Capacitance measurement circuit and load detection device

Abstract

This capacitance measurement circuit comprises: a reference capacitor (Cr); a switching element (12a) for switching between application and non-application of a voltage to the reference capacitor (Cr); a switching element (12b) for transferring a charge of the reference capacitor (Cr) to a measurement capacitor (Cs); a switching element (13) for connecting a negative electrode of the measurement capacitor (Cs) to the ground or to a wiring having the same potential as a positive electrode of the measurement capacitor (Cs); a measurement unit (14) for measuring the voltage of the measurement capacitor (Cs); and a control unit (11). The control unit (11) executes: first control for connecting the negative electrode of the measurement capacitor (Cs) to the ground and causing the switching element (12b) to transfer the charge; second control for connecting the negative electrode of the measurement capacitor (Cs) to the abovementioned wiring and causing the switching element (12b) to transfer the charge; and, after the charge is transferred by each control, a process for calculating the capacitance value of the measurement capacitor (Cs) from the error capacitance of the reference capacitor (Cr) and the voltage value measured by the measurement unit (14).

Description

Capacitance measurement circuit and load detection device

[0001] The present invention relates to a capacitance measurement circuit for measuring capacitance, and a load detection device for detecting a load based on the result of measuring capacitance.

[0002] Conventionally, capacitance-type load sensors have been known in which the capacitance of an element changes depending on the load. In this type of load sensor, for example, the capacitance of the element is detected based on a change in voltage when a voltage is applied to the element. A load detection device using this type of load sensor is described, for example, in Patent Document 1 below.

[0003] Japanese Patent Application Laid-Open No. 2021-81209

[0004] In a capacitance-type load sensor, in addition to the method based on the voltage change as described above, the capacitance of the element unit can also be detected from, for example, the amount of charge accumulated in the element unit when a voltage is applied to the element unit. In this case, for example, the amount of charge accumulated in the element unit can be calculated by measuring the amount of current flowing through the element unit during the period from when a voltage is applied to the element unit until the accumulated charge is saturated. Such measurement of the amount of current can be performed, for example, by sampling and integrating the current value during this period using an AD converter.

[0005] However, when the load applied to the element is small, the capacitance of the element is small, and the period from application of voltage to saturation of the accumulated charge is short. Therefore, measuring the amount of current described above requires a high-speed, high-precision AD converter to sample the current value that changes over a short period of time. However, even when such an AD converter is used, the period until the amount of current saturates is significantly short when the load is relatively small, making it difficult to stably measure the amount of current during this period.

[0006] Furthermore, the capacitance measurement results are affected by parasitic capacitance due to wiring, other electrical elements, etc. Therefore, the calculated capacitance contains errors due to the parasitic capacitance, and these errors make it difficult to detect the load accurately.

[0007] In view of the above problem, an object of the present invention is to provide a capacitance measuring circuit and a load detecting device that are capable of measuring capacitance even in a small range stably and accurately.

[0008] A first aspect of the present invention relates to a capacitance measurement circuit, which includes a reference capacitance having a predetermined capacitance value, a switching unit that switches between applying and not applying a voltage to the reference capacitance, a transfer unit that transfers charge accumulated in the reference capacitance to a measurement capacitance, a connection unit that connects a negative electrode of the measurement capacitance to ground or a wiring having the same potential as a positive electrode of the measurement capacitance, a measurement unit that measures the voltage of the measurement capacitance, and a control unit that controls the switching unit, the transfer unit, and the connection unit. The control unit executes a first control in which, after applying a voltage to the reference capacitance, the transfer unit transfers charge while the negative electrode of the measurement capacitance is connected to the ground, and after the charge transfer is completed, the control unit acquires a first voltage value measured by the measurement unit; a second control in which, after applying a voltage to the reference capacitance, the transfer unit transfers charge while the negative electrode of the measurement capacitance is connected to the wiring at the same potential as the positive electrode of the measurement capacitance, and after the charge transfer is completed, the control unit acquires a second voltage value measured by the measurement unit; and a process of calculating the capacitance value of the measurement capacitance using the first voltage value, the second voltage value, and the capacitance value of an error capacitance, which is an error component of the reference capacitance, and acquires the capacitance value of the error capacitance by applying the first voltage value and the second voltage value acquired by the first control and the second control, respectively, to the calculation process using a test capacitance with a known capacitance value instead of the measurement capacitance.

[0009] According to the capacitance measurement circuit of this aspect, the capacitance value of the measurement capacitance is calculated based on the voltage value after the charge is transferred from the reference capacitance, allowing stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, in the second control, the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance, so the measured voltage value is largely unaffected by the measurement capacitance and is primarily affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, so the measured voltage value is affected not only by the reference capacitance and parasitic capacitance, but also by the measurement capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, a capacitance value free from the influence of parasitic capacitance can be calculated. Furthermore, the capacitance value of the measurement capacitance is calculated by taking into account the capacitance value of the error capacitance (effective equivalent capacitance of the error component), which is an error component of the reference capacitance, allowing for accurate acquisition of the capacitance value of the measurement capacitance.

[0010] A second aspect of the present invention relates to a capacitance measurement circuit, which includes a reference capacitor having a predetermined capacitance value, a switching unit that switches between applying and not applying a voltage to the measurement capacitor, a transfer unit that transfers charge accumulated in the measurement capacitor to the reference capacitor, a connection unit that connects 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 that measures the voltage of the measurement capacitor, and a control unit that controls the switching unit, the transfer unit, and the connection unit. The control unit executes a first control in which, with the negative electrode of the capacitance to be measured connected to the ground, a voltage is applied to the capacitance to be measured, and then the transfer unit transfers charge, and after the charge has been transferred, a first voltage value measured by the measurement unit is acquired; a second control in which, with the negative electrode of the capacitance to be measured connected to a wiring having the same potential as the positive electrode of the capacitance to be measured, a voltage is applied to the capacitance to be measured, and then the transfer unit transfers charge, and after the charge has been transferred, a second voltage value measured by the measurement unit is acquired; and a process of calculating the capacitance value of the capacitance to be measured using the first voltage value, the second voltage value, and a capacitance value of an error capacitance that is an error component of the reference capacitance, and acquires the capacitance value of the error capacitance by applying the first voltage value and the second voltage value acquired by the first control and the second control, respectively, to the calculation process using a test capacitance with a known capacitance value instead of the capacitance to be measured.

[0011] According to the capacitance measurement circuit of this aspect, the capacitance value of the measurement capacitance is calculated based on the voltage value after charge is transferred from the measurement capacitance, allowing stable measurement of capacitance values ​​over a small range without using a high-precision AD converter. Furthermore, in the second control, the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance, and a voltage is applied to the measurement capacitance. This means that almost no charge accumulates in the measurement capacitance, and charge accumulates in the parasitic capacitance. Therefore, the voltage value measured by the second control is largely unaffected by the measurement capacitance, and is primarily affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, and a voltage is applied to the measurement capacitance. This means that charge is applied to the measurement capacitance as well as the parasitic capacitance. Therefore, the voltage value measured by the first control is affected by the measurement capacitance, as well as the reference capacitance and parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, a capacitance value free from the influence of parasitic capacitance can be calculated. Furthermore, since the capacitance value of the error capacitance (effective equivalent capacitance of the error component), which is an error component of the reference capacitance, is taken into account when calculating the capacitance value of the measurement capacitance, the capacitance value of the measurement capacitance can be obtained with high accuracy.

[0012] 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 unit whose capacitance changes in response to a load, and the capacitance measurement circuit according to the first or second aspect. The control unit performs the first control, the second control, and the calculation process of the capacitance value using the element unit as the measurement capacitance.

[0013] According to the load detection device of this aspect, since it includes the capacitance measurement circuit of the first or second aspect, it can stably obtain a capacitance value corresponding to the load even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since it includes the capacitance measurement circuit of the first or second aspect, it can accurately obtain a capacitance value in which the effects of parasitic capacitance and error capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0014] As described above, the present invention can provide a capacitance measuring circuit and a load detecting device that can measure capacitance even in a small range stably and accurately.

[0015] The effects and significance of the present invention will become more apparent from the following description of the embodiments, however, the embodiments shown below are merely examples of how the present invention can be implemented, and the present invention is not limited to the embodiments described below.

[0016] FIG. 1 is a diagram showing the configuration of a capacitance measurement circuit according to embodiment 1. FIGS. 2(a) and 2(b) are diagrams showing the operation of the capacitance measurement circuit according to embodiment 1 when measuring the capacitance value of a capacitance to be measured. FIGS. 3(a) and 3(b) are diagrams showing the operation of the capacitance measurement circuit according to embodiment 1 when measuring the capacitance value of a capacitance to be measured. FIGS. 4(a) and 4(b) are diagrams showing the operation of the capacitance measurement circuit according to embodiment 1 when measuring the capacitance value of a capacitance to be measured. FIGS. 5(a) and 5(b) are diagrams showing the operation of the capacitance measurement circuit according to embodiment 1 when measuring the capacitance value of a capacitance to be measured. FIGS. 6(a) and 6(b) are diagrams showing the operation of the capacitance measurement circuit according to embodiment 1 when measuring the capacitance value of a capacitance to be measured. FIG. 7 is a flowchart showing the calculation process of the capacitance value of a capacitance to be measured according to Reference Example 1. FIG. 8(a) is a flowchart showing the calculation process of the capacitance value of a capacitance to be measured according to embodiment 1. FIG. 8(b) is a flowchart showing the calculation process of the capacitance value of an error capacitance according to embodiment 1. FIG. 9 is a graph showing measurement results when a reference capacitance with a known capacitance value is measured using the calculation method of the first embodiment and the calculation method of the first reference example. FIG. 10 is a diagram showing a configuration of a capacitance measurement circuit according to the first embodiment, in which the capacitance measurement circuit includes a test capacitor and a switching unit. FIG. 11 is a diagram showing a configuration of a capacitance measurement circuit according to the second embodiment. FIGS. 12(a) and 12(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to the second embodiment. FIGS. 13(a) and 13(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to the second embodiment. FIGS. 14(a) and 14(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to the second embodiment. FIGS. 15(a) and 15(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to the second embodiment. FIGS. 16(a) and 16(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of the measurement capacitance according to the second embodiment. FIG. 17 is a flowchart illustrating a process for calculating the capacitance value of the measurement capacitance according to the second embodiment.FIG. 18 is a diagram showing the configuration of a capacitance measurement circuit according to embodiment 2, when the capacitance measurement circuit includes a test capacitor and a switching unit. FIG. 19 is a diagram showing the configuration of a capacitance measurement circuit according to embodiment 3. FIG. 20 is a diagram showing the configuration of a capacitance measurement circuit according to embodiment 4. FIG. 21(a) is a perspective view schematically showing a base member and a conductive elastic body installed on the upper surface of the base member according to embodiment 5. FIG. 21(b) is a perspective view schematically showing a state in which a conductor wire is installed on the structure of FIG. 21(a) according to embodiment 5. FIG. 22(a) is a perspective view schematically showing a state in which a thread is installed on the structure of FIG. 21(b) according to embodiment 5. FIG. 22(b) is a perspective view schematically showing a state in which a base member is installed on the structure of FIG. 22(a) according to embodiment 5. FIGS. 23(a) and 23(b) are each a diagram schematically showing a cross section of a load sensor according to embodiment 5. FIG. 24 is a plan view schematically showing the internal configuration of a load sensor according to embodiment 5. Fig. 25 is a diagram showing the configuration of a load detection device according to embodiment 5. Fig. 26 is a diagram showing the operation of the load detection device according to embodiment 5 when detecting the capacitance value of the element portion to be measured. Fig. 27 is a diagram showing the operation of the load detection device according to embodiment 5 when detecting the capacitance value of the error capacitance. Fig. 28 is a diagram showing the operation of the load detection device according to embodiment 5 when detecting the capacitance value of the error capacitance. Fig. 29 is a diagram showing the configuration of a load detection device according to embodiment 6. Fig. 30 is a diagram showing the operation of the load detection device according to embodiment 6 when detecting the capacitance value of the error capacitance. Fig. 31 is a diagram showing the configuration of a load detection device according to embodiment 7. Fig. 32 is a diagram showing the configuration of a load detection device according to embodiment 8.

[0017] However, the drawings are for illustrative purposes only and do not limit the scope of the present invention.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In embodiments 1 to 4, the configuration of a capacitance measurement circuit is shown, and in embodiments 5 to 8, the configuration of a load detection device is shown.

[0019] In the first to fourth embodiments, the switch element 12a, the switch element 12b, and the switch element 13 correspond to the "switching unit," the "transfer unit," and the "connection unit" described in the claims, respectively. However, this description is merely intended to associate the configurations of the claims with the configurations of the embodiments, and the above association does not in any way limit the invention described in the claims to the configurations of the embodiments. Furthermore, the configurations that realize the invention described in the claims are not limited to the following first to eighth embodiments.

[0020] First Embodiment FIG. 1 is a diagram showing the configuration of a capacitance measuring circuit 10 according to a first embodiment.

[0021] 1, the capacitance measurement circuit 10 includes a control unit 11, switch elements 12a to 12c, a switch element 13, a measurement unit 14, and a reference capacitance Cr. The reference capacitance Cr is connected in parallel to a measurement capacitance Cs via a switch element 12b. The measurement capacitance Cs is the capacitance to be measured.

[0022] The control unit 11 is configured with a microcomputer, FPGA, or the like, and controls the switch elements 12a to 12c and 13. The control unit 11 also calculates the capacitance value of the measurement capacitance Cs based on the voltage value measured by the measurement unit .

[0023] The switch element 12a switches between applying and not applying the power supply voltage Vdd to the reference capacitance Cr. When the switch element 12a changes from a non-conductive state to a conductive state, the power supply voltage Vdd is applied to the reference capacitance Cr, and charge is accumulated in the reference capacitance Cr.

[0024] The switch element 12b switches the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs between a connected state and a disconnected state. When the switch element 12b changes from a non-conductive state to a conductive state, the positive electrode of the reference capacitance Cr and the positive electrode of the measurement capacitance Cs are connected, and the charge accumulated in the reference capacitance Cr is transferred to the measurement capacitance Cs. In this way, the switch element 12b transfers the charge accumulated in the reference capacitance Cr to the measurement capacitance Cs.

[0025] The switch element 12c switches between a connected state and a disconnected state between the positive electrode of the capacitance Cs to be measured and the ground. When the switch element 12c changes from a non-conductive state to a conductive state, the positive electrode of the capacitance Cs to be measured is connected to the ground, and the charge accumulated in the capacitance Cs to be measured is discharged to the ground.

[0026] The switch elements 12a and 12b are configured by P-type FETs and become conductive when a low-level gate signal is applied to their gates. The switch element 12c is configured by N-type FETs and becomes conductive when a high-level gate signal is applied to its gate. The switch elements 12a to 12c may be switch elements of a type other than FETs.

[0027] The switch element 13 connects the negative electrode of the capacitance Cs to ground or the positive electrode of the capacitance Cs. When the positive and negative electrodes of the capacitance Cs are connected by the switch element 13, the positive and negative electrodes have the same potential, so the capacitance Cs is in a state where it disappears (is disabled) in terms of the circuit.

[0028] The measurement unit 14 measures the voltage of the measurement capacitance Cs. When the switch element 12b is turned on while the switch element 13 is connected to ground, the charge of the reference capacitance Cr is transferred to and distributed to the measurement capacitance Cs. As a result, a voltage corresponding to the capacitance ratio between the capacitance value of the reference capacitance Cr and the capacitance value of the measurement capacitance Cs is generated in the measurement capacitance Cs. The measurement unit 14 measures this voltage.

[0029] The capacitance value of the reference capacitance Cr is set to a value that allows the measurement unit 14 to accurately measure the voltage generated across the measurement capacitance Cs after the charge is distributed in this manner. In other words, the capacitance value of the reference capacitance Cr is set so that the voltage generated across the measurement capacitance Cs after the charge is distributed as described above is at least equal to or greater than the lower limit of the measurable range of the measurement unit 14.

[0030] Next, the operation of the capacitance measuring circuit 10 when measuring the capacitance value of the target capacitance Cs will be described with reference to FIGS. 2(a) to 6(b).

[0031] 2(a) to 6(b), the switch elements 12a to 12c that are in an operating state and the paths through which the switch elements charge, discharge, or transfer electric charges are indicated by thick lines. Furthermore, when the reference capacitance Cr and the measurement capacitance Cs are in a charged state, these capacitances are indicated by diagonal hatching.

[0032] 2A, with switch element 13 connected to ground, switch elements 12a and 12c are each switched to a conductive state. This applies power supply voltage Vdd to reference capacitance Cr, causing charge to accumulate in reference capacitance Cr. Furthermore, the positive electrode of measurement capacitance Cs is connected to ground, causing discharge to occur to measurement capacitance Cs. Switch element 12a remains in a conductive state at least until reference capacitance Cr reaches a fully charged state. Whether reference capacitance Cr has reached a fully charged state can be determined, for example, by measuring the voltage of reference capacitance Cr using a measurement unit separate from measurement unit 14 and determining whether the measurement result reaches power supply voltage Vdd and stabilizes.

[0033] Next, as shown in FIG. 2B, the switch element 12a is switched to a non-conductive state, disconnecting the reference capacitance Cr from the power supply voltage Vdd. Also, as shown in FIG. 3A, the switch element 12c is switched to a non-conductive state, disconnecting the positive electrode of the measurement capacitance Cs from ground. Then, as shown in FIG. 3B, the switch element 12b is switched to a conductive state, connecting the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs. This transfers the charge stored in the reference capacitance Cr to the measurement capacitance Cs.

[0034] Immediately after the switch element 12b is switched to the conductive state, the measurement value of the measurement unit 14 becomes a voltage value corresponding to the accumulated charge in the reference capacitance Cr, i.e., a voltage value approximately equal to the power supply voltage Vdd. Thereafter, as the transfer of charge to the measurement capacitance Cs progresses, the measurement value of the measurement unit 14 gradually decreases, and when the transfer of charge is completed, the measurement value of the measurement unit 14 stabilizes (saturates) at a constant value corresponding to the capacitance ratio between the reference capacitance Cr and the measurement capacitance Cs.

[0035] 4A, after the voltage value has stabilized, the voltage value measured by the measurement unit 14 is acquired as the first voltage value Vx1. As described above, this first voltage value Vx1 is determined mainly according to the capacitance ratio between the reference capacitance Cr and the measurement capacitance Cs, but is also affected by parasitic capacitances due to the wiring between the reference capacitance Cr and the measurement capacitance Cs and the switch elements 12b and 13. Therefore, if the capacitance value of the measurement capacitance Cs is calculated from only the first voltage value Vx1, errors due to these parasitic capacitances will be included in the calculation result.

[0036] To avoid this, in this embodiment, an operation for suppressing errors due to parasitic capacitance is further performed.

[0037] That is, as shown in FIG. 4B, the switch element 13 is switched to the positive electrode side of the capacitance Cs to be measured. Next, as shown in FIG. 5A, the switch elements 12a and 12c are each switched to a conductive state. As a result, the power supply voltage Vdd is applied to the reference capacitance Cr, and charge is accumulated in the reference capacitance Cr. Furthermore, the positive electrode of the capacitance Cs to be measured is connected to ground, and the capacitance Cs to be measured is discharged. The switch element 12a is set to a conductive state at least until the reference capacitance Cr is fully charged.

[0038] As shown in Fig. 4(b), since the reference capacitance Cr still has charge after distribution, the charging of the reference capacitance Cr in Fig. 5(a) is performed more quickly than in the case of Fig. 2(a). In other words, rather than proceeding from the state of Fig. 4(b) to the operation of Fig. 5(a) by temporarily discharging the charge of the reference capacitance Cr and then proceeding to the operation of Fig. 5(a), the operational sequence can be speeded up by proceeding directly from the state of Fig. 4(b) to the operation of Fig. 5(a) as described above.

[0039] 5A, since the switch element 13 is connected to the positive electrode of the capacitance Cs to be measured, the charge accumulated in the capacitance Cs to be measured as well as the charge accumulated in the parasitic capacitance of the switch element 13 and the wiring between the switch element 13 and the positive electrode of the capacitance Cs to be measured are also discharged to ground. This makes it possible to more reliably eliminate the influence of the parasitic capacitance.

[0040] Thereafter, as shown in FIG. 5B, the switch element 12a is switched to a non-conductive state, disconnecting the reference capacitance Cr from the power supply voltage Vdd. The switch element 12c is switched to a non-conductive state, disconnecting the positive electrode of the measurement capacitance Cs from ground. Then, as shown in FIG. 6A, the switch element 12b is switched to a conductive state, connecting the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs. This transfers the charge stored in the reference capacitance Cr.

[0041] 6A, since the switch element 13 is switched to the positive side of the capacitance Cs to be measured, the positive and negative electrodes of the capacitance Cs to be measured are at the same potential. Therefore, during this charge transfer, no charge is distributed to the capacitance Cs to be measured, but the charge is distributed to parasitic capacitances other than the capacitance Cs to be measured. Therefore, in this case, the measurement value of the measurement unit 14 stabilizes at a voltage value corresponding to the charge distribution to the parasitic capacitances.

[0042] After the voltage value has stabilized, the voltage value measured by the measurement unit 14 is acquired as the second voltage value Vx2, as shown in Fig. 6(b). Then, the capacitance value of the measurement capacitance Cs is calculated from the acquired second voltage value Vx2 and the first voltage value Vx1 acquired during the operation shown in Fig. 4(a).

[0043] <Calculation Method According to Reference Example 1> The electrostatic capacitance value of the measurement capacitance Cs is calculated as follows.

[0044] First, as shown in FIG. 2A, the charge amount Qr of the reference capacitance Cr when the reference capacitance Cr is fully charged is expressed by the following equation, where Cr is the electrostatic capacitance value (known) of the reference capacitance Cr.

[0045] Qr=Cr×Vdd (1) Furthermore, in the state where the charge transfer is completed as shown in FIG. 4A, if the capacitance value of the measurement capacitance Cs is Cs1, the following relationship holds:

[0046] Qr=(Cr+Cs1)×Vx1 (2) Therefore, the following relational expression can be derived from the expressions (1) and (2).

[0047]

[0048] However, as described above, the capacitance value Cs1 includes an error component due to the parasitic capacitance. The error component Ce can be expressed by the following equation using the second voltage value Vx2 obtained by the operation of FIG. 6B.

[0049]

[0050] 5(a) to 6(b), the positive and negative electrodes of the measurement capacitance Cs are at the same potential, so the measurement capacitance Cs is invalidated, and only the reference capacitance Cr and the parasitic capacitance are capacitance components. Therefore, the capacitance value of the parasitic capacitance, i.e., the error component Ce, can be expressed by the above equation (4).

[0051] The capacitance value Cs of the measured capacitance Cs is obtained by subtracting the error component Ce from the capacitance value Cs1 of equation (3), and is calculated from the above equations (3) and (4) using the following equation:

[0052]

[0053] 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 by the operations shown in Figures 4(a) and 6(b). Therefore, the capacitance value of the measured capacitance Cs can be calculated from equation (5).

[0054] FIG. 7 is a flowchart showing a process for calculating the capacitance value of the measurement capacitance Cs according to the first reference example.

[0055] In FIG. 7, steps S101 to S105 correspond to a first control C1 for obtaining a first voltage value Vx1, and steps S106 to S110 correspond to a second control C2 for obtaining a second voltage value Vx2.

[0056] First, as shown in FIG. 2A, the control unit 11 connects the negative electrode of the measurement capacitance Cs to ground (S101), then charges the reference capacitance Cr and discharges the measurement capacitance Cs (S102). After charging the reference capacitance Cr, the control unit 11 disconnects the positive electrode of the reference capacitance Cr from the power supply voltage Vdd and the positive electrode of the measurement capacitance Cs from ground (S103), as shown in FIGS. 2B and 3A. Then, as shown in FIG. 3B, the control unit 11 connects the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs and transfers the charge of the reference capacitance Cr to the measurement capacitance Cs (S104). After a period of time has elapsed until the measurement value of the measurement unit 14 stabilizes (saturates), the control unit 11 acquires the measurement value of the measurement unit 14 as a first voltage value Vx1 (S105), as shown in FIG. 4A. This completes the first control C1.

[0057] Next, the control unit 11 connects the negative electrode of the measurement capacitance Cs to the positive electrode of the measurement capacitance Cs (S106), as shown in FIG. 4(b), and then charges the reference capacitance Cr and discharges the measurement capacitance Cs (S107), as shown in FIG. 5(a). After charging the reference capacitance Cr, the control unit 11 disconnects the positive electrode of the reference capacitance Cr from the power supply voltage Vdd and the positive electrode of the measurement capacitance Cs from ground (S108), as shown in FIG. 5(b). Then, the control unit 11 connects the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs, as shown in FIG. 6(a), and transfers the charge of the reference capacitance Cr (S109). After a period of time has passed until the measurement value of the measurement unit 14 stabilizes (saturates), the control unit 11 acquires the measurement value of the measurement unit 14 as the second voltage value Vx2 (S110), as shown in FIG. 6(b). This completes the second control C2.

[0058] Then, the control unit 11 applies the acquired first voltage value Vx1 and second voltage value Vx2 to the above formula (5) to calculate the capacitance value of the measurement capacitance Cs (S111). In this manner, the control unit 11 ends the process of FIG.

[0059] Calculation Method According to First Embodiment As described above, in the calculation method of Reference Example 1, by applying the first voltage value Vx1 and the second voltage value Vx2 to the above equation (5), it is possible to calculate the capacitance value of the measurement capacitance Cs with the influence of parasitic capacitance suppressed. However, on the other hand, the capacitance value of the reference capacitance Cr may contain error components that cannot be suppressed by the above equation (5), such as parasitic capacitance within the devices that constitute the reference capacitance Cr and parasitic capacitance in the switch elements 12a and 12b connected to the reference capacitance Cr. If such error components are included, the calculation method using the above equation (5), which treats the capacitance value of the reference capacitance Cr as a true value, will result in a decrease in the accuracy of the capacitance value of the measurement capacitance Cs.

