Sensor device

Abstract

To provide a sensor device with low power consumption.SOLUTION: A sensor device comprises: a sensor electrode operable as a heating element; an electrostatic detection circuit that detects a capacitance between the sensor electrode and an object; a high-side switch connected to a power supply that supplies electric power for heating to the sensor electrode; a decoupling switch; a low-side switch; a voltage supply circuit that supplies a voltage to a node between the decoupling switch and one end of the sensor electrode such that a voltage of the node is higher than a voltage of a reference potential point; an electronic element constituted by a resistor or a switch provided between a connection point of the high-side switch and the decoupling switch, and the reference potential point; and a control unit that controls the high-side switch, the decoupling switch, and the low-side switch. A source of the high-side switch and a source of the decoupling switch are connected to the connection point and are also connected to the reference potential point via the electronic element.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a sensor device. [Background technology]

[0002] Conventionally, there has been a sensor device including an electrode assembly having a heating element as a sensor electrode, a detection device that detects the capacitance of the sensor electrode, a high-side switch provided between a heating power supply and the heating element, a low-side switch provided between the heating element and a reference potential point, a gate controller that opens the high-side switch and the low-side switch in a detection mode, and a decoupling circuit having a decoupling MOSFET connected between the high-side switch and the heating element. The gate controller conducts the decoupling MOSFET in the heating mode and opens the decoupling MOSFET in the detection mode. In the detection mode, the decoupling circuit supplies a third potential to a first node connected between the high-side switch and the decoupling MOSFET. A potential different from the third potential is supplied to a node between the low-side switch and the heating element. The high-side switch is an N-channel MOSFET, the low-side switch is a P-channel MOSFET, and the decoupling circuit is an N-channel MOSFET (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2023 / 0046256 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, P-channel MOSFETs have a higher on-resistance and consume more power than N-channel MOSFETs.

[0005] Therefore, an object of the present invention is to provide a sensor device that consumes less power. [Means for solving the problem]

[0006] A sensor device according to an embodiment of the present disclosure includes a sensor electrode operable as a heating element, an electrostatic detection circuit that detects electrostatic capacitance between the sensor electrode and an object, a high-side switch connected to a power source that supplies heating power to the sensor electrode, a decoupling switch provided between the high-side switch and one end of the sensor electrode, a low-side switch provided between the other end of the sensor electrode and a reference potential point, a voltage supply circuit that supplies a voltage to the node between the decoupling switch and the one end of the sensor electrode so that the voltage of the node is higher than the voltage of the reference potential point, an electronic element configured of a resistor or a switch provided between the connection point of the high-side switch and the decoupling switch and the reference, and and a control unit that controls a high-side switch, the decoupling switch, and the low-side switch, wherein the voltage of the power supply is higher than the voltage of the reference potential point, the high-side switch, the decoupling switch, and the low-side switch are N-channel MOSFETs, the drain of the high-side switch is connected to the power supply, the drain of the decoupling switch is connected to the node, the drain of the low-side switch is connected to the other end of the sensor electrode, the source of the low-side switch is connected to the reference potential point, and the sources of the high-side switch and the decoupling switch are connected to the connection point and to the reference potential point via the electronic element. [Effects of the Invention]

[0007] A sensor device with low power consumption can be provided. [Brief explanation of the drawings]

[0008] [Figure 1]1 is a diagram schematically illustrating a steering wheel on which a sensor device according to an embodiment is mounted; [Figure 2] FIG. 2 is a diagram illustrating an example of a circuit configuration of a sensor device according to an embodiment. [Figure 3A] FIG. 10 is a diagram showing an example of the parasitic capacitance Coss between the drain and source of the high-side MOSFET, the low-side MOSFET, and the decoupling MOSFET in non-heating mode. [Figure 3B] FIG. 10 is a diagram showing an example of the parasitic capacitance Coss between the drain and source of the high-side MOSFET, the low-side MOSFET, and the decoupling MOSFET in non-heating mode. [Figure 4] FIG. 1 is a diagram showing an example of electrical characteristics of an N-channel MOSFET. [Figure 5] FIG. 10 is a diagram illustrating an example of a circuit configuration of a sensor device according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment to which the sensor device of the present disclosure is applied will be described.

[0010] <Embodiment> 1 is a diagram schematically illustrating a steering wheel 10 equipped with a sensor device 100 according to an embodiment. The sensor device 100 includes a sensor electrode 110, a heater driving circuit 120, an electrostatic detection circuit 130, and a control circuit 140. The control circuit 140 is an example of a control unit.

[0011] A steering wheel 10 is mounted on a vehicle, and a sensor electrode 110 of a sensor device 100 is mounted on the inside of the surface of the rim 11. The sensor electrode 110 can operate as a heating element. The sensor device 100 determines whether the driver's hand is in contact with the rim 11 of the steering wheel 10. The sensor device 100 also warms the steering wheel 10 by supplying heating power to the sensor electrode 110. In other words, the sensor device 100 has both the functions of HOD (Hands On Detect) and a steering heater. A hand is an example of an object. The rim 11 of the steering wheel 10 is an example of a fixed part to which the sensor electrode 110 is fixed. The surface 11A of the rim 11 is an example of a contact part that can be contacted by a detection object.

[0012] Hereinafter, the driver of the vehicle will be referred to as the operator of the sensor device 100. The operator's touching the rim 11 of the steering wheel 10 on which the sensor electrode 110 is provided will be referred to as the operator's operation.

[0013] The steering wheel 10 has a rim 11, a hub 12, and spokes 13. The rim 11, hub 12, and spokes 13 shown in FIG. 1 are core metal portions of the rim 11, hub 12, and spokes 13. In FIG. 1, the surface 11A of the rim 11 is shown separated from the rim 11 in order to show the sensor electrode 110. Also, in FIG. 1, covers that cover the hub 12 and spokes 13 are omitted.

[0014] The ground terminal of the steering wheel 10 is electrically connected to a core metal that is provided around the entire circumference of the rim 11 of the steering wheel 10. By connecting the core metal to the ground terminals of the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 via connectors (not shown), the ground potentials of the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 become equal to the ground potential of the steering wheel 10.

[0015] <Schematic configuration of sensor device 100> The sensor device 100 includes a sensor electrode 110, a heater driving circuit 120, an electrostatic detection circuit 130, and a control circuit 140. The control circuit 140 may be an ECU (Electronic Control Unit). Although Fig. 1 shows a simplified connection relationship between the sensor electrode 110, the heater driving circuit 120, the electrostatic detection circuit 130, and the control circuit 140, the control circuit 140 is also connected to the heater driving circuit 120 via a cable, a connector, etc. (not shown).

[0016] The sensor device 100 has two modes: a heating mode in which heating power is supplied from the vehicle's power supply to the sensor electrode 110, and a non-heating mode in which heating power is not supplied. The control circuit 140 switches the mode of the sensor device 100 in a time-division manner. That is, the control circuit 140 has times when it sets the sensor device 100 to the heating mode and times when it sets the sensor device 100 to the non-heating mode.

[0017] <Sensor electrode 110> The sensor electrode 110 is provided around the rim 11 of the steering wheel 10 while being insulated from a core metal that is provided around the rim 11 of the steering wheel 10. The sensor electrode 110 is connected to the heater drive circuit 120, the electrostatic detection circuit 130, and the control circuit 140 via signal lines and the like. The sensor electrode 110 is a thin, sheet-like, strip-shaped electrode that is provided around the rim 11, and can be produced, for example, by applying a conductor such as silver paste to the surface of a resin film.

[0018] <Heater driving circuit 120> The heater driving circuit 120 is connected to the sensor electrode 110, and supplies heating power to the sensor electrode 110 from the vehicle power supply in the heating mode.

[0019] <Static electricity detection circuit 130> The electrostatic detection circuit 130 is connected to the sensor electrode 110 and detects the electrostatic capacitance between the sensor electrode 110 and the operator's hand.

[0020] <Control circuit 140> The control circuit 140 is realized by a computer including a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), an input / output interface, an internal bus, etc. The control circuit 140 switches the mode of the sensor device 100 between a heating mode and a non-heating mode. In the heating mode, the control circuit 140 heats the sensor electrode 110 and warms the rim 11 of the steering wheel 10. In the non-heating mode, the control circuit 140 determines whether a hand is touching the rim 11 of the steering wheel 10 based on the output of the electrostatic detection circuit 130. Details of the control performed by the control circuit 140 in the non-heating mode and the heating mode will be described later.

[0021] <Circuit configuration of sensor device 100> Fig. 2 is a diagram showing an example of the circuit configuration of the sensor device 100. Fig. 2 also shows a power supply circuit 50 of the vehicle 1 on which the sensor device 100 is mounted. The power supply circuit 50 has a power supply 51 and a relay 52. ​​The power supply 51 is, for example, a battery of the vehicle 1. In Fig. 2, the power supply 51 is described as being a battery, but the power supply 51 may also include a generator, a regenerative device, or the like of the vehicle 1 in addition to the battery. The output voltage of the power supply 51 is V1.

[0022] The power supply circuit 50 includes a power supply 51 and a relay 52. ​​The relay 52 is inserted in series in a power supply path between the power supply 51 and the heater drive circuit 120. The relay 52 is controlled to open and close by, for example, a body ECU (not shown).

[0023] <Sensor electrode 110> The sensor electrode 110 is provided on the steering wheel 10 and connected to the heater drive circuit 120. More specifically, the sensor electrode 110 is a conductor having two ends as shown in FIG. 1 , and one end is connected to a node 125. The other end of the sensor electrode 110 is connected to the drain of the low-side MOSFET 122.

[0024] The parasitic capacitance between the sensor electrode 110 and the ground potential point is Crgl, and the parasitic capacitance between the sensor electrode 110 and the hand H is Chg. The parasitic capacitance Chg changes significantly depending on whether the hand H is in contact with the sensor electrode 110 or not.

[0025] <Heater driving circuit 120> The heater driving circuit 120 includes a high-side MOSFET 121, a low-side MOSFET 122, a decoupling MOSFET 123, a switching MOSFET 124, a node 125, and a voltage regulator 126. The high-side MOSFET 121 is an example of a high-side switch, the low-side MOSFET 122 is an example of a low-side switch, and the decoupling MOSFET 123 is an example of a decoupling switch. The switching MOSFET 124 is an example of an electronic element. The voltage regulator 126 is an example of a voltage supply circuit.

[0026] The high-side MOSFET 121, the low-side MOSFET 122, the decoupling MOSFET 123, and the switching MOSFET 124 are configured by N-channel MOSFETs. N-channel MOSFETs have a smaller on-resistance than P-channel MOSFETs, and therefore have the advantage of making it easier to reduce power consumption.

[0027] The high-side MOSFET 121 has a drain connected to the power supply 51 via the relay 52, a source connected to the source of the decoupling MOSFET 123, and a gate connected to the control circuit 140. A voltage V1 from the power supply 51 is supplied to the drain of the high-side MOSFET 121. For this reason, the drain of the high-side MOSFET 121 is denoted as V1. The high-side MOSFET 121 is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0028] The low-side MOSFET 122 has a drain connected to the sensor electrode 110, a source connected to a reference potential point (V2), and a gate connected to the control circuit 140. The reference potential point is a ground potential point, and the voltage at the reference potential point is V2 (GND). The low-side MOSFET 122 is provided between the sensor electrode 110 and the reference potential point, and is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0029] The decoupling MOSFET 123 is provided between the high-side MOSFET 121 and the sensor electrode 110. The drain of the decoupling MOSFET 123 is connected to the node 125, the source is connected to the source of the high-side MOSFET 121, and the gate is connected to the control circuit 140. The point where the source of the decoupling MOSFET 123 and the source of the high-side MOSFET 121 are connected is the connection point 123A. The connection point 123A is the connection point between the high-side MOSFET 121 and the decoupling MOSFET 123. The decoupling MOSFET 123 is driven by a PWM gate drive signal supplied to its gate from the control circuit 140.

[0030] In the heating mode, the control circuit 140 sets the gate voltages of the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122 to an H (High) level, thereby turning on the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122. When switching to the non-heating mode, the control circuit 140 first sets the gate voltages of the high-side MOSFET 121 and the decoupling MOSFET 123 to an L (Low) level, thereby turning on the high-side MOSFET 121 and the decoupling MOSFET 123. Next, the control circuit 140 sets the gate voltage of the low-side MOSFET 122 to a (Low) level, thereby turning off the low-side MOSFET 122. When switching to the non-heating mode, a period is provided during which the high-side MOSFET 121 and the decoupling MOSFET 123 are in an open state and the low-side MOSFET is in a conductive state, thereby setting the potential of the sensor electrode 110 to the reference potential (GND) in the non-heating mode.

[0031] The gate drive signals that drive the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are not limited to PWM signals. When the sensor electrode 110 is not heated, each gate drive signal may be held at an L level. The body ECU may adjust the temperature of the sensor electrode 110 (heating element) by changing the voltage of V1. In this case, the control circuit 140 may fix the time for which the gate drive signal is held at an H level and the time for which it is held at an L level.

[0032] The switching MOSFET 124 is connected to a line 123B that connects the connection point 123A and the reference potential point. The switching MOSFET 124 has a drain connected to the connection point 123A, a source connected to the reference potential point, and a gate connected to the control circuit 140. The switching MOSFET 124 is driven by a gate drive signal supplied to the gate from the control circuit 140. The line 123B is a line that connects the connection point 123A and the reference potential point, and is connected to the source of the low-side MOSFET 122 on the reference potential side. The switching MOSFET 124 is always in a conductive state (ON) in the heating mode, and is always in an open state (OFF) in the non-heating mode.

[0033] Node 125 is a node between the drain of decoupling MOSFET 123 and sensor electrode 110. Node 125 is connected to voltage regulator 126 and is supplied with voltage V3 output by voltage regulator 126. The voltage of node 125 is higher than the voltage of reference potential point V2. Node 125 is located between the drain of decoupling MOSFET 123, sensor electrode 110, and capacitor 134 of electrostatic detection circuit 130.

[0034] Voltage regulator 126 is connected to node 125 and outputs voltage V3 to node 125. Voltage regulator 126 converts voltage V1 supplied from power supply 51 to voltage V3. Voltage V3 output by voltage regulator 126 is lower than voltage V1 of power supply 51. Note that a voltage divider resistor may be used instead of voltage regulator 126 to convert voltage V1 to voltage V3. Diode 125A may be provided between voltage regulator 126 and node 125 to prevent backflow to voltage regulator 126. Note that if a switch is provided between voltage regulator 126 and node 125 and the switch is turned off in heating mode, voltage V3 output by voltage regulator 126 can be made higher than voltage V1 of power supply 51.

[0035] <Static electricity detection circuit 130> The electrostatic detection circuit 130 includes a charge amplifier 131, an AC signal source 132, an amplitude adjustment unit 133, and a capacitor 134. The electrostatic detection circuit 130 detects the electrostatic capacitance of the sensor electrode 110 using the self-capacitance method. The AC signal source 132 is an example of a sine wave signal source. Since the electrostatic detection circuit 130 detects the electrostatic capacitance using the self-capacitance method, it is possible to improve the sensitivity of the electrostatic capacitance of the sensor electrode 110. The electrostatic detection circuit 130 may detect the electrostatic capacitance of the sensor electrode 110 using the self-capacitance method only in the non-heating mode.

[0036] Charge amplifier 131 has a non-inverting input terminal (+) connected to the output terminal of amplitude adjustment unit 133, an inverting input terminal (-) connected to sensor electrode 110 via capacitor 134, and an output terminal connected to control circuit 140. The output voltage of the output terminal of charge amplifier 131 is V0. Charge amplifier 131 is a differential amplifier that amplifies the difference between the input at the non-inverting input terminal (+) and the input at the inverting input terminal (-) and outputs an output signal.

[0037] AC signal source 132 is connected to amplitude adjustment unit 133 and is also connected to sensor electrode 110 via capacitor 134. AC signal source 132 outputs an AC signal (sine wave signal) that drives sensor electrode 110. AC signal source 132 may stop outputting the AC signal in the heating mode.

[0038] When the hand H, which is an object, is not present near the sensor electrode 110 (when the parasitic capacitance Crg is zero), the amplitude adjustment unit 133 eliminates the difference between the inverting input terminal (-) and the non-inverting input terminal (+), and adjusts the amplitude so that the output voltage V0 of the charge amplifier 131 becomes extremely small.

[0039] Capacitor 134 has an inverting input terminal (-) of charge amplifier 131, a terminal (the terminal on the left side in FIG. 2) connected to amplitude adjustment unit 133, and a terminal connected to sensor electrode 110. That is, capacitor 134 is inserted in series between the inverting input terminal (-) of charge amplifier 131 and sensor electrode 110. Capacitor 134 is an example of a DC separation capacitor provided to block DC components between heater drive circuit 120 and electrostatic detection circuit 130. Capacitor 134 has a capacitance of Cd.

[0040] <Control circuit 140> The control circuit 140 outputs gate drive signals to the gates of the high-side MOSFET 121, the low-side MOSFET 122, the decoupling MOSFET 123, and the switching MOSFET 124, thereby controlling switching between a conductive state and an open state.

[0041] In the non-heating mode, the control circuit 140 outputs an L (Low) level gate drive signal to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123, and outputs an H (High) level gate drive signal to the gate of the switching MOSFET 124.

[0042] As a result, in the non-heating mode, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are in an open state (off). With the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 in an open state (off), the sensor electrode 110 becomes equivalent to a state in which the power supply circuit 50 is not present.

[0043] The control circuit 140 digitally converts the signal output from the charge amplifier 131 and demodulates it using a demodulation signal having the same frequency as the AC signal. Based on the demodulated output, the control circuit 140 determines whether the hand H is touching the sensor electrode 110. The control circuit 140 may determine whether the hand H is touching the sensor electrode 110 only in a non-heated state.

[0044] In addition, in the heating mode, the control circuit 140 outputs H-level PWM gate drive signals synchronized at the same frequency to the gates of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123, and outputs an L-level gate drive signal to the gate of the switching MOSFET 124. As a result, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are in a conductive state (ON), and the switching MOSFET 124 is in an open state (OFF). Therefore, current flows from the power supply 51 through the high-side MOSFET 121, the decoupling MOSFET 123, the sensor electrode 110, and the low-side MOSFET 122 toward the reference potential point. As a result, the sensor electrode 110 generates heat and functions as a heater.

[0045] The duty ratio of the PWM gate drive signal (PWM signal) may be determined by the control circuit 140 through feedback control based on the target temperature of the heater of the steering wheel 10, the current temperature of the heater of the steering wheel 10, etc. The temperature of the heater of the steering wheel 10 may be measured by providing a temperature sensor in the steering wheel 10.

[0046] Note that a high-resistance resistor may be provided on line 123B instead of switching MOSFET 124. By providing a high-resistance resistor on line 123B instead of switching MOSFET 124, node 123A can be maintained at the reference potential in the non-heating mode. Furthermore, in the heating mode, almost no current flows through the high-resistance resistor, allowing current to flow from the high-side MOSFET 121 through a path passing through decoupling MOSFET 123, sensor electrode 110, and low-side MOSFET 122, thereby heating the sensor electrode 110. However, to reduce the power consumed by the resistor in the heating mode, the resistance value is set to greater than 1 kΩ. Furthermore, to shorten the time it takes for the voltage at node 123A to reach V2 when switching to the non-heating mode, the resistance value is set to less than 100 kΩ.

[0047] <Parasitic capacitances of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123> 3A is a diagram showing an example of the parasitic capacitance Coss between the drain and source of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 in the non-heating mode. The high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are, for example, the same type of N-channel MOSFET, and the characteristics of the parasitic capacitance Coss with respect to the drain-source voltage VDS are assumed to be equal to each other.

[0048] 2, the sensor electrode 110, the high-side MOSFET 121, the low-side MOSFET 122, the decoupling MOSFET 123, the node 125, and the capacitor 134 of the electrostatic detection circuit 130. In addition, in FIG. 3A, the switching MOSFET 124, which is turned on in the non-heating mode, is shown as a switch in a closed state, and the power supply 51 is shown as a power supply V1, with other components being omitted.

[0049] Parasitic capacitance Coss exists between the drain and source of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123. MOSFETs have electrical characteristics in which the drain-source parasitic capacitance Coss changes with the voltage between the drain and source, and generally, the parasitic capacitance Coss decreases as the voltage between the drain and source increases. For this reason, in an N-channel MOSFET, the parasitic capacitance Coss decreases as the voltage of the drain relative to the source increases.

[0050] The parasitic capacitance Coss affects the detection sensitivity when detecting the capacitance of the sensor electrode 110. That is, in the sensor device 100, in the non-heating mode in which the capacitance of the sensor electrode 110 is detected, in order to minimize the decrease in detection sensitivity and obtain good detection sensitivity, it is preferable to reduce the parasitic capacitance Coss of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 to some extent.

[0051] 3A, in the non-heating mode, the switching MOSFET 124 is in a conductive state (ON), and the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all in an open state (OFF). The decoupling MOSFET 123 has its drain-source connected in the opposite direction to that of the high-side MOSFET 121 and the low-side MOSFET 122 between the power supply V1 and the reference potential point.

[0052] Fig. 3B is a diagram showing a further modification of the configuration shown in Fig. 3A. In Fig. 3B, the high-side MOSFET 121 and the decoupling MOSFET 123 are shown folded downward with respect to the sensor electrode 110, and the power supply V1 is indicated by the symbol for a DC power supply. Also, in Fig. 3B, in order to show a state in which the switching MOSFET 124 is in a conductive state (ON) in the non-heating mode, as in Fig. 3A, the switching MOSFET 124 provided on the line 123B is omitted, and only the position of the switching MOSFET 124 is indicated by a dashed square.

[0053] In the sensor device 100, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all N-channel types. To achieve this configuration, the decoupling MOSFET 123 is connected between the power supply V1 and the reference potential point, with its drain connected to the reference potential point and its source connected to the power supply V1. To enable the decoupling MOSFET 123 connected in this manner to operate, a voltage V3 is applied to the drain of the decoupling MOSFET 123 from a voltage regulator 126.

[0054] Also, in the non-heating mode, all of the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are turned off (in an open state). In this state, since the high-side MOSFET 121 is connected in parallel with the line 123B connected to the reference potential point when viewed from the connection point 123A, it is equivalent to the state where the high-side MOSFET 121 does not exist, and the parasitic capacitance Coss between the drain and source of the high-side MOSFET 121 does not affect the sensor electrode 110.

[0055] Therefore, in the non-heating mode, the parasitic capacitance Crgl of the sensor electrode 110 is the total capacitance of the parasitic capacitance Coss between the drain and source of the low-side MOSFET 122 and the parasitic capacitance Coss between the drain and source of the decoupling MOSFET 123. Also, since the parasitic capacitance Crgl of the sensor electrode 110 is not affected by the parasitic capacitance Coss between the drain and source of the high-side MOSFET 121, it is not affected by the influence of the parasitic capacitance Coss between the drain and source of the high-side MOSFET 121 due to the voltage fluctuation of the power supply V1.

[0056] Since the low-side MOSFET 122 and the decoupling MOSFET 123 are connected via the sensor electrode 110, the voltage between the drain and source of the low-side MOSFET 122 and the decoupling MOSFET 123 in the non-heating mode becomes approximately equal to the voltage V3.

[0057] <An Example of Electrical Characteristics of MOSFET> FIG. 4 is a diagram showing an example of the electrical characteristics of an N-channel type MOSFET. In FIG. 4, the horizontal axis represents the drain-to-source voltage VDS (V) of the N-channel type MOSFET with respect to the source. In FIG. 4, the vertical axis represents the parasitic capacitance Coss (pF). In the region where the voltage on the horizontal axis is about 1 V or more in FIG. 4, the parasitic capacitance Coss rapidly decreases.

[0058] In the sensor device 100, the voltage VDS of the low-side MOSFET 122 and the decoupling MOSFET 123 in the non-heating mode is approximately equal to the voltage V3. Therefore, if the voltage V3 is set to approximately 1 V or higher, the parasitic capacitance Coss of both the low-side MOSFET 122 and the decoupling MOSFET 123 can be reduced.

[0059] As a result, it is possible to reduce the parasitic capacitance Crgl of the sensor electrode 110. Furthermore, it is possible to prevent the parasitic capacitance Crgl of the sensor electrode 110 from being affected by voltage fluctuations of the power supply V1.

[0060] For example, if the power supply V3 is set to about 3 V, the parasitic capacitance Coss of each of the low-side MOSFET 122 and the decoupling MOSFET 123 will be a very small value of about 200 pF. The sum of the two parasitic capacitances Coss is about 400 pF, and this total parasitic capacitance becomes the parasitic capacitance Crgl between the sensor electrode 110 and the ground potential point, so the parasitic capacitance Crgl between the sensor electrode 110 and the ground potential point is very small.

[0061] In the sensor device 100 of the embodiment, the parasitic capacitance Crgl of the sensor electrode 110 in the non-heating mode is extremely small, and good detection sensitivity can be obtained by minimizing the decrease in detection sensitivity when detecting the capacitance of the sensor electrode 110. In addition, in this sensor device 100, the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all N-channel MOSFETs. N-channel MOSFETs consume less power than P-channel MOSFETs.

[0062] Therefore, even if the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all in a conductive state in the heating mode, the power consumption is low.

[0063] <Effects> The sensor device 100 includes a sensor electrode 110 operable as a heating element, an electrostatic detection circuit 130 that detects the electrostatic capacitance between the sensor electrode 110 and an object, a high-side MOSFET 121 connected to a power supply 51 that supplies heating power to the sensor electrode 110, a decoupling MOSFET 123 provided between the high-side MOSFET 121 and one end of the sensor electrode 110, a low-side MOSFET 122 provided between the other end of the sensor electrode 110 and a reference potential point, a voltage regulator 126 that supplies a voltage to a node 125 between the decoupling MOSFET 123 and one end of the sensor electrode 110 so that the voltage of the node 125 is higher than the voltage of the reference potential point, a switching MOSFET 124 configured as a resistor or a switch provided between a connection point 123A of the high-side MOSFET 121 and the decoupling MOSFET 123 and a reference, and a high-side MOSFET 121 connected to a power supply 51 that supplies heating power to the sensor electrode 110, a decoupling MOSFET 123 provided between the high-side MOSFET 121 and one end of the sensor electrode 110, a low-side MOSFET 122 provided between the other end of the sensor electrode 110 and a reference potential point, a voltage regulator 126 that supplies a voltage to the node 125 so that the voltage of the node 125 is higher than the voltage of the reference potential point, a connection point 123A of the high-side MOSFET 121 and the decoupling MOSFET 123, and a reference. a control circuit 140 that controls the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122; a voltage V1 of the power supply 51 is higher than a voltage V2 of a reference potential point; the high-side MOSFET 121, the decoupling MOSFET 123, and the low-side MOSFET 122 are N-channel MOSFETs; the drain of the high-side MOSFET 121 is connected to the power supply 51; the drain of the decoupling MOSFET 123 is connected to a node 125; the drain of the low-side MOSFET 122 is connected to the other end of the sensor electrode 110; the source of the low-side MOSFET 122 is connected to the reference potential point; and the sources of the high-side MOSFET 121 and the decoupling MOSFET 123 are connected to a connection point 123A and are also connected to the reference potential point via a switching MOSFET 124. Since the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all N-channel MOSFETs, power consumption is low even if the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all in a conductive state in the heating mode.

[0064] Therefore, it is possible to provide a sensor device 100 with low power consumption. Furthermore, since the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 are all N-channel MOSFETs, manufacturing is easy, product variations can be suppressed, and electrical reliability can be improved. Furthermore, manufacturing costs can be reduced.

[0065] The sensor may further include a capacitor 134 for DC isolation provided between the sensor electrode 110 and the electrostatic detection circuit 130. The electrostatic detection circuit 130 can be isolated from DC signals, allowing the electrostatic capacitance of the sensor electrode 110 to be accurately detected.

[0066] Furthermore, the voltage regulator 126 may be a constant voltage regulator that outputs a voltage V3 higher than the voltage V1 of the power supply 51. By increasing the voltage V3 without being restricted by the voltage V1 of the power supply 51, the parasitic capacitance Coss between the drain and source of the low-side MOSFET 122 and the decoupling MOSFET 123 can be reduced, and the parasitic capacitance Crgl of the sensor electrode 110 can be reduced. This improves the sensitivity of electrostatic detection.

[0067] The source of the high-side MOSFET 121 and the source of the decoupling MOSFET 123 are connected to a reference potential point via a switch (124), which may be an N-channel MOSFET having a drain connected to the source of the high-side MOSFET 121 and the source of the decoupling MOSFET 123 and a source connected to the reference potential point. Using an N-channel MOSFET as the switch (124) makes manufacturing easier, further reduces product variations, and further improves electrical reliability. This also reduces manufacturing costs.

[0068] The source of the high-side MOSFET 121 and the source of the decoupling MOSFET 123 are connected to the reference potential point via a resistor 124, and the resistor preferably has a resistance value of 1 kΩ to 100 kΩ. In the heating mode, current flow from the connection point 123A to the reference potential point can be suppressed, and in the non-heating mode, the connection point 123A can be reliably maintained at the reference potential. Furthermore, the configuration is very simple, which can improve electrical reliability and reduce manufacturing costs.

[0069] The electrostatic detection circuit 130 may also detect electrostatic capacitance using a self-capacitance method, which can improve the sensitivity of the electrostatic capacitance at the sensor electrode 110.

[0070] Furthermore, when supplying heating power from the power supply 51 to the sensor electrode 110, the control circuit 140 may control the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 to a conductive state, and when stopping the supply of heating power from the power supply 51 to the sensor electrode 110, the control circuit 140 may control the high-side MOSFET 121 and the decoupling MOSFET 123 to an open state and then control the low-side MOSFET 122 to an open state. By switching the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 between a conductive state and an open state, a circuit in heating mode and a circuit in non-heating mode can be easily realized. Furthermore, when stopping the supply of heating power from the power supply 51 to the sensor electrode 110, safety can be improved by turning off the side closest to the power supply 51 first.

[0071] Alternatively, the electronic element may be a switch (124). When supplying heating power from the power supply 51 to the sensor electrode 110, the control circuit 140 controls the switch (124) to an open state. When stopping the supply of heating power from the power supply 51 to the sensor electrode 110, the control circuit 140 may control the high-side MOSFET 121 and the decoupling MOSFET 123 to an open state, and after controlling the switch to a conductive state, control the low-side switch to an open state. By switching the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 between a conductive state and an open state, a circuit in a heating mode and a circuit in a non-heating mode can be easily realized. By switching the high-side MOSFET 121, the low-side MOSFET 122, and the decoupling MOSFET 123 between a conductive state and an open state and the switch (124), a circuit in a heating mode and a circuit in a non-heating mode can be easily realized. Furthermore, when stopping the supply of heating power from the power supply 51 to the sensor electrode 110, safety can be improved by turning off the side closest to the power supply 51 first.

[0072] The electronic element may be a resistor 124. The electronic element can be realized with a simple configuration.

[0073] <Modifications of the embodiment> Fig. 5 is a diagram showing an example of a circuit configuration of a sensor device 100M1 according to a modified example of the embodiment, and also shows a power supply circuit 50 of a vehicle 1 on which the sensor device 100M1 is mounted.

[0074] The sensor device 100M1 has a configuration in which an active shield electrode 150 is added to the sensor device 100 shown in Fig. 2. Furthermore, in order to prevent backflow to the voltage regulator 126, a switch 125B may be provided between the voltage regulator 126 and the node 125. The switch 125B is provided in place of the diode 125A shown in Fig. 2. The rest is the same as the sensor device 100 shown in Fig. 2.

[0075] The active shield electrode 150 is disposed on the rear side of the sensor electrode 110 and in the vicinity of the sensor electrode 110. The rear side of the sensor electrode 110 refers to the side opposite to the side of the sensor electrode 110 that the hand H approaches. Additionally, the vicinity of the sensor electrode 110 refers to the proximity of the sensor electrode 110 and the active shield electrode 150 being close enough to be capacitively coupled to each other. The capacitance between the sensor electrode 110 and the active shield electrode 150 is denoted by Crs.

[0076] The active shield electrode 150 is connected to an AC signal source 132 and is driven by a signal containing an AC component of the same frequency and phase as the AC component contained in the signal supplied to the sensor electrode 110. The amplitude of the AC component of the signal supplied to the active shield electrode 150 is greater than the amplitude of the AC component of the signal supplied to the sensor electrode 110.

[0077] The active shield electrode 150 is provided to shield the sensor electrode 110 from noise and to suppress the effects of parasitic capacitance. The active shield electrode 150 is arranged near the sensor electrode 110 at a predetermined distance so as to be able to shield the sensor electrode 110 from noise mainly from a reference potential point such as the ground and to suppress the effects of parasitic capacitance between the sensor electrode 110 and the reference potential point.

[0078] The amplitude adjustment unit 133 adjusts the current flowing from the active shield electrode 150 through the capacitance Crs to the sensor electrode 110 and the current flowing from the sensor electrode 110 through the parasitic capacitor Crgl to the reference potential point so as to cancel each other out. That is, in a state where the hand H, which is an object close to the sensor electrode 110, is not present (a state where the capacitance Crg is zero), the amplitude is adjusted so that the drive current flowing through the sensor electrode 110 becomes zero.

[0079] The sensor device 100M1 of the modified embodiment further includes an active shield electrode 150 arranged near the sensor electrode 110. Therefore, the active shield electrode 150 can reduce the effects of noise and parasitic capacitance in the sensor electrode 110, as well as the effects of noise and parasitic capacitance in the wiring and the like included in the electrostatic detection circuit 130.

[0080] The above describes a sensor device according to an exemplary embodiment of the present disclosure. However, the present disclosure is not limited to the specifically disclosed embodiment, and various modifications and variations are possible without departing from the scope of the claims.

[0081] The following additional notes are provided regarding the above-described embodiments. (Appendix 1) a sensor electrode operable as a heating element; an electrostatic detection circuit that detects the electrostatic capacitance between the sensor electrode and the object; a high-side switch connected to a power supply that supplies power for heating the sensor electrode; a decoupling switch provided between the high-side switch and one end of the sensor electrode; a low-side switch provided between the other end of the sensor electrode and a reference potential point; a voltage supply circuit that supplies a voltage to a node between the decoupling switch and the one end of the sensor electrode so that the voltage of the node is higher than the voltage of the reference potential point; an electronic element configured by a resistor or a switch provided between a connection point of the high-side switch and the decoupling switch and the reference; a control unit that controls the high-side switch, the decoupling switch, and the low-side switch; Equipped with the voltage of the power supply is higher than the voltage of the reference potential point; the high-side switch, the decoupling switch, and the low-side switch are N-channel MOSFETs; The drain of the high-side switch is connected to the power supply; The drain of the decoupling switch is connected to the node; a drain of the low-side switch connected to the other end of the sensor electrode; a source of the low-side switch is connected to the reference potential point; The sensor device, wherein a source of the high-side switch and a source of the decoupling switch are connected to the connection point and are also connected to the reference potential point via the electronic element. (Appendix 2) 2. The sensor device of claim 1, further comprising a capacitor for DC isolation provided between the sensor electrode and the electrostatic detection circuit. (Appendix 3) 3. The sensor device according to claim 1, wherein the voltage supply circuit is a constant voltage regulator that outputs a voltage higher than the voltage of the power supply. (Appendix 4) a source of the high-side switch and a source of the decoupling switch are connected to the reference potential point via the switch; 4. The sensor device according to claim 1, wherein the switch is an N-channel MOSFET having a drain connected to a source of the high-side switch and a source of the decoupling switch, and a source connected to the reference potential point. (Appendix 5) a source of the high-side switch and a source of the decoupling switch are connected to the reference potential point via the resistor; 4. The sensor device according to claim 1, wherein the resistor has a resistance value greater than 1 kΩ and less than 100 kΩ. (Appendix 6) The sensor device according to any one of appendixes 1 to 5, wherein the electrostatic detection circuit detects the electrostatic capacitance using a self-capacitance method. (Appendix 7) 7. The sensor device of claim 1, further comprising an active shield electrode disposed adjacent to the sensor electrode. (Appendix 8) The control unit When the heating power is supplied from the power supply to the sensor electrode, the high-side switch, the low-side switch, and the decoupling switch are controlled to be in a conductive state; The sensor device according to any one of appendixes 1 to 7, wherein, when the supply of the heating power from the power source to the sensor electrode is stopped, the high-side switch and the decoupling switch are controlled to an open state, and then the low-side switch is controlled to an open state. (Appendix 9) the electronic element is the switch, The control unit When the power source supplies the heating power to the sensor electrode, the switch is controlled to an open state; 8. The sensor device according to claim 1, wherein, when the supply of heating power from a power source to the sensor electrode is stopped, the high-side switch and the decoupling switch are controlled to an open state, and after the switches are controlled to a conductive state, the low-side switch is controlled to an open state. (Appendix 10) The sensor circuit according to claim 1 , wherein the electronic element is the resistor. [Explanation of symbols]

[0082] 51 Power supply 100 Sensor Device 110 Sensor electrode 120 Heater drive circuit 121 High-side MOSFET (an example of a high-side switch) 122 Low-side MOSFET (an example of a low-side switch) 123 Decoupling MOSFET 123A connection point 123B Railroad 124 Switching MOSFET (an example of an electronic element) 125 nodes 126 Voltage regulator (an example of a voltage supply circuit) 130 Electrostatic detection circuit 132 AC signal source 134 Capacitor 140 Control circuit 150 Active Shield Electrode

Claims

1. a sensor electrode operable as a heating element; an electrostatic detection circuit that detects the electrostatic capacitance between the sensor electrode and the object; a high-side switch connected to a power supply that supplies power for heating the sensor electrode; a decoupling switch provided between the high-side switch and one end of the sensor electrode; a low-side switch provided between the other end of the sensor electrode and a reference potential point; a voltage supply circuit that supplies a voltage to a node between the decoupling switch and the one end of the sensor electrode so that the voltage of the node is higher than the voltage of the reference potential point; an electronic element configured by a resistor or a switch provided between a connection point of the high-side switch and the decoupling switch and the reference; a control unit that controls the high-side switch, the decoupling switch, and the low-side switch; Equipped with the voltage of the power supply is higher than the voltage of the reference potential point; the high-side switch, the decoupling switch, and the low-side switch are N-channel MOSFETs, The drain of the high-side switch is connected to the power supply; The drain of the decoupling switch is connected to the node; a drain of the low-side switch connected to the other end of the sensor electrode; a source of the low-side switch is connected to the reference potential point; The sensor device, wherein a source of the high-side switch and a source of the decoupling switch are connected to the connection point and are also connected to the reference potential point via the electronic element.

2. The sensor device according to claim 1 , further comprising a capacitor for DC isolation provided between the sensor electrode and the electrostatic detection circuit.

3. 2. The sensor device according to claim 1, wherein the voltage supply circuit is a constant voltage regulator that outputs a voltage higher than a voltage of the power supply.

4. a source of the high-side switch and a source of the decoupling switch are connected to the reference potential point via the switch; 4. The sensor device according to claim 1, wherein the switch is an N-channel MOSFET having a drain connected to a source of the high-side switch and a source of the decoupling switch, and a source connected to the reference potential point.

5. a source of the high-side switch and a source of the decoupling switch are connected to the reference potential point via the resistor; The sensor device according to claim 1 , wherein the resistor has a resistance value greater than 1 kΩ and less than 100 kΩ.

6. The sensor device according to claim 1 , wherein the electrostatic detection circuit detects the electrostatic capacitance by a self-capacitance method.

7. The sensor device of claim 1 , further comprising an active shield electrode disposed adjacent the sensor electrode.

8. The control unit When the heating power is supplied from the power supply to the sensor electrode, the high-side switch, the low-side switch, and the decoupling switch are controlled to be in a conductive state; 2. The sensor device according to claim 1, wherein, when the supply of the heating power from the power source to the sensor electrode is stopped, the high-side switch and the decoupling switch are controlled to an open state, and then the low-side switch is controlled to an open state.

9. the electronic element is the switch, The control unit When the power source supplies the heating power to the sensor electrode, the switch is controlled to an open state; 2. The sensor device according to claim 1, wherein, when the supply of the heating power from the power source to the sensor electrode is stopped, the high-side switch and the decoupling switch are controlled to an open state, and the switches are controlled to a conductive state, and then the low-side switch is controlled to an open state.

10. The sensor device according to claim 1 , wherein the electronic element is the resistor.

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