JPH05248976A - Capacitance sensing circuit for electrostatic capacitance varying type sensor - Google Patents

Abstract

PURPOSE:To eliminate error in measuring and provide accurate measurability for the actual change value by determining the actual measuring electrostatic capacitance value from the difference between the varying electrode part and the electrostatic capacitance value determined by a reference electrode part. CONSTITUTION:The undersurface of a deadweight 16 supported in cantilever form by a beam 15 is set at a movable electrode 17, and an upper stationary electrode plate 18 is installed confrontingly on a fixation base board 13 mating therewith so as to form a varying electrode part 19. The undersurface of a small protrusion 20 projecting at a supporting frame 14 in a single piece therewith is set at a stationary electrode 21, and a small stationary electrode plate 22 is installed confrontingly on the base board 13 so as to form 5 reference electrode-part 23 which has a constant pitch in the direction up and down, i.e., constant electrostatic capacitance. When an acceleration acts on an acceleration sensor 11 to cause the weight 16 to move, the change value of the electrostatic capacitance determined by the electrode part 19 and the reference value for the electrostatic capacitance determined by the reference electrode part 23 are fed to a calculator circuit. There the reference value is subtracted from the change value, and the resultant is amplified, converted into the measuring voltage value. and given as output. This permits obtaining the actual measuring electrostatic capacitance value having got rid of the floating electrostatic capacitance to enable precise sensing of the acceleration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for detecting the electrostatic capacitance of an electrostatic capacitance change type acceleration sensor or an electrostatic capacitance change type pressure sensor used for detecting the acceleration of an automobile. The present invention relates to a detection circuit of a capacitance change type sensor.

[0002]

2. Description of the Related Art Generally, as shown in FIGS. 7 to 9, a capacitance change type acceleration sensor has a weight portion 62 and a supporting frame 63 around the weight portion 62 in a central portion of a substrate 61 made of a semiconductor. The weight portion 62 is formed by etching, and is supported in a cantilever manner on the support frame 63 by a pair of parallel beam portions 64.

The substrate 61 has, for example, a fixed substrate 6 on one side.
5 is used in a state of being installed opposite to each other, and a predetermined gap is formed between the fixed substrate 65 and the facing weight portion 62 so that the weight portion 62 is movable in the plane direction of the fixed substrate 65. ,
One surface of the weight portion 62 in the changing direction is set as a movable electrode 66, and a fixed electrode 67 is provided on a fixed substrate 65 facing the movable electrode 66 to form an electrode portion for acceleration measurement.

The capacitance change type acceleration sensor 68 thus configured detects the change in the capacitance between the movable electrode 66 and the fixed electrode 67 when the weight portion 62 moves due to acceleration. Seeking acceleration.

However, at the time of this measurement, the stray capacitance may be captured by the electrode portion due to the adverse effect of disturbance or the like, and in this case, there is a problem in that an erroneous measurement cannot be performed to accurately measure the acceleration.

Further, as shown in FIG. 10, the above-mentioned circuit for detecting the electrostatic capacitance uses the above-mentioned acceleration sensor 68,
It is a general method to configure the oscillation circuit 73 with the resistors 69 and 70 and the inverters 71 and 72, and to take out the capacitance change of the acceleration sensor 68 as the frequency change of the oscillation circuit 73. For example, in the case of suspension control of an automobile, etc.), an analog signal input is requested from the control system side. It needs to be converted to a signal.

However, when the detection circuit is constructed as described above, there are the following problems.

That is, the cost is increased by using the FV converter 74, and further the acceleration sensor 68 is used.
The capacitance of is generally several pF to several tens of pF, while
Since the frequency of the oscillating circuit 73 is several MHz to several tens of MHz, it is necessary to use a special F-V converter 74 for dealing with these, which further increases the cost.

Further, the resistors 69 used in the oscillation circuit 73,
If 70 has a temperature characteristic, the acceleration sensor 68 also has a temperature characteristic, so that the characteristic of the capacitance change type acceleration sensor that originally has a good temperature characteristic is impaired.

[0010]

An object of the invention of claim 1 of the present invention is to obtain an accurate actual change value by eliminating an error during measurement by obtaining a reference value in addition to the change value of capacitance. Is to provide a capacitance detection circuit of a capacitance change type sensor capable of obtaining

Further, the object of the invention of claim 2 of the present invention is to detect the electrostatic capacity at a cost lower than that of the oscillation circuit, and to prevent the temperature characteristic of the sensor from deteriorating. A detection circuit is provided.

[0012]

According to a first aspect of the present invention, a weight portion is elastically supported at a central portion of a semiconductor substrate from a fixed support portion of an outer frame through a beam portion, and the weight portion fluctuates. A capacitance change type sensor for electrically detecting a quantity to obtain a variation value, wherein one surface of the weight portion in the variation direction is set as a movable electrode, and a fixed substrate facing the movable electrode with a predetermined gap therebetween. A variable electrode portion having a fixed electrode provided opposite to the reference electrode, and a reference electrode having one surface of the fixed support portion set as a fixed electrode and the fixed electrode provided opposite to the fixed substrate with a predetermined gap therebetween. And a detection circuit for obtaining an actually-measured capacitance value from the difference in capacitance value between the variation value of capacitance obtained by the varying electrode portion and the reference value of capacitance obtained by the reference electrode portion. It is also characterized by being a capacitance change type capacitance detection circuit.

According to a second aspect of the present invention, the weight portion is elastically supported at the central portion of the semiconductor substrate from the fixed support portion of the outer frame via the beam portion, and the variation amount of the weight portion is electrically detected. In the electrostatic capacitance change sensor, the one surface of the weight portion in the changing direction is set as the movable electrode, and the fixed electrode is provided on the fixed substrate facing the movable electrode via a predetermined gap. And a reference electrode section in which one surface of the fixed support section is set as a fixed electrode, and a fixed electrode is opposed to a fixed substrate facing the fixed support section through a predetermined gap, and the variable electrode section. It is characterized in that it is an electrostatic capacitance change type capacitance detection circuit provided with a detection circuit which divides an AC voltage between the portion and the reference electrode portion, and converts the divided voltage into impedance to extract a detection signal.

[0014]

In the capacitance detecting circuit of the electrostatic capacitance change type sensor according to the first aspect of the present invention, when the weight portion moves due to acceleration or the like, the detection circuit detects the capacitance detected by the variable electrode portion. The actual capacitance value is obtained in consideration of the difference between the variation value and the reference value of the capacitance detected by the reference electrode unit.

According to a second aspect of the present invention, in the capacitance detection circuit of the capacitance change type sensor, when the weight portion moves due to acceleration or the like, the detection circuit causes an alternating current between the fluctuating electrode portion and the reference electrode portion. The voltage is divided, and the divided voltage is impedance-converted to take out a detection signal.

[0016]

According to the first aspect of the present invention, at the time of measuring acceleration, even if the stray capacitance is captured by the electrode portion due to an adverse effect such as a disturbance, the reference value of the signal obtained by the reference electrode portion. By comparing with, it is possible to obtain an accurate measured value that eliminates the adverse effect, and as a result, it is possible to obtain a highly reliable and accurate measured value that is not adversely affected by disturbance or the like.

According to the second aspect of the present invention, since the detection signal of the electrostatic capacitance change type sensor can be obtained as an analog signal, the circuit configuration is smaller than that when an oscillation circuit and an FV converter are used. It becomes easy and cost can be reduced. Further, since a resistor having a temperature characteristic is not used in the detection unit like the oscillator circuit, the temperature characteristic can be completely eliminated.

[0018]

Embodiments of the present invention will be described in detail below with reference to the drawings. 1 and 2 show a capacitance change type acceleration sensor 1
1 shows a semiconductor substrate 1 provided also as an electrode material
2 and an insulating fixed substrate 13 which is superposed on the lower surface thereof and integrally faces the same.

The semiconductor substrate 12 has a weight portion 16 in the vertical direction in the central portion through a pair of beam portions 15, 15 parallel to the center from one side of the support frame 14 forming the outer frame of the semiconductor substrate 12. It is elastically supported and cantilevered.
Is set to the movable electrode 17, and the fixed substrate 13 facing the lower side with a predetermined gap therebetween.
A fixed electrode plate 18 is provided on the upper side to form a variable electrode section 19 for detecting a change in electrostatic capacitance between the upper and lower electrodes 17 and 18 during acceleration measurement.

Further, a small projecting portion 20 is integrally projected from the supporting frame 14 into a rectangular space surrounded by the pair of left and right beam portions 15, 15, the supporting frame 14 and the weight portion 16, and the small projecting portion 20 is projected. The lower surface of 20 is set as a fixed electrode 21, and the small fixed electrode plate 2 is mounted on the fixed substrate 13 facing the fixed electrode 21 with a predetermined gap.
2 are provided in pairs, and the electrodes 21 and 22 are arranged at regular intervals above and below.
A reference electrode portion 23 that detects a reference electrostatic capacitance that occurs between them is configured. In this case, the electrode interval of the reference electrode portion 23 does not change due to the acceleration, so that the electrostatic capacity also becomes constant, and this becomes the reference electrostatic capacity.

Then, the above-mentioned variable electrode unit 19 detects the change in electrostatic capacitance when acceleration is applied to obtain the acceleration, but there is a possibility that the floating electrostatic capacitance that induces a measurement error at the time of measurement may be captured. , The reference electrode unit 2 to correct this value
By calculating the reference value of the electrostatic capacitance in step 3 and comparing the fluctuation value of the variable electrode section 19 with the reference value of the signal obtained by this reference electrode section when measuring the acceleration, the adverse effect is corrected accurately. This is to obtain a measured value.

FIG. 3 is a block diagram of the capacitance detection circuit of the capacitance change type acceleration sensor. When the acceleration is measured, the capacitance change value Csen obtained by the changing electrode section 19 and the reference electrode section 23 are obtained. The calculated reference value Cref of the capacitance is input to the arithmetic circuit 31, where the reference value Cref is subtracted from the fluctuation value Csen to obtain an accurate value of the acceleration. The conversion circuit 33 converts the measured voltage value and outputs it.

At this time, the variation value Csen of the above-mentioned electrostatic capacitance.
And the reference value Cref include both the stray capacitance Cf, but the actual capacitance values not including the stray capacitance Cf are Cseno, C
If refo can be expressed as Csen = Cseno + Cf Cref = Crefo + Cf, the measured capacitance value obtained by removing the stray capacitance Cf is obtained as Csen-Cref = Cseno-Crefo, and as a result, highly accurate acceleration can be detected. You can

In the electrostatic capacitance change type acceleration sensor 11 thus constructed, when the weight portion 16 moves due to acceleration, the capacitance of the electrostatic capacitance detected by the arithmetic circuit 31 of the capacitance detecting circuit is detected by the variable electrode portion 19. The acceleration can be obtained by calculating the difference between the fluctuation value Csen and the reference value Cref of the electrostatic capacitance detected by the reference electrode portion 23.

At this time, even if the stray electrostatic capacitance which induces a measurement error between the respective electrode portions is captured, the reference electrode portion 23 is calculated from the variation value of the signal obtained by the variable electrode portion 19 in order to correct this value.
By subtracting the reference value of the signal obtained in step 1, it is possible to measure a reliable and accurate acceleration in which adverse effects are eliminated.

FIGS. 4 and 5 show a capacitance change type acceleration sensor 41 according to another embodiment of the present invention, in which a semiconductor substrate 42 is sandwiched between insulating fixed substrates 43 and 44. The variable electrode section 45 similar to that of the above-described embodiment is formed below the semiconductor substrate 42.
The reference electrode portion 46 is formed on the upper side of the semiconductor substrate 42.

In the reference electrode portion 46, the upper surface of the small protruding portion 20 described in the above embodiment is set as the fixed electrode 47, and the small fixed electrode plate 48 is provided opposite to the fixed substrate 43 facing the upper surface. And constitutes a reference electrode portion 46.

By forming the reference electrode portion 46 on the upper surface of the semiconductor substrate 42, in addition to obtaining the reference value at the time of acceleration measurement, the electrode action occurring during this period is caused by the movement of the variable electrode portion 45 side. This has the effect of suppressing the flow of air that flows and improving impact resistance.

As described above, when measuring the acceleration, even if the stray capacitance is captured by the electrode part due to the adverse effect of disturbance or the like, the adverse effect is eliminated by comparing it with the reference value of the signal obtained by the reference electrode part. It is possible to obtain an accurate measured value, and as a result, it is possible to measure a reliable and accurate acceleration that is not adversely affected by disturbance or the like.

FIG. 6 shows another example of the capacitance detecting circuit. The oscillating section 51 generates an AC voltage V1 to be applied to the acceleration sensor 11 (or 41), and the capacitance detecting circuit 52 changes the AC voltage V1 described above to the variable electrode. Part 19 (or 45) and reference electrode part 2
Partial pressure at 3 (or 46). In this state, current cannot be taken out with high impedance, so FET53, resistor 54
Is converted into a low-impedance voltage by a source follower circuit using, and the converted voltage V2 is rectified by the rectification unit 55, amplified by the amplification unit 56, adjusted in voltage, and output as a detection signal.

The voltage value of the converted voltage V2 described above is expressed by the following equation. V2 / V1 = C1 / (C1 + C2) Here, C1 is the electrostatic capacitance value of the variable electrode portion 19 (or 45), and C2 is the electrostatic capacitance value of the reference electrode portion 23 (or 46). In comparison with the above configuration, an analog voltage output can be obtained with a simpler circuit configuration, and since a resistor having a temperature characteristic is not used, the temperature characteristic can be completely eliminated. For example, the variable electrode section 19 (or 4
Even if 5) and the reference electrode portion 23 (or 46) have a temperature characteristic, it can be eliminated by canceling with the numerator and denominator in the above equation.