[0060] Therefore, in the calculation method of the first embodiment, the calculation formula for the measured capacitance Cs is changed to one that further takes into account the error component. That is, when the capacitance value Cx of the error capacitance, which is the effective equivalent capacitance of the error component, is taken into consideration, the capacitance value Cr of the reference capacitance Cr in the above formula (5) is changed to Cr+Cx. Therefore, the calculation formula for the capacitance value of the measured capacitance Cs is changed to the following formula:

[0061]

[0062] Here, the capacitance value Cx of the error capacitance can be obtained by substituting a test capacitance Ct, the capacitance value of which is known, for the measured capacitance Cs and applying the first voltage value Vx1 and the second voltage value Vx2 obtained by the first control C1 and the second control C2, respectively, to equation (6). That is, by substituting the capacitance value Cs of the measured capacitance Cs with the capacitance value Ct of the test capacitance Ct in equation (6) and transforming equation (6), the capacitance value Cx of the error capacitance can be obtained by the following equation.

[0063]

[0064] In this way, by substituting the previously obtained capacitance value Cx of the error capacitance into the above equation (6), the parameters required for calculating equation (6) become only the first voltage value Vx1 and the second voltage value Vx2. Therefore, when measuring the measurement capacitance Cs, the above-described first control C1 and second control C2 are executed, and the first voltage value Vx1 and the second voltage value Vx2 obtained by these controls are applied to equation (6), thereby obtaining the capacitance value Cs of the measurement capacitance Cs.

[0065] FIG. 8A is a flowchart showing a process for calculating the capacitance value of the measurement capacitance Cs according to the first embodiment.

[0066] When calculating the capacitance value of the measurement capacitance Cs, the measurement capacitance Cs is connected to the capacitance measurement circuit 10 as shown in Fig. 1. Prior to this calculation process, the capacitance value Cx of the error capacitance is obtained in advance using the test capacitance Ct as described above, and is applied to the above equation (6).

[0067] 7, the control unit 11 executes the first control C1 to obtain the first voltage value Vx1 (S11), and then executes the second control C2 to obtain the second voltage value Vx2 (S12). The control unit 11 then calculates the capacitance value of the measurement capacitance Cs from the first voltage value Vx1 and the second voltage value Vx2 using the above-mentioned equation (6) to which the capacitance value Cx of the error capacitance is applied (S13). This causes the control unit 11 to end the process of FIG. 8(a).

[0068] FIG. 8B is a flowchart showing a calculation process of the capacitance value of the error capacitance according to the first embodiment.

[0069] When calculating the capacitance value of the error capacitance, a test capacitance Ct is connected to the capacitance measurement circuit 10 instead of the measurement capacitance Cs shown in FIG. 1 . As in FIG. 7 , the control unit 11 executes the first control C1 to obtain a first voltage value Vx1 (S21), and then executes the second control C2 to obtain a second voltage value Vx2 (S22). The control unit 11 then applies the obtained first voltage value Vx1 and second voltage value Vx2 and the capacitance value Ct of the test capacitance Ct to the above equation (7) to calculate the capacitance value Cx of the error capacitance (S23). This causes the control unit 11 to end the process of FIG. 8(b).

[0070] FIG. 9 is a graph showing the measurement results when a reference capacitance having a known capacitance value is measured using the calculation method of the first embodiment and the calculation method of the first reference example.

[0071] FIG. 9 includes a graph showing the expected value of the reference capacitance, along with the measurement results using the calculation method of Embodiment 1 and the calculation method of Reference Example 1. As shown in FIG. 9, the measurement results using the calculation method of Reference Example 1 were slightly lower than the expected value of the reference capacitance, and an error occurred between the two. In contrast, the measurement results using the calculation method of Embodiment 1 substantially overlapped the expected value, and there was almost no error between the two. This confirms that the capacitance value of the measurement capacitance Cs can be measured more accurately by using a calculation formula that takes into account the error component of the reference capacitance Cr, as in the above formula (6).

[0072] The capacitance value of the error capacitance is calculated by measuring the test capacitance Ct when the capacitance measurement circuit 10 is shipped, for example, and is stored in memory in the control unit 11. Alternatively, the capacitance measurement circuit 10 may include the test capacitance Ct and a switching unit that selectively connects either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under the control of the control unit 11, so that the capacitance value of the error capacitance can be acquired appropriately at any timing.

[0073] FIG. 10 is a diagram showing the configuration of the capacitance measurement circuit when the capacitance measurement circuit 10 includes a test capacitance Ct and a switching unit.

[0074] In the configuration of FIG. 10, switch elements 15a, 15b, 16a, and 16b constitute a switching unit that selectively connects either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11.

[0075] In the mode for calculating the capacitance value of the error capacitance, the control unit 11 opens the switch elements 15a and 15b and closes the switch elements 16a and 16b. In this state, the control unit 11 executes the process of Fig. 8(b) to calculate the capacitance value of the error capacitance from the above equation (7), and stores the calculated capacitance value of the error capacitance in the internal memory.

[0076] In the mode for calculating the capacitance value of the capacitance Cs to be measured, the control unit 11 opens the switches 16a and 16b and closes the switches 15a and 15b. In this state, the control unit 11 executes the process shown in Fig. 8(a) to calculate the capacitance value of the capacitance Cs to be measured using the above formula (6).

[0077] 10, the capacitance value of the error capacitance can be obtained by connecting the test capacitance Ct to the capacitance measurement circuit at any time. Therefore, even if the capacitance value of the error capacitance changes over time, the capacitance value of the error capacitance at each time can be properly obtained, and the capacitance value of the measurement capacitance Cs can be obtained with high accuracy.

[0078] 10, one test capacitance Ct is arranged in the capacitance measurement circuit 10, but multiple test capacitances Ct having different capacitance values ​​may be arranged in the capacitance measurement circuit 10. In this case, switch elements 16a and 16b similar to those in FIG. 10 are arranged for each test capacitance Ct, and each test capacitance Ct is individually controlled to be connected or disconnected from the capacitance measurement circuit 10.

[0079] In this configuration, when measuring the capacitance value of the error capacitance, the control unit 11 connects each test capacitance Ct to the capacitance measurement circuit 10 in order and calculates the capacitance value of the error capacitance for each test capacitance Ct. Then, the control unit 11, for example, averages the calculated capacitance values ​​of the error capacitance and stores this average value in internal memory. When measuring the capacitance value of the measurement capacitance Cs, the control unit 11 applies this average value as the capacitance value of the error capacitance in the above equation (6) and executes the process of FIG. 8(a).

[0080] In this way, by calculating the capacitance value of the error capacitance using a plurality of test capacitances Ct with different capacitance values, the capacitance value of the error capacitance can be obtained accurately and stably, and therefore the capacitance value of the measurement capacitance Cs can be obtained accurately.

[0081] <Effects of First Embodiment> As shown in FIGS. 2A to 6B and 8A, the control unit 11 executes a first control C1 (S11) in which, after applying a voltage to the reference capacitance Cr, the control unit 11 causes the switch element 12b (transfer unit) to transfer charge while the negative electrode of the measurement capacitance Cs is connected to ground, and after the charge transfer is completed, the control unit 11 acquires a first voltage value Vx1 measured by the measurement unit 14. A second control (S12) in which, after applying a voltage to the reference capacitance Cr, the control unit 11 causes the switch element 12b (transfer unit) to transfer charge while the negative electrode of the measurement capacitance Cs is connected to a wiring having the same potential as the positive electrode of the measurement capacitance Cs, and after the charge transfer is completed, the control unit 11 acquires a second voltage value Vx2 measured by the measurement unit 14. A process (S13) in which the control unit 11 calculates the capacitance value Cs of the measurement capacitance Cs using the first voltage value Vx1, the second voltage value Vx2, and the capacitance value Cx of the error capacitance, which is the error component of the reference capacitance Cr, according to the above formula (6). Furthermore, as shown in FIG. 8(b), the control unit 11 obtains the capacitance value Cx of the error capacitance by applying the first voltage value Vx1 and the second voltage value Vx2 obtained by the first control C1 (S21) and the second control C2 (S22), respectively, using the test capacitance Ct with a known capacitance value instead of the measurement capacitance Cs, to the above equation (7), which is a modification of the above equation (6) (S23).

[0082] With this configuration, the capacitance value of the measurement capacitance Cs is calculated based on the voltage value after the charge is transferred from the reference capacitance Cr, allowing stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, in the second control C2, the negative electrode of the measurement capacitance Cs is connected to a wiring having the same potential as the positive electrode of the measurement capacitance Cs. Therefore, the measured second voltage value Vx2 is largely unaffected by the measurement capacitance Cs, and is primarily affected by the reference capacitance Cr and parasitic capacitance. In contrast, in the first control C1, the negative electrode of the measurement capacitance Cs is connected to ground. Therefore, the measured first voltage value Vx1 is affected by the measurement capacitance Cs as well as the reference capacitance Cr and parasitic capacitance. Therefore, by calculating the capacitance value Cs of the measurement capacitance Cs from these two voltage values ​​using the above equation (6), the capacitance value Cs free from the influence of parasitic capacitance can be calculated. Furthermore, since the capacitance value Cx of the error capacitance (effective equivalent capacitance of the error component), which is the error component of the reference capacitance Cr, is taken into account when calculating the capacitance value Cs of the measurement capacitance Cs, the capacitance value Cs of the measurement capacitance Cs can be obtained with high accuracy.

[0083] As shown in FIG. 1, the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitance Cs and the ground.

[0084] According to this configuration, by measuring the voltage between the positive electrode of the measurement capacitance Cs and ground and performing the first control C1 and the second control C2, it is possible to calculate the capacitance value Cs that is not affected by the parasitic capacitance and the error capacitance.

[0085] Here, the control unit 11 calculates the capacitance value Cs of the measured capacitance Cs using the above formula (6) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the value Vdd of the voltage applied to the reference capacitance Cr, the capacitance value Cr of the reference capacitance Cr, and the capacitance value Cx of the error capacitance.

[0086] As a result, as shown in FIG. 9, the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance Cs to be measured can be suppressed, and the capacitance value Cs of the capacitance Cs to be measured can be obtained with high accuracy.

[0087] As shown in FIG. 10, the capacitance measurement circuit 10 may include a test capacitance Ct and switch elements 15a, 15b, 16a, and 16b (switching units) that selectively connect either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11.

[0088] With this configuration, the test capacitance Ct can be connected to the capacitance measurement circuit 10 at any time to acquire the capacitance value Cx of the error capacitance. Therefore, even if the capacitance value Cx of the error capacitance changes over time, the capacitance value Cx at each time can be properly acquired, and the capacitance value Cs of the measurement capacitance Cs can be acquired with high accuracy.

[0089] In the first embodiment, the charge stored in the reference capacitance Cr is distributed to the measurement capacitance Cs to calculate the capacitance value, whereas in the second embodiment, the charge stored in the measurement capacitance Cs is distributed to the reference capacitance Cr to calculate the capacitance value.

[0090] FIG. 11 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the second embodiment.

[0091] 11, the arrangements of the reference capacitance Cr, the measurement capacitance Cs, the switch element 13, and the measurement unit 14 are changed compared to FIG. 1. That is, the measurement capacitance Cs is arranged upstream of the reference capacitance Cr (on the power supply voltage Vdd side), and accordingly, the arrangements of the switch element 13 and the measurement unit 14 are changed. The functions of the switch element 13 and the measurement unit 14 are the same as in the first embodiment. Of the switch elements 12a to 12c, the switch element 12b can be changed to an N-type FET. The configurations and functions of the switch elements 12a and 12c are the same as in the first embodiment.

[0092] 12(a) to 16(b) are diagrams showing the operation of the capacitance measurement circuit 10 when measuring the capacitance value of the target capacitance Cs. Fig. 17 is a flowchart showing the processing of the control unit 11 when measuring the capacitance value of the target capacitance Cs.

[0093] First, as shown in Fig. 12(a), the control unit 11 connects the negative electrode of the capacitance Cs to ground (S201), switches the switch elements 12a and 12c to a conductive state, and charges the capacitance Cs and discharges the reference capacitance Cr (S202). Then, as shown in Fig. 12(b), the control unit 11 disconnects the positive electrode of the reference capacitance Cr from ground. After the capacitance Cs is fully charged, the control unit 11 disconnects the positive electrode of the capacitance Cs from ground (S203), as shown in Fig. 13(a). Whether the capacitance Cs is fully charged can be determined by whether the voltage of the capacitance Cs reaches the power supply voltage Vdd and stabilizes, as in the above embodiment.

[0094] Next, as shown in Fig. 13(b), the control unit 11 switches the switch element 12b to a conductive state and transfers the charge of the measurement capacitance Cs to the reference capacitance Cr (S204). Then, the control unit 11 waits for a period until this transfer is completed, and then, as shown in Fig. 14(a), acquires the measurement value of the measurement unit 14 as the first voltage value Vx1 (S205). This completes the first control C1.

[0095] Next, the control unit 11 switches the switch element 13 to the positive electrode side of the measurement capacitance Cs to connect the positive electrode and negative electrode of the measurement capacitance Cs (S206), as shown in Fig. 14(b).Then, the control unit 11 switches the switch elements 12b and 12c to the conductive state, as shown in Fig. 15(a), to discharge the reference capacitance Cr and the measurement capacitance Cs (S207).

[0096] 15B, the control unit 11 switches the switch elements 12b and 12c to the non-conductive state, and then switches the switch element 12a to the conductive state to connect the positive electrode of the capacitance Cs to the power supply voltage Vdd (S208). Here, the positive electrode and the negative electrode of the capacitance Cs are connected, so that the positive electrode and the negative electrode of the capacitance Cs are at the same potential. Therefore, the capacitance Cs is not charged, and the parasitic capacitance other than the capacitance Cs is charged.

[0097] Next, the control unit 11 sets the switch element 12a to a non-conductive state to disconnect the positive electrode of the measurement capacitance Cs from the power supply voltage Vdd (S209). Furthermore, as shown in FIG. 16A, the control unit 11 switches the switch element 12b to a conductive state to connect the positive electrode of the measurement capacitance Cs to the positive electrode of the reference capacitance Cr, thereby transferring charge to the reference capacitance Cr (S210). Since no charge is stored in the measurement capacitance Cs as described above, the charge stored in the parasitic capacitance is transferred to the reference capacitance Cr. After the charge is transferred, the control unit 11 acquires the measurement value of the measurement unit 14 as the first voltage value Vx1 (S211), as shown in FIG. 16B. This completes the second control C2.

[0098] The control unit 11 calculates the capacitance value of the measurement capacitance Cs from the first voltage value Vx1 and the second voltage value Vx2 using a calculation formula to which the capacitance value Cx of the error capacitance of the reference capacitance Cr is applied (S212).

[0099] The capacitance value of the measurement capacitance Cs is calculated as follows.

[0100] <Calculation Method According to Reference Example 2> Prior to the description of the calculation method according to the second embodiment, the calculation method according to Reference Example 2 will be described.

[0101] First, as shown in FIG. 12A, when the measurement capacitance Cs is fully charged, the charge amount Qs of the measurement capacitance Cs is expressed by the following equation, where the capacitance value of the measurement capacitance Cs is Cs1.

[0102] Qs=Cs1×Vdd (8) Furthermore, in the state where the charge transfer is completed as shown in FIG. 13B, the following relationship holds when the capacitance value of the reference capacitance Cr is Cr.

[0103] Qs=(Cr+Cs1)×Vx1 (9) Therefore, the following relational expression can be derived from the expressions (8) and (9).

[0104]

[0105] However, as described above, the capacitance value Cs1 includes an error component due to the parasitic capacitance. The error component Ce can be expressed by the following equation using the second voltage value Vx2 obtained by the operation of FIG. 16(b).

[0106]

[0107] 15(a) to 16(b), the positive and negative electrodes of the measurement capacitance Cs are at the same potential, so the measurement capacitance Cs is invalidated, and only the reference capacitance Cr and the parasitic capacitance are capacitance components. Therefore, the capacitance value of the parasitic capacitance, i.e., the error component Ce, can be expressed by the above equation (9).

[0108] The capacitance value Cs of the measured capacitance Cs is obtained by subtracting the error component Ce from the capacitance value Cs of equation (10), and is therefore calculated from the above equations (10) and (11) using the following equation:

[0109]

[0110] In equation (12), 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 by the operations of Figures 14(a) and 16(b). Therefore, the capacitance value of the measured capacitance Cs can be calculated from equation (12) above.

[0111] Calculation Method According to Embodiment 2 As described above, in the calculation method of Reference Example 1, the capacitance value of the measurement capacitance Cs can be calculated with the influence of parasitic capacitance suppressed by applying the first voltage value Vx1 and the second voltage value Vx2 to the above equation (5). However, as described in the above embodiment 1, the capacitance value of the reference capacitance Cr may include an error component that cannot be completely suppressed by the above equation (12).

[0112] In the calculation method of the first embodiment, the calculation formula for the measured capacitance Cs is changed to one that further takes this difference component into account. That is, when the capacitance value Cx of the error capacitance corresponding to the error component is taken into consideration, the capacitance value Cr of the reference capacitance Cr in the above formula (12) is changed to Cr+Cx. Therefore, the calculation formula for the capacitance value of the measured capacitance Cs is changed to the following formula:

[0113]

[0114] Here, the capacitance value Cx of the error capacitance can be obtained by substituting a test capacitance Ct, the capacitance value of which is known, for the measured capacitance Cs and applying the first voltage value Vx1 and the second voltage value Vx2 obtained by the first control C1 and the second control C2, respectively, to equation (13). That is, by substituting the capacitance value Cs of the measured capacitance Cs with the capacitance value Ct of the test capacitance Ct in equation (13) and transforming equation (13), the capacitance value Cx of the error capacitance can be obtained by the following equation.

[0115]

[0116] In this way, by substituting the previously obtained capacitance value Cx of the error capacitance into the above equation (13), the parameters required for calculating equation (13) become only the first voltage value Vx1 and the second voltage value Vx2. Therefore, when measuring the measurement capacitance Cs, the first voltage value Vx1 and the second voltage value Vx2 are obtained by executing the first control C1 and the second control C2 in FIG. 17 , and the first voltage value Vx1 and the second voltage value Vx2 are applied to equation (13) in step S212, thereby obtaining the capacitance value Cs of the measurement capacitance Cs.

[0117] The capacitance value Cx of the error capacitance is calculated by the same process as in Fig. 8(b). In the second embodiment, the first control C1 and the second control C2 in Fig. 17 are executed as the processes in steps S21 and S22, respectively. Then, in step S23, the capacitance value Cx of the error capacitance is obtained by applying the first voltage value Vx1 and the second voltage value Vx2 obtained in steps S21 and S22, the capacitance value Ct of the test capacitance Ct, and the above equation (14).

[0118] The control unit 11 stores the acquired capacitance value Cx in an internal memory and applies it to the above equation (13) in the process of calculating the measured capacitance Cs (step S212 in FIG. 17 ), thereby acquiring the capacitance value of the measured capacitance Cs in which the influence of the error capacitance is further suppressed.

[0119] As in the first embodiment, the capacitance value of the error capacitance is calculated by measuring the test capacitance Ct, for example, when the capacitance measurement circuit 10 is shipped, and is stored in the memory of the control unit 11. Alternatively, so that the capacitance of the error capacitance can be acquired appropriately at any timing, the capacitance measurement circuit 10 may include the test capacitance Ct and a switching unit that selectively connects either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11. In this case, the capacitance measurement circuit 10 may be configured as shown in FIG.

[0120] 10 , in a mode for calculating the capacitance value of the error capacitance, the control unit 11 opens the switch elements 15a and 15b and closes the switch elements 16a and 16b, and calculates the capacitance value of the error capacitance from the above equation (14). Also, in a mode for calculating the capacitance value of the measurement capacitance Cs, the control unit 11 opens the switch elements 16a and 16b and closes the switch elements 15a and 15b, and calculates the capacitance value of the measurement capacitance Cs from the above equation (13).

[0121] 18, the capacitance value of the error capacitance can be obtained by connecting the test capacitance Ct to the capacitance measurement circuit at any time. Therefore, even if the capacitance value of the error capacitance changes over time, the capacitance value of the error capacitance at each time can be properly obtained, and the capacitance value of the measurement capacitance Cs can be obtained with high accuracy.

[0122] 10 , a plurality of test capacitances Ct having different capacitance values ​​may be arranged in the capacitance measurement circuit 10. In this case, switch elements 16 a and 16 b similar to those in FIG. 18 are arranged for each test capacitance Ct, and each test capacitance Ct is individually controlled to be connected or disconnected from the capacitance measurement circuit 10.

[0123] When measuring the capacitance value of the error capacitance, the control unit 11 connects each test capacitance Ct to the capacitance measurement circuit 10 in order and calculates the error capacitance for each test capacitance Ct. Then, for example, the control unit 11 stores the average value of these calculated error capacitances in an internal memory, and when measuring the capacitance value of the measurement capacitance Cs, the control unit 11 applies this average value to the capacitance value of the error capacitance in the above equation (13) to execute the process of Fig. 17. This makes it possible to accurately and stably obtain the capacitance value of the error capacitance, and to accurately obtain the capacitance value of the measurement capacitance Cs.

[0124] 12A to 17A, the control unit 11 applies a voltage to the capacitance Cs to be measured with the negative electrode of the capacitance Cs to be measured connected to ground, and then causes the switch element 12b (transfer unit) to transfer charges. After the transfer of the charges has been completed, the control unit 11 acquires the first voltage value Vx1 measured by the measurement unit 14 through a first control C1 (S201 to S205). The control unit 11 also applies a voltage to the capacitance Cs to be measured with the negative electrode of the capacitance Cs to be measured connected to a wiring having the same potential as the positive electrode of the capacitance Cs to be measured. After applying the voltage, the control unit 11 causes the switch element 12b (transfer unit) to transfer the charge, and after the charge transfer is completed, executes a second control C2 (S206 to S211) to acquire a second voltage value Vx2 measured by the measurement unit 14, and a process (S212) to calculate the capacitance value Cs of the measured capacitance Cs using the first voltage value Vx1, the second voltage value Vx2, and the capacitance value Cx of the error capacitance, which is an error component of the reference capacitance Cr, according to the above formula (13). Similarly to the process of FIG. 8B , the control unit 11 acquires the capacitance value Cx of the error capacitance by applying the first voltage value Vx1 and the second voltage value Vx2 acquired by the first control C1 and the second control C2, respectively, to the above formula (14), which is a modification of the above formula (13).

[0125] With this configuration, the capacitance value Cs of the target capacitance Cs is calculated based on the voltage value after charge is transferred from the target capacitance Cs, allowing stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, in the second control C2, the negative electrode of the target capacitance Cs is connected to a wiring having the same potential as the positive electrode of the target capacitance Cs, and a voltage is applied to the target capacitance Cs. This means that almost no charge accumulates in the target capacitance Cs, and instead, charge accumulates in the parasitic capacitance. Therefore, the second voltage value Vx2 measured by the second control C2 is largely unaffected by the target capacitance Cs, and is primarily affected by the reference capacitance Cr and the parasitic capacitance. In contrast, in the first control C1, the negative electrode of the target capacitance Cs is connected to ground, and a voltage is applied to the target capacitance Cs. This means that charge is applied to the target capacitance Cs as well as the parasitic capacitance. Therefore, the first voltage value Vx1 measured by the first control C1 is affected by the target capacitance Cs, as well as the reference capacitance Cr and the parasitic capacitance. Therefore, by calculating the capacitance value Cs of the measurement capacitance Cs from these two voltage values, it is possible to calculate the capacitance value Cs that is not affected by parasitic capacitance. Furthermore, since the capacitance value Cx of the error capacitance (effective equivalent capacitance of the error component), which is an error component of the reference capacitance Cr, is taken into account in the calculation of the capacitance value Cs of the measurement capacitance Cs, it is possible to obtain the capacitance value Cs of the measurement capacitance Cs with high accuracy.

[0126] As shown in FIG. 11, the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitance Cs and the ground.

[0127] According to this configuration, by measuring the voltage between the positive electrode of the measurement capacitance Cs and ground and performing the first control C1 and the second control C2, it is possible to calculate the capacitance value Cs that is not affected by the parasitic capacitance and the error capacitance.

[0128] Here, the control unit 11 calculates the capacitance value Cs of the measurement capacitance Cs using the above formula (13) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the value Vdd of the voltage applied to the measurement capacitance Cs, the capacitance value Cr of the reference capacitance Cr, and the capacitance value Cx of the error capacitance.

[0129] This makes it possible to suppress the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance Cs to be measured, and to obtain the capacitance value Cs of the capacitance Cs to be measured with high accuracy.

[0130] As shown in FIG. 18, the capacitance measurement circuit 10 may include a test capacitance Ct and switch elements 15a, 15b, 16a, and 16b (switching units) that selectively connect either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11.

[0131] With this configuration, the test capacitance Ct can be connected to the capacitance measurement circuit 10 at any time to acquire the capacitance value Cx of the error capacitance. Therefore, even if the capacitance value Cx of the error capacitance changes over time, the capacitance value Cx of the error capacitance at each time can be properly acquired, and the capacitance value Cs of the measurement capacitance Cs can be acquired with high accuracy.

[0132] In the first embodiment, the capacitance value of the capacitance Cs to be measured is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the ground by the measuring unit 14. In contrast, in the third embodiment, the capacitance value of the capacitance Cs to be measured is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd) by the measuring unit 14.

[0133] FIG. 19 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the third embodiment.

