JP2008107108A - Capacitive detector for mechanical quantity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacitive detector for mechanical quantity capable of simultaneously performing acceleration detection and self-diagnosis of a sensor part. <P>SOLUTION: A movable part 5 is oscillated at a frequency higher than an upper bound of a frequency at which acceleration to be detected changes. On the basis of sensor signals that are output from an acceleration sensor 30 at this time, a determining part 24 performs self-diagnosis on anomalies of the sensor part 20. Sensor signals from the acceleration sensor 30 are filter-processed at a digital filter 32 to remove a frequency component corresponding to an oscillation frequency of the movable part 5. As a result, it is possible to acquire signals based on acceleration applied to the movable part 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes a sensor unit in which the capacitance between the movable electrode and the fixed electrode changes when the movable electrode is displaced according to the application of a mechanical quantity, and in particular, self-diagnosis of an abnormality of the movable electrode. The present invention relates to a capacitive mechanical quantity detection device having a diagnostic function.

As a capacitive mechanical quantity detection device having a self-diagnosis function, for example, a device described in Patent Document 1 is known. In the apparatus described in Patent Document 1, a period for detecting a change in capacitance and a period for displacing the movable electrode are set separately. In other words, during the period of detecting the capacitance change, the CV conversion circuit applies a periodically changing signal between the movable electrode and the fixed electrodes arranged on both sides of the movable electrode. Acceleration is detected by outputting a voltage corresponding to a change in differential capacitance, which is a difference in capacitance between the movable electrode and the fixed electrodes on both sides. On the other hand, during the period in which the movable electrode is displaced, a self-diagnosis is performed by giving a drive signal for displacing the movable electrode as if acceleration is acting on the movable electrode 2d.
JP 2000-81449 A

  As described above, in the conventional apparatus, the period for detecting the capacitance change according to the acceleration is divided from the period for performing the self-diagnosis by displacing the movable electrode. For this reason, when performing self-diagnosis, it is necessary to interrupt detection of acceleration, and when performing acceleration detection, self-diagnosis cannot be performed.

  The present invention has been made in view of the above-described points, and an object of the present invention is to provide a capacitive dynamic quantity detection device capable of simultaneously executing detection of a dynamic quantity and self-diagnosis.

In order to achieve the above object, the capacitive mechanical quantity detection device according to claim 1,
It consists of a movable electrode that is displaced in response to the application of a mechanical quantity that is a detection target, and a fixed electrode that is disposed opposite to the movable electrode. When the movable electrode is displaced in response to the application of a mechanical quantity, the movable electrode is fixed. A sensor unit in which the capacitance between the electrodes changes;
A CV conversion circuit for converting a change in capacitance in the sensor unit into a change in voltage signal;
Drive means for applying a drive voltage for vibrating the movable electrode at a frequency higher than the upper limit of the frequency at which the mechanical quantity to be detected changes, between the movable electrode and the fixed electrode;
Self-diagnosis means for diagnosing an abnormality of the movable electrode based on a voltage signal output from the CV conversion circuit when a drive voltage is applied between the movable electrode and the fixed electrode by the drive means;
The voltage signal converted by the CV conversion circuit is subjected to filter processing for removing a frequency component corresponding to the vibration frequency of the movable electrode by the driving means, and a signal corresponding to the mechanical quantity applied to the movable electrode is output. And a filter means.

  As described above, in the capacitive mechanical quantity detection device according to claim 1, when the movable electrode is vibrated at a frequency higher than the upper limit of the frequency at which the mechanical quantity to be detected changes, the CV conversion circuit Based on the output voltage signal, self-diagnosis of abnormality of the movable electrode is performed. That is, if the movable electrode vibrates according to the drive voltage, the movable electrode is normal, and if it does not vibrate, it can be diagnosed that an abnormality such as sticking has occurred. The capacitive mechanical quantity detection device according to claim 1 further includes a filter process for removing a frequency component corresponding to the vibration frequency of the movable electrode by the driving means from the voltage signal converted by the CV conversion circuit. The filter means which performs is provided. Since the vibration frequency of the movable electrode is different from the frequency at which the dynamic quantity to be detected changes, the filter means generates a frequency component corresponding to the vibration frequency of the movable electrode from the voltage signal output from the CV conversion circuit. Can be removed. As a result, a signal corresponding to the mechanical quantity applied to the movable electrode can be obtained from the voltage signal output from the CV conversion circuit. In this manner, the capacitive mechanical quantity detection device according to claim 1 can simultaneously execute the detection of the mechanical quantity and the self-diagnosis.

