Capacitance measurement circuit and load detection device

Abstract

A capacitance measurement circuit is provided with: a reference capacitance (Cr); a switching element (12a) for switching between applying a voltage to the reference capacitance (Cr) and not applying the voltage to the reference capacitance (Cr); a switching element (12b) that transfers the charge of the reference capacitance (Cr) to the measurement capacitance (Cs); a switching element (13) that connects the negative electrode of the measurement capacitor (Cs) to ground or to a wiring having the same potential as the positive electrode of the measurement capacitor (Cs); a measurement unit that measures the voltage of the measurement capacitor (Cs); and a control unit (11). The control unit (11) executes: a first control for causing the switching element (12b) to transfer charges in a state in which the negative electrode of the measurement capacitor (Cs) is connected to ground; a second control for causing the switching element (12b) to transfer charges in a state in which the negative electrode of the measurement capacitor (Cs) is connected to a wiring line having the same potential as the positive electrode of the measurement capacitor (Cs); and a process for calculating the capacitance value of the measurement capacitor (Cs) on the basis of the voltage value measured after the charge has been transferred by each control.

Description

Technical Field

[0001] The present invention relates to an electrostatic capacitance measurement circuit for measuring electrostatic capacitance, and a load detection device that detects a load based on a measurement result of the electrostatic capacitance. Background Art

[0002] Conventionally, an electrostatic capacitance type load sensor in which the electrostatic capacitance of a component part changes according to a load has been known. In such a load sensor, for example, the electrostatic capacitance of the component part is detected based on a change in voltage when a voltage is applied to the component part. A load detection device using such a load sensor is described in, for example, Patent Document 1 below.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-81209 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In an electrostatic capacitance type load sensor, in addition to the method based on the change in voltage as described above, for example, the electrostatic capacitance of the component part can also be detected based on the amount of charge accumulated in the component part when a voltage is applied to the component part. In this case, for example, the amount of charge accumulated in the component part can be calculated by measuring the amount of current flowing through the component part during the period from when the voltage is applied to the component part until the charge accumulation saturates. Such measurement of the amount of current can be performed, for example, by using an AD converter to sample and integrate the current value during this period.

[0008] However, if the load applied to the component part is small, the electrostatic capacitance of the component part becomes small, and the period from when the voltage is applied to the component part until the charge accumulation saturates becomes short. Therefore, in the above measurement of the amount of current, a high-speed and high-precision AD converter is required in order to sample the current value that changes within a short time. However, even when such an AD converter is used, in the range where the load is relatively small, the period until the amount of current saturates is significantly short, so it is difficult to stably measure the amount of current during this period.

[0009] In addition, the measurement result of the electrostatic capacitance is affected by parasitic capacitance based on wiring, other electrical components, etc. Therefore, the calculated electrostatic capacitance includes an error component based on the parasitic capacitance, and it is difficult to detect the load with high precision due to this error component.

[0010] In view of such problems, an object of the present invention is to provide an electrostatic capacitance measurement circuit and a load detection device that can also stably and highly accurately measure the electrostatic capacitance in a small range.

[0011] Solution for solving problems

[0012] The first aspect of the present invention relates to a capacitance measurement circuit. The capacitance measurement circuit according to this aspect includes: a reference capacitor having a predetermined capacitance value; a switching unit for switching between applying a voltage to the reference capacitor and not applying a voltage; a transfer unit for transferring the charge accumulated in the reference capacitor to a measurement capacitor; a connection unit for connecting the negative electrode of the measurement capacitor to the ground or a wiring having the same potential as the potential of the positive electrode of the measurement capacitor; a measurement unit for measuring the voltage of the measurement capacitor; and a control unit for controlling the switching unit, the transfer unit, and the connection unit. The control unit performs: a first control of causing the transfer unit to transfer charge in a state where the negative electrode of the measurement capacitor is connected to the ground after applying a voltage to the reference capacitor; a second control of causing the transfer unit to transfer charge in a state where the negative electrode of the measurement capacitor is connected to the wiring having the same potential as the potential of the positive electrode of the measurement capacitor after applying a voltage to the reference capacitor; and a process of calculating the capacitance value of the measurement capacitor based on the voltage values measured by the measurement unit after the charge transfer is respectively performed by the first control and the second control.

[0013] According to the capacitance measurement circuit according to this aspect, since the capacitance value of the measurement capacitor is calculated based on the voltage value after the charge is transferred from the reference capacitor, even without using a high-precision AD converter, it is possible to stably measure the capacitance value in a small range. In addition, in the second control, since the negative electrode of the measurement capacitor is connected to the wiring having the same potential as the potential of the positive electrode of the measurement capacitor, the measured voltage value is hardly affected by the measurement capacitor, but is mainly affected by the reference capacitor and the parasitic capacitance. In contrast, in the first control, since the negative electrode of the measurement capacitor is connected to the ground, the measured voltage value is affected by the reference capacitor, the parasitic capacitance, and the measurement capacitor. Therefore, by calculating the capacitance value of the measurement capacitor based on these two voltage values, it is possible to calculate the capacitance value without the influence of the parasitic capacitance. Therefore, it is possible to measure the capacitance value of the measurement capacitor with high precision.

[0014] A second aspect of the present invention relates to a capacitance measurement circuit. The capacitance measurement circuit according to this aspect includes: a reference capacitor having a predetermined capacitance value; a switching unit for switching between applying a voltage to the measurement capacitor and not applying a voltage; a transfer unit for transferring the charge accumulated in the measurement capacitor to the reference capacitor; a connection unit for connecting the negative electrode of the measurement capacitor to ground or a wiring having the same potential as the positive electrode of the measurement capacitor; a measurement unit for measuring the voltage of the measurement capacitor; and a control unit for controlling the switching unit, the transfer unit, and the connection unit, wherein the control unit performs: a first control of causing the transfer unit to transfer charge after applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to ground; a second control of causing the transfer unit to transfer charge after applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to a wiring having the same potential as the positive electrode of the measurement capacitor; and a process of calculating the capacitance value of the measurement capacitor based on the voltage values measured by the measurement unit after the charge transfer is performed by the first control and the second control respectively.

[0015] According to the capacitance measurement circuit of this aspect, since the capacitance value of the measurement capacitor is calculated based on the voltage value after the charge is transferred from the measurement capacitor, it is possible to stably measure a small range of capacitance values without using a high-precision AD converter. In addition, in the second control, since the negative electrode of the measurement capacitor is connected to a wiring having the same potential as the positive electrode of the measurement capacitor and a voltage is applied to the measurement capacitor, almost no charge is accumulated in the measurement capacitor, and charge is accumulated in the parasitic capacitance. Therefore, the voltage value measured by the second control is hardly affected by the measurement capacitor, but is mainly affected by the reference capacitor and the parasitic capacitance. In contrast, in the first control, since the negative electrode of the measurement capacitor is connected to ground and a voltage is applied to the measurement capacitor, charge is applied to both the parasitic capacitance and the measurement capacitor. Therefore, the voltage values measured by the first and second controls are affected by the reference capacitor, the parasitic capacitance, and the measurement capacitor. Thus, by calculating the capacitance value of the measurement capacitor based on these two voltage values, it is possible to calculate the capacitance value without the influence of the parasitic capacitance. Therefore, it is possible to measure the capacitance value of the measurement capacitor with high precision.

[0016] A third aspect of the present invention relates to a load detection device. The load detection device according to this aspect includes: a load sensor having an element portion whose capacitance changes according to a load; and the capacitance measurement circuit of the first aspect or the second aspect. The control unit performs the first control, the second control, and the capacitance calculation process using the element portion as the measurement capacitor.

[0017] According to the load detection device related to this method, since it includes the capacitance measurement circuit related to the first method or the second method, even within the range where the load applied to the element part is small and the capacitance is small, it is possible to stably obtain the capacitance corresponding to the load. In addition, since it includes the capacitance measurement circuit related to the first method or the second method, it is possible to obtain the capacitance value with the influence of parasitic capacitance suppressed with high precision. Therefore, it is possible to stably and highly accurately detect a small range of loads.

[0018] Effects of the Invention

[0019] As described above, according to the present invention, it is possible to provide a capacitance measurement circuit and a load detection device that can also stably and highly accurately measure a small range of capacitance.

[0020] The effects or significance of the present invention are further clarified by the description of the embodiments shown below. However, the embodiments shown below are merely an example when implementing the present invention, and the present invention is not limited by any of the contents described in the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a diagram showing the structure of the capacitance measurement circuit according to Embodiment 1.

[0022] Figure 2 (a) and (b) of are respectively diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to Embodiment 1.

[0023] Figure 3 (a) and (b) of are respectively diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to Embodiment 1.

[0024] Figure 4 (a) and (b) of are respectively diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to Embodiment 1.

[0025] Figure 5 (a) and (b) of are respectively diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to Embodiment 1.

[0026] Figure 6 (a) and (b) of are respectively diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to Embodiment 1.

[0027] Figure 7It is a flowchart showing the calculation process of the capacitance value of the measured capacitance according to Embodiment 1.

[0028] Figure 8 It is a flowchart showing the calculation process of the capacitance value of the measured capacitance according to Modification 1 of Embodiment 1.

[0029] Figure 9 It is a diagram showing the structure of the capacitance measurement circuit according to Modification 2 of Embodiment 1.

[0030] Figure 10 It is a diagram showing the structure of the capacitance measurement circuit according to Embodiment 2.

[0031] Figure 11 (a) and (b) thereof are diagrams showing the operations of the capacitance measurement circuit when measuring the capacitance value of the measured capacitance according to Embodiment 2.

[0032] Figure 12 (a) and (b) thereof are diagrams showing the operations of the capacitance measurement circuit when measuring the capacitance value of the measured capacitance according to Embodiment 2.

[0033] Figure 13 (a) and (b) thereof are diagrams showing the operations of the capacitance measurement circuit when measuring the capacitance value of the measured capacitance according to Embodiment 2.

[0034] Figure 14 (a) and (b) thereof are diagrams showing the operations of the capacitance measurement circuit when measuring the capacitance value of the measured capacitance according to Embodiment 2.

[0035] Figure 15 (a) and (b) thereof are diagrams showing the operations of the capacitance measurement circuit when measuring the capacitance value of the measured capacitance according to Embodiment 2.

[0036] Figure 16 It is a flowchart showing the calculation process of the capacitance value of the measured capacitance according to Embodiment 2.

[0037] Figure 17 (a) and (b) thereof are graphs showing the simulation results of the capacitance according to Embodiments 1 and 2.

[0038] Figure 18 It is a flowchart showing the calculation process of the capacitance value of the measured capacitance according to Modification 1 of Embodiment 2.

[0039] Figure 19 It is a diagram showing the structure of the capacitance measurement circuit according to Modification 2 of Embodiment 2.

[0040] Figure 20 Figure (a) schematically shows a perspective view of a base member according to Embodiment 3 and a conductive elastomer provided on the upper surface of the base member. Figure 20 Figure (b) schematically shows in Figure 20 the structure of Figure (a) with a conductor wire provided therein.

[0041] Figure 21 Figure (a) schematically shows in Figure 20 the structure of Figure (b) with a wire provided therein. Figure 21 Figure (b) schematically shows in Figure 21 the structure of Figure (a) with a base member provided therein.

[0042] Figure 22 Figures (a) and Figure 22 Figure (b) are respectively diagrams schematically showing screenshots of a load sensor according to Embodiment 3.

[0043] Figure 23 is a top view schematically showing the internal structure of the load sensor according to Embodiment 3.

[0044] Figure 24 is a diagram showing the structure of a load detection device according to Embodiment 3.

[0045] Figure 25 is a diagram showing the operation of the load detection device when detecting the capacitance value of an element part to be measured according to Embodiment 3.