[0134] 19 , the measurement unit 14 measures the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd). The process of calculating the capacitance Cs is similar to the process shown in FIGS. 2A to 6B and 8A in the first embodiment. However, in the third embodiment, the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd) is acquired as the first voltage value Vx1 and the second voltage value Vx2, and therefore the formula for calculating the capacitance Cs in step S13 in FIG. 8A is changed to the following formula:

[0135]

[0136] Along with the change in the calculation formula for the measured capacitance Cs, the calculation formula for the error capacitance is also changed to the following formula.

[0137]

[0138] The error capacitance calculation process is the same as that shown in Fig. 8(b). In step S23 of Fig. 8(b), the capacitance value Cx of the error capacitance is calculated using the above equation (16). The control unit 11 stores the calculated capacitance value Cx in its internal memory, and in the measurement mode of Fig. 8(a), applies the capacitance value Cx to equation (15) to execute the process of Fig. 8(a).

[0139] 10 , in the third embodiment, the capacitance measurement circuit 10 may include a test capacitance Ct and a switching unit that selectively connects either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11. In this case, multiple test capacitances Ct having different capacitance values ​​may be arranged in the capacitance measurement circuit 10, and the average capacitance value of the error capacitance obtained for each test capacitance Ct may be applied to Cx in equation (15) to calculate the capacitance value of the measurement capacitance Cs.

[0140] <Effects of Third Embodiment> In the configuration of the third embodiment, similar to the first embodiment, even in a small capacitance range, the capacitance value Cs of the measurement capacitance Cs can be obtained with high accuracy with reduced parasitic capacitance and error capacitance.

[0141] As shown in FIG. 19, the measurement unit 14 measures the voltage between the positive electrode of the capacitance Cs to be measured and the power supply.

[0142] According to this configuration, by measuring the voltage between the positive electrode of the measurement capacitance Cs and the power supply and performing the first control C1 and the second control C2, it is possible to calculate the capacitance value Cs that is not affected by the parasitic capacitance and the error capacitance.

[0143] Here, the control unit 11 calculates the capacitance value Cs of the measurement capacitance Cs using the above formula (15) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the value Vdd of the voltage applied to the reference capacitance Cr, the capacitance value Cr of the reference capacitance Cr, and the capacitance value Cx of the error capacitance.

[0144] This makes it possible to suppress the influence of parasitic capacitance and error capacitance on the capacitance value of the capacitance Cs to be measured, and to obtain the capacitance value of the capacitance Cs to be measured with high accuracy.

[0145] In the second embodiment, the capacitance value of the capacitance Cs to be measured is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the ground by the measuring unit 14. In contrast, in the fourth embodiment, the capacitance value of the capacitance Cs to be measured is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd) by the measuring unit 14.

[0146] FIG. 20 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the fourth embodiment.

[0147] 20 , the measurement unit 14 measures the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd). The process of calculating the capacitance Cs to be measured is similar to the process shown in FIGS. 12A to 16B and 17 in the second embodiment. However, in the fourth embodiment, the voltage between the positive electrode of the capacitance Cs to be measured and the power supply (power supply voltage Vdd) is acquired as the first voltage value Vx1 and the second voltage value Vx2, and therefore the formula for calculating the capacitance Cs to be measured in step S212 in FIG. 17 is changed to the following formula:

[0148]

[0149] Along with the change in the calculation formula for the measured capacitance Cs, the calculation formula for the error capacitance is also changed to the following formula.

[0150]

[0151] The calculation process of the error capacitance is the same as that shown in FIG. 8B . In steps S21 and S22 of FIG. 8B , the control unit 11 executes the first control C1 and the second control C2, respectively, similar to those in the second embodiment, and acquires the first voltage value Vx1 and the second voltage value Vx2 using the measurement unit 14 shown in FIG. 20 . The control unit 11 applies the acquired first voltage value Vx1 and the second voltage value Vx2, along with the capacitance value Ct of the test capacitance Ct, to the above equation (18) to calculate the capacitance value Cx of the error capacitance. The control unit 11 stores the calculated capacitance value Cx in its internal memory, and in the measurement mode of FIG. 17 , applies the capacitance value Cx to equation (17) to calculate the capacitance value of the measurement capacitance Cs.

[0152] 18 , in the fourth embodiment, the capacitance measurement circuit 10 may include a test capacitance Ct and a switching unit (switch elements 15a, 15b, 16a, 16b) that selectively connects either the measurement capacitance Cs or the test capacitance Ct to the capacitance measurement circuit 10 under control of the control unit 11. In this case, multiple test capacitances Ct having different capacitance values ​​may be arranged in the capacitance measurement circuit 10, and the average capacitance value of the error capacitance obtained for each test capacitance Ct may be applied to Cx in equation (17) to calculate the capacitance value of the measurement capacitance Cs.

[0153] <Effects of Fourth Embodiment> In the configuration of the fourth embodiment, similar to the second embodiment, even in a small capacitance range, the capacitance value Cs of the measurement capacitance Cs can be obtained with high accuracy, with the parasitic capacitance and error capacitance suppressed.

[0154] As shown in FIG. 20, the measurement unit 14 measures the voltage between the positive electrode of the capacitance Cs to be measured and the power supply.

[0155] According to this configuration, by measuring the voltage between the positive electrode of the measurement capacitance Cs and the power supply and performing the first control C1 and the second control C2, it is possible to calculate the capacitance value Cs that is not affected by the parasitic capacitance and the error capacitance.

[0156] Here, the control unit 11 calculates the capacitance value Cs of the measured capacitance Cs using the above formula (17) from the first voltage value Vx1 obtained by the first control C1, the second voltage value Vx2 obtained by the second control C2, the value Vdd of the voltage applied to the reference capacitance Cr, the capacitance value Cr of the reference capacitance Cr, and the capacitance value Cx of the error capacitance.

[0157] This makes it possible to suppress the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance Cs to be measured, and to obtain the capacitance value Cs of the capacitance Cs to be measured with high accuracy.

[0158] Fifth Embodiment In the fifth embodiment, a configuration example is shown in which the capacitance measurement circuit 10 of the first embodiment is applied to a load detection device. The load detection device detects a load using a capacitance-type load sensor. This type of load detection device can be applied to various systems. The load sensor included in the load detection device may also be called a "capacitive pressure-sensitive sensor element," a "capacitive pressure detection sensor element," a "pressure-sensitive switch element," or the like.

[0159] First, the configuration of the load sensor 20 will be described with reference to Figures 21(a) to 24. For convenience, mutually orthogonal X, Y, and Z axes are indicated in Figures 21(a) to 24. The Z axis direction is the thickness direction of the load sensor 20.

[0160] FIG. 21A is a perspective view that schematically shows a base member 21 and a conductive elastic body 22 that is placed on the upper surface (the surface on the positive side of the Z axis) of the base member 21. FIG.

[0161] The base member 21 is an elastic, insulating, flat-plate member. The base member 21 has a rectangular shape in a plan view. The thickness of the base member 21 is constant. 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 called 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.

[0162] The resin material used for the base member 21 is, for example, at least one resin material selected from the group consisting of styrene-based resins, silicone-based resins (such as polydimethylpolysiloxane (PDMS)), acrylic-based resins, rotaxane-based resins, and urethane-based resins. The rubber material used 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, epichlorohydrin rubber, urethane rubber, and natural rubber.

[0163] The conductive elastic bodies 22 are arranged on the upper surface (the surface on the positive side of the Z axis) of the base member 21. In FIG. 21( a ), three conductive elastic bodies 22 are arranged on the upper surface of the base member 21. The conductive elastic bodies 22 are conductive members having elasticity. Each conductive elastic body 22 has a strip-like shape that is long in the Y axis direction. The three conductive elastic bodies 22 are arranged side by side at a predetermined interval in the X axis direction. Wiring W2 electrically connected to the conductive elastic bodies 22 is installed at the end of each conductive elastic body 22 on the negative side of the Y axis.

[0164] The conductive elastic body 22 is formed on the upper surface of the base member 21 by a printing method such as screen printing, gravure printing, flexographic printing, offset printing, or gravure offset printing. These printing methods make it possible to form the conductive elastic body 22 on the upper surface of the base member 21 with a thickness of about 0.001 mm to 0.5 mm.

[0165] The conductive elastic body 22 is made of a resin material with a conductive filler dispersed therein, or a rubber material with a conductive filler dispersed therein.

[0166] The resin material used for the conductive elastic body 22 is the same as the resin material used for the base member 21 described above, and is at least one resin material selected from the group consisting of, for example, styrene-based resins, silicone-based resins (polydimethylpolysiloxane (e.g., PDMS)), acrylic-based resins, rotaxane-based resins, and urethane-based resins.

[0167] The rubber material used for the conductive elastic body 22 is the same as the rubber material used for the base member 21 described above, and is at least one rubber material selected from the group consisting of, for example, silicone rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, polyisobutylene, ethylene propylene rubber, chlorosulfonated polyethylene, acrylic rubber, fluororubber, epichlorohydrin rubber, urethane rubber, and natural rubber.

[0168] The conductive filler used in the conductive elastic body 22 may be, for example, Au (gold), Ag (silver), Cu (copper), C (carbon), ZnO (zinc oxide), In ２ O ３ (indium(III) oxide), and SnO ２ The conductive material is at least one material selected from the group consisting of metal materials such as tin (IV) oxide, conductive polymer materials such as PEDOT:PSS (i.e., a composite of poly3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS)), and conductive fibers such as metal-coated organic fibers and metal wires (in a fibrous state).

[0169] FIG. 21B is a perspective view that schematically shows a state in which a conductor wire 23 is installed in the structure of FIG. 21A.

[0170] The conductor wires 23 are linear members and are arranged overlapping on the upper surfaces of the conductive elastic bodies 22 shown in Fig. 21(a). In this embodiment, three conductor wires 23 are arranged overlapping on the upper surfaces of the three conductive elastic bodies 22. The three conductor wires 23 are arranged side by side at a predetermined interval along the longitudinal direction (Y-axis direction) of the conductive elastic bodies 22 so as to intersect with the conductive elastic bodies 22. Each conductor wire 23 is arranged extending in the X-axis direction so as to straddle the three conductive elastic bodies 22.

[0171] The conductor wire 23 is, for example, a coated copper wire, and is made up of a linear conductive member 23a and a dielectric 23b formed on the surface of the conductive member 23a.

[0172] FIG. 22(a) is a perspective view that schematically shows a state in which a thread 24 is installed in the structure of FIG. 21(b).

[0173] After the conductor wires 23 are arranged as shown in Fig. 21(b), each conductor wire 23 is connected to the base member 21 by threads 24 so as to be movable in the longitudinal direction (X-axis direction) of the conductor wire 23. In the example shown in Fig. 22(a), 12 threads 24 connect the conductor wires 23 to the base member 21 at positions other than the positions where the conductive elastic bodies 22 and the conductor wires 23 overlap. The threads 24 are made of chemical fibers, natural fibers, a mixture of these fibers, or the like.

[0174] FIG. 22(b) is a perspective view that schematically shows a state in which a base member 25 is installed on the structure of FIG. 22(a).

[0175] A base member 25 is placed from above (the positive side of the Z axis) the structure shown in FIG. 22( a). The base member 25 is an insulating member. The base member 25 is made of at least one resin material selected from the group consisting of polyethylene terephthalate, polycarbonate, polyimide, and the like. The base member 25 may be made of the same material as the base member 21. The base member 25 has a flat plate shape parallel to the XY plane and has the same size and shape as the base member 21 in a planar view. The thickness of the base member 25 in the Z axis direction is, for example, 0.01 mm to 2 mm.

[0176] The four outer periphery sides of the base member 25 are connected to the four outer periphery sides of the base member 21 with a silicone rubber adhesive, thread, or the like. This fixes the base member 25 to the base member 21. The conductor wire 23 is sandwiched between the conductive elastic body 22 and the base member 25. In this way, the load sensor 20 is completed as shown in Fig. 22(b). The load sensor 20 can be used in a state where it is turned upside down from the state shown in Fig. 22(b).

[0177] 23(a) and 23(b) are diagrams schematically showing a cross section of the load sensor 20 when the load sensor 20 is cut along a plane parallel to the YZ plane at the center position in the X-axis direction of the conductive elastic body 22. Fig. 23(a) shows the cross section when no load is applied, and Fig. 23(b) shows the cross section when a load is applied.

[0178] 23(a) and 23(b), the conductor wire 23 is composed of a conductive member 23a and a dielectric member 23b formed on the conductive member 23a. The conductive member 23a is a linear member having electrical conductivity. The dielectric member 23b covers the surface of the conductive member 23a. The conductive member 23a is made of, for example, copper. The diameter of the conductive member 23a is, for example, approximately 60 μm.

[0179] The dielectric 23b has electrical insulation properties and is made of, for example, a resin material, a ceramic material, a metal oxide material, etc. The dielectric 23b may be at least one resin material selected from the group consisting of polypropylene resin, polyester resin (for example, polyethylene terephthalate resin), polyimide resin, polyphenylene sulfide resin, polyvinyl formal resin, polyurethane resin, polyamideimide resin, polyamide resin, etc., and may be Al ２ O ３ and Ta ２ O ５ The dielectric 23b may be at least one metal oxide material selected from the group consisting of: etc. The dielectric 23b is formed at least in the range of the conductor line 23 that overlaps the conductive elastic body 22.

