JP2000221054A - Capacitive physical quantity detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a cycle for sample holding, to enhance precision for capacity detection, and to highly precisely detect a physical quantity. SOLUTION: In this detector, a charge in response to a physical quantity is output from a sensor element part 1 by impressing rectangular waves P1, P2 reversed each other in phases to fixed electrodes 11, 13, the charges are held in a capacitor 22, a voltage corresponding to the charge is output from an operation amplifier 21, and the output voltage is sample-held in a signal processing part 2 to be signal-processed. A reset means comprising switches 23, 24 and a capacitor 25 is provided between an inverting input terminal and an output terminal of the amplifier 21, the switches 23, 24 are opened and closed respectively in respective inversions of the rectangular waves P1, P2 to give the charges accumulated in the capacitor 25 into a capacitor 22, and a charge in response to the output of the amplifier 21 is held in the capacitor 25 for the next charging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type physical quantity detection device using a variable capacitance which changes according to a physical quantity.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No. Hei 8-145717 discloses a sensor element part whose capacity changes due to mechanical energy such as acceleration and pressure, and a CV converter for converting a change in capacity of this sensor element part into a voltage. A capacitance change detection circuit of a capacitive sensor including a circuit and a sample and hold circuit that samples and holds an output voltage of the CV conversion circuit is described. The CV conversion circuit in this circuit includes a sensor element unit. An operational amplifier having an output terminal connected to the inverting input terminal, a switch connected between the inverting input terminal and the output terminal of the operational amplifier, and a switched capacitor including a capacitor connected in parallel with the switch. Have been. In addition, the above-mentioned switch is configured to be closed after the sample hold, and when the switch is closed, both ends of the capacitor are short-circuited.
The electric charge stored in the capacitor is discharged.

[0003]

In the above configuration, the amount of charge held in the sample-and-hold circuit changes due to the leak current of the switch. Therefore, it is necessary to shorten the time for holding the charge as much as possible. However, in the above-described conventional device, the time for discharging the capacitor is sampled and held after the output of the operational amplifier is sampled and held, so that the period of the sample and hold cannot be shortened. There is a problem that an error due to charge loss increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a capacitance type physical quantity detection device capable of shortening a sample-and-hold cycle, increasing the accuracy of capacitance detection, and detecting a physical quantity with high accuracy. And

[0005]

In order to achieve the above object, according to the first to twelfth aspects of the present invention, at least one of the first and second capacitors varies in accordance with a physical quantity and is electrically connected in series. And a second capacitor, and configured to apply first and second rectangular waves having opposite phases to nodes at both ends of the first and second capacitors, respectively. An operational amplifier (21) having an inverting input terminal connected to a connection point of the first and second capacitors, and a first reference voltage source connected to a non-inverting input terminal; and an inverting input terminal of the operational amplifier. A third capacitor (22) connected between output terminals and holding a charge corresponding to a difference in capacitance between the first and second capacitors caused by inversion of the first and second rectangular waves; Charge corresponding to the output voltage of the operational amplifier Lifting and, wherein after the first, second
Reset means (23, 2) for charging the held capacitor to the third capacitor at the timing when the rectangular wave of
3 ′, 23 ″, 23a, 24, 24 ′, 24 ″, 2
4a, 25, 25a), and a signal processing unit (3) that samples and holds the output voltage of the operational amplifier and performs signal processing.
It is characterized by having.

According to the present invention, the electric charge corresponding to the output voltage of the operational amplifier (21) is held, and thereafter, the electric charge held at the timing when the first and second rectangular waves are inverted is charged to the third capacitor. Since the reset means (23, 24, 25, etc.) is provided, an effect equivalent to discharging the charge of the capacitor by short-circuiting both ends of the capacitor by the switch means after the sample hold as in the conventional one is obtained. Therefore, there is no need to provide a reset period unlike the conventional one. For this reason, the sample-and-hold cycle is shortened, the accuracy of capacitance detection is increased, and highly accurate physical quantity detection becomes possible.

Further, in the invention according to claim 13, at least one of the capacitances changes according to a physical quantity, and has first and second capacitors electrically connected in series. A sensor element (1) configured to apply first and second rectangular waves having opposite phases to nodes at both ends of the second capacitor, and a connection point between the first and second capacitors. An operational amplifier (2) having an inverting input terminal connected thereto and a first reference voltage source connected to a non-inverting input terminal.
1) and third and fourth capacitors (2) provided in parallel between the inverting input terminal and the output terminal of the operational amplifier.
05, 215), and connecting one of the third and fourth capacitors between the inverting input terminal and the output terminal of the operational amplifier to generate the first and second rectangular waves. One of the capacitors holds a charge corresponding to a difference between the capacitances of the first and second capacitors, and a discharge path is formed in the other capacitor to discharge the charge accumulated in the other capacitor. Means (201-204, 21) for alternately switching the capacitor and the other capacitor each time the first and second rectangular waves are inverted.
1-214), and a signal processing section (3) for performing signal processing by sampling and holding the output voltage of the operational amplifier.

According to the present invention, two capacitors (2
05, 206) is connected between the inverting input terminal and the output terminal of the operational amplifier (21), and the other capacitor is discharged between the two terminals. Are alternately repeated every time the inversion is performed, so that the present invention has the same effect as the first aspect.

Note that the reference numerals in parentheses indicate the correspondence with specific means described in the embodiments described later.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. (First Embodiment) A capacitive physical quantity detection device according to a first embodiment of the present invention comprises a sensor element unit 1, a CV conversion circuit 2, and a signal processing unit 3, as shown in FIG.

The sensor element 1 includes a fixed electrode 11,
13 and a movable electrode 12 that is displaced according to a physical quantity (for example, acceleration, yaw rate, etc.). A first capacitor (capacity is C1) is formed between the fixed electrode 11 and the movable electrode 12, and the fixed electrode A second capacitor (capacitance is C2) is formed between the movable electrode 13 and the movable electrode 12, and the capacitances C1 and C2 constitute a differential capacitance. The first and second capacitors are electrically connected in series, and are connected to nodes at both ends (outside) of the fixed electrodes 11 and 13 in opposite phases, which are inverted at a frequency sufficiently higher than the resonance frequency of the movable electrode 12. Rectangular waves P1 and P2 are applied, respectively.

The CV conversion circuit 2 includes an operational amplifier 21 and
A third capacitor (capacitance is assumed to be Cf) 22 connected between the inverting input terminal and the output terminal of the operational amplifier 21 and a switch 23 connected in series between the inverting input terminal and the output terminal of the operational amplifier 21 , 24 and a fourth capacitor (capacitance is Cr) 25 connected between the connection point of the switches 23 and 24 and the ground potential as the first reference voltage source. The switches 23 and 24 are opened and closed by switch signals CS1 and CS2 synchronized with the rectangular waves P1 and P2.

The signal processing section 3 samples and holds the output of the operational amplifier 21 at a predetermined timing, performs predetermined signal processing, and outputs a physical quantity detection signal corresponding to the physical quantity acting on the movable electrode 12. The operation of the above configuration will be described with reference to a timing chart shown in FIG.

Fixed electrode 1 in sensor element 1
Rectangular waves P1 and P2 (see FIG. 2) from a rectangular wave signal generating means (not shown) are applied to 1 and 13, respectively. The frequencies of the rectangular waves P1 and P2 are preferably set sufficiently higher than the resonance frequency in order to prevent the movable electrode 12 from vibrating due to inversion of the rectangular waves P1 and P2. However, the square wave P1,
Charge corresponding to the capacitance difference between the capacitances C1 and C2 caused by the inversion of P2 is stored in the third capacitor 22, and the frequency is set so that the operation is not inverted until the output of the operational amplifier 21 is stabilized.

The movable electrode 12 is held at the ground potential as the first reference voltage source by the operation of the operational amplifier 21. Here, the rectangular wave P1 has a high level Hi (voltage:
V) and P2 are at the low level Lo (voltage: 0),
The first capacitor formed between the fixed electrode 11 and the movable electrode 12 stores an electric charge Q represented by Q1 = C1 · V, and the second capacitor formed between the fixed electrode 13 and the movable electrode 12 The electric charge represented by Q2 = C2 · 0 = 0 is stored in the capacitor. When P1 is Lo and P2 is Hi, the first capacitor stores the charge Q ′ represented by Q1 ′ = C1 · 0 = 0, and the second capacitor stores the charge Q ′.
The charge represented by Q2 ′ = C2 · V is stored. Accordingly, by inverting the rectangular waves P1 and P2, respectively,
The electric charge of ΔQ = (C1−C2) · V enters and exits the sensor element unit 1.

First, in the initial state, the charge amounts of the third and fourth capacitors 22 and 25 are 0, the output voltage of the operational amplifier 21 is 0 V, and the switches 23 and 24 are open. From this state, when the rectangular wave P1 is inverted from Lo to Hi and the rectangular wave P2 is inverted from Hi to Lo,-(C1-C2)
The electric charge of V (a negative sign indicates that negative electric charge is stored on the movable electrode 12 side of the first capacitor) flows into the sensor element unit 1, and the electric charge stored in the third capacitor 22 is It becomes (C1−C2) · V of the opposite polarity to the charge flowing into the section 1.

Here, when the switch 23 is closed by the switch signal CS1 shown in FIG. 2 after the inversion of the rectangular waves P1 and P2, the electric charge of the fourth capacitor 25 is fed back to the third capacitor 22, but the initial state. Since the charge amount of the fourth capacitor 25 is 0, the charge Qf stored in the electrode on the inverting input terminal side of the third capacitor 22 is
Is Qf = (C1−C2) · V, and the operational amplifier 21
Generates a voltage of Vc =-(C1-C2) .V / Cf.

Thereafter, the switch signals CS1 and CS1 shown in FIG.
When the switch 23 is opened and the switch 24 is closed by CS2, the fourth capacitor 25 is charged with the output voltage of the operational amplifier 21. The electric charge Qr stored in the fourth capacitor 25 is expressed as Qr = Cr.Vc =-(C1-C2).
V / Cf. At the same time, the subsequent signal processing unit 3
In accordance with the timing signal SH1 shown in FIG.
Is sampled and held (sampled when SH1 is Hi, and held at Lo). The switch 24
Open before the rectangular waves P1 and P2 are inverted.

Next, when the rectangular waves P1 and P2 are inverted, respectively, the charges having the opposite polarity to the previous one, ie,-(C1-C2) .multidot.
The charge V flows into the third capacitor 22. Subsequently, when the switch 23 is closed, the charge of the fourth capacitor 25 is fed back to the third capacitor 22.
As a result, the charge Qf ′ of the third capacitor 22 is combined with the charge before inversion, and Qf ′ = Qf + Qr− (C1−C
2) · V = (C1-C2) · V-Cr · (C1-C2)
V / Cf- (C1-C2) V = -Cr. (C1-C
2) V / Cf, and the output of the operational amplifier 21 is V
A voltage of c ′ = Cr · (C1−C2) · V / Cf ² is generated.

At the same time, the signal processing unit 3 at the subsequent stage samples and holds the output voltage of the operational amplifier 21 in accordance with the timing signal SH2 shown in FIG. 2, and the difference from the voltage sampled and held at SH1, that is, Vc-Vc '. =-(1+
(Cr / Cf). (C1-C2) .V / Cf is output.
Therefore, if the difference between the capacitances of the first and second capacitors (C1−C2) changes depending on the physical quantity, the output O of the signal processing unit 3 is changed.
The UT changes, and a physical quantity can be detected.

The capacitances Cf of the capacitors 22 and 25,
If the ratio of Cr is appropriately selected, an output having a desired sensitivity can be obtained. For example, if Cr = Cf, the output OUT =
−2 (C1−C2) · V / Cf, and the output voltage is the difference between the capacitances of the first and second capacitors (C1−C2), the amplitude V of the rectangular waves P1 and P2, and the capacitance Cf of the third capacitor 22.
The voltage value is determined by

As described above, according to the present embodiment, the reset means constituted by the switches 23 and 24 and the fourth capacitor 25 is provided. However, the same effect as the reset can be obtained. Therefore,
There is no need to provide a reset period unlike the conventional one, and the frequencies of the rectangular waves P1 and P2 can be increased. For this reason, it is possible to suppress the change in the charge held in the capacitor due to the leakage of the switch, and it is possible to detect the capacitance with high accuracy, and to detect the physical quantity with high accuracy.

The above-mentioned signal processing unit 3 can be realized by a circuit configuration as shown in FIGS. FIG.
Then, the output of the operational amplifier 21 is sampled and held at the timings of the signals SH1 and SH2 by using the two sample-hold circuits 31 and 32, and the differential amplifier 33 obtains the difference voltage. At this stage, since high-frequency noise at the time of sample hold is included, the noise is removed by the low-pass filter (LPF) 34.

FIG. 4 shows a similar function realized by a switched capacitor circuit. According to the circuit configuration as shown in FIG. 4, the sample and hold circuit and the differential amplifier shown in FIG. 3 can be eliminated. Further, although the filter characteristic of the circuit of FIG. 4 is primary, a higher-order filter characteristic can be used. (Second Embodiment) FIG. 5 shows the configuration of a capacitive physical quantity detection device according to a second embodiment of the present invention. The difference from the first embodiment is that the reset means is composed of first reset means including switches 23 and 24 and a fourth capacitor 25 and switch 2.
That is, two sets of reset means, ie, second reset means including 3a, 24a and a fifth capacitor 25a, are used.

The operation in this case will be described with reference to the timing chart of FIG. In the first embodiment, the rectangular wave P
In order to alternately open and close the switches 23 and 24 each time the inversion of P1 and P2, the switch signals CS1 and CS2 are alternately set to Hi, but in the second embodiment, as shown in FIG. The signals CS1 and CS2 each have a rectangular wave P
1. The state is Hi in synchronization with P2.

According to this configuration, when the rectangular wave P1 is Hi, the fourth capacitor 25 charges the third capacitor 22, and the fifth capacitor 25a connects the operational amplifier 2
Charging with the output voltage of 1 is performed. On the other hand, when the square wave P1 is L
In the state of o, the fourth capacitor 25 charges the output voltage, and the fifth capacitor 25a charges the third capacitor 22.

As described above, the charging of the third capacitor 22 and the charging of the output voltage are simultaneously performed by alternately repeating the charging of the third capacitor 22 and the charging of the output voltage by using two sets of the resetting means. Can be. Also, as shown in FIG. 6, the switch signals CS1, CS2
Are also synchronized with the sample and hold signals SH1 and SH2. Therefore, it is possible to share the sample and hold signals SH1 and SH2 and the switch signals CS1 and CS2.

In the first embodiment, the rectangular wave P1,
Although it was necessary to open and close the switches 23 and 24 at twice the frequency of P2, in the second embodiment, the square waves P1 and P2
Switches 23, 23a, 24, 24a at the same frequency as
Can be opened and closed, and the sample and hold timing can be shared, so that there is an advantage that the control signal can be simplified. (Third Embodiment) FIG. 7 shows the configuration of a capacitive physical quantity detection device according to a third embodiment of the present invention. In the first embodiment,
Although the reset means is constituted by the switches 23 and 24 and the fourth capacitor 25, in the third embodiment,
A switch 23 'is provided between the first capacitor 25 and the first reference voltage source (ground potential).
Switch 2 between the non-inverting input terminal of
4 'is provided. In this case, the fourth capacitor 2
Since there are switches on both sides of 5, the effect of the parasitic capacitance can be canceled out, and more accurate capacitance detection becomes possible. (Fourth Embodiment) FIG. 8 shows the configuration of a capacitive physical quantity detection device according to a fourth embodiment of the present invention. C as shown in FIG.
In the −V conversion circuit 2, the amount of charge for charging and discharging the fourth capacitor 25 differs between when the rectangular wave P 1 is in the Hi state and when the rectangular wave P 1 is in the Lo state due to the displacement of the movable electrode 12 and the parasitic capacitance. there is a possibility. When this happens,
Even if the physical quantity is 0, a rectangular wave is generated in the output voltage Vc of the operational amplifier 21 and is detected as an offset.

Therefore, in the fourth embodiment, in order to cancel the offset, as shown in FIG. 8, the second reference voltage source Vr having a voltage different from that of the first reference voltage source (ground potential). And switches 23 ″ and 24 ″ are connected in series between the first reference voltage source and the second reference voltage source, and a fourth capacitor 25 is connected to the connection point of the switches 23 ″ and 24 ″. Are connected at one end.

The operation of this embodiment will be described with reference to the timing chart of FIG. Switch 23 '', 2
The operation other than 4 ″ is the same as that of the first embodiment, except that the switches 23 ″ and 24 ″
1, and are opened and closed by switch signals CS3 and CS4 synchronized with P2. As a result, when the rectangular wave P1 is in the Hi state and the Lo state, the charging and discharging of the fourth capacitor 25 is performed with reference to different voltages, so that the electric charge charged in the third capacitor 22 is changed. The amount can be different between when the rectangular wave P1 is in the Hi state and when it is in the Lo state.
Therefore, the offset can be canceled by adjusting the potential difference between the first reference voltage source and the second reference voltage source. (Fifth Embodiment) FIG. 10 shows the configuration of a capacitive physical quantity detection device according to a fifth embodiment of the present invention. In the fifth embodiment, an electrostatic force that displaces the movable electrode 12 is generated between the fixed electrodes 11 and 13 and the movable electrode 12 to forcibly displace the movable electrode 12, and the signal processing unit 3 The self-diagnosis function for detecting the abnormality of the sensor element unit 1 from the output voltage of the first embodiment is added.

For this reason, in this embodiment, the voltage applied to the non-inverting input terminal of the operational amplifier 21 is switched by the switches 26 and 27. The switches 26 and 27 are connected to the switch signals CST and CST bar (C
It is opened and closed by a signal obtained by inverting ST. The operation of the fifth embodiment will be described with reference to a timing chart shown in FIG. The difference from the first embodiment is that, as shown in FIG. 11, a period (self-diagnosis period) for applying an electrostatic force is provided in addition to the normal operation, and the switches 23 and 24 are closed during this electrostatic force applying period. In addition, the switch 27 is closed, and the self-diagnosis voltage source Vst is applied to the movable electrode 12 via the switch 27.

During the period of applying the electrostatic force, an electrostatic force is generated between the fixed electrode 11 and the movable electrode 12 due to a potential difference of (V−Vst). Electrostatic potential is generated due to the potential difference. Since the direction and size of displacement of the movable electrode 12 are determined from the difference between the respective electrostatic forces, a failure or a change over time can be detected from a change in the output voltage of the signal processing unit 3 after the application of the electrostatic force.

Further, instead of the structure shown in FIG.
The self-diagnosis can be performed in the same manner as shown in FIG. That is, in the configuration shown in FIG. 12, the first reference voltage source (ground potential) is connected to the non-inverting input terminal of the operational amplifier 21, and the switch 26 is connected between the movable electrode 12 and the inverting input terminal of the operational amplifier 21. The switch 27 is provided between the movable electrode 12 and the self-diagnosis voltage source Vst.

During the self-diagnosis in the fifth embodiment, the charges of the third and fourth capacitors 22 and 25 are discharged, and the operational amplifier 21 outputs the same voltage as that of the first reference voltage source. . Sixth Embodiment FIG. 13 shows the configuration of a capacitive physical quantity detection device according to a sixth embodiment of the present invention. In the first embodiment, the third capacitor 22 is connected between the inverting input terminal and the output terminal of the operational amplifier 21, but in the sixth embodiment, the third capacitor 22 is connected between the inverting input terminal and the output terminal of the operational amplifier 21. Are provided with third and fourth capacitors 205 and 215, and switches 201 to 204 and 211 to 214 are connected to a switch signal C.
Opening and closing by S1 and CS2, connecting one of the third and fourth capacitors 205 and 215 between the inverting input terminal and the output terminal of the operational amplifier 21, and connecting the other to the reference voltage source to discharge. The same effect as that of the first embodiment is obtained by alternately repeating each time the rectangular waves P1 and P2 are inverted.
The timing chart in this case is the same as FIG.

In any of the above-described embodiments, the signals CS1 and CS2 for controlling the switches, CS3 and CS4, and SH1 and SH2 are timings such that the Hi states do not overlap with each other during normal operation. It is desirable that The switches 23, 2
3 ′, 23 ″, 23a, 24, 24 ′, 24 ″, 2
4a, 201 to 204 and 211 to 214 are configured as switching means using a semiconductor switching element or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a capacitive physical quantity detection device according to a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a diagram showing a configuration of a signal processing unit 3 in FIG. 1;

FIG. 4 is a diagram illustrating another configuration of the signal processing unit 3 in FIG. 1;

FIG. 5 is a diagram showing a configuration of a capacitive physical quantity detection device according to a second embodiment of the present invention.

FIG. 6 is a timing chart for explaining the operation of the embodiment shown in FIG. 5;

FIG. 7 is a diagram illustrating a configuration of a capacitive physical quantity detection device according to a third embodiment of the present invention.

FIG. 8 is a diagram illustrating a configuration of a capacitive physical quantity detection device according to a fourth embodiment of the present invention.

FIG. 9 is a timing chart for explaining the operation of the embodiment shown in FIG. 8;

FIG. 10 is a diagram showing a configuration of a capacitive physical quantity detection device according to a fifth embodiment of the present invention.

FIG. 11 is a timing chart for explaining the operation of the embodiment shown in FIG. 10;

FIG. 12 is a diagram showing a configuration of a capacitive physical quantity detection device according to a modification of the fifth embodiment of the present invention.

FIG. 13 is a diagram showing a configuration of a capacitive physical quantity detection device according to a sixth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sensor element part, 2 ... CV conversion circuit, 3 ... Signal processing part, 11, 13 ... Fixed electrode, 12 ... Movable electrode, 2
1 ... operational amplifier, 22 ... third capacitor, 23, 24
... switch, 25 ... fourth capacitor.

Claims (13)

[Claims] At least one of the capacitors has first and second capacitors that vary in accordance with a physical quantity and are electrically connected in series. Nodes at both ends of the first and second capacitors are connected to each other. A non-inverting input terminal, wherein an inverting input terminal is connected to a connection point between the sensor element portion (1) configured to apply first and second rectangular waves having opposite phases, and the first and second capacitors; An operational amplifier (21) having a terminal connected to a first reference voltage source, and an operational amplifier (21) connected between an inverting input terminal and an output terminal of the operational amplifier, the first and second rectangular waves being generated by inversion of the first and second rectangular waves. (1) a third capacitor (22) for holding a charge corresponding to the difference between the capacitances of the second and third capacitors, and a charge for holding a charge corresponding to the output voltage of the operational amplifier, and thereafter the first and second rectangles At the timing when the wave is inverted, the held charge is Reset means (23, 23 ', 23'', 23a, 24, 2) for charging the third capacitor.
4 ′, 24 ″, 24a, 25, 25a) and a signal processing unit (3) that samples and holds the output voltage of the operational amplifier and performs signal processing. . 2. The capacitance type physical quantity detection device according to claim 1, wherein the capacitances of the first and second capacitors are differential capacitances. 3. The signal processing unit according to claim 1, wherein the output voltage of the operational amplifier when the first rectangular wave is at a high level and the output voltage of the first rectangular wave are high.
3. The capacitive physical quantity detection device according to claim 1, wherein a difference from the output voltage of the operational amplifier when the rectangular wave is at a low level is output as a physical quantity detection signal. 4. 4. The capacitive physical quantity detection device according to claim 3, wherein the signal processing unit is constituted by a switched capacitor. 5. The reset means according to claim 3, wherein said reset means outputs a charge amount substantially equal to the charge amount stored in said third capacitor.
The capacitance type physical quantity detection device according to any one of claims 1 to 4, wherein the capacitor is charged. 6. The reset means charges the third capacitor with a charge corresponding to the output voltage of the operational amplifier every time the first and second rectangular waves are inverted, and resets the charge for the next charge. A charge corresponding to an output voltage of the operational amplifier.
6. The capacitance-type physical quantity detection device according to any one of items 5 to 5. 7. The reset means includes: a fourth capacitor (25) having one end connected to the first reference voltage source; and a second capacitor connected between the other end of the fourth capacitor and an inverting input terminal of the operational amplifier. First switch means (23) connected to
And second switch means (24) connected between the other end of the fourth capacitor and the output terminal of the operational amplifier, wherein the first and second switch means are connected to the second switch means (24). 1. Opening and closing each time the second rectangular wave is inverted, charges the electric charge accumulated in the fourth capacitor to the third capacitor, and changes the output voltage of the operational amplifier for the next charging. 7. The capacitance type physical quantity detection device according to claim 6, wherein a corresponding electric charge is held in the fourth capacitor. 8. The one end of the fourth capacitor and the first capacitor.
The third switch means (23 ') is connected between the reference voltage sources of the first and second, and the fourth switch means (24') is connected between one end of the fourth capacitor and the inverting input terminal of the operational amplifier. Wherein the third switch means opens and closes at the same timing as the first switch means, and the fourth switch means opens and closes at the same timing as the second switch means. Claim 7
4. The capacitive physical quantity detection device according to 1. 9. One end of the fourth capacitor is connected to the first reference voltage source via third switch means (23 ''), and the second end is connected via fourth switch means. And the third and fourth switch means are alternately opened and closed with the inversion of the first and second rectangular waves. The capacitance-type physical quantity detection device according to claim 7. 10. The capacitance type physical quantity detection device according to claim 7, wherein the third capacitor and the fourth capacitor have substantially the same capacitance. 11. The reset means includes: fourth and fifth capacitors (25, 25a) having one ends connected to the first reference voltage source; and the other end of the fourth capacitor (25); First switch means (23) connected between the inverting input terminals of the operational amplifier; and second switch means (24) connected between the other end of the fourth capacitor and the output terminal of the operational amplifier. ), Third switch means (24a) connected between the other end of the fifth capacitor (25a) and the inverting input terminal of the operational amplifier, and the other end of the fifth capacitor and the operational amplifier And a fourth switch means (23a) connected between the output terminals of the first and second switches. The first and fourth switch means and the second and third switch means are connected to the first and second switch means. Open and close alternately with the inversion of the square wave When the first and fourth switch means are closed, the electric charge accumulated in the fourth capacitor is charged to the third capacitor, and the fifth capacitor is charged for the next charge. Therefore, the electric charge corresponding to the output voltage of the operational amplifier is held, and the electric charge accumulated in the fifth capacitor is transferred to the third capacitor when the second and third switch means are closed. 7. The capacitance type physical quantity detection method according to claim 6, wherein the fourth capacitor is configured to hold a charge corresponding to an output voltage of the operational amplifier for the next charge. apparatus. 12. At the time of self-diagnosis, all switch means connected between an inverting input terminal and an output terminal of the operational amplifier are closed, and a predetermined point is connected to a connection point between the first and second capacitors. 12. The capacitive physical quantity detecting device according to claim 7, wherein a voltage is applied to apply an electrostatic force corresponding to a predetermined physical quantity to the first and second capacitors. 13. At least one of the capacitors has first and second capacitors that change in accordance with a physical quantity and are electrically connected in series, and nodes at both ends of the first and second capacitors are connected to each other. A non-inverting input terminal, wherein an inverting input terminal is connected to a connection point between the sensor element portion (1) configured to apply first and second rectangular waves having opposite phases, and the first and second capacitors; An operational amplifier (21) having a terminal connected to a first reference voltage source, and third and fourth capacitors (205, 2) provided in parallel between the inverting input terminal and the output terminal of the operational amplifier.
15) and connecting one of the third and fourth capacitors between an inverting input terminal and an output terminal of the operational amplifier, and connecting the first and second rectangular waves by inverting the first and second rectangular waves. A charge corresponding to the difference in the capacitance of the second capacitor is held in the one capacitor, and a charge path is formed in the other capacitor to discharge the charge accumulated in the other capacitor. Means (201-204, 211-214) for alternately switching the other capacitor each time the first and second rectangular waves are inverted, and signal processing for sampling and holding the output voltage of the operational amplifier to perform signal processing (3) A capacitive physical quantity detection device, comprising: