Input Devices

Abstract

Provided is an input device in which the influence of a light-emitting state of a light-emitting diode on the detection capacity of an electrostatic sensor is suppressed.　This input device includes: a light-emitting diode; a switching element which is connected in series to the light-emitting diode and switches on / off the light-emitting diode; an electrostatic sensor which has a detection electrode capacitively coupled with a circuit portion between the light-emitting diode and the switching element; and a capacitor having a first terminal connected to the circuit portion and a second terminal connected to a fixed potential point.

Description

[Technical Field]

[0001] The present disclosure relates to an input device. [Background technology]

[0002] Conventionally, there has been an LED lighting device comprising a power supply unit having at least a pair of AC input terminals and a pair of DC output terminals, and an LED unit including an LED (light-emitting diode) circuit to which DC current is supplied via a pair of power lines connected to the DC output terminals of the power supply unit, the LED having a conductive part electrostatically coupled to the LED via a dielectric. The power supply unit includes a DC-DC converter circuit, and the secondary-side ground or primary-side ground of the DC-DC converter circuit is connected to the conductive part of the LED unit via a first capacitor, and the capacitance of the first capacitor is set larger than the stray capacitance formed between the LED in the LED unit and the conductive part (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-245570 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the detection capacitance of the electrostatic sensor may differ depending on whether the light-emitting diode is in an on state or an off state. In such cases, the detection capacitance of the electrostatic sensor will fluctuate depending on the light-emitting state of the light-emitting diode.

[0005] Therefore, an object of the present invention is to provide an input device that suppresses the influence of the light emitting state of the light emitting diode on the detection capacitance of the electrostatic sensor. [Means for solving the problem]

[0006] An input device according to an embodiment of the present disclosure includes a light-emitting diode, a switching element connected in series with the light-emitting diode and configured to switch the light-emitting diode on and off, an electrostatic sensor having a detection electrode capacitively coupled to a circuit portion between the light-emitting diode and the switching element, and a capacitor having a first terminal connected to the circuit portion and a second terminal connected to a fixed potential point. [Effects of the Invention]

[0007] It is possible to provide an input device in which the influence of the light emitting state of the light emitting diode on the detection capacitance of the electrostatic sensor is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of the configuration of an input device 100. FIG. [Figure 2] 1 is a diagram showing an example of a model of an equivalent circuit used for simulating the detection capacitance of the electrostatic sensor 110 of the input device 100. FIG. [Figure 3] 10 is a diagram showing calculation results of capacitances Ct1 and Ct2 of the detection electrode 111 when the capacitance Cx of the capacitor 160 is changed in the input device 100 of the embodiment. FIG. [Figure 4A] 10A and 10B are diagrams illustrating variations of the circuit portion 105. FIG. [Figure 4B] 10A and 10B are diagrams illustrating variations of the circuit portion 105. FIG. [Figure 4C] 10A and 10B are diagrams illustrating variations of the circuit portion 105. FIG. [Figure 5] FIG. 10 is a diagram illustrating an example of a model of an equivalent circuit used for simulating the detection capacitance of an input device 100M according to a modified example of the embodiment. [Figure 6] FIG. 10 is a diagram showing calculation results of capacitances Ctm1 and Ctm2 of the detection electrodes 111 when the capacitance Cx of the capacitor 160 is changed in an input device 100M according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] <Embodiment> <Configuration of input device 100> 1 is a diagram showing an example of the configuration of an input device 100. The input device 100 includes an operation surface 101, an electrostatic sensor 110, an LED (light-emitting diode) 130, a MOSFET (metal-oxide semiconductor field-effect transistor) 140, a light-emission control unit 150, and a capacitor 160. The input device 100 also includes a circuit portion 105.

[0011] The input device 100 is a device that allows input operations to be performed by operating the operation surface 101 with an object such as a fingertip. As an example, the LED 130 illuminates the operation surface 101. For example, the operation surface 101 may be provided with symbols representing symbols, characters, etc. to be operated. In such a case, a light-transmitting portion having the shape of the symbol may be provided on the operation surface 101, and the symbol may be illuminated by the LED 130 from the rear side of the operation surface 101.

[0012] Such an input device 100 may be provided, for example, in the interior of a vehicle and in an operating section of an audio system, a navigation system, an air conditioner, or the like installed in the vehicle. In such a case, the input device 100 may be provided, for example, in a steering wheel, a center console, or the like. The input device 100 may also be a tablet computer, a smartphone, a game console, or the like used by an individual. The input device 100 may also be, for example, a tablet-type input device or an input section of an ATM (Automatic Teller Machine) that is placed in a store, facility, or the like and used by an unspecified number of users.

[0013] The electrostatic sensor 110 has a detection electrode 111 and a detection unit 115. The operation surface 101 is provided on top of the detection electrode 111 and is part of the surface of the input device 100 or the housing or cover of a device including the input device 100. A user performs an operation on the detection electrode 111 from above the operation surface 101.

[0014] Although FIG. 1 shows one detection electrode 111, the electrostatic sensor 110 may have a plurality of detection electrodes 111. The detection electrode 111 can be made of a conductor such as metal or ITO (indium tin oxide). The detection electrode 111 is a single electrode made of a conductor. In the following, for simplicity of explanation, it is assumed that there is one detection electrode 111, and that an operation on the detection electrode 111 is synonymous with an operation on the electrostatic sensor 110.

[0015] The electrostatic sensor 110 is a capacitance type sensor provided to detect the proximity or contact of an object such as a fingertip with the operation surface 101 by a change in the capacitance of a detection electrode 111. The electrostatic sensor 110 detects an object such as a fingertip by a self-capacitance type. A detection unit 115 is connected to the detection electrode 111.

[0016] An operation in which a fingertip or the like comes into contact with the operation surface 101 is a touch (contact) operation, and an operation in which a fingertip or the like is brought close to the operation surface 101 without touching it (non-contact) is a hover operation. Also, "close" means that the fingertip or the like comes close to the operation surface 101 to such an extent that a change in the capacitance of the electrostatic sensor 110 that can be detected by the input device 100 occurs.

[0017] The detection unit 115 detects the capacitance of the detection electrode 111 of the electrostatic sensor 110 and outputs detection data representing the capacitance. The detection unit 115 digitally converts the capacitance (analog value) of the detection electrode 111 input from the detection electrode 111 and outputs detection data representing the capacitance in digital value. A computer or microcomputer is connected to the output side of the detection unit 115, but is not illustrated here, and determines the proximity or contact of a fingertip or the like with the operation surface 101 based on the output of the detection unit 115.

[0018] Although detailed description will be omitted here, when the electrostatic sensor 110 has a plurality of detection electrodes 111, the detection unit 115 may function as a selection unit that applies a voltage to select one of the plurality of detection electrodes 111 in a time-division manner. When the plurality of detection electrodes 111 are arranged in the X direction and the Y direction, the detection unit 115 may function as a selection unit that applies a voltage to select one of the plurality of detection electrodes 111 in the X direction and the Y direction in a time-division manner.

[0019] The LED 130 has an anode connected to the power supply 103 and a cathode connected to the drain of the MOSFET via the circuit part 105. The power supply 103 is supplied from a device including the input device 100. The LED 130 is switched on / off by the MOSFET 140. As an example, the LED 130 illuminates the operation surface 101 as described above.

[0020] The MOSFET 140 has a drain connected to the cathode of the LED 130 via the circuit part 105, a source connected to the ground (GND), and a gate connected to the light-emission control unit 150. The ground is an example of a fixed potential point. The drain-source of the MOSFET 140 is connected in series to the LED 130 between the power supply 103 and the ground. Note that the inverted triangle in FIG. 1 represents the ground. Instead of the ground of the inverted triangle in FIG. 1, it may be connected to a point of a fixed potential other than 0 V.

[0021] When the MOSFET 140 is turned on and a current flows between the drain and source, a current flows from the power supply 103 to the LED 130, turning the LED 130 on (emitting light). When the MOSFET 140 is turned off and no current flows between the drain and source, no current flows from the power supply 103 to the LED 130, so the LED 130 turns off (goes unlit).

[0022] The light-emission control unit 150 controls the driving of the MOSFET 140 by, for example, outputting a pulse signal to the gate of the MOSFET 140. The light-emission control unit 150 controls the driving of the MOSFET 140, thereby controlling the light emission of the LED 130. The light-emission control unit 150 is composed of, for example, a pulse generator that generates a pulse signal and a microcomputer that controls the pulse generator.

[0023] Circuit portion 105 is a circuit portion between the cathode of LED 130 and the drain of MOSFET 140, and includes resistor R. Resistor R is provided to limit the current flowing through LED 130. Circuit portion 105 is part of the wiring for supplying current to LED 130, and passes near detection electrode 111. Therefore, circuit portion 105 and detection electrode 111 are capacitively coupled. Capacitive coupling between circuit portion 105 and detection electrode 111 means that there is a non-negligible amount of capacitance between detection electrode 111 and circuit portion 105, with detection electrode 111 detecting the electrostatic capacitance of an object such as a fingertip using a self-capacitance method.

[0024] The capacitor 160 has a first terminal 161 connected to the circuit portion 105 and a second terminal 162 connected to a fixed potential point. The first terminal 161 is connected to the electrode of the capacitor 160 on the right side in FIG. 1, and the second terminal 162 is connected to the electrode of the capacitor 160 on the left side in FIG. 1. The first terminal 161 is connected to the circuit portion 105. More specifically, the first terminal 161 is connected to the cathode of the LED 130 via the circuit portion 105. The second terminal 162 is connected to ground (GND). Next, the reason for providing the capacitor 160 will be explained.

[0025] <Impedance of circuit portion 105> Here, the impedance of the circuit part 105 will be described using the input device 100 of the embodiment and an input device for comparison. The input device for comparison has a configuration in which the capacitor 160 is removed from the input device 100 of the embodiment. That is, in the input device for comparison, the capacitor 160 is not connected to the circuit part 105.

[0026] In the comparative input device, when the MOSFET 140 is on, the LED 130 is on, and when the MOSFET 140 is off, the LED 130 is off. When the MOSFET 140 and the LED 130 are on, the circuit part 105 is connected to ground through the drain-source of the MOSFET 140, but when the MOSFET 140 and the LED 130 are off, the circuit part 105 is at a floating potential. Therefore, it is considered that the impedance of the circuit part 105 is low when the LED 130 is on and high when it is off. In other words, it is considered that the impedance of the circuit part 105 connected to the cathode of the LED 130 varies depending on whether the LED 130 is turned on or off in accordance with whether the MOSFET 140 is turned on or off.

[0027] In the input device 100 of the embodiment, the LED 130 is on when the MOSFET 140 is on. At that time, the circuit part 105 is connected to the ground through the drain-source of the MOSFET 140, and the impedance is low.

[0028] On the other hand, when the MOSFET 140 is off, the LED 130 is off. In this case, the circuit part 105 is not connected to ground through the drain-source of the MOSFET 140. However, even when the LED 130 is off, the circuit part 105 has a sufficiently large capacitive coupling with the ground through the capacitor 160, and does not become a floating potential in terms of AC. Therefore, it is considered that the impedance of the circuit part 105 is as low as when the LED 130 is on.

[0029] From the above, it can be considered that in the input device 100 of the embodiment including the capacitor 160, the impedance of the circuit portion 105 connected to the cathode of the LED 130 is approximately equal when the LED 130 is on and when the LED 130 is off.

[0030] As described above, by connecting the capacitor 160 to the circuit part 105, it is possible to suppress the difference in impedance between the circuit part 105 when the LED 130 is on and the circuit part 105 when the LED 130 is off, and therefore the input device 100 uses the capacitor 160. The effect of the difference in impedance on the detection capacitance will be explained in the following simulation.

[0031] <Simulation> 2 is a diagram showing an example of a model of an equivalent circuit used for simulating the detection capacitance of the electrostatic sensor 110 of the input device 100. Here, an equivalent circuit when a user operates the input device 100 with a fingertip FT will be described.

[0032] The fingertip FT is connected to the user's body, and because the user's body has a large surface area, it is coupled to the environmental ground with a sufficiently large capacitance. From the viewpoint of capacitance detection, it is safe to consider that the fingertip FT is connected to the ground through the user's body. Therefore, when operating the input device 100 with the fingertip FT, a parasitic capacitance Cfs occurs between the fingertip FT and the detection electrode 111. The parasitic capacitance Cfs increases as the fingertip FT approaches the detection electrode 111.

[0033] It can also be considered that there is a parasitic capacitance Csg between the detection electrode 111 and ground, a parasitic capacitance Cls between the detection electrode 111 and the circuit section 105, and a parasitic capacitance Clg between the circuit section 105 and ground. For this reason, the equivalent circuit of FIG. 2 is obtained by adding the parasitic capacitances Cfs, Csg, Cls, and Clg to the configuration diagram of FIG. 1. In addition, in FIG. 2, the capacitance of the capacitor 160 is set to Cx for simulation purposes. While the input device 100 of the embodiment includes the capacitor 160, the comparative input device does not include the capacitor 160, so Cx = 0 (pF) for the comparative input device.

[0034] As a condition for the simulation, the resistance value when the LED 130 is on is 0Ω, and when it is off, it is open (open state) and treated as a 0 pF capacitor. Also, the resistance value of the resistor R of the circuit part 105 is assumed to be negligibly small.

[0035] As shown in this equivalent circuit model for simulation, the input device 100 of the embodiment includes a capacitor 160 connected between the cathode of the LED 130 and ground. However, the comparative input device does not include the capacitor 160. Therefore, in addition to the parasitic capacitance Cfs between the detection electrode 111 and the fingertip FT and the parasitic capacitance Csg between the detection electrode 111 and ground, the detection electrode 111 is connected to the circuit part 105 via a parasitic capacitance Cls, and further connected to the circuit part 105 via a parasitic capacitance Clg between the circuit part 105 and ground. This is because the electrostatic sensor 110 and the LED 130 are disposed close to each other, which generates a parasitic capacitance Cls between the detection electrode 111 and the circuit part 105.

[0036] In the comparative input device, when the LED 130 is turned on, the MOSFET 140 is turned on, and therefore the circuit part 105 is connected to ground through the drain-source of the MOSFET 140. In addition, when the LED 130 is turned off, the MOSFET 140 is turned off, and therefore, in the comparative input device, a parasitic capacitance Clg occurs between the circuit part 105 and ground. It is believed that such a difference in the capacitance of the circuit part 105 due to the on / off of the LED 130 affects the fluctuation in the detection capacitance of the electrostatic sensor 110 in the comparative input device.

[0037] In contrast, the input device 100 of the embodiment includes the capacitor 160 connected between the cathode of the LED 130 and the ground, and therefore can be considered to be able to mitigate fluctuations in the capacitance of the detection electrode 111 due to the on / off of the LED 130.

[0038] Based on the above considerations, the capacitance of the detection electrode 111 can be expressed by the following formula:

[0039] In the input device 100 of the embodiment, the capacitance Ct1 (composite capacitance) of the detection electrode 111 when the LED 130 is turned on can be calculated by the following equation (1) assuming that the circuit part 105 has a sufficiently low impedance. Ct1=Cfs+Csg+Cls (1)

[0040] Furthermore, in the comparative input device, the capacitance Ct (composite capacitance) of the detection electrode 111 when the LED 130 is turned on can be calculated using the above formula (1) in the same way as in the input device 100 of the embodiment, assuming that the circuit part 105 has sufficiently low impedance.

[0041] In the input device 100 of the embodiment, the capacitance Ct2 (composite capacitance) of the detection electrode 111 when the LED 130 is turned off can be calculated by the following equation (2) taking into account the parasitic capacitance Clg and the capacitance Cx of the capacitor 160. Ct2=Cfs+Csg+Cls×(Clg+Cx) / (Cls+Clg+Cx) (2)

[0042] Furthermore, since the comparative input device does not include the capacitor 160, the capacitance Ct3 (composite capacitance) of the detection electrode 111 when the LED 130 is turned off in the comparative input device can be calculated using the following equation (3) by setting Cx to 0 pF in equation (2). Ct3=Cfs+Csg+Cls×Clg / (Cls+Clg) (3)

[0043] As described above, the capacitance Ct1 of the detection electrode 111 when the LED 130 is turned on in the input device 100 of the embodiment can be expressed by equation (1), and the capacitance Ct of the detection electrode 111 when the LED 130 is turned on in the comparative input device can also be expressed by equation (1).

[0044] In addition, the capacitance Ct2 (see equation (2)) of the detection electrode 111 when the LED 130 is off in the input device 100 of the embodiment and the capacitance Ct3 (see equation (3)) of the detection electrode 111 when the LED 130 is off in the comparative input device differ by the capacitance Cx of the capacitor 160.

[0045] <Simulation results using equation (2)> 3 is a diagram showing calculation results of the capacitances Ct1 and Ct2 of the detection electrode 111 when the capacitance Cx of the capacitor 160 is changed in the input device 100 of the embodiment. In Fig. 3, the horizontal axis represents the capacitance Cx (pF) of the capacitor 160 in logarithm, and the vertical axis represents the capacitance Ct1 or Ct2 (pF) of the detection electrode 111. Note that the capacitance of the detection electrode 111 of the comparative input device is a value when the capacitance Cx is set to 0 pF, but is not shown here because the capacitance Cx on the horizontal axis is represented in logarithm.

[0046] In the simulation, the parasitic capacitance Cfs between the fingertip FT and the detection electrode 111 when the fingertip FT is in contact with the operation surface 101 was set to 2 pF, the parasitic capacitance Cfs between the fingertip FT and the detection electrode 111 when no operation is being performed with the fingertip FT was set to 0 pF, the parasitic capacitance Csg between the detection electrode 111 and ground was set to 20 pF, the parasitic capacitance Cls between the detection electrode 111 and the circuit part 105 was set to 10 pF, and the parasitic capacitance Clg between the circuit part 105 and ground was set to 10 pF.

[0047] 3, the solid line indicates the capacitance Ct1 (ON / no operation) of the detection electrode 111 when the LED 130 is turned on and no operation is being performed with the fingertip FT, and the dashed line indicates the capacitance Ct1 (ON / operation) of the detection electrode 111 when the fingertip FT is in contact with the operation surface 101. In addition, the dashed line indicates the capacitance Ct2 (OFF / no operation) of the detection electrode 111 when the LED 130 is turned off and no operation is being performed with the fingertip FT, and the dashed line indicates the capacitance Ct2 (OFF / operation) of the detection electrode 111 when the fingertip FT is in contact with the operation surface 101.

[0048] 3, when comparing the capacitance Ct1 (ON / no operation) with the capacitance Ct1 (ON / operation), the capacitance Ct1 (ON / operation) is increased by an amount equivalent to the parasitic capacitance Cfs between the fingertip FT and the detection electrode 111. Similarly, when comparing the capacitance Ct2 (OFF / no operation) with the capacitance Ct2 (OFF / operation), the capacitance Ct2 (OFF / operation) is increased by an amount (Cd1) equivalent to the parasitic capacitance Cfs between the fingertip FT and the detection electrode 111.

[0049] Furthermore, when comparing the capacitance Ct1 (ON / no operation) and the capacitance Ct2 (OFF / no operation), a tendency was observed in which the difference between the capacitance Ct1 (ON / no operation) and the capacitance Ct2 (OFF / no operation) became smaller as the capacitance Cx of the capacitor 160 increased. In particular, when the capacitance Cx of the capacitor 160 became 500 pF or greater, the capacitance Ct1 (ON / no operation) and the capacitance Ct2 (OFF / no operation) became substantially the same. This indicates that, when no fingertip FT operation is being performed, the capacitance of the detection electrode 111 does not fluctuate depending on whether the LED 130 is turned on or off. Note that when the capacitance Cx of the capacitor 160 is a very small value, such as 1 pF, the difference Cd2 between the capacitance Ct1 (ON / no operation) and the capacitance Ct2 (OFF / no operation) is the difference in capacitance of the detection electrode 111 depending on whether the LED 130 is turned on or off.

[0050] Furthermore, comparing the capacitance Ct1 (ON / operated) with the capacitance Ct2 (OFF / operated), it was found that the difference between the capacitance Ct1 (ON / operated) and the capacitance Ct2 (OFF / operated) tended to decrease as the capacitance Cx of the capacitor 160 increased. In particular, when the capacitance Cx of the capacitor 160 reached 500 pF or more, the capacitance Ct1 (ON / operated) and the capacitance Ct2 (OFF / operated) became approximately the same. This indicates that the capacitance of the detection electrode 111 does not fluctuate depending on whether the LED 130 is turned on or off when the fingertip FT is in contact with the operation surface 101. Note that the capacitance Cx of 500 pF corresponds to 50 times the parasitic capacitance Cls (10 pF) between the detection electrode 111 and the circuit part 105.

[0051] In this way, the fluctuation in capacitance of the detection electrode 111 due to the on / off of the LED 130 is suppressed when no operation is being performed with the fingertip FT and when the fingertip FT is in contact with the operation surface 101, so it can be considered that the same applies when a hover operation is performed without the fingertip FT being in contact with the operation surface 101.

[0052] <Effects> The input device 100 includes an LED 130, a MOSFET 140 connected in series to the LED 130 and switching the LED 130 on and off, an electrostatic sensor 110 having a detection electrode 111 capacitively coupled to a circuit portion 105 between the LED 130 and the MOSFET 140, and a capacitor 160 having a first terminal 161 connected to the circuit portion 105 and a second terminal 162 connected to ground. Connecting the capacitor 160 between the cathode of the LED 130 and ground can suppress fluctuations in the capacitance of the detection electrode 111 caused by turning the LED 130 on and off.

[0053] Therefore, it is possible to provide the input device 100 in which the influence of the light emitting state of the LED 130 on the detection capacitance of the electrostatic sensor 110 is suppressed.

[0054] Furthermore, since the MOSFET 140 is used as a switching element, highly reliable switching can be achieved in the current path of the LED 130.