[0046] Figure 26 is a diagram showing the structure of a load detection device according to Embodiment 4.

[0047] Figure 27 is a diagram showing the operation of the load detection device when detecting the capacitance value of an element part to be measured according to Embodiment 4.

[0048] However, the drawings are mainly for illustration and do not limit the scope of the present invention. Detailed Embodiments

[0049] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In Embodiments 1 and 2, the structure of a capacitance measurement circuit is shown, and in Embodiments 3 and 4, the structure of a load detection device is shown.

[0050] In Embodiments 1 and 2, the switching element 12a, the switching element 12b, and the switching element 13 respectively correspond to the "switching unit", the "transfer unit", and the "connection unit" described in the claims. However, this description is always for the purpose of associating the structure of the claims with the structure of the embodiments, and the invention described in the claims is not limited by the structure of the embodiments due to the above association. In addition, the structure for implementing the invention described in the claims is not limited to the following Embodiments 1 to 4.

[0051] <Embodiment 1>

[0052] Figure 1 FIG. is a diagram showing the structure of the capacitance measurement circuit 10 according to Embodiment 1.

[0053] As Figure 1 shown, the capacitance measurement circuit 10 includes a control unit 11, switching elements 12a to 12c, a switching element 13, a measurement unit 14, and a reference capacitor Cr. The reference capacitor Cr is connected in parallel with the measurement capacitor Cs via the switching element 12b. The measurement capacitor Cs is the capacitance of the object to be measured. The capacitance value of the reference capacitor Cr is larger than the capacitance value of the measurement capacitor Cs.

[0054] The control unit 11 is composed of a microcomputer, an FPGA, etc., and is used to control the switching elements 12a to 12c and 13. In addition, the control unit 11 calculates the capacitance value of the measurement capacitor Cs based on the voltage value measured by the measurement unit 14.

[0055] The switching element 12a is used to switch between applying the power supply voltage Vdd to the reference capacitor Cr and not applying the power supply voltage Vdd. When the switching element 12a changes from the non-conductive state to the conductive state, the power supply voltage Vdd is applied to the reference capacitor Cr, and charges are accumulated in the reference capacitor Cr.

[0056] The switching element 12b is used to switch the positive electrode of the reference capacitor Cr between the connected state and the non-connected state with the positive electrode of the measurement capacitor Cs. When the switching element 12b changes from the non-conductive state to the conductive state, the positive electrode of the reference capacitor Cr is connected to the positive electrode of the measurement capacitor Cs, and the charges accumulated in the reference capacitor Cr are transferred to the measurement capacitor Cs. Thus, the switching element 12b is used to transfer the charges accumulated in the reference capacitor Cr to the measurement capacitor Cs.

[0057] The switching element 12c is used to switch the positive electrode of the measurement capacitor Cs between the connected state and the non-connected state with the ground. When the switching element 12c changes from the non-conductive state to the conductive state, the positive electrode of the measurement capacitor Cs is connected to the ground, and the charges accumulated in the measurement capacitor Cs are discharged to the ground.

[0058] The switching elements 12a and 12b are composed of P-type FETs and are turned on by applying a low-level gate signal to the gate. The switching element 12c is composed of an N-type FET and is turned on by applying a high-level gate signal to the gate. The switching elements 12a to 12c may also be other switching elements in forms other than FETs.

[0059] The switching element 13 connects the negative electrode of the measurement capacitor Cs to the ground or the positive electrode of the measurement capacitor Cs. When the positive electrode and the negative electrode of the measurement capacitor Cs are connected by the switching element 13, these positive and negative electrodes become the same potential. Therefore, the measurement capacitor Cs becomes a state of disappearing in the circuit (invalidated state).

[0060] The measurement unit 14 measures the voltage of the measurement capacitor Cs. When the switching element 12b is turned on while the switching element 13 is connected to the ground, the charge of the reference capacitor Cr is transferred and distributed to the measurement capacitor Cs. As a result, a voltage corresponding to the capacitance ratio of the electrostatic capacitance value of the reference capacitor Cr to the electrostatic capacitance value of the measurement capacitor Cs is generated in the measurement capacitor Cs. The measurement unit 14 measures this voltage.

[0061] In addition, the electrostatic capacitance value of the reference capacitor Cr is set so that the measurement unit 14 can accurately measure the magnitude of the voltage generated in the measurement capacitor Cs after the charge is distributed in this way. That is, the electrostatic capacitance value of the reference capacitor Cr is set so that the voltage generated in the measurement capacitor Cs after the charge is distributed as described above is at least above the lower limit value of the measurable range of the measurement unit 14.

[0062] Next, with reference to Figure 2 of (a) to Figure 6 of (b), the operation of the electrostatic capacitance measurement circuit 10 when measuring the electrostatic capacitance value of the measurement capacitor Cs will be described.

[0063] For convenience, in Figure 2 of (a) to Figure 6 of (b), the switching elements 12a to 12c in the operating state and the paths for charging, discharging, or transferring charges using these switching elements are shown in thick lines. In addition, when the reference capacitor Cr and the measurement capacitor Cs are in the charged state, these capacitors are marked with diagonal hatching.

[0064] First, as Figure 2As shown in (a), with the switching element 13 connected to the ground, the switching elements 12a and 12c are respectively switched to the conducting state. Thereby, the power supply voltage Vdd is applied to the reference capacitor Cr, and charge is accumulated in the reference capacitor Cr. In addition, the positive electrode of the measurement capacitor Cs is connected to the ground to discharge the measurement capacitor Cs. The switching element 12a is set to the conducting state at least until the reference capacitor Cr becomes fully charged. For example, a measurement unit different from the measurement unit 14 can be used to measure the voltage of the reference capacitor Cr, and it can be determined whether the reference capacitor Cr is fully charged based on whether the measurement result reaches the power supply voltage Vdd and is stable.

[0065] Next, as Figure 2 shown in (b), the switching element 12a is switched to the non-conducting state, and the reference capacitor Cr is disconnected from the power supply voltage Vdd. In addition, as Figure 3 shown in (a), the switching element 12c is switched to the non-conducting state, and the positive electrode of the measurement capacitor Cs is disconnected from the ground. Then, as Figure 3 shown in (b), the switching element 12b is switched to the conducting state, and the positive electrode of the reference capacitor Cr is connected to the positive electrode of the measurement capacitor Cs. Thereby, the charge accumulated in the reference capacitor Cr is transferred to the measurement capacitor Cs.

[0066] The measured value of the measurement unit 14 immediately after the switching element 12b is switched to the conducting state is a voltage value corresponding to the accumulated charge of the reference capacitor Cr, that is, a voltage value approximately equal to the power supply voltage Vdd. After that, when the charge transfer to the measurement capacitor Cs is further performed, the measured value of the measurement unit 14 gradually decreases, and when the charge transfer is completed, the measured value of the measurement unit 14 stabilizes at a fixed value (saturation) corresponding to the capacitance ratio of the reference capacitor Cr and the measurement capacitor Cs.

[0067] In this way, after the voltage value stabilizes, as Figure 4 shown in (a), the voltage value measured by the measurement unit 14 is obtained as the first voltage value Vx1. As described above, this first voltage value Vx1 is mainly determined by the capacitance ratio of the reference capacitor Cr and the measurement capacitor Cs, but is also affected by the wiring between the reference capacitor Cr and the measurement capacitor Cs, and the parasitic capacitances of the switching elements 12b, 13, etc. Therefore, if the capacitance value of the measurement capacitor Cs is calculated only based on the first voltage value Vx1, the calculation result includes an error based on these parasitic capacitances.

[0068] To avoid this situation, in the present embodiment, an operation for suppressing the error based on the parasitic capacitance is also performed.

[0069] That is, as Figure 4 shown in (b), the switching element 13 is switched to the positive electrode side of the measurement capacitor Cs. Next, as Figure 5As shown in (a) thereof, the switching elements 12a and 12c are respectively switched to the conducting state. Thereby, the power supply voltage Vdd is applied to the reference capacitor Cr, and charges are accumulated in the reference capacitor Cr. In addition, the positive electrode of the measurement capacitor Cs is connected to the ground, and the measurement capacitor Cs is discharged. The switching element 12a is set to the conducting state at least until the reference capacitor Cr becomes fully charged.

[0070] In addition, as Figure 4 shown in (b) thereof, since there are remaining distributed charges in the reference capacitor Cr, compared with the case of Figure 2 (a), the charging of the reference capacitor Cr is performed more rapidly in Figure 5 (a). That is, compared with the operation of discharging the charges of the reference capacitor Cr temporarily from the state of Figure 4 (b) and then entering the operation of Figure 5 (a), as described above, directly entering the operation of Figure 4 (a) from the state of Figure 5 (b) can further speed up the operation sequence.

[0071] In addition, in Figure 5 (a), since the switching element 13 is connected to the positive electrode side of the measurement capacitor Cs, in addition to the charges accumulated in the measurement capacitor Cs, the charges accumulated in the parasitic capacitance such as the switching element 13 and the wiring between the switching element 13 and the positive electrode of the measurement capacitor Cs are also discharged to the ground. Thereby, the influence caused by the parasitic capacitance can be removed more reliably.

[0072] After that, as Figure 5 (b) shows, the switching element 12a is switched to the non-conducting state, and the reference capacitor Cr is disconnected from the power supply voltage Vdd. In addition, the switching element 12c is switched to the non-conducting state, and the positive electrode of the measurement capacitor Cs is disconnected from the ground. Then, as Figure 6 (a) shows, the switching element 12b is switched to the conducting state, and the positive electrode of the reference capacitor Cr is connected to the positive electrode of the measurement capacitor Cs. Thereby, the charges accumulated in the reference capacitor Cr are transferred.

[0073] In this case, as Figure 6 (a) shows, since the switching element 13 is switched to the positive electrode side of the measurement capacitor Cs, the positive electrode and the negative electrode of the measurement capacitor Cs become the same potential. Therefore, when this charge transfer is performed, the charges are not distributed to the measurement capacitor Cs, and the charges are distributed to the parasitic capacitance other than the measurement capacitor Cs. Thus, in this case, the measured value of the measurement unit 14 is stabilized at a voltage value corresponding to the charge distribution to the parasitic capacitance.

[0074] In this way, after the voltage value is stabilized, as Figure 6As shown in (b) thereof, the voltage value measured by the measurement unit 14 is obtained as the second voltage value Vx2. Then, based on the obtained second voltage value Vx2 and the first voltage value Vx1 obtained during the operation of (a) of Figure 4 , the capacitance value of the measurement capacitor Cs is calculated.

[0075] The capacitance value of the measurement capacitor Cs is calculated as follows.

[0076] First, if the capacitance value (known) of the reference capacitor Cr is set as Cr, then as Figure 2 in (a) thereof, the charge amount Qr of the reference capacitor Cr when the reference capacitor Cr is fully charged is expressed by the following formula.

[0077] Qr = Cr × Vdd…(1)

[0078] In addition, if the capacitance value of the measurement capacitor Cs is set as Cs1, then in the state where the transfer of charge is completed as in Figure 4 (a) thereof, the following relationship holds.

[0079] Qr = (Cr + Cs1) × V×1…(2)

[0080] Therefore, based on formulas (1) and (2), the following relational formula is derived.

[0081] [Equation 1]

[0082]

[0083] Among them, as described above, the capacitance value Cs1 includes an error component based on the parasitic capacitance. The error component Ce can be expressed by the following formula using the second voltage value Vx2 obtained through the operation of (b) of Figure 6 .

