JPH10111207A - Capacitive pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve S/N ratio of an output signal when a capacitive pressure sensor is connected to a ground line of high noise level and used. SOLUTION: A detecting capacitor CD is constituted of a movable electrode arranged on a diaphragm part and a fixed electrode which faces the movable electrode, having a specified gap. A reference capacitor CR is constituted of a pair of fixed electrodes. The respective one side electodes of the detecting capacitor CD and the reference capacitor CR are grounded to a chassis. A first low-pass filter 19 constituted of an impedance element Z1 and the detecting capacitor CD AM-modulates a carrier signal Sc from an oscillation circuit 17, with an amplification factor corresponding to the capacitance of the detecting capacitor CD. A second low-pass filter 20 constituted of an impedance element Z2 and the reference capacitor CR AM-modulates the carrier signal Sc with an amplification factor corresponding to the capacitance of the reference capacitor CR. A differential amplification circuit 22 amplifies the deviation of the above AM modulation outputs. A band-pass filter 24 receiving the amplified output is so set that the center frequency of the pass band coincides with the frequency of the carrier signal Sc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a detection capacitor composed of a movable electrode on the diaphragm side and a fixed electrode opposed to the movable electrode with a predetermined gap, and based on the capacitance of the detection capacitor. The present invention relates to a capacitance type pressure sensor for detecting a pressure acting on a diaphragm.

[0002]

2. Description of the Related Art As an example of this type of capacitance type pressure sensor, a pair of flat plates facing each other with a predetermined gap has been conventionally provided, and detection is performed by a pair of detection electrodes provided at the center of the flat plates. It is considered that a capacitor is formed and a reference capacitor is formed by a pair of reference electrodes provided on the outer periphery of the flat plate. In this device, one of the flat plates functions as a diaphragm, and the detection capacitor located at the center of the flat plate has a large change in capacitance due to the pressure applied to the flat plate. Even when pressure is applied, the capacitance does not change much.

In such a capacitance type pressure sensor, the pressure applied to the flat plate is detected by extracting the deviation of the capacitance between the detection capacitor and the reference capacitor using an oscillation circuit. Thus, the configuration is such that the occurrence of an error due to an assembly error, a temperature drift, or the like is suppressed.

[0004]

In the capacitance type pressure sensor having such a configuration, in order to take out the deviation of the capacitance between the detection capacitor and the reference capacitor, one electrode of each of the detection capacitor and the reference capacitor is used. There is a case where a circuit configuration for grounding the electrodes is adopted. In particular, when the pressure sensor is mounted on a vehicle, the respective electrodes may be grounded to a chassis. However, since it is inevitable that noise due to the operation of the engine and various noises due to turning on / off the load for the vehicle are superimposed on the chassis ground line of the vehicle, a capacitance type using the above-described circuit configuration is adopted. In the pressure sensor, the S / N of the output signal
There is a problem that the ratio is greatly reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an S / S signal for an output signal even when used while connected to a ground line having a high noise level. An object of the present invention is to provide a capacitance-type pressure sensor having an effect of eliminating the possibility that the N ratio is reduced.

[0006]

According to the first aspect of the present invention, the first modulating means AM-modulates the carrier signal from the oscillating circuit with an amplification factor corresponding to the capacitance of the detecting capacitor. The second modulating means AM-modulates the carrier signal with an amplification factor corresponding to the capacitance of the reference capacitor, and the deviation of the modulation output of each modulating means is amplified by the amplifying means.

In this case, the capacitance of the reference capacitor composed of a pair of fixed electrodes shows a constant value, but the detection capacitance is composed of a movable electrode provided on the diaphragm and a fixed electrode facing the movable electrode with a predetermined gap. The capacitance of a capacitor will change with the pressure acting on its diaphragm. Therefore, the amplitude level of the carrier signal amplified by the amplifying means indicates the magnitude of the pressure acting on the diaphragm.

[0008] The carrier signal output from the amplifying means passes through a band-pass filter set so that the center frequency of the pass band coincides with the frequency of the carrier signal. The magnitude of the pressure acting on the diaphragm can be detected based on the amplitude level of the signal. For this reason, even in a situation in which one electrode of each of the detection capacitor and the reference capacitor is connected to a ground line on which various noises are superimposed, the noise component is removed by the bandpass filter. As a result, there is no possibility that the S / N ratio of the output signal indicating the detected pressure decreases.

According to the second aspect of the present invention, the signal generating means generates a clock signal having the same frequency as the carrier signal by shaping the waveform of the carrier signal from the oscillation circuit. , The center frequency of the pass band of the band-pass filter is changed. Therefore, even in a situation where the oscillation frequency of the oscillation circuit, that is, the frequency of the carrier signal fluctuates due to a temperature drift or the like, the carrier signal output from the amplifying means is attenuated in the process of passing through the band-pass filter. As a result, the S / N ratio of the output signal can always be maintained in a good state.

According to the third aspect of the present invention, the diaphragm functioning as a movable electrode of the detection capacitor is formed integrally with a metal housing main body having a pressure receiving port into which a medium to be subjected to pressure detection enters. In order to form a closed space for applying pressure to the diaphragm, a special sealing structure is not required, and a configuration capable of detecting high pressure can be easily realized. Become. Further, there is no possibility that the reliability with respect to the service life is reduced due to the deterioration of the seal structure portion, and the structure can be simplified. Moreover, since the movable electrode is grounded via the metal housing,
The structure for the ground can be simplified.

According to the fourth aspect of the present invention, the fixed electrode of the detection capacitor is formed on the substrate fixed to the housing via a spacer in a state where the fixed electrode faces the diaphragm portion, and one of the reference capacitors is provided. Is formed so as to face the housing main body, the housing main body functions as the other electrode of the reference capacitor. Therefore, the gap between the movable electrode and the fixed electrode forming the detection capacitor is formed. The size and the gap size between the pair of fixed electrodes forming the reference capacitor can be easily managed.

In this case, when the capacitance of the detection capacitor fluctuates due to an assembly error or the like,
Since the capacitance of the reference capacitor also fluctuates similarly, the fluctuation of the capacitance of the detection capacitor as described above is
This can be offset by the fluctuation of the capacitance of the reference capacitor following this, and as a result, the pressure detection accuracy can be improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied as a fuel injection pressure detecting sensor for a vehicle diesel engine will be described below with reference to the drawings. In FIG. 3 showing the entire vertical sectional structure, a metal housing 1 is shown.
Is a pressure receiving port 2a into which a medium (fluid) to be subjected to pressure detection enters.
A cylindrical housing body 2 having a pressure receiving port 2
In this structure, a circular diaphragm portion 3 positioned so as to face a is integrally formed. That is, the diaphragm part 3 is provided in a form in which the upper part of the cylindrical housing main body part 2 is closed, whereby the lower surface of the diaphragm part 3 functions as a pressure receiving surface.
In this embodiment, the housing 1 is made of stainless steel (for example, SUS630) or high-carbon steel (for example, S4
5C) and the like, by performing a cutting process, a polishing process, and the like on a metal material having a large yield resistance.

A mounting opening (not shown) formed in the outer periphery of the housing main body 2 at a pressure detection target portion (a fuel pressure feeding path in a fuel injection pump for a diesel engine).
Threaded portion 2b for screwing into
A flange portion 2c having a hexagonal cross section used for fastening the screw portion 2b is formed on the head of the housing body portion 2.

A flange 2c is provided on the upper part of the housing 1.
A trapezoidal portion 2d having a smaller diameter is formed.
On the substrate d, a ceramic substrate 4 is bonded and fixed with a predetermined gap between the substrate 4 and the base 2d.

FIG. 4 shows the housing 1 and the substrate 4.
The vertical cross-sectional structure of the portion is schematically shown, and will be described below with reference to FIG. That is, the substrate 4 is formed in a flat plate shape, and the diaphragm portion 3
A circular detection electrode 5 (corresponding to a fixed electrode for a detection capacitor in the present invention) facing a top surface (a surface opposite to the pressure receiving surface) of the device with a predetermined gap therebetween;
An annular reference electrode 6 (corresponding to a fixed electrode for a reference capacitor in the present invention) is formed concentrically with respect to a peripheral portion of d with a gap having the same size as the above-mentioned gap. . In addition, it is configured such that a predetermined insulation distance exists between the detection electrode (fixed electrode) 5 and the reference electrode (fixed electrode) 6.

As a result, the upper surface of the metal diaphragm portion 3 functions as the movable electrode 3a of the present invention, and is provided between the movable electrode 3a and the detection electrode 5 according to the deformation of the diaphragm portion 3. Capacitor C whose capacitance changes (increases in accordance with proximity deformation to the detection electrode 5 side)
D is formed. Housing body 2 also made of metal
The upper surface of the (trap-shaped portion 2d) functions as a fixed electrode 2e, and a reference capacitor CR having a constant capacitance is formed between the fixed electrode 2e and the reference electrode 6. .

Accordingly, the pressure acting on the diaphragm 3 can be detected based on the capacitance of the detection capacitor CD. In this case, the diameter and thickness of the diaphragm 3 are determined according to the magnitude of the pressure to be detected.
By setting the thickness to 8 mm and the thickness in the range of 0.4 to 3 mm, a pressure from several tens of atmospheres to about 3000 atmospheres can be detected.

Specifically, when the material of the housing 1 is the above-mentioned high yielding resistance metal material, the diameter of the diaphragm 3 is set to 8 mm, and the thickness is set to 0.6 mm, thereby setting the pressure to 100 atm. To the extent detectable. The diameter of the diaphragm 3 is 4 mm, and the thickness is 3 mm.
By setting to mm, it is possible to detect up to about 3000 atmospheres. However, in this embodiment, the diameter of the diaphragm 3 is set to 6 mm and the thickness is set to 1.7 mm in order to detect a pressure of about 1500 atm.

In the present embodiment, the respective areas of the detection electrode 5 and the reference electrode 6 are set to be equal to each other and slightly less than 0.3 cm ² , and the gap between the movable electrode 3 a and the detection electrode 5, and the fixed electrode The gap between the reference capacitor 6 and the reference electrode 6 is set to be equal to about 75 μm.
Each capacitance of R is configured to be about 3.3 pF. Specifically, by setting the diameter of the detection electrode 5 to 6 mm (same as the diameter of the diaphragm portion 3) and setting the inner and outer diameters of the reference electrode 6 to 12 mm and 13.42 mm, respectively, the area of the electrodes 5 and 6 is increased. Is set to be slightly less than 0.3 cm ² .

In this embodiment, the upper surface of the trapezoidal portion 2d is formed in a flat shape, so that the movable electrode 3a on the diaphragm 3 side and the fixed electrode 2e on the housing body 2 side are flush with each other. It is configured so that

The bonding between the trapezoid 2d and the substrate 4 is performed at a position between the detection electrode 5 and the reference electrode 6 on the substrate 4. In this case, the bonding is performed by using a flexible adhesive 8 having a small Young's modulus containing a plurality of resin beads 7 as spacers, and such an adhesive 8 surrounds the detection electrode 5. It is configured to have a shape. That is, by selecting the diameter of the resin bead 7, the gap size between the movable electrode 3a and the detection electrode 5 and the gap size between the fixed electrode 2e and the reference electrode 6 are set. In general, the resin beads have a small Young's modulus, but the resin beads 7 used in this embodiment may have a Young's modulus as close as possible to the Young's modulus of the flexible adhesive 8. desirable.

An LSI 9 (bare chip) for a processing circuit is die-bonded on the upper surface of the substrate 4 with the aim of reducing the weight of components on the substrate 4 in order to minimize noise due to vibration. The processing circuit LSI 9 has a function of detecting a pressure acting on the diaphragm unit 3 based on a deviation of each capacitance of the detection capacitor CD and the reference capacitor CR, as described later. Bonding wires 1 to the conductive patterns 4a formed in
0. The conductive pattern 4a
Are connected to the detection electrode 5 and the reference electrode 6 via through holes formed in the substrate 4. The substrate 4 also has an air vent hole (not shown) for communicating a space formed between the diaphragm 3 and the detection electrode 5 with the outside (it can also be used as a through hole for each of the electrodes 5 and 6). Is formed.

Turning back to FIG. 3, a holder 11 made of a resin such as PBT (polybutylene terephthalate) is arranged on the trapezoidal portion 2d of the housing 1 so as to cover the substrate 4 part. The connector terminal 12 is provided on the holder 11 by, for example, insert molding. The connector terminal 12
Supplies power to the processing circuit LSI 9 and
This is provided to extract an output signal from the LSI 9, and when the power supply side and the output signal extraction side share a ground terminal, three (only one is shown in FIG. 3) are prepared.

In this case, the base of the connector terminal 12 is connected to one end of a lead wire 13 made of a flexible conductive material, for example, in the form of a strip. The substrate 4 is inserted into the through hole 11a and the intermediate portion is bent.
It is connected to the upper conductive pattern 4a (see FIG. 4). Further, a connector housing 14 made of, for example, PBT is arranged on the holder 11 in a stacked manner, and the connector terminal 12 projects into the connector housing 14 in a state of penetrating the bottom of the connector housing 14. ing.

The holder 11 and the connector housing 14 as described above are integrated by a metal ring 15 provided so as to cover the periphery thereof. It is connected to the upper surface by welding and its upper edge is swaged. Thereby, the housing 1, the holder 11, the connector housing 14, and the like are integrated. An O-ring 16 is provided between the peripheral portions of the connector housing 14 to prevent moisture or the like from entering.

FIG. 1 shows an electric circuit configuration, which will be described below. In FIG. 1,
Circuit elements other than the detection capacitor CD and the reference capacitor CR are the parts constituted by the LSI 9. Further, in the present embodiment, the metal housing 1 is in a so-called chassis ground state by being screwed in a fuel pumping path in a fuel injection pump for a diesel engine of a vehicle. One of the electrodes of the reference capacitor CR (the movable electrode 3a and the fixed electrode 2e shown in FIG. 4) is grounded to the chassis.

In FIG. 1, an oscillation circuit 17 supplied with power from a power supply terminal + Vcc generates a carrier signal Sc having a predetermined frequency. The clock generation circuit 18 (corresponding to a signal generation unit) also supplied with power from the power supply terminal + Vcc shapes the carrier wave signal Sc to form a waveform.
And generates a rectangular pulse-shaped clock signal Pc having a frequency synchronized with the clock pulse Pc. Note that the oscillation circuit 17 is provided with a voltage adjusting element 17a for initially setting the amplitude of the carrier signal Sc.

The first low-pass filter 19 (corresponding to the first modulating means) to which the carrier signal Sc is applied is composed of a series circuit of an impedance element Z1 (a resistance element of about 210 KΩ in this embodiment) and the detection capacitor CD. .
The second low-pass filter 20 (corresponding to the second modulating means) to which the carrier signal Sc is also provided includes an impedance element Z2 (a resistance element of about 210 KΩ which is the same as the impedance element Z1 in this embodiment) and the reference capacitor. It consists of a series circuit of CR.

When the resistance value of the impedance element Z2 is Rz2 and the capacitance of the reference capacitor CR is C2, the cutoff frequency fo of the second low-pass filter 20 is fo = 1 / (2π · C2 Rz2). In the case of the present embodiment, since C2 = 3.3 pF and Rz2 = 210 KΩ, the cutoff frequency fo is about 230 KHz. Also, for the first low-pass filter 19,
Since the circuit constant (the value in the initial state where no pressure is applied to the diaphragm 3) is the same as that of the second low-pass filter 20, the cutoff frequency is also fo.

The frequency F of the carrier signal Sc is determined in consideration of the relationship with the cutoff frequency fo. Specifically, F = 0.5 · fo to 2 · f so that the pressure detection sensitivity through the detection capacitor CD becomes the highest.
o, and in this embodiment, F = 3
It is 30 KHz.

Thus, the first low-pass filter 19
Outputs a signal Sc 'obtained by AM-modulating the carrier signal Sc with an amplification factor corresponding to the capacitance of the detection capacitor CD. The amplitude of the AM-modulated signal Sc' acts on the diaphragm section 3. It decreases as the pressure increases. The second low-pass filter 20 outputs a signal Sc ″ obtained by AM-modulating the carrier signal Sc with an amplification factor corresponding to the capacitance of the reference capacitor CR. The amplitude of the AM-modulated signal Sc ″ is output. Is a constant value.

The AM modulated signal Sc 'output from the first low-pass filter 19 is connected to a resistor 21a and a capacitor 2a.
The AM modulated signal Sc ″ supplied to one input terminal of the differential amplifier circuit 22 (corresponding to amplifying means) via the low-pass filter 21 composed of the resistor 23 a and the capacitor 23 b The signal is supplied to the other input terminal of the differential amplifier circuit 22 via a low-pass filter 23 composed of 23b.

FIG. 2 shows an equivalent circuit of the first low-pass filter 19 and the low-pass filter 21 when viewed from the chassis ground side. As is apparent from FIG. 2, when viewed from the chassis ground side, the detection capacitor CD and the impedance element Z1 in the first low-pass filter 19 constitute a high-pass filter HPF. A relatively high frequency noise component is likely to enter.

The low-pass filters 21 and 23 are for removing noise passing through the high-pass filter HPF as described above, and have a cut-off frequency of 6 Hz.
It is set to about 00 KHz. In addition, low-pass filter 2
The capacitors 21b and 23b included in 1 and 23 are analog grounded through a ground terminal GND provided in the processing circuit LSI 9.

The signal output from the differential amplifier circuit 22 is
The signal is output from an output terminal Vout after passing through a band-pass filter 24 and a detection circuit 25. The band-pass filter 24 is set so that the center frequency fc of the pass band coincides with the frequency F of the carrier signal Sc, and attenuates signal components of frequencies other than the frequency F. In this case, the band-pass filter 24 is constituted by a well-known switched capacitor filter, and changes its center frequency fc in synchronization with the clock signal Pc from the clock signal generation circuit 18. . The detection circuit 25 also performs its detection operation in synchronization with the clock signal Pc.

The output voltage VPRE from the differential amplifier circuit 22 can be approximated by the following equation when the time t is used as a parameter.

[0038]

(Equation 1) Here, k is a proportional constant, ωc = 2π · F, ωs = 2π · F
s and Fs are the frequencies of the pressure detection signal (the voltage component of the voltage component of the output voltage Vpre corresponding to the amount of change in the capacitance of the detection capacitor CD).

Here, A given to the differential amplifier circuit 22
Since the frequencies of the M modulated signals Sc 'and Sc ", that is, the frequency F (= 330 KHz) of the carrier signal Sc is sufficiently higher than the frequency Fs of the pressure detection signal, the frequency component of the signal indicating the pressure detection signal Is 330KH
It exists in a narrow range centered on z. Accordingly, by passing the output signal of the differential amplifier circuit 22 through the band-pass filter 24 whose center frequency fc of the pass band is equal to the frequency F, it is possible to remove almost all noise components included in the output signal.

In short, according to the configuration of the present embodiment, the pressure acting on the diaphragm 3 can be detected based on the deviation between the capacitance of the detection capacitor CD and the capacitance of the reference capacitor CR.

Specifically, the first low-pass filter 19
Modulates the carrier signal Sc having a frequency of 330 KHz with an amplification factor corresponding to the capacitance of the detection capacitor CD, and the second low-pass filter 20 converts the carrier signal Sc according to the capacitance of the reference capacitor CR. The AM modulation is performed with the increased amplification rate.
And Sc ″ are amplified by the differential amplifier circuit 22. At this time, the capacitance of the reference capacitor CR shows a constant value, but the capacitance of the detection capacitor CD acts on the diaphragm unit 3. As a result, the amplitude level of the signal amplified by the differential amplifier circuit 22 indicates the magnitude of the pressure acting on the diaphragm unit 3.

In this embodiment, the differential amplifier circuit 2 includes the pressure detection signal superimposed on the carrier signal Sc.
2 is detected after passing through a band-pass filter 24 set so that the center frequency fc of the pass band coincides with the frequency of the carrier signal Sc. Based on the amplitude level, the magnitude of the pressure acting on the diaphragm 3 can be detected.

In this case, as described above, since the output signal of the differential amplifier circuit 22 is passed through the band-pass filter 24, the noise component contained in the output signal is almost removed. Even when one of the electrodes of the reference capacitor CR is connected to the chassis ground on which various noises are superimposed, there is no possibility that the S / N ratio of the output signal indicating the detected pressure is reduced.

Further, according to the present embodiment, the center frequency fc of the pass band of the band-pass filter 24 is equal to the carrier signal S
Since the configuration is changed in synchronization with the clock signal Pc that changes in synchronization with the frequency of the signal c, the oscillation frequency of the oscillation circuit 17, that is, the frequency of the carrier signal Sc fluctuates due to temperature drift or the like. However, there is no possibility that the output signal from the differential amplifier circuit 22 is attenuated in the process of passing through the band-pass filter 24, and as a result, the S / N ratio of the output signal can always be maintained in a good state. Become like

Further, according to the present embodiment, the diaphragm 3 forming the movable electrode 3a of the detection capacitor CD is
Since it is configured integrally with the metal housing main body 2 having the pressure receiving port 2a, a special seal is formed to form a closed space for applying pressure to the diaphragm 3. There is no need to provide a structure,
A configuration capable of detecting a high pressure can be easily realized, and there is no possibility that the reliability with respect to the life is reduced due to the deterioration of the seal structure.

In addition, the surface of the metal diaphragm 3 can be used as the movable electrode 3a necessary for forming the detection capacitor CD, and a seal structure using another component can be eliminated, thereby simplifying the structure. At the same time. Further, when the metal housing 1 is mounted on a predetermined portion, the movable electrode 3a is grounded through the chassis via the housing 1, so that the structure for grounding can be simplified.

