the effective capacitor of the sensor electrode and the known capacitance of the reference capacitor. The voltage established across the reference capacitor accordingly (which can be read or measured by the AD converter, in particular by the evaluation unit of the sensor device) indirectly reflects the capacitance of the effective capacitor of the sensor electrode, and thus whether the sensor electrode is touched or approached by the user.

[0017] This capacitance detection method is particularly the so-called capacitance divider method, also known as the CVD method. The sensor electrode forms a capacitance to ground with the surrounding environment, and this capacitance increases when a user approaches or touches the sensor electrode. This capacitance change is reflected in the changing equilibrium potential, and thus the approach or touch action can be detected accordingly.

[0018] If the matching capacitor is removed from the parallel circuit, for example, it is isolated from the ground and thus switched to zero potential. This means that it has no electrical influence on the reference capacitor and is thus effectively removed. In any case, when the matching capacitor is removed from the parallel circuit, it does not affect the voltage available at the input of the AD converter, and during the charge redistribution phase, no charge flows from the effective capacitor of the sensor electrode to the matching capacitor, especially during the charging phase, and the matching capacitor is not charged either.

[0019] On the other hand, if the matching capacitor is connected to the parallel circuit with the reference capacitor, especially during the charging phase, the charge redistribution phase, and the measurement by the analog-to-digital converter, the total capacitance related to the readout voltage corresponds to the sum of the capacitances of the matching capacitor and the reference capacitor. Therefore, the sensor device according to the present invention can use only the capacitance of the reference capacitor according to the measurement mode, or use the sum of the capacitances of the matching capacitor and the reference capacitor. Thus, if necessary, the measurement range within which it is reliably detected that the sensor electrode is touched or approached can be increased, for example, to adapt it to the size and / or other physical characteristics of the sensor electrode. In addition, by specifically connecting the matching capacitor to the parallel circuit with the reference capacitor or removing it from this parallel circuit, the capacitance change of the effective capacitor of the sensor electrode caused by changes in environmental conditions, especially changes in ambient temperature and / or ambient humidity, can also be compensated.

[0020] In addition, the sensor device according to the present invention can be used to verify the reasonableness of the measurement result by performing two or more measurements on different states of the matching capacitor, that is, especially by performing measurements when the matching capacitor is connected to the parallel circuit and when the matching capacitor is removed from the parallel circuit. For example, the capacitance of the effective capacitor of the sensor electrode can be determined respectively when the matching capacitor is connected to the parallel circuit and when the matching capacitor is removed from the parallel circuit under the same environmental conditions. In both cases, within the measurement accuracy range, the capacitance value of the effective capacitor of the sensor electrode should be the same.

[0021] According to at least one embodiment of the sensor device, the sensor device has at least one control unit configured to control a first, a second, and a third switching element. For example, the control unit of the sensor device is configured to control the first, the second, and the third switching element. Alternatively, the control unit of the sensor device is configured to control the first and the second switching element, and another control unit of the sensor device is configured to control the third switching element.

[0022] According to at least one embodiment, the at least one control unit is configured to, during a charging phase, link a sensor electrode to the at least one first potential connection terminal by controlling the first switching element and link a first connection terminal of a reference capacitor to the at least one second potential connection terminal by controlling the second switching element.

[0023] This can in particular be understood as the at least one control unit being configured to control the first and the second switching element such that at the start of the charging phase, the sensor electrode is linked to the at least one first potential connection terminal and remains connected during the entire charging phase, and the first connection terminal of the reference capacitor, in particular while the sensor electrode is linked to the at least one first potential connection terminal, is linked to the at least one second potential connection terminal and remains connected during the entire charging phase.

[0024] In a first interconnection example, the first reference potential P1 corresponds to the ground potential, i.e., 0 V, and the second reference potential P2 corresponds to a positive potential, for example 5 V. The second connection terminal of the reference capacitor is in particular linked to the at least one first potential connection terminal. In a second interconnection example, the second reference potential P2 corresponds to the ground potential, i.e., 0 V, and the first reference potential P1 corresponds to a positive potential, for example 5 V. The second connection terminal of the reference capacitor is in particular linked to the at least one second potential connection terminal. However, the following explanations can be applied analogously to any other example.

[0025] In the first interconnection example, during the charging phase, the sensor electrode is not charged or discharged relative to the ground, or is charged to 0 V, and the reference capacitor is charged to a voltage U = P1, for example 5 V. If a matching capacitor is connected in parallel with the reference capacitor during the charging phase, it is also charged to the voltage U. In the second interconnection example, during the charging phase, the reference capacitor is not charged or discharged, or is charged to 0 V, and the sensor electrode is charged to a voltage U' = P1, for example 5 V, relative to the ground. If a matching capacitor is connected in parallel with the reference capacitor during the charging phase, it is also discharged or charged to 0 V.

[0026] According to at least one embodiment, the at least one control unit is configured to switch the sensor electrode to a high-impedance state by controlling the first switching element and to link the first connection terminal of the reference capacitor to the input of the AD converter by controlling the second switching element, particularly during a charge redistribution phase immediately following a charging phase.

[0027] This can be understood in particular as the at least one control unit being configured to control the first and second switching elements such that at the start of the charge redistribution phase, the sensor electrode is switched to the high-impedance state and remains in the switched state during the entire charge redistribution phase, and the first connection terminal of the reference capacitor, particularly simultaneously with the sensor electrode being switched to the high-impedance state, is linked to the input of the AD converter and remains linked during the entire charge redistribution phase.

[0028] According to at least one embodiment, the at least one control unit is configured to connect the matching capacitor to a parallel circuit with the reference capacitor or to remove it from the parallel circuit by controlling the third switching element during the charging phase and during the charge redistribution phase according to a predefined measurement pattern.

[0029] First, it is assumed that according to a first measurement pattern, particularly during the charging phase and the charge redistribution phase, the matching capacitor is connected in parallel with the reference capacitor. During the charge redistribution phase, the charge stored on the sensor electrode and / or on the parallel circuit including the reference capacitor and the matching capacitor is redistributed via the resistive component according to the respective capacitances of the effective capacitances of the reference capacitor, the matching capacitor, or the sensor electrode with respect to ground. Then, a voltage is generated across the parallel circuit, which depends both on whether the sensor electrode is touched or approached and on the sum of the capacitances of the reference capacitor and the matching capacitor. Then, this voltage can be measured by the AD converter, particularly in a readout phase after the charge redistribution phase, by an analog-to-digital converter.

[0030] On the other hand, if according to a second measurement pattern, particularly during the charging phase and the charge redistribution phase, the matching capacitor is removed from the parallel circuit with the reference capacitor, then during the charge redistribution phase, the charge stored on the sensor electrode and / or on the reference capacitor is redistributed via the resistive component according to the respective capacitances of the effective capacitances of the reference capacitor or the sensor electrode with respect to ground. Then, a voltage is generated across the parallel circuit, which depends both on whether the sensor electrode is touched or approached and on the capacitance of the reference capacitor, but is independent of the capacitance of the matching capacitor. Then, this voltage can be measured by the AD converter, particularly in the readout phase, by an analog-to-digital converter.

[0031] According to at least one embodiment, the second connection terminal of the reference capacitor is linked to the at least one first potential connection terminal. The first connection terminal of the matching capacitor can be linked to the at least one first potential connection terminal via a third switching element or can be switched to a high impedance state. The second connection terminal of the matching capacitor is linked to the first connection terminal of the reference capacitor.

[0032] Therefore, by linking the first connection terminal of the matching capacitor to the at least one first potential connection terminal, it can be made to be in parallel with the reference capacitor; and by switching its first connection terminal to a high impedance state, it can be removed from the parallel circuit.

[0033] For example, this is the case in the above first interconnection example. In particular, in such an embodiment, the first reference potential corresponds to the ground potential, in particular 0V, while the second reference potential is non-zero, for example positive, for example 5V relative to the ground.

[0034] According to at least one embodiment, the second connection terminal of the reference capacitor is linked to the at least one second potential connection terminal. The first connection terminal of the matching capacitor can be linked to the at least one second potential connection terminal via a third switching element of the sensor device or can be switched to a high impedance state. The second connection terminal of the matching capacitor is linked to the first connection terminal of the reference capacitor.

[0035] Therefore, by linking the first connection terminal of the matching capacitor to the at least one second potential connection terminal, it can be made to be in parallel with the reference capacitor; by switching its first connection terminal to a high impedance state, it can be removed from the parallel circuit.

[0036] For example, this is the case in the above second interconnection example. In particular, in such an embodiment, the second reference potential corresponds to the ground potential, in particular 0V, while the first reference potential is non-zero, for example positive, for example 5V relative to the ground.

[0037] In such an embodiment, touching or approaching the sensor electrode during the charge redistribution phase and during the charging phase affects the voltage established across the reference capacitor during the charge redistribution phase.

[0038] According to at least one embodiment, the capacitance of the reference capacitor is greater than the capacitance of the matching capacitor, in particular at least twice the capacitance of the matching capacitor, for example at least three times the capacitance of the matching capacitor.

[0039] For example, the capacitance of the reference capacitor is in the range of [2*C A , 8*C A , where C A represents the capacitance of the matching capacitor.

[0040] According to at least one embodiment, the sensor electrode has a first connection terminal linked to a first switching element.

[0041] For example, the sensor electrode has no other connection terminals. Then, the resistance component is arranged specifically between the first connection terminal of the sensor electrode and the first connection terminal of the reference capacitor.

[0042] According to at least one embodiment, the sensor electrode has a first connection terminal that can be linked to the at least one first potential connection terminal or switched to a high impedance state via a first switching element. The sensor electrode has a second connection terminal that is linked to the first connection terminal of the reference capacitor via a resistance component.

[0043] Such embodiments allow for a functional check of the sensor electrode. For this purpose, during a test phase, for example, a defined potential curve can be applied to one of the two connection terminals of the sensor electrode, and the potential curve generated at the other connection terminal of the sensor electrode can be measured using an AD converter, for example. For example, a damaged condition of the sensor electrode can be identified.

[0044] According to at least one embodiment, the sensor device has another sensor electrode that is designed and arranged to be touchable by a user and can be linked to the at least one first potential connection terminal or switched to a high impedance state via another first switching element of the sensor device. The sensor device has another resistance component for linking the another sensor electrode to the first connection terminal of the reference capacitor.

[0045] The explanations regarding the sensor electrode, the first switching element, and the resistance component can be similarly applied to the another sensor electrode, the another first switching element, and the another resistance component. Thus, in such an embodiment, only one analog-to-digital converter can be used to perform touch or proximity detection on both the sensor electrode and the another sensor electrode. Nor is another reference capacitor and / or matching capacitor required.

[0046] Depending on the design of the capacitance and resistance, it is possible to check the touch or proximity of both the sensor electrode and the another sensor electrode with just one measurement. Alternatively, the sensor electrode and the another sensor electrode can also be checked alternately.

[0047] According to at least one embodiment, the sensor device has a microcontroller that includes an analog-to-digital converter, a first switching element, and a second switching element. The sensor electrode and the reference capacitor are arranged outside the microcontroller, that is, they are not part of the microcontroller. The sensor electrode is linked to a first contact of the microcontroller, where the first contact is linked to the first switching element. The first connection terminal of the reference capacitor is linked to a second contact of the microcontroller, where the second contact is linked to the second switching element.

[0048] The first contact and / or the second contact, which may also be referred to as the corresponding contact pins, may be, for example, general-purpose input / output (GPIO) pins of a microcontroller. In particular, the first contact and the second contact may be located on the same port of the microcontroller.

[0049] The microcontroller is typically (and preferably in this case) configured such that the contacts of the microcontroller, in particular the GPIO pins, can be switched to a first or a second different output state, where in this case, the first output state corresponds to being linked to a first electrical reference potential, and the second output state corresponds to being linked to a second electrical reference potential. In other words, in the first output state, the first electrical reference potential can be output at the corresponding contact; or, in the second output state, the second electrical reference potential can be output. In addition, the contacts of the microcontroller, in particular the GPIO pins, can be switched to an input state corresponding to a high-impedance state. For this purpose, for example, the corresponding contact can be disconnected, or it can be linked to a component with a high resistance, such as the input of an AD converter.

[0050] For example, during the charging phase, the first contact can be switched to the first output state to link the sensor electrode to the first electrical reference potential. For example, during the charging phase, the second contact can be switched to the second output state to link the first connection terminal of the reference capacitor to the second electrical reference potential. For example, during the charge redistribution phase, the first contact can be switched to the input state to switch the sensor electrode to the high-impedance state. For example, during the charge redistribution phase, the second contact can be switched to the input state to link the first connection terminal of the reference capacitor to the input of the AD converter.

[0051] According to at least one embodiment, the microcontroller includes a third switching element and at least one control unit.

[0052] In an alternative embodiment, the at least one control unit includes a control unit for controlling the first and second switching elements and another control unit for controlling the third switching element. The control unit is part of the microcontroller, and the other control unit and the third switching element are provided outside the microcontroller.

[0053] For example, this may be advantageous for the functional safety of the entire sensor device.

[0054] According to at least one embodiment, a matching capacitor is provided outside the microcontroller, and the microcontroller includes a third switching element. The matching capacitor (in particular, the first connection terminal of the matching capacitor) is linked to the third contact (in particular, a general-purpose input / output (GPIO) pin) of the microcontroller, where the third contact is linked to the third switching element.

[0055] In an alternative embodiment, the microcontroller includes a matching capacitor and a third switching element. For example, the matching capacitor may correspond to a sample-and-hold capacitor of an analog-to-digital converter or another analog-to-digital converter of the microcontroller. This makes it possible to dispense with an additional component as the matching capacitor.

[0056] According to another aspect of the present invention, there is provided an input device for a motor vehicle for capturing user input. The input device has a sensor device according to the present invention.

[0057] In particular, the input device may have a processing unit that is capable of detecting a user input as a touch on or proximity to a sensor electrode based on a voltage determined by an analog-to-digital converter during a readout phase.

[0058] According to another aspect of the present invention, there is provided a hand detection device for a motor vehicle steering wheel. The hand detection device has a sensor device according to the present invention.

[0059] The sensor electrode may in particular be arranged on the motor vehicle steering wheel such that it can be inferred from a touch on the sensor electrode that the user's hand is placed on the motor vehicle steering wheel.

[0060] Furthermore, according to other aspects of the present invention, there is provided a motor vehicle steering wheel having a hand detection device according to the present invention, and a motor vehicle having an input device according to the present invention and / or a motor vehicle steering wheel according to the present invention.

