Capacitance measuring circuit and load detecting device

Abstract

A capacitance measuring circuit (10) comprises: a reference capacitor (Cr) that has a prescribed capacitance value; a switch element (12a) that switches between application and non-application of a voltage to the reference capacitor (Cr); a switch element (12b) that transfers charge accumulated in the reference capacitor (Cr) to a measurement capacitor (Cs); a measuring unit (14) that measures the voltage across the measurement capacitor (Cs); a noise suppressing unit (switch elements (12a, 12d) and a holding capacitor (Ch)) that suppresses the inflow of noise to the measuring unit (14) from the ground and a power supply; and a control unit. The control unit: applies the voltage to the reference capacitor (Cr) and then performs control for causing the switch element (12b) to transfer the charge; and, after the charge has been transferred, performs processing for calculating the capacitance value of the measurement capacitor (Cs) on the basis of the voltage value measured by the measuring unit (14) in a state in which the inflow of noise is suppressed by the noise suppressing unit.

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, noise may be transmitted from a common power supply or ground to the capacitance measurement circuit that measures the capacitance of the element unit. If noise is transmitted to the capacitance measurement circuit, stable voltage measurement of the element unit cannot be performed, resulting in a decrease in load detection accuracy.

[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. The capacitance measurement circuit according to this aspect 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 stored in the reference capacitance to a measurement capacitance, a measurement unit that measures the voltage of the measurement capacitance, a noise suppression unit that suppresses noise from the ground and power supply from the measurement unit, and a control unit that controls the switching unit, the transfer unit, and the noise suppression unit. The control unit applies a voltage to the reference capacitance and then controls the transfer unit to transfer the charge, and after the charge transfer, calculates the capacitance value of the measurement capacitance from the voltage value measured by the measurement unit while the noise suppression unit suppresses the noise from being transferred.

[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, so that capacitance values ​​over a small range can be measured stably without using a high-precision AD converter. Furthermore, after the charge transfer, the voltage value of the measurement capacitance is acquired while suppressing the inflow of noise from the ground and power supply to the measurement unit, so that the influence of this noise on the measurement result of the voltage value can be suppressed. Therefore, the capacitance value of the measurement capacitance can be measured accurately.

[0010] A second aspect of the present invention relates to a capacitance measurement circuit. The capacitance measurement circuit according to this aspect includes a switching unit that switches between applying and not applying a voltage to a capacitance to be measured, a transfer unit that transfers charge accumulated in the capacitance to be measured to the reference capacitance, a measurement unit that measures the voltage of the capacitance to be measured, a noise suppression unit that suppresses noise from entering the measurement unit from ground, and a control unit that controls the switching unit, the transfer unit, and the noise suppression unit. The control unit applies a voltage to the capacitance to be measured and then controls the transfer unit to transfer the charge, and after the charge transfer, calculates the capacitance value of the capacitance to be measured from the voltage value measured by the measurement unit while the noise suppression unit suppresses the noise from entering.

[0011] According to the capacitance measurement circuit of this aspect, the capacitance value of the target capacitance is calculated based on the voltage value after charge is transferred from the target capacitance, so that capacitance values ​​over a small range can be measured stably without using a high-precision AD converter. Furthermore, after the charge is transferred, the voltage value of the target capacitance is acquired while suppressing the inflow of noise from the ground and power supply to the measurement unit, so that the influence of this noise on the measurement result of the voltage value can be suppressed. Therefore, the capacitance value of the target capacitance can be measured accurately.

[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 controls the charge transfer and calculates the capacitance using the element unit as the measurement capacitance.

[0013] The load detection device according to this aspect includes the capacitance measurement circuit according to the first or second aspect, so that it can stably obtain a capacitance corresponding to the load even when the load applied to the element unit is small and the capacitance is small. Furthermore, since it includes the capacitance measurement circuit according to the first or second aspect, it can accurately obtain a capacitance value in which the influence of noise is suppressed. Therefore, it can detect a small range of loads stably and with high accuracy.

[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 embodiment 1. FIGS. 8(a) and 8(b) are diagrams showing the configuration of a capacitance measurement circuit according to Reference Example 1 and a schematic diagram showing the influence of noise from ground. 9(a) and 9(b) are diagrams showing the configuration of a capacitance measurement circuit according to Modification Example 1 and a diagram schematically showing the influence of noise from ground, respectively. FIG. 10 is a diagram showing the configuration of a capacitance measurement circuit according to Embodiment 2. FIGS. 11(a) and 11(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to Embodiment 2. FIGS. 12(a) and 12(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to Embodiment 2. FIGS. 13(a) and 13(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to Embodiment 2. FIGS. 14(a) and 14(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to Embodiment 2. FIGS. 15(a) and 15(b) are diagrams showing the operation of the capacitance measurement circuit when measuring the capacitance value of a capacitance to be measured according to Embodiment 2. FIG. 16 is a flowchart showing the calculation process of the capacitance value of a capacitance to be measured according to Embodiment 2. 17A and 17B are a diagram showing the configuration of a capacitance measuring circuit and a diagram showing the influence of noise from the ground, respectively, according to Reference Example 2.18(a) and 18(b) are respectively a diagram showing the configuration of a capacitance measurement circuit according to Modification Example 2 and a diagram schematically showing the influence of noise from ground. FIG. 19 is a diagram showing the configuration of a capacitance measurement circuit according to Embodiment 3. FIG. 20 is a flowchart showing a process for calculating a capacitance value of a measured capacitance according to Embodiment 3. FIG. 21 is a diagram showing the configuration of a capacitance measurement circuit according to Reference Example 3. FIG. 22 is a diagram showing the configuration of a capacitance measurement circuit according to Modification Example 3. FIG. 23 is a diagram showing the configuration of a capacitance measurement circuit according to Embodiment 4. FIG. 24 is a flowchart showing a process for calculating a capacitance value of a measured capacitance according to Embodiment 4. FIG. 25 is a diagram showing the configuration of a capacitance measurement circuit according to Reference Example 4. FIG. 26 is a diagram showing the configuration of a capacitance measurement circuit according to Modification Example 4. FIG. 27(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. 27(b) is a perspective view schematically showing a state in which a conductor wire is installed in the structure of FIG. 27(a) according to Embodiment 5. FIG. 28( a) is a perspective view schematically showing a state in which a thread is installed in the structure of FIG. 27( b) according to the fifth embodiment. FIG. 28( b) is a perspective view schematically showing a state in which a base member is installed in the structure of FIG. 28( a) according to the fifth embodiment. FIGS. 29( a) and 29(b) are each a diagram schematically showing a cross section of a load sensor according to the fifth embodiment. FIG. 30 is a plan view schematically showing the internal configuration of a load sensor according to the fifth embodiment. FIG. 31 is a diagram showing the configuration of a load detection device according to the fifth embodiment. FIG. 32 is a diagram showing the operation of the load detection device when detecting the capacitance value of the element unit of the measurement target according to the fifth embodiment. FIG. 33 is a diagram showing the configuration of a load detection device according to a fifth modified example. FIG. 34 is a diagram showing the configuration of a load detection device according to the sixth embodiment. FIG. 35 is a diagram showing the operation of the load detection device when detecting the capacitance value of the element unit of the measurement target according to the sixth embodiment. FIG. 36 is a diagram showing the configuration of a load detection device according to the sixth modified example. FIG. 37 is a diagram showing the configuration of a load detection device according to the seventh embodiment. Fig. 38 is a diagram showing the operation of the load detection device when detecting the capacitance value of the element portion to be measured according to the seventh embodiment. Fig. 39 is a diagram showing the configuration of the load detection device according to the seventh modified example.Fig. 40 is a diagram showing the configuration of a load detection device according to embodiment 8. Fig. 41 is a diagram showing the operation of the load detection device according to embodiment 8 when detecting the capacitance value of the element portion to be measured. Fig. 42 is a diagram showing the configuration of a load detection device according to modified example 8. Figs. 43(a) and (b) are diagrams showing the configurations of capacitance measurement circuits according to modified examples 9 and 10, respectively. Figs. 44(a) and (b) are diagrams showing the configurations of capacitance measurement circuits according to modified examples 11 and 12, respectively. Figs. 45(a) and (b) are diagrams showing the configurations of capacitance measurement circuits according to modified examples 13 and 14, respectively.

[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 elements 12a, 12b, and 13 correspond to the "switching unit," "transfer unit," and "connection unit" recited in the claims, respectively. In the first and second embodiments, the switch elements 12a and 12d and the holding capacitance Ch correspond to the "noise suppression unit" recited in the claims, and in the third and fourth embodiments, the switch elements 12c and 12e and the holding capacitance Ch correspond to the "noise suppression unit" recited in the claims.

[0020] 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 inventions described in the claims to the configurations of the embodiments. Furthermore, the configurations for realizing the inventions described in the claims are not limited to the following embodiments 1 to 8.

[0021] First Embodiment FIG. 1 is a diagram showing the configuration of a capacitance measuring circuit 10 according to a first embodiment.

[0022] 1, the capacitance measurement circuit 10 includes a control unit 11, switch elements 12a to 12d, a switch element 13, a measurement unit 14, a reference capacitance Cr, and a holding capacitance Ch. 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.

[0023] The negative electrode of the holding capacitor Ch is connected to the ground 16 and is connected in parallel to the switch element 12d. The capacitance of the holding capacitor Ch is set to a value that can hold the ground potential and that prevents noise from the ground 16 from affecting the negative electrode of the measurement unit 14. The holding capacitor Ch may be adjusted to absorb noise from the ground 16 and prevent it from propagating to the measurement capacitor Cs and the reference capacitor Cr.

[0024] The control unit 11 is configured with a microcomputer, FPGA, or the like, and controls the switch elements 12a to 12d 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 .

[0025] 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. Furthermore, when the switch element 12a is set to the non-conductive state, noise from the power supply 15 (power supply voltage Vdd) is prevented from propagating to the measurement capacitance Cs and the reference capacitance Cr.

[0026] 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.

[0027] The switch element 12c, together with the switch element 12d, switches between a connected state and a disconnected state between the positive electrode of the capacitance Cs to be measured and the ground 16. When the switch elements 12c and 12d change from a non-conductive state to a conductive state, the positive electrode of the capacitance Cs to be measured is connected to the ground 16, and the charge accumulated in the capacitance Cs to be measured is discharged to the ground 16.

[0028] 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 elements 12c and 12d are configured by N-type FETs and become conductive when a high-level gate signal is applied to their gates. The switch elements 12a to 12d may be switch elements of a type other than FETs.

[0029] The switch element 13 connects the negative electrode of the capacitance Cs to ground 16 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, these electrodes have the same potential, so that the capacitance Cs is in a state where it disappears (is disabled) in terms of the circuit.

[0030] 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 the ground 16, 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.

[0031] 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.

[0032] 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).

[0033] 2(a) to 6(b), the switch elements 12a to 12d 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.

[0034] 2A, with switch element 13 connected to ground 16, 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 16, causing discharge of measurement capacitance Cs. At this time, discharge of holding capacitance Ch also occurs. Switch element 12a remains conductive 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 with a measurement unit separate from measurement unit 14 and determining whether the measurement result reaches power supply voltage Vdd and stabilizes.

[0035] Next, as shown in Fig. 2(b), 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. 3(a), the switch element 12c is switched to a non-conductive state, disconnecting the positive electrode of the measurement capacitance Cs from ground 16. Then, as shown in Fig. 3(b), 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.

[0036] 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.

[0037] After the voltage value has stabilized, as shown in FIG. 4A , the switch element 12d is set to a non-conductive state, disconnecting the positive electrode of the holding capacitance Ch and the negative electrode of the measurement unit 14 from the ground 16. In this state, 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 primarily by 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, the switch elements 12b and 13, and the like. 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.

[0038] To avoid this, in this embodiment, an operation for suppressing errors due to parasitic capacitance is further performed.

[0039] That is, as shown in FIG. 4B, switch element 13 is switched to the positive electrode side of the capacitance Cs to be measured. Next, as shown in FIG. 5A, switch elements 12a, 12c, and 12d are each switched to a conductive state. As a result, power supply voltage Vdd is applied to reference capacitance Cr, and charge is accumulated in reference capacitance Cr. In addition, the positive electrode of measurement capacitance Cs is connected to ground 16, and the measurement capacitance Cs is discharged. At this time, the holding capacitance Ch is also discharged. Switch element 12a is set to a conductive state at least until reference capacitance Cr is fully charged.

[0040] 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.

[0041] 5A, since the switch element 13 is connected to the positive electrode side of the capacitance Cs to be measured, not only the charge stored in the capacitance Cs to be measured but also the charge stored 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 discharged to the ground 16. This makes it possible to more reliably eliminate the influence of the parasitic capacitance.

[0042] Thereafter, as shown in Fig. 5(b), 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 the ground 16. Then, as shown in Fig. 6(a), 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.

[0043] 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.

[0044] After the voltage value has stabilized, as shown in FIG. 6B, the switch element 12d is set to a non-conductive state, and the positive electrode of the holding capacitor Ch and the negative electrode of the measurement unit 14 are disconnected from the ground 16. In this state, the voltage value measured by the measurement unit 14 is acquired as the second voltage value Vx2. The capacitance value of the measurement capacitor Cs is then calculated from the acquired second voltage value Vx2 and the first voltage value Vx1 acquired during the operation shown in FIG.

[0045] The capacitance value of the measurement capacitance Cs is calculated as follows.

[0046] 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.

[0047] 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:

[0048] Qr=(Cr+Cs1)×Vx1 (2) Therefore, the following relational expression can be derived from the expressions (1) and (2).

[0049]

[0050] 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.

[0051]

[0052] 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).

[0053] 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:

[0054]

[0055] 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).

[0056] FIG. 7 is a flowchart showing the process of calculating the capacitance value of the measurement capacitance Cs through the operations shown in FIGS.

[0057] 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.

[0058] First, as shown in Fig. 2(a), the control unit 11 connects the negative electrode of the measurement capacitance Cs to ground 16 (S101), and then charges the reference capacitance Cr and discharges the measurement capacitance Cs and the holding capacitance Ch (S102). After the charging of the reference capacitance Cr is completed, 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 16 (S103), as shown in Fig. 2(b) and Fig. 3(a). Then, as shown in Fig. 3(b), 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 that, after a period of time has passed until the measurement value of the measurement unit 14 becomes stable (saturated), the control unit 11 acquires the measurement value of the measurement unit 14 as the first voltage value Vx1 with the positive electrode of the storage capacitor Ch disconnected from the ground 16, as shown in Fig. 4(a) (S105). In this way, the first control C1 ends.

[0059] 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 and the holding capacitance Ch (S107), as shown in Fig. 5(a). After the charging of the reference capacitance Cr is completed, 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 16 (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 that, 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 with the positive electrode of the storage capacitor Ch disconnected from the ground 16, as shown in Fig. 6(b) (S110). In this way, the second control C2 ends.

[0060] 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. 7.

[0061] 4A and 6B, the measurement unit 14 only needs to measure the stable (saturated) voltage values ​​(first voltage value Vx1, second voltage value Vx2) after the charge is transferred from the reference capacitance Cr. This allows stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, after the charge is transferred, the voltage value of the target capacitance Cs is acquired in a state where the switch elements 12a and 12d are non-conductive, i.e., in a state where the inflow of noise from the ground 16 and the power supply 15 to the measurement unit 14 is suppressed. Therefore, the influence of this noise on the measurement results of the voltage value can be suppressed. Therefore, the capacitance value of the target capacitance Cs can be measured with high accuracy.

[0062] As shown in FIG. 1, the capacitance measurement circuit 10 includes a switch element 13 (connection unit) that connects the negative electrode of the capacitance Cs to ground 16 or a wiring having the same potential as the positive electrode of the capacitance Cs, and as shown in FIG. 7, the control unit 11 controls the switch element 13 to execute a first control C1 and a second control C2 when measuring the capacitance value of the capacitance Cs.

[0063] According to this configuration, in the second control C2, step S106 connects the negative electrode of the measurement capacitance Cs to the positive electrode (a wiring having the same potential as the positive electrode). 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, step S101 connects the negative electrode of the measurement capacitance Cs to ground 16. 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 of the measurement capacitance Cs from these two voltage values, a capacitance value unaffected by parasitic capacitance can be calculated. This allows the capacitance value of the measurement capacitance Cs to be measured with high accuracy.

[0064] As shown in FIG. 1, the capacitance measurement circuit 10 includes a holding capacitor Ch whose negative electrode is connected to ground 16, and the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitor Cs and the positive electrode of the holding capacitor Ch.

[0065] With this configuration, the holding capacitance Ch can suppress the inflow of noise from the ground 16 into the measurement unit 14. Furthermore, because the potential of the negative electrode of the measurement unit 14 is held at ground level by the holding capacitance Ch, the voltage of the measurement capacitance Cs can be measured stably. Therefore, the capacitance value of the measurement capacitance Cs can be measured with high accuracy.

[0066] 7, the control unit 11 calculates the capacitance value of the measurement capacitance Cs using the first voltage value Vx1 acquired by the first control C1, the second voltage value Vx2 acquired by the second control C2, the power supply voltage Vdd applied to the reference capacitance Cr, and the capacitance value of the reference capacitance Cr, using the above formula (5). As a result, as described above, the influence of error components due to parasitic capacitance on the capacitance value of the measurement capacitance Cs can be suppressed, and the capacitance value of the measurement capacitance Cs can be acquired with high accuracy.

[0067] 8(a), the switch element 12d and the holding capacitance Ch are omitted from the configuration of FIG. 1, and the negative electrode of the measurement unit 14 is directly connected to the ground 16. Therefore, as shown in FIG. 8(b), if noise is generated from the ground 16 when measuring the voltage of the measurement capacitance Cs, this noise propagates to the measurement unit 14, the measurement capacitance Cs, and the reference capacitance Cr. Therefore, in the configuration of Reference Example 1, this noise may prevent the first voltage value Vx1 and the second voltage value Vx2 from being stably acquired from the measurement capacitance Cs, and the capacitance value of the measurement capacitance Cs may not be measured accurately.

[0068] 1 according to the first embodiment, the capacitance measurement circuit 10 is provided with the switch element 12d and the holding capacitor Ch (noise suppression unit), which at least suppresses noise from the ground 16 from propagating to the measurement unit 14. Furthermore, the noise is absorbed by the holding capacitor Ch, thereby suppressing the influence of the noise on the measurement capacitor Cs and the reference capacitor Cr. Therefore, the configuration of the first embodiment allows the capacitance value of the measurement capacitor Cs to be measured with high accuracy.

[0069] <Modification 1> FIG. 9A is a diagram showing the configuration of a capacitance measuring circuit 10 according to Modification 1.

[0070] 1 , in the first modification, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the positive electrode of the storage capacitance Ch. That is, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the ground 16 via the storage capacitance Ch. The measurement process for the measurement capacitance Cs is performed in the same manner as in FIG. 7 .

[0071] 9B , when measuring the voltage of the measurement capacitance Cs, it is possible to more reliably prevent noise from the ground 16 from propagating to the measurement capacitance Cs and the reference capacitance Cr. Therefore, the capacitance value of the measurement capacitance Cs can be measured more accurately.

[0072] 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.

[0073] FIG. 10 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the second embodiment.

[0074] 10, 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 12d, the switch element 12b can be changed to an N-type FET. The configurations and functions of the switch elements 12a, 12c, and 12d are the same as in the first embodiment.