  As described in claim 2, the fixed electrode includes a first fixed electrode and a second fixed electrode provided on both sides of the movable electrode along the displacement direction of the movable electrode. The difference between the first capacitance between the movable electrode and the first fixed electrode and the second capacitance between the movable electrode and the second fixed electrode is converted into a voltage signal. A potential difference is applied between one of the first and second fixed electrodes and the movable electrode so as to displace the movable electrode, and the movable electrode is not displaced between the other of the first and second fixed electrodes and the movable electrode. In a mode in which a potential difference of magnitude is given and these potential differences are periodically switched, a driving voltage is given between the movable electrode and the first and second fixed electrodes, and the magnitude of the displacement of the movable electrode by a signal output from the filter means Offset correction method to correct the offset according to the potential difference It may be configured with.

  As described above, the CV conversion circuit converts the difference between the first capacitance between the movable electrode and the first fixed electrode and the second capacitance between the movable electrode and the second fixed electrode into a voltage signal. By doing so, the detection accuracy of the displacement of the movable electrode can be improved. Further, when the driving means applies the driving voltage as described above between the movable electrode and the first and second fixed electrodes, the movable electrode is displaced between one of the first and second fixed electrodes and the movable electrode. It is only necessary to periodically apply a voltage having a magnitude to be applied. However, in this case, since the movable electrode vibrates in a manner approaching only one of the first and second fixed electrodes, the filter means smoothes and removes the high-frequency component included in the voltage signal by the vibration. If there exists, a filter means will output the signal which added the smoothed component to the signal corresponding to the original mechanical quantity.

  Therefore, the capacitive mechanical quantity detection device according to claim 2 includes an offset correction unit, and drives the signal output from the filter unit so as to cancel the component added to the signal corresponding to the original mechanical quantity. Offset correction is performed according to the voltage. As a result, even when the above-described configuration is employed, a signal corresponding to the mechanical quantity applied to the movable electrode can be obtained.

  As described in claim 3, the driving means may intermittently apply a driving voltage for vibrating the movable electrode between the movable electrode and the fixed electrode. In this case, even if an abnormality occurs in the movable electrode, there is a possibility that the abnormality cannot be detected immediately, but there is an advantage that power consumption for self-diagnosis can be reduced. Further, when the movable electrode is vibrated intermittently, the smoothing component added to the original mechanical quantity is also reduced, so that the offset correction means can be omitted.

  In the case of performing self-diagnosis by intermittently vibrating the movable electrode, as described in claim 4, the drive means provides a drive voltage for vibrating the movable electrode when the voltage signal does not change for a predetermined time. It is preferable to apply between the movable electrode and the fixed electrode. This is because when the signal output from the filter means does not change for a predetermined time, there is a possibility that an abnormality such as the sticking of the movable electrode has occurred.

  The voltage signal converted by the CV conversion circuit is stopped when the filter means stops performing the filter process while the drive voltage for vibrating the movable electrode is not applied by the drive means. Is preferably output as it is. When the filter processing is performed, there is a considerable delay in the phase of the signal. Therefore, if a drive voltage for vibrating the movable electrode is not applied by the drive means, it is preferable to stop the filter process and output a signal without phase delay.

  In order for the self-diagnosis means to diagnose the abnormality of the movable electrode based on the voltage signal output from the CV conversion circuit, as described in claim 6, before the drive voltage is applied, C- The voltage signal output from the V conversion circuit is compared with the voltage signal output from the CV conversion circuit when the drive voltage is applied, and the voltage signal fluctuates when the drive voltage is applied. Or determining whether the voltage signal fluctuates in accordance with the driving voltage by comparing the signals before and after the filtering process by the filter means. May be.