[0061] According to another aspect of the present invention, there is provided a method for capacitive touch detection, in particular implemented by a sensor device according to the present invention. During a charging phase, a sensor electrode designed to be touched by a user is connected to a first electrical reference potential. A first connection terminal of a reference capacitor (wherein the first connection terminal is connected to the sensor electrode via a resistive component) is connected to a second electrical reference potential during the charging phase. During a charge redistribution phase after the charging phase, the sensor electrode is switched to a high impedance state, and the first connection terminal of the reference capacitor is connected to an input terminal of an analog-to-digital converter during the charge redistribution phase. During a readout phase after the charge redistribution phase, the voltage of the reference capacitor is measured by the analog-to-digital converter, i.e., the voltage applied between the first connection terminal and the second connection terminal of the reference capacitor. During the charging phase and the charge redistribution phase, based on a predefined measurement pattern, a matching capacitor is connected in parallel with the reference capacitor or removed from the parallel circuit.

[0062] According to at least one embodiment, in particular by a processing unit, a touch of the user on the sensor electrode or the proximity of a body part of the user (in particular a finger or a hand) to the sensor electrode is detected based on the measured voltage.

[0063] For application scenarios or situations that may result from this method and are not explicitly described herein, according to this method, it is possible to provide an output error message and / or request user feedback as input, and / or set default settings and / or a predetermined initial state.

[0064] Further embodiments of the method according to the invention can be directly derived from the various configurations of the sensor device according to the invention, the input device according to the invention, and the hand detection device according to the invention, and vice versa. In particular, the individual features of the various embodiments of the sensor device according to the invention, the input device according to the invention, and the hand detection device according to the invention, as well as the corresponding explanations and advantages, can be applied in a similar manner to the corresponding embodiments of the method according to the invention. In particular, the sensor device according to the invention is designed or programmed to execute the method according to the invention. In particular, the sensor device according to the invention executes the method according to the invention.

[0065] Other features of the present invention can be derived from the claims, the drawings, and the description of the drawings. The features and combinations of features mentioned in the above description, as well as those mentioned in the following description of the drawings and / or shown in the drawings, can be included in the present invention not only in the respective specified combinations, but also in other combinations. In particular, embodiments and combinations of features of all the features of the claims without the original wording can also be included in the present invention. In addition, embodiments and combinations of features that go beyond or are different from the combinations of features listed in the reference relationships of the claims can also be included in the present invention.

[0066] The present invention will be described in more detail below based on specific exemplary embodiments and related schematic drawings. In the drawings, identical or functionally identical elements can be denoted by the same reference numerals. Regarding different drawings, the description of identical or functionally identical elements will not necessarily be repeated.

[0067] In the drawings:

[0068] Figure 1 A schematic block diagram of an exemplary embodiment of the sensor device according to the invention is shown;

[0069] Figure 2 A schematic view of a motor vehicle according to the invention is shown;

[0070] Figure 3 A schematic block diagram of another exemplary embodiment of the sensor device according to the invention is shown;

[0071] Figure 4 A schematic block diagram of another exemplary embodiment of the sensor device according to the invention is shown;

[0072] Figure 5Shows a schematic block diagram of another exemplary embodiment of a sensor device according to the present invention;

[0073] Figure 6 Illustrates a schematic block diagram of another exemplary embodiment of a sensor device according to the present invention; and

[0074] Figure 7 Illustrates a schematic block diagram of another exemplary embodiment of a sensor device according to the present invention.

[0075] Figure 1 Illustrates a schematic block diagram of an exemplary embodiment of a sensor device 1 for capacitive touch detection according to the present invention. The sensor device 1 has an AD converter 9 and sensor electrodes 6 designed to be touchable by a user. The sensor device 1 has at least one first potential connection terminal 14, which is respectively connected to a first electrical reference potential, such as a ground potential, which, by definition, corresponds to a voltage of 0V, for example. The sensor device 1 has at least one second potential connection terminal 15, which is respectively connected to a second electrical reference potential, such as a potential different from the ground potential, which, by definition, corresponds to a positive supply voltage U, for example. According to the design of the sensor device 1, the supply voltage can be, for example, 5V with respect to the ground potential.

[0076] For example, the input terminal 17 of the AD converter 9 corresponds to a high-impedance connection. The sensor device 1 can have one or more other high-impedance connection terminals 16, 19, which can be, for example, floating connection terminals, such that the corresponding link thus corresponds to an open circuit. Alternatively, the high-impedance connection terminals 16, 19 can be linked to a high resistance (not shown), such that practically no relevant current flows via the high-impedance connection terminals 16, 19. Alternatively, the high-impedance connection terminals 16, 19 can be linked to the input terminal 17 of the AD converter 9.

[0077] The sensor electrode 6 can be connected to one of the first potential connection terminals 14 or the high-impedance connection terminal 16 through a first switching element 20 of the sensor device 1. The sensor device 1 also has a reference capacitor 7, which has a first connection terminal that can be connected to one of the second potential connection terminals 15 or the input 17 of the analog-to-digital converter 9 through a second switching element 21 of the sensor device 1. The second connection terminal of the reference capacitor is linked to one of the first potential connection terminals 14. A resistor assembly 12 is arranged between the sensor electrode 6 and the first connection terminal of the reference capacitor 7, such that the first switching element 20 is connected between the sensor electrode 6 and the resistor assembly 12. For example, another resistor assembly 11 is arranged between the sensor electrode 6 and the resistor assembly 12, such that the first switching element 20 is connected between the resistor assembly 11 and the resistor assembly 12. For electrostatic discharge (ESD) protection, a varistor 13 can be optionally provided between the sensor electrode 6 and the ground.

[0078] The capacitance of the effective capacitor formed by the sensor electrode 6 with respect to ground depends on whether the user touches the sensor electrode 6 or the proximity of the user's body part (such as a finger or a hand) to the sensor electrode 6. This capacitance may also be affected by environmental conditions (such as humidity or ambient temperature).

[0079] The sensor device 1 also has a matching capacitor 8, which can be connected to a parallel circuit with the reference capacitor 7 through the third switching element 22 of the sensor device 1 or removed from this parallel circuit. For this purpose, the first connection end of the matching capacitor 8 can be linked to one of the first potential connection ends 14 and the high-impedance connection end 19 through the third switching element 22, for example. As described above, the high-impedance connection end 19 can be linked to the input end 17 of the AD converter 9 or corresponding thereto. The second connection end of the matching capacitor 8 is linked to the first input end of the reference capacitor 7, that is to say, like the first input end of the reference capacitor 7, in each case it is linked to one of the second potential connection ends 15 or the input end 17 of the analog-to-digital converter 9 through the second switching element 21. Therefore, when the first connection end of the matching capacitor 8 is linked to the corresponding first potential connection end 14, the matching capacitor 8 is connected in parallel with the reference capacitor 7; and when the connection end of the matching capacitor 8 is linked to the high-impedance connection end 19, the matching capacitor 8 is removed from the parallel circuit.

[0080] The switching elements 20, 21, 22 can be in the form of transistors, in particular field-effect transistors, which can be controlled, that is, switched, by at least one control unit (not shown) of the sensor device 1.

[0081] The method for capacitive touch detection according to the present invention can be implemented by using the sensor device 1. For this purpose, the matching capacitor 8 is either permanently connected in parallel with the reference capacitor 7 during the charging phase and the subsequent charge redistribution phase according to a predefined measurement mode, or permanently removed from the parallel circuit during the charging phase and the charge redistribution phase as described above.

[0082] During the charging phase, the sensor electrode 6 is linked to the first potential connection end 14, for example, and the first connection end of the reference capacitor 7 is linked to the second potential connection end. Therefore, the voltage across the effective capacitor formed by the sensor electrode 6 with respect to ground is 0V, and the voltage across the reference capacitor 7 is the supply voltage U. If the matching capacitor 8 is connected in parallel with the reference capacitor 7, the supply voltage U is also established across the matching capacitor 8. The duration of the charging phase can be adjusted accordingly especially according to the existing capacitance and resistance.

[0083] After the charging phase has ended, the charge redistribution phase is initiated by switching the first and second switching elements 20, 21 (in particular simultaneously), so as to link the sensor electrode 6 to the high-impedance connection terminal 16 and to link the first connection terminal of the reference capacitor 7 to the input terminal 17 of the analog-to-digital converter 9. As already mentioned, in this case, the third switching element 22 is not switched, and thus the matching capacitor 8 remains connected in parallel with the reference capacitor 7 or remains removed from the parallel circuit, depending on the measurement mode.

[0084] Accordingly, during the charge redistribution phase, charge flows out of the reference capacitor 7 and, if the matching capacitor 8 is connected in parallel with the reference capacitor 7, flows to the sensor electrode 6. Correspondingly, a voltage is established across the reference capacitor 7, which depends on the ratio of the capacitance of the effective capacitor of the sensor electrode 6 to the sum of the capacitances of the reference capacitor 7 and the matching capacitor 8 (if the matching capacitor 8 is connected in parallel with the reference capacitor 7), or else on the ratio of the capacitance of the effective capacitor of the sensor electrode 6 to the capacitance of the reference capacitor 7. Accordingly, this voltage also appears at the input terminal 17 of the AD converter. The duration of the charge redistribution phase can be adjusted, in particular, according to the capacitances and resistances present, such that the charge redistribution is completed or substantially completed at the end of the charge redistribution phase.

[0085] In the readout phase following the charge redistribution phase, the voltage at the input terminal 17 of the analog-to-digital converter 9 can then be measured by the AD converter. The sensor device 1 can, for example, have an evaluation unit 10, which is linked to the output terminal 18 of the analog-to-digital converter and is configured to detect a touch of the sensor electrode 6 by a user or the approach of a body part to the sensor electrode 6 based on the measured voltage. For example, the measured voltage can be compared with one or more predefined thresholds. For example, if the user touches the sensor electrode 6, in particular during the charge redistribution phase, the capacitance of the effective capacitor of the sensor electrode 6 relative to ground is greater than when the user is not touching, since the touch acts as an additional parallel capacitance.

[0086] In addition, as described above, the measured voltage also depends on whether the matching capacitor 8 is connected in parallel with the reference capacitor 7 during the charging phase and the charge redistribution phase (i.e., the measurement mode). This can be advantageously utilized in various ways. For example, by selecting the measurement mode, the measurement range enabling reliable touch detection can be adapted to the size of the sensor electrode 6 and / or the material properties of the sensor electrode 6 and / or the geometric design of the sensor electrode 6, so that the sensor device 1 can be flexibly used for different sensor electrodes 6 and applications. In addition, by selecting the measurement mode, the influence of environmental conditions (especially the ambient temperature) on the capacitance of the effective capacitor of the sensor electrode 6 can be at least partially compensated, because the capacitances of the reference capacitor 7 and the matching capacitor 8 are generally much less affected by environmental conditions than the capacitance of the effective capacitor of the sensor electrode 6.

[0087] A plausibility check of the measured voltage can also be performed by purposefully using two different measurement modes. When the state of the sensor electrode 6 remains unchanged with respect to the touch or proximity of a user or other conductive object, and the environmental conditions remain unchanged, the capacitance of the effective capacitor of the sensor electrode 6 also remains unchanged. Therefore, the measured voltage expected in each measurement mode, or the ratio between them, can be calculated or estimated within the measurement accuracy range. For example, if a significant deviation occurs, a malfunction or defect of the sensor device can be inferred.

[0088] Figure 2 A motor vehicle 5 having an exemplary embodiment of the sensor device 1 according to the present invention is schematically shown, as described in connection with Figure 1 in particular. The sensor device 1 can be, for example, part of an input device 2 for capturing user input according to the present invention. The sensor device 1 can also be part of a hand detection device 3 for a motor vehicle steering wheel 4 according to the present invention. In this case, the sensor electrode 6 is particularly attached to the motor vehicle steering wheel 4 of the motor vehicle 5.

[0089] Figures 3 to 7 Other exemplary embodiments of the sensor device 1 for capacitive touch detection according to the present invention are shown, which are based on Figure 1 the embodiments. For the sake of clarity, the various components of the sensor device 1 (such as the switching elements 20, 21, 22, the analog-to-digital converter 9, and the evaluation unit 10) are not shown in Figures 3 to 7 In the Figures 3 to 7 embodiment, the sensor device 1 has a microcontroller 23 including an analog-to-digital converter 9, a first switching element 20, and a second switching element 21. The evaluation unit 10 can also be part of the microcontroller 23 or be provided separately from the microcontroller 23. The microcontroller 23 further includes a control unit for controlling the first switching element 20 and the second switching element 21.

[0090] The microcontroller 23 has a first contact 24, which is specifically designed as a GPIO pin and is linked to the first switching element 20. The sensor electrode 6 is correspondingly linked to the first contact 24. The microcontroller 23 has a second contact 25 (which is switchable or specifically designed as a GPIO pin) and / or an analog-to-digital converter, and the second contact 25 is linked to the second switching element 21. The first connection end of the reference capacitor 7 and the second connection end of the matching capacitor 8 are correspondingly linked to the second contact 24.

[0091] The microcontroller 23 may further include a third switching element 22 and a third contact 26, which is specifically designed as a general-purpose input / output (GPIO) pin and is linked to the third switching element 22. The first connection end of the matching capacitor 8 is correspondingly linked to the third contact 26. In this case, the control unit can also control the third switching element 22. In an alternative embodiment, the matching capacitor 8 can also be integrated in the microcontroller 23. Even so, the control unit can still control the third switching element 22.

[0092] In yet another alternative embodiment, both the third switching element 22 and the matching capacitor 8 can be arranged outside the microcontroller 23. In this case, for example, the sensor device 1 has another control unit arranged outside the microcontroller 23 to control the third switching element 22. In terms of functional safety, this may be advantageous.

[0093] In a design example, the nominal resistances of the resistance components 11, 12 can be, for example, 4.7 kΩ respectively, the nominal capacitance of the reference capacitor 7 can be, for example, 10 pF, and the nominal capacitance of the matching capacitor 8 can be, for example, 2 pF.

[0094] For example, in Figure 3 the illustrated embodiment, the sensor electrode 6 has only one first connection end. Therefore, this configuration can also be referred to as a single-ended configuration. On the other hand, in Figure 4 the illustrated embodiment, the sensor electrode has a first connection end and a second connection end. Therefore, this configuration can also be referred to as a differential configuration. For example, in Figure 4 the illustrated embodiment, the resistance components 11, 12 are replaced by a resistance component 28 between the first connection end of the sensor electrode and the first contact 24 or the first switching element 20 and a resistance component 27 between the second connection end of the sensor electrode 6 and the first connection end of the reference capacitor 7.

[0095] In a design example, the nominal resistance of the resistance component 27 can be, for example, 10 kΩ, the nominal resistance of the resistance component 28 can be, for example, 1 kΩ, the nominal capacitance of the reference capacitor 7 can be, for example, 10 pF, and the nominal capacitance of the matching capacitor 8 can be, for example, 2 pF.

[0096] Figure 5 The illustrated embodiment is based on Figure 3 the illustrated embodiment. Here, the sensor device 1 also has another sensor electrode 6' with a corresponding optional varistor 13'. This another sensor electrode 6' is linked to another first contact 24' of the microcontroller 23, such as a GPIO pin. This another first contact 24' is linked to another first switching element (not shown) of the microcontroller 23, through which this another sensor electrode 6' can be linked to one of the first potential connection terminal 14 and the high-impedance connection terminal 16, or linked to another high impedance connection. Additional resistor components 11', 12' are provided, which are similar to the resistor components 11, 12 for the sensor electrode 6, to connect this another sensor electrode 6' to the first connection end of the reference capacitor 7 and the second contact 25 of the microcontroller 23. As described for the sensor electrode 6, it is thus possible to detect whether this another sensor electrode 6' is touched without the need for another AD converter, another reference capacitor or another matching capacitor.

[0097] Figure 6 The illustrated embodiment is based on Figure 4 the illustrated embodiment, wherein, as with Figure 5 the illustrated embodiment, another sensor electrode 6' is also provided. In Figure 6 the illustrated embodiment, both sensor electrodes 6, 6' are designed and interconnected according to the differential variant. Accordingly, additional resistor components 27', 28' are provided for this another sensor electrode, similar to the resistor components 27, 28.

[0098] Figure 7 The illustrated embodiment is based on Figure 3 the illustrated embodiment and is provided with another sensor electrode 6'. However, in this embodiment, another reference capacitor 7', another matching capacitor 8' and additional resistor components 11', 12' are provided, as well as additional contacts 24', 25' of the microcontroller 23, another first switching element and another second switching element (not shown). Figure 1 and Figure 3 the descriptions regarding the reference capacitor 7, the matching capacitor 8, the resistor components 11, 12, the contacts 24, 25, the first switching element and the second switching element can be similarly applied to this another reference capacitor 7', this another matching capacitor 8', the resistor components 11', 12', the contacts 24', 25', this another first switching element and another second switching element.

[0099] However, the first connection end of this another matching capacitor 8' is linked to the third contact 26 of the microcontroller 23 in the same way as the first connection end of the matching capacitor 8, so that this contact can be advantageously utilized twice.

[0100] Specifically described in conjunction with the accompanying drawings, when the capacitance measurement principle is adopted for a large measurement range or different measurement ranges, the present invention can improve the reliability of touch detection.

[0101] In particular, the present invention allows for a flexible selection of the reference capacitance, which can correspond to the capacitance of the reference capacitor according to the measurement mode, or the sum of the capacitance of the reference capacitor and the matching capacitor. It can also be extended by one or more additional matching capacitors, and each additional matching capacitor can be added to or removed from the parallel circuit according to the measurement mode.

[0102] For some applications (such as hand detection on a motor vehicle steering wheel), the measurement range may be very small (for example, at low temperature, low humidity, and / or when the user's hand is not on the steering wheel), but it may also be very large (for example, at high temperature, high humidity, and / or when the hand covers the steering wheel to the maximum extent). In each case, the present invention can achieve high measurement resolution by making the measured capacitance and the reference capacitance as close as possible or the same.

[0103] The present invention can improve the quality of the measurement signal. A sanity check can also be performed to check the entire measurement chain. Although the change in the reference capacitance will result in different measurement values, a transfer function or a look-up table can be used to perform a sanity or consistency check on the measurement values of the measurement with the matching capacitor connected and the matching capacitor not connected, which improves the error detection ability of the entire measurement and evaluation chain.

Claims

1. A sensor device (1) for capacitive touch detection, the sensor device (1) having: At least one first potential connection terminal (14, 15) and at least one second potential connection terminal (14, 15), the at least one first potential connection terminal (14, 15) being for connecting the sensor device (1) to a first electrical reference potential respectively, and the at least one second potential connection terminal (14, 15) being for connecting the sensor device (1) to a second electrical reference potential respectively; An analog-to-digital converter (9) and sensor electrodes (6), the sensor electrodes (6) being designed to be touched by a user and being linkable to the at least one first potential connection terminal (14, 15) or switchable to a high impedance state through a first switching element (20) of the sensor device (1); - A reference capacitor (7, 7') having a first connection terminal, the first connection terminal being linkable to the at least one second potential connection terminal (14, 15) or the input terminal (17) of the analog-to-digital converter (9) through a second switching element (21) of the sensor device (1); and A resistor assembly (12, 27) for linking the sensor electrodes (6) to the first connection terminal of the reference capacitor (7, 7'); Characterized in that The sensor device (1) has a matching capacitor (8, 8'), the matching capacitor being connectable to a parallel circuit with the reference capacitor (7, 7') or removable from the parallel circuit through a third switching element (22) of the sensor device (1).

2. The sensor device (1) according to claim 1, Characterized in that The sensor device (1) has at least one control unit, the at least one control unit being configured to, during a charging phase, link the sensor electrodes (6) to the at least one first potential connection terminal (14, 15) by controlling the first switching element (20), and link the first connection terminal of the reference capacitor (7, 7') to the at least one second potential connection terminal (14, 15) by controlling the second switching element (21).

3. The sensor device (1) according to claim 2, Characterized in that The at least one control unit is configured to, during a charge redistribution phase after the charging phase, switch the sensor electrodes (6) to the high impedance state by controlling the first switching element (20), and link the first connection terminal of the reference capacitor (7, 7') to the input terminal (17) of the analog-to-digital converter (9) by controlling the second switching element (21).