[0075] 11A to 15B are diagrams showing the operation of the capacitance measurement circuit 10 when measuring the capacitance value of the target capacitance Cs. Fig. 16 is a flowchart showing the processing of the control unit 11 when measuring the capacitance value of the target capacitance Cs.

[0076] First, as shown in Fig. 11(a), the control unit 11 connects the negative electrode of the capacitance Cs to ground 16 (S201), sets the switch elements 12a, 12c, and 12d to a conductive state, and charges the capacitance Cs and discharges the reference capacitance Cr and the storage capacitance Ch (S202). Then, as shown in Fig. 11(b), the control unit 11 disconnects the positive electrode of the reference capacitance Cr from ground 16. After the capacitance Cs is fully charged, the control unit 11 disconnects the positive electrode of the capacitance Cs from the power supply 15 (power supply voltage Vdd) (S203), as shown in Fig. 12(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.

[0077] Next, as shown in Fig. 12(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. 13(a), acquires the measurement value of the measurement unit 14 as a first voltage value Vx1 with the positive electrode of the storage capacitance Ch disconnected from ground 16 (S205). This completes the first control C1.

[0078] 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. 13(b).Then, the control unit 11 switches the switch elements 12b, 12c, and 12d to the conductive state, as shown in Fig. 14(a), to discharge the reference capacitance Cr, the measurement capacitance Cs, and the holding capacitance Ch (S207).

[0079] Thereafter, 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 as shown in FIG. 14(b) 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.

[0080] 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). Then, as shown in FIG. 15A, 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 disconnects the positive electrode of the storage capacitance Ch from ground 16, as shown in FIG. 15B, and acquires the measurement value of the measurement unit 14 as the second voltage value Vx2 (S211). This completes the second control C2.

[0081] Then, 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 acquired in the first control C1 and the second control C2, respectively (S212).

[0082] The capacitance value of the measurement capacitance Cs is calculated as follows.

[0083] First, as shown in FIG. 11A, 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.

[0084] Qs=Cs1×Vdd (6) Furthermore, in the state where the charge transfer is completed as shown in FIG. 2B, the following relationship holds when the capacitance value of the reference capacitance Cr is Cr.

[0085] Qs=(Cr+Cs1)×Vx1 (7) Therefore, the following relational expression can be derived from the expressions (6) and (7).

[0086]

[0087] 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. 15(b).

[0088]

[0089] 14(a) to 15(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).

[0090] The capacitance value Cs of the measured capacitance Cs is obtained by subtracting the error component Ce from the capacitance value Cs of equation (8), and is calculated from the above equations (8) and (9) using the following equation:

[0091]

[0092] In equation (10), 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 13(a) and 15(b). Therefore, the capacitance value of the measured capacitance Cs can be calculated from equation (10) above.

[0093] 13( a) and 15(b), since the measurement unit 14 only needs to measure stable (saturated) voltage values ​​(first voltage value Vx1, second voltage value Vx2) after the charge transfer, it is possible to stably measure capacitance values ​​over a small range without using a high-precision AD converter. Furthermore, after the charge transfer, the voltage value of the target capacitance Cs is acquired in a state where the switch elements 12a and 12d are set to a non-conductive state, i.e., in a state where the inflow of noise from the ground 16 and the power supply 15 to the measurement unit 14 is suppressed. This prevents these noises from affecting the measurement results of the voltage value. Therefore, the capacitance value of the target capacitance Cs can be measured with high accuracy.

[0094] As shown in FIG. 16 , first control C1 and second control C2 are executed to measure the capacitance value of the target capacitance Cs. In the second control C2, step S206 connects the negative electrode of the target capacitance Cs to the positive electrode (a wiring having the same potential as the positive electrode). Therefore, the measured second voltage value Vx2 is largely unaffected by the target capacitance Cs, and is primarily affected by the reference capacitance Cr and parasitic capacitance. In contrast, in the first control C1, step S201 connects the negative electrode of the target capacitance Cs to ground 16. Therefore, the measured first voltage value Vx1 is affected by the target capacitance Cs as well as the reference capacitance Cr and parasitic capacitance. Therefore, by calculating the capacitance value of the target capacitance Cs from these two voltage values, a capacitance value unaffected by parasitic capacitance can be calculated. This allows the capacitance value of the target capacitance Cs to be measured accurately.

[0095] As shown in FIG. 10, the capacitance measurement circuit 10 includes a holding capacitor Ch whose negative electrode is connected to ground 16, and the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitor Cs and the positive electrode of the holding capacitor Ch.

[0096] With this configuration, the holding capacitance Ch can suppress the inflow of noise from the ground 16 into the measurement unit 14. Furthermore, because the potential of the negative electrode of the measurement unit 14 is held at ground level by the holding capacitance Ch, the voltage of the measurement capacitance Cs can be measured stably. Therefore, the capacitance value of the measurement capacitance Cs can be measured with high accuracy.

[0097] 16 , the control unit 11 calculates the capacitance value of the measurement capacitance Cs using the first voltage value Vx1 acquired by the first control C1, the second voltage value Vx2 acquired by the second control C2, the power supply voltage Vdd applied to the measurement capacitance Cs, and the capacitance value of the reference capacitance Cr, using the above formula (10). As a result, as described above, the influence of error components due to parasitic capacitance on the capacitance value of the measurement capacitance Cs can be suppressed, and the capacitance value of the measurement capacitance Cs can be acquired with high accuracy.

[0098] 17(a), the switch element 12d and the holding capacitance Ch are omitted from the configuration of FIG. 10, and the negative electrode of the measurement unit 14 is directly connected to the ground 16. Therefore, as shown in FIG. 17(b), if noise is generated from the ground 16 when measuring the voltage of the measurement capacitance Cs, this noise propagates to the measurement unit 14, the measurement capacitance Cs, and the reference capacitance Cr. Therefore, in the configuration of Reference Example 2, this noise may prevent the first voltage value Vx1 and the second voltage value Vx2 from being stably acquired from the measurement capacitance Cs, and the capacitance value of the measurement capacitance Cs may not be measured accurately.

[0099] 10 according to the second embodiment, the capacitance measurement circuit 10 is provided with the switch element 12d and the holding capacitor Ch (noise suppression unit), which at least suppresses the propagation of noise from the ground 16 to the measurement unit 14. Furthermore, the noise is absorbed by the holding capacitor Ch, thereby suppressing the influence of the noise on the measurement capacitor Cs and the reference capacitor Cr. Therefore, the configuration of the second embodiment allows the capacitance value of the measurement capacitor Cs to be measured with high accuracy.

[0100] <Modification 2> FIG. 18A is a diagram showing the configuration of the capacitance measuring circuit 10 according to Modification 2.

[0101] 10 , in the second modification, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the positive electrode of the storage capacitance Ch. That is, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the ground 16 via the storage capacitance Ch. The measurement process for the measurement capacitance Cs is performed in the same manner as in FIG. 16 .

[0102] 18B , when measuring the voltage of the measurement capacitance Cs, it is possible to more reliably prevent noise from the ground 16 from propagating to the measurement capacitance Cs and the reference capacitance Cr. Therefore, the capacitance value of the measurement capacitance Cs can be measured more accurately.

[0103] In the first embodiment, the capacitance value of the capacitance Cs is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the ground 16 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 15 (power supply voltage Vdd) by the measuring unit 14.

[0104] FIG. 19 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the third embodiment.

[0105] 1, switch element 12d is omitted from Fig. 1, and switch element 12e is arranged between power supply 15 and switch element 12a. Switch element 12e is configured by a P-type FET, and is turned on when a low-level gate signal is applied to its gate. In addition, a holding capacitance Ch is arranged in parallel with switch element 12e, and the voltage between the negative electrode of holding capacitance Ch and the positive electrode of measurement capacitance Cs is measured by measurement unit 14.

[0106] FIG. 20 is a flowchart showing a process for calculating the capacitance value of the measurement capacitance Cs according to the third embodiment.

[0107] The flowchart in Fig. 20 is similar to the flowchart in Fig. 7 in that the charge stored in the reference capacitance Cr is transferred to the measurement capacitance Cs and then the voltage of the measurement capacitance Cs is measured. However, in the flowchart in Fig. 20, when measuring the voltage of the measurement capacitance Cs, the switch element 12e is set to a non-conductive state, and the positive electrode of the storage capacitance Ch is disconnected from the power supply 15 (power supply voltage Vdd).

[0108] The control unit 11 controls the switch element 13 to connect the negative electrode of the measurement capacitance Cs to the ground 16 (S121), and executes charging of the reference capacitance Cr and discharging of the measurement capacitance Cs (S122). At this time, the switch elements 12a, 12c, and 12e are set to the conductive state, and the switch element 12b is set to the non-conductive state.

[0109] When charging of the reference capacitance Cr is completed, the control unit 11 sets the switch elements 12a to 12c to a non-conductive state, disconnecting 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 16 (S123). The control unit 11 then switches the switch element 12b to a conductive state, connecting the positive electrode of the reference capacitance Cr to the positive electrode of the measurement capacitance Cs and transferring the charge of the reference capacitance Cr to the measurement capacitance Cs (S124). After a period of time has passed until the measurement value of the measurement unit 14 stabilizes (saturates), the control unit 11 switches the switch element 12e to a non-conductive state, disconnecting the negative electrode of the storage capacitance Ch from the power supply 15 (power supply voltage), and acquiring the measurement value of the measurement unit 14 as the first voltage value Vx1 (S125). This completes the first control C1.

[0110] Next, the control unit 11 controls the switch element 13 to connect the negative electrode of the measurement capacitance Cs to the positive electrode of the measurement capacitance Cs (S126). Similar to step S122, the control unit 11 then charges the reference capacitance Cr and discharges the measurement capacitance Cs (S127). After the charging of the reference capacitance Cr is completed, 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 16 (S128), similar to step S123. Then, similar to step S124, 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 (S129). After a period of time has elapsed until the measurement value of the measurement unit 14 stabilizes (saturates), the control unit 11 disconnects the negative electrode of the storage capacitance Ch from the power supply 15 (power supply voltage) and acquires the measurement value of the measurement unit 14 as the second voltage value Vx2 (S110), similar to step S125. Thus, the second control C2 ends.

[0111] Then, 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 acquired in the first control C1 and the second control C2, respectively (S131).

[0112] The capacitance value of the measurement capacitance Cs is calculated using the following formula.

[0113]

[0114] According to this equation (11), the error component due to the parasitic capacitance is cancelled out from the capacitance value of the measurement capacitance Cs. Then, the control unit 11 ends the processing of FIG.

[0115] <Effects of Embodiment 3> As shown in FIG. 19 , the capacitance measurement circuit 10 includes, as a noise suppression unit, a holding capacitor Ch whose positive electrode is connected to a power supply 15 and a switch element 12 e, and the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitor Cs and the negative electrode of the holding capacitor Ch.

[0116] With this configuration, the holding capacitance Ch can suppress the inflow of noise from the power supply 15 into the measurement unit 14. Furthermore, the holding capacitance Ch maintains the potential of the positive electrode of the measurement unit 14 at the level of the power supply voltage Vdd, allowing the voltage of the measurement capacitance Cs to be measured stably. Therefore, the capacitance value of the measurement capacitance Cs can be measured with high accuracy.

[0117] 20 , the control unit 11 calculates the capacitance value of the measurement capacitance Cs using the first voltage value Vx1 acquired by the first control C1, the second voltage value Vx2 acquired by the second control C2, the power supply voltage Vdd applied to the measurement capacitance Cs, and the capacitance value of the reference capacitance Cr, using the above formula (11). As a result, similar to the first embodiment, the influence of error components due to parasitic capacitance on the capacitance value of the measurement capacitance Cs can be suppressed, and the capacitance value of the measurement capacitance Cs can be accurately acquired.

[0118] 21 (Reference Example 3) does not include the switch element 12e and the holding capacitance Ch in the configuration of FIG. 19, and the positive electrode of the measurement unit 14 is directly connected to the power supply 15. Therefore, as shown in FIG. 21, if noise is generated from the power supply 15 when measuring the voltage of the capacitance Cs to be measured, this noise propagates to the measurement unit 14. Therefore, in the configuration of Reference Example 3, this noise may prevent the first voltage value Vx1 and the second voltage value Vx2 from being stably acquired from the capacitance Cs to be measured, and the capacitance value of the capacitance Cs to be measured may not be measured accurately.

[0119] 19 according to the third embodiment, the switch element 12e and the holding capacitor Ch (noise suppression unit) are provided in the capacitance measurement circuit 10, which at least suppresses noise from the power supply 15 from propagating to the measurement unit 14. Therefore, according to the configuration of the third embodiment, the capacitance value of the measurement capacitor Cs can be measured with high accuracy.

[0120] In the configuration of Reference Example 3, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are directly connected to ground 16, and therefore noise from ground 16 can propagate to the measurement capacitance Cs and the reference capacitance Cr, similar to Reference Example 1 in Fig. 8(a) . Therefore, in the configuration of Reference Example 3, this noise can also prevent the capacitance value of the measurement capacitance Cs from being measured accurately.

[0121] <Modification 3> FIG. 22 is a diagram showing the configuration of the capacitance measuring circuit 10 according to Modification 3.

[0122] 19 , in the third modification, similar to the first embodiment, a switch element 12d and another holding capacitance Ch' are provided as a noise suppression unit for suppressing noise from ground 16, and the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the positive electrode of the holding capacitance Ch'. That is, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to ground 16 via the holding capacitance Ch'. The measurement process for the measurement capacitance Cs is performed in the same manner as in FIG. 20 .

[0123] Effect of Modification 3 According to the configuration of Modification 3, the negative electrodes of the reference capacitance Cr and the measurement capacitance Cs are connected to ground 16 via another holding capacitance Ch'. Therefore, when measuring the voltage of the measurement capacitance Cs, propagation of noise from ground 16 to the measurement capacitance Cs and the reference capacitance Cr can be more reliably suppressed than with the other holding capacitance Ch'. Therefore, the capacitance value of the measurement capacitance Cs can be measured with higher accuracy.

[0124] In the second embodiment, the capacitance value of the capacitance Cs is calculated by acquiring the voltage between the positive electrode of the capacitance Cs to be measured and the ground 16 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 15 (power supply voltage Vdd) by the measuring unit 14.

[0125] FIG. 23 is a diagram showing the configuration of a capacitance measuring circuit 10 according to the fourth embodiment.

[0126] 23, compared to FIG. 10, switch element 12d is omitted, and switch element 12e is arranged between power supply 15 and switch element 12a. Switch element 12e is configured by a P-type FET, and is turned on when a low-level gate signal is applied to its gate. In addition, a holding capacitance Ch is arranged in parallel with switch element 12e, and the voltage between the negative electrode of holding capacitance Ch and the positive electrode of measurement capacitance Cs is measured by measurement unit 14.

[0127] FIG. 24 is a flowchart showing a process for calculating the capacitance value of the measurement capacitance Cs according to the fourth embodiment.

[0128] The flowchart in Fig. 24 is similar to the flowchart in Fig. 16 in that the voltage of the measurement capacitance Cs is measured after the charge stored in the measurement capacitance Cs is transferred to the reference capacitance Cr. However, in the flowchart in Fig. 24, when the voltage of the measurement capacitance Cs is measured, the switch element 12e is set to a non-conductive state, and the positive electrode of the storage capacitance Ch is disconnected from the power supply 15 (power supply voltage Vdd).

[0129] The control unit 11 controls the switch 13 to connect the negative electrode of the capacitance Cs to ground 16 (S221), and then sets the switch elements 12a, 12c, and 12e to a conductive state to charge the capacitance Cs and discharge the reference capacitance Cr (S222). The control unit 11 then sets the switch element 12c to a non-conductive state to disconnect the positive electrode of the reference capacitance Cr from ground 16. After the capacitance Cs is fully charged, the control unit 11 sets the switch elements 12a and 12b to a non-conductive state to disconnect the positive electrode of the capacitance Cs from the power supply 15 (power supply voltage Vdd) (S223). 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.

[0130] Next, the control unit 11 switches the switch element 12b to the conductive state to transfer the charge of the measurement capacitance Cs to the reference capacitance Cr (S224). The control unit 11 waits for a period until this transfer is completed, and then sets the switch element 12e to the non-conductive state to disconnect the negative electrode of the storage capacitance Ch from the power supply 15, and acquires the measurement value of the measurement unit 14 as the first voltage value Vx1 (S225). This completes the first control C1.

[0131] Next, the control unit 11 switches the switch element 13 to the positive electrode side of the measurement capacitance Cs, connecting the positive electrode and negative electrode of the measurement capacitance Cs (S226), and then switches the switch elements 12b and 12c to the conductive state, thereby discharging the reference capacitance Cr and the measurement capacitance Cs (S227).

[0132] Thereafter, the control unit 11 switches the switch elements 12b and 12c to the non-conductive state, and further switches the switch elements 12a and 12e to the conductive state, thereby connecting the positive electrode of the capacitance Cs to the power supply voltage Vdd (S228). Here, since the positive electrode and negative electrode of the capacitance Cs are connected, the capacitance Cs is not charged, and the parasitic capacitance other than the capacitance Cs is charged.

[0133] 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 (S229), and then 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 (S230). This transfers the charge accumulated in the parasitic capacitance to the reference capacitance Cr. After the charge transfer, the control unit 11 disconnects the positive electrode of the storage capacitance Ch from ground 16, and acquires the measurement value of the measurement unit 14 as a second voltage value Vx2 (S231). This completes the second control C2.

[0134] Then, 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 acquired in the first control C1 and the second control C2, respectively (S232).

[0135] The capacitance value of the measurement capacitance Cs is calculated using the following formula.

[0136]

[0137] According to this equation (12), the error component due to the parasitic capacitance is cancelled out from the capacitance value of the measurement capacitance Cs. Then, the control unit 11 ends the processing of FIG.

[0138] <Effects of Embodiment 4> As shown in FIG. 23 , the capacitance measurement circuit 10 includes, as a noise suppression unit, a holding capacitor Ch whose positive electrode is connected to a power supply 15 and a switch element 12 e, and the measurement unit 14 measures the voltage between the positive electrode of the measurement capacitor Cs and the negative electrode of the holding capacitor Ch.

[0139] With this configuration, the holding capacitance Ch can suppress the inflow of noise from the power supply 15 into the measurement unit 14. Furthermore, the holding capacitance Ch maintains the potential of the positive electrode of the measurement unit 14 at the level of the power supply voltage Vdd, allowing the voltage of the measurement capacitance Cs to be measured stably. Therefore, the capacitance value of the measurement capacitance Cs can be measured with high accuracy.

[0140] 24 , the control unit 11 calculates the capacitance value of the capacitance to be measured Cs using the first voltage value Vx1 acquired by the first control method C1, the second voltage value Vx2 acquired by the second control method C2, the power supply voltage Vdd applied to the capacitance to be measured Cs, and the capacitance value of the reference capacitance Cr, using the above formula (12). As a result, as in the second embodiment, the influence of error components due to parasitic capacitance on the capacitance value of the capacitance to be measured Cs can be suppressed, and the capacitance value of the capacitance to be measured Cs can be acquired with high accuracy.

[0141] 25 (Reference Example 4) does not include the switch element 12e and the holding capacitance Ch in the configuration of FIG. 23, and the positive electrode of the measurement unit 14 is directly connected to the power supply 15. Therefore, if noise is generated from the power supply 15 when measuring the voltage of the capacitance Cs to be measured, the noise propagates to the measurement unit 14, as shown in FIG. 25. Therefore, in the configuration of Reference Example 5, the noise may prevent the first voltage value Vx1 and the second voltage value Vx2 from being stably acquired from the capacitance Cs to be measured, and the capacitance value of the capacitance Cs to be measured may not be measured accurately.

[0142] 23 according to the fourth embodiment, the switch element 12e and the holding capacitor Ch (noise suppression unit) are provided in the capacitance measurement circuit 10, which at least suppresses noise from the power supply 15 from propagating to the measurement unit 14. Therefore, the configuration of the fourth embodiment allows the capacitance value of the measurement capacitor Cs to be measured with high accuracy.

[0143] In the configuration of Reference Example 4, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are directly connected to ground 16, and therefore noise from ground 16 can propagate to the measurement capacitance Cs and the reference capacitance Cr, similar to Reference Example 2 in Fig. 17(a) . Therefore, in the configuration of Reference Example 4, this noise can also prevent the capacitance value of the measurement capacitance Cs from being measured accurately.

[0144] <Modification 4> FIG. 26 is a diagram showing the configuration of the capacitance measuring circuit 10 according to Modification 4.

[0145] 23 , in the fourth modification, similar to the second embodiment, a switch element 12d and another holding capacitance Ch' are arranged as a noise suppression unit for suppressing noise from ground 16, and the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to the positive electrode of the holding capacitance Ch'. That is, the negative electrodes of the measurement capacitance Cs and the reference capacitance Cr are connected to ground 16 via the holding capacitance Ch'. The measurement process for the measurement capacitance Cs is performed in the same manner as in FIG. 20 .

[0146] 16 , the capacitance measurement circuit 10 includes another holding capacitor Ch', and the negative electrodes of the reference capacitor Cr and the measurement capacitor Cs are connected to ground 16 via the other holding capacitor Ch'. Therefore, when measuring the voltage of the measurement capacitor Cs, the propagation of noise from ground 16 to the measurement capacitor Cs and the reference capacitor Cr can be more reliably suppressed than with the other holding capacitor Ch'. Therefore, the capacitance value of the measurement capacitor Cs can be measured more accurately.

[0147] 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.

[0148] First, the configuration of the load sensor 20 will be described with reference to Figures 27(a) to 30. For convenience, mutually orthogonal X, Y, and Z axes are indicated in Figures 27(a) to 30. The Z axis direction is the thickness direction of the load sensor 20.

[0149] FIG. 27( a ) is a perspective view that schematically shows the base member 21 and the 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 .

[0150] 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.

[0151] 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.

[0152] 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. 27( 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.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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).

[0158] FIG. 27(b) is a perspective view that schematically shows a state in which the conductor wire 23 is installed in the structure of FIG. 27(a).

[0159] The conductor wires 23 are linear members and are arranged overlapping on the upper surfaces of the conductive elastic bodies 22 shown in Fig. 27(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.

[0160] 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.

[0161] FIG. 28(a) is a perspective view that schematically shows a state in which the thread 24 is installed in the structure of FIG. 27(b).

[0162] After the conductor wires 23 are arranged as shown in Fig. 27(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. 28(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.

[0163] FIG. 28(b) is a perspective view that schematically shows a state in which a base member 25 is installed on the structure of FIG. 28(a).

[0164] A base member 25 is placed from above (the positive side of the Z axis) the structure shown in FIG. 28( 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.

[0165] 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. 28(b). The load sensor 20 can be used in a state where it is turned upside down from the state shown in Fig. 28(b).

[0166] 29(a) and 29(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. 29(a) shows the cross section when no load is applied, and Fig. 29(b) shows the cross section when a load is applied.

[0167] 29(a) and 29(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.

[0168] 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.

[0169] 29( 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. 29( b), the conductive elastic body 22 and the base member 21 are deformed by the conductor wire 23.

[0170] 29(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 causes a change in 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.

[0171] Fig. 30 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. 30.

[0172] 30 , 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.

[0173] 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. 29(a) and 29(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. 29(a) and 29(b)) included in the conductor wire 23 corresponds to the dielectric that defines the capacitance in the load sensor 20 (capacitive load sensor).

[0174] 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.

[0175] 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.

[0176] FIG. 31 is a diagram showing the configuration of a load detection device 1 according to the fifth embodiment.

[0177] For convenience, FIG. 31 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.

[0178] The load detection device 1 includes the capacitance measurement circuit 10 according to the first embodiment and the load sensor 20 shown in Fig. 28(b). Here, the nine element units A11 to A33 shown in Fig. 30 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.

[0179] 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. 30. The element selection unit 17 includes switch elements 17a to 17c, and the element selection unit 18 includes switch elements 18a to 18d.

[0180] 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.

[0181] 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. 31 , 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. 31 to equalize the potential of the potential line L2 with the potential of the potential line L1.

[0182] 31 shows the states of the switch elements 17a-17c and 18a-18d under the first control C1 when measuring the capacitance value of the element unit A11. In this state, the conductor wires 23 (positive poles) of the topmost element units A11-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.

[0183] In this state, the control unit 11 executes the first control C1 in FIG. 7 to obtain the first voltage value Vx1. Next, in step S106 of the second control C2 in FIG. 7, the control unit 11 switches the switch element 17a to the potential line L2 side as shown in FIG. 32, and executes the processes of steps S107 to S110. As a result, the control unit 11 obtains the second voltage value Vx2. Then, the control unit 11 executes the process of step S111 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.

[0184] 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 S101 of the first control C1 in FIG. 7. The control unit 11 also maintains the switch elements 18a to 18d in the state shown in FIG. 31. In this state, the control unit 11 executes the processing from step S102 onward in FIG. 7. In step S106, the switch element 17b is switched to the potential line L2 side, and the processing from step S107 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.

[0185] Effect of Embodiment 5 The load detection device 1 according to embodiment 5 includes the capacitance measurement circuit 10 according to embodiment 1, and therefore can stably obtain a capacitance value corresponding to the load even when the load applied to the element units A11 to A33 is small and the capacitance is small. Furthermore, since the load detection device 1 includes the capacitance measurement circuit 10 according to embodiment 1, it can accurately obtain a capacitance value in which the effects of noise from the power supply 15 and ground 16 and the effects of parasitic capacitance are suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0186] The load sensor 20 includes a plurality of element units A11 to A33, and the capacitance measurement circuit 10 includes element selection units 17 and 18 for switching between the element units to be measured. This allows load detection over a wide range where the plurality of element units A11 to A33 are arranged. By switching between the element units to be measured using the element selection units 17 and 18, the capacitance value of each element unit can be measured stably and accurately using processing similar to that shown in FIG.

[0187] 31, the parasitic capacitance increases because more switch elements 17a to 17c, 18a to 18d and wiring are arranged, and furthermore, the equipotential generator 19 is arranged, compared to the configuration of Fig. 1. However, even in this case, the effect of the parasitic capacitance is suppressed by the above formula (5), so that the capacitance value of each element can be calculated with high accuracy, and the load applied to each element can be detected with high accuracy.

[0188] <Modification 5> FIG. 33 is a diagram showing the configuration of the load detection device 1 according to Modification 5.

[0189] 33, the configuration of the capacitance measurement circuit 10 in the configuration of FIG. 31 is replaced with the configuration of FIG. 9A according to Modification Example 1. The other configurations and the process of detecting the capacitance of each element unit are the same as those in the fifth embodiment.

[0190] According to the configuration of the fifth modification, the negative electrodes of the reference capacitance Cr and the element unit (measurement capacitance Cs), as well as the negative electrode of the measurement unit 14, are connected to the positive electrode of the holding capacitance Ch, which further suppresses noise from the ground 16 from propagating to the reference capacitance Cr and the element unit (measurement capacitance Cs) when measuring the voltage of the element unit (measurement capacitance Cs). This allows for more accurate detection of the load applied to each element unit.

[0191] 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.

[0192] FIG. 34 is a diagram showing the configuration of a load detection device 1 according to the sixth embodiment.

[0193] As in FIG. 31, for convenience, FIG. 34 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 linearly.

[0194] The load detection device 1 includes the capacitance measurement circuit 10 according to the second embodiment and the load sensor 20 shown in Fig. 28(b). As in the fifth embodiment, the nine element units A11 to A33 shown in Fig. 30 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.

[0195] The configurations of switch elements 17a to 17c and switch elements 18a to 18d are the same as in Fig. 31. Also, as in Fig. 31, an equipotential generator 19 is provided to equalize the potential of potential line L2 with the potential of potential line L1.

[0196] 31, Fig. 34 shows the states of the switch elements 17a to 17c and 18a to 18d under the first control C1 when measuring the capacitance value of the element unit A11. In this case, as in Fig. 31, only the element unit A11 to be measured is connected to the capacitance measurement circuit 10.

[0197] In this state, the control unit 11 executes the first control C1 in FIG. 16 to obtain the first voltage value Vx1. Next, in step S206 of the second control C2 in FIG. 16, the control unit 11 switches the switch element 17a to the potential line L2 side as shown in FIG. 35, 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.

[0198] 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. 16. The control unit 11 also maintains the switch elements 18a to 18d in the state shown in FIG. 26. In this state, the control unit 11 executes the processing from step S202 onward in FIG. 16. 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.

[0199] Effect of Embodiment 6 The load detection device 1 according to Embodiment 6 includes the capacitance measurement circuit 10 according to Embodiment 2, so that it can stably obtain capacitance values ​​corresponding to the load even when the load applied to the element units A11 to A33 is small and the capacitance is small. Furthermore, since it includes the capacitance measurement circuit 10 according to Embodiment 2, it can accurately obtain capacitance values ​​in which the effects of noise from the power supply 15 and ground 16 and the effects of parasitic capacitance are suppressed. Therefore, it is possible to stably and accurately detect loads over a small range. Furthermore, by switching the element unit to be measured using the element selection units 17 and 18, it is possible to stably and accurately measure the capacitance value of each element unit by processing similar to that shown in FIG. 16 .

[0200] 34, the parasitic capacitance increases because more switch elements 17a to 17c, 18a to 18d and wiring are arranged, and furthermore, the equipotential generator 19 is arranged, compared to the configuration of Fig. 10. However, even in this case, the effect of the parasitic capacitance is suppressed by the above formula (10), so that the capacitance value of each element can be calculated with high accuracy, and the load applied to each element can be detected with high accuracy.

[0201] <Modification 6> FIG. 36 is a diagram showing the configuration of the load detection device 1 according to Modification 6.

[0202] 36, the configuration of the capacitance measurement circuit 10 in the configuration of FIG. 34 is replaced with the configuration of FIG. 18(a) according to Modification Example 2. The other configurations and the process of detecting the capacitance of each element unit are the same as those in Embodiment 6.

[0203] According to the configuration of the sixth modification, the negative electrode of the reference capacitance Cr and the negative electrode of the element unit (measurement capacitance Cs) are connected to the positive electrode of the holding capacitance Ch, in addition to the negative electrode of the measurement unit 14, which further suppresses noise from the ground 16 from propagating to the reference capacitance Cr and the element unit (measurement capacitance Cs) when measuring the voltage of the element unit (measurement capacitance Cs). Thus, the load applied to each element unit can be detected more accurately.

[0204] 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.

[0205] FIG. 37 is a diagram showing the configuration of a load detection device 1 according to the seventh embodiment.

[0206] The load detection device 1 includes the capacitance measurement circuit 10 according to the third embodiment and the load sensor 20 shown in Fig. 28(b). As in the fifth embodiment, the nine element units A11 to A33 shown in Fig. 30 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.

[0207] In this configuration, as in the above-described embodiments 5 and 6, the control unit 11 controls the switch elements 17a to 17c and 18a to 18d to sequentially switch the element unit to be measured. Then, for each element unit to be measured, the control unit 11 executes the process of Fig. 20 to calculate the capacitance, and calculates the load applied to that element unit from the calculation result.

[0208] For example, in load detection for element unit A1, control unit 11 sets switch elements 17a to 17c and 18a to 18d to the states shown in FIG. 37, executes first control C1 in FIG. 20, and obtains a first voltage value Vx1. Next, control unit 11 sets switch elements 17a to 17c and 18a to 18d to the states shown in FIG. 38, executes second control C2 in FIG. 20, and obtains a second voltage value Vx2. Then, control unit 11 executes the process of step S131 in FIG. 20 to calculate the capacitance value of element unit A11 and calculates the load applied to element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than control unit 11 from the capacitance value calculated by control unit 11.

[0209] <Effects of embodiment 7> The load detection device 1 of embodiment 7 includes the capacitance measurement circuit 10 of embodiment 3, so as in embodiments 5 and 6, even when the load applied to the element parts A11 to A33 is small and the capacitance is small, it is possible to stably obtain a capacitance value corresponding to the load, and to accurately obtain a capacitance value in which the influence of noise from the power supply 15 and ground 16 and the influence of parasitic capacitance are suppressed.

[0210] <Seventh Modification> FIG. 39 is a diagram showing the configuration of the load detection device 1 according to a seventh modification.

[0211] 39, the configuration of the capacitance measuring circuit 10 in the configuration of FIG. 37 is replaced with the configuration of FIG. 22 according to Modification Example 3. The other configurations and the process of detecting the capacitance of each element unit are the same as those in the seventh embodiment.

[0212] According to the configuration of the seventh modification, the negative electrode of the reference capacitance Cr and the negative electrode of the element unit (measurement capacitance Cs) are connected to the positive electrode of the storage capacitance Ch′, which further suppresses noise from the ground 16 from propagating to the reference capacitance Cr and the element unit (measurement capacitance Cs) when measuring the voltage of the element unit (measurement capacitance Cs). Thus, the load applied to each element unit can be detected more accurately.

[0213] Eighth Embodiment In an eighth embodiment, a configuration example in which the capacitance measurement circuit 10 of the fourth 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.

[0214] FIG. 40 is a diagram showing the configuration of the load detection device 1 according to the eighth embodiment.

[0215] The load detection device 1 includes the capacitance measurement circuit 10 according to the fourth embodiment and the load sensor 20 shown in Fig. 28(b). As in the fifth embodiment, the nine element units A11 to A33 shown in Fig. 30 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.

[0216] In this configuration, as in the above-described embodiments 5 to 7, the control unit 11 controls the switch elements 17a to 17c and 18a to 18d to sequentially switch the element unit to be measured. Then, for each element unit to be measured, the control unit 11 executes the process of Fig. 24 to calculate the capacitance, and calculates the load applied to that element unit from the calculation result.

[0217] For example, in load detection for element unit A1, control unit 11 sets switch elements 17a to 17c and 18a to 18d to the states shown in FIG. 40, executes first control C1 in FIG. 24, and obtains a first voltage value Vx1. Next, control unit 11 sets switch elements 17a to 17c and 18a to 18d to the states shown in FIG. 41, executes second control C2 in FIG. 24, and obtains a second voltage value Vx2. Then, control unit 11 executes the process of step S232 in FIG. 24 to calculate the capacitance value of element unit A11 and calculates the load applied to element unit A11 from the calculated capacitance value. The load may be calculated by a processing unit other than control unit 11 from the capacitance value calculated by control unit 11.

[0218] <Effects of embodiment 8> The load detection device 1 of embodiment 8 includes the capacitance measurement circuit 10 of embodiment 4, so similar to embodiments 5 to 7, even when the load applied to the element parts A11 to A33 is small and the capacitance is small, it is possible to stably obtain a capacitance value corresponding to the load, and to accurately obtain a capacitance value in which the influence of noise from the power supply 15 and ground 16 and the influence of parasitic capacitance are suppressed.

[0219] <Modification 8> FIG. 42 is a diagram showing the configuration of the load detection device 1 according to Modification 8.

[0220] 42, the configuration of the capacitance measuring circuit 10 in the configuration of Fig. 40 is replaced with the configuration of Fig. 26 according to Modification 4. The other configurations and the process of detecting the capacitance of each element unit are the same as those in the eighth embodiment.

[0221] According to the configuration of the eighth modification, the negative electrode of the reference capacitance Cr and the negative electrode of the element unit (measurement capacitance Cs) are connected to the positive electrode of the storage capacitance Ch′, which further suppresses noise from the ground 16 from propagating to the reference capacitance Cr and the element unit (measurement capacitance Cs) when measuring the voltage of the element unit (measurement capacitance Cs). Thus, the load applied to each element unit can be detected more accurately.

[0222] <Other Modifications> In the above-described first to eighth embodiments, the switch elements 12a to 12e are configured with P-type or N-type FETs, but the switch elements 12a to 12e may be configured with switch elements other than FETs. Similarly, various types of switch elements can be used for the switch element 13 as long as the connection destination of the negative electrode of the measurement capacitance Cs can be switched between ground and the positive electrode. Similarly, in the configurations of Figures 31 to 42, various types of switch elements can be used as the switch elements 17a to 17c and the switch elements 18a to 18d.

[0223] In addition, in the above-described first embodiment, after the switch element 13 is switched in FIG. 4(b), the reference capacitance Cr is not discharged, and the reference capacitance Cr is charged in FIG. 5(a). However, the reference capacitance Cr may be discharged once, and then the reference capacitance Cr may be charged in FIG. 5(a).

[0224] 31 to 42, 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, the switch elements 17b and 17c may be configured so that their negative poles are connected to the ground line L3. In this case, the capacitances of the element units A12 and A13 are included in the parasitic capacitance described above and are therefore canceled out by the above equations (5), (10), (11), and (12). Therefore, the capacitance of the element unit A11 to be measured can be obtained with high accuracy.

[0225] 1 may be modified to the configuration of Modification 9 shown in FIG. 43(a). In this case, switch element 12f is set to the non-conductive state in steps S105 and S110 of FIG. 7, and is set to the conductive state in the other steps. This prevents noise from ground 16 from affecting the measurement results of the first voltage value Vx1 and the second voltage value Vx2 in steps S105 and S110. Similarly, the configuration of Embodiment 2 shown in FIG. 10 may be modified to the configuration of Modification 10 shown in FIG. 43(b).

[0226] However, in these configurations, the negative electrode of the measurement unit 14 is floating when measuring the first voltage value Vx1 and the second voltage value Vx2, which may cause unstable measurement of the first voltage value Vx1 and the second voltage value Vx2 by the measurement unit 14. In contrast, in the configurations of FIGS. 1 and 10 , the negative electrode of the measurement unit 14 is connected to the positive electrode of the holding capacitance Ch, so the negative electrode of the measurement unit 14 can be held at ground level when measuring the first voltage value Vx1 and the second voltage value Vx2, allowing the measurement unit 14 to stably measure the first voltage value Vx1 and the second voltage value Vx2. Therefore, in order to accurately measure the first voltage value Vx1 and the second voltage value Vx2, it is preferable to connect the negative electrode of the measurement unit 14 to the positive electrode of the holding capacitance Ch, as shown in FIGS. 1 and 10 .