[0180] 23( a), when no load is applied, the force applied between the conductive elastic body 22 and the conductor wire 23 and the force applied between the base member 25 and the conductor wire 23 are substantially zero. From this state, when a load is applied to the surface on the negative side of the Z axis of the base member 21, as shown in FIG. 23( b), the conductive elastic body 22 and the base member 21 are deformed by the conductor wire 23.

[0181] 23(b), when a load is applied, the conductor wire 23 is brought closer to the conductive elastic body 22 so that it is wrapped in the conductive elastic body 22. As a result, the contact area between the conductor wire 23 and the conductive elastic body 22 increases. This changes the capacitance between the conductive member 23a and the conductive elastic body 22. By detecting the capacitance between the conductive member 23a and the conductive elastic body 22, the load applied to this area can be obtained.

[0182] Fig. 24 is a plan view schematically showing the internal configuration of the load sensor 20. For convenience, the thread 24 and the base member 25 are omitted from Fig. 24.

[0183] 24 , element portions A11, A12, A13, A21, A22, A23, A31, A32, and A33 whose capacitance changes depending on the load are formed at positions where three conductive elastic bodies 22 and three conductor wires 23 intersect. Each element portion includes the conductive elastic body 22 and the conductor wire 23 near the intersection of the conductive elastic body 22 and the conductor wire 23.

[0184] In each element portion, the conductor wire 23 constitutes one pole (e.g., anode) of the capacitance, and the conductive elastic body 22 constitutes the other pole (e.g., cathode) of the capacitance. That is, the conductive member 23a (see FIGS. 23(a) and 23(b)) in the conductor wire 23 constitutes 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 (see FIGS. 23(a) and 23(b)) included in the conductor wire 23 corresponds to the dielectric that determines the capacitance in the load sensor 20 (capacitive load sensor).

[0185] When a load is applied to each element in the Z-axis direction, the conductor wire 23 is wrapped in the conductive elastic body 22. This changes the contact area between the conductor wire 23 and the conductive elastic body 22, changing the capacitance between the conductor wire 23 and the conductive elastic body 22. The end of the conductor wire 23 on the negative side of the X-axis and the end of the wire W2 installed on the conductive elastic body 22 on the negative side of the Y-axis are connected to a capacitance measurement circuit 10, which will be described later with reference to FIG.

[0186] When a load is applied to element portion A11, the contact area between the conductive member 23a of the conductor wire 23 and the conductive elastic body 22 increases via the dielectric 23b in element portion A11. In this case, the load applied to element portion A11 can be calculated by detecting the capacitance between the conductive elastic body 22 furthest on the X-axis negative side and the conductor wire 23 furthest on the Y-axis positive side. Similarly, in other element portions, the load applied to the other element portions can be calculated by detecting the capacitance between the conductive elastic body 22 and the conductor wire 23 that intersect in the other element portions.

[0187] FIG. 25 is a diagram showing the configuration of the load detection device 1.

[0188] For convenience, FIG. 25 shows only the conductor wire 23 and the conductive elastic body 22 as components of the load sensor 20, and the conductive elastic body 22 is shown in a linear form.

[0189] The load detection device 1 includes the capacitance measurement circuit 10 according to the first embodiment and the load sensor 20 shown in Fig. 22(b). Here, the nine element units A11 to A33 shown in Fig. 24 each correspond to a capacitance Cs to be measured. The conductor wires 23 (conductive members 23a) of the element units A11 to A33 correspond to the positive electrode of the capacitance Cs to be measured, and the conductive elastic bodies 22 of the element units A11 to A33 correspond to the negative electrode of the capacitance Cs to be measured.

[0190] The capacitance measuring circuit 10 includes element selection units 17 and 18 for switching the element unit to be measured among the nine element units A11 to A33 shown in Fig. 24. The element selection unit 17 includes switch elements 17a to 17c, and the element selection unit 18 includes switch elements 18a to 18d.

[0191] The switch elements 17a to 17c connect the wiring W2 drawn out from the conductive elastic body 22 to either the ground line L3 or the potential line L2. These switch elements 17a to 17c correspond to the switch element 13 in FIG. 1. The switch element 18d connects the potential line L1 to one of the switch elements 18a to 18c. The switch elements 18a to 18c connect the wiring W1 drawn out from the conductor line 23 (conductive member 23a) to either the output terminal of the switch element 18d or the ground line L3.

[0192] The capacitance measurement circuit 10 also includes an equipotential generator 19 for generating a potential equal to the potential of the potential line L1. In the configuration of FIG. 1, one terminal of the switch element 17a is directly connected to the wiring between the switch elements 12b and 12c to equalize the positive and negative electrodes of the capacitance Cs to be measured. In contrast, in FIG. 25, in addition to the switch element 17a, other circuit components such as the switch elements 17b and 17c, the wiring W2, and the conductive elastic body 22 are connected to the potential line L2 to which one terminal of the switch element 17a is connected. This increases the impedance of these circuit components compared to the configuration of FIG. 1. For this reason, the equipotential generator 19 is provided in the configuration of FIG. 25 to equalize the potential of the potential line L2 with the potential of the potential line L1.

[0193] 10, the switch elements 15a, 15b, and 16a to 16c are used to connect or disconnect the measurement capacitance Cs (load sensor 20) to or from the capacitance measurement circuit 10, and the switch elements 16a and 16b are used to connect or disconnect the test capacitance Ct to or from the capacitance measurement circuit 10. The switch element 16c is used to connect the negative electrode of the test capacitance Ct to the ground line L3 or the potential line L2.

[0194] 25 shows the states of switch elements 15a, 15b, 16a to 16c, 17a to 17c, and 18a to 18d under first control C1 when measuring the capacitance value of element unit A11. In this state, switch elements 15a and 15b are closed, connecting load sensor 20 to capacitance measurement circuit 10, and switch elements 16a and 16b are open, disconnecting test capacitance Ct from capacitance measurement circuit 10.

[0195] Furthermore, the conductor wires 23 (positive poles) of the topmost element units A11 to A13 of the nine element units are connected to the potential line L1. As a result, the remaining six element units are disconnected from the circuit. Furthermore, the equipotential generator 19 applies the same potential as the potential line L1 to the conductive elastic bodies 22 of the element units A12 and A13, disabling the element units A12 and A13. Therefore, only the element unit A11 to be measured is connected to the capacitance measurement circuit 10.

[0196] In this state, the control unit 11 executes step S11 (first control C1) in FIG. 8A to obtain a first voltage value Vx1. Next, in step S12 (second control C2) in FIG. 8A, the control unit 11 switches the switch element 17a to the potential line L2 side as shown in FIG. 26 to obtain a second voltage value Vx2. The control unit 11 then executes the process of step S13 to calculate the capacitance value of the element unit A11. Furthermore, the control unit 11 calculates the load applied to the element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than the control unit 11 from the capacitance value calculated by the control unit 11. In this way, the processing for the element unit A11 is completed.

[0197] The control unit 11 controls the switch elements 17a to 17c and 18a to 18d to sequentially switch the element unit to be measured. For example, if the element unit A12 is the object of measurement, the control unit 11 connects the switch element 17b to the ground line L3 and the switch elements 17a and 17c to the potential line L2 in step S11 (first control C1) of FIG. 8A. The control unit 11 also maintains the switch elements 18a to 18d in the state shown in FIG. 25. In this state, the control unit 11 executes the process of step S11 (first control C1). In step S12 (second control C2) of FIG. 8A, the control unit 11 switches the switch element 17b to the potential line L2 side and executes the second control C2. Thereafter, the control unit 11 executes step S13 to calculate the capacitance value of the element unit A12 and calculates the load applied to the element unit A12 from the calculation result.

[0198] FIG. 27 is a diagram showing the states of the switch elements 15a, 15b, 16a to 16c, 17a to 17c, and 18a to 18d in the first control C1 when measuring the error capacitance of the reference capacitance Cr.

[0199] In this state, the switch elements 15a and 15b are open, disconnecting the load sensor 20 from the capacitance measurement circuit 10, and the switch elements 16a and 16b are closed, connecting the test capacitance Ct to the capacitance measurement circuit 10. In addition, the switch element 16c is connected to the ground line L3, connecting the negative electrode of the test capacitance Ct to the ground line L3.

[0200] In this state, the control unit 11 executes step S21 (first control C1) in FIG. 8B to acquire the first voltage value Vx1. Next, in step S22 (second control C2) in FIG. 8B, the control unit 11 switches the switch element 16c to the side of the potential line L2, as shown in FIG. 28, to acquire the second voltage value Vx2. Then, the control unit 11 executes the process of step S23 to calculate the capacitance value Cx of the error capacitance from the above equation (7) and stores the calculated capacitance value Cx in the internal memory. In this way, the control unit 11 ends the error capacitance measurement process.

[0201] <Effects of embodiment 5> As shown in Figure 25, the load detection device 1 includes a load sensor 20 having an element unit whose capacitance changes depending on the load, and the capacitance measurement circuit 10 of embodiment 1, and the control unit 11 performs first control C1, second control C2, and calculation processing of the capacitance value of the element unit, using the element unit as the measurement capacitance Cs.

[0202] According to this configuration, since the capacitance measurement circuit 10 of the first embodiment is included, a capacitance value corresponding to the load can be stably obtained even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since the capacitance measurement circuit 10 of the first embodiment is included, a capacitance value in which the influence of parasitic capacitance and error capacitance is suppressed can be accurately obtained. Therefore, a small range of load can be detected stably and with high accuracy.

[0203] As shown in FIGS. 24 and 25, the load sensor 20 includes a plurality of element units A11 to A33, and the capacitance measuring circuit 10 includes element selection units 17 and 18 that switch the element unit to be measured.

[0204] This configuration allows load detection over a wide range where multiple element units are arranged. Furthermore, by switching the element unit to be measured using element selectors 17 and 18, the capacitance value of each element unit can be measured stably and accurately.

[0205] Sixth Embodiment In a sixth embodiment, a configuration example in which the capacitance measurement circuit 10 of the second embodiment is applied to a load detection device is shown. The load detection device detects a load using a load sensor similar to that of the fifth embodiment.

[0206] FIG. 29 is a diagram showing the configuration of a load detection device 1 according to the sixth embodiment.

[0207] As in FIG. 25, for convenience, FIG. 29 shows only the conductor wire 23 and the conductive elastic body 22 as components of the load sensor 20, and the conductive elastic body 22 is shown in a linear form.

[0208] The load detection device 1 includes the capacitance measurement circuit 10 according to the second embodiment and the load sensor 20 shown in Fig. 22(b). As in the fifth embodiment, the nine element units A11 to A33 shown in Fig. 24 each correspond to a capacitance Cs to be measured. The conductor wires 23 (conductive members 23a) of the element units A11 to A33 correspond to the positive electrode of the capacitance Cs to be measured, and the conductive elastic bodies 22 of the element units A11 to A33 correspond to the negative electrode of the capacitance Cs to be measured.

[0209] The configurations of switch elements 17a to 17c and switch elements 18a to 18d are the same as in Fig. 25. Also, as in Fig. 25, an equipotential generator 19 is provided to equalize the potential of potential line L2 with the potential of potential line L1. As in Fig. 25, capacitance measurement circuit 10 further includes switch elements 15a, 15b, 16a to 16c, and a test capacitance Ct.

[0210] As in Fig. 25, Fig. 29 shows the states of switch elements 17a to 17c and 18a to 18d under first control C1 when measuring the capacitance value of element unit A11. In this case, as in Fig. 25, only element unit A11 to be measured is connected to capacitance measurement circuit 10. The states of switch elements 17a to 17c and 18a to 18d are the same as in Fig. 25.

[0211] In this state, the control unit 11 executes the first control C1 in FIG. 17 to obtain the first voltage value Vx1. Next, in step S206 of the second control C2 in FIG. 17, the control unit 11 switches the switch element 17a to the side of the potential line L2 and executes the processes of steps S207 to S211. As a result, 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. Furthermore, the control unit 11 calculates the load applied to the element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than the control unit 11 from the capacitance value calculated by the control unit 11. In this way, the process for the element unit A11 is completed.

[0212] The control unit 11 controls the switch elements 17a to 17c and 18a to 18d to sequentially switch the element unit to be measured. For example, when the element unit A12 is the object of measurement, the control unit 11 connects the switch element 17b to the ground line L3 and the switch elements 17a and 17c to the potential line L2 in step S201 of the first control C1 in FIG. 17. The control unit 11 also maintains the switch elements 18a to 18d in the state shown in FIG. 29. In this state, the control unit 11 executes the processing from step S202 onward in FIG. 17. In step S206, the switch element 17b is switched to the potential line L2 side, and the processing from step S207 onward is executed. 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 from the calculation result.

[0213] 30, when measuring the error capacitance of the reference capacitance Cr, the control unit 11 opens the switch elements 15a and 15b to disconnect the load sensor 20 from the capacitance measurement circuit 10, and closes the switch elements 16a and 16b to connect the test capacitance Ct to the capacitance measurement circuit 10. In addition, the control unit 11 connects the switch element 16c to the ground line L3 side to connect the negative electrode of the test capacitance Ct to the ground line L3.

[0214] In this state, the control unit 11 executes the first control C1 in FIG. 17 to obtain the first voltage value Vx1. Next, the control unit 11 switches the switch element 16c to the side of the potential line L2, executes the second control C2 in FIG. 17, and obtains the second voltage value Vx2. Then, the control unit 11 executes the process of step S212 in FIG. 17 to calculate the capacitance value Cx of the error capacitance from the above equation (17), and stores the calculated capacitance value Cx in the internal memory. In this way, the control unit 11 ends the error capacitance measurement process.

[0215] Effect of Embodiment 6 According to the configuration of Embodiment 6, since it includes the capacitance measurement circuit 10 of Embodiment 2, it is possible to stably obtain a capacitance value corresponding to the load even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since it includes the capacitance measurement circuit 10 of Embodiment 2, it is possible to accurately obtain a capacitance value in which the effects of parasitic capacitance and error capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0216] Seventh Embodiment In a seventh embodiment, a configuration example in which the capacitance measurement circuit 10 of the third embodiment is applied to a load detection device is shown. The load detection device detects a load using a load sensor similar to that of the fifth embodiment.

[0217] FIG. 31 is a diagram showing the configuration of a load detection device 1 according to the seventh embodiment.

[0218] FIG. 31 shows the states of the switch elements 15a, 15b, 16a to 16c, 17a to 17c, and 18a to 18d under the first control C1 when measuring the capacitance value of the element portion A11.

[0219] The operation of measuring the capacitance value of the target capacitance Cs (element portion) is the same as the measurement operation in embodiment 5 described with reference to Figures 25 and 26. In embodiment 7, during this measurement operation, the first voltage value Vx1 and the second voltage value Vx2 acquired by the first control C1 and the second control C2, respectively, are applied to the above formula (15) to calculate the capacitance value of the target capacitance Cs (element portion).

[0220] The operation of measuring the capacitance value of the error capacitance of the reference capacitance Cr is similar to the measurement operation in the fifth embodiment described with reference to Figures 27 and 28. In the seventh embodiment, during this measurement operation, the first voltage value Vx1 and the second voltage value Vx2 acquired in the first control C1 and the second control C2, respectively, are applied to the above formula (16) to calculate the capacitance value of the error capacitance.

[0221] Effect of Embodiment 7 According to the configuration of Embodiment 7, since it includes the capacitance measurement circuit 10 of Embodiment 3, it is possible to stably obtain a capacitance value corresponding to the load even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since it includes the capacitance measurement circuit 10 of Embodiment 3, it is possible to accurately obtain a capacitance value in which the effects of parasitic capacitance and error capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0222] Eighth Embodiment In an eighth embodiment, a configuration example is shown in which the capacitance measurement circuit 10 of the fourth embodiment is applied to a load detection device. The load detection device detects a load using a load sensor similar to that of the fifth embodiment.

[0223] FIG. 32 is a diagram showing the configuration of a load detection device 1 according to the eighth embodiment.

[0224] FIG. 32 shows the states of the switch elements 15a, 15b, 16a to 16c, 17a to 17c, and 18a to 18d under the first control C1 when measuring the capacitance value of the element portion A11.

[0225] The operation of measuring the capacitance value of the target capacitance Cs (element portion) is the same as the measurement operation in the sixth embodiment described with reference to Fig. 29. In the eighth embodiment, during this measurement operation, the first voltage value Vx1 and the second voltage value Vx2 acquired in the first control C1 and the second control C2, respectively, are applied to the above formula (17) to calculate the capacitance value of the target capacitance Cs (element portion).

[0226] The operation of measuring the capacitance value of the error capacitance of the reference capacitance Cr is similar to the measurement operation in the sixth embodiment described with reference to Fig. 30. In the eighth embodiment, during this measurement operation, the first voltage value Vx1 and the second voltage value Vx2 acquired in the first control C1 and the second control C2, respectively, are applied to the above equation (18) to calculate the capacitance value of the error capacitance.

[0227] Effect of Embodiment 8 According to the configuration of Embodiment 8, since it includes the capacitance measurement circuit 10 of Embodiment 4, it is possible to stably obtain a capacitance value corresponding to the load even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since it includes the capacitance measurement circuit 10 according to Embodiment 4, it is possible to accurately obtain a capacitance value in which the effects of parasitic capacitance and error capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0228] <Other Modifications> In the above-described first to eighth embodiments, the capacitance value of the error capacitance is acquired prior to measuring the capacitance value of the measurement capacitance Cs, but the timing of acquiring the capacitance value of the error capacitance is not limited to this. For example, in the first embodiment, the measurement routine for the capacitance value of the measurement capacitance Cs shown in FIG. 8A may be executed first to store the uncertain equation (6) in which only the capacitance value Cx is indeterminate, and then the measurement routine for the capacitance value of the error capacitance shown in FIG. 8B may be executed to acquire the capacitance value Cx of the error capacitance, and the acquired capacitance value Cx may be applied to the uncertain equation (6) to acquire the capacitance value Cs of the measurement capacitance Cs.

[0229] That is, the measurement routine for the measurement capacitance Cs and the measurement routine for the error capacitance may be performed separately, and either may be performed first. The claimed invention does not particularly limit the order in which the measurement routine for the measurement capacitance Cs and the measurement routine for the error capacitance are performed, and includes embodiments in which the measurement routine for the error capacitance is performed first, as described in the first to eighth embodiments, as well as embodiments in which the measurement routine for the measurement capacitance Cs is performed first, as described above.

[0230] In the above-described first to eighth embodiments, the switch elements 12a to 12c are configured as P-type or N-type FETs, but the switch elements 12a to 12c may be configured as switch elements other than FETs. Similarly, the switch element 13 may be configured as various types of switch elements as long as it is possible to switch the connection destination of the negative electrode of the measurement capacitance Cs between ground and the positive electrode. Similarly, in the configurations of Figures 25 to 32, various types of switch elements may be used as the switch elements 17a to 17c and the switch elements 18a to 18d.

[0231] In the first embodiment, after the switching element 13 is switched in FIG. 4B, the reference capacitance Cr is charged in FIG. 5A without being discharged. However, the reference capacitance Cr may be discharged once and then charged in FIG. 5A. However, in this case, it takes longer for the reference capacitance Cr to be fully charged than when the reference capacitance Cr is charged without being discharged as described above. Therefore, in order to proceed with the process more quickly, it is preferable to charge the reference capacitance Cr without discharging it, as shown in FIG. 5A. This also applies to the flow from the operation in FIG. 14B to the operation in FIG. 15A in the second embodiment.

[0232] Furthermore, in the above-described first to fourth embodiments, the capacitance value of the reference capacitance Cr is fixed, but the capacitance value of the reference capacitance Cr may be variable. This allows the capacitance value of the reference capacitance to be adjusted to a value appropriate for the dynamic range of the capacitance to be measured. Therefore, even if the dynamic range of the capacitance to be measured is changed, the capacitance value of the capacitance to be measured Cs can be measured appropriately within that dynamic range.

[0233] 25 to 32, the element units A12 and A13 other than the element unit A11 to be measured are disabled by applying an equal potential to their positive and negative poles. However, switch elements 17b and 17c may be configured so that their negative poles are connected to ground line L3. In this case, the capacitances of element units A12 and A13 are included in the parasitic capacitance described above and are therefore canceled out by the above equations (6), (13), (15), and (17). Therefore, the capacitance of element unit A11 to be measured can be obtained with high accuracy.

[0234] 25 to 32, the two conductor lines 23 (conductive members 23a) other than the conductor line 23 (conductive member 23a) constituting the positive electrode of the element portion A11 to be measured are connected to the ground line L3 by the switch elements 18b and 18c, but the switch elements 18b and 18c may be connected to the output line side of the switch element 18d, and the element portion having these two conductor lines 23 (conductive member 23a) as the positive electrode may be set in a floating state. In this case, too, the parasitic capacitances other than those of the element portion A11 to be measured are canceled out by the above equations (6), (13), (15), and (17), so that the capacitance of the element portion A11 to be measured can be obtained with high accuracy.

[0235] The configuration and switching form of the element selection units 17 and 18 may be other configurations and switching forms as long as the negative electrode of the element unit to be measured can be connected to ground or a wiring having the same potential as the positive electrode of the element unit to be measured, and the capacitance of element units other than the object to be measured can be canceled together with other parasitic capacitances by the above equations (6), (13), (15), and (17).

[0236] In the above-described fifth to eighth embodiments, the conductor wire 23 is made of a coated copper wire, but the present invention is not limited to this and may be made of a linear conductive member made of a material other than copper and a dielectric coating the conductive member. Also, the conductive member may be made of a twisted wire.

[0237] Furthermore, in the above-described fifth to eighth embodiments, the conductive elastic body 22 is provided only on the surface of the base member 21 on the positive side of the Z axis, but a conductive elastic body may also be provided on the surface of the base member 25 on the negative side of the Z axis. In this case, the conductive elastic body on the base member 25 side is configured similarly to the conductive elastic body 22 on the base member 21 side and is arranged so as to overlap the conductive elastic body 22 with the conductor wire 23 sandwiched between them in a plan view. The wiring extending from the conductive elastic body on the base member 25 side is connected to the wiring W2 extending from the conductive elastic body 22 opposite in the Z axis direction. In this way, when conductive elastic bodies are provided above and below the conductor wire 23, the change in capacitance in the element unit is approximately doubled in correspondence with the upper and lower conductive elastic bodies, thereby improving the detection sensitivity of the load applied to the element unit.

[0238] Furthermore, in the above-described embodiments 5 to 8, the dielectric 23b is formed on the conductive member 23a so as to cover the outer periphery of the conductive member 23a, but instead, the dielectric 23b may be formed on the upper surface of the conductive elastic body 22. In this case, in response to the application of a load, the conductive member 23a sinks into the conductive elastic body 22 and the dielectric 23b so as to be enveloped by the conductive elastic body 22, and the contact area between the conductive member 23a and the conductive elastic body 22 changes. This makes it possible to detect a load applied to the element portion, as in the above-described embodiments.

[0239] Furthermore, in the above-described fifth to eighth embodiments, the load sensor 20 is configured so that nine element units are arranged in a matrix of three rows and three columns, but the number and arrangement of the element units in the load sensor 20 are not limited to this. For example, the load sensor 20 may be configured so that 16 element units are arranged in a matrix of four rows and four columns, or the load sensor 20 may be configured so that a plurality of element units are arranged in only one column. Alternatively, the load sensor 20 may be configured to include only one element unit.

[0240] In addition, in the above-described fifth to eighth embodiments, the element portion is formed by the crossing of the conductive elastic body 22 and the conductor wire 23, but the configuration of the element portion is not limited to this. For example, the element portion may be formed by a configuration in which a dielectric is sandwiched between a hemispherical conductive elastic body and a flat electrode. In this case, the dielectric may be formed on the surface of the electrode facing the conductive elastic body, or on the surface of the hemispherical conductive elastic body.

[0241] Furthermore, the capacitance measured by the capacitance measuring circuit 10 according to the present invention is not limited to the element portion of a load sensor, but may be other capacitances. For example, the capacitance measured by the capacitance measuring circuit 10 may be a capacitive element formed in an electrostatic touch panel or a semiconductor device, an electrolytic capacitor, a ceramic capacitor, or the like.

[0242] In addition, the embodiments of the present invention can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims.

[0243] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0244] (Technology 1) A device includes: a reference capacitance having a predetermined capacitance value; a switching unit that switches between applying and not applying a voltage to the reference capacitance; a transfer unit that transfers charge accumulated in the reference capacitance to a measurement capacitance; a connection unit that connects a negative electrode of the measurement capacitance to ground or a wiring having the same potential as the positive electrode of the measurement capacitance; a measurement unit that measures the voltage of the measurement capacitance; and a control unit that controls the switching unit, the transfer unit, and the connection unit, wherein the control unit performs a first control that applies a voltage to the reference capacitance, and then causes the transfer unit to transfer charge while the negative electrode of the measurement capacitance is connected to the ground, and obtains a first voltage value measured by the measurement unit after the charge transfer has been completed; and a second control that applies a voltage to the reference capacitance, and then causes the transfer unit to transfer charge while the negative electrode of the measurement capacitance is connected to the wiring having the same potential as the positive electrode of the measurement capacitance, and obtains a second voltage value measured by the measurement unit after the charge transfer has been completed. a process of calculating a capacitance value of the measurement capacitance using the first voltage value, the second voltage value, and a capacitance value of an error capacitance that is an error component of the reference capacitance; and acquiring the capacitance value of the error capacitance by applying the first voltage value and the second voltage value acquired by the first control and the second control, respectively, to the calculation process using a test capacitance whose capacitance value is known instead of the measurement capacitance.

