JPH11258090A - Electrostatic capacity type sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic capacity type sensor device capable of restraining the influence of electrostatic attractive force applied to an electrode of the electrostatic capacity type sensor, simply correcting the sensitivity and offset peculiar to the electrostatic capacity type sensor causing no mechanical shift in setting. SOLUTION: A pressure sensor 3 is connected to a CR oscillating circuit 12 to determine the oscillation frequency. In an electrostatic capacity detecting circuit 2, the drive of each part is controlled by a timing generator 17 and frequency signals CK2 are counted for a unit hour to take a difference from a reference count value to output a pulse string Pout for the count difference. In applying bias to the pressure sensor for starting the CR oscillation circuit 12, bias is applied immediately before the start of oscillation, and when the oscillation is stopped, immediately it is returned to zero bias. A constant K of unit hour and the preset value Pps of the reference count value are variably stored in a non-voltage memory 18 to be used for the operation of each part. The sensitivity can be adjusted according to the constant K, and the offset is adjusted according to the preset value Pps and corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor device for detecting a physical quantity such as pressure by a capacitance type sensor in which a fixed electrode is opposed to a movable electrode made of a semiconductor. TECHNICAL FIELD The present invention relates to a capacitance-type sensor device that outputs a pulse train according to a change in capacitance of a capacitance-type sensor.

[0002]

2. Description of the Related Art Capacitive sensors made of semiconductors have been widely put to practical use because of their small size and high resolution. For example, as disclosed in Japanese Patent Application Laid-Open No. 9-5192 (G01L 9/12). It is already well known. In other words, a conventional technique will be described with reference to FIG. 2 according to the present invention. FIG. 2 is an exploded perspective view showing an example of a capacitance type pressure sensor, in which a fixed electrode 8 is provided on a diaphragm 6a made of a semiconductor. They are opposed to each other, receive pressure on the back side of the diaphragm 6a, and output a change in the received pressure as a change in capacitance.

In general, the capacitance is converted into a digital signal by an A / D converter after analog measurement, and the digital signal is input to a microcomputer or the like as a control system to perform a counting process. At the same time, various determinations are made and a control command is output to a predetermined device as needed.

However, in the conversion by the A / D converter, an expensive A / D converter having a large number of bits is required in order to reduce a bit error at the time of conversion, and this is a bottleneck in reducing the cost of the device.

For this reason, for example, Japanese Patent Application Laid-Open No. 6-307979
There is a concept of using a capacitance detection circuit disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, and it is possible to output digital data according to the capacitance of a capacitance type sensor without providing an A / D converter. . That is, it functions as a capacitance type sensor device called by the present applicant. In this capacitance detection circuit, a capacitance type sensor is used as a capacitor constituting a CR oscillation circuit, and pressure is applied. Then, the capacitance changes and the oscillation frequency also changes.

Accordingly, the number of pulses output per unit time also changes, so that the pressure can be detected from the number of pulses generated within a certain time. Then, the output becomes digital data composed of a pulse train, and if it is directly supplied to the computer, the computer can calculate the pressure value by counting the number of pulses of the pulse train.

[0007]

However, such a conventional capacitance-type sensor device (capacitance detection circuit) has the following problems.

That is, the capacitance type pressure sensor 3
Since a predetermined voltage is applied between the diaphragm (movable electrode) 6a and the fixed electrode 8 of the CR oscillation circuit, a potential difference is generated between the electrodes. Then, an electrostatic attraction based on the potential difference is generated, so that the diaphragm 6a is pulled by the electrostatic attraction, thereby changing the capacitance generated between the electrodes and causing an error.

When the CR oscillation circuit is constituted by, for example, a logic gate as shown in FIG. 8, the circuit includes a NOT 21 and a two-input NAND 22 and a NOT 24 which are connected in sequence and the output of the NOT 24 is connected to a fixed resistor 3.
The pressure sensor 3 is connected in parallel to both the NOT 21 and the NAND 22 by connecting to the input of the NOT 21 via 0 and a loop circuit. Then, and as a control terminal T ₀ the one input of NAND22, when the control terminal T ₀ and the high level NAND22
Operates as an inverter and becomes active.

Therefore, the oscillation operation of this CR oscillation circuit is
This corresponds to the state of the control terminal T ₀ , and a voltage as shown in FIG. 9 is applied to each part. In other words, this CR oscillation circuit has the control terminal T
Oscillation starts when _{0 is set} to high level, and stops when control terminal T ₀ is returned to low level. And
Before and after the oscillation operation, one of the electrodes of the pressure sensor 3 is at a high level and the other is at a low level, and a potential difference equal to the power supply voltage is applied between the two electrodes. For this reason, the electrostatic attraction continues to be applied between the two electrodes of the pressure sensor 3 while the oscillation is stopped during the non-measurement period. And
Since the pressure sensor 3 is required to detect a minute pressure, the thickness of the diaphragm 6a is made extremely thin, and the interval between the diaphragm 6a and the fixed electrode 8 is extremely narrow. As a result, the distance between the electrodes is reduced, and the capacitance is increased. In other words, even when the measurement pressure is not applied, an output of a predetermined magnitude is output and the pressure is applied.
The error influence on the detection output increases.

The capacitance type pressure sensor 3 has a slight variation in the sensitivity characteristic and the operating point of each manufactured sensor. This is related to the fact that the pressure sensor 3 makes the thickness of the diaphragm extremely thin as described above and extremely narrows the interval between the pressure electrode 3 and the fixed electrode. Have an influence on the sensitivity characteristic and the operating point.

For this reason, as the capacitance detecting circuit, C
By changing the resistor 30 that constitutes the R oscillation circuit,
The sensitivity and the operating point (offset) of the pressure sensor 3 are adjusted. That is, the conventional technique will be described with reference to FIG. 1 according to the present invention.
1 and the third CR oscillation circuit 1
The fixed resistor 50 connected to 3 is a variable resistor, and the oscillation frequency (CK1) of the first CR oscillation circuit 11 is changed by changing the resistor 40, thereby adjusting the offset. Then, the oscillation frequency (CK3) of the third CR oscillation circuit 13 is changed by changing the resistance 50, thereby adjusting the sensitivity.

However, in this case, fine adjustment is difficult because the adjustment is performed by mechanically displacing the variable resistor, and there is a limit in matching to the true value, and an error cannot be avoided. Further, if the device is vibrated during measurement or transportation, the set value of the variable resistor may be shifted, causing an error. Also, in order to prevent the deviation of the set value due to this mechanical vibration, the adjusted variable resistor is potted with silicon or the like, but stress distortion occurs during potting hardening. May occur.

Therefore, there is an idea that laser trimming is performed on a circuit board without using a variable resistor which cannot avoid a mechanical error as a resistor. However, in that case, a ceramic substrate and a thick-film resistor are required, which results in high cost and high cost. Further, the laser trimming device itself is expensive, and the trimming process is also expensive. In laser trimming, components must be arranged so that trimming processing is easy, and the arrangement of components is restricted, which is not suitable for miniaturization.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background, and has as its object to solve the above-mentioned problems and suppress the influence of electrostatic attraction acting on the electrodes of a capacitance type sensor. It is an object of the present invention to provide a capacitance-type sensor device which can easily correct the sensitivity and offset inherent to the capacitance-type sensor element and does not cause a mechanical setting deviation.

[0016]

In order to achieve the above-mentioned object, in a capacitance type sensor device according to the present invention, a capacitance type sensor whose capacitance changes according to a change in a detected amount; An oscillating unit that oscillates at a frequency corresponding to the capacitance of the capacitance type sensor, a counting unit that counts the output of the oscillating unit for a unit time, takes a difference from a reference count value, and outputs a pulse train of a counting difference. In applying a bias to the capacitive sensor to activate the oscillating means, a bias is applied immediately before the start of oscillation, and the bias is immediately returned to zero bias when the oscillation stops. (Claim 1).