[0227] The configurations of Modifications 9 and 10 shown in FIGS. 43( a) and 43(b) may be modified to configurations of Modifications 11 and 12 shown in FIGS. 44(a) and 44(b). In these configurations of Modifications 11 and 12, when measuring the first voltage value Vx1 and the second voltage value Vx2, the switch element 12f is set to a non-conductive state, and only the negative electrode of the measurement unit 14 is disconnected from the ground 16. With this configuration, for example, when the measurement target is a load sensor 20 as shown in FIG. 28(b), noise picked up by the measurement capacitance Cs is prevented from propagating to the measurement unit 14. Therefore, such noise does not affect the measurement results of the first voltage value Vx1 and the second voltage value Vx2, and the capacitance of the measurement capacitance Cs can be calculated with high accuracy.

[0228] Furthermore, in the above-described first to fourth embodiments, the holding capacitance Ch is disposed between the ground 16 or the power supply 15 and the measurement unit 14, but the holding capacitance Ch and a resistor may be connected in series between the ground 16 or the power supply 15 and the measurement unit 14. For example, in the configuration of the above-described first embodiment, as in Modification 13 of FIG. 45( a), the holding capacitance Ch and a resistor R may be connected in series between the ground 16 and the negative electrode of the measurement unit 14. Furthermore, in the configuration of the above-described second embodiment, as in Modification 14 of FIG. 45( b), the holding capacitance Ch and a resistor R may be connected in series between the ground 16 and the negative electrode of the measurement unit 14.

[0229] According to these configurations, the filter configuration consisting of the holding capacitance Ch and the resistance R can more reliably prevent noise from the ground 16 from propagating to the measurement unit 14. In the configurations of the third and fourth embodiments, the holding capacitance Ch and the resistance R may also be provided on the node side between the power supply 15 and the positive electrode of the measurement unit 14. The same applies to the other modified examples.

[0230] 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.

[0231] Furthermore, in the above-described first to fourth embodiments, the first control C1 and the second control C2 are performed to suppress the influence of parasitic capacitance. However, if suppressing the influence of parasitic capacitance is not necessary, only the first control C1 may be performed. In this case, the switch element 13 is omitted, and the negative electrode of the measurement capacitance Cs is connected to ground directly or via another storage capacitance Ch'. Furthermore, the capacitance value of the measurement capacitance Cs is calculated using only the first capacitance value calculation formula using the first voltage value Vx1, omitting the second capacitance value calculation formula using the second voltage value Vx2 from the right-hand sides of the above-described equations (5), (10), (11), and (12). For example, in the configuration of the first embodiment, the capacitance value Cs1 calculated using equation (3) is acquired as the capacitance value of the measurement capacitance Cs. This configuration also suppresses the influence of noise from the power supply 15 and ground 16 on the calculation results of the measurement capacitance Cs.

[0232] 31 to 42, 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 by switch elements 18b and 18c, but switch elements 18b and 18c may be connected to the output line side of switch element 18d, and the element portion having these two conductor lines 23 (conductive member 23a) as the positive electrode may be set to 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 (5) and (10), so the capacitance of the element portion A11 to be measured can be obtained with high accuracy.

[0233] 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 formulas (5), (10), (11), and (12).

[0234] 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.

[0235] 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.

[0236] Furthermore, in the above-described fifth to eighth embodiments, 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 fifth to eighth embodiments.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0242] (Technology 1) A capacitance measurement circuit comprising: 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 measurement unit that measures the voltage of the measurement capacitance; a noise suppression unit that suppresses noise from flowing into the measurement unit from a ground and a power supply; and a control unit that controls the switching unit, the transfer unit, and the noise suppression unit, wherein the control unit performs control to apply a voltage to the reference capacitance, and then cause the transfer unit to transfer charge; and, after the charge has been transferred, calculates the capacitance value of the measurement capacitance from the voltage value measured by the measurement unit with the noise suppression unit suppressing the inflow of noise.

[0243] According to this technology, the capacitance value of the measurement capacitance is calculated based on the voltage value after the charge is transferred from the reference capacitance, so that capacitance values ​​over a small range can be measured stably without using a high-precision AD converter. Furthermore, after the charge transfer, the voltage value of the measurement capacitance is acquired while suppressing the inflow of noise from the ground and power supply to the measurement unit, so that the influence of this noise on the measurement result of the voltage value can be suppressed. Therefore, the capacitance value of the measurement capacitance can be measured with high accuracy.

[0244] (Technology 2) The capacitance measurement circuit according to Technology 1, further comprising a connection unit that connects a negative electrode of the measurement capacitance to ground or to a wiring having the same potential as the positive electrode of the measurement capacitance, wherein the control unit executes: a first control that applies a voltage to the reference capacitance and then causes the transfer unit to transfer charge in a state where the negative electrode of the measurement capacitance is connected to the ground; a second control that applies a voltage to the reference capacitance and then causes the transfer unit to transfer charge in a state where 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 a process that calculates a capacitance value of the measurement capacitance from voltage values ​​measured by the measurement unit in a state where the inflow of noise is suppressed by the noise suppression unit after the charge has been transferred by the first control and the second control.

[0245] According to this technology, 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 hardly affected by the measurement capacitance, but is affected mainly 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 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, it is possible to calculate a capacitance value that is not affected by parasitic capacitance. This allows for more accurate measurement of the capacitance value of the measurement capacitance.

[0246] (Technology 3) In the capacitance measurement circuit according to Technology 2, the noise suppression unit includes a holding capacitor having a negative electrode connected to ground, and the measurement unit measures a voltage between a positive electrode of the measurement capacitor and a positive electrode of the holding capacitor.

[0247] This technology uses a storage capacitor to suppress the inflow of noise from the ground into the measurement unit. Furthermore, the storage capacitor maintains the potential of the negative electrode of the measurement unit at ground level, allowing for stable measurement of the voltage of the measurement capacitor. This allows for accurate measurement of the capacitance value of the measurement capacitor.

[0248] (Technology 4) In the capacitance measurement circuit according to Technology 3, the negative electrode of the reference capacitance and the negative electrode of the measurement capacitance are connected to ground via the storage capacitance.

[0249] This technique can prevent noise from the ground from propagating to the measurement capacitor and the reference capacitor when measuring the voltage of the measurement capacitor, thereby enabling the capacitance value of the measurement capacitor to be measured with higher accuracy.

[0250] (Technology 5) In the capacitance measurement circuit according to Technology 3 or 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, and the capacitance value Cr of the reference capacitance, using the following formula:

[0251]

[0252] According to this technique, the influence of error components due to parasitic capacitance on the capacitance value of the capacitance to be measured can be suppressed, and the capacitance value of the capacitance to be measured can be obtained with high accuracy.

[0253] (Technology 6) In the capacitance measurement circuit according to Technology 2, the noise suppression unit includes a holding capacitor having a positive electrode connected to a power supply, and the measurement unit measures a voltage between the positive electrode of the measurement capacitor and the negative electrode of the holding capacitor.

[0254] This technology uses a storage capacitor to suppress the inflow of noise from the power supply into the measurement unit. Furthermore, the storage capacitor maintains the potential of the positive electrode of the measurement unit at the power supply voltage level, allowing for stable measurement of the voltage of the measurement capacitor. This allows for accurate measurement of the capacitance value of the measurement capacitor.

[0255] (Technology 7) In the capacitance measurement circuit according to Technology 6, the noise suppression unit includes another holding capacitor having a negative electrode connected to ground, and the negative electrodes of the reference capacitance and the measurement capacitance are connected to ground via the other holding capacitor.

[0256] This technique can prevent noise from the ground from propagating to the measurement capacitor and the reference capacitor when measuring the voltage of the measurement capacitor, thereby enabling the capacitance value of the measurement capacitor to be measured with higher accuracy.

[0257] (Technology 8) In the capacitance measurement circuit according to Technology 6 or 7, 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, and the capacitance value Cr of the reference capacitance by the following formula:

[0258]

[0259] According to this technique, the influence of error components due to parasitic capacitance on the capacitance value of the capacitance to be measured can be suppressed, and the capacitance value of the capacitance to be measured can be obtained with high accuracy.

[0260] (Technology 9) A capacitance measurement circuit comprising: a reference capacitance having a predetermined capacitance value; a switching unit that switches between applying and not applying a voltage to a measurement capacitance; a transfer unit that transfers charge accumulated in the measurement capacitance to the reference capacitance; a measurement unit that measures the voltage of the measurement capacitance; a noise suppression unit that suppresses noise from flowing into the measurement unit from ground; and a control unit that controls the switching unit, the transfer unit, and the noise suppression unit, wherein the control unit performs control to apply a voltage to the measurement capacitance, and then cause the transfer unit to transfer charge; and after the charge has been transferred, calculates the capacitance value of the measurement capacitance from the voltage value measured by the measurement unit with the noise suppression unit suppressing the inflow of noise.

[0261] According to this technology, the capacitance value of the target capacitance is calculated based on the voltage value after charge is transferred from the target capacitance, allowing stable measurement of a small range of capacitance values ​​without using a high-precision AD converter. Furthermore, after the charge transfer, the voltage value of the target capacitance is acquired while suppressing the inflow of noise from the ground and power supply to the measurement unit, preventing these noises from affecting the voltage measurement results. Therefore, the capacitance value of the target capacitance can be measured accurately.

[0262] (Technology 10) The capacitance measurement circuit according to Technology 9, further comprising a connection unit that connects a negative electrode of the capacitance to be measured to ground or to a wiring having the same potential as the positive electrode of the capacitance to be measured, wherein the control unit executes: a first control that applies a voltage to the capacitance to be measured with the negative electrode of the capacitance to be measured connected to the ground, and then causes the transfer unit to transfer charge; a second control that applies 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 causes the transfer unit to transfer charge; and a process that calculates a capacitance value of the capacitance to be measured from voltage values ​​measured by the measurement unit with the inflow of noise suppressed by the noise suppression unit after the charge has been transferred by the first control and the second control, respectively.

[0263] According to this technology, 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, but charge accumulates in the parasitic capacitance. Therefore, the voltage value measured in 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 in 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 unaffected by parasitic capacitance can be calculated. This allows the capacitance value of the measurement capacitance to be measured with high accuracy.