[0245] This technology calculates the capacitance value of the measurement capacitance based on the voltage value after the charge is transferred from the reference capacitance, enabling stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, in the second control, the negative electrode of the measurement capacitance is connected to a wiring at the same potential as the positive electrode of the measurement capacitance, so the measured voltage value is largely unaffected by the measurement capacitance and is primarily affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, so the measured voltage value is affected by both the reference capacitance and parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, a capacitance value unaffected by parasitic capacitance can be calculated. Furthermore, the capacitance value of the measurement capacitance is calculated by taking into account the capacitance value of the error capacitance (effective equivalent capacitance of the error component), which is an error component of the reference capacitance, allowing for accurate determination of the capacitance value of the measurement capacitance.

[0246] (Technology 2) In the capacitance measurement circuit according to Technology 1, the measurement unit measures a voltage between a positive electrode of the capacitance to be measured and ground.

[0247] According to this technique, the capacitance value Cs can be calculated without being affected by parasitic capacitance and error capacitance by measuring the voltage between the positive electrode of the measurement capacitance and ground and performing the first control and second control.

[0248] (Technology 3) In the capacitance measuring circuit according to Technology 2, the control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, the value Vdd of the voltage applied to the reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

[0249]

[0250] According to this technique, the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance to be measured can be suppressed, and the capacitance value Cs of the capacitance to be measured can be obtained with high accuracy.

[0251] (Technology 4) In the capacitance measurement circuit according to Technology 1, the measurement unit measures a voltage between a positive electrode of the capacitance to be measured and a power supply.

[0252] According to this technique, the first control and the second control are performed by measuring the voltage between the positive electrode of the measurement capacitance and the power supply, so that the capacitance value Cs can be calculated without being affected by the parasitic capacitance and the error capacitance.

[0253] (Technology 5) In the capacitance measuring circuit according to Technology 4, the control unit calculates the capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, the value Vdd of the voltage applied to the reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

[0254]

[0255] According to this technique, the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance to be measured can be suppressed, and the capacitance value Cs of the capacitance to be measured can be obtained with high accuracy.

[0256] (Technology 6) The capacitance measurement circuit according to any one of technologies 1 to 5, further comprising: the test capacitor; and a switching unit that selectively connects either the measurement capacitor or the test capacitor to the capacitance measurement circuit under control of the control unit.

[0257] This technology allows the test capacitor to be connected to the capacitance measurement circuit at any time to acquire the error capacitance, so that even if the error capacitance changes over time, the error capacitance can be properly acquired at each time, and the capacitance value of the measurement capacitor Cs can be acquired with high accuracy.

[0258] (Technology 7) A device comprising: a reference capacitor having a predetermined capacitance value; a switching unit that switches between applying and not applying a voltage to a measurement capacitor; a transfer unit that transfers charge accumulated in the measurement capacitor to the reference capacitor; a connection unit that connects a 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 that measures the voltage of the measurement capacitor; and a control unit that controls the switching unit, the transfer unit, and the connection unit, wherein the control unit performs a first control that applies a voltage to the measurement capacitor with the negative electrode of the measurement capacitor connected to the ground, and then causes the transfer unit to transfer charge, and obtains a first voltage value measured by the measurement unit after the charge has been transferred; and a second control that applies a voltage to the measurement capacitor with the negative electrode of the measurement capacitor connected to a wiring having the same potential as the positive electrode of the measurement capacitor, and then causes the transfer unit to transfer charge, and obtains a second voltage value measured by the measurement unit after the charge has been transferred. a process of calculating a capacitance value of the measurement capacitance using the first voltage value, the second voltage value, and a capacitance value of an error capacitance that is an error component of the reference capacitance; and acquiring the capacitance value of the error capacitance by applying the first voltage value and the second voltage value acquired by the first control and the second control, respectively, to the calculation process using a test capacitance whose capacitance value is known instead of the measurement capacitance.

[0259] According to this technology, the capacitance value of the measurement capacitance is calculated based on the voltage value after charge is transferred from the measurement capacitance, enabling stable measurement of capacitance values ​​over a small range without using a high-precision AD converter. Furthermore, in the second control, the negative electrode of the measurement capacitance is connected to a wiring having the same potential as the positive electrode of the measurement capacitance, and a voltage is applied to the measurement capacitance. This means that almost no charge accumulates in the measurement capacitance, and charge accumulates in the parasitic capacitance. Therefore, the voltage value measured using the second control is largely unaffected by the measurement capacitance, and is primarily affected by the reference capacitance and parasitic capacitance. In contrast, in the first control, the negative electrode of the measurement capacitance is connected to ground, and a voltage is applied to the measurement capacitance. This means that charge is applied to the measurement capacitance as well as the parasitic capacitance. Therefore, the voltage value measured using the first control is affected by the measurement capacitance as well as the reference capacitance and parasitic capacitance. Therefore, by calculating the capacitance value of the measurement capacitance from these two voltage values, a capacitance value free from the influence of parasitic capacitance can be calculated. Furthermore, since the capacitance value of the error capacitance (effective equivalent capacitance of the error component), which is an error component of the reference capacitance, is taken into account in the calculation of the capacitance value of the measurement capacitance, the capacitance value of the measurement capacitance can be obtained with high accuracy.

[0260] (Technology 8) In the capacitance measurement circuit according to Technology 7, the measurement unit measures a voltage between a positive electrode of the capacitance to be measured and ground.

[0261] According to this technique, the capacitance value Cs can be calculated without being affected by parasitic capacitance and error capacitance by measuring the voltage between the positive electrode of the measurement capacitance and ground and performing the first control and second control.

[0262] (Technology 9) In the capacitance measurement circuit described in Technology 8, the control unit calculates the capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, the value Vdd of the voltage applied to the measurement capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

[0263]

[0264] According to this technique, the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance to be measured can be suppressed, and the capacitance value Cs of the capacitance to be measured can be obtained with high accuracy.

[0265] (Technology 10) The capacitance measuring circuit according to Technology 7, wherein the measuring unit measures a voltage between a positive electrode of the capacitance to be measured and a power supply.

[0266] According to this technique, the capacitance value Cs can be calculated without being affected by parasitic capacitance and error capacitance by measuring the voltage between the positive electrode of the measurement capacitance and the power supply and performing the first control and second control.

[0267] (Technology 11) In the capacitance measuring circuit according to Technology 10, the control unit calculates a capacitance value Cs of the measurement capacitance from the first voltage value Vx1 acquired by the first control, the second voltage value Vx2 acquired by the second control, the value Vdd of the voltage applied to the reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

[0268]

[0269] According to this technique, the influence of parasitic capacitance and error capacitance on the capacitance value Cs of the capacitance to be measured can be suppressed, and the capacitance value Cs of the capacitance to be measured can be obtained with high accuracy.

[0270] (Technology 12) The capacitance measurement circuit according to any one of Technologies 7 to 11, further comprising: the test capacitor; and a switching unit that selectively connects either the measurement capacitor or the test capacitor to the capacitance measurement circuit under control of the control unit.

[0271] This technology allows the test capacitor to be connected to the capacitance measurement circuit at any time to acquire the error capacitance, so that even if the error capacitance changes over time, the error capacitance can be properly acquired at each time, and the capacitance value Cs of the measurement capacitor can be acquired with high accuracy.

[0272] (Technology 13) A load detection device comprising: a load sensor having an element part whose capacitance changes depending on the load; and a capacitance measurement circuit according to any one of technologies 1 to 12; wherein the control part performs the first control, the second control, and the calculation process of the capacitance value using the element part as the measurement capacitance.

[0273] According to this technology, since the capacitance measurement circuit according to the first or second aspect is included, it is possible to stably obtain a capacitance value corresponding to the load even when the load applied to the element unit is small and the capacitance value is small. Furthermore, since the capacitance measurement circuit according to the first or second aspect is included, it is possible to accurately obtain a capacitance value in which the effects of parasitic capacitance and error capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0274] (Technology 14) In the load detection device described in Technology 13, the load sensor includes a plurality of the element units, and the capacitance measurement circuit includes an element selection unit that switches the element unit to be measured.

[0275] This technology allows load detection over a wide area where multiple element units are arranged. Also, by switching the element unit to be measured using the element selection unit, the capacitance value of each element unit can be measured stably and accurately.

[0276] 1 Load detection device 10 Capacitance measurement circuit 11 Control unit 20 Load sensor 10a Switch element (switching unit) 10b Switch element (transfer unit) 13 Switch element (connection unit) 14 Measurement unit 15a, 15b, 16a, 16b Switch elements (switching units) 17, 18 Element selection unit 17a to 17c Switch elements (connection units) C1 First control C2 Second control Cr Reference capacitance Cs Measurement capacitance Ct Test capacitance A11 to A33 Element unit (measurement capacitance)

Claims

a control unit for controlling the switching unit, the transfer unit, and the connection unit, wherein the control unit performs a first control for applying a voltage to the reference capacitance, and then having the transfer unit transfer the charge while the negative electrode of the measurement capacitance is connected to the ground, and then obtaining a first voltage value measured by the measurement unit after the charge has been transferred; and a second control for applying a voltage to the reference capacitance, and then having the transfer unit transfer the charge while the negative electrode of the measurement capacitance is connected to the ground, and then obtaining a second voltage value measured by the measurement unit after the charge has been transferred. a process of calculating a capacitance value of the measurement capacitance using the first voltage value and the second voltage value and a capacitance value of an error capacitance that is an error component of the reference capacitance; and acquiring the capacitance value of the error capacitance by applying to the calculation process the first voltage value and the second voltage value obtained by the first control and the second control, respectively, using a test capacitance having a known capacitance value instead of the measurement capacitance.

2. The capacitance measuring circuit according to claim 1, wherein the measuring section measures the voltage between the positive electrode of the capacitance to be measured and ground.

3. A capacitance measuring circuit as claimed in claim 2, characterized in that the control unit calculates the capacitance value Cs of the measurement capacitance from 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 reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

4. The capacitance measuring circuit according to claim 1, wherein the measuring section measures the voltage between the positive electrode of the capacitance to be measured and a power source.

5. A capacitance measuring circuit as claimed in claim 4, characterized in that the control section calculates a capacitance value Cs of the measurement capacitance from 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 reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, by the following formula:

6. A capacitance measuring circuit as claimed in claim 1, comprising: the test capacitance; and a switching section which selectively connects either the measurement capacitance or the test capacitance to the capacitance measuring circuit under control of the control section.

7. A device comprising: a reference capacitance having a predetermined capacitance value; a switching unit for switching between application and non-application of a voltage to a capacitance to be measured; a transfer unit for transferring charges accumulated in the capacitance to be measured to the reference capacitance; a connection unit for connecting a negative electrode of the capacitance to ground or a wiring having the same potential as the positive electrode of the capacitance to be measured; a measurement unit for measuring a voltage of the capacitance to be measured; and a control unit for controlling the switching unit, the transfer unit and the connection unit, wherein the control unit performs a first control for applying a voltage to the capacitance to be measured with the negative electrode of the capacitance to be measured connected to the ground, and then causing the transfer unit to transfer charges, and obtaining a first voltage value measured by the measurement unit after the charges have been transferred; and a second control for applying a voltage to the capacitance to be measured with the negative electrode of the capacitance to be measured connected to a wiring having the same potential as the positive electrode of the capacitance to be measured, and then causing the transfer unit to transfer charges, and obtaining a second voltage value measured by the measurement unit after the charges have been transferred. a process of calculating a capacitance value of the measurement capacitance using the first voltage value and the second voltage value and a capacitance value of an error capacitance that is an error component of the reference capacitance; and acquiring the capacitance value of the error capacitance by applying to the calculation process the first voltage value and the second voltage value obtained by the first control and the second control, respectively, using a test capacitance having a known capacitance value instead of the measurement capacitance.

8. The electrostatic capacitance measuring circuit according to claim 7, wherein the measuring section measures the voltage between the positive electrode of the capacitance to be measured and ground.

9. A capacitance measuring circuit as claimed in claim 8, characterized in that the control unit calculates the capacitance value Cs of the measurement capacitance from 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 capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, by the following formula:

10. The capacitance measuring circuit according to claim 7, wherein the measuring section measures the voltage between the positive electrode of the capacitance to be measured and a power source.

11. A capacitance measuring circuit as claimed in claim 10, characterized in that the control unit calculates the capacitance value Cs of the measurement capacitance from 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 reference capacitance, the capacitance value Cr of the reference capacitance, and the capacitance value Cx of the error capacitance, using the following formula:

12. A capacitance measuring circuit as claimed in claim 7, comprising: the test capacitance; and a switching unit which selectively connects either the measurement capacitance or the test capacitance to the capacitance measuring circuit under control of the control unit.

13. A load detection device comprising: a load sensor having an element portion whose capacitance changes depending on the load; and a capacitance measurement circuit as described in any one of claims 1 to 12, wherein the control portion performs the first control, the second control, and the calculation process of the capacitance value using the element portion as the measurement capacitance.

14. A load detection device according to claim 13, wherein the load sensor comprises a plurality of the element units, and the capacitance measurement circuit comprises an element selection unit that switches between the element units to be measured.

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