[0084] [Equation 2]

[0085]

[0086] That is, during the operations of (a) to (b) of Figure 5 , the positive and negative electrodes of the measurement capacitor Cs are at the same potential, so the measurement capacitor Cs is invalidated, and only the reference capacitor Cr and the parasitic capacitance are capacitance components. Therefore, the capacitance value of the parasitic capacitance, that is, the error component Ce, can be expressed by the above formula (4). Figure 6 The capacitance value Cs of the measurement capacitor Cs is the value obtained by removing the error component Ce from the capacitance value Cs1 of formula (3). Therefore, it is calculated by the following formula based on the above formulas (3) and (4).

[0087]

[0088] [Number 3]

[0089]

[0090] In Equation (5), the capacitance value Cr and the power supply voltage Vdd are known, and the first voltage value Vx1 and the second voltage value Vx2 are obtained through Figure 4 the operation of (a) of Figure 6 and the operation of (b) of

[0091] Figure 7 is a flowchart showing the calculation process of the capacitance value of the measurement capacitance Cs through the operation of (a) to Figure 2 the operation of (b) of Figure 6 Therefore, the capacitance value of the measurement capacitance Cs can be calculated according to the above Equation (5).

[0092] In Figure 7 , steps S101 to S105 correspond to the first control C1 for obtaining the first voltage value Vx1, and steps S106 to S110 correspond to the second control C2 for obtaining the second voltage value Vx2.

[0093] First, as shown in (a) of Figure 2 , the control unit 11 connects the negative electrode of the measurement capacitance Cs to the ground (S101), and performs charging of the reference capacitance Cr and discharging of the measurement capacitance Cs (S102). When the charging of the reference capacitance Cr is completed, the control unit 11, as shown in (b) of Figure 2 and (a) of Figure 3 , disconnects the positive electrode of the reference capacitance Cr from the power supply voltage Vdd and disconnects the positive electrode of the measurement capacitance Cs from the ground (S103). Then, the control unit 11, as shown in (b) of Figure 3 , connects the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs to transfer the charge of the reference capacitance Cr to the measurement capacitance Cs (S104). After that, after the period until the measured value of the measurement unit 14 becomes stable (saturated), the control unit 11, as shown in (a) of Figure 4 , obtains the measured value of the measurement unit 14 as the first voltage value Vx1 (S105). Thus, the first control C1 ends.

[0094] Next, the control unit 11, as shown in (b) of Figure 4 , connects the negative electrode of the measurement capacitance Cs to the positive electrode of the measurement capacitance Cs (S106), and performs charging of the reference capacitance Cr and discharging of the measurement capacitance Cs, as shown in (a) of Figure 5 . When the charging of the reference capacitance Cr is completed, the control unit 11, as shown in Figure 5As shown in (b), disconnect the positive electrode of the reference capacitor Cr from the power supply voltage Vdd, and disconnect the positive electrode of the measurement capacitor Cs from the ground (S108). Then, as shown in Figure 6 (a), the control unit 11 connects the positive electrode of the reference capacitor Cr to the positive electrode of the measurement capacitor Cs to transfer the charge of the reference capacitor Cr (S109). After that, after the period until the measured value of the measurement unit 14 stabilizes (saturates), the control unit 11, as shown in Figure 6 (b), obtains the measured value of the measurement unit 14 as the second voltage value Vx2 (S110). Thus, the second control C2 ends.

[0095] Then, the control unit 11 applies the obtained first voltage value Vx1 and second voltage value Vx2 to the above formula (5) to calculate the capacitance value of the measurement capacitor Cs (S111). Thus, the control unit 11 ends Figure 7 the process.

[0096] <Effects of Embodiment 1>

[0097] As shown in Figure 4 (a) and Figure 6 (b), it is only necessary to measure the stabilized (saturated) voltage values (the first voltage value Vx1 and the second voltage value Vx2) after the charge is transferred from the reference capacitor Cr by the measurement unit 14. Therefore, even without using a high-precision AD converter, it is possible to stably measure a small-range capacitance value. In addition, in the second control C2 shown in Figure 7 , by connecting the negative electrode of the measurement capacitor Cs to the positive electrode (the wiring having the same potential as the positive electrode) in step S106, the measured second voltage value Vx2 is hardly affected by the measurement capacitor Cs, but is mainly affected by the reference capacitor Cr and the parasitic capacitance. In contrast, in the first control C1, by connecting the negative electrode of the measurement capacitor Cs to the ground in step S101, the measured first voltage value Vx1 is affected by the reference capacitor Cr, the parasitic capacitance, and the measurement capacitor Cs. Therefore, by calculating the capacitance value of the measurement capacitor Cs based on these two voltage values, it is possible to calculate the capacitance value without the influence of the parasitic capacitance. Therefore, the capacitance value of the measurement capacitor Cs can be measured with high precision.

[0098] Here, the control unit 11 calculates the capacitance value of the measurement capacitor Cs through the above formula (5) based on the first voltage value Vx1 obtained through the first control C1, the second voltage value Vx2 obtained through the second control C2, the power supply voltage Vdd applied to the reference capacitor Cr, and the capacitance value of the reference capacitor Cr. Thus, as described above, it is possible to suppress the influence of the error component generated by the parasitic capacitance on the capacitance value of the measurement capacitor Cs, and it is possible to accurately obtain the capacitance value of the measurement capacitor Cs.

[0099] <Modification Example 1>

[0100] In the above Embodiment 1, in Figure 7 the first control C1, after the charge of the reference capacitor Cr is transferred to the measurement capacitor Cs (S104), after a fixed period until the transfer is completed and the measured value of the measurement unit 14 becomes stable (saturated), the acquisition of the first voltage value Vx1 is performed (S105). Here, this fixed period is defined according to the relationship with the upper limit value of the range (measurement range) that can be assumed as the capacitance value of the measurement capacitor Cs. That is, when the capacitance value of the measurement capacitor Cs is the upper limit value, a period slightly longer than the period from the start of the transfer of the charge of the reference capacitor Cr to the stabilization (saturation) of the measured value of the measurement unit 14 is set as this fixed period.

[0101] However, when the actual capacitance value of the measurement capacitor Cs is considerably smaller than the upper limit, although the measured value of the measurement unit 14 quickly stabilizes (saturates) after the charge transfer, it is necessary to wait for the acquisition of the first voltage value Vx1 until the fixed period elapses. Therefore, the processing sequence is delayed accordingly, and the measurement result of the measurement capacitor Cs cannot be obtained quickly. The wider the measurement range of the measurement capacitor Cs, the more obvious this problem becomes.

[0102] In Modification Example 1, in order to eliminate such a problem, a part of the Figure 7 processing is changed.

[0103] Figure 8 is a flowchart showing the calculation process of the capacitance value of the measurement capacitor Cs according to Modification Example 1.

[0104] Compared with Figure 7 in the Figure 8 processing, steps S121 to S124 are added. The processing of steps S101 to S111 is the same as the corresponding steps in Figure 7 .

[0105] In step S121, the control unit 11 sets a standby period Tw. Here, for example, when the measured capacitance value of the capacitance Cs is the lower limit value of the measurement range, the initially set standby period Tw is set to be slightly longer than the period until the measurement value of the charge transfer to the measurement unit 14 becomes stable (saturated). Then, the control unit 11 performs the processes of steps S102 to S104 in the same manner as Figure 7 the case of Figure 7 . After starting the charge transfer in step S104, the control unit 11 waits for the standby period Tw to elapse (S122). When the standby period Tw has elapsed (S122: "Yes"), the control unit 11 acquires the measurement result at that time of the measurement unit 14 as the first voltage value Vx1 (S105).

[0106] The control unit 11 determines whether the acquired first voltage value Vx1 is a voltage value after saturation (stabilization) (S123). When the acquired first voltage value Vx1 is not a voltage value after saturation (stabilization) (S123: "No"), the control unit 11 returns the process to step S121 and re-sets the standby period Tw.

[0107] For example, the control unit 11 sets the current standby period Tw to be longer than the previous standby period Tw by a specified time. Then, the control unit 11 performs the processes after step S102 in the same manner. As a result, the standby period Tw from the start of the charge transfer in step S104 until the first voltage value Vx1 is acquired is extended by the specified time. Therefore, in step S105, it is easy to acquire the voltage value after saturation (stabilization) as the first voltage value Vx1.

[0108] In this way, the control unit 11 re-sets the standby period Tw (S121) and repeats the processes after step S102 until the first voltage value Vx1 acquired in step S105 becomes a voltage value after saturation (stabilization) (S123: "No"). Then, when the determination in step S123 is "Yes", the control unit 11 holds the first voltage value Vx1 acquired at that time as the first voltage value Vx1 used in the capacitance value calculation process (S111).

[0109] Here, the determination in step S123 is performed as follows, for example.

[0110] For example, the control unit 11 determines whether the first voltage value Vx1 obtained through the processing of the previous step S105 is substantially the same as the first voltage value Vx1 obtained this time (the difference between the two is within the allowable variation range). Alternatively, the control unit 11 determines whether the first voltage values Vx1 obtained through the processing of step S105 in the past several times (for example, five times) including this time are substantially the same. Then, when these determinations are "yes", the control unit 11 sets the determination of step S123 to "yes".

[0111] However, the method for determining whether the first voltage value Vx1 obtained in step S105 is a saturated (stable) voltage value is not limited to these methods, and this determination can also be made by other methods.

[0112] After that, the control unit 11 performs the processing of steps S106 to S109 in the same manner as Figure 7 the case. Then, the control unit 11 waits for the standby period Tw (S124) to elapse since the charge transfer started in step S109. This standby period Tw is set to the last standby period Tw repeatedly reset by step S121. Generally, the parasitic capacitance is smaller than the measurement capacitance Cs. Therefore, if the standby period Tw of step S124 is set in this way, the measurement result (second voltage value Vx2) of the measurement unit 14 after the standby period Tw has elapsed is in a stable state.

[0113] In addition, the standby period Tw of step S124 can also be set to a fixed period according to the relationship with the electrostatic capacitance value of the parasitic capacitance that can generally be assumed. That is, a period slightly longer than the period until the charge of the reference capacitance Cr is distributed to the parasitic capacitance of the electrostatic capacitance value that can generally be assumed can also be set as the standby period Tw of step S124.

[0114] When the standby period Tw has elapsed (S124: "yes"), the control unit 11 obtains the measurement result of the measurement unit 14 at this time point as the second voltage value Vx2 (S110). Then, the control unit 11 applies the obtained second voltage value Vx2 and the first voltage value Vx1 when the determination of step S123 is "yes" to the above formula (5) to calculate the electrostatic capacitance value of the measurement capacitance Cs (S111).

[0115] <Effect of Modification Example 1>

[0116] As Figure 8As shown, while changing the standby period Tw from when the charge is transferred through step S104 to when the first voltage value Vx1 is obtained through step S105 (S121), the control unit 11 repeats the first control C1 (steps S101 to S105) until the first voltage value Vx1 saturates (S123: "No"), and calculates the capacitance value using the saturated first voltage value Vx1 (S111). Therefore, when the capacitance value of the measurement capacitor Cs is small and the measured value of the measurement unit 14 saturates and stabilizes in advance, the first voltage value Vx1 can be quickly obtained through a short standby period Tw. Therefore, the calculation process of the capacitance value of the measurement capacitor Cs can be quickly performed.

[0117] In addition, each time the control unit 11 repeats the first control C1, it extends the standby period Tw. Thereby, the standby period Tw can be gradually made closer to the length that saturates the first voltage value Vx1. Therefore, the standby period Tw suitable for measuring the capacitor Cs can be set smoothly.

[0118] Furthermore, as described above, the method of changing the standby period Tw in step S121 is not limited to the method of gradually increasing from the minimum value. For example, it can also be that the standby period Tw is decreased and increased by a specified length starting from near the middle of the available range (set range) of the standby period Tw. If at least two of the first voltage values Vx1 obtained from these three standby periods Tw are substantially the same, one of these two first voltage values Vx1 is used for the capacitance calculation process. If at least two of the first voltage values Vx1 obtained from the three standby periods Tw are substantially different, the standby period is increased from the maximum value of these three standby periods until the first voltage value Vx1 saturates, thereby obtaining the first voltage value Vx1 for calculating the capacitance.

