Capacitance sensor

Abstract

An electrostatic capacitance sensor. Provided is a capacitance sensor capable of detecting capacitance with high accuracy. A capacitance sensor is provided with: a package; the oscillation circuit is arranged in the package; and a first electrode and a second electrode provided outside the package, the oscillation circuit having: an amplifier; and an oscillator provided inside the package and connected between an input node and an output node of the amplifier, the first electrode being a sensing electrode connected to one of the input node and the output node of the amplifier, the second electrode being an electrode having a fixed potential, and the oscillator being provided inside the package and connected between the input node and the output node of the amplifier. The oscillation frequency of the oscillation circuit varies in accordance with a first capacitance between the first electrode and the second electrode.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrostatic capacitance sensor. BACKGROUND

[0002] In Patent Literature 1, a liquid level detector is described which makes an oscillation circuit oscillate with an electrostatic capacitance and a resistance which vary in accordance with a change in a measured liquid level as an oscillation time constant, and outputs a digital signal corresponding to the change in the liquid level based on an output signal of the oscillation circuit.

[0003] Patent Literature 1: Japanese Patent Application Laid-Open No. 2003-57095

[0004] However, in the liquid level detector described in Patent Literature 1, the oscillation circuit is oscillated by charging and discharging of the electrostatic capacitance, and thus the oscillation frequency of the oscillation circuit is easily varied by external amplitude noise, and it is difficult to achieve high detection accuracy. SUMMARY

[0005] One embodiment of the electrostatic capacitance sensor according to the present application includes:

[0006] a package;

[0007] an oscillation circuit provided inside the package; and

[0008] a first electrode and a second electrode provided outside the package,

[0009] the oscillation circuit has:

[0010] an amplifier; and

[0011] a vibrator provided inside the package, connected between an input node and an output node of the amplifier,

[0012] the first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier,

[0013] the second electrode is a potential-fixed electrode,

[0014] an oscillation frequency of the oscillation circuit is varied in accordance with a first electrostatic capacitance between the first electrode and the second electrode.

[0015] Another embodiment of the electrostatic capacitance sensor according to the present application includes:

[0016] an oscillation circuit; and

[0017] a first electrode and a second electrode,

[0018] the oscillation circuit has:

[0019] an amplifier; and

[0020] a vibrator connected between an input node and an output node of the amplifier,

[0021] the first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier,

[0022] the second electrode is a potential-fixed electrode,

[0023] a first electrostatic capacitance between the first electrode and the second electrode varies depending on a state of an object to be detected,

[0024] an oscillation frequency of the oscillation circuit varies depending on the first electrostatic capacitance. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a diagram showing an appearance of an electrostatic capacitance sensor of a first embodiment.

[0026] Figure 2 is a plan view showing an example of an internal structure of an oscillator.

[0027] Figure 3 is a plan view showing another example of an internal structure of an oscillator.

[0028] Figure 4 is a diagram showing a use example of an electrostatic capacitance sensor.

[0029] Figure 5 is a functional block diagram of the electrostatic capacitance sensor of the first embodiment.

[0030] Figure 6 is a diagram showing a structure example of a drive circuit and a buffer circuit.

[0031] Figure 7 is a diagram showing an equivalent circuit of a vibrator.

[0032] Figure 8 is a diagram showing an example of a relationship between a load capacitance C L and a reference frequency Δf / f0.

[0033] Figure 9 is a timing chart of various signals.

[0034] Figure 10 is a diagram showing a comparison of frequency variable characteristics of an LC oscillation circuit and an oscillation circuit using a vibrator with respect to a load capacitance C L .

[0035] Figure 11 is a diagram showing an appearance of an electrostatic capacitance sensor of a second embodiment.

[0036] Figure 12 is a functional block diagram of the electrostatic capacitance sensor of the second embodiment.

[0037] Figure 13 is a diagram showing a structural example of a drive circuit and a buffer circuit.

[0038] Explanation of reference numerals

[0039] 1: electrostatic capacitance sensor; 2: circuit device; 3: vibrator; 3a: excitation electrode; 3b: excitation electrode; 4: package; 5: cover; 6: land; 7: bonding wire; 8: electrode; 9: electrode; 10: oscillator; 11: electrically conductive bonding member; 12a, 12b: electrode; 15: cable; 20: oscillation circuit; 21: drive circuit; 30: buffer circuit; 31: capacitor; 32: CMOS inverter circuit; 33: resistor; 40: measurement circuit; 41: frequency division circuit; 42: counter; 50: clock generation circuit; 60: control circuit; 70: register; 80: interface circuit; 90: capacitor; 100: sensing portion; 101, 102, 103, 104: electrode; 110: substrate; 200: MCU; 211: amplifier; 212, 213: resistor; 300: detection object. DETAILED DESCRIPTION

[0040] Hereinafter, preferred embodiments of the present application will be described in detail with reference to the accompanying drawings. Furthermore, the embodiments described below do not unduly limit the content of the present application described in the claims. In addition, the structures described below are not necessarily all the essential structural elements of the present application.

[0041] 1. First Embodiment

[0042] 1-1. Structure of electrostatic capacitance sensor

[0043] Figure 1 is a diagram showing the appearance of the electrostatic capacitance sensor 1 of the first embodiment. As shown in Figure 1 , the electrostatic capacitance sensor 1 of the first embodiment is provided with an oscillator 10, a sensing portion 100, and a cable 15 connecting the oscillator 10 and the sensing portion 100.

[0044] Figure 2 is a plan view showing an example of the internal structure of the oscillator 10. As shown in Figure 1 and Figure 2 , the oscillator 10 includes a circuit device 2, a vibrator 3, a package 4, and a cover 5. Furthermore, in Figure 2 , the illustration of the cover 5 is omitted.

[0045] The oscillator 10 is, for example, a single-seal configuration oscillator, and the package 4 is a container that houses the circuit device 2 and the vibrator 3 in the same space. That is, the circuit device 2 and the vibrator 3 are provided inside the package 4. Specifically, a recess is provided in the package 4, and the circuit device 2 and the vibrator 3 are housed by covering the recess with the lid 5. Alternatively, the oscillator 10 can not be a single-seal configuration, and for example, the package 4 can be a container that houses the circuit device 2 and the vibrator 3 in different spaces. Specifically, two recesses can be provided in opposite faces of the package 4, and the vibrator 3 can be housed by covering one of the recesses with the lid 5, and the circuit device 2 can be housed by covering the other recess with a sealing member.

[0046] In the present embodiment, the circuit device 2 is implemented by a single-chip integrated circuit. However, at least a part of the circuit device 2 can also be constituted by discrete components. In the case of a multi-chip configuration, the circuit device 2 can be constituted by a plurality of integrated circuits. Figure 2 In the example shown in FIG. 1, the circuit device 2 is mounted to the inner bottom face of the package 4 in a manner in which a face on which a plurality of pads 6 are formed is the upper face, via an adhesive or the like. The plurality of pads 6 are each connected to any one of a plurality of electrodes 8 formed on the surface of the recess of the package 4, using a bonding wire 7.

[0047] The vibrator 3 is a piezoelectric vibrator that uses a piezoelectric single crystal such as quartz, lithium tantalate, lithium niobate, or a piezoelectric ceramic such as lead zirconate titanate, as a substrate material. Alternatively, it is a MEMS (Micro Electro Mechanical Systems) vibrator that uses a silicon substrate or the like as a substrate material and is excited by electrostatic attraction. For example, the vibrator 3 is a quartz vibrator that uses quartz as a substrate material, and in the example shown in FIG. 1, it is a tuning fork type quartz vibrator. The two support arms of the vibrator 3 are each bonded to one of two electrodes 9 formed on the surface of the recess of the package 4, using a conductive bonding member 11. That is, each support arm of the vibrator 3 is fixed to and electrically connected to each electrode 9. The two electrodes 9 are each electrically connected to the two electrodes 8 and the two pads 6 of the circuit device 2, specifically, to the XD terminal and the XG terminal of the circuit device 2 described below, using a wiring provided to the package 4. Figure 2 Figure 5

[0048] Electrode patterns not shown are formed on the two support arms and the two vibration arms of the vibrator 3. Furthermore, a signal generated at one of the electrode patterns is supplied from one of the electrodes 9 to the XG terminal of the circuit device 2, and an amplifier possessed by the circuit device 2 amplifies the signal, and the amplified signal is supplied from the XD terminal to the vibrator 3 via the other electrode 9, whereby the two vibration arms of the vibrator 3 continuously vibrate like a tuning fork. Thus, the oscillator circuit including the vibrator 3 and the amplifier oscillates.

[0049] Figure 3 is a plan view showing another example of the internal structure of the oscillator 10. In​​Figure 3 In the example of FIG. 1, the circuit device 2 is mounted on the bottom surface of the recess of the package 4, and the vibrator 3 is mounted on the upper portion of the circuit device 2 with a gap.

[0050] In Figure 3 the example, the vibrator 3 is an AT-cut quartz vibrator. The vibrator 3 has metal excitation electrodes 3a, 3b on its front surface and back surface, respectively, to vibrate at a desired frequency corresponding to the shape and mass of the vibrator 3 including the excitation electrodes 3a, 3b. The excitation electrodes 3a, 3b are joined to two electrodes 12a, 12b formed on the surface of the recess of the package 4, respectively. The package 4 is provided with wiring not shown for electrically connecting two terminals of the circuit device 2, specifically, the XD terminal and the XG terminal described later, to the electrodes 12a, 12b, respectively. Also, a signal generated in one of the excitation electrodes 3a, 3b is supplied to the XG terminal of the circuit device 2, and an amplifier possessed by the circuit device 2 amplifies the signal, and the amplified signal is supplied from the XD terminal to the vibrator 3 via the other of the excitation electrodes 3a, 3b, whereby the thickness shear vibration in which the front surface and the back surface of the vibrator 3 move in opposite directions to each other is continuously performed. Thus, the oscillation circuit including the vibrator 3 and the amplifier oscillates. Figure 5

[0051] The oscillator 10 is provided with a plurality of external connection terminals not shown on the back surface of the package 4 as the bottom surface. In addition, the package 4 is provided with wiring not shown for electrically connecting each terminal of the circuit device 2 to each external connection terminal provided on the bottom surface of the package 4.

[0052] As Figure 1 shown in FIG. 2, the sensing section 100 is provided outside the package 4 of the oscillator 10 and connected to the oscillator 10 with a cable 15. The cable 15 can be, for example, a coaxial cable, a flexible flat cable, or the like.

[0053] The sensing section 100 has a substrate 110 having a surface 110a and a surface 110b which is the back surface of the surface 110a. The electrodes 101, 102, 103 are provided on the surface 110a of the substrate 110. The electrodes 101, 102, 103 are each in an elongated rectangular shape, and the electrode 102 is positioned between the electrode 101 and the electrode 103. The electrode 104 is provided on the surface 110b of the substrate 110 at a position opposite to the arrangement region of the electrodes 101, 102, 103 in the surface 110a. For example, the electrode 104 is provided on substantially the entire surface of the surface 110b.

[0054] The electrodes 101, 102, 103, 104 are each connected to the external connection terminal of the oscillator 10 with the wiring included in the cable 15. Thus, the electrodes 101, 102, 103, 104 are each connected to the terminal of the circuit device 2 via the external connection terminal of the oscillator 10. ​

[0055] In the present embodiment, the electrode 101 is a sensing electrode connected to one of the XD terminal and the XG terminal of the circuit device 2, and the electrode 103 is a sensing electrode connected to the other of the XD terminal and the XG terminal of the circuit device 2. The electrode 102 is a potential-fixed electrode. For example, the electrode 102 is connected to a ground terminal of the circuit device 2, and the potential is fixed to a ground potential. The electrode 104 is connected to the ground terminal of the circuit device 2, and the potential is fixed to the ground potential.

[0056] The sensing section 100 is configured so that the electrodes 101, 102, 103 face the detection object of the electrostatic capacitance. The electrostatic capacitance CD between the electrodes 101 and 102 and the electrostatic capacitance CG between the electrodes 103 and 102 vary depending on the dielectric constant of the detection object.

[0057] As described later, when the electrostatic capacitances CD, CG vary, the load capacitance C L of the vibrator 3 also varies, the oscillation frequency f of the oscillation circuit varies, and therefore, the circuit device 2 measures the oscillation frequency f and outputs the measured value of the oscillation frequency f to the outside of the oscillator 10. An external device can capture the variation of the electrostatic capacitances CD, CG based on the measured value of the oscillation frequency f and determine the state of the detection object. Furthermore, in a case where an object other than the detection object is located at a position facing the face 110b of the substrate 110, the electrode 104 functions as a shielding member for reducing the influence of the object on the electrostatic capacitances CD, CG.

[0058] Figure 4 is a diagram showing a use example of the electrostatic capacitance sensor 1. In Figure 4 the example, the detection object 300 of which the electrostatic capacitance is detected is a container that accommodates a liquid LQ. The internal space of the detection object 300 is filled with the liquid LQ and air AR, and when the liquid LQ decreases, the air AR increases, and when the liquid LQ increases, the air AR decreases. The dielectric constant of the liquid LQ is several tens of times the dielectric constant of the air AR, and the more the liquid LQ, the larger the effective dielectric constant of the inside of the detection object 300. On the other hand, the electrostatic capacitances CD, CG increase and decrease in proportion to the dielectric constant of the detection object 300. Therefore, the larger the dielectric constant of the detection object 300, that is, the more the liquid LQ, the larger the electrostatic capacitances CD, CG, and therefore, the load capacitance C L of the vibrator 3. Therefore, an external device can calculate the amount of the liquid LQ accommodated in the detection object 300 based on the measured value of the oscillation frequency f output from the oscillator 10.

[0059] 1-2. Functional configuration of electrostatic capacitance sensor

[0060] Figure 5 is a functional block diagram of the electrostatic capacitance sensor 1 of the first embodiment. As Figure 5As shown, the electrostatic capacitance sensor 1 of the first embodiment includes the circuit device 2 and the sensing portion 100.

[0061] The circuit device 2 includes a drive circuit 21, a buffer circuit 30, a measurement circuit 40, a clock generation circuit 50, a control circuit 60, a register 70, and an interface circuit 80. In addition, the circuit device 2 can be configured to omit or change a part of these elements, or add other elements.

[0062] The circuit device 2 has a VDD terminal as a power supply terminal and a VSS terminal as a ground terminal, and the potential of the VDD terminal is set to a power supply potential and the potential of the VSS terminal is set to a ground potential, and each circuit operates. In addition, the circuit device 2 has an XD terminal and an XG terminal, and the XD terminal and the XG terminal are connected to both ends of the vibrator 3. Furthermore, the circuit device 2 has a terminal not shown for data communication with the MCU 200 as an external device of the circuit device 2.

[0063] The drive circuit 21 is connected to the XD terminal and the XG terminal, and causes the vibrator 3 to vibrate to generate an oscillation signal OSCO. The drive circuit 21 amplifies a signal input from the vibrator 3 via the XG terminal, and outputs the amplified signal to the vibrator 3 via the XD terminal. Thus, the two vibration arms of the vibrator 3 vibrate, and the drive circuit 21 outputs the signal input from the vibrator 3 via the XG terminal as the oscillation signal OSCO. The oscillation circuit 20 is configured by the vibrator 3 and the drive circuit 21.

[0064] The buffer circuit 30 buffers the oscillation signal OSCO output from the drive circuit 21, and outputs a signal BFO of a rectangular wave. In addition, the rectangular wave of the signal BFO includes not only a strict rectangular wave, but also a case where a waveform close to a rectangular wave is included.

[0065] Figure 6 is a diagram showing a configuration example of the drive circuit 21 and the buffer circuit 30. As shown, the drive circuit 21 includes an amplifier 211 and resistors 212 and 213. Figure 6

[0066] The amplifier 211 amplifies a signal output from the vibrator 3, and outputs the amplified signal to the vibrator 3 via the resistor 213. In the example shown in Figure 6 , the amplifier 211 is a CMOS inverter circuit, but can be a bipolar transistor.

[0067] The vibrator 3 is connected between a node NG and a node ND. The node NG is an input node of the amplifier 211, and a signal output from the vibrator 3 is input to the amplifier 211 from the node NG. The node ND is an output node of the amplifier 211, and a signal output from the amplifier 211 is output to the node ND via the resistor 213. The node NG is connected to the XG terminal, and the node ND is connected to the XD terminal.​

[0068] The signal output from the amplifier 211 is a rectangular wave signal which is input to the vibrator 3. As shown in Figure 2 and Figure 3 indicated, the vibrator 3 is, for example, a tuning fork type quartz vibrator, an AT-cut quartz vibrator, has a very high Q value, and thus, the signal output from the vibrator 3 is a signal having little noise and close to a sine wave. The signal output from the vibrator 3 to the node NG is input to the buffer circuit 30 as an oscillation signal OSCO. Further, the rectangular wave of the signal output from the amplifier 211 includes not only a strict rectangular wave but also a case where a waveform close to a rectangular wave is included.

[0069] The buffer circuit 30 includes a capacitor 31, a CMOS inverter circuit 32, and a resistor 33. The oscillation signal OSCO is input to the CMOS inverter circuit 32 via the capacitor 31, and the CMOS inverter circuit 32 outputs a rectangular wave signal BFO.

[0070] Here, Figure 7 is a diagram showing an equivalent circuit of the vibrator 3 as a quartz vibrator, and as equivalent constants of the vibrator 3, a series inductance LI, a series capacitance CI, a series resistance Rl, and a parallel capacitance CO can be cited. At this time, the series resonance frequency fo of the vibrator 3 is represented by Expression (1).

[0071]

[0072] The oscillation frequency f of the oscillation circuit 20 constituted by the vibrator 3 and the drive circuit 21 varies according to the load capacitance C L , and the reference frequency Δf / fo of the oscillation circuit 20 is represented by Expression (2).

[0073]

[0074] In Expression (2), γ is the ratio of the parallel capacitance CO to the series capacitance CI, and is represented by Expression (3).

[0075]

[0076] Figure 8 is a diagram showing an example of the relationship between the load capacitance C L and the reference frequency Δf / fo. In Figure 8 , the solid line is a curve in a case where the vibrator 3 is a tuning fork type quartz vibrator, and the broken line is a curve in a case where the vibrator 3 is an AT-cut quartz vibrator. According to Figure 8 , when the load capacitance C L varies in the range of 0 to 30 pF, the reference frequency Δf / fo also varies, and the change rate of the tuning fork type quartz vibrator is greater.

[0077] Electrode 101 of sensing unit 100 is connected to one of the input node NG and output node ND of amplifier 211, and electrode 103 of sensing unit 100 is connected to the other of the input node NG and output node ND of amplifier 211. Figure 5 and Figure 6 In this configuration, electrode 101 is connected to the output node ND of amplifier 211, and electrode 103 is connected to the input node NG of amplifier 211. Additionally, electrode 102 of the sensing unit 100 is connected to ground. Therefore, the load capacitance C of the oscillator 3... L It consists of the electrostatic capacitance CD between electrodes 101 and 102 and the electrostatic capacitance CG between electrodes 103 and 102, and is represented by equation (4). In equation (4), CS is the parasitic capacitance, which is about pF.

[0078]

[0079] According to equations (1) to (4), the oscillation frequency f of the oscillation circuit 20 varies depending on the electrostatic capacitors CD and CG. The frequency of the oscillation signal OSCO output from the drive circuit 21 is the oscillation frequency f, and the frequency of the signal BFO ​​output from the buffer circuit 30 is also consistent with the oscillation frequency f.

[0080] like Figure 5 As shown, the measurement circuit 40 measures the frequency of the signal BFO ​​output from the buffer circuit 30. That is, the measurement circuit 40 measures the oscillation frequency f. For example, the measurement circuit 40 includes a frequency divider circuit 41 and a counter 42.

[0081] Frequency divider circuit 41 outputs a gating time signal GT after dividing the signal BFO. Counter 42 counts the number of pulses of clock signal CK contained within the time specified by the gating time signal GT, and outputs the count value CNT. For example, as Figure 9 As shown in the timing diagram, the frequency divider circuit 41 outputs a high-level gating signal GT during a specified period of the output signal BFO. The counter 42 outputs a count value CNT representing the number of pulses of the clock signal CK contained during the period when the gating signal GT is high. In this case, the time during which the gating signal GT is high corresponds to the gating time.

[0082] The count value CNT is equivalent to the ratio of the frequency of the clock signal CK to the frequency of the signal BFO. The higher the frequency of the signal BFO, the smaller the count value CNT. That is, there is a one-to-one relationship between the frequency of the signal BFO ​​and the count value CNT. The count value CNT is equivalent to the measured value of the frequency of the signal BFO, i.e., the oscillation frequency f. The count value CNT is stored in register 70.

[0083] The longer the gate time, the higher the measurement resolution based on the measurement circuit 40, but the longer the time required for measurement. Therefore, the gate time is appropriately set according to the upper limit value of the measurement time allowed, for example, to several hundred milliseconds.

[0084] The clock signal CK is output from the clock generation circuit 50. The higher the frequency of the clock signal CK, the higher the measurement resolution based on the measurement circuit 40, and therefore, for example, the clock generation circuit 50 can also be a ring oscillator capable of outputting a signal of several tens of MHz to several hundred MHz. In addition, the clock signal CK from the clock generation circuit 50 can be output only during the period in which the gate time signal GT is a prescribed logic level, that is, the gate time, for example, can be output only during the period in which the gate time signal GT is a high level. Therefore, although the clock signal CK can be continuously output from the clock generation circuit 50 also during the period in which the electrostatic capacitance sensor 1 is operating, it is also possible to provide a period during which the output of the clock signal CK from the clock generation circuit 50 is stopped outside the gate time. In this case, it is possible to reduce the power consumption of the electrostatic capacitance sensor 1.

[0085] The control circuit 60 controls the operation of the oscillation circuit 20. For example, the control circuit 60 outputs an enable signal to the oscillation circuit 20, and the oscillation circuit 20 oscillates when the enable signal is a high level and stops oscillating when the enable signal is a low level. In addition, the control circuit 60 controls the operation of the measurement circuit 40. For example, the control circuit 60 outputs a signal indicating the start of measurement to the measurement circuit 40, and the measurement circuit 40 performs a measurement process in accordance with the signal indicating the start of measurement.

[0086] The interface circuit 80 is a circuit for performing data communication with the MCU 200. For example, the interface circuit 80 overwrites a prescribed bit of the register 70 from 0 to 1 when a request for measurement is received from the MCU 200. The control circuit 60 causes the oscillation circuit 20 to start the oscillation operation when it detects that the bit has been overwritten, and outputs a signal indicating the start of measurement to the measurement circuit 40 after a prescribed wait time has elapsed.

[0087] In addition, for example, the interface circuit 80 reads out the count value CNT stored in the register 70 when a read request for the measurement value is received from the MCU 200, and transmits the count value CNT to the MCU 200. The MCU 200 can receive the count value CNT, and calculate the load capacitance C L based on the count value CNT, and can also determine the state of the detection object.

[0088] The interface circuit 80 can be, for example, an interface circuit for an SPI bus, or an interface circuit for an I 2 2C bus. SPI is an abbreviation for Serial Peripheral Interface, and I 2C is an abbreviation for Inter-Integrated Circuit.

[0089] Further, the electrode 101 is an example of a "first electrode", the electrode 102 is an example of a "second electrode", the electrode 103 is an example of a "third electrode", and the electrode 104 is an example of a "ground electrode". In addition, the electrostatic capacitor CD is an example of a "first electrostatic capacitor", and the electrostatic capacitor CG is an example of a "second electrostatic capacitor". In addition, the surface 110a of the substrate 110 is an example of a "first surface", and the surface 110b of the substrate 110 is an example of a "second surface".

[0090] 1-3. Effects

[0091] As explained above, in the electrostatic capacitor sensor 1 of the first embodiment, the oscillation circuit 20 does not oscillate based on the CR oscillation of the charging and discharging of the electrostatic capacitors CD, CG, but oscillates based on the resonance of the vibrator 3 and the electrostatic capacitors CD, CG, and thus is less likely to be affected by external amplitude noise. Therefore, according to the electrostatic capacitor sensor 1 of the first embodiment, the electrostatic capacitor can be detected with high precision.

[0092] In addition, in the electrostatic capacitor sensor 1 of the first embodiment, since the oscillation frequency of the oscillation circuit 20 varies depending on the electrostatic capacitors CD, CG, the variable range of the oscillation frequency can be enlarged compared to the case where there is no electrostatic capacitor CG, that is, the case where there is no electrode 103 in the sensing portion 100. Therefore, according to the electrostatic capacitor sensor 1 of the first embodiment, the detection sensitivity of the electrostatic capacitor can be improved.

[0093] In addition, in the electrostatic capacitor sensor 1 of the first embodiment, the vibrator 3 has a very high Q value, and thus functions also as a noise filter. The signal output from the vibrator 3 to the input node NG of the amplifier 211 is a signal with little noise and close to a sine wave. Therefore, according to the electrostatic capacitor sensor 1 of the first embodiment, since a spike due to noise does not occur in the output signal of the buffer circuit 30, the possibility of erroneous measurement by the measurement circuit 40 can be reduced.

[0094] In addition, in the electrostatic capacitor sensor 1 of the first embodiment, the electrode 104 is provided in the surface 110b of the substrate 110 at a position opposite to the arrangement region of the electrodes 101, 102, 103 in the surface 110a, and thus in the case where an object that is not a detection target is located at a position opposite to the surface 110b, the influence of the object on the electrostatic capacitors CD, CG can be reduced. Therefore, according to the electrostatic capacitor sensor 1 of the first embodiment, the detection precision of the electrostatic capacitor can be improved.

[0095] In addition, as explained above, Figure 10As shown, the variable range of the oscillation frequency of the LC oscillation circuit using the LC resonance based on the inductor and the electrostatic capacitor is wider than that of the oscillation circuit using the vibrator and the electrostatic capacitor. Figure 10 is a graph showing the relationship between the reference frequency Δf / f0. The solid line is the curve in the case where the vibrator 3 is a tuning fork type quartz vibrator, which corresponds to L the solid line of FIG. 6. The broken line is the curve in the case of the LC oscillation circuit. As is apparent from Figure 8 , the variable range of the oscillation frequency of the oscillation circuit using the vibrator and the electrostatic capacitor is extremely narrow compared to that of the LC oscillation circuit. Figure 10

[0096] Therefore, an electrostatic capacitor sensor having a high detection sensitivity using the LC oscillation circuit is also considered. However, in the case where, for example, the electrostatic capacitor sensor using the LC oscillation circuit detects the electrostatic capacitor of the order of pF, if a small inductor of the order of nH is used in order to realize low cost, the oscillation frequency becomes of the order of GHz, and various problems such as an increase in the size and power consumption of the circuit for measuring the electrostatic capacitor occur. On the contrary, in order to make the oscillation frequency of the order of MHz, a large inductor of the order of μH needs to be used, which hinders the low size and low cost of the electrostatic capacitor sensor.

[0097] In contrast, in the electrostatic capacitor sensor 1 of the present embodiment, the oscillation circuit 20 using the vibrator 3 and the electrostatic capacitors CD, CG, although the variable range of the oscillation frequency is relatively narrow compared to the LC oscillation circuit, can easily realize the oscillation frequency of the order of kHz, MHz using a small vibrator 3, and, for example, with respect to the electrostatic capacitor of the order of pF, can obtain the variable range of the oscillation frequency required in practice as shown in Figure 8 . Furthermore, the inductance value of the inductor is determined by the size, and therefore, it is difficult to reduce the size of the inductor without changing the inductance value, but in contrast, the vibrator 3 can be further downsized and low cost due to the progress of the manufacturing process in the future. Therefore, the electrostatic capacitor sensor 1 according to the first embodiment can realize low size and low cost compared to the electrostatic capacitor sensor using the LC oscillation circuit, and therefore, for example, even if the detection object is a small object, it can be easily used.

[0098] 2. Second Embodiment

[0099] Hereinafter, with respect to the second embodiment, the same reference numerals are assigned to the same structures as those of the first embodiment, and the same explanation as that of the first embodiment is omitted or simplified, and the contents different from those of the first embodiment are mainly explained.

[0100] Figure 11 is a graph showing the appearance of the electrostatic capacitor sensor 1 of the second embodiment. As Figure 11 ​As shown, the electrostatic capacitive sensor 1 of the second embodiment is the same as that of the electrostatic capacitive sensor 1 of the first embodiment, including an oscillator 10, a sensing unit 100, and a cable 15 connecting the oscillator 10 and the sensing unit 100. The structure of the oscillator 10 is the same as that of the first embodiment, so its illustration and description are omitted.

[0101] like Figure 11 As shown, the sensing unit 100 is disposed outside the package 4 of the oscillator 10 and is connected to the oscillator 10 via a cable 15. The cable 15 may be, for example, a coaxial cable, a flexible flat cable, etc.

[0102] The sensing unit 100 includes a substrate 110, which has a surface 110a and a back surface 110b of the surface 110a. Electrodes 101 and 102 are provided on the surface 110a of the substrate 110. On the surface 110b of the substrate 110, an electrode 104 is provided at a position opposite to the arrangement area of ​​the electrodes 101 and 102 in the surface 110a. For example, the electrode 104 is provided on approximately the entire surface of the surface 110b.

[0103] Electrodes 101, 102, and 104 are connected to the external connection terminals of the oscillator 10 via wiring included in cable 15. Therefore, electrodes 101, 102, and 104 are connected to the terminals of the circuit device 2 via the external connection terminals of the oscillator 10.

[0104] In this embodiment, electrode 101 is a sensing electrode connected to the XD terminal of circuit device 2, and electrode 102 is an electrode with a fixed potential. For example, electrode 102 is connected to the ground terminal, i.e., the VSS terminal, of circuit device 2, and its potential is fixed at ground potential. Electrode 104 is connected to the VSS terminal of circuit device 2, and its potential is fixed at ground potential.

[0105] The sensing unit 100 is arranged with electrodes 101 and 102 facing the object to be detected by electrostatic capacitance. The electrostatic capacitance CD between electrodes 101 and 102 varies according to the dielectric constant of the object to be detected.

[0106] When the electrostatic capacitance CD changes, the load capacitance C of oscillator 3... L The oscillation frequency f of the oscillation circuit 20 also changes. Therefore, the circuit device 2 measures the oscillation frequency f and outputs the measured value of the oscillation frequency f to the outside of the oscillator 10. The external device can detect the change in electrostatic capacitance CD based on the measured value of the oscillation frequency f and determine the state of the object being detected. In addition, when an object that is not the object being detected is located opposite the surface 110b of the substrate 110, the electrode 104 functions as a shielding component to reduce the influence of the object on the electrostatic capacitance CD.

[0107] Figure 12is a functional block diagram of the electrostatic capacity sensor 1 of the second embodiment. As shown in Figure 12 The electrostatic capacity sensor 1 of the second embodiment has the circuit device 2 and the sensing portion 100, like the electrostatic capacity sensor 1 of the first embodiment.

[0108] The circuit device 2 has the drive circuit 21, the buffer circuit 30, the measurement circuit 40, the clock generation circuit 50, the control circuit 60, the register 70, and the interface circuit 80, like the first embodiment, and further has the capacitor 90. Further, the circuit device 2 can be configured to omit or change a part of these elements, or add other elements.

[0109] Figure 13 is a diagram showing a configuration example of the drive circuit 21 and the buffer circuit 30 in the second embodiment. As shown in Figure 13 The drive circuit 21 contains the amplifier 211 and the resistors 212, 213, like the first embodiment. Further, the buffer circuit 30 contains the capacitor 31, the CMOS inverter circuit 32, and the resistor 33, like the first embodiment. The structure and functions of the drive circuit 21, the buffer circuit 30, the measurement circuit 40, the clock generation circuit 50, the control circuit 60, the register 70, and the interface circuit 80 are the same as those of the first embodiment, and thus the description thereof is omitted.

[0110] The electrode 101 of the sensing portion 100 is connected to one of the input node NG and the output node ND of the amplifier 211, and the electrode 102 of the sensing portion 100 is connected to the ground. Further, one end of the capacitor 90 is connected to the other of the input node NG and the output node ND of the amplifier 211, and the other end of the capacitor 90 is connected to the ground. In Figure 12 and Figure 13 the electrode 101 is connected to the output node ND of the amplifier 211, and one end of the capacitor 90 is connected to the input node NG of the amplifier 211.

[0111] The capacitor 90 is built in the circuit device 2, and is not formed in the sensing portion 100, and thus the electrostatic capacity CG of the capacitor 90 is a fixed value. The electrostatic capacity CG is, for example, several pF to several tens of pF. Further, the capacitor 90 can be provided inside the package 4, or can be provided outside the circuit device 2.

[0112] The load capacity C L is composed of the electrostatic capacity CD between the electrode 101 and the electrode 102 and the electrostatic capacity CG of the capacitor 90, and is represented by the above-described equation (4). Further, according to the above-described equations (1) to (4), the oscillation frequency f of the oscillation circuit 20 varies depending on the electrostatic capacity CD.

[0113] The other structure and operation of the electrostatic capacitance sensor 1 of the second embodiment are the same as those of the electrostatic capacitance sensor 1 of the first embodiment, and thus the description thereof is omitted.

[0114] Further, the electrode 101 is an example of the "first electrode", the electrode 102 is an example of the "second electrode", and the electrode 104 is an example of the "ground electrode". In addition, the electrostatic capacitance CD is an example of the "first electrostatic capacitance". In addition, the surface 110a of the substrate 110 is an example of the "first surface", and the surface 110b of the substrate 110 is an example of the "second surface".

[0115] In the electrostatic capacitance sensor 1 of the second embodiment described above, the oscillation circuit 20 does not oscillate based on the CR oscillation of the charging and discharging of the electrostatic capacitance CD, but oscillates based on the resonance of the vibrator 3 and the electrostatic capacitance CD, and thus is less likely to be affected by external amplitude noise. Therefore, according to the electrostatic capacitance sensor 1 of the second embodiment, the electrostatic capacitance can be detected with high precision.

[0116] In addition, in the electrostatic capacitance sensor 1 of the second embodiment, the vibrator 3 has a very high Q value, and thus functions also as a noise filter. Noise input from the electrode 101 of the sensing portion 100 connected to the output node ND of the amplifier 211 is greatly reduced by the vibrator 3, and the signal output from the vibrator 3 to the input node NG of the amplifier 211 is a signal with little noise and close to a sine wave. Therefore, according to the electrostatic capacitance sensor 1 of the second embodiment, the possibility that the detection precision is reduced due to noise input from the electrode 101 is reduced.

[0117] In addition, in the electrostatic capacitance sensor 1 of the second embodiment, the electrode 104 is provided in the surface 110b of the substrate 110 at a position opposite to the arrangement region of the electrodes 101 and 102 in the surface 110a, and thus in a case where an object that is not a detection target is located at a position opposite to the surface 110b, it is possible to reduce the influence of the object on the electrostatic capacitance CD. Therefore, according to the electrostatic capacitance sensor 1 of the second embodiment, it is possible to improve the detection precision of the electrostatic capacitance.

[0118] In addition, according to the electrostatic capacitance sensor 1 of the second embodiment, compared to an electrostatic capacitance sensor using an LC oscillation circuit, it is possible to realize low size and low cost, and thus for example, even if the detection target is a small object, it is possible to easily use the electrostatic capacitance sensor.

[0119] 3. Modification

[0120] The present application is not limited to the present embodiments, and various modifications can be made within the scope of the present application.

[0121] For example, in the above-described second embodiment, the electrode 101 of the sensing portion 100 is connected to the output node ND of the amplifier 211, and the capacitor 90 is connected to the input node NG of the amplifier 211, but the electrode 101 can be connected to the input node NG, and the capacitor 90 can be connected to the output node ND.

[0122] In addition, in each of the above-described embodiments, the circuit device 2 measures the oscillation frequency f based on the signal BFO, and outputs the measured value of the oscillation frequency f to the outside of the oscillator 10, but the signal BFO can be output to the outside. Also, an external device can measure the oscillation frequency f as the frequency of the signal BFO, and calculate the value of the load capacitance C based on the measured value of the oscillation frequency f. In this case, the circuit device 2 can not have the measurement circuit 40. Alternatively, the circuit device 2 can calculate the value of the load capacitance C based on the oscillation frequency f, and output the value of the load capacitance C to the outside. L L L

[0123] In addition, the oscillator 10 of each of the above-described embodiments is a simple oscillator such as an SPXO, but can be an oscillator having a temperature compensation function such as a TCXO, and can be an oscillator having a frequency control function such as a VCXO. SPXO is an abbreviation for Simple Packaged Crystal Oscillator. TCXO is an abbreviation for Temperature Compensated Crystal Oscillator. VCXO is an abbreviation for Voltage Controlled Crystal Oscillator. In addition, the oscillator 10 can be an oscillator having a temperature compensation function and a frequency control function such as a VC-TCXO, and can be an oscillator having a temperature control function such as an OCXO, and the like. VC-TCXO is an abbreviation for Voltage Controlled Temperature Compensated Crystal Oscillator. In addition, OCXO is an abbreviation for Oven Controlled Crystal Oscillator.

[0124] ​​​In addition, in each of the above-described embodiments, an example in which the electrostatic capacity sensor 1 is used as a sensor for detecting the amount of liquid in a container is described, but the electrostatic capacity sensor 1 can also be used as various sensors such as a proximity sensor that detects the approach of an object, a touch sensor that detects the contact of an object, a sensor that detects rain, fog, ice, snow, gas, and the like. For example, the electrostatic capacity sensor 1 can be used as a sensor that detects the approach or contact of a finger to a door in the opening and closing of the door and outputs an unlock signal of the door. The electrostatic capacity sensor 1 can be used not only as a sensor for discriminating the amount, approach, or contact of an object but also as a sensor for discriminating the kind, liquid concentration, or the like of an object.

