Patent Description:
Patent Literature <NUM> discloses an acceleration sensor that includes a fixed electrode, a moving electrode and a detector. The moving electrode is movable in accordance with an acceleration given from the outside. The detector is configured to detect an acceleration in a prescribed direction based on a change in a capacitance between the moving electrode and the fixed electrode.

Regarding the acceleration sensor (inertial sensor) as disclosed in Patent Literature <NUM>, it is considered that a configuration for diagnosing abnormality of the detector is added to the detector itself.

It is therefore an object of the present disclosure to provide an inertial detection circuit, an inertial sensor and an inertial detection method, all of which can suppress that a configuration of a detector is complicated, while enabling abnormality diagnosis of the detector. Examples, aspects and embodiments not necessarily falling under the scope of the claims are provided in the application to better understand the invention.

An inertial detection circuit according to an aspect of the present disclosure includes a signal generator and a processing unit. The signal generator is configured to generate a signal to be output to a detector. The detector is configured to convert an inertial force to an electrical signal. The processing unit is configured to process the electrical signal output from the detector. The detector includes a fixed electrode and a moving electrode. The moving electrode is disposed to face the fixed electrode. The moving electrode is movable with respect to the fixed electrode in a facing direction in which the moving electrode and the fixed electrode face each other. The signal generator includes a drive voltage generator and a test voltage generator. The drive voltage generator is configured to apply to the fixed electrode a drive voltage with a first frequency to make the moving electrode vibrate. The test voltage generator is configured to apply to the fixed electrode a test voltage with a second frequency lower than the first frequency to make the moving electrode vibrate. The processing unit includes a detection processor and a diagnostic processor. The detection processor is configured to perform a detection processing of detecting a capacitance between the fixed electrode and the moving electrode based on a detection signal. The detection signal corresponds to a component of an inertial force applied to the moving electrode, of the electrical signal output from the moving electrode. The diagnostic processor is configured to perform a diagnostic processing of diagnosing abnormality of the detector based on a diagnostic signal. The diagnostic signal corresponds to a component of the second frequency, of the electrical signal output from the moving electrode.

An inertial sensor according to an aspect of the present disclosure includes the inertial detection circuit and the detector.

An inertial detection method according to an aspect of the present disclosure includes a signal generating step and a processing step. The signal generating step includes generating a signal to be output to a detector. The detector is configured to convert an inertial force to an electrical signal. The processing step includes processing the electrical signal output from the detector. The detector includes a fixed electrode and a moving electrode. The moving electrode is disposed to face the fixed electrode. The moving electrode is movable with respect to the fixed electrode in a facing direction in which the moving electrode and the fixed electrode face each other. The signal generating step includes a drive voltage generating step and a test voltage generating step. The drive voltage generating step includes applying to the fixed electrode a drive voltage with a first frequency to make the moving electrode vibrate. The test voltage generating step includes applying to the fixed electrode a test voltage with a second frequency lower than the first frequency to make the moving electrode vibrate. The processing step includes a detection processing and a diagnostic processing. The detection processing includes detecting a capacitance between the fixed electrode and the moving electrode based on a detection signal. The detection signal corresponds to a component of an inertial force applied to the moving electrode, of the electrical signal output from the moving electrode. The diagnostic processing includes diagnosing abnormality of the detector based on a diagnostic signal. The diagnostic signal corresponds to a component of the second frequency, of the electrical signal output from the moving electrode.

Hereinafter, an inertial detection circuit, an inertial sensor and an inertial detection method according to each of aspects of the present disclosure will be described with reference to the drawings. Each aspect described below is merely one example of various aspects of the present disclosure. Each aspect described below may be readily modified in various manners depending on a design choice or any other factor, as long as the purpose of the present disclosure can be attained. Note that, each aspect in the following description may be adopted in combination as appropriate.

As illustrated in <FIG>, an inertial sensor <NUM> according to the present aspect includes an inertial detection circuit <NUM> and a detector <NUM>. The inertial sensor <NUM> is configured to detect an inertial force. A capacitance C<NUM> of the detector <NUM> is changed depending on a magnitude of an inertial force applied to the detector <NUM>. Accordingly, the inertial sensor <NUM> can detect the magnitude of the inertial force applied to the detector <NUM> by detecting the capacitance C<NUM> of the detector <NUM>.

Examples of the inertial force include an acceleration and an angular acceleration. The basic detection principle when the inertial force is the acceleration is the same as that when the inertial force is the angular acceleration. In the present aspect, the case that the inertial sensor <NUM> detects the acceleration as the inertial force will be described as a representative example.

The inertial detection circuit <NUM> applies, to the detector <NUM>, a drive voltage D1 (clock signal), which is an AC voltage, to detect the capacitance C<NUM> of the detector <NUM>. Also, the inertial detection circuit <NUM> applies, to the detector <NUM>, a test voltage T1, which is an AC voltage, to diagnose (presence or absence of) abnormality of the detector <NUM>. In the present aspect, the inertial detection circuit <NUM> applies, to the detector <NUM>, a voltage where the drive voltage D1 and the test voltage T1 are superimposed with each other. Thus, the inertial detection circuit <NUM> also diagnoses the abnormality of the detector <NUM>, while detecting the capacitance C<NUM> of the detector <NUM>.

The inertial detection circuit <NUM> includes a signal generator <NUM> and a processing unit <NUM>. The signal generator <NUM> is configured to generate a signal to be output to the detector <NUM>. The detector <NUM> is configured to convert an inertial force to an electrical signal. The processing unit <NUM> is configured to process the electrical signal output from the detector <NUM>. The detector <NUM> includes a fixed electrode <NUM> and a moving electrode <NUM>. The moving electrode <NUM> is disposed to face the fixed electrode <NUM>. The moving electrode <NUM> is movable with respect to the fixed electrode <NUM> in a facing direction in which the moving electrode <NUM> and the fixed electrode <NUM> face each other. The signal generator <NUM> includes a drive voltage generator <NUM> and a test voltage generator <NUM>. The drive voltage generator <NUM> is configured to apply to the fixed electrode <NUM> the drive voltage D1 with a first frequency to make the moving electrode <NUM> vibrate. The test voltage generator <NUM> is configured to apply to the fixed electrode <NUM> the test voltage T1 with a second frequency lