Static capacitance detection device and input device

Abstract

The electrostatic capacitance detection device (3) comprises: a first capacitor (C1) arranged on a path between a first node (N1) connected to a detection electrode (Es) and a second node (N2); a second capacitor (C2) arranged on a path between the first node (N1) and the ground; a third capacitor (C3) arranged on a path between a third node (N3) connected to a shielding electrode (Ea) arranged close to the detection electrode (Es) and the first node (N1); an AC voltage output circuit (31) outputting a first AC voltage (Vas) to the third node (N3); a first attenuation circuit (32) outputting a second AC voltage (Vdvr) obtained by attenuating the amplitude of the first AC voltage (Vas); and a charge amplifier (33) supplying charge to the first capacitor (C1) via the second node (N2) and outputting a detection signal (Vo) corresponding to the supplied charge.

Description

Technical Field

[0001] The present invention relates to an electrostatic capacitance detection device and an input device. Background Art

[0002] In a self-capacitance type electrostatic capacitance sensor that detects the electrostatic capacitance between an object such as a finger and a detection electrode, the parasitic capacitance between an object other than the object and the detection electrode becomes an error in the detection result. As a method of reducing such an error, there is a known method of arranging a shielding electrode (also called an active shield) having the same potential as the detection electrode around the detection electrode. The following patent document 1 describes a technology for further reducing the influence of the above-mentioned parasitic capacitance in an electrostatic capacitance detection device having a shielding electrode.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2018 / 116706

[0006] Patent Document 2: International Publication No. 2016 / 059967

[0007] Patent Document 3: International Publication No. 2018 / 159460

[0008] Patent Document 4: International Publication No. 2019 / 069650

[0009] Patent Document 5: Japanese Patent Application Publication No. 2001-021519 Summary of the invention

[0010] -Problems to be solved by the invention-

[0011] However, since the shielding electrode and the detection electrode are arranged close to each other, the shielding electrode and the detection electrode may be in a short-circuited state due to poor manufacturing, degradation caused by use, etc. In addition, when the sensor part (detection electrode, shielding electrode) in contact with the object and the electronic circuit for detecting the electrostatic capacitance are connected by a cable, sometimes the sensor part and the electronic circuit are electrically disconnected from each other due to the disconnection of the cable. In the case of such a short-circuited state or open-circuited state, the detection result of the electrostatic capacitance shows an abnormal value, but it is difficult to accurately determine the short-circuited state and the open-circuited state only by the detection result of the electrostatic capacitance. In order to determine the short-circuited state and the open-circuited state, a dedicated circuit can also be provided, but the number of components increases and the structure becomes complicated.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrostatic capacitance detection device capable of determining a short-circuit state and an open-circuit state with a simple structure, and an input device including such an electrostatic capacitance detection device.

[0013] -Methods for solving the problem-

[0014] A first aspect of the present invention is an electrostatic capacitance detection device, which detects the electrostatic capacitance between an object and a detection electrode, and comprises: a first capacitor, which is arranged on a path between a first node connected to the detection electrode and a second node; a second capacitor, which is arranged on a path between the first node and the ground; a third capacitor, which is arranged on a path between a third node connected to a shielding electrode arranged close to the detection electrode and the first node; an AC voltage output circuit, which outputs a first AC voltage to the third node; a first attenuation circuit, which outputs a second AC voltage obtained by attenuating the amplitude of the first AC voltage; and a charge amplifier, which supplies charge to the first capacitor via the second node and outputs a detection signal corresponding to the supplied charge, wherein the charge amplifier supplies the charge to the first capacitor so that the voltage generated at the second node is close to the second AC voltage.

[0015] According to this structure, when at least one of the path between the detection electrode and the first node and the path between the shielding electrode and the third node is electrically cut off in an open circuit state, the parasitic capacitance between the detection electrode and the shielding electrode is no longer connected in parallel with the third capacitor. Therefore, the static capacitance between the first node and the third node is reduced, the amplitude of the AC voltage between the first node and the third node is increased, and the amplitude of the AC voltage in the first node is reduced. On the other hand, when the detection electrode and the shielding electrode are in a short circuit state, the first node and the third node are connected, so the amplitude of the AC voltage in the first node is increased to an amplitude substantially equal to that of the first AC voltage. That is, the amplitude of the AC voltage in the first node decreases when it becomes the open circuit state, and increases when it becomes the short circuit state. As a result, the change in the accumulated charge in the first capacitor when the voltage amplitude of the first capacitor changes with the change in the amplitude of the AC voltage in the first node is opposite in sign when it becomes the open circuit state and when it becomes the short circuit state. Since the detection signal is a signal corresponding to the charge supplied from the charge amplifier to the first capacitor, when the sign of the change of the accumulated charge in the first capacitor is opposite, the detection signal also changes in the opposite direction. Therefore, the open circuit state and the short circuit state can be determined based on the fact that the detection signal changes in the opposite directions when the open circuit state and the short circuit state are achieved.

[0016] Preferably, the charge amplifier includes a feedback capacitor, which is arranged on a path between a fourth node outputting the detection signal and the second node, and the charge is supplied from the feedback capacitor to the first capacitor via the second node, and the first attenuation circuit maintains an attenuation ratio which is a ratio of the amplitude of the second AC voltage to the amplitude of the first AC voltage so that the amplitude of the voltage of the detection signal becomes close to zero in a non-detection state in which the object is not present.

[0017] According to this structure, in the non-detection state in which the object does not exist, the amplitude of the voltage of the detection signal becomes close to zero. In addition, the larger the static capacitance between the object and the detection electrode (hereinafter, sometimes referred to as "detection object capacitance"), the larger the amplitude of the voltage of the detection signal. Therefore, the range in which the voltage of the detection signal changes according to the change of the detection object capacitance becomes wider, and it is easy to improve the detection sensitivity of the detection object capacitance.

[0018] In addition, when the amplitude of the voltage of the detection signal becomes near zero in the non-detection state, the amplitude of the voltage generated in the feedback capacitor is approximately equal to the amplitude of the second AC voltage. At this time, the amplitude of the voltage generated in the first capacitor is approximately equal to the amplitude obtained by multiplying the amplitude of the second AC voltage by a certain coefficient (the static capacitance ratio of the first capacitor and the feedback capacitor). In this non-detection state, assuming that the static capacitance of the second capacitor is zero, no charge is accumulated in the second capacitor, so the amplitude of the voltage of the first node becomes larger. In this case, the amplitude of the voltage generated in the first capacitor becomes larger, and the amplitude of the voltage of the detection signal deviates from near zero. In the case where the amplitude of the voltage of the detection signal deviates from near zero, as a method of making the amplitude close to zero, there is a method of increasing the amplitude of the second AC voltage and a method of reducing the static capacitance of the third capacitor.

[0019] In the case of adopting the method of increasing the amplitude of the second AC voltage, the amplitude of the voltage of the second node increases and approaches the amplitude of the voltage of the first node, and the amplitude of the voltage generated in the first capacitor decreases. However, when the amplitude of the voltage of the second node increases, when the amplitude of the AC voltage in the first node increases to an amplitude substantially equal to the first AC voltage in the short-circuit state, the change in the voltage amplitude of the first capacitor accompanying the increase in the amplitude is suppressed. When the change in the voltage amplitude of the first capacitor is suppressed, the change in the voltage amplitude of the detection signal is suppressed, so it is difficult to determine the short-circuit state based on the change in the voltage amplitude of the detection signal. In addition, in the case of adopting the method of increasing the amplitude of the second AC voltage, the difference between the voltage amplitude of the second node (the amplitude of the second AC voltage) and the voltage amplitude of the third node (the amplitude of the first AC voltage) decreases, so the difference between the voltage amplitude of the first node and the voltage amplitude of the third node (the amplitude of the first AC voltage) also decreases. Therefore, when the electrostatic capacitance between the first node and the third node decreases in the open state, the change in the amplitude of the voltage between the first node and the third node (increase in the voltage amplitude) is suppressed, and the change in the voltage amplitude of the first capacitor is suppressed. When the change in the voltage amplitude of the first capacitor is suppressed, the change in the voltage amplitude of the detection signal is suppressed, so it is difficult to determine the open state based on the change in the voltage amplitude of the detection signal.