[0125] In addition, a part of a vehicle body of a vehicle can be used as at least a part of the sensing portion 100. For example, a first insulating layer is provided on one of the front surface and the back surface of a metal plate used as a material of the vehicle body, and at least one of the electrode 101 and the electrode 103 of the sensing portion 100 is provided on the surface of the first insulating layer on the side opposite to the metal plate. Further, a second insulating layer is provided on the other of the front surface and the back surface of the metal plate. When a part of a human body such as a finger or a hand contacts the surface of the second insulating layer on the side opposite to the metal plate, the ground capacitance value of the metal plate changes. The ground capacitance and the capacitance between the metal plate and the electrode provided on the surface of the first insulating layer on the side opposite to the metal plate are connected in series between the ground potential and the XG terminal or between the ground potential and the XD terminal. According to this structure, a touch sensor that uses the surface of the second insulating layer on the side opposite to the metal plate as a contact surface can be realized. That is, an electrostatic capacity sensor in which the oscillation frequency changes depending on whether or not there is contact with the contact surface can be realized. Further, a third insulating layer can be provided on the surface of the electrode provided on the surface of the first insulating layer on the side opposite to the metal plate on the side opposite to the first insulating layer. Thus, a touch sensor that uses the surface of the third insulating layer on the side opposite to the electrode as a contact surface can be realized. The metal plate can be a sheet of iron, a sheet of aluminum, or the like. In addition, the first insulating layer and the second insulating layer can be a coating provided on the metal plate. For example, the electrostatic capacity sensor can be used as a touch sensor for vehicle theft prevention.

[0126] The above-described embodiments and modified examples are one example and are not limited thereto. For example, each of the embodiments and each of the modified examples can be appropriately combined.

[0127] The present application includes structures substantially the same as those described in the embodiments, such as structures having the same functions, methods, and results, or structures having the same objects and effects. In addition, the present application includes structures in which non-essential parts of the structures described in the embodiments are replaced. In addition, the present application includes structures that have the same functional effects as the structures described in the embodiments, or structures that can achieve the same objects. In addition, the present application includes structures to which publicly known technologies are added to the structures described in the embodiments.

[0128] The following is derived from the above-described embodiments and modified examples.

[0129] One embodiment of an electrostatic capacitance sensor includes:

[0130] a package;

[0131] an oscillation circuit provided inside the package; and

[0132] a first electrode and a second electrode provided outside the package,

[0133] the oscillation circuit has:

[0134] an amplifier; and

[0135] a resonator provided inside the package, connected between an input node and an output node of the amplifier,

[0136] the first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier,

[0137] the second electrode is a potential-fixed electrode,

[0138] an oscillation frequency of the oscillation circuit varies according to a first electrostatic capacitance between the first electrode and the second electrode.

[0139] In the electrostatic capacitance sensor, the oscillation circuit does not oscillate based on charging and discharging of the first electrostatic capacitance between the first electrode and the second electrode, but oscillates based on resonance of the resonator and the first electrostatic capacitance, and thus is less likely to be affected by external amplitude noise. Therefore, according to the electrostatic capacitance sensor, an electrostatic capacitance can be detected with high precision.

[0140] Further, the variable range of the oscillation frequency of the LC oscillation circuit using the LC resonance based on the inductor and the electrostatic capacity is wider than that of the oscillation circuit using the vibrator and the electrostatic capacity, and therefore, an electrostatic capacity sensor using the LC oscillation circuit having high detection sensitivity is also considered. However, in the case where the electrostatic capacity sensor using the LC oscillation circuit detects, for example, the electrostatic capacity of the order of pF, if a small inductor of the order of nH is used in order to realize low cost, the oscillation frequency becomes of the order of GHz, and various problems such as increase in size and power consumption of the circuit for measuring the electrostatic capacity occur. On the contrary, in order to make the oscillation frequency of the order of MHz, a large inductor of the order of μH is required, and this hinders the low size and low cost of the electrostatic capacity sensor.

[0141] On the contrary, the oscillation circuit using the vibrator and the electrostatic capacity has a relatively narrow variable range of the oscillation frequency compared with the LC oscillation circuit, but can easily realize the oscillation frequency of the order of kHz or MHz using a small vibrator, and for example, can obtain a practically required variable range of the oscillation frequency for the electrostatic capacity of the order of pF. Further, the inductance value of the inductor is determined by the size, and therefore, it is difficult to reduce the size of the inductor without changing the inductance value, but on the contrary, the vibrator can be further reduced in size and cost due to the progress of the manufacturing process in the future. Therefore, according to the electrostatic capacity sensor, the low size and low cost can be realized compared with the electrostatic capacity sensor using the LC oscillation circuit.

[0142] Another aspect of the electrostatic capacity sensor includes:

[0143] an oscillation circuit; and

[0144] a first electrode and a second electrode,

[0145] the oscillation circuit has:

[0146] an amplifier; and

[0147] a vibrator connected between an input node and an output node of the amplifier,

[0148] the first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier,

[0149] the second electrode is a potential-fixed electrode,

[0150] a first electrostatic capacity between the first electrode and the second electrode changes according to a state of an object to be detected,

[0151] an oscillation frequency of the oscillation circuit changes according to the first electrostatic capacity.

[0152] In this electrostatic capacitance sensor, the oscillation circuit does not oscillate based on the charging and discharging of the first electrostatic capacitance between the first and second electrodes (CR oscillation), but rather on the resonance between the oscillator and the first electrostatic capacitance. Therefore, it is less susceptible to external amplitude noise. Consequently, this electrostatic capacitance sensor can accurately detect the electrostatic capacitance corresponding to the state of the object being detected.

[0153] Furthermore, this electrostatic capacitive sensor can achieve smaller size and lower cost compared to electrostatic capacitive sensors that use LC oscillation circuits, so it can be easily used even if the object being detected is a small object.

[0154] Another method for using the electrostatic capacitive sensor is...

[0155] The electrostatic capacitive sensor includes:

[0156] A buffer circuit, which receives a signal from the oscillator output to the input node of the amplifier; and

[0157] A measurement circuit that measures the frequency of the signal output from the buffer circuit.

[0158] In this electrostatic capacitive sensor, the oscillator has a very high Q value, thus also functioning as a noise filter. The signal output from the oscillator to the input node of the amplifier is a low-noise, near-sine wave signal. Therefore, according to this electrostatic capacitive sensor, since no noise-induced spikes are generated in the output signal of the buffer circuit, the possibility of erroneous measurements by the measurement circuit can be reduced.

[0159] Another method for using the electrostatic capacitive sensor is...

[0160] The electrostatic capacitive sensor includes a substrate having a first surface and a second surface that serves as the back surface of the first surface.

[0161] The first electrode and the second electrode are disposed on the first surface of the substrate.

[0162] On the second surface of the substrate, a ground electrode is provided at a position opposite to the configuration area of ​​the first electrode and the second electrode on the first surface.

[0163] In this electrostatic capacitance sensor, a ground electrode is provided on the second surface of the substrate, opposite to the arrangement area of ​​the first and second electrodes on the first surface. Therefore, when an object not being detected is located opposite the second surface, the influence of that object on the first electrostatic capacitance is reduced. Thus, according to this electrostatic capacitance sensor, the detection accuracy of electrostatic capacitance can be improved.

[0164] In one embodiment of the electrostatic capacitance sensor, it can also be that

[0165] The first electrode is connected to the output node of the amplifier.

[0166] In the electrostatic capacitance sensor, the vibrator has a very high Q value, and thus functions also as a noise filter. Noise input from the first electrode connected to the output node of the amplifier is greatly reduced by the vibrator, and a signal output from the vibrator to the input node of the amplifier is a signal with little noise and close to a sine wave. Therefore, according to the electrostatic capacitance sensor, the likelihood of a decrease in detection accuracy due to noise input from the first electrode is reduced.

[0167] One embodiment of the electrostatic capacitance sensor can also be that

[0168] The electrostatic capacitance sensor includes a third electrode provided outside the package,

[0169] The third electrode is a sensing electrode connected to the other of the input node and the output node of the amplifier,

[0170] The oscillation frequency of the oscillation circuit varies in accordance with the first electrostatic capacitance and a second electrostatic capacitance between the third electrode and the second electrode.

[0171] In the electrostatic capacitance sensor, since the oscillation frequency of the oscillation circuit varies in accordance with the first electrostatic capacitance and the second electrostatic capacitance, the variable range of the oscillation frequency can be expanded compared to a case where there is no second electrostatic capacitance. Therefore, according to the electrostatic capacitance sensor, the detection sensitivity of the electrostatic capacitance can be improved.

[0172] One embodiment of the electrostatic capacitance sensor can also be that

[0173] The electrostatic capacitance sensor includes a substrate having a first surface and a second surface that is a back surface of the first surface,

[0174] The first electrode, the second electrode, and the third electrode are provided on the first surface of the substrate,

[0175] The second electrode is located between the first electrode and the third electrode,

[0176] A ground electrode is provided on the second surface of the substrate at a position opposite to a configuration region of the first electrode, the second electrode, and the third electrode in the first surface.

[0177] In the electrostatic capacity sensor, a ground electrode is provided in the second surface of the substrate at a position opposite the arrangement region of the first electrode, the second electrode, and the third electrode in the first surface, so that in a case where an object other than the detection object is located at a position opposite the second surface, the influence of the object on the first electrostatic capacity and the second electrostatic capacity is reduced. Thus, according to the electrostatic capacity sensor, the detection accuracy of the electrostatic capacity can be improved.

Claims

1. An electrostatic capacitive sensor, comprising: Encapsulation; An oscillation circuit is disposed inside the package; and The first electrode and the second electrode are disposed on the outside of the package. The oscillation circuit has the following characteristics: Amplifier; and An oscillator, disposed inside the package, connects between the input and output nodes of the amplifier. The first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier. The second electrode is an electrode with a fixed potential. The oscillation frequency of the oscillation circuit varies according to the first electrostatic capacitance between the first electrode and the second electrode.

2. The electrostatic capacitive sensor according to claim 1, wherein, The electrostatic capacitive sensor includes: A buffer circuit, which receives a signal from the oscillator output to the input node of the amplifier; and A measurement circuit that measures the frequency of the signal output from the buffer circuit.

3. The electrostatic capacitive sensor according to claim 1, wherein, The electrostatic capacitive sensor includes a substrate having a first surface and a second surface that serves as the back surface of the first surface. The first electrode and the second electrode are disposed on the first surface of the substrate. On the second surface of the substrate, a ground electrode is provided at a position opposite to the configuration area of ​​the first electrode and the second electrode on the first surface.

4. The electrostatic capacitive sensor according to claim 1, wherein, The first electrode is connected to the output node of the amplifier.

5. The electrostatic capacitive sensor according to claim 1, wherein, The electrostatic capacitive sensor includes a third electrode disposed outside the package. The third electrode is a sensing electrode connected to the other of the input node and the output node of the amplifier. The oscillation frequency of the oscillation circuit varies according to the first electrostatic capacitor and the second electrostatic capacitor between the third electrode and the second electrode.

6. The electrostatic capacitive sensor according to claim 5, wherein, The electrostatic capacitive sensor includes a substrate having a first surface and a second surface that serves as the back surface of the first surface. The first electrode, the second electrode, and the third electrode are disposed on the first surface of the substrate. The second electrode is located between the first electrode and the third electrode. On the second surface of the substrate, a ground electrode is provided at a position opposite to the arrangement area of ​​the first electrode, the second electrode, and the third electrode on the first surface.

7. An electrostatic capacitive sensor, comprising: Oscillating circuit; and Electrode 1 and Electrode 2, The oscillation circuit has the following characteristics: Amplifier; and An oscillator, which is connected between the input and output nodes of the amplifier. The first electrode is a sensing electrode connected to one of the input node and the output node of the amplifier. The second electrode is an electrode with a fixed potential. The first electrostatic capacitance between the first electrode and the second electrode changes according to the state of the object being detected. The oscillation frequency of the oscillation circuit varies according to the first electrostatic capacitor.

8. The electrostatic capacitive sensor according to claim 7, wherein, The electrostatic capacitive sensor includes: A buffer circuit, which receives a signal from the oscillator output to the input node of the amplifier; and A measurement circuit that measures the frequency of the signal output from the buffer circuit.

9. The electrostatic capacitive sensor according to claim 7, wherein, The electrostatic capacitive sensor includes a substrate having a first surface and a second surface that serves as the back surface of the first surface. The first electrode and the second electrode are disposed on the first surface of the substrate. On the second surface of the substrate, a ground electrode is provided at a position opposite to the configuration area of ​​the first electrode and the second electrode on the first surface.

10. The electrostatic capacitive sensor according to claim 7, wherein, The first electrode is connected to the output node of the amplifier.

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