In the correspondence between the present invention and the configuration of the above-described embodiment, the fixed support portion of the present invention corresponds to the support frame 1 of the embodiment.
Similarly, the detection circuit for obtaining the actually measured capacitance value of claim 1 corresponds to the arithmetic circuit 31, and the detection circuit for extracting the detection signal of claim 2 corresponds to the source follower circuit by the FET 53. However, the present invention is not limited to the configurations of the above-described embodiments.

For example, the capacitance detection circuit of the present invention is not limited to the capacitance change type acceleration sensor of the embodiment, but can be used as a capacitance detection circuit of another capacitance change type sensor such as a capacitance change type pressure sensor. Of course you can.

[Brief description of drawings]

FIG. 1 is a plan view showing a capacitance change type acceleration sensor of the present invention.

FIG. 2 is a sectional view showing a capacitance change type acceleration sensor of the present invention.

FIG. 3 is a block diagram of a capacitance detection circuit of the capacitance change type acceleration sensor of the present invention.

FIG. 4 is a partially cutaway plan view of a capacitance change type acceleration sensor according to another embodiment of the present invention.

FIG. 5 is a sectional view of a capacitance change type acceleration sensor showing another embodiment of the present invention.

FIG. 6 is a block diagram of a capacitance detection circuit of a capacitance change type acceleration sensor according to another embodiment of the present invention.

FIG. 7 is a partially cutaway perspective view showing a conventional capacitance change type acceleration sensor.

FIG. 8 is a plan view showing a conventional capacitance change type acceleration sensor.

FIG. 9 is a sectional view showing a conventional electrostatic capacitance change type semiconductor acceleration sensor.

FIG. 10 is a capacitance detection circuit diagram of a conventional capacitance change type acceleration sensor.

[Explanation of symbols]

 11, 41 ... Capacitance change type semiconductor acceleration sensor 12, 42 ... Semiconductor substrate 13, 43, 44 ... Fixed substrate 14 ... Support frame 15 ... Beam portion 16 ... Weight portion 17 ... Movable electrode 18 ... Fixed electrode plate 19, 45 ... Fluctuating electrode part 20 ... Small protruding part 21, 47 ... Fixed electrode 22, 48 ... Small fixed electrode plate 23, 46 ... Reference electrode part 31 ... Arithmetic circuit 53 ... FET Csen ... Fluctuating value Cref ... Reference value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keisuke Uno, 10 Hanazono Dodocho, Ukyo-ku, Kyoto Prefecture Kyoto Prefecture Omron Co., Ltd. (72) Inventor Masatoshi Oba, 10 Hanazono Doudocho, Ukyo-ku, Kyoto Prefecture Omron Incorporated (72) Inventor Shiro Fujioka, 10 Hanazono Todocho, Ukyo-ku, Kyoto, Kyoto Prefecture Omron Co., Ltd. 72) Inventor, Masakazu Shiiki, Omron Co., Ltd.

Claims (2)

[Claims] 1. An electrostatic device for elastically supporting a weight portion from a fixed support portion of an outer frame through a beam portion at a central portion of a semiconductor substrate, and electrically detecting a variation amount of the weight portion to obtain a variation value. A capacitance change type sensor, wherein one surface of the weight portion in the changing direction is set as a movable electrode, and a variable electrode portion is formed by facing a fixed electrode on a fixed substrate facing the movable electrode with a predetermined gap, One surface of the fixed supporting portion is set as a fixed electrode, and a fixed electrode facing the fixed electrode with a predetermined gap is provided between the fixed electrode and a reference electrode portion. A capacitance change type capacitance detection circuit provided with a detection circuit for obtaining an actually measured capacitance value from a difference in capacitance value between a variation value and a reference value of capacitance obtained at a reference electrode section. 2. An electrostatic device in which a weight portion is elastically supported from a fixed support portion of an outer frame through a beam portion to a central portion of a semiconductor substrate, and a variation amount of the weight portion is electrically detected and used as a detection signal. A capacitance change type sensor, wherein one surface of the weight portion in the changing direction is set as a movable electrode, and a variable electrode portion is formed by facing a fixed electrode on a fixed substrate facing the movable electrode with a predetermined gap, A fixed electrode is set on one surface of the fixed supporting portion, and a fixed electrode is provided to face a fixed substrate facing the fixed electrode with a predetermined gap, and an alternating current is applied between the variable electrode portion and the reference electrode portion. A capacitance detection circuit of a capacitance change type provided with a detection circuit that divides a voltage, converts the divided voltage into an impedance, and extracts a detection signal.