[0055] Furthermore, since the capacitance Cx of the capacitor 160 is 50 times or more the parasitic capacitance Cls between the detection electrode 111 and the circuit part 105, the capacitance of the detection electrode 111 does not fluctuate depending on whether the LED 130 is turned on or off, and approximately the same capacitance is obtained. Therefore, it is possible to provide an input device 100 in which the effect of the light emission state of the LED 130 on the detection capacitance of the capacitive sensor 110 is more effectively suppressed.

[0056] <Variations of circuit part 105> 4A to 4C are diagrams illustrating variations of the circuit portion 105. Figures 4A to 4C show modified examples of the connection relationship between the LED 130, MOSFET 140, and circuit portion 105 between the power supply 103 and ground in Figure 1, and modified examples of the connection of the capacitor 160. Note that the light-emission control unit 150 is omitted from Figures 4A to 4C.

[0057] In Figure 4A, the positions of the LED 130 and the resistor R are interchanged compared to Figure 1. As an example, in Figure 4A, the placement of the resistor R that limits the current is changed compared to Figure 1.

[0058] In FIG. 4A, between the power supply 103 and ground, the anode of the LED 130 is connected to the power supply 103, the cathode of the LED 130 is connected to the MOSFET 140 via the circuit portion 105, and the capacitor 160 is connected to the cathode of the LED 130 via the circuit portion 105.

[0059] 4A, the distance between the power supply 103 and the LED 130 is longer than in FIG. 1, and the distance between the LED 130 and the MOSFET 140 is shorter. In FIG. 4A, the resistor R may be a wiring resistor. In FIG. 4A, the distance between the LED 130 and the MOSFET 140 is short, so the resistor R is not shown in the circuit portion 105 between the LED 130 and the MOSFET 140. Even in the circuit configuration shown in FIG. 4A, by connecting a capacitor 160 between the circuit portion 105 and ground, it is possible to suppress fluctuations in the capacitance of the detection electrode 111 due to the on / off of the LED 130, as in the input device 100 having the circuit configuration shown in FIG. 1.

[0060] 4B, the positions of the LED 130 and the MOSFET 140 are swapped compared to FIG. 1. In FIG. 4B, a circuit portion 105 is provided between the MOSFET 140 on the power supply 103 side and the LED 130 on the ground side. That is, in FIG. 4B, between the power supply 103 and the ground, the MOSFET 140 is connected to the power supply 103, the anode of the LED 130 is connected to the MOSFET 140 via the circuit portion 105, the cathode of the LED 130 is connected to the ground, and the capacitor 160 is connected to the anode of the LED 130 via the circuit portion 105. By connecting the capacitor 160 between the circuit portion 105 and the ground, it is possible to suppress fluctuations in the capacitance of the detection electrode 111 due to the on / off of the LED 130, as in the input device 100 having the circuit configuration shown in FIG. 1.

[0061] In FIG. 4C , the positions of the LED 130 and the resistor R are swapped compared to FIG. 4B . As an example, the arrangement of the resistor R that limits the current is changed in FIG. 4C compared to FIG. 1 . Also, in FIG. 4A , the distance between the LED 130 and ground is longer than in FIG. 4B , and the distance between the LED 130 and the MOSFET 140 is shorter. In FIG. 4C , the resistor R may be a wiring resistor. In FIG. 4C , because the distance between the LED 130 and the MOSFET 140 is short, the resistor R is not shown in the circuit portion 105 between the LED 130 and the MOSFET 140. In the circuit configuration shown in FIG. 4C , by connecting a capacitor 160 between the circuit portion 105 and ground, fluctuations in the capacitance of the detection electrode 111 due to the on / off of the LED 130 can be suppressed, similar to the input device 100 having the circuit configuration shown in FIG. 1 .

[0062] <Mutual capacitance input device 100M> 5 is a diagram showing an example of a model of an equivalent circuit used to simulate the detection capacitance of the input device 100M according to the modified example of the embodiment. Here, an equivalent circuit when a user operates the input device 100M with a fingertip FT will be described. The input device 100M differs from the input device 100 shown in FIGS. 1 and 2 in that the input device 100M detects capacitance using a mutual capacitance method.

[0063] The input device 100M includes an electrostatic sensor 110M instead of the electrostatic sensor 110 of the input device 100 shown in FIGS. 1 and 2. The electrostatic sensor 110M is a mutual capacitance electrostatic sensor that has a detection electrode 111, a drive electrode 112, a detection unit 115, and a mutual capacitance drive unit 116, and detects the electrostatic capacitance of the detection electrode 111 relative to the drive electrode 112. The detection electrode 111 and drive electrode 112 of the electrostatic sensor 110M are disposed near the LED 130. The drive electrode 112 is provided on the opposite side of the detection electrode 111 from the operation surface 101. The mutual capacitance drive unit 116 is connected to the drive electrode 112, and outputs an AC voltage for driving.

[0064] 2, a parasitic capacitance Cf occurs between the fingertip FT and the detection electrode 111. Since the input device 100M is of a mutual capacitance type, it is considered that only the parasitic capacitance Cf changes when the fingertip FT approaches.

[0065] It can also be considered that there is a parasitic capacitance Cds between the detection electrode 111 and the drive electrode 112, a parasitic capacitance Cls between the detection electrode 111 and the circuit part 105, a parasitic capacitance Cld between the drive electrode 112 and the circuit part 105, and a parasitic capacitance Clg between the circuit part 105 and ground.

[0066] In the input device 100M described above, the capacitance Ctm1 (composite capacitance) of the detection electrode 111 when the LED 130 is turned on can be calculated by the following equation (4), assuming that the impedance of the circuit part 105 is sufficiently low. Ctm1=Cds (4)

[0067] In the input device 100M of the embodiment, the capacitance Ctm2 (composite capacitance) of the detection electrode 111 when the LED 130 is turned off can be calculated by the following equation (5) taking into account the parasitic capacitance Clg and the capacitance Cx of the capacitor 160. Ctm2=Cds+Cld / (Cld+Clg+Cx)×(Cld×Cls) / (Cld+Cls) (5)

[0068] <Simulation results using equation (5)> 6 is a diagram showing calculation results of the capacitances Ctm1 and Ctm2 of the detection electrode 111 when the capacitance Cx of the capacitor 160 is changed in an input device 100M according to a modified example of the embodiment. In FIG. 6, the horizontal axis represents the capacitance Cx (pF) of the capacitor 160 in logarithm, and the vertical axis represents the capacitance Ctm1 or Ctm2 (pF) of the detection electrode 111.

[0069] In the simulation, the parasitic capacitance Cds between the detection electrode 111 and the drive electrode 112 was set to 5 pF. The parasitic capacitance Cld between the drive electrode 112 and the circuit part 105 was set to 10 pF, the parasitic capacitance Cls between the detection electrode 111 and the circuit part 105 was set to 10 pF, and the parasitic capacitance Clg between the circuit part 105 and ground was set to 10 pF. The change ΔCf in the parasitic capacitance Cds when the fingertip FT is in contact with the operation surface 101 compared to when the fingertip FT is not in contact with the operation surface 101 was set to -0.3 pF.

[0070] 6, the solid line indicates the capacitance Ctm1 (ON / no operation) of the detection electrode 111 when the LED 130 is turned on and no operation is being performed with the fingertip FT, and the dashed line indicates the capacitance Ctm1 (ON / operation) of the detection electrode 111 when the fingertip FT is in contact with the operation surface 101. Also, the dashed-dotted line indicates the capacitance Ctm2 (OFF / no operation) of the detection electrode 111 when the LED 130 is turned off and no operation is being performed with the fingertip FT, and the dashed-two-dotted line indicates the capacitance Ctm2 (OFF / operation) of the detection electrode 111 when the fingertip FT is in contact with the operation surface 101.

[0071] As shown in Figure 6, when comparing capacitance Ctm1 (ON / no operation) with capacitance Ctm1 (ON / operated), the capacitance Ctm1 (ON / operated) is reduced by the change in parasitic capacitance Cds ΔCf (-0.3 pF) due to fingertip FT. Similarly, when comparing capacitance Ctm2 (OFF / no operation) with capacitance Ctm2 (OFF / operated), the capacitance Ctm2 (OFF / operated) is reduced by the change in parasitic capacitance Cds ΔCf due to fingertip FT.

[0072] Furthermore, when comparing the capacitance Ctm1 (ON / no operation) with the capacitance Ctm2 (OFF / no operation), it was found that the capacitance Ctm2 (OFF / no operation) decreased as the capacitance Cx of the capacitor 160 increased, and the difference between the capacitance Ctm1 (ON / no operation) and the capacitance Ctm2 (OFF / no operation) tended to become smaller. In particular, when the capacitance Cx of the capacitor 160 became 500 pF or more, the capacitance Ctm1 (ON / no operation) and the capacitance Ctm2 (OFF / no operation) became approximately the same. This indicates that when no operation of the fingertip FT is being performed, the capacitance of the detection electrode 111 does not fluctuate depending on whether the LED 130 is turned on or off. In addition, when the capacitance Cx of the capacitor 160 is a very small value such as 1 pF, the difference Cd3 between the capacitance Ctm1 (ON / no operation) and the capacitance Ctm2 (OFF / no operation) is the difference in capacitance of the detection electrode 111 when the LED 130 is on and off.

[0073] Furthermore, comparing the capacitance Ctm1 (ON / operated) with the capacitance Ctm2 (OFF / operated), it was found that as the capacitance Cx of the capacitor 160 increased, the capacitance Ctm2 (OFF / operated) decreased, and the difference between the capacitance Ctm1 (ON / operated) and the capacitance Ctm2 (OFF / operated) tended to become smaller. In particular, when the capacitance Cx of the capacitor 160 became 500 pF or greater, the capacitance Ctm1 (ON / operated) and the capacitance Ctm2 (OFF / operated) became approximately the same. This indicates that the capacitance of the detection electrode 111 does not fluctuate depending on whether the LED 130 is turned on or off when the fingertip FT is in contact with the operation surface 101. Note that the capacitance Cx of 500 pF corresponds to 50 times the parasitic capacitance Cls (10 pF) between the detection electrode 111 and the circuit part 105.

[0074] In this way, the fluctuation in capacitance of the detection electrode 111 due to the on / off of the LED 130 is suppressed when no operation is being performed with the fingertip FT and when the fingertip FT is in contact with the operation surface 101, so it can be considered that the same applies when a hover operation is performed without the fingertip FT being in contact with the operation surface 101.

[0075] Although details will not be given here, in a comparative modified input device in which the capacitor 160 is omitted from the input device 100M of the modified embodiment, the capacitance of the detection electrode 111 when the LED 130 is turned off is such that the capacitance Cx of the capacitor 160 in equation (5) becomes 0 pF, and therefore it is considered that the capacitance of the detection electrode 111 fluctuates depending on whether the LED 130 is turned on or off.

[0076] <Effects> The input device 100M includes an LED 130, a MOSFET 140 connected in series to the LED 130 and switching the LED 130 on and off, an electrostatic sensor 110M having a detection electrode 111 capacitively coupled to a circuit portion 105 between the LED 130 and the MOSFET 140, and a capacitor 160 having a first terminal 161 connected to the circuit portion 105 and a second terminal 162 connected to ground. By connecting the capacitor 160 between the cathode of the LED 130 and ground, the input device 100M can suppress fluctuations in the capacitance of the detection electrode 111 caused by turning the LED 130 on and off.

[0077] Therefore, it is possible to provide the input device 100M that suppresses the influence of the light emission state of the LED 130 on the detection capacitance of the electrostatic sensor 110. In addition to the above-mentioned effects, the input device 100M also exhibits the same effects as the input device 100 shown in FIGS.

[0078] The above describes an input device according to an exemplary embodiment of the present disclosure, but 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.

[0079] This international application claims priority based on Japanese Patent Application No. 2022-117780, filed on July 25, 2022, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0080] 100, 100M input device 110, 110M electrostatic sensor 111 Detection electrode 112 Drive electrode 115 Detector 116 Mutual capacitance driver 130 LED (an example of a light-emitting diode) 140 MOSFET (an example of a switching element) 150 Light emission control unit 160 capacitor 161 1st terminal 162 2nd terminal

Claims

1. A light emitting diode, a switching element connected in series to the light-emitting diode and configured to switch the light-emitting diode on and off; an electrostatic sensor having a detection electrode capacitively coupled to a circuit portion between the light-emitting diode and the switching element; a capacitor having a first terminal connected to the circuit portion and a second terminal connected to a fixed potential point; an input device,

2. The input device of claim 1 , wherein the switching element is a metal oxide semiconductor field effect transistor.

3. The input device according to claim 1 , wherein the capacitance of the capacitor is 50 times or more the capacitance between the detection electrode and the circuit portion.

4. Between the power supply and the fixed potential point, an anode of the light-emitting diode connected to the power supply, a cathode of the light-emitting diode connected to the switching element via the circuit portion, and the capacitor connected to the cathode of the light-emitting diode via the circuit portion; or 4. The input device according to claim 1, wherein the switching element is connected to the power supply, the anode of the light-emitting diode is connected to the switching element via the circuit portion, the cathode of the light-emitting diode is connected to the fixed potential point, and the capacitor is connected to the anode of the light-emitting diode via the circuit portion.

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