[0020] On the other hand, when the method of reducing the electrostatic capacitance of the third capacitor is adopted, the amplitude of the voltage at the first node becomes smaller and approaches the amplitude of the voltage at the second node, thereby reducing the amplitude of the voltage generated in the first capacitor. However, if the electrostatic capacitance of the third capacitor is reduced, it is easy to be affected by external noise transmitted from the detection electrode, and the noise tolerance is reduced.

[0021] Therefore, by setting the second capacitor having an appropriate static capacitance between the first node and the ground, the static capacitance of the third capacitor can be increased and the influence of external noise can be reduced. When the short circuit state and the open circuit state occur, the voltage amplitude of the detection signal changes significantly, making it easy to accurately determine the short circuit state and the open circuit state.

[0022] Preferably, in an open circuit state in which at least one of the path between the detection electrode and the first node and the path between the shielding electrode and the third node is electrically cut off, the amplitude of the voltage of the detection signal becomes maximum, and in a short circuit state in which a short circuit occurs between the detection electrode and the shielding electrode, the amplitude of the voltage of the detection signal becomes maximum, and the phase of the voltage of the detection signal relative to the first AC voltage is reversed compared to the open circuit state.

[0023] According to this configuration, the open state and the short state can be determined more accurately based on the amplitude of the voltage of the detection signal and the phase of the voltage of the detection signal with respect to the first AC voltage.

[0024] Preferably, the first attenuation circuit includes a series circuit of a fourth capacitor and a fifth capacitor, the AC voltage output circuit applies the first AC voltage to both ends of the series circuit, and the first attenuation circuit outputs the AC voltage generated at both ends of the fifth capacitor as the second AC voltage.

[0025] According to this configuration, the first AC voltage is applied to the series circuit of the fourth capacitor and the fifth capacitor, and the second AC voltage corresponding to the first AC voltage is generated in the fifth capacitor. Therefore, compared with the case of using an attenuator based on a resistor, the noise of the second AC voltage is reduced.

[0026] Preferably, the electrostatic capacitance of the fourth capacitor and the electrostatic capacitance of the fifth capacitor are each set so that the amplitude of the voltage of the detection signal becomes close to zero in the non-detection state.

[0027] According to this configuration, the attenuation ratio, which is a ratio of the amplitude of the second AC voltage to the amplitude of the first AC voltage, is determined based on the electrostatic capacitance of the fourth capacitor and the electrostatic capacitance of the fifth capacitor. The electrostatic capacitance of the fourth capacitor and the electrostatic capacitance of the fifth capacitor are set so that the attenuation ratio is obtained so that the amplitude of the voltage of the detection signal becomes close to zero in the non-detection state in which the object does not exist.

[0028] Preferably, the fifth capacitor is capable of adjusting an electrostatic capacitance value, and the electrostatic capacitance value is adjusted so that the amplitude of the voltage of the detection signal becomes close to zero in the non-detection state.

[0029] According to this configuration, the amplitude of the second AC voltage is adjusted by adjusting the electrostatic capacitance value of the fifth capacitor, and by adjusting the amplitude, the amplitude of the voltage of the detection signal becomes close to zero in the non-detection state where the object does not exist.

[0030] Preferably, the charge amplifier includes: an operational amplifier that amplifies the voltage difference between an inverting input terminal connected to the second node and a non-inverting input terminal to which the second AC voltage is applied, and outputs the detection signal corresponding to the amplified voltage difference to a fourth node; and a feedback circuit that is arranged on a path between the fourth node and the second node, and the electrostatic capacitance detection device has a subtraction circuit that subtracts a reference signal from the detection signal, which is equivalent to a signal output from the operational amplifier as the detection signal in a non-detection state in which the object is not present.

[0031] According to this structure, the reference signal corresponding to the signal output from the operational amplifier as the detection signal in the non-detection state in which the object does not exist is subtracted from the detection signal. The signal obtained as a result of the subtraction operation has an amplitude corresponding to the detection object capacitance, which is small in the non-detection state. Therefore, the dynamic range of the detection signal corresponding to the change of the detection object capacitance becomes larger, and the detection sensitivity of the detection object capacitance is improved.

[0032] Preferably, there is provided a second attenuation circuit configured to output an AC voltage obtained by attenuating the amplitude of the first AC voltage as the reference signal.

[0033] According to this structure, the reference signal subtracted from the detection signal in the subtraction circuit is a voltage obtained by attenuating the first AC voltage, so the noise component included in the detection signal and the noise component included in the reference signal have a high correlation. As a result, the noise component of the signal obtained as a result of the subtraction operation of the subtraction circuit is reduced.

[0034] Preferably, a first resistor is provided on a path between the second node and the first capacitor, and the feedback circuit includes a feedback capacitor provided on a path between the fourth node and the second node and a feedback resistor connected in parallel with the feedback capacitor.

[0035] According to this configuration, since the feedback capacitor, the first resistor, and the operational amplifier constitute a low-pass filter, noise input via the detection electrode is attenuated, thereby suppressing a decrease in detection accuracy.

[0036] Preferably, a circuit substrate having the first node and the second node is provided, and the first capacitor, the second capacitor, and the third capacitor are mounted on the circuit substrate.

[0037] The second aspect of the present invention is an input device, comprising: a detection electrode, the electrostatic capacitance between which changes according to the proximity of the object; a shielding electrode, which is arranged close to the detection electrode; and the electrostatic capacitance detection device described in the first aspect, which detects the electrostatic capacitance between the object and the detection electrode.

[0038] -Effects of the Invention-

[0039] According to the present invention, it is possible to provide an electrostatic capacitance detection device capable of determining a short-circuit state and an open-circuit state with a simple configuration, and an input device including such an electrostatic capacitance detection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a diagram showing an example of the structure of the input device involved in this embodiment.

[0041] Figure 2 It is a diagram showing an example of the configuration of the electrostatic capacitance detection device according to the present embodiment.

[0042] Figure 3A to Figure 3D It is a diagram illustrating the signal waveforms of each part of the electrostatic capacitance detection device.

[0043] Figure 4 It is a diagram showing a modified example of the input device involved in this embodiment. DETAILED DESCRIPTION

[0044] Figure 1 It is a diagram showing an example of the structure of the input device involved in this embodiment. Figure 1 The input device shown includes a sensor unit 1 , a cable 2 , a capacitance detection device 3 , a processing unit 4 , a storage unit 5 , and an interface unit 6 .

[0045] When an object 9 such as a finger or a pen approaches the sensor unit 1, the input device according to the present embodiment detects the electrostatic capacitance between the detection electrode Es provided in the sensor unit 1 and the object 9, and inputs information corresponding to the approach of the object 9 based on the detection result. For example, the input device obtains information related to the proximity of the object 9 relative to the sensor unit 1 and the distance between the sensor unit 1 and the object 9 based on the detection result of the electrostatic capacitance. For example, the input device is applied to a user interface device such as a touch sensor and a touch pad. In addition, "approach" in this specification means being in the vicinity, and does not limit whether the approaching objects are in contact with each other.

[0046] The sensor unit 1 includes: a detection electrode Es that generates electrostatic capacitance between the detection electrode Es and an object 9 such as a finger or a pen that is a conductor; and a shielding electrode Ea that is arranged close to the detection electrode Es. The sensor unit 1 has a detection area where the object 9 can approach the detection electrode Es. The surface of the detection area is covered with, for example, an insulating covering layer, and the detection electrode Es is arranged on the lower layer side than the covering layer. The shielding electrode Ea is an electrostatic shield for preventing electrostatic coupling between objects other than the object 9 and the detection electrode Es, and is arranged, for example, at a position on the lower layer side than the detection electrode Es in the detection area.