(First embodiment)
Hereinafter, a capacitive dynamic quantity detection device according to a first embodiment of the present invention will be described with reference to the drawings. In addition, although this embodiment demonstrates the example actualized as the capacitive acceleration detection apparatus which detects an acceleration as a dynamic quantity, it is also applicable to the use which detects an angular velocity, a pressure, etc. as a dynamic quantity in addition to this. It is.

  First, a sensor unit in a capacitive acceleration detecting device will be described with reference to FIG. FIG. 1 is a perspective sectional view of a sensor unit 20 in a capacitive acceleration detection device.

  As shown in FIG. 1, the sensor unit 20 includes an SOI (Silicon On Insulator) in which an insulating layer 3 made of, for example, silicon oxide is formed between a first semiconductor layer 1 made of, for example, silicon and a second semiconductor layer 2. The substrate 4 is formed by a well-known micromachining technique using a semiconductor manufacturing technique. Specifically, the sensor unit 20 has a movable part 5 formed from the second semiconductor layer 2, a pair of fixed parts 6 and 7 provided on both sides of the movable part 5, and a surrounding part 8 surrounding them. In addition, a predetermined gap is provided between the portions 5 to 8 and insulated from each other.

  The movable part 5 is composed of a movable electrode 9, a weight part 10, a beam part 11, an anchor 12, and a movable electrode pad 13, and both ends of the weight part 10 as a mass part on which acceleration acts are provided with a rectangular frame-shaped beam part. 11 is connected to an anchor 12 connected to the insulating layer 3 through 11. The movable electrodes 9 are formed so as to protrude from both side surfaces of the weight portion 10 so as to be orthogonal to the longitudinal direction of the weight portion 10, and for example, three movable electrodes 9 are provided on each side surface.

  Immediately below the movable electrode 9, the weight portion 10, and the beam portion 11, the insulating layer 3 is removed by selective etching and a hollow portion exists. Further, the beam portion 11 connected to the weight portion 10 has a spring function of being displaced in a direction orthogonal to the longitudinal direction. Therefore, when the weight part 10 receives an acceleration including a component in the longitudinal direction, the weight part 10 and the movable electrode 9 are displaced along the longitudinal direction of the weight part 10 and return to the original position due to the disappearance of the acceleration.

  A movable electrode pad 13 is formed at a predetermined position of one anchor 12 in the movable portion 5, and a drive voltage can be applied to the movable portion 5 through the movable electrode pad 13.

  The fixed portions 6 and 7 are composed of fixed electrodes 14a and 14b, fixed electrode wiring portions 15a and 15b, and fixed electrode pads 16a and 16b, respectively. Each is fixed on the first semiconductor layer 1 via an insulating layer 3. The fixed electrode wiring portions 15 a and 15 b are arranged in parallel with the weight portion 10. The fixed electrodes 14a and 14b extending from the fixed electrode wiring portions 15a and 15b are opposed to the movable electrode 9 protruding from both side surfaces of the weight portion 10 in a parallel state while having a predetermined detection interval (gap). Be placed.

  Here, the fixed electrodes 14a and 14b are arranged so that the fixed electrode 14b faces the side surface opposite to the side surface of the movable electrode 9 to which the fixed electrode 14a faces. The fixed electrodes 14 a and 14 b are provided in the same number as the movable electrodes 9. Fixed electrode wiring portions 15a and 15b are connected to fixed electrode pads 16a and 16b, respectively, and a drive voltage can be applied to the fixed portions 6 and 7 via the fixed electrode pads 16a and 16b. .

  In the sensor unit 20 configured as described above, when the acceleration in the longitudinal direction of the weight part 10 is received, the weight part 10 is displaced, and accordingly, the movable electrode 9 is also displaced. For this reason, the distance between the opposed surface of the movable electrode 9 and the opposed surfaces of the fixed electrodes 14a and 14b disposed to face the movable electrode 9 increases or decreases. Therefore, when acceleration is applied, one of the capacitances of the capacitors formed between the movable electrode 9 and the fixed electrodes 14a and 14b increases and the other decreases. Since the magnitude of the difference in capacitance varies depending on the magnitude of applied acceleration, the acceleration can be detected based on the difference in capacitance.

  In the present embodiment, in the sensor unit 20, the sum of the capacitances of the capacitor composed of the movable electrode 9 and the fixed electrode 14a is CS1, and the sum of the capacitances of the capacitor composed of the movable electrode 9 and the fixed electrode 14b. Is CS2, the size, shape, initial position, etc. of each electrode 9, 14a, 14b are set so that the capacitance difference ΔC (= CS1-CS2) is substantially zero when no acceleration is applied. Is set.

  A processing circuit for detecting acceleration will be described with reference to FIG. 2 showing the overall configuration of the capacitive acceleration detecting device according to the present embodiment. As shown in FIG. 2, in addition to the sensor unit 20 described above, the acceleration sensor 30 includes a CV conversion circuit 21, a sample-and-hold differential amplifier circuit 22, an AMP 23, and a control unit configured integrally with the sensor unit 20. Signal processing circuits such as a circuit 24 and a self-diagnosis circuit 25 are also provided.

  The CV conversion circuit 21 inputs a signal output from the sensor unit 20 corresponding to the difference in capacitance according to the applied acceleration, and converts the signal corresponding to the difference in capacitance into a voltage signal. To do. The sample and hold differential amplifier circuit 22 samples the voltage signal output from the CV conversion circuit 21 at a predetermined cycle, amplifies the voltage signal, and outputs the amplified signal.

  An example of the circuit configuration of the CV conversion circuit 21 and the sample-and-hold differential amplifier circuit 22 will be described with reference to FIG. First, the CV conversion circuit (switched capacitor circuit) 21 includes an electrostatic capacity CS1 of a capacitor 50 composed of the movable electrode 9 and the fixed electrode 14a, and an electrostatic capacity of a capacitor 51 composed of the movable electrode 9 and the fixed electrode 14b. A difference from the capacitor CS2 is converted into a voltage and output, and as shown in FIG. 3, it is composed of an operational amplifier 61, a capacitor 62, and a switch 63.

  The inverting input terminal of the operational amplifier 61 is connected to the movable electrode 9 via the movable electrode pad 13, and a capacitor 62 and a switch 63 are connected in parallel between the inverting input terminal and the output terminal. A voltage V0 / 2 is input to the non-inverting input terminal of the operational amplifier 61 from a voltage source (not shown). Therefore, a driving voltage having a potential of V0 / 2 is applied to the movable electrode 9.

  Further, the drive voltage signal 1 and the drive voltage signal 2 are input to the pair of fixed electrodes 14a and 14b via the fixed electrode pads 16a and 16b, respectively. The drive voltage signal 1 is alternately and periodically changed between a voltage V1 that generates an electrostatic force that can displace the movable portion 5 and 0 (v). On the other hand, the drive voltage signal 2 is alternately and periodically changed between the voltages V0 (<V1) and 0 (v) that cannot displace the movable portion 5, The phase is 180 ° out of phase with the driving voltage signal 1.

  The voltage switching frequency in the drive voltage signal 1 and the drive voltage signal 2 is set to a frequency higher than the upper limit of the frequency at which the acceleration that is the detection target changes. For example, when the capacitive acceleration detection device according to the present embodiment is mounted on a vehicle and acceleration acting on the vehicle is detected, the upper limit of the frequency at which the acceleration changes is about 10 Hz. Therefore, in such an application, the voltage of the drive voltage signals 1 and 2 is switched at a frequency higher than 10 Hz.

When the drive voltage signal 1 rises and at the same time the drive voltage signal 2 falls, the capacitor 50 is charged and the capacitor 51 is discharged. Conversely, when the drive voltage signal 1 falls and the drive voltage signal 2 rises, the capacitor 50 is discharged and the capacitor 51 is charged. If the movable electrode 9 is displaced by application of acceleration when the capacitors 50 and 51 are charged and discharged, the capacitances CS1 and CS2 of the capacitors 50 and 51 change, so the charge and discharge amount Also changes. The electric charge corresponding to the charge / discharge amount in the capacitors 50 and 51 is stored in the capacitor 62, and the voltage Vout output by the operational amplifier 61 according to the electric charge stored in the capacitor 62 is expressed as follows.
(Equation 1)
Vout =-(CS1 / V1-CS2 / V0) / Cf + V0 / 2
In the CV conversion circuit 21, the switch 63 is opened and closed with a predetermined cycle in accordance with the cycle of the drive voltage signals 1 and 2 in order to cancel the charge of the capacitor 62. Vout is output.

  When the voltage Vout corresponding to the acceleration is output from the CV conversion circuit 21, the sample hold differential amplifier circuit 22 samples, amplifies and outputs the voltage. As shown in FIG. 3, the sample-and-hold differential amplifier circuit 22 includes a switch 71, an operational amplifier 72, and a capacitor 73.

  The switch 71 is turned on when the voltage Vout corresponding to the acceleration is output from the CV conversion circuit 21, and samples and holds the voltage Vout in the capacitor 73. The voltage Vout sampled and held by the capacitor 73 is amplified by the operational amplifier 72 and output to the AMP 23 described later.

  When the drive voltage signals 1 and 2 as described above are applied to the pair of fixed electrodes 14a and 14b, the movable part 5 of the sensor part 20 vibrates at a frequency higher than the change in acceleration to be detected. This vibration is generated in such a manner that the drive voltage signal 1 having the potential V1 for displacing the movable electrode 9 is given only to the fixed electrode 14a, so that the vibration is periodically displaced toward the fixed electrode 14a.

  When the movable electrode 9 (movable part 5) vibrates in this way, the output voltage Vout from the CV conversion circuit 21 is changed by the sample-and-hold differential amplifier circuit 22 to the voltage switching period in the drive voltage signals 1 and 2. By performing sample and hold at a predetermined cycle earlier than that, a voltage signal corresponding to the sensor signal shown in FIG. 4 is continuously output from the sample and hold differential amplifier circuit 22.

  When the movable part 5 of the sensor unit 20 is vibrating, a sensor signal that increases or decreases in accordance with the vibration is output from the CV conversion circuit 21 (sample hold differential amplifier circuit 22) as shown in FIG. The Accordingly, if the sensor signal that vibrates at the frequency equivalent to the voltage switching frequency of the drive voltage signals 1 and 2 as shown in FIG. Is normal and cannot be detected, it can be diagnosed that the moving part 5 has an abnormality such as sticking.

  Returning to FIG. 2 again, the remaining configuration of the processing circuit for detecting acceleration will be described. In FIG. 2, the AMP 23 further amplifies and outputs the voltage signal output from the sample and hold differential amplifier circuit 22. The control circuit 24 controls the opening / closing timing of the switch 63 in the CV conversion circuit 21 and the switch 71 in the sample-and-hold differential amplifier circuit 22 described above. The control circuit 24 instructs the self-diagnosis circuit 25 to generate the drive voltage signals 1 and 2 based on a diagnosis instruction signal from the microcomputer 40 described later. The self-diagnosis circuit 25 generates drive voltage signals 1 and 2 based on instructions from the control circuit 24 and supplies them to the fixed electrode pads 16a and 16b, respectively.

  Next, a configuration for self-diagnosis of the presence or absence of abnormality of the movable part 5 based on a sensor signal output from the acceleration sensor 30 will be described. This self-diagnosis is executed by a microcomputer 40 provided separately from the acceleration sensor 30. In FIG. 2, various functions executed in the microcomputer 40 are shown as a block diagram.

  The microcomputer 40 includes an A / D conversion circuit 31 that performs analog-digital conversion on the input sensor signal. The sensor signal converted into a digital value by the A / D conversion circuit 31 is input to the digital filter 32 and the determination unit 34. The digital filter 32 executes a low-pass filter process for removing a frequency component corresponding to the vibration frequency of the movable part 5 in order to remove the influence of the vibration of the movable part 5 on the sensor signal due to the drive voltage signals 1 and 2 described above. Is.

  Since the frequency of vibration of the movable part 5 is different from the frequency at which the acceleration that is the detection target changes, the digital filter 32 can remove only the frequency component corresponding to the frequency of vibration of the movable part 5 from the sensor signal. it can. However, if the digital filter 32 smoothes and removes the high-frequency component contained in the sensor signal due to the vibration of the movable part 5, the smoothed signal output from the digital filter 32 is not included in the smoothed signal output from the digital filter 32 as shown in FIG. The smoothed component is added to the signal corresponding to the original acceleration.

  Therefore, the microcomputer 40 includes an offset correction unit 33. The offset correction unit 33 corrects the smoothing signal output from the digital filter 32 according to the voltage V1 in the drive voltage signal 1 so as to cancel out the component added to the signal corresponding to the original acceleration. That is, since the displacement amount of the movable part 5 due to the voltage V1 is known in advance, the smoothing signal is corrected so as to reduce the displacement amount due to the voltage V1. Thereby, the offset correction unit 33 of the microcomputer 40 outputs a signal corresponding to the displacement due to the applied acceleration.

  The determination unit 34 inputs the smoothed signal from the digital filter 32 in addition to the output signal of the A / D conversion circuit 31 described above. Then, by comparing these signals, it is determined whether or not a sensor signal that vibrates at a frequency corresponding to the voltage switching frequency of the drive voltage signals 1 and 2 is output from the acceleration sensor 30. In this determination, when it is determined that the sensor signal is not oscillating, an abnormality signal is output and output of the diagnostic instruction signal to the acceleration sensor 30 is stopped. On the other hand, if it is determined that the sensor signal is vibrating, the diagnosis instruction signal is continuously output to the acceleration sensor 30 in order to monitor the occurrence of the abnormality.

  As described above, according to the capacitive acceleration detection device of the present embodiment, it is possible to simultaneously execute acceleration detection and self-diagnosis of the sensor unit 20.

(Second Embodiment)
Next, a capacitive mechanical quantity detection device (capacitive acceleration detection device) according to a second embodiment of the present invention will be described with reference to the drawings.

  In the capacitive acceleration detecting device according to the first embodiment, the drive voltage signals 1 and 2 for constantly vibrating the movable portion 5 are applied between the movable electrode 9 and the pair of fixed electrodes 14a and 14b. In this way, when an abnormality occurs in the movable part 5, there is an advantage that the abnormality can be detected without delay.

  However, when an abnormality occurs in the movable part 5, there may be a case (use) that does not matter so much even if there is a certain time delay until the abnormality is detected. In the present embodiment, paying attention to such points, the movable part 5 is intermittently vibrated to perform self-diagnosis of the movable part 5. Thus, if the movable part 5 is vibrated intermittently, the power consumption required for the vibration generation can be reduced and the smoothing component added to the original acceleration is also reduced, so that the offset correction part can be omitted. There are benefits.

  FIG. 5 is a block diagram showing the overall configuration of the capacitive acceleration detecting device according to the present embodiment. In the present embodiment, a diagnosis instruction output unit 35 for generating a diagnosis instruction signal for the acceleration sensor 30 at a predetermined timing (predetermined cycle) is added to the microcomputer 40. When the control circuit 24 of the acceleration sensor 30 receives this diagnostic instruction signal, as shown in FIG. 6, the control circuit 24 of the acceleration sensor 30 only once between the movable electrode 9 and the fixed electrode 14 a as shown in FIG. 6. Is instructed to apply a voltage V1 for displacing. The self-diagnostic circuit 25 generates the voltage V1 when it is instructed to apply the voltage V1 from the control circuit 24, and supplies it to the fixed electrode pad 16a. This is applied to the pad 16a.

  As a result, the acceleration signal output from the acceleration sensor 30 vibrates only when the voltage V1 is applied. When this vibration occurs, the determination unit 34 takes in sensor signals before and after the filtering process by the digital filter 32 and self-diagnose the presence or absence of an abnormality in the acceleration sensor 30 based on whether or not the sensor signal is vibrating.

  In the configuration shown in FIG. 5, as described above, since the influence on the sensor signal due to the vibration of the movable portion 5 is so small that it can be almost ignored, the offset correction unit 33 is omitted, and the digital filter 32 directly A signal indicating the applied acceleration is output.

(Third embodiment)
In 2nd Embodiment mentioned above, the movable part 5 of the acceleration sensor 30 was vibrated intermittently with a predetermined period. On the other hand, in the capacitive mechanical quantity detection device (capacitive acceleration detection device) according to the third embodiment, the movable part 5 of the acceleration sensor 30 vibrates when the sensor signal output from the acceleration sensor 30 does not change for a predetermined time. Thus, the self-diagnosis of the acceleration sensor 30 is performed.

  While the acceleration acting on the acceleration sensor 30 is changing, if the acceleration sensor 30 functions normally, the sensor signal output from the acceleration sensor 30 also changes. When the sensor signal is changing, it can be considered that no abnormality such as sticking occurs in the movable part 5. In other words, when an abnormality such as sticking occurs in the movable part 5, the sensor signal does not change and becomes constant.

  In view of such a point, the capacitive acceleration detection device according to the present embodiment is when the sensor signal output from the acceleration sensor 30 does not change for a predetermined time and there is a possibility that an abnormality has occurred in the acceleration sensor 30. Only conduct self-diagnosis.

  The configuration of the capacitive acceleration detection device according to the present embodiment is basically the same as the configuration of the capacitive acceleration detection device according to the second embodiment. However, the determination unit 34 may determine whether the sensor signal from the acceleration sensor 30 is constant without changing for a predetermined time in addition to the determination for self-diagnosis whether the sensor signal is vibrating. judge. Specifically, as illustrated in FIG. 7, when the time during which the change width of the sensor signal is within a predetermined range reaches a predetermined time, the determination unit 34 determines that the sensor signal is constant for a predetermined time.

  When the determination unit 34 determines that the sensor signal is constant for a predetermined time, the determination unit 34 instructs the diagnosis instruction output unit 35 to output a diagnosis instruction signal. Thereby, in the acceleration sensor 30, the self-diagnosis is performed when the sensor signal does not change for a predetermined time.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. is there.

  For example, when the self-diagnosis is performed by intermittently vibrating the movable part 5 as in the second and third embodiments described above, the filter by the digital filter 32 is used in a period other than the self-diagnosis period. The processing may be stopped and the sensor signal of the acceleration sensor 30 may be output as it is. When the filter processing by the digital filter 32 is performed, as shown in FIG. 4, there is a considerable delay in the phase of the signal when the sensor signal changes. Therefore, if the drive voltage signals 1 and 2 for vibrating the movable part 5 are not given, it is preferable to stop the filter processing by the digital filter 32 and output a signal without phase delay. .

  Moreover, in each embodiment mentioned above, it was determined whether the sensor signal was vibrating by comparing the signal before and behind the filter process of the digital filter 32. FIG. However, when self-diagnosis is performed by intermittently vibrating the movable portion 5 as in the second and third embodiments described above, the sensor signal is obtained by comparing the sensor signals before and after the vibration. It can also be determined whether or not it is vibrating.

  Further, in each of the above-described embodiments, the configuration in which the capacitive acceleration detection device includes the acceleration sensor 30 and the microcomputer 40 has been described. However, as shown in FIG. 8, the acceleration sensor 30 may have all the configurations. That is, as shown in FIG. 8, instead of the digital filter 32, the acceleration sensor 30 performs LPF 132 that performs filter processing with analog signals, a correction circuit 133 that performs offset correction on the smoothed signal output by the LPF 132, and A determination unit 134 that performs self-diagnosis by comparing signals before and after the filter processing by the LPF 132 may be provided.

It is a perspective sectional view of the sensor part in the capacity type acceleration sensing device by a 1st embodiment. It is a block diagram which shows the whole structure of the capacitive acceleration detection apparatus by 1st Embodiment. 2 is a circuit diagram illustrating an example of a circuit configuration of a CV conversion circuit 21 and a sample-and-hold differential amplifier circuit 22. FIG. It is a wave form diagram which shows the signal waveform of each part in the capacitive acceleration detection apparatus by 1st Embodiment. It is a block diagram which shows the whole structure of the capacitive acceleration detection apparatus by 2nd Embodiment. It is a wave form diagram which shows the signal waveform of each part in the capacitive acceleration detection apparatus by 2nd Embodiment. It is a wave form diagram which shows the signal waveform of each part in the capacitive acceleration detection apparatus by 3rd Embodiment. It is a block diagram which shows the structure of the capacitive acceleration detection apparatus by a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Sensor part 21 CV conversion circuit 22 Sample hold differential amplifier circuit 24 Control circuit 25 Self-diagnosis circuit 30 Acceleration sensor 31 A / D conversion circuit 32 Digital filter 33 Offset correction part 34 Determination part

Claims (7)

The movable electrode includes a movable electrode that is displaced in response to application of a mechanical quantity that is a detection target, and a fixed electrode that is disposed to face the movable electrode. When the movable electrode is displaced in response to application of the mechanical quantity, the movable electrode is moved. A sensor unit in which the capacitance between the electrode and the fixed electrode changes;
A CV conversion circuit for converting a change in capacitance in the sensor unit into a change in voltage signal;
Drive means for applying a drive voltage for oscillating the movable electrode at a frequency higher than the upper limit of the frequency at which the dynamic quantity to be detected changes, between the movable electrode and the fixed electrode;
Self-diagnosis means for diagnosing abnormality of the movable electrode based on a voltage signal output from the CV conversion circuit when the driving voltage is applied between the movable electrode and the fixed electrode by the driving means;
The voltage signal converted by the CV conversion circuit is subjected to filter processing for removing a frequency component corresponding to the vibration frequency of the movable electrode by the driving means, and according to a mechanical quantity applied to the movable electrode. A capacitive mechanical quantity detection device having a self-diagnosis function, comprising: a filter means for outputting a detected signal. The fixed electrode comprises a first fixed electrode and a second fixed electrode provided on both sides of the movable electrode along the displacement direction of the movable electrode,
The CV conversion circuit converts a difference between a first capacitance between the movable electrode and the first fixed electrode and a second capacitance between the movable electrode and the second fixed electrode into a voltage signal. Is to convert,
The driving means gives a potential difference of a magnitude that displaces the movable electrode between one of the first and second fixed electrodes and the movable electrode, and between the other of the first and second fixed electrodes and the movable electrode, In a mode in which a potential difference of a magnitude that does not cause displacement of the movable electrode is given and the potential difference is periodically switched, a driving voltage is applied between the movable electrode and the first and second fixed electrodes,
2. The capacitive mechanical quantity detection device according to claim 1, further comprising offset correction means for correcting an offset of a signal output from the filter means in accordance with a potential difference of a magnitude that displaces the movable electrode.   The capacitive mechanical quantity detection device according to claim 1, wherein the driving unit intermittently applies a driving voltage for vibrating the movable electrode between the movable electrode and the fixed electrode.   4. The capacitive type according to claim 3, wherein the driving unit applies a driving voltage for vibrating the movable electrode between the movable electrode and the fixed electrode when the voltage signal does not change for a predetermined time. Mechanical quantity detection device.   While the drive voltage for vibrating the movable electrode is not given by the drive means, the filter means stops the filter processing and outputs the voltage signal converted by the CV conversion circuit as it is. The capacitive mechanical quantity detection device according to claim 3 or 4, characterized in that:   The self-diagnosis means includes a voltage signal output from the CV conversion circuit before the drive voltage is applied, and a voltage output from the CV conversion circuit when the drive voltage is applied. 6. The abnormality of the movable electrode is diagnosed by determining whether or not the voltage signal fluctuates when the driving voltage is applied in comparison with a signal. The capacity type mechanical quantity detection device according to claim 1.   The self-diagnosis means compares the signals before and after being filtered by the filter means, and determines whether the voltage signal is fluctuating according to the drive voltage. 6. The capacitive mechanical quantity detection device according to claim 1, wherein diagnosis is performed.

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