With this configuration, a potential difference is set for both electrodes of the capacitance-type sensor immediately before the oscillation means starts oscillating, but the potential is immediately returned to the same potential when oscillation stops, so that no electrostatic attraction acts. . Since the capacitance type sensor has a poor response to the electrostatic attraction due to the power supply voltage, it is also possible to bias the two electrodes immediately before the start of the oscillation and to return to the zero bias immediately after the oscillation stops. Also, oscillation related to measurement can be started and stopped before the movable electrode of the capacitance type sensor is displaced by the electrostatic attraction.

Further, there is provided storage means for changingably storing a base value per unit time and an initial value of a reference count value when the counting means performs a counting operation (claim 2). Then, the storage means stores information such as a base value per unit time when the counting means performs a counting operation and an initial value of the reference count value, and the like. Sensitivity and offset can be adjusted and corrected. That is,
The sensitivity can be adjusted by changing the base value of the unit time of the counting operation, and the offset can be adjusted and corrected by changing the initial value of the reference count value.

[0019]

FIG. 1 is a configuration diagram showing an embodiment of a capacitance type sensor device according to the present invention. As shown in FIG. 1, a capacitance type sensor device 1 includes a capacitance type pressure sensor 3 made of a semiconductor and a capacitance change amount of the pressure sensor 3, that is, a capacitance which outputs a detected pressure as a digital pulse train. And a capacitance detection circuit 2.

The pressure sensor 3 detects a gas pressure. As shown in FIG. 2, a diaphragm 6a is formed on the surface of the silicon substrate 6, and the diaphragm 6a becomes a movable electrode and varies with pressure. The surface of the diaphragm 6a is formed in a recess slightly lower than the surface of the silicon substrate 6 by one step.
The portion a is very thin, and easily bends under pressure. That is, the bottom surface side of the silicon substrate 6 on which the diaphragm 6a is formed is also a largely removed concave portion, and the lower surface of the diaphragm 6a becomes a pressure receiving surface. On the other hand, a glass substrate 7 is stacked on the upper surface of the silicon substrate 6, and a fixed electrode 8 is formed on the surface of the glass substrate 7 facing the diaphragm 6a. The two electrodes are electrically connected to wire bonding pads 9 formed on the surface of the silicon substrate 6, and the wire bonding pads 9 are directly connected to the input terminals of the capacitance detection circuit 2.
Alternatively, they are connected indirectly via an amplifier.

The diaphragm 6a maintains a horizontal state when there is no load. When pressure is applied to the pressure receiving surface of the diaphragm 6a, the diaphragm 6a expands toward the glass substrate 7, so that the distance between the diaphragm 6a and the glass substrate 7 changes. Accordingly, the capacitance between both electrodes also changes. That is, the pressure sensor 3 also constitutes a kind of variable capacitor.

The capacitance detecting circuit 2 is configured such that the drive of each section is controlled by a timing generator 17, and an equivalent capacitor 4 for adjusting the displacement or offset of the operating point of the pressure sensor 3. When,
The pressure sensor 3 and a reference capacitor 5 for generating a reference clock are connected to the first CR oscillation circuit 11, the second CR oscillation circuit 12, and the third CR oscillation circuit 13, respectively. Each CR oscillation circuit 11-13 has a fixed resistor 40, 3
0, 50 are connected to each other, and the oscillation frequency is determined to be a predetermined value in combination with each of the capacitors 4, 3, and 5.

The frequency signals CK1 to CK3 are output from the CR oscillation circuits 11 to 13. The frequency signals CK1 to CK3 are square wave clock signals. The frequency signals CK1 and CK2 are sent to the selector 14, respectively, and the frequency signal CK3 is sent to the up / down counter 15, the output circuit 16 and the timing generator 17. . Further, an enable signal is sent from the timing generator 17 to the first and second CR transmission circuits 11 and 12, respectively.