In addition, according to the present embodiment, the housing 1
On the other hand, on a substrate 4 fixed via a flexible adhesive 8 containing a plurality of resin beads 7 as spacers,
The detection electrode 5 of the detection capacitor CD is formed so as to face the movable electrode 3a on the diaphragm 3 side, and the reference electrode 6 of the reference capacitor CR is formed to face the fixed electrode 2e on the housing main body 2 side. Therefore, the management of the gap size between the movable electrode 3a and the detection electrode 5 forming the detection capacitor CD and the gap size between the fixed electrode 2e and the reference electrode 6 forming the reference capacitor CR is performed by the above resin. It can be easily performed by selecting the diameter of the beads 7.

In this case, when the capacitance of the detection capacitor CD fluctuates due to an assembling error or temperature drift, the capacitance of the reference capacitor CR also fluctuates. Such fluctuations in the capacitance of the detection capacitor CD can be offset by fluctuations in the capacitance of the reference capacitor CR following the fluctuation, and consequently the pressure detection accuracy can be improved.

Note that the present invention is not limited to the above-described embodiment, and the following modifications or extensions are possible. As the first modulation means, a first low-pass filter 19 is provided in which a detection capacitor CD is combined with an impedance element Z1 composed of a resistance element. The first modulation means may be configured by combining active elements such as. Also, the second modulating means may employ a configuration in which the same element or an active element as described above is combined with the reference capacitor CR.

Although a metal material having a large yield resistance is used as the material of the housing 1, such a structure is not always necessary, and a material having a general yield resistance (for example, S15C or the like) is used. Carbon steel) may be used. The present invention can be widely applied not only to a fuel injection pressure detecting sensor of a vehicle diesel engine but also to a general capacitive pressure sensor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a partial equivalent circuit diagram for explaining operation.

FIG. 3 is an overall vertical sectional view.

FIG. 4 is a longitudinal sectional view schematically showing a configuration of a main part.

[Explanation of symbols]

In the drawings, 1 is a housing, 2 is a housing body, 2a
Is a pressure receiving port, 2e is a fixed electrode, 3 is a diaphragm part, 3a
Is a movable electrode, 4 is a substrate, 5 is a detection electrode (fixed electrode), 6
Is a reference electrode (fixed electrode), 7 is a resin bead (spacer), 8 is a flexible adhesive, 9 is an LSI for a processing circuit, 17
Is an oscillation circuit, 18 is a clock generation circuit (signal generation means), 19 is a first low-pass filter (first AM modulation means), 20 is a second low-pass filter (second AM modulation means), and 22 is a difference. A dynamic amplifier circuit (amplifying means), 24 is a band-pass filter, 25 is a detection circuit, CD is a detection capacitor, and CR is a reference capacitor.

Claims (4)

[Claims] 1. A detection capacitor comprising a movable electrode provided on a diaphragm portion and a fixed electrode opposed to the movable electrode with a predetermined gap therebetween, and one of the electrodes of the detection capacitor is used in a grounded state. In a capacitance type pressure sensor, a reference capacitor constituted by a pair of fixed electrodes and one of the electrodes is grounded; an oscillation circuit for generating a carrier signal of a predetermined frequency; First modulation means for performing AM modulation at an amplification rate corresponding to the capacity; second modulation means for performing AM modulation on the carrier signal at an amplification rate corresponding to the capacitance of the reference capacitor; and the first and second modulation means Amplifying means for amplifying a deviation of each modulation output by the modulating means; and a center of a pass band provided so as to pass the signal amplified by the amplifying means. A band-pass filter having a frequency set to match the frequency of the carrier signal. 2. A signal generator for generating a clock signal having the same frequency as the carrier signal by shaping the waveform of the carrier signal from the oscillation circuit, wherein the band-pass filter sets a center frequency of the pass band to The capacitance type pressure sensor according to claim 1, wherein the capacitance type pressure sensor is configured to change in synchronization with a frequency of the clock signal. 3. A metal housing which is formed integrally with said diaphragm portion and a housing main body portion having a pressure receiving port into which a medium to be subjected to pressure detection enters, and grounds the housing, and receives pressure from the diaphragm. The capacitance type pressure sensor according to claim 1, wherein a surface opposite to the surface functions as the movable electrode. 4. A substrate fixed to the housing via a spacer, wherein a fixed electrode of the detection capacitor is formed on the substrate so as to face the diaphragm, and one of the reference capacitors is provided. The capacitance type pressure according to claim 3, wherein the electrode is formed so as to face the housing main body so that the housing main body functions as the other electrode of the reference capacitor. Sensor.