4. The sensor device (1) according to claim 3, Characterized in that The at least one control unit is configured to, during the charging phase and the charge redistribution phase, connect the matching capacitor (8, 8') to the parallel circuit with the reference capacitor (7, 7') or remove it from the parallel circuit by controlling the third switching element (22) based on a predefined measurement pattern.

5. The sensor device (1) according to any one of the preceding claims, characterized in that - the second connection end of the reference capacitor (7, 7') is linked to the at least one first potential connection end (14, 15), and the first connection end of the matching capacitor (8, 8') can be linked to the at least one first potential connection end (14, 15) or switched to a high-impedance state through the third switching element (22) of the sensor device (1), and the second connection end of the matching capacitor (8, 8') is linked to the first connection end of the reference capacitor (7, 7'); or - the second connection end of the reference capacitor (7, 7') is linked to the at least one second potential connection end (14, 15), and the first connection end of the matching capacitor (8, 8') can be linked to the at least one second potential connection end (14, 15) or switched to a high-impedance state through the third switching element (22) of the sensor device (1), and the second connection end of the matching capacitor (8, 8') is linked to the first connection end of the reference capacitor (7, 7').

6. The sensor device (1) according to any one of the preceding claims, characterized in that the capacitance of the reference capacitor (7, 7') is greater than the capacitance of the matching capacitor (8, 8'), in particular at least twice the capacitance of the matching capacitor (8, 8').

7. The sensor device (1) according to any one of the preceding claims, characterized in that - the sensor electrode (6) has a first connection end, which can be linked to the at least one first potential connection end (14, 15) or switched to a high-impedance state through the first switching element (20) of the sensor device (1); - the sensor electrode (6) has a second connection end, which is linked to the first connection end of the reference capacitor (7, 7') via the resistor assembly (27, 27').

8. The sensor device (1) according to any one of the preceding claims, characterized in that - the sensor device (1) has another sensor electrode (6'), which is designed to be touchable by a user, and the another sensor electrode (6') can be linked to the at least one first potential connection end (14, 15) or switched to a high-impedance state through another first switching element of the sensor device (1); and - another resistor assembly (12', 27'), which is used to link the another sensor electrode (6') to the first connection end of the reference capacitor (7, 7').

9. The sensor device (1) according to any one of the preceding claims, characterized in that - The sensor device (1) has a microcontroller (23), and the microcontroller (23) includes an analog-to-digital converter (9), the first switching element (20), and the second switching element (21), wherein the sensor electrode (6) and the reference capacitors (7, 7') are arranged outside the microcontroller (23); - The sensor electrode (6) is linked to the first contacts (24, 24') of the microcontroller (23), and the first contacts (24, 24') are linked to the first switching element (20); and - The first connection ends of the reference capacitors (7, 7') are linked to the second contacts (25, 25') of the microcontroller (23), and the second contacts (25, 25') are linked to the second switching element (21).

10. The sensor device (1) according to claim 9, characterized in that the first contacts (24, 24') and / or the second contacts (25, 25') are designed as general-purpose input / output (GPIO) pins of the microcontroller (23).

11. The sensor device (1) according to any one of claims 9 and 10, characterized in that - The matching capacitors (8, 8') are arranged outside the microcontroller (23), and the microcontroller (23) includes the third switching element (22); and - The matching capacitors (8, 8') are linked to the third contact (26) of the microcontroller (23), and the third contact (26) is linked to the third switching element (22).

12. An input device (2) for a motor vehicle (5) for capturing user input, the input device having a sensor device (1) according to any one of the preceding claims.

13. A hand detection device (3) for a motor vehicle steering wheel (4), having a sensor device (1) according to any one of claims 1 to 11.

14. A capacitive touch detection method, wherein - The sensor electrode (6) designed to be touched by a user is linked to a first electrical reference potential during a charging phase; - During the charging phase, the first connection end of the reference capacitor (7, 7') linked to the sensor electrode (6) via a resistance component (12, 27) is linked to a second electrical reference potential; - During a charge redistribution phase after the charging phase, the sensor electrode (6) is switched to a high-impedance state; - During the charge redistribution phase, the first connection end of the reference capacitor (7, 7') is linked to the input terminal (17) of the analog-to-digital converter (9); and - During a readout phase after the charge redistribution phase, the voltage of the reference capacitor (7, 7') is measured by the analog-to-digital converter (9); characterized in that - During the charging phase and the charge redistribution phase, based on a predefined measurement pattern, the matching capacitor (8, 8') is connected to a parallel circuit with the reference capacitor (7, 7'), or removed from the parallel circuit.

15. The method according to claim 14, characterized in that - based on the predefined measurement pattern, during the charging phase and the charge redistribution phase, a first connection end of the matching capacitor (8, 8') is linked to the first electrical reference potential or switched to a high impedance state, wherein a second connection end of the reference capacitor (7, 7') is linked to the first electrical reference potential; or - based on the predefined measurement pattern, during the charging phase and the charge redistribution phase, a first connection end of the matching capacitor (8, 8') is linked to a second electrical reference potential or switched to a high impedance state, wherein a second connection end of the reference capacitor (7, 7') is linked to the second electrical reference potential.

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