The second CR oscillation circuit 12, as shown in FIG. 3, is constituted by a logic gate. That is, N
An OT 21, a two-input NAND (first NAND) 22 and a two-input NAND (second NAND) 23 are connected in order, and an output of the second NAND 23 is connected to a NOT 2 via a fixed resistor 30.
1 is connected to an input to form a loop circuit, and the pressure sensor 3
Are connected in parallel to both the NOT 21 and the NAND 22.

One input of the first NAND 22 is a first control terminal T _1, and when the first control terminal T ₁ is at a high level, the first NAND 2
2 operates as an inverter and becomes active. 2nd NAN
One input of the D23 has a second control terminal T _2, the second control when the terminal T ₂ is at the low level becomes incompetent first 2NAND23, output is fixed to the high level.

Therefore, the oscillation operation of the second CR oscillation circuit 12 corresponds to the state of the _two control terminals T ₁ and T ₂ , and a voltage as shown in FIG. 4 is applied to each part. . That is, the second CR oscillation circuit 12
The second control terminal T ₂ starts oscillating when a high level, and becomes the first control terminal T ₁ is also a high level, the two control terminals at both low level to stop the oscillation. Then, even if the second control terminal T ₂ is at a high level, the first control terminal T ₁
If is low level, oscillation does not start. Pressure sensor 3
Both electrodes are fixed at a high level when oscillation stops, and the power supply voltage is applied.

Before the start of the oscillation, when the second control terminal T ₂ is at a high level, the electrode connected to the fixed resistor 30 is at a low level, and a potential difference is set between the electrode and the opposite electrode. Therefore, preferably, as shown in FIG. 5, a second control terminal T ₂ is desired to be also low before the oscillation start, that case was confirmed by experiment that the stability of the oscillation is deteriorated. Therefore, the second control terminal T ₂ are the high level immediately before the start of the oscillation is controlled so as to return immediately to the low level when the oscillation stop.

As described above, the potential difference between the two electrodes of the pressure sensor 3 is set immediately before the second CR oscillation circuit 12 starts oscillating, but the potential is immediately returned to the same potential when the oscillation is stopped. Does not work. Since the pressure sensor 3 has a poor response to the electrostatic attraction due to the power supply voltage, even if the electrostatic attraction is generated by biasing between both electrodes immediately before the start of oscillation, the pressure sensor 3
Oscillation related to measurement is started before the diaphragm is displaced by the electrostatic attraction. Therefore, the pressure sensor 3
The effect of the electrostatic attraction acting on the electrodes can be sufficiently suppressed.

The selector 14 selects and outputs one of the frequency signals CK1 and CK2 sent from the first and second CR oscillation circuits 11 and 12 according to the select signal. It is sent from the timing generator 17.

The output of the selector 14 is connected to an up / down counter 15. The up / down counter 15 functions as an up / down counter in response to an up / down signal, and counts up / down for each pulse of the input signal. The up / down signal is also sent from the timing generator 17, and counts up when the up / down signal is at a low level and counts down when the up / down signal is at a high level. The up / down counter 15 has a preset value P
ps is read from the memory 18 and set.

The output circuit 16 is an open / close switch, and outputs a frequency signal CK sent from the third CR oscillation circuit 13.
3, the count output of the up / down counter 15 is output as Pout.

The timing generator 17 is provided with a plurality of different circuit portions for executing a timing signal generation algorithm, and is selectively operated by connecting them in parallel. That is, the frequency signal CK3 is input to the timing generator 17 from the third CR oscillation circuit 13, and the frequency signal CK3
Is internally divided to generate a timing signal for driving and controlling each unit. The timing signal is output to each unit at a desired timing based on the set value K read from the memory 18. Configuration. As each timing signal, an enable signal to the first and second CR oscillation circuits 11 and 12 and a selector circuit 14
The up / down signal for determining the function of the up / down counter 15 is output from the timing generator 17.

The memory 18 is a non-volatile memory whose contents can be rewritten from the outside, and stores a preset value Pps and a count constant K for determining a count time. The preset value Pps is read out and set in the up / down counter 15, and the count constant K is read out and set in the timing generator 17. The timing generator 17 performs frequency division so that the count time becomes a predetermined value based on the read count constant K. In this case, the frequency signal CK3 is frequency-divided to obtain a sensitivity described later. Is determined, the sensitivity is changed and adjusted in steps of 2 ⁿ times.

Therefore, in the capacitance detection circuit 2, each CR
The oscillating circuits 11 to 13 oscillate according to the capacitances of the capacitors 3 to 5, and the first C connected to the equivalent capacitor 4
Frequency signal CK1 of R oscillation circuit 11 and reference capacitor 5
The frequency signal CK3 of the third CR oscillation circuit 13 connected to
Is fixed during at least one measurement. The capacitance C2 of the pressure sensor 3 increases as the gas pressure increases, and the oscillation frequency decreases.

When monitoring the gas pressure using the capacitance type sensor device 1, a predetermined gas pressure is applied to the pressure sensor 3 in a normal state, and the gas pressure decreases when an abnormal state due to gas leakage or the like occurs. , The capacitance C2 also decreases. Therefore, the capacitance C2 when a predetermined gas pressure is applied in a normal state is set to be equal to the capacitance C1 of the equivalent capacitor 4. Thus, in the normal state, the frequency signals CK1 and CK2 become equal. The equivalent capacitor 4 and the reference capacitor 5 preferably have the same or similar temperature characteristics as the pressure sensor 3.
Moreover, the respective pressure sensors 3, the equivalent capacitors 4, and the reference capacitors 5 are arranged close to each other.

The capacitance detection circuit 2 performs signal processing at the timing shown in FIG. 6, and generates a pulse output P corresponding to the gas pressure (the capacitance C2 of the pressure sensor 3).
out is generated. This processing algorithm is disclosed in JP-A-6-307949 and JP-A-9-519.
It is basically the same as that disclosed in No. 2.

That is, during monitoring of the gas pressure, the pressure sensor 3
Is applied to the second CR oscillating circuit 12, and oscillates at a predetermined oscillating frequency to output a frequency signal CK2. Also,
The first and third CR oscillation circuits 11, 13 also have capacitances C1, C
3, the frequency signals CK1, CK2 of the predetermined oscillation frequency determined in
CK3 is output. Either CK1 or CK2 is selectively input to the up / down counter 15, and the up / down counter 15 can set a preset value Pps.

Accordingly, first, a predetermined value is set in advance in the up / down counter 15 as the preset value Pps, and the frequency signal CK1 is supplied to the up / down counter 15 for a predetermined time Tup.
Just enter. At this time, it is operated as an up counter. Then, the count value after the elapse of Tup becomes a value obtained by adding the number of pulses generated during the predetermined time Tup to the preset value Pps. Next, the frequency signal CK2 is input to the up / down counter 15 for a predetermined time Tdown. At this time, it operates as a down counter. Then Tdown
The count value at the time of elapse is a value obtained by subtracting the number of pulses generated during the predetermined time Tdown from the value obtained by counting up. The times Tup and Tdown are set equal. Thereafter, the countdown is performed until the count value of the up / down counter 15 becomes zero, and one pulse is output each time the count value is decremented by one.

When the gas pressure is in a normal state, the capacitance C
1, C2 are equal, and the first and second CR oscillation circuits 11,
Since the twelve oscillation frequencies CK1 and CK2 are equal, the number of output pulses Pout is equal to the preset value Pps.
When the gas pressure decreases, the capacitance C2 of the pressure sensor 3 decreases, so that the oscillation frequency of the frequency signal CK2 increases, and the number of pulses Pout generated during the predetermined time Tdown increases. Therefore, the value is smaller than the preset value Pps. Then, the gas pressure can be detected based on the output pulse number Pout from the capacitance (gas pressure) corresponding to the preset value Pps and the sensitivity characteristics of the pressure sensor 3.

Here, the sensitivity refers to the amount of change in gas pressure corresponding to one bit of output (the amount of change in gas pressure due to the increase or decrease of one output pulse). Since there is slight variation in each of the individual components, the sensitivity and the operating point (offset) can be adjusted.

That is, the number of output pulses Pout is:
The count time Tup of the frequency signal CK1, the count time Tdown of CK2, and the preset value Pps of the up / down counter 15 are given by the following equations.

Pout = Pps + Tup × CK1−Tdown × CK2 where Tup × CK1 and Tdown × CK2 are integers. If Tup = Tdown = TcCK1-CK2 = Δf, the above equation (1) becomes Pout = Tc × Δf + Pps Becomes

Therefore, when the count time Tc of the up / down counter 15 is lengthened, the amount of change (sensitivity) of the output with respect to the frequency difference Δf increases, and the up / down counter 1
By changing the preset value Pps of 5, the offset can be changed. Further, since the count time Tc is generated from the reference frequency signal CK3, Tc = K / CK3, and the sensitivity can be changed by changing the frequency signal CK3 or the count constant K.

Here, in the present invention, the contents stored in the memory 18 are rewritten to adjust the sensitivity and offset of the pressure sensor 3. That is, for example, the initial setting stored in the nonvolatile memory 18 is the preset value P
Suppose that ps = 250 and the count constant K = 100. Then, adjustment is performed so that an output of 1 pulse / 1 psi is obtained in a measurement pressure range of 0 to 500 psi. For the adjustment, first, the pressure sensor 3 is connected to the capacitance detection circuit 2, and the pressure is measured. With this measurement, the pressure sensor 3
Is only 0.8 times the target value, the count constant K becomes 125 at 100 / 0.8.
What is necessary is just to rewrite the count constant K = 125 and the storage of the nonvolatile memory 18. Thereafter, the pressure is measured again, and the offset of the pressure sensor 3 is, for example, 50 psi below the target value.
If it is larger by an amount, the equation (1) is adjusted so that 250 pulses are output at 250 psi.
The preset value Pps becomes 300 at 250 + 50, and the preset value Pps = 300 and the storage in the nonvolatile memory 18 may be rewritten, whereby the adjustment of the sensitivity and the offset is completed.

As described above, the sensitivity and offset of the pressure sensor 3 can be adjusted and corrected only by rewriting the contents stored in the nonvolatile memory 18. Rewriting of the non-volatile memory 18 is an electrical operation, so it can be easily performed, and there is essentially no mechanical setting deviation caused by the conventional adjustment using the variable resistor. Then, the nonvolatile memory 18
Since a personal computer or the like can be used for rewriting, the equipment cost can be reduced. Of course, there is no problem caused by laser trimming, and it is suitable for miniaturization. Further, even if the characteristics of the pressure sensor 3 change due to aging, the correction can be easily made because the nonvolatile memory 18 may be simply rewritten.

Further, as the capacitance type sensor device 1,
The pressure sensor 3 and the capacitance detection circuit 2 may be completely sealed in a package. At this time, it is necessary to provide a write terminal for accessing the non-volatile memory 18, but this enables rewriting adjustment after sealing, so that sensitivity and offset due to stress distortion generated at the time of sealing the package are obtained. Can also be corrected.

* Experimental Results FIG. 7 is a graph showing the experimental results of measuring output pulse fluctuations due to electrostatic attraction. 8 shows the measured values of the oscillation circuit according to the present invention of FIG. 3 by solid lines, and FIG.
The measured value of the conventional oscillation circuit of FIG. These measured values are the results of measuring the pressure every 100 msec. More specifically, the two control terminals T ₁ and T ₂ are controlled to oscillate the pressure sensor for 20 msec, calculate the pressure based on the number of output pulses at that time, and then stop the oscillation for 80 msec. Like that. According to the present invention, a potential difference is generated between both terminals of the pressure sensor immediately before the start of the oscillation so that the oscillation can be stably started just before the start of the oscillation. Are set to the same potential so that no electrostatic attraction is generated.

After the oscillation is stopped, the potential is set to the same value.
Before starting the next oscillation, it is necessary to bias the terminals so as to generate a potential difference. However, in this embodiment, the power supply is once turned off while maintaining the same potential (this prevents a voltage from being applied between both terminals). Therefore, a potential difference does not occur again), and the power is turned on again immediately before the start of the next measurement, and a potential difference is generated. Of course not limited to this, the second control after the oscillation stop terminal T ₂
The holds state dropped L, and to start the next oscillation (the first control terminal T ₁ is switched to the high level) before, various methods such as to switch the second control terminal T ₂ to the high level Can be taken.

Thus, in the conventional oscillating circuit, since the electrostatic attraction is always applied between the electrodes even when the oscillation is stopped, the diaphragm is gradually attracted to the fixed electrode side. Since the measurement is repeated before the displacement returns, the output pulse fluctuation increases with each measurement and saturates as time elapses. On the other hand, in the oscillation circuit according to the present invention, since the electrostatic attraction does not occur during most of the period during which the oscillation is stopped, the influence of the electrostatic attraction can be suppressed, and the output pulse fluctuation is small.

[0050]

As described above, in the capacitance-type sensor device according to the present invention, the potential difference is set for both electrodes of the capacitance-type sensor immediately before the oscillation means starts to oscillate, but the oscillation stops. Sometimes, the potential is immediately returned to the same potential, so that the electrostatic attraction does not act, and since the sensor element has a poor response to the electrostatic attraction due to the power supply voltage, there is no adverse effect even if a bias is applied between both electrodes immediately before the start of oscillation. . Therefore, the effect of the electrostatic attraction acting on the electrodes of the capacitance type sensor can be sufficiently suppressed.

The storage means stores the base value of the unit time and the initial value of the reference count value when the counting means performs the counting operation. Therefore, the capacitance type sensor can be obtained simply by rewriting the stored contents. Can be adjusted and corrected. That is, the sensitivity can be adjusted by changing the base value of the unit time of the counting operation, and the offset can be adjusted and corrected by changing the initial value of the reference count value. Since the rewriting of the storage means is an electrical operation, the rewriting can be easily performed, and there is an excellent effect that there is essentially no mechanical setting deviation caused by the conventional adjustment using the variable resistor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a capacitance type sensor device according to the present invention.

FIG. 2 is an exploded perspective view showing an example of a capacitance type pressure sensor.

FIG. 3 is a configuration diagram showing one embodiment of a CR oscillation circuit according to the present invention.

FIG. 4 is a timing chart showing a voltage waveform of the CR oscillation circuit of FIG. 3;

5 is a timing chart showing a voltage waveform of the CR oscillation circuit of FIG. 3 by another control.

FIG. 6 is a timing chart showing voltage waveforms of the capacitance type sensor device of FIG. 1;

FIG. 7 is a graph showing experimental results obtained by measuring output pulse fluctuations due to electrostatic attraction.

FIG. 8 is a configuration diagram illustrating an example of a conventional CR oscillation circuit.

FIG. 9 is a timing chart showing voltage waveforms of the CR oscillation circuit of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitance sensor device 2 Capacitance detection circuit (counting means) 3 Pressure sensor (capacitance sensor) 11 2nd CR oscillation circuit (oscillation means) 18 Nonvolatile memory (storage means)

Claims (2)

[Claims] 1. An electrostatic capacitance sensor whose capacitance changes according to a change in an amount to be detected, an oscillating unit that oscillates at a frequency corresponding to the capacitance of the electrostatic capacitance sensor, and an output of the oscillating unit. And a counting means for counting the unit time and taking a difference from the reference count value, and outputting a pulse train of the counting difference, wherein the capacitive sensor is used to activate the oscillation means. When applying a bias, the bias is applied immediately before the start of oscillation, and the bias is returned to zero when the oscillation stops. 2. The apparatus according to claim 1, further comprising a storage unit that stores a base value per unit time and an initial value of a reference count value when the counting unit performs a counting operation in a changeable manner. Capacitive sensor device.