[0047] like Figure 1 As shown, a parasitic capacitance component Crg is formed between the detection electrode Es and the object 9. A parasitic capacitance component Crs is formed between the shield electrode Ea and the detection electrode Es. A parasitic capacitance component Csg is formed between the shield electrode Ea and the ground.

[0048] The electrostatic capacitance detection device 3 detects the electrostatic capacitance of the capacitance component Crg formed between the object 9 and the detection electrode Es (hereinafter sometimes referred to as "detection target capacitance Crg") and outputs a signal Ds indicating the detection result. The electrostatic capacitance detection device 3 is connected to the detection electrode Es and the shielding electrode Ea of the sensor unit 1 via the cable 2.

[0049] The processing unit 4 is a circuit that controls the overall operation of the input device, and includes, for example, one or more processors (CPU, DSP, etc.) that perform processing according to the instruction code of the program stored in the storage unit 5. In addition, the processing unit 4 may also include dedicated hardware (ASIC, FPGA, etc.) configured to perform specific functions. The processing of the processing unit 4 can be implemented by the processor executing the instruction code of the program, or at least a part of it can be implemented by dedicated hardware.

[0050] The processing unit 4 determines whether the object 9 is close to the sensor unit 1, calculates the distance between the object 9 and the sensor unit 1, determines the open circuit state and the short circuit state described later, etc. based on the signal Ds of the detection result output from the electrostatic capacitance detection device 3. Figure 4 As in the modified example of FIG. 1 , the sensor unit 1 may also include a plurality of detection electrodes Es, and the electrostatic capacitance detection device 3 may also detect the detection object capacitance Crg for each of the plurality of detection electrodes Es. In this case, the processing unit 4 may also calculate the proximity position of the object 9 in the detection area of ​​the sensor unit 1, the size of the object 9, etc. based on the signal Ds of the detection result obtained for each detection electrode Es.

[0051] The storage unit 5 stores programs including instruction codes executed by the processor of the processing unit 4, data used in processing in the processing unit 4, data temporarily held during processing, etc. The storage unit 5 is configured using one or more storage devices such as DRAM, SRAM, flash memory, and hard disk.

[0052] The interface unit 6 is a circuit for exchanging data between the input device and other devices (e.g., a main controller of an electronic device equipped with the input device). The processing unit 4 outputs information (the presence or absence of the object 9, the proximity position of the object 9, the distance to the object 9, the size of the object 9, etc.) obtained based on the detection result of the electrostatic capacitance detection device 3 to a higher-level device (not shown) through the interface unit 6. In the higher-level device, this information is used to construct a user interface for, for example, recognizing instruction operations, gesture operations, etc.

[0053] Next, the structure of the electrostatic capacitance detection device 3 will be described. Figure 2 It is a diagram showing an example of the structure of the electrostatic capacitance detection device 3 according to the present embodiment. Figure 2 The electrostatic capacitance detection device 3 shown has a first capacitor C1, a second capacitor C2, a third capacitor C3, a first resistor R1, an AC voltage output circuit 31, a first attenuation circuit 32, a charge amplifier 33, a second attenuation circuit 34, a subtraction circuit 35 and a demodulation circuit 36.

[0054] The first capacitor C1 is provided in a path between the first node N1 and the second node N2. The first node N1 is connected to the detection electrode Es via the cable 2. The second node N2 is connected to the charge amplifier 33. Figure 2 In the example of FIG. 1 , a first resistor R1 is provided on a path between the second node N2 and the first capacitor C1.

[0055] The second capacitor C2 is provided in a path between the first node N1 and the ground.

[0056] The third capacitor C3 is provided in a path between the third node N3 and the first node N1. The third node N3 is connected to the shielding electrode Ea via the cable 2.

[0057] The AC voltage output circuit 31 outputs the first AC voltage Vas to the third node N3. For example, the AC voltage output circuit 31 outputs the first AC voltage Vas as a sinusoidal wave having a fixed amplitude and frequency.

[0058] exist Figure 2In the example, the AC voltage output circuit 31 includes: a constant voltage source 311 that outputs a DC voltage; an oscillator 312 that generates an oscillation signal of a sinusoidal wave having a given frequency; an operational amplifier OP2; and resistors R3 and R4. The DC voltage of the constant voltage source 311 is applied to the non-inverting input terminal of the operational amplifier OP2, and the oscillation signal of the oscillator 312 is input to the inverting input terminal of the operational amplifier OP2 via the resistor R3. Resistor R4 is provided on the path between the output terminal and the inverting input terminal of the operational amplifier OP2. The output terminal of the operational amplifier OP2 is connected to the third node N3. The operational amplifier OP2 outputs a first AC voltage Vas having a DC component corresponding to the DC voltage of the constant voltage source 311 from the output terminal to the third node N3. Figure 2 In the example, the resistance value of the resistor R4 can be adjusted, and the resistance value of the resistor R4 is adjusted so that the first AC voltage Vas has a given amplitude.

[0059] The first attenuation circuit 32 outputs a second AC voltage Vdrv obtained by attenuating the amplitude of the first AC voltage Vas output by the AC voltage output circuit 31. The first attenuation circuit 32 maintains the attenuation ratio K, which is the ratio of the amplitude of the second AC voltage Vdrv to the amplitude of the first AC voltage Vas, at a ratio such that the voltage amplitude of the detection signal Vo of the charge amplifier 33 described later becomes close to zero in a non-detection state in which the object 9 does not exist.

[0060] exist Figure 2 In the example of FIG. 1 , the first attenuation circuit 32 includes a fourth capacitor C4 and a fifth capacitor C5 connected in series, and a resistor R2 connected in parallel with the fourth capacitor C4. The AC voltage output circuit 31 applies a first AC voltage Vas to the series circuit of the fourth capacitor C4 and the fifth capacitor C5. One terminal of the fourth capacitor C4 is connected to the third node N3, and the other terminal of the fourth capacitor C4 is connected to the ground via the fifth capacitor C5. The first attenuation circuit 32 outputs the AC voltage generated in the fifth capacitor C5 as a second AC voltage Vdrv. The static capacitance of the fourth capacitor C4 and the static capacitance of the fifth capacitor C5 are respectively set so that the voltage amplitude of the detection signal Vo of the charge amplifier 33 becomes close to zero in the non-detection state where the object 9 does not exist.

[0061] exist Figure 2In the example of , the fifth capacitor C5 can adjust the electrostatic capacitance value, and the electrostatic capacitance value of the fifth capacitor C5 is adjusted so that the voltage amplitude of the detection signal Vo of the charge amplifier 33 becomes close to zero in the non-detection state without the object 9. The fifth capacitor C5 can also be a component formed in a semiconductor chip or the like inside the IC. In this case, for example, the fifth capacitor C5 is composed of a plurality of capacitors connected in parallel, and the electrostatic capacitance value is adjusted by selecting the number of capacitors connected in parallel by laser trimming or the like. In addition, the fifth capacitor C5 can also be a discrete component capable of adjusting the element value.

[0062] The fifth node N5 connecting the fourth capacitor C4 and the fifth capacitor C5 is connected to the third node N3 via the resistor R2. Since the input of the charge amplifier 33 connected to the fifth node N5 (the non-inverting input terminal of the operational amplifier OP1 described later) has an input impedance sufficiently large compared to the resistance value of the resistor R2, the DC potential of the fifth node N5 is substantially equal to the DC potential of the third node N3. Figure 2 In the example of FIG. 1 , the resistance value of the resistor R2 can be adjusted during manufacturing, and by adjusting the resistance value, the phase of the second AC voltage Vdrv relative to the first AC voltage Vas can be adjusted.

[0063] The charge amplifier 33 supplies charges to the first capacitor C1 via the second node N2 and outputs a detection signal Vo corresponding to the supplied charges. The charge amplifier 33 supplies charges to the first capacitor C1 so that a voltage generated at the second node N2 approaches the second AC voltage Vdrv.

[0064] exist Figure 2 In the example of FIG. 3 , the charge amplifier 33 has a feedback circuit 331 and an operational amplifier OP1. The operational amplifier OP1 amplifies the voltage difference between the inverting input terminal connected to the second node N2 and the non-inverting input terminal to which the second AC voltage Vdrv is applied, and outputs a detection signal Vo corresponding to the amplified voltage difference to the fourth node N4. The feedback circuit 331 is provided in a path between the fourth node N4 and the second node N2. Figure 2 In the example of FIG. 3 , the feedback circuit 331 includes a feedback capacitor Cag provided in a path between the fourth node N4 and the second node N2 and a feedback resistor Rag connected in parallel to the feedback capacitor Cag.

[0065] exist Figure 2In the example, the static capacitance value of the feedback capacitor Cag and the resistance value of the feedback resistor Rag can be adjusted. By adjusting the values ​​of these components, the phase difference between the first AC voltage Vas and the second AC voltage Vdrv and the detection signal Vo, and the gain of the amplitude of the detection signal Vo relative to the static capacitance value of the detection object capacitor Crg are adjusted. The feedback capacitor Cag and the feedback resistor Rag can be components inside the IC whose component values ​​can be adjusted by laser trimming or the like, or they can be discrete components whose component values ​​can be adjusted.

[0066] The subtraction circuit 35 subtracts the reference signal Vs, which is a signal outputted from the operational amplifier OP1 as the detection signal Vo in the non-detection state in which the object 9 does not exist, from the detection signal Vo, and outputs a signal Vm indicating the result of the subtraction operation. For example, the subtraction circuit 35 includes a fully differential amplifier, and outputs the signal Vm, which is the result of the subtraction operation, as a differential signal. In addition, in order to suppress aliasing associated with AD conversion in the subsequent demodulation circuit 36, the subtraction circuit 35 may also have a function as a low-pass filter that attenuates frequency components in a higher frequency band than a given frequency band.

[0067] The second attenuation circuit 34 outputs an AC voltage obtained by attenuating the amplitude of the first AC voltage Vas as a reference signal Vs. For example, the second attenuation circuit 34 can adjust the ratio of the amplitude of the reference signal Vs to the amplitude of the first AC voltage Vas, and adjust the ratio so that in a non-detection state in which the object 9 does not exist, the amplitude of the signal Vm output by the subtraction circuit 35 becomes close to zero.

[0068] The demodulation circuit 36 ​​generates a signal Ds corresponding to the amplitude of the AC component of the signal Vm output from the subtraction circuit 35, that is, the AC component having the same frequency as the first AC voltage Vas. For example, the demodulation circuit 36 ​​includes: an A / D converter that converts the signal Vm output from the subtraction circuit 35 into a digital signal; a multiplier that multiplies the digital signal converted in the A / D converter by a signal having the same frequency as the first AC voltage Vas; and a low-pass filter that removes the AC component from the signal of the multiplication result of the multiplication by the multiplier and outputs it as the signal Ds. As described later, since the detection signal Vo has an amplitude corresponding to the detection target capacitance Crg, the signal Ds corresponding to the amplitude of the signal Vm having the same frequency as the first AC voltage Vas has a value corresponding to the detection target capacitance Crg.

[0069] For example, Figure 2As shown, the electronic components constituting the electrostatic capacitance detection device 3 are mounted on a circuit substrate 7 provided with a first node N1 and a third node N3 connected to the cable 2. The first capacitor C1, the second capacitor C2, and the third capacitor C3 may be mounted on the circuit substrate 7 as discrete components, or may be capacitors inside an IC mounted on the circuit substrate 7.

[0070] Next, the operation of the input device having the above configuration will be described. In the following description, the reference numerals (C1 to C5) of capacitors represent their electrostatic capacitances, and the reference numerals (Vas, Vdrv, Vo) of AC voltages represent their amplitudes.

[0071] (Action in normal state)

[0072] Without considering the change in the phase of the AC voltage due to the influence of the resistance value of the resistor R2, the input impedance of the operational amplifier OP1, etc., it can be considered that the phases of the AC voltages generated in the capacitors connected to the fifth node N5 are substantially equal. In this case, if the total of the charges of the capacitors connected to the fifth node N5 is saved, the following equation holds.

[0073] [Mathematical formula 1]

[0074] C4·(Vas-Vdrv)=C5·Vdrv+C0p·Vdrv…(1)

[0075] In the formula (1), "C0p" represents the static capacitance of the parasitic capacitance component C0p formed between the non-inverting input terminal of the operational amplifier OP1 and the ground. According to the formula (1), the attenuation ratio K of the first attenuation circuit 32 is expressed by the following formula.

[0076] [Mathematical formula 2]

[0077] Vdrv=K·Vas…(2-1)

[0078]

[0079] In addition, without considering the change in the phase of the AC voltage caused by the resistance value of the first resistor R1, the resistance value of the feedback resistor Rag, the input impedance of the operational amplifier OP1, etc., the phase of the AC voltage generated in each capacitor connected to the first node N1 is considered to be approximately equal. In this case, if the sum of the charges of each capacitor connected to the first node N1 is saved, the following equation holds.

[0080] [Mathematical formula 3]

[0081] (Crg+C2)·Vrx+(C3+Crs)·(Vrx-Vas)=C1·(Vdrv-Vrx)…(3)

[0082] In the formula (3), "Vrx" represents the amplitude of the AC voltage Vrx at the first node N1. According to the formula (3), the amplitude of the AC voltage Vrx at the first node N1 is expressed by the following formula.

[0083] [Formula 4]

[0084]

[0085] When equation (2-1) is applied to equation (4), the amplitude of the AC voltage Vrx at the first node N1 is expressed by the following equation.

[0086] [Formula 5]

[0087]

[0088] Furthermore, without considering the change in the phase of the AC voltage caused by the resistance value of the first resistor R1, the resistance value of the feedback resistor Rag, and the input impedance of the operational amplifier OP1, the phases of the AC voltages generated in the capacitors connected to the second node N2 are considered to be substantially equal. In this case, if the sum of the charges of the capacitors connected to the second node N2 is saved, the following equation holds.

[0089] [Mathematical formula 6]

[0090] C1·(Vdrv-Vrx)+(Cp+COn)·Vdrv=Cag·(Vo-Vdrv)…(6)

[0091] In formula (6), "Cp" represents the static capacitance of the parasitic capacitance component Cp formed between the path from the first capacitor C1 to the first resistor R1 and the ground, and "C0n" represents the static capacitance of the parasitic capacitance component C0n formed between the inverting input terminal of the operational amplifier OP1 and the ground. According to formula (6), the voltage amplitude of the detection signal Vo is expressed by the following formula.

[0092] [Formula 7]

[0093]

[0094] In the non-detection state where the object 9 does not exist, the static capacitance of the capacitance component Crg formed between the object 9 and the detection electrode Es becomes zero. The amplitude "Vrx0" of the AC voltage Vrx at the first node N1 in the non-detection state is expressed by the following equation by setting "Crg" in equation (5) to zero.

[0095] [Mathematical formula 8]

[0096]

[0097] Since the attenuation ratio K of the first attenuation circuit 32 is set so that the voltage amplitude of the detection signal Vo is close to zero in the non-detection state where the object 9 does not exist, the following equation holds.

[0098] [Mathematical formula 9]

[0099]

[0100] In the non-detection state where the object 9 does not exist, as shown in formula (9), the voltage amplitude of the detection signal Vo becomes close to zero. If the object 9 approaches the detection electrode Es and the static capacitance of the capacitance component Crg increases, the static capacitance between the first node N1 and the ground increases, so according to formula (5), the amplitude of the AC voltage Vrx of the first node N1 decreases. When the amplitude of the AC voltage Vrx decreases, according to formula (7), the voltage amplitude of the detection signal Vo increases. In the case where the voltage amplitude of the detection signal Vo increases as the amplitude of the AC voltage Vrx decreases, the phase of the detection signal Vo is approximately the same as the phase of the first AC voltage Vas.