[0119] <Modification Example 2>

[0120] In the above-described Embodiment 1, the capacitance value of the reference capacitor Cr is fixed, but in Modification Example 2, the capacitance value of the reference capacitor Cr can be changed.

[0121] Figure 9 It is a diagram showing the structure of the capacitance measurement circuit 10 according to Modification Example 2.

[0122] As Figure 9As shown, the capacitance measurement circuit 10 according to Modification Example 2 includes four capacitors Cra to Crd, four switching elements 16a to 16d, and a capacitance selection unit 15 as a capacitance value changing unit for changing the capacitance value of the reference capacitance Cr. The switching elements 16a to 16d are switched between conduction / non-conduction by the capacitance selection unit 15. When the switching elements 16a to 16d are conductive, the capacitors Cra to Crd are respectively connected between the wiring between the switching elements 12a and 12b and the ground.

[0123] In this structure, the reference capacitance Cr is constituted by the combined capacitance of the capacitors among the four capacitors Cra to Crd that are connected between this wiring and the ground. Figure 1 Therefore, the capacitance value of the reference capacitance Cr changes according to which of the switching elements 16a to 16d is made conductive by the capacitance selection unit 15.

[0124] The control unit 11 changes the switching element made conductive by the capacitance selection unit 15 according to the measurement range (dynamic range) of the measured capacitance Cs, and sets the capacitance value of the reference capacitance Cr to a value suitable for this dynamic range. That is, as described above, the capacitance value of the reference capacitance Cr is set so that the measurement unit 14 can appropriately measure the voltage value of the measured capacitance Cs after the charge is transferred from the reference capacitance Cr to the measured capacitance Cs. The dynamic range of the measured capacitance Cs is set in the control unit 11 by the user using an upper terminal (not shown), for example.

[0125] <Effect of Modification Example 2>

[0126] According to Modification Example 2, as described above, the capacitance value of the reference capacitance Cr can be adjusted to a value suitable for the dynamic range of the measured capacitance Cs. Therefore, even when the dynamic range of the measured capacitance Cs is changed, the capacitance value of the measured capacitance Cs can be appropriately measured within this dynamic range.

[0127] In addition, in Figure 9 the structure, four capacitors Cra to Crd and four switching elements 16a to 16d are arranged to change the capacitance value of the reference capacitance Cr, but the number of groups of capacitors and switching elements is not limited to this. The number of this group may be set to a prescribed number of two or more according to the relationship with the range of the corresponding dynamic range.

[0128] In addition, the structure for changing the capacitance value of the reference capacitance Cr is not limited to Figure 19In the structure shown, for example, a variable capacitor may also be configured to replace the four capacitors Cra to Crd and the four switching elements 16a to 16d. In this case, the control unit 11 only needs to control the capacitance value of the variable capacitor to a capacitance value corresponding to the measurement range (dynamic range) of the measurement capacitor Cs.

[0129] <Embodiment 2>

[0130] In the above-described Embodiment 1, the charge charged to the reference capacitor Cr is distributed to the measurement capacitor Cs and the capacitance value is calculated. In contrast, in Embodiment 2, the charge charged to the measurement capacitor Cs is distributed to the reference capacitor Cr and the capacitance value is calculated.

[0131] Figure 10 FIG. is a diagram showing the structure of the capacitance measurement circuit 10 according to Embodiment 2.

[0132] In Figure 10 compared with Figure 1 the arrangement of the reference capacitor Cr, the measurement capacitor Cs, the switching element 13, and the measurement unit 14 is changed. That is, the measurement capacitor Cs is arranged at a position upstream (power supply voltage Vdd side) of the reference capacitor Cr, and accordingly, the arrangements of the switching element 13 and the measurement unit 14 are changed. The functions of the switching element 13 and the measurement unit 14 are the same as those in the above-described Embodiment 1. The switching element 12b among the switching elements 12a to 12c can be changed to an N-type FET. The structures and functions of the switching elements 12a and 12c are the same as those in the above-described Embodiment 1.

[0133] Figure 11 (a) to Figure 15 (b) of FIG. are diagrams showing the operation of the capacitance measurement circuit 10 when measuring the capacitance value of the measurement capacitor Cs. Figure 16 FIG. is a flowchart showing the processing of the control unit 11 when measuring the capacitance value of the measurement capacitor Cs.

[0134] First, as shown in Figure 11 (a) of FIG., the control unit 11 switches the switching elements 12a and 12c to the on state in a state where the negative electrode of the measurement capacitor Cs is connected to the ground (S201) to charge the measurement capacitor Cs and discharge the reference capacitor Cr (S202). After that, the control unit 11 disconnects the positive electrode of the reference capacitor Cr from the ground as shown in Figure 11 (b) of FIG., and after the measurement capacitor Cs becomes fully charged, disconnects the positive electrode of the measurement capacitor Cs from the ground as shown in Figure 12 (a) of FIG. (S203). Similar to the above-described embodiment, it is possible to determine whether the measurement capacitor Cs is fully charged by determining whether the voltage of the measurement capacitor Cs reaches the power supply voltage Vdd and is stable.

[0135] Next, the control unit 11 switches the switching element 12b to the conducting state as shown in (b) of Figure 12 to transfer the charge of the measurement capacitor Cs to the reference capacitor Cr (S204). Then, the control unit 11 waits for the period until the transfer is completed, and then obtains the measurement value of the measurement unit 14 as the first voltage value Vx1 as shown in (a) of Figure 13 Thereby, the first control C1 is completed.

[0136] Next, the control unit 11 switches the switching element 13 to the positive electrode side of the measurement capacitor Cs as shown in (b) of Figure 13 to connect the positive electrode and the negative electrode of the measurement capacitor Cs (S206). Then, the control unit 11 switches the switching elements 12b and 12c to the conducting state as shown in (a) of Figure 14 to discharge the reference capacitor Cr and the measurement capacitor Cs (S207).

[0137] After that, the control unit 11 switches the switching elements 12b and 12c to the non-conducting state, and switches the switching element 12a to the conducting state as shown in (b) of Figure 14 to connect the positive electrode of the measurement capacitor Cs to the power supply voltage Vdd (S208). Here, since the positive electrode and the negative electrode of the measurement capacitor Cs are connected, the positive electrode and the negative electrode of the measurement capacitor Cs become the same potential. Therefore, the measurement capacitor Cs is not charged, and the parasitic capacitance other than the measurement capacitor Cs is charged.

[0138] Next, the control unit 11 sets the switching element 12a to the non-conducting state to disconnect the positive electrode of the measurement capacitor Cs from the power supply voltage Vdd (S209), and switches the switching element 12b to the conducting state as shown in (a) of Figure 15 to connect the positive electrode of the measurement capacitor Cs to the positive electrode of the reference capacitor Cr, thereby transferring the charge to the reference capacitor Cr (S210). Here, as described above, no charge is accumulated in the measurement capacitor Cs, so the charge accumulated in the parasitic capacitance is transferred to the reference capacitor Cr. After the charge is transferred, the control unit 11 obtains the measurement value of the measurement unit 14 as the first voltage value Vx1 as shown in (b) of Figure 15 Thereby, the second control C2 is completed.

[0139] Then, the control unit 11 calculates the capacitance value of the measurement capacitor Cs based on the first voltage value Vx1 and the second voltage value Vx2 respectively obtained in the first control C1 and the second control C2 (S212).

[0140] The calculation of the capacitance value of the measurement capacitor Cs is performed as follows.

[0141] First, if the electrostatic capacitance value of the measurement capacitor Cs is set to Cs1, then as shown in (a) of Figure 11 , the charge amount Qs of the measurement capacitor Cs when it becomes fully charged is expressed by the following formula.

[0142] Qs = Cs1 × Vdd…(6)

[0143] In addition, if the electrostatic capacitance value of the reference capacitor Cr is set to Cr, then in the state where the transfer of charge is completed as shown in (b) of Figure 2 , the following relationship holds.

[0144] Qs = (Cr + Cs1) × Vx1…(7)

[0145] Therefore, the following relational expression is derived from formulas (6) and (7).

[0146] [Equation 4]

[0147]

[0148] Among them, as described above, the electrostatic capacitance value Cs1 includes an error component based on parasitic capacitance. The error component Ce can be expressed by the following formula using the second voltage value Vx2 obtained through the operation of (b) of Figure 15 .

[0149] [Equation 5]

[0150]

[0151] That is, during the operations of (a) to Figure 14 and (b) of Figure 15 , the positive and negative electrodes of the measurement capacitor Cs are at the same potential, so the measurement capacitor Cs is invalidated, and only the reference capacitor Cr and the parasitic capacitance are the capacitive components. Therefore, the electrostatic capacitance value of the parasitic capacitance, that is, the error component Ce, can be expressed by the above formula (9).

[0152] The electrostatic capacitance value Cs of the measurement capacitor Cs is the value obtained by removing the error component Ce from the electrostatic capacitance value Cs in formula (8). Therefore, it is calculated by the following formula based on the above formulas (8) and (9).

[0153] [Equation 6]

[0154]

[0155] In formula (10), the electrostatic capacitance value Cr and the power supply voltage Vdd are known, and the first voltage value Vx1 and the second voltage value Vx2 are obtained through (a) of Figure 13 and Figure 15The operation of (b) is used to obtain it, so the electrostatic capacitance value of the measurement capacitance Cs can be calculated according to the above formula (10).

[0156] Figure 17 (a) and (b) respectively show Figure 7 (Embodiment 1) and Figure 16 (Embodiment 2) are graphs showing the simulation results of the electrostatic capacitance detected by the electrostatic capacitance detection process.

[0157] In this simulation, when the electrostatic capacitance value in the measurement capacitance Cs is changed, the electrostatic capacitance value of the measurement capacitance Cs is calculated by the above Figure 7 and Figure 16 processes. In Figure 17 (a) and (b), the horizontal axis is the electrostatic capacitance value set for the measurement capacitance Cs, and the vertical axis is the electrostatic capacitance value calculated by the above processes.

[0158] As Figure 17 (a) and (b) show, the electrostatic capacitance values calculated by the processes of the above Embodiment 1 and Embodiment 2 roughly conform to the electrostatic capacitance value set for the measurement capacitance Cs, and a linear approximate straight line is obtained from the plot of the simulation results. Thus, it can be confirmed that, according to these processes, an electrostatic capacitance value that effectively suppresses the influence of parasitic capacitance can be obtained for the measurement capacitance Cs.

[0159] <Effect of Embodiment 2>

[0160] As Figure 13 (a) and Figure 15 (b) show, it is only necessary to measure the stable (saturated) voltage values (the first voltage value Vx1, the second voltage value Vx2) after the charge transfer by the measurement unit 14. Therefore, even without using a high-precision AD converter, the electrostatic capacitance value in a small range can be measured stably. In addition, in the second control C2 shown in Figure 16 , the negative electrode of the measurement capacitance Cs is connected to the positive electrode (the wiring having the same potential as the positive electrode) through step S206. Therefore, the measured second voltage value Vx2 is hardly affected by the measurement capacitance Cs, but is mainly affected by the reference capacitance Cr and the parasitic capacitance. In contrast, in the first control C1, the negative electrode of the measurement capacitance Cs is connected to the ground through step S201. Therefore, the measured first voltage value Vx1 is affected by the reference capacitance Cr, the parasitic capacitance, and the measurement capacitance Cs. Thus, by calculating the electrostatic capacitance value of the measurement capacitance Cs based on these two voltage values, the electrostatic capacitance value without the influence of parasitic capacitance can be calculated. Therefore, the electrostatic capacitance value of the measurement capacitance Cs can be measured with high precision.

[0161] Here, the control unit 11 calculates the capacitance value of the measurement capacitor Cs by the above formula (10) based on the first voltage value Vx1 obtained through the first control C1, the second voltage value Vx2 obtained through the second control C2, the power supply voltage Vdd applied to the measurement capacitor Cs, and the capacitance value of the reference capacitor Cr. Thus, as described above, it is possible to suppress the influence of the error component caused by the parasitic capacitance on the capacitance value of the measurement capacitor Cs, and the capacitance value of the measurement capacitor Cs can be obtained with high precision.

[0162] <Modified Example 1>

[0163] In the above-described Embodiment 1, in Figure 7 the first control C1, after the charge of the reference capacitor Cr is transferred to the measurement capacitor Cs (S204), after a fixed period until the transfer is completed and the measured value of the measurement unit 14 becomes stable (saturated), the first voltage value Vx1 is obtained (S205). In contrast, in Modified Example 1, similar to Modified Example 1 of the above-described Embodiment 1, the first voltage value Vx1 is obtained while changing the standby period Tw.

[0164] Figure 18 is a flowchart showing the calculation process of the capacitance value of the measurement capacitor Cs according to Modified Example 1.

[0165] In Figure 18 too, similar to Figure 8 the control unit 11 changes the standby period Tw (S221) and obtains the first voltage value Vx1 (S205) until the first voltage value Vx1 becomes saturated (stable) (S223: "No"). That is, the standby period Tw from the start of charge transfer in step S204 through Figure 16 to the acquisition of the first voltage value Vx1 is changed (S222), and the first voltage value Vx1 is obtained (S205). The control unit 11 obtains the measured value at the time point when the measured value of the measurement unit 14 becomes saturated (stable) as the first voltage value Vx1 used in the calculation of the capacitance value (S212).

[0166] In this case, similar to Figure 8 the case of, the standby period Tw gradually becomes longer from the minimum value of the set range. However, in this case, similar to Figure 8 the case of, the method of changing the standby period Tw is not limited to this, and it may be changed by other methods. In addition, as long as the determination in step S223 is made in the same manner as the determination in step S123 of Figure 8 it is sufficient.

[0167] After that, the control unit 11 is the same as Figure 16Similarly, the processes of steps S206 to S210 are performed to obtain the second voltage value Vx2. After the control unit 11 starts the transfer of charges in step S210, it waits for the standby period Tw (S224) when the determination in step S222 is "Yes", and obtains the measured value at the time point after the standby period Tw of the measurement unit 14 as the second voltage value Vx2 (S211).

[0168] In this case, as in Figure 8 the case of, the standby period Tw of step S224 can also be set to a fixed period according to the relationship with the capacitance value of the parasitic capacitance that can be generally assumed. That is, a period slightly longer than the period until the charge is completely distributed from the parasitic capacitance with the capacitance value that can be generally assumed to the reference capacitor Cr can also be set as the standby period Tw of step S224.

[0169] After that, the control unit 11 applies the obtained second voltage value Vx2 and the first voltage value Vx1 when the determination in step S223 is "Yes" to the above formula (10) to calculate the capacitance value of the measurement capacitor Cs. Thus, the control unit 11 ends Figure 18 the process.

[0170] <Effect of Modification Example 1>

[0171] According to Figure 18 the process, while changing the standby period Tw from the transfer of charges through step S204 to the acquisition of the first voltage value Vx1 through step S205 (S221), the control unit 11 repeatedly executes the first control C1 (steps S201 to S205) until the first voltage value Vx1 saturates (S223: "No"), and uses the saturated first voltage value Vx1 to calculate the capacitance value (S212). Therefore, in the case where the capacitance value of the measurement capacitor Cs is small and the measured value of the measurement unit 14 saturates and stabilizes in advance, the first voltage value Vx1 can be quickly obtained through a short standby period Tw. Therefore, the calculation process of the capacitance value of the measurement capacitor Cs can be quickly performed.

[0172] In addition, the control unit 11 extends the standby period Tw every time the first control C1 is repeated. Thus, the standby period Tw can be gradually made close to the length that saturates the first voltage value Vx1. Therefore, the standby period Tw suitable for the measurement capacitor Cs can be smoothly set.

[0173] <Modification Example 2>

[0174] In this modification example 2, the capacitance value of the reference capacitor Cr can be changed in the same manner as in modification example 2 of the above-described embodiment 1.

[0175] Figure 191 is a diagram showing a configuration of the capacitance measurement circuit 10 according to Modification Example 2.

[0176] like Figure 19 As shown, the electrostatic capacitance measuring circuit 10 according to the modification example 2 is Figure 9 Similarly, four capacitors Cra to Crd, four switch elements 16a to 16d, and a capacitor selection unit 15 are provided as a capacitance value change unit for changing the electrostatic capacitance value of the reference capacitor Cr. The switch elements 16a to 16d can be changed to N-type FETs. By turning on the switch elements 16a to 16d using the capacitor selection unit 15, the capacitors Cra to Crd are respectively connected between the wiring between the switch elements 12b and 12c and the ground.

[0177] According to this structure, the combined capacitance of the capacitors connected between the wiring and the ground among the four capacitors Cra to Crd is also formed. Figure 10 The reference capacitance Cr is thus changed according to which of the switch elements 16a to 16d is turned on by the capacitance selection unit 15. Thus, the capacitance value of the reference capacitance Cr can be adjusted to a value suitable for the dynamic range of the measurement capacitance Cs. Therefore, even when the dynamic range of the measurement capacitance Cs is changed, the capacitance value of the measurement capacitance Cs can be appropriately measured within the dynamic range.

[0178] <Implementation Method 3>

[0179] In Embodiment 3, a configuration example is shown in which the electrostatic capacitance measuring circuit 10 of Embodiment 1 is applied to a load detection device. The load detection device detects the load using an electrostatic capacitance type load sensor. Such a load detection device can be applied to various systems. The load sensor included in the load detection device is sometimes referred to as an "electrostatic capacitance type pressure sensitive sensor element", "capacitive pressure detection sensor element", "pressure sensitive switch element", etc.

[0180] First, refer to Figure 20 (a)~ Figure 23 To illustrate the structure of the load sensor 20. Figure 20 (a)~ Figure 23 X, Y, and Z axes that are orthogonal to each other are indicated in the figure. The Z axis direction is the thickness direction of the load sensor 20.

[0181] Figure 20 (a) is a perspective view schematically showing the base member 21 and the conductive elastic body 22 provided on the upper surface (the surface on the positive side of the Z axis) of the base member 21 .

[0182] The base member 21 is an elastic and insulating flat member. The base member 21 has a rectangular shape when viewed from above. The thickness of the base member 21 is fixed. The thickness of the base member 21 is, for example, 0.01 mm to 2 mm. When the thickness of the base member 21 is small, the base member 21 is sometimes referred to as a sheet member or a film member. The base member 21 is made of a non-conductive resin material or a non-conductive rubber material.

[0183] The resin material for the base member 21 is, for example, at least one resin material selected from the group consisting of styrene resins, silicone resins (such as polydimethylsiloxane (PDMS), etc.), acrylic resins, rotaxane resins, and polyurethane resins. The rubber material for the base member 21 is, for example, at least one rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene-propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, chlorinated ether rubber, polyurethane rubber, and natural rubber.

[0184] The conductive elastomer 22 is disposed on the upper surface (the surface on the positive Z-axis side) of the base member 21. In Figure 20 (a) of, three conductive elastomers 22 are disposed on the upper surface of the base member 21. The conductive elastomer 22 is an elastic and conductive member. Each conductive elastomer 22 has a strip shape that is long in the Y-axis direction. The three conductive elastomers 22 are arranged and disposed at a predetermined interval in the X-axis direction. At the end on the negative Y-axis side of each conductive elastomer 22, a wiring W2 electrically connected to the conductive elastomer 22 is provided.

[0185] The conductive elastomer 22 is formed on the upper surface of the base member 21 by printing methods such as screen printing, gravure printing, flexographic printing, offset printing, and intaglio offset printing. According to these printing methods, the conductive elastomer 22 can be formed on the upper surface of the base member 21 with a thickness of about 0.001 mm to 0.5 mm.

[0186] The conductive elastomer 22 is composed of a resin material and conductive fillers dispersed therein, or a rubber material and conductive fillers dispersed therein.

[0187] The resin material for the conductive elastomer 22 is, in the same manner as the above-mentioned resin material for the base member 21, for example, at least one resin material selected from the group consisting of styrene resins, silicone resins (such as polydimethylsiloxane (PDMS), etc.), acrylic resins, rotaxane resins, and polyurethane resins.

[0188] The rubber material for the conductive elastomer 22 is, for example, at least one rubber material selected from the group consisting of silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene-propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, chlorinated ether rubber, polyurethane rubber, and natural rubber, the same as the rubber material for the base member 21 described above.

[0189] The conductive filler for the conductive elastomer 22 is, for example, at least one material selected from the group consisting of metal materials such as Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In2O3 (indium(III) oxide), and SnO2 (tin(IV) oxide), conductive polymer materials such as PEDOT:PSS (i.e., a composite composed of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonic acid (PSS)), metal-coated organic fibers, and conductive fibers such as metal wires (in a fibrous state).

[0190] Figure 20 (b) schematically shows Figure 20 a perspective view of the state in which the conductor line 23 is provided in the structure of (a).

[0191] The conductor line 23 is a linear member and is arranged in a superimposed manner on Figure 20 the upper surface of the conductive elastomer 22 shown in (a). In the present embodiment, three conductor lines 23 are arranged in a superimposed manner on the upper surfaces of three conductive elastomers 22. The three conductor lines 23 are arranged at a predetermined interval along the long side direction (Y-axis direction) of the conductive elastomer 22 in a manner intersecting the conductive elastomer 22. Each conductor line 23 is arranged to extend in the X-axis direction so as to straddle three conductive elastomers 22.

[0192] The conductor line 23 is, for example, a copper wire with a coating. The conductor line 23 is composed of a linear conductive member 23a and a dielectric 23b formed on the surface of the conductive member 23a.

[0193] Figure 21 (a) schematically shows Figure 20 a perspective view of the state in which the wire 24 is provided in the structure of (b).

[0194] After arranging the conductor lines 23 as in Figure 20 (b), each conductor line 23 is connected to the base member 21 through the wire 24 in a manner capable of moving along the long side direction (X-axis direction) of the conductor line 23. In Figure 21In the example shown in (a), twelve wires 24 connect the conductor wire 23 to the base member 21 at positions other than the position where the conductive elastomer 22 overlaps the conductor wire 23. The wire 24 is made of chemical fiber, natural fiber, or a mixed fiber thereof, etc.

[0195] Figure 21 (b) schematically shows Figure 21 a perspective view of the state in which the base member 25 is provided in the structure of (a).

[0196] From Figure 21 above the structure shown in (a) (the positive Z-axis side), the base member 25 is provided. The base member 25 is an insulating member. The base member 25 is, for example, at least one resin material selected from the group consisting of polyethylene terephthalate, polycarbonate, and polyimide, etc. The base member 25 may also be made of the same material as the base member 21. The base member 25 has a flat plate shape parallel to the X-Y plane and has the same size and shape as the base member 21 when viewed from above. The thickness of the base member 25 in the Z-axis direction is, for example, 0.01 mm to 2 mm.

[0197] The outer peripheral four sides of the base member 25 are connected to the outer peripheral four sides of the base member 21 by a silicone rubber-based adhesive, wire, etc. Thus, the base member 25 is fixed to the base member 21. The conductor wire 23 is sandwiched between the conductive elastomer 22 and the base member 25. In this way, as Figure 21 shown in (b), the load sensor 20 is completed. The load sensor 20 can be used in a state where it is flipped forward and backward from the state of (b). Figure 21

[0198] Figure 22 (a) and Figure 22 (b) are diagrams schematically showing the cross-section of the load sensor 20 when the load sensor 20 is cut along a plane parallel to the Y-Z plane at the central position in the X-axis direction of the conductive elastomer 22. Figure 22 Figure 22

[0199] Figure 22

[0200] As Figure 22 shown in (a) and (b), the conductor wire 23 is composed of a conductive member 23a and a dielectric 23b formed on the conductive member 23a. The conductive member 23a is a linear member having conductivity. The dielectric 23b covers the surface of the conductive member 23a. The conductive member 23a is made of copper, for example. The diameter of the conductive member 23a is about 60 μm, for example.

[0200] The dielectric 23b has electrical insulation properties and is composed of, for example, resin materials, ceramic materials, metal oxide materials, etc. The dielectric 23b can be at least one resin material selected from the group consisting of polypropylene resin, polyester resin (e.g., polyethylene terephthalate resin), polyimide resin, polyphenylene sulfide resin, polyvinyl formal resin, polyurethane resin, polyamideimide resin, polyamide resin, etc., or can be at least one metal oxide material selected from the group consisting of Al2O3 and Ta2O5, etc. The dielectric 23b is formed at least in the range where the conductor line 23 overlaps with the conductive elastomer 22.

[0201] As Figure 22 (a) of shows, in the case where no load is applied, the force applied between the conductive elastomer 22 and the conductor line 23, and the force applied between the base member 25 and the conductor line 23 are substantially zero. If a load is applied to the surface on the negative Z-axis side of the base member 21 as shown in Figure 22 (b) of from this state, the conductive elastomer 22 and the base member 21 are deformed by the conductor line 23.

[0202] As Figure 22 (b) of shows, due to the application of the load, the conductor line 23 approaches the conductive elastomer 22 in a manner surrounded by the conductive elastomer 22. Along with this, the contact area between the conductor line 23 and the conductive elastomer 22 increases. As a result, the electrostatic capacitance between the conductive member 23a and the conductive elastomer 22 changes. By detecting the electrostatic capacitance between the conductive member 23a and the conductive elastomer 22, the load applied to this area is obtained.

[0203] Figure 23 is a top view schematically showing the internal structure of the load sensor 20. In Figure 23 , for convenience, the illustration of the line 24 and the base member 25 is omitted.

[0204] As Figure 23 shows, at the positions where the three conductive elastomers 22 intersect with the three conductor lines 23, element parts A11, A12, A13, A21, A22, A23, A31, A32, A33 whose electrostatic capacitance changes according to the load are formed. Each element part includes the conductive elastomer 22 and the conductor line 23 near the intersection of the conductive elastomer 22 and the conductor line 23.

[0205] In each element part, the conductor line 23 constitutes one pole (e.g., anode) of the electrostatic capacitance, and the conductive elastomer 22 constitutes the other pole (e.g., cathode) of the electrostatic capacitance. That is, the conductive member 23a in the conductor line 23 (refer to Figure 22(a) and (b) thereof constitute one electrode of the load sensor 20 (capacitive load sensor), the conductive elastic body 22 constitutes the other electrode of the load sensor 20 (capacitive load sensor), and the dielectric 23b included in the conductor line 23 (refer to Figure 22 (a) and (b) thereof corresponds to the dielectric that defines the capacitance in the load sensor 20 (capacitive load sensor).

[0206] If a load is applied to each component portion in the Z-axis direction, the conductor line 23 is wrapped by the conductive elastic body 22. As a result, the contact area between the conductor line 23 and the conductive elastic body 22 changes, and the capacitance between the conductor line 23 and the conductive elastic body 22 changes. The end portion on the negative X-axis side of the conductor line 23 and the end portion on the negative Y-axis side of the wiring W2 provided on the conductive elastic body 22 are connected to the Figure 24 capacitance measurement circuit 10 described later.

[0207] If a load is applied to the component portion A11, in the component portion A11, the contact area between the conductive member 23a of the conductor line 23 and the conductive elastic body 22 across the dielectric 23b increases. In this case, the load applied to the component portion A11 can be calculated by detecting the capacitance between the conductive elastic body 22 closest to the negative X-axis side and the conductor line 23 closest to the positive Y-axis side. Similarly, in other component portions, the load applied to the other component portion can also be calculated by detecting the capacitance between the conductive elastic body 22 and the conductor line 23 that intersect in the other component portion.

[0208] Figure 24 is a diagram showing the structure of the load detection device 1.

[0209] In Figure 24 , for convenience, as the structure of the load sensor 20, only the conductor line 23 and the conductive elastic body 22 are shown, and the conductive elastic body 22 is shown as a line.

[0210] The load detection device 1 includes the capacitance measurement circuit 10 according to the above-described Embodiment 1 and Figure 21 the load sensor 20 shown in (b) thereof. Here, Figure 23 The nine component portions A11 to A33 shown respectively correspond to the measurement capacitance Cs. The conductor line 23 (conductive member 23a) of the component portions A11 to A33 corresponds to the positive electrode of the measurement capacitance Cs, and the conductive elastic body 22 of the component portions A11 to A33 corresponds to the negative electrode of the measurement capacitance Cs.

[0211] The capacitance measurement circuit 10 includes means for Figure 23Element selection units 17 and 18 that switch the element unit to be measured among the nine element units A11 to A33 shown. The element selection unit 17 includes switching elements 17a to 17c, and the element selection unit 18 includes switching elements 18a to 18d.

[0212] The switching elements 17a to 17c connect the wiring W2 led out from the conductive elastomer 22 to either the ground line L3 or the potential line L2. These switching elements 17a to 17c correspond to Figure 1 the switching element 13. The switching element 18d connects the potential line L1 to any one of the switching elements 18a to 18c. The switching elements 18a to 18c connect the wiring W1 respectively led out from the conductor line 23 (conductive member 23a) to either the output terminal of the switching element 18d or the ground line L3.

[0213] In addition, the capacitance measurement circuit 10 includes an equipotential generation unit 19 that generates a potential equal to the potential of the potential line L1. In Figure 1 this structure, in order to make the positive and negative electrodes of the measured capacitance Cs have the same potential, one terminal of the switching element 17a is directly connected to the wiring between the switching elements 12b and 12c. In contrast, in Figure 24 the potential line L2 to which one terminal of the switching element 17a is connected is connected to other circuit parts such as the switching elements 17b and 17c, the wiring W2, and the conductive elastomer 22 in addition to being connected to the switching element 17a. Therefore, compared with Figure 1 the case of Figure 24 the impedance of these circuit parts becomes higher. Therefore, in Figure 24 this structure, the equipotential generation unit 19 is arranged so that the potential of the potential line L2 is equal to the potential of the potential line L1.

[0214] In Figure 24 the states of the switching elements 17a to 17c and 18a to 18d in the first control C1 when measuring the capacitance value of the element unit A11 are shown. In this state, the conductor lines 23 (positive electrodes) of the uppermost element units A11 to A13 among the nine element units are connected to the potential line L1. Therefore, the remaining six element units are in an open state in the circuit. In addition, since the equipotential generation unit 19 applies a potential equal to the potential of the potential line L1 to the conductive elastomers 22 of the element units A12 and A13, the element units A12 and A13 are invalidated. As a result, only the element unit A11 to be measured is in a state of being connected to the capacitance measurement circuit 10.

[0215] In this state, the control unit 11 executes Figure 7 the first control C1 to obtain the first voltage value Vx1. Next, in step S106 of the second control C2 in Figure 7 the control unit 11, as in Figure 25The switching element 17a is switched to the potential line L2 side as described above to perform the processes of steps S107 to S110. Thereby, the control unit 11 acquires the second voltage value Vx2. Then, the control unit 11 performs the process of step S111 to calculate the capacitance value of the element unit A11. And the control unit 11 calculates the load applied to the element unit A11 based on the calculated capacitance value. Regarding the calculation of the load, it may also be calculated by a processing unit other than the control unit 11 based on the capacitance value calculated by the control unit 11. Thus, the processing of the element unit A11 is completed.

[0216] The control unit 11 controls the switching elements 17a to 17c, 18a to 18d to sequentially switch the element units to be measured. For example, when the element unit A12 is the measurement object, in Figure 7 step S101 of the first control C1, the switching element 17b is connected to the ground line L3, and the switching elements 17a, 17c are connected to the potential line L2. In addition, the control unit 11 keeps the switching elements 18a to 18d Figure 24 in the state. In this state, the control unit 11 performs Figure 7 the processes after step S102. In step S106, the switching element 17b is switched to the potential line L2 side to perform the processes after step S107. Thus, the control unit 11 calculates the capacitance value of the element unit A12 and calculates the load applied to the element unit A12 based on the calculation result.

[0217] <Effects of Embodiment 3>

[0218] According to the load detection device 1 according to Embodiment 3, since it includes the capacitance measurement circuit 10 according to Embodiment 1, even in the range where the loads applied to the element units A11 to A33 are small and the capacitance is small, the capacitance value corresponding to the load can be stably acquired. In addition, since it includes the capacitance measurement circuit 10 according to Embodiment 1, the capacitance value with the influence of parasitic capacitance suppressed can be acquired with high precision. Therefore, the load in a small range can be detected stably and with high precision.

[0219] In addition, the load sensor 20 includes a plurality of element units A11 to A33, and the capacitance measurement circuit 10 includes the element selection units 17, 18 for switching the element units to be measured. Thereby, the load can be detected in a wide range where a plurality of element units A11 to A33 are arranged. In addition, by switching the element units to be measured using the element selection units 17, 18, the capacitance values of the respective element units can be measured stably and with high precision through Figure 7 the same processing.

[0220] In addition, in Figure 24In the structure of, compared with Figure 1 the structure of, many switching elements 17a to 17c, 18a to 18d and wirings are arranged, and an equipotential generation unit 19 is also arranged, so the parasitic capacitance increases. However, in this case, the influence of the parasitic capacitance is also suppressed by the above formula (5), so the electrostatic capacitance values of the respective element parts can be calculated with high precision, and the loads applied to the respective element parts can be detected with high precision.

[0221] In addition, the process of calculating the electrostatic capacitance values of the respective element parts can also be changed to Figure 8 the process of. Thereby, the calculation process of the electrostatic capacitance value can be quickly performed for each element part, and the load detection process for the entire nine element parts can be quickly performed.

[0222] And Figure 9 the structure of the modification example 2 shown in can also be applied to Figure 24 the structure of. Thereby, for example, even if the load sensor 20 as the measurement object is changed and the dynamic range of the element part is changed, the electrostatic capacitance values of the respective element parts can be appropriately measured, and the loads of the respective element parts can be detected with high precision.

[0223] <Embodiment 4>

[0224] In Embodiment 4, a structural example is shown in the case where the electrostatic capacitance measurement circuit 10 of the above Embodiment 2 is applied to a load detection device. The load detection device detects a load using the same load sensor as in the above Embodiment 3.

[0225] Figure 26 FIG. is a diagram showing the structure of the load detection device 1 according to Embodiment 4.

[0226] Similar to Figure 24 In, for convenience, as the structure of the load sensor 20, only the conductor line 23 and the conductive elastic body 22 are illustrated, and the conductive elastic body 22 is illustrated as a line shape. Figure 26

[0227] The load detection device 1 includes the electrostatic capacitance measurement circuit 10 according to the above Embodiment 2 and Figure 21 the load sensor 20 shown in (b) of. Here, similar to the above Embodiment 3, Figure 23 the nine element parts A11 to A33 shown in respectively correspond to the measurement capacitor Cs. The conductor lines 23 (conductive members 23a) of the element parts A11 to A33 correspond to the positive electrode of the measurement capacitor Cs, and the conductive elastic bodies 22 of the element parts A11 to A33 correspond to the negative electrode of the measurement capacitor Cs.

[0228] The structures of the switching elements 17a to 17c and the switching elements 18a to 18d are the same as Figure 24 ​The same applies. In addition, similar to the case of Figure 24 an equipotential generation unit 19 is provided to make the potential of the potential line L2 equal to the potential of the potential line L1.

[0229] Similar to Figure 24 in the same way, in Figure 26 the states of the switching elements 17a to 17c and 18a to 18d in the first control C1 in the case of measuring the capacitance value of the measurement element unit A11 are shown. In this case, similar to Figure 24 the case of, only the element unit A11 to be measured is connected to the capacitance measurement circuit 10.

[0230] In this state, the control unit 11 executes Figure 16 the first control C1 of to obtain the first voltage value Vx1. Then, in step S206 of the second control C2 of the control unit 11 in Figure 16 as in Figure 27 the switching element 17a is switched to the potential line L2 side to execute the processes of steps S207 to S211. Thus, the control unit 11 obtains the second voltage value Vx2. Then, the control unit 11 executes the process of step S212 to calculate the capacitance value of the element unit A11. And the control unit 11 calculates the load applied to the element unit A11 based on the calculated capacitance value. Regarding the calculation of the load, it may also be calculated by other processing units other than the control unit 11 based on the capacitance value calculated by the control unit 11. In this way, the processing of the element unit A11 is completed.

[0231] The control unit 11 controls the switching elements 17a to 17c and 18a to 18d to sequentially switch the element units to be measured. For example, when the element unit A12 is the measurement object, in step S201 of the first control C1 of the control unit 11 in Figure 16 the switching element 17b is connected to the ground line L3, and the switching elements 17a and 17c are connected to the potential line L2. In addition, the control unit 11 keeps the switching elements 18a to 18d in Figure 26 the state of. In this state, the control unit 11 executes Figure 16 the processes after step S202 of. In step S206, the switching element 17b is switched to the potential line L2 side to perform the processes after step S207. In this way, the control unit 11 calculates the capacitance value of the element unit A12 and calculates the load applied to the element unit A12 based on the calculation result.

[0232] <Effects of Embodiment 4>

[0233] According to the load detection device 1 according to Embodiment 4, since it includes the capacitance measurement circuit 10 according to Embodiment 2, even within a range where the load applied to the element units A11 to A33 is small and the capacitance is small, it is possible to stably obtain the capacitance value corresponding to the load. In addition, since it includes the capacitance measurement circuit 10 according to Embodiment 2, it is possible to obtain a capacitance value with the influence of parasitic capacitance suppressed with high precision. Therefore, it is possible to stably and highly accurately detect a small range of loads. In addition, by using the element selection units 17 and 18 to switch the element units to be measured, it is possible to stably and highly accurately measure the capacitance values of the respective element units by Figure 16 the same processing.

[0234] In addition, in the Figure 26 structure, compared with the Figure 10 structure, many switching elements 17a to 17c, 18a to 18d and wirings are arranged, and an equipotential generation unit 19 is also arranged, so the parasitic capacitance increases. However, in this case, the influence of the parasitic capacitance is also suppressed by the above formula (10), so it is possible to calculate the capacitance values of the respective element units with high precision, and it is possible to highly accurately detect the load applied to each element unit.

[0235] In addition, the process of calculating the capacitance values of the respective element units can also be changed to Figure 18 the process. Thereby, it is possible to quickly perform the calculation process of the capacitance value for each element unit, and it is possible to quickly perform the load detection process for the entire nine element units.

[0236] And, Figure 19 the structure of Modification 2 shown can also be applied to the Figure 26 structure. Thereby, for example, even if the load sensor 20 to be measured is changed or the dynamic range of the element unit is changed, it is possible to appropriately measure the capacitance values of the respective element units, and it is possible to highly accurately detect the loads of the respective element units.

[0237] <Other Modifications>

[0238] In the above Embodiments 1 and 2, the switching elements 12a to 12c are composed of P-type or N-type FETs, but the switching elements 12a to 12c can also be composed of other switching elements other than FETs. Similarly for the switching element 13, as long as it can switch the connection destination of the negative electrode of the measurement capacitor Cs between the ground and the positive electrode, various types of switching elements can be used. Similarly, in the Figures 24 - 26 structure, as the switching elements 17a to 17c and the switching elements 18a to 18d, various types of switching elements can also be used.

[0239] In addition, in the above Embodiment 1, in theFigure 4 After the switching element 13 is switched in (b) of [], the reference capacitor Cr is not discharged, but in Figure 5 of (a), the reference capacitor Cr is charged, but it is also possible to charge the reference capacitor Cr after it is temporarily discharged, and then in Figure 5 of (a), the reference capacitor Cr is charged. However, in this case, compared with the case where the reference capacitor Cr is charged without being discharged as described above, the time until the reference capacitor Cr becomes fully charged becomes longer. Therefore, in order to process more quickly, it is preferable to charge the reference capacitor Cr without discharging it as in Figure 5 of (a). This is the same in the process from the operation of (b) to the operation of (a) in Embodiment 2. Figure 13 of (b) to Figure 14 of (a).

[0240] In addition, in Embodiments 3 and 4, as shown in Figures 24 - 26 , in the element parts A12 and A13 other than the element part A11 to be measured, an equal potential is applied to the positive electrode and the negative electrode to invalidate the element parts A12 and A13, but it is also possible to set the switching elements 17b and 17c such that their negative electrodes are connected to the ground wire L3. In this case, the electrostatic capacitances of the element parts A12 and A13 are also included in the above-mentioned parasitic capacitance, and thus are eliminated by the above formulas (5) and (10). Therefore, the electrostatic capacitance of the element part A11 to be measured can be obtained with high precision.

[0241] In addition, in Figures 24 - 26 , two conductor lines 23 (conductive members 23a) other than the conductor line 23 (conductive member 23a) constituting the positive electrode of the element part A11 to be measured are connected to the ground wire through the switching elements 18b and 18c, but it is also possible to connect the switching elements 18b and 18c to the output line side of the switching element 18d and set the element part with these two conductor lines 23 (conductive members 23a) as the positive electrode to a floating state. In this case, the parasitic capacitance other than the element part A11 to be measured is also eliminated by the above formulas (5) and (10), so that the electrostatic capacitance of the element part A11 to be measured can be obtained with high precision.

[0242] The structures and switching methods of the element selection parts 17 and 18 only need to be able to connect the negative electrode of the element part to be measured to the ground or a wiring having the same potential as the positive electrode of the element part to be measured, and to eliminate the electrostatic capacitance of the element parts other than the measurement object together with other parasitic capacitances by the above formulas (5) and (10), and other structures and switching methods may be used.

[0243] In addition, in the above-described Embodiments 3 and 4, the conductor wire 23 is composed of a copper wire covered with a tape, but it is not limited thereto, and it may also be composed of a linear conductive member including a substance other than copper and a dielectric covering the conductive member. In addition, the conductive member may be composed of stranded wires.

[0244] In addition, in the above-described Embodiments 3 and 4, the conductive elastomer 22 is provided only on the surface on the positive Z-axis side of the base member 21, but a conductive elastomer may also be provided on the surface on the negative Z-axis side of the base member 25. In this case, the conductive elastomer on the base member 25 side is configured in the same manner as the conductive elastomer 22 on the base member 21 side, and is arranged to overlap the conductive elastomer 22 so as to sandwich the conductor wire 23 in a plan view. Moreover, the wiring led out from the conductive elastomer on the base member 25 side is connected to the wiring W2 led out from the conductive elastomer 22 facing in the Z-axis direction. Thus, when the conductive elastomers are provided above and below with respect to the conductor wire 23, the change in capacitance in the element portion is approximately doubled corresponding to the upper and lower conductive elastomers, and therefore the detection sensitivity of the load applied to the element portion can be improved.

[0245] In addition, in the above-described Embodiments 3 and 4, the dielectric 23b is formed around the outer periphery of the conductive member 23a, but instead, the dielectric 23b may be formed on the upper surface of the conductive elastomer 22. In this case, the conductive member 23a sinks in a manner surrounded by the conductive elastomer 22 and the dielectric 23b according to the application of a load, and the contact area between the conductive member 23a and the conductive elastomer 22 changes. Thereby, the load applied to the element portion can be detected in the same manner as in the above-described embodiment.

[0246] In addition, in the above-described Embodiments 3 and 4, the load sensor 20 is configured such that nine element portions are arranged in a matrix of three rows and three columns, but the number and arrangement of the element portions in the load sensor 20 are not limited thereto. For example, the load sensor 20 may be configured such that sixteen element portions are arranged in a matrix of four rows and four columns, or the load sensor 20 may be configured such that a plurality of element portions are arranged in only one column. Alternatively, the load sensor 20 may have a structure in which only one element portion is provided.

[0247] In addition, in the above-described Embodiments 3 and 4, the element portion is formed by the intersection of the conductive elastomer 22 and the conductor wire 23, but the structure of the element portion is not limited thereto. For example, the element portion may be formed by a structure in which a hemispherical conductive elastomer and a flat electrode sandwich a dielectric. In this case, the dielectric may be formed on the surface of the electrode facing the conductive elastomer or on the surface of the hemispherical conductive elastomer.

[0248] In addition, the measured capacitance measured by the capacitance measurement circuit 10 according to the present invention is not limited to the element portion of the load sensor, and may be other measured capacitances. For example, a capacitance element formed in an electrostatic touch panel, a semiconductor device, an electrolytic capacitor, a ceramic capacitor, etc. may be used as the measured capacitance of the capacitance measurement circuit 10.

[0249] In addition, the embodiments of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

[0250] (Supplementary Note)

[0251] Based on the description of the above embodiments, the following technologies are disclosed.

[0252] (Technology 1)

[0253] A capacitance measurement circuit, characterized by comprising:

[0254] A reference capacitance having a predetermined capacitance value;

[0255] A switching unit for switching between applying a voltage to the reference capacitance and not applying a voltage;

[0256] A transfer unit for transferring the charge stored in the reference capacitance to the measured capacitance;

[0257] A connection unit for connecting the negative electrode of the measured capacitance to the ground or a wiring having the same potential as the potential of the positive electrode of the measured capacitance;

[0258] A measurement unit for measuring the voltage of the measured capacitance; and

[0259] A control unit for controlling the switching unit, the transfer unit, and the connection unit,

[0260] wherein the control unit performs:

[0261] First control, after applying a voltage to the reference capacitance, in a state where the negative electrode of the measured capacitance is connected to the ground, causing the transfer unit to transfer charge;

[0262] Second control, after applying a voltage to the reference capacitance, in a state where the negative electrode of the measured capacitance is connected to the wiring having the same potential as the potential of the positive electrode of the measured capacitance, causing the transfer unit to transfer charge; and

[0263] Processing for calculating the capacitance value of the measured capacitance based on the voltage values measured by the measurement unit after the charge transfer is respectively performed by the first control and the second control.

[0264] According to this technique, since the electrostatic capacitance value of the measurement capacitor is calculated based on the voltage value after the charge is transferred from the reference capacitor, even without using a high-precision AD converter, it is possible to stably measure the electrostatic capacitance value in a small range. Additionally, in the second control, since the negative electrode of the measurement capacitor is connected to a wiring having the same potential as the positive electrode of the measurement capacitor, the measured voltage value is hardly affected by the measurement capacitor, but is mainly affected by the reference capacitor and the parasitic capacitance. In contrast, in the first control, since the negative electrode of the measurement capacitor is connected to the ground, the measured voltage value is affected by the reference capacitor, the parasitic capacitance, and the measurement capacitor. Therefore, by calculating the electrostatic capacitance value of the measurement capacitor based on these two voltage values, it is possible to calculate the electrostatic capacitance value without the influence of the parasitic capacitance. Thus, it is possible to measure the electrostatic capacitance value of the measurement capacitor with high precision.

[0265] (Technique 2)

[0266] The electrostatic capacitance measurement circuit according to Technique 1 is characterized in that

[0267] The control unit calculates the electrostatic capacitance value Cs of the measurement capacitor by the following formula based on the first voltage value Vx1 obtained through the first control, the second voltage value Vx2 obtained through the second control, the value Vdd of the voltage applied to the reference capacitor, and the electrostatic capacitance value Cr of the reference capacitor.

[0268] [Equation 7]

[0269]

[0270] According to this technique, it is possible to suppress the influence of the error component generated by the parasitic capacitance on the electrostatic capacitance value of the measurement capacitor Cs, and it is possible to obtain the electrostatic capacitance value of the measurement capacitor Cs with high precision.

[0271] (Technique 3)

[0272] An electrostatic capacitance measurement circuit is characterized by comprising:

[0273] A reference capacitor having a specified electrostatic capacitance value;

[0274] A switching unit for switching between applying a voltage to the measurement capacitor and not applying a voltage;

[0275] A transfer unit for transferring the charge accumulated in the measurement capacitor to the reference capacitor;

[0276] A connection unit for connecting the negative electrode of the measurement capacitor to the ground or a wiring having the same potential as the positive electrode of the measurement capacitor;

[0277] A measurement unit for measuring the voltage of the measurement capacitor; and

[0278] A control unit that controls the switching unit, the transfer unit, and the connection unit,

[0279] wherein the control unit performs:

[0280] A first control that, after applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to the ground, causes the transfer unit to transfer charge;

[0281] A second control that, after applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to a wiring having the same potential as the positive electrode of the measurement capacitor, causes the transfer unit to transfer charge; and

[0282] A process of calculating the capacitance value of the measurement capacitor based on the voltage values measured by the measurement unit after the charge transfer is performed respectively by the first control and the second control.

[0283] According to this technique, since the capacitance value of the measurement capacitor is calculated based on the voltage value after the charge is transferred from the measurement capacitor, it is possible to stably measure the capacitance value in a small range even without using a high-precision AD converter. In addition, in the second control, since the negative electrode of the measurement capacitor is connected to a wiring having the same potential as the positive electrode of the measurement capacitor and a voltage is applied to the measurement capacitor, almost no charge accumulates in the measurement capacitor, and charge accumulates in the parasitic capacitance. Therefore, the voltage value measured by the second control is hardly affected by the measurement capacitor, but is mainly affected by the reference capacitor and the parasitic capacitance. In contrast, in the first control, since the negative electrode of the measurement capacitor is connected to the ground and a voltage is applied to the measurement capacitor, charge is applied to both the parasitic capacitance and the measurement capacitor. Therefore, the voltage values measured by the first and second controls are affected by the reference capacitor, the parasitic capacitance, and the measurement capacitor. Thus, by calculating the capacitance value of the measurement capacitor based on these two voltage values, it is possible to calculate the capacitance value without the influence of the parasitic capacitance. Therefore, it is possible to measure the capacitance value of the measurement capacitor with high precision.

[0284] (Technique 4)

[0285] The capacitance measurement circuit according to Technique 3, characterized in that

[0286] the control unit calculates the capacitance value Cs of the measurement capacitor by the following formula based on the first voltage value Vx1 obtained by the first control, the second voltage value Vx2 obtained by the second control, the value Vdd of the voltage applied to the measurement capacitor, and the capacitance value Cr of the reference capacitor.

[0287] [Number 8]

[0288]

[0289] According to this technique, it is possible to suppress the influence of error components generated by parasitic capacitance on the electrostatic capacitance value of the measurement capacitance, and the electrostatic capacitance value of the measurement capacitance can be obtained with high precision.

[0290] (Technique 5)

[0291] The electrostatic capacitance measurement circuit according to any one of Techniques 1 to 4, characterized in that

[0292] The control unit repeats the first control until the voltage value saturates while changing the standby period from transferring the charge to obtaining the voltage value, and calculates the electrostatic capacitance value using the saturated voltage value.

[0293] According to this technique, when the electrostatic capacitance value of the measurement capacitance is small and the measurement value of the measurement unit saturates and stabilizes in advance, the first voltage value Vx1 can be quickly obtained through a short standby period. Therefore, the calculation process of the electrostatic capacitance value of the measurement capacitance can be quickly performed.

[0294] (Technique 6)

[0295] The electrostatic capacitance measurement circuit according to Technique 5, characterized in that

[0296] The control unit extends the standby period every time the first control is repeated.

[0297] According to this technique, the standby period can be gradually made close to the length that saturates the first voltage value Vx1. Therefore, the standby period suitable for the measurement capacitance can be set smoothly.

[0298] (Technique 7)

[0299] The electrostatic capacitance measurement circuit according to any one of Techniques 1 to 6, characterized in that

[0300] It further includes a capacitance value changing unit that changes the electrostatic capacitance value of the reference capacitance.

[0301] According to this technique, the electrostatic capacitance value of the reference capacitance can be adjusted to a value suitable for the dynamic range of the measurement capacitance. Therefore, even when the dynamic range of the measurement capacitance is changed, the electrostatic capacitance value of the measurement capacitance can be appropriately measured within this dynamic range.

[0302] (Technique 8)

[0303] The load detection device according to Technique 7, characterized by comprising:

[0304] A load sensor having an element portion whose electrostatic capacitance varies according to a load; and

[0305] The electrostatic capacitance measurement circuit according to any one of Technologies 1 to 7,

[0306] wherein the control unit performs the first control, the second control, and the calculation process of the electrostatic capacitance using the element portion as the measurement capacitance.

[0307] According to this technology, since it includes the electrostatic capacitance measurement circuit according to any one of Technologies 1 to 7, even in a range where the load applied to the element portion is small and the electrostatic capacitance is small, it is possible to stably obtain the electrostatic capacitance corresponding to the load. In addition, since it includes the electrostatic capacitance measurement circuit according to any one of Technologies 1 to 7, it is possible to obtain an electrostatic capacitance value that suppresses the influence of parasitic capacitance with high accuracy. Therefore, it is possible to stably and highly accurately detect a small range of loads.

[0308] (Technology 9)

[0309] The load detection device according to Technology 8, characterized in that

[0310] the load sensor includes a plurality of the element portions,

[0311] the electrostatic capacitance measurement circuit includes an element selection unit for switching the element portion to be measured.

[0312] According to this technology, by switching the element portion to be measured using the element selection units 17 and 18, it is possible to stably and highly accurately measure the electrostatic capacitance values of the respective element portions by the electrostatic capacitance measurement circuit.

[0313] Explanation of Reference Numerals

[0314] 1: Load detection device; 10: Electrostatic capacitance measurement circuit; 11: Control unit; 20: Load sensor; 10a: Switching element (switching unit); 10b: Switching element (transfer unit); 13: Switching element (connection unit); 14: Measurement unit; 15: Capacitance selection unit (capacitance value change unit); 16a to 16d: Switching elements (capacitance value change unit); 17, 18: Element selection units; 17a to 17c: Switching elements (connection unit); Cra to Crd: Capacitors (capacitance value change unit); Cr: Reference capacitance; Cs: Measurement capacitance; A11 to A33: Element portions (measurement capacitance).

Claims

1. An electrostatic capacitance measurement circuit, characterized in that, Comprising: A reference capacitor having a predetermined capacitance value; A switching unit for switching between applying a voltage to the reference capacitor and not applying a voltage; A transfer unit for transferring the charge stored in the reference capacitor to a measurement capacitor; A connection unit for connecting the negative electrode of the measurement capacitor to the ground or a wiring having the same potential as the potential of the positive electrode of the measurement capacitor; A measurement unit for measuring the voltage of the measurement capacitor; And A control unit for controlling the switching unit, the transfer unit, and the connection unit, wherein the control unit performs: First control: After applying a voltage to the reference capacitor, in a state where the negative electrode of the measurement capacitor is connected to the ground, causing the transfer unit to transfer charge; Second control: After applying a voltage to the reference capacitor, in a state where the negative electrode of the measurement capacitor is connected to the wiring having the same potential as the potential of the positive electrode of the measurement capacitor, causing the transfer unit to transfer charge; and A process of calculating the capacitance value of the measurement capacitor based on the voltage values measured by the measurement unit after the charge transfer is respectively performed by the first control and the second control.

2. The electrostatic capacitance measurement circuit according to claim 1, characterized in that, The control unit repeats the first control until the voltage value saturates while varying the standby period from when the charge is transferred until the voltage value is obtained, and uses the saturated voltage value to calculate the capacitance value.

3. The electrostatic capacitance measurement circuit according to claim 2, characterized in that, The control unit extends the standby period each time the first control is repeated.

4. The electrostatic capacitance measurement circuit according to claim 1, characterized in that, The control unit calculates the capacitance value Cs of the measurement capacitor by the following formula based on the first voltage value Vx1 obtained through the first control, the second voltage value Vx2 obtained through the second control, the value Vdd of the voltage applied to the reference capacitor, and the capacitance value Cr of the reference capacitor. [Equation 1] 5. The electrostatic capacitance measurement circuit according to claim 1, characterized in that, It further comprises a capacitance value changing unit for changing the capacitance value of the reference capacitor.

6. An electrostatic capacitance measurement circuit, characterized in that, Comprising: A reference capacitor having a predetermined capacitance value; A switching unit for switching between applying a voltage to the measurement capacitor and not applying a voltage; A transfer unit for transferring the charge stored in the measurement capacitor to the reference capacitor; A connection unit for connecting the negative electrode of the measurement capacitor to the ground or a wiring having the same potential as the potential of the positive electrode of the measurement capacitor; A measurement unit for measuring the voltage of the measurement capacitor; And A control unit for controlling the switching unit, the transfer unit, and the connection unit, wherein the control unit performs: First control: After applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to the ground, causing the transfer unit to transfer charge; Second control: After applying a voltage to the measurement capacitor in a state where the negative electrode of the measurement capacitor is connected to the wiring having the same potential as the potential of the positive electrode of the measurement capacitor, causing the transfer unit to transfer charge; and A process of calculating the capacitance value of the measurement capacitor based on the voltage values measured by the measurement unit after the charge transfer is respectively performed by the first control and the second control.

7. The electrostatic capacitance measurement circuit according to claim 6, characterized in that, The control unit repeats the first control until the voltage value saturates while changing a standby period from when the charge is transferred to when the voltage value is obtained, and calculates the electrostatic capacitance value using the saturated voltage value.

8. The electrostatic capacitance measurement circuit according to claim 7, wherein, The control unit extends the standby period each time the first control is repeated.

9. The electrostatic capacitance measurement circuit according to claim 6, wherein, The control unit calculates the electrostatic capacitance value Cs of the measurement capacitor by the following formula based on the first voltage value Vx1 obtained through the first control, the second voltage value Vx2 obtained through the second control, the value Vdd of the voltage applied to the measurement capacitor, and the electrostatic capacitance value Cr of the reference capacitor. [Equation 2] 10. The electrostatic capacitance measurement circuit according to claim 6, wherein, It further includes a capacitance value changing unit that changes the electrostatic capacitance value of the reference capacitor.

11. A load detection device, wherein, It includes: a load sensor having an element portion whose electrostatic capacitance changes according to a load; and the electrostatic capacitance measurement circuit according to any one of claims 1 to 10, wherein the control unit performs the first control, the second control, and the electrostatic capacitance calculation process with the element portion as the measurement capacitor.

12. The load detection device according to claim 11, wherein, The load sensor includes a plurality of the element portions. The electrostatic capacitance measurement circuit includes an element selection unit for switching the element portion to be measured.

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