[0264] (Technology 11) In the capacitance measurement circuit according to Technology 10, the noise suppression unit includes a holding capacitor having a negative electrode connected to ground, and the measurement unit measures a voltage between a positive electrode of the measurement capacitor and a positive electrode of the holding capacitor.

[0265] This technology uses a storage capacitor to suppress the inflow of noise from the ground into the measurement unit. Furthermore, the storage capacitor maintains the potential of the negative electrode of the measurement unit at ground level, allowing for stable measurement of the voltage of the measurement capacitor. This allows for accurate measurement of the capacitance value of the measurement capacitor.

[0266] (Technology 12) The capacitance measurement circuit according to claim 11, wherein the negative electrode of the reference capacitance and the negative electrode of the measurement capacitance are connected to ground via the storage capacitance.

[0267] This technique can prevent noise from the ground from propagating to the measurement capacitor and the reference capacitor when measuring the voltage of the measurement capacitor, thereby enabling the capacitance value of the measurement capacitor to be measured with higher accuracy.

[0268] (Technology 13) In the capacitance measurement circuit according to Technology 11 or 12, 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, and the capacitance value Cr of the reference capacitance, using the following formula:

[0269]

[0270] According to this technique, the influence of error components due to parasitic capacitance on the capacitance value of the capacitance to be measured can be suppressed, and the capacitance value of the capacitance to be measured can be obtained with high accuracy.

[0271] (Technology 14) In the capacitance measurement circuit according to Technology 10, the noise suppression unit includes a holding capacitor having a positive electrode connected to a power supply, and the measurement unit measures a voltage between the positive electrode of the measurement capacitor and the negative electrode of the holding capacitor.

[0272] This technology uses a storage capacitor to suppress the inflow of noise from the power supply into the measurement unit. Furthermore, the storage capacitor maintains the potential of the positive electrode of the measurement unit at the power supply voltage level, allowing for stable measurement of the voltage of the measurement capacitor. This allows for accurate measurement of the capacitance value of the measurement capacitor.

[0273] (Technology 15) In the capacitance measurement circuit according to Technology 14, the noise suppression unit includes another holding capacitor having a negative electrode connected to ground, and the negative electrodes of the reference capacitance and the measurement capacitance are connected to ground via the other holding capacitor.

[0274] This technique can prevent noise from the ground from propagating to the measurement capacitor and the reference capacitor when measuring the voltage of the measurement capacitor, thereby enabling the capacitance value of the measurement capacitor to be measured with higher accuracy.

[0275] (Technology 16) In the capacitance measurement circuit according to Technology 14 or 15, 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, and the capacitance value Cr of the reference capacitance, using the following formula:

[0276]

[0277] According to this technique, the influence of error components due to parasitic capacitance on the capacitance value of the capacitance to be measured can be suppressed, and the capacitance value of the capacitance to be measured can be obtained with high accuracy.

[0278] (Technology 17) 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 16; wherein the control unit controls the transfer of the charge and calculates the capacitance using the element part as the measurement capacitance.

[0279] 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 corresponding to the load even when the load applied to the element unit is small and the capacitance 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 influence of noise is suppressed. Therefore, it is possible to stably and accurately detect a small range of loads.

[0280] (Technology 18) In the load detection device described in Technology 17, 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.

[0281] This technology allows load detection over a wide area where multiple element units are arranged. In addition, 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.

[0282] In addition, in the configurations of reference examples 1 to 4, the above description also discloses a technology for executing the first control C1 and the second control C2 similar to those of embodiments 1 to 4, and for performing a process for calculating the capacitance value of the measurement capacitance Cs based on the first voltage value Vx1 and the second voltage value Vx2.

[0283] Although this technique cannot suppress the influence of noise from the power supply and ground, it can suppress the influence of parasitic capacitance on the capacitance value of the capacitance to be measured, thereby enabling the capacitance value of the capacitance to be obtained with high accuracy.

[0284] REFERENCE SIGNS LIST 1 Load detection device 10 Capacitance measurement circuit 11 Control unit 20 Load sensor 12a Switch element (switching unit, noise suppression unit) 12b Switch element (transfer unit) 12d Switch element (noise suppression unit) 13 Switch element (connection unit) 14 Measurement unit 17, 18 Element selection unit Cr Reference capacitance Cs Measurement capacitance Ch Storage capacitance (noise suppression unit) A11 to A33 Element unit (measurement capacitance)

Claims

1. A capacitance measurement circuit comprising: 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 measurement unit that measures the voltage of the measurement capacitance; a noise suppression unit that suppresses noise from flowing into the measurement unit from ground and a power supply; and a control unit that controls the switching unit, the transfer unit, and the noise suppression unit, wherein the control unit performs control to apply a voltage to the reference capacitance, and then cause the transfer unit to transfer charge; and after the charge has been transferred, a process of calculating a capacitance value of the measurement capacitance from the voltage value measured by the measurement unit with the inflow of noise suppressed by the noise suppression unit.

2. A capacitance measuring circuit as claimed in claim 1, further comprising a connection section for connecting the negative electrode of the capacitance to be measured to ground or to a wiring having the same potential as the positive electrode of the capacitance to be measured, wherein the control section executes the following steps: a first control for causing the transfer section to transfer charge with the negative electrode of the capacitance to be measured connected to the ground after applying a voltage to the reference capacitance; a second control for causing the transfer section to transfer charge with the negative electrode of the capacitance to be measured connected to the wiring having the same potential as the positive electrode of the capacitance to be measured after applying a voltage to the reference capacitance; and a process for calculating a capacitance value of the capacitance to be measured from the voltage values ​​measured by the measurement section with the inflow of noise suppressed by the noise suppression section after the charge has been transferred by the first control and the second control.

3. A capacitance measuring circuit as claimed in claim 2, characterized in that the noise suppression section includes a holding capacitance having a negative electrode connected to ground, and the measurement section measures the voltage between the positive electrode of the measurement capacitance and the positive electrode of the holding capacitance.

4. The electrostatic capacitance measuring circuit according to claim 3, wherein the negative electrode of the reference capacitance and the negative electrode of the measurement capacitance are connected to ground via the holding capacitance.

5. A capacitance measuring circuit as claimed in claim 3, 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, and the capacitance value Cr of the reference capacitance, according to the following formula:

6. A capacitance measuring circuit as claimed in claim 2, wherein the noise suppression section includes a holding capacitance having a positive electrode connected to a power source, and the measurement section measures the voltage between the positive electrode of the measurement capacitance and the negative electrode of the holding capacitance.

7. A capacitance measuring circuit as claimed in claim 6, wherein the noise suppression section includes another holding capacitance having a negative electrode connected to ground, and the negative electrodes of the reference capacitance and the measurement capacitance are connected to ground via the other holding capacitance.

8. A capacitance measuring circuit as claimed in claim 6, 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, and the capacitance value Cr of the reference capacitance, according to the following formula:

9. A capacitance measuring circuit comprising: a reference capacitance having a predetermined capacitance value; a switching unit which switches between application and non-application of a voltage to a measurement capacitance; a transfer unit which transfers charge accumulated in the measurement capacitance to the reference capacitance; a measurement unit which measures the voltage of the measurement capacitance; a noise suppression unit which suppresses noise from flowing into the measurement unit from ground; and a control unit which controls the switching unit, the transfer unit, and the noise suppression unit, wherein the control unit performs control to cause the transfer unit to transfer charge after applying a voltage to the measurement capacitance; and a process of calculating a capacitance value of the measurement capacitance from the voltage value measured by the measurement unit after the charge has been transferred, with the inflow of noise suppressed by the noise suppression unit.

10. A capacitance measuring circuit as claimed in claim 9, further comprising a connection section for connecting the negative electrode of the capacitance to be measured to ground or to a wiring having the same potential as the positive electrode of the capacitance to be measured, wherein the control section executes the following steps: 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 section to transfer charge; 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 section to transfer charge; and a process for calculating a capacitance value of the capacitance to be measured from the voltage values ​​measured by the measurement section with the inflow of noise suppressed by the noise suppression section after the charge has been transferred by the first control and the second control, respectively.

11. A capacitance measuring circuit as claimed in claim 10, wherein the noise suppression section includes a holding capacitance having a negative electrode connected to ground, and the measurement section measures the voltage between the positive electrode of the measurement capacitance and the positive electrode of the holding capacitance.

12. The electrostatic capacitance measuring circuit according to claim 11, wherein the negative electrode of the reference capacitance and the negative electrode of the measurement capacitance are connected to ground via the holding capacitance.

13. A capacitance measuring circuit as described in claim 11, 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, and the capacitance value Cr of the reference capacitance, using the following formula:

14. A capacitance measuring circuit as claimed in claim 10, wherein the noise suppression section includes a holding capacitance having a positive electrode connected to a power source, and the measurement section measures the voltage between the positive electrode of the measurement capacitance and the negative electrode of the holding capacitance.

15. A capacitance measuring circuit as claimed in claim 14, characterized in that the noise suppression section includes another holding capacitance having a negative electrode connected to ground, and the negative electrodes of the reference capacitance and the measurement capacitance are connected to ground via the other holding capacitance.

16. A capacitance measuring circuit as claimed in claim 14, characterized in that the control unit 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, and the capacitance value Cr of the reference capacitance, using the following formula:

17. A load detection device comprising: a load sensor having an element portion whose capacitance changes according to the load; and a capacitance measurement circuit as claimed in any one of claims 1 to 16, wherein the control unit performs transfer control of the charge and calculation processing of the capacitance using the element portion as the measurement capacitance.

18. A load detection device as described in claim 17, characterized in that the load sensor includes a plurality of the element units, and the capacitance measurement circuit includes an element selection unit that switches between the element units to be measured.

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