[0101] Figure 3A An example of the waveform of the first AC voltage Vas is shown. Figure 3B An example of a voltage waveform of the detection signal Vo is shown. Figure 3B As shown, when the static capacitance of the capacitance component Crg is approximately zero in the non-detection state without the object 9, the voltage amplitude of the detection signal Vo is near zero. When the static capacitance of the capacitance component Crg increases as the object 9 approaches, the voltage amplitude of the detection signal Vo having approximately the same phase as the first AC voltage Vas increases.

[0102] In the subtraction circuit 35, a signal Vm is generated as a result of subtracting the reference signal Vs from the detection signal Vo. In the non-detection state, since the detection signal Vo is substantially equal to the reference signal Vs, the amplitude of the signal Vm is near zero, and the larger the voltage amplitude of the detection signal Vo, the larger the amplitude of the signal Vm. In the demodulation circuit 36, a signal Ds corresponding to the amplitude of the AC component of the signal Vm having the same frequency as the first AC voltage Vas is generated. The signal Ds has a value corresponding to the voltage amplitude of the detection signal Vo, that is, a value corresponding to the static capacitance of the capacitance component Crg. In the processing unit 4, based on the static capacitance of the capacitance component Crg shown by the signal Ds, it is determined whether the object 9 is close to the sensor unit 1, the distance between the object 9 and the sensor unit 1 is calculated, and the open circuit state and the short circuit state are determined.

[0103] (Action in open circuit state)

[0104] The state in which at least one of the path between the detection electrode Es and the first node N1 and the path between the shielding electrode Ea and the third node N3 is electrically cut off is referred to as an "open state". For example, the open state occurs when one or both of the wiring of the cable 2 is cut off or when poor contact occurs at the end of the cable 2. If the open state occurs, the parasitic capacitance component Crs formed between the detection electrode Es and the shielding electrode Ea is no longer connected in parallel with the third capacitor C3, and the parasitic capacitance component Crg formed between the object 9 and the detection electrode Es is no longer connected in parallel with the second capacitor C2.

[0105] The static capacitance of the capacitance component Crg formed between the object 9 and the detection electrode Es is sufficiently small compared to the static capacitance of the capacitance component Crs formed between the detection electrode Es and the shielding electrode Ea, and is also sufficiently small compared to the static capacitances of the first capacitor C1 to the third capacitor C3. In this case, the change in the amplitude of the AC voltage Vrx caused by becoming an open circuit state is mainly caused by the change of the static capacitance of the capacitance component Crs to zero, and the influence caused by the change of the static capacitance of the capacitance component Crg can be ignored. Therefore, if only the static capacitance of the capacitance component Crs changes to zero, the static capacitance between the first node N1 and the third node N3 decreases from "C3+Crs" to "C3", thereby increasing the amplitude of the AC voltage between the first node N1 and the third node N3. The AC voltage Vrx of the first node N1 and the AC voltage (first AC voltage Vas) of the third node N3 have substantially the same phase, and the amplitude of the AC voltage (first AC voltage Vas) of the third node N3 does not change, so the increase in the amplitude of the AC voltage between the first node N1 and the third node N3 is equivalent to the decrease in the amplitude of the AC voltage Vrx between the first node N1 and the ground. That is, in the case of an open circuit state, the amplitude of the AC voltage Vrx of the first node N1 decreases.

[0106] If the amplitude of the AC voltage Vrx at the first node N1 in the open state is defined as “Vrx_opn”, the amplitude “Vrx_opn” is expressed by the following equation by setting the electrostatic capacitance of the capacitance components Crs and Crg to zero in equation (5).

[0107] [Formula 10]

[0108]

[0109] When the AC voltage Vrx shown in formula (5) is regarded as a function of "Crs", the denominator "Crg+C2+C1+C3" in formula (5) is larger than the numerator "K·C1+C3", so the sign of the derivative function obtained by differentiating the AC voltage Vrx with "Crs" is always positive. Therefore, if the value of "Crs" is reduced, the amplitude of the AC voltage Vrx decreases monotonically. If the static capacitance of the capacitance component Crg is sufficiently small and can be ignored, the amplitude "Vrx_opn" of the AC voltage Vrx in the open circuit state shown in formula (10) is approximately equal to the amplitude when the value of "Crs" is reduced to zero under the AC voltage Vrx shown in formula (5), and therefore becomes smaller than the amplitude of the AC voltage Vrx in the normal state shown in formula (5). Therefore, according to the relationship between formula (7) and formula (10), when the AC voltage Vrx of the first node N1 becomes open circuit, the amplitude becomes smaller.

[0110] If the amplitude of the voltage of the detection signal Vo in the open state is defined as "Vo_opn", the amplitude "Vo_opn" is expressed by the following equation by applying equation (10) to equation (7).

[0111] [Mathematical formula 11]

[0112]

[0113] Since "Vrx_opn" in equation (11) is smaller than "Vrx" in equation (7), the amplitude "Vo_opn" of the voltage of the detection signal Vo in the open circuit state increases toward the positive side compared to the amplitude of the detection signal Vo in the normal state. That is, in the case of the open circuit state, the amplitude of the voltage of the detection signal Vo having the same phase as the first AC voltage Vas increases.

[0114] Figure 3C is a diagram showing an example of a voltage waveform of the detection signal Vo in an open circuit state. Figure 3C In the example, the amplitude of the voltage of the detection signal Vo is the largest. That is, the peak value in the positive direction of the voltage waveform of the detection signal Vo is limited to the maximum voltage, and the peak value in the negative direction is limited to the minimum voltage. Figure 3C In the example, the voltage waveform of the detection signal Vo becomes a waveform close to a trapezoidal wave. In addition, the phase of the voltage of the detection signal Vo in the open circuit state is Figure 3A The phases of the first AC voltages Vas shown are substantially the same.

[0115] (Action in short circuit state)

[0116] The state in which the detection electrode Es and the shielding electrode Ea are short-circuited is referred to as a "short-circuit state". For example, when the detection electrode Es and the shielding electrode Ea are in contact in the sensor unit 1, or when the wiring connected to the detection electrode Es and the wiring connected to the shielding electrode Ea are in contact in the cable 2, a short-circuit state is achieved. When the short-circuit state is achieved, the AC voltage Vrx of the first node N1 is substantially equal to the first AC voltage Vas. According to formula (5), the amplitude of the first AC voltage Vas is greater than the amplitude of the AC voltage Vrx of the first node N1 in the normal state. Therefore, in the case of a short-circuit state, the amplitude of the AC voltage Vrx of the first node N1 becomes larger, contrary to the case of an open circuit state.

[0117] If the amplitude of the voltage of the detection signal Vo in the short-circuit state is defined as "Vo_sht", the amplitude "Vo_sht" is expressed by the following equation by replacing "Vrx" in equation (7) with "Vas".

[0118] [Mathematical formula 12]

[0119]

[0120] Since "Vas" in equation (12) is greater than "Vrx" in equation (5), the voltage amplitude "Vo_sht" of the detection signal Vo in the open circuit state becomes larger toward the negative side than the amplitude of the detection signal Vo in the normal state. That is, in the case of the open circuit state, the voltage amplitude of the detection signal Vo having a phase opposite to that of the first AC voltage Vas becomes larger.

[0121] Figure 3D FIG. 1 is a diagram showing an example of a voltage waveform of a detection signal Vo in a short-circuit state. Figure 3D In the example, the voltage amplitude of the detection signal Vo is the largest. That is, the voltage waveform of the detection signal Vo is Figure 3C Similarly, the voltage waveform of the open circuit state shown in FIG. 1 is limited to the maximum voltage in the positive direction and the minimum voltage in the negative direction. However, the phase of the voltage of the detection signal Vo in the short circuit state is reversed relative to the phase of the voltage of the detection signal Vo of the first AC voltage Vas compared to the open circuit state. That is, the phase of the voltage of the detection signal Vo in the short circuit state is reversed relative to the phase of the voltage of the detection signal Vo of the first AC voltage Vas. Figure 3A The phase of the first AC voltage Vas is shown to be reversed.

[0122] (Determination of open circuit and short circuit states)

[0123] As described above, the amplitude of the AC voltage Vrx of the first node N1 decreases when it is in an open circuit state, and increases when it is in a short circuit state. On the other hand, the amplitude of the AC voltage of the second node N2 is the same as the amplitude of the second AC voltage Vdrv, and does not change even when it is in an open circuit state or a short circuit state. Therefore, when the amplitude of the AC voltage Vrx of the first node N1 changes by only "ΔVrx", the amplitude (Vrx-Vdrv) of the AC voltage generated in the first capacitor C1 also changes by only "ΔVrx".

[0124] When the voltage change "ΔVrx" of the first capacitor C1 is generated along with the change "ΔVrx" of the amplitude of the AC voltage Vrx at the first node N1, the change of the stored charge in the first capacitor C1 is "C1·ΔVrx". When the change of the amplitude "ΔVrx" becomes negative due to the open circuit state and when the change of the amplitude "ΔVrx" becomes positive due to the short circuit state, the sign of the change of the stored charge in the first capacitor C1 "C1·ΔVrx" is opposite. Since the detection signal Vo is a signal corresponding to the charge supplied from the charge amplifier 33 to the first capacitor C1, when the sign of the change of the stored charge in the first capacitor C1 "C1·ΔVrx" is opposite, the amplitude of the detection signal Vo also changes in the opposite direction.

[0125] The change in the amplitude of the detection signal Vo corresponding to the change "C1·ΔVrx" of the accumulated charge in the first capacitor C1 is "-(C1 / Cag)·ΔVrx" according to formula (7). When the sign of "ΔVrx" is reversed, the sign of "-(C1 / Cag)·ΔVrx" is also reversed. When the sign of "-(C1 / Cag)·ΔVrx" is reversed, the amplitude of the detection signal Vo changes in the opposite direction. In the case of an open circuit state, since the sign of "ΔVrx" is negative, the amplitude of the detection signal Vo having the same phase as the first AC voltage Vas increases. In the case of a short circuit state, since the sign of "ΔVrx" is positive, the amplitude of the detection signal Vo having the same phase as the first AC voltage Vas decreases (in other words, the amplitude of the detection signal Vo having the opposite phase to the first AC voltage Vas increases). Therefore, when the amplitude of the detection signal Vo is maximum, it can be determined to be an open circuit state or a short circuit state. Furthermore, since the detection signal Vo changes in opposite directions when the state is open and when the state is short, the open state and the short state can be determined.

[0126] In addition, in the present embodiment, when the ratio (C1 / Cag) of the static capacitance of the first capacitor C1 to the static capacitance of the feedback capacitor Cag becomes larger, the change "-(C1 / Cag)·ΔVrx" of the amplitude of the detection signal Vo corresponding to the change "ΔVrx" of the amplitude of the AC voltage Vrx becomes larger. When the change "ΔVrx" of the amplitude of the AC voltage Vrx in the open circuit state and the short circuit state is sufficiently large compared to the normal state, by appropriately setting the ratio (C1 / Cag) of the static capacitance, the amplitude of the detection signal Vo can be maximized only in the open circuit state and the short circuit state. For example, it is possible to Figure 3C as well as Figure 3D As shown, in the open circuit state and the short circuit state, the amplitude of the detection signal Vo is maximized. On the other hand, in the normal state, as shown in FIG. Figure 3C As shown, the amplitude of the detection signal Vo is not maximized.

[0127] Thus, in the present embodiment, the amplitude of the detection signal Vo can be maximized in each state of the open circuit state and the short circuit state, and the phase of the detection signal Vo relative to the first AC voltage Vas can be reversed in the open circuit state and the short circuit state. Thus, the value of the signal Ds of the demodulation circuit 36 ​​generated in the open circuit state and the short circuit state can be set to a large value or a small value that is impossible in the normal state, and can be set to a value separated to the maximum in the open circuit state and the short circuit state. For example, the value of the signal Ds can be set to the maximum value in the open circuit state and the minimum value in the short circuit state. Therefore, the processing unit 4 that processes the signal Ds as the static capacitance of the capacitance component Crg can determine the open circuit state and the short circuit state based on the value of the signal Ds. For example, the processing unit 4 can determine that the open circuit state is when the value of the signal Ds is equal to the maximum value or is greater than the upper limit threshold, and determine that the short circuit state is when the value of the signal Ds is equal to the minimum value or is less than the lower limit threshold.

[0128] (Function of the second capacitor C2)

[0129] As described above, in the non-detection state where the object 9 does not exist, the attenuation ratio K of the first attenuation circuit 32 is set so that the amplitude of the voltage of the detection signal Vo becomes close to zero. When the amplitude of the voltage of the detection signal Vo becomes close to zero, the voltage of the feedback capacitor Cag is substantially equal to the second AC voltage Vdrv. At this time, if the capacitance component Cp and the tiny static capacitance of C0n are ignored, the amplitude of the voltage generated in the first capacitor C1 is expressed by the following formula.

[0130] [Mathematical formula 13]

[0131]

[0132] As shown in equation (13), the amplitude (Vrx0-Vdrv) of the voltage generated in the first capacitor C1 is substantially equal to the amplitude obtained by multiplying the amplitude of the second AC voltage Vdrv by a certain coefficient (Cag / C1).

[0133] In this non-detection state, it is assumed that the static capacitance of the second capacitor C2 is zero (hereinafter sometimes referred to as a "hypothetical state"). In this hypothetical state, since no charge is accumulated in the second capacitor C2, the amplitude of the AC voltage Vrx at the first node N1 becomes larger. By setting "C2" to zero in equation (8), the amplitude "Vrx1" of the AC voltage Vrx in the hypothetical state is expressed by the following equation.

[0134] [Mathematical formula 14]

[0135]

[0136] Since "Vrx1" is greater than "Vrx0", the following equation holds.

[0137] [Mathematical formula 15]

[0138]

[0139] In this assumed state, the amplitude of the voltage generated in the first capacitor C1 becomes larger and no longer satisfies the condition of formula (13), so the amplitude of the voltage of the detection signal Vo deviates from near zero. When the amplitude of the voltage of the detection signal Vo deviates from near zero, as a method of making the amplitude close to zero (i.e., a method of changing the inequality sign of formula (15) to an equality sign), there are a method of increasing the amplitude of the second AC voltage Vdrv and a method of reducing the static capacitance of the third capacitor C3.

[0140] In the case of adopting the method of increasing the amplitude of the second AC voltage Vdrv, the amplitude of the voltage at the second node N2 increases and approaches the amplitude "Vrx1" of the AC voltage Vrx at the first node N1, and the voltage amplitude (Vrx1-Vdrv) generated in the first capacitor C1 becomes smaller. According to formula (2-1), increasing the amplitude of the second AC voltage Vdrv is equivalent to making the attenuation ratio K close to 1. If the attenuation ratio K is close to 1, according to formula (14), the amplitude "Vrx1" of the AC voltage Vrx at the first node N1 is close to the amplitude of the first AC voltage Vas, and the amplitude of the second AC voltage Vdrv is also close to the amplitude of the first AC voltage Vas. Therefore, the left side of formula (15) becomes smaller. On the other hand, if the amplitude of the second AC voltage Vdrv is increased, the right side of formula (15) becomes larger. Therefore, by increasing the amplitude of the second AC voltage Vdrv, the inequality in equation (15) can be changed to an equality, and the amplitude of the voltage of the detection signal Vo can be made close to zero.

[0141] However, when the amplitude (Vdrv) of the AC voltage at the second node N2 increases, the amplitude of the AC voltage Vrx at the first node N1 increases to an amplitude substantially equal to the first AC voltage Vas in the short-circuit state, and the change in the voltage amplitude (Vas-Vrx) of the first capacitor C1 accompanying the increase in the amplitude is suppressed. If the change in the voltage amplitude (Vas-Vrx1) of the first capacitor C1 is suppressed, the change in the voltage amplitude of the detection signal Vo is suppressed, and therefore it is difficult to determine the short-circuit state based on the change in the voltage amplitude of the detection signal Vo.

[0142] In addition, when the method of increasing the amplitude of the second AC voltage Vdrv is adopted, the difference between the voltage amplitude (Vdrv) of the second node N2 and the voltage amplitude (Vas) of the third node N3 becomes smaller, so the difference between the voltage amplitude (vrx1) of the first node N1 and the voltage amplitude (Vas) of the third node N3 also becomes smaller. Therefore, when the static capacitance between the first node N1 and the third node N3 decreases in the open circuit state, the change in the amplitude of the voltage between the first node N1 and the third node N3 (the increase in the voltage amplitude) is suppressed, and the change in the voltage amplitude of the first node N1 (the decrease in the voltage amplitude) is suppressed. It can be seen that when the attenuation ratio K in formula (14) is close to 1, the change of "Vrx1" relative to the change of "Crs" becomes smaller. When the change of the voltage amplitude (Vrx1) of the first node N1 is suppressed, the change of the voltage amplitude of the first capacitor C1 is suppressed, and the change of the voltage amplitude of the detection signal Vo is suppressed, so it is difficult to determine the open circuit state based on the change of the voltage amplitude of the detection signal Vo.

[0143] In this way, when the method of increasing the amplitude of the second AC voltage Vdrv is adopted, the change in the voltage amplitude of the detection signal Vo in the open circuit state and the short circuit state is suppressed, and it is difficult to determine the open circuit state and the short circuit state based on the change in the voltage amplitude of the detection signal Vo.

[0144] On the other hand, when the method of reducing the static capacitance of the third capacitor C3 is adopted, it can be seen from formula (14) that the voltage amplitude (Vrx1) of the first node N1 becomes smaller. By reducing the voltage amplitude (Vrx1) of the first node N1 and approaching the voltage amplitude (Vdrv) of the second node N2, the amplitude (Vrx1-Vdrv) of the voltage generated in the first capacitor C1 becomes smaller, so the inequality in formula (15) can be changed to an equality. However, if the static capacitance of the third capacitor C3 is reduced, the static capacitance detection device 3 is easily affected by the external noise transmitted from the detection electrode Es, and the noise tolerance is reduced.

[0145] Therefore, by setting a second capacitor C2 with appropriate static capacitance between the first node N1 and the ground, the static capacitance of the third capacitor C3 can be increased and the influence of external noise can be reduced. In addition, when a short circuit state or an open circuit state occurs, the voltage amplitude of the detection signal Vo can be changed significantly, making it easy to accurately determine the short circuit state and the open circuit state.

[0146] Next, refer to Figure 4 A modification of the input device according to this embodiment will be described. Figure 4 In the input device shown in FIG. 1 , the sensor unit 1 includes a plurality of groups of detection electrodes Es and detection electrodes Es arranged close to each other (hereinafter, sometimes referred to as “detection electrode groups”). Figure 4 In the example, there are four electrode groups) connected to the electrostatic capacitance detection device 3 via cables 2. The input device of this variant can be Figure 4 In addition to the electrostatic capacitance detection device 3 shown in the figure, it also has Figure 1 The input device shown has the same structure (processing unit 4, storage unit 5, interface unit 6).

[0147] exist Figure 4 In the input device shown in FIG. 1 , the electrostatic capacitance detection device 3 has a plurality of circuit blocks 30, which include Figure 2 The first capacitor C1, the second capacitor C2, the third capacitor C3 and the first resistor R1 of the electrostatic capacitance detection device 3 shown in the figure have the same structure. Figure 4 In the example, four circuit blocks 30 are connected to the plurality of detection electrode groups of the sensor unit 1 via cables 2. The connection relationship between one detection electrode group (Es, Ea) and one circuit block 30 (C1 to C3, R1) is the same as Figure 2 The electrostatic capacitance detection device 3 shown is the same.

[0148] Furthermore, in Figure 4 In a modified example, the electrostatic capacitance detection device 3 includes a switch circuit 37 that connects one circuit block 30 selected from a plurality of circuit blocks 30 to the input (second node N2) of the charge amplifier 33. Figure 4 In the example of FIG. 1 , the switch circuit 37 includes a plurality of switches SA corresponding to the plurality of circuit blocks 30 and a plurality of switches SB corresponding to the plurality of circuit blocks 30. One switch SA is provided in a path between the first resistor R1 included in one circuit block 30 corresponding to the one switch SA and the second node N2. One switch SB is provided in a path between an intermediate node connecting the first resistor R1 included in one circuit block 30 corresponding to the one switch SB and the first capacitor C1 and the third node N3.

[0149] The switch circuit 37 turns only one switch SA among the multiple switches SA into the on state and turns the other switches SA into the off state. In addition, the switch circuit 37 turns one switch SB connected to the same circuit block 30 as the one switch SA in the on state into the off state and turns the other switches SB into the on state. Thus, the circuit block 30 connected only to the switch SA in the on state is connected to the input (second node N2) of the charge amplifier 33, and the electrostatic capacitance is detected only in the detection electrode group connected to the circuit block 30 via the cable 2. In addition, in the other circuit blocks 30 not connected to the input (second node N2) of the charge amplifier 33, the voltage amplitude (Vrx) of the first node N1 in the other circuit blocks 30 is substantially equal to the voltage amplitude (Vas) of the third node N3 by turning the switch SB into the on state. Thus, in the other circuit blocks 30 and the detection electrode group connected thereto, the accumulated charge of the capacitor (C3, Crs) connected between the first node N1 and the third node N3 is difficult to change, so the generation of noise can be suppressed. Figure 4 Other structures of the electrostatic capacitance detection device 3 shown in FIG. Figure 2 The electrostatic capacitance detection device 3 shown is the same.

[0150] In the input device of this modification, as in the previously described input device, the open circuit state and the short circuit state can be determined for each of the plurality of detection electrode groups and each of the plurality of cables 2 based on the detection signal Vo of the charge amplifier 33 .

[0151] (Summarize)

[0152] According to the present embodiment, the change in the amplitude of the AC voltage Vrx in the first node N1 is opposite when it becomes an open circuit state and when it becomes a short circuit state. If the change in the amplitude of the AC voltage Vrx is opposite, the positive and negative signs (positive and negative) of the changes in the accumulated charge in the first capacitor C1 when the voltage amplitude of the first capacitor C1 changes with the change in the amplitude of the AC voltage Vrx are opposite. As a result, the detection signal Vo changes in opposite directions when it becomes an open circuit state and when it becomes a short circuit state. Therefore, based on the fact that the detection signal Vo changes in opposite directions when it becomes an open circuit state and when it becomes a short circuit state, the open circuit state and the short circuit state can be determined.

[0153] According to the present embodiment, in the non-detection state where the object 9 does not exist, the amplitude of the voltage of the detection signal Vo becomes close to zero. In addition, the larger the detection object capacitance Crg between the object 9 and the detection electrode Es is, the larger the amplitude of the voltage of the detection signal Vo is. Therefore, the range in which the voltage of the detection signal Vo changes according to the change of the detection object capacitance Crg becomes wider, and it is easy to improve the detection sensitivity of the detection object capacitance Crg.

[0154] According to this embodiment, by providing a second capacitor C2 having an appropriate static capacitance between the first node N1 and the ground, the static capacitance of the third capacitor C3 can be increased and the influence of external noise can be reduced compared to a case where the second capacitor C2 is not provided, and when a short circuit state or an open circuit state occurs, the voltage amplitude of the detection signal Vo can be changed significantly, making it easy to accurately determine these states.

[0155] According to the present embodiment, in the open circuit state, the amplitude of the voltage of the detection signal Vo becomes the maximum. In addition, in the short circuit state, the amplitude of the voltage of the detection signal Vo becomes the maximum, and the phase of the voltage of the detection signal Vo relative to the first AC voltage Vas is reversed compared to the open circuit state. Therefore, the open circuit state and the short circuit state can be determined more accurately based on the amplitude of the voltage of the detection signal Vo and the phase of the voltage of the detection signal Vo relative to the first AC voltage Vas.

[0156] According to this embodiment, a first AC voltage Vas is applied to the series circuit of the fourth capacitor C4 and the fifth capacitor C5, and a second AC voltage Vdrv corresponding to the first AC voltage Vas is generated in the fifth capacitor C5. Therefore, compared with the case of using a resistor-based attenuator as the first attenuation circuit 32, the noise of the second AC voltage Vdrv can be reduced.

[0157] According to the present embodiment, the reference signal Vs, which is equivalent to the signal outputted from the operational amplifier OP1 as the detection signal Vo in the non-detection state where the object 9 does not exist, is subtracted from the detection signal Vo. The signal Vm obtained as a result of the subtraction operation has an amplitude corresponding to the detection object capacitance Crg, which is small in the non-detection state. Therefore, the dynamic range of the detection signal Vo corresponding to the change of the detection object capacitance Crg can be made larger, and the detection sensitivity of the detection object capacitance Crg can be improved.

[0158] According to the present embodiment, the reference signal Vs subtracted from the detection signal Vo in the subtraction circuit 35 is a voltage obtained by attenuating the first AC voltage Vas in the second attenuation circuit 34, so the noise component included in the detection signal Vo and the noise component included in the reference signal Vs have a high correlation. As a result, the noise component of the signal Vm obtained as a result of the subtraction operation of the subtraction circuit 35 can be reduced.

[0159] According to the present embodiment, since the feedback capacitor Cag, the first resistor R1 and the operational amplifier OP1 constitute a low-pass filter, it is possible to attenuate noise input via the detection electrode Es, thereby suppressing a decrease in detection accuracy.

[0160] The input device of the present invention is not limited to a user interface device that inputs information by operation of a finger, etc. That is, the input device of the present invention can be widely applied to devices that detect electrostatic capacitance between various objects not limited to human bodies and detection electrodes.

[0161] -Description of Reference Numerals-

[0162] 1…sensor unit, 2…cable, 3…capacitance detection device, 4…processing unit, 5…storage unit, 6…interface unit, 7…circuit board, 9…object, 30…circuit block, 31…AC voltage output circuit, 32…first attenuation circuit, 33…charge amplifier, 331…feedback circuit, 34…second attenuation circuit, 35…subtraction circuit, 36…demodulation circuit, 37…switch circuit, C1…first capacitor, C2…second capacitor, C3…third capacitor, C4…fourth capacitor, C5…fifth capacitor, OP1, OP 2…operational amplifier, Es…detection electrode, Ea…shielding electrode, SA, SB…switch, Rag…feedback resistor, Cag…feedback capacitor, R1…first resistor, Crg…capacitance component (capacitance to be detected), Crs, Csg, C0n, C0p, Cp…capacitance component, Vas…first AC voltage, Vdrv…second AC voltage, Vrx…AC voltage, Vo…detection signal, N1…first node, N2…second node, N3…third node, N4…fourth node, N5…fifth node, K…attenuation ratio.

Claims

1. An electrostatic capacitance detection device for detecting the electrostatic capacitance between an object and a detection electrode, It is characterized in that have: A first capacitor is provided on a path between a first node and a second node connected to the detection electrode via a cable; A second capacitor is arranged on a path between the first node and the ground; a third capacitor provided on a path between a third node connected to a shielding electrode disposed close to the detection electrode and the first node, the third node being connected to the shielding electrode via the cable; an AC voltage output circuit, outputting a first AC voltage to the third node; a first attenuation circuit, outputting a second AC voltage obtained by attenuating the amplitude of the first AC voltage; as well as a charge amplifier connected to the second node, supplying charge to the first capacitor via the second node, and outputting a detection signal corresponding to the supplied charge, The charge amplifier supplies the charge to the first capacitor so that the voltage generated at the second node approaches the second AC voltage.

2. The electrostatic capacitance detection device according to claim 1, in, The charge amplifier includes: a feedback capacitor, which is arranged on a path between a fourth node outputting the detection signal and the second node, supplying the charge from the feedback capacitor to the first capacitor via the second node, The first attenuation circuit maintains an attenuation ratio, which is a ratio of the amplitude of the second AC voltage to the amplitude of the first AC voltage, at a ratio such that the amplitude of the voltage of the detection signal is close to zero in a non-detection state where the object is not present.

3. The electrostatic capacitance detection device according to claim 2, in, In an open circuit state in which at least one of a path between the detection electrode and the first node and a path between the shielding electrode and the third node is electrically cut off, the amplitude of the voltage of the detection signal becomes maximum, In the short-circuit state where the detection electrode and the shield electrode are short-circuited, the amplitude of the voltage of the detection signal becomes maximum, and the phase of the voltage of the detection signal with respect to the first AC voltage is reversed compared with the open-circuit state.

4. The electrostatic capacitance detection device according to claim 2, in, The first attenuation circuit includes a series circuit of a fourth capacitor and a fifth capacitor, The AC voltage output circuit applies the first AC voltage to both ends of the series circuit. The first attenuation circuit outputs the AC voltage generated across the fifth capacitor as the second AC voltage.

5. The electrostatic capacitance detection device according to claim 4, in, The electrostatic capacitance of the fourth capacitor and the electrostatic capacitance of the fifth capacitor are electrostatic capacitances set so that the amplitude of the voltage of the detection signal in the non-detection state becomes close to zero.

6. The electrostatic capacitance detection device according to claim 5, in, The fifth capacitor is capable of adjusting an electrostatic capacitance value, and the electrostatic capacitance value is adjusted so that the amplitude of the voltage of the detection signal becomes close to zero in the non-detection state.

7. The electrostatic capacitance detection device according to any one of claims 1 to 6, in, The charge amplifier comprises: an operational amplifier that amplifies a voltage difference between an inverting input terminal connected to the second node and a non-inverting input terminal to which the second AC voltage is applied, and outputs the detection signal corresponding to the amplified voltage difference to a fourth node; and a feedback circuit, arranged on a path between the fourth node and the second node, The electrostatic capacitance detection device includes a subtraction circuit that subtracts, from the detection signal, a reference signal corresponding to a signal output from the operational amplifier as the detection signal in a non-detection state in which the object is not present.

8. The electrostatic capacitance detection device according to claim 7, in, The electrostatic capacitance detection device includes a second attenuation circuit configured to output an AC voltage obtained by attenuating the amplitude of the first AC voltage as the reference signal.

9. The electrostatic capacitance detection device according to claim 7, in, The electrostatic capacitance detection device comprises: a first resistor, which is arranged on a path between the second node and the first capacitor; The feedback circuit comprises: a feedback capacitor disposed on a path between the fourth node and the second node; and A feedback resistor is connected in parallel with the feedback capacitor.

10. The electrostatic capacitance detection device according to any one of claims 1 to 6, in, The electrostatic capacitance detection device comprises: a circuit substrate provided with the first node and the second node; The first capacitor, the second capacitor, and the third capacitor are mounted on the circuit substrate.

11. An input device for inputting information corresponding to the approach of an object, It is characterized in that The input device has: a detection electrode, wherein an electrostatic capacitance between the detection electrode and the object changes according to the approach of the object; A shielding electrode, arranged close to the detection electrode; as well as The electrostatic capacitance detection device according to any one of claims 1 to 10 detects the electrostatic capacitance between the object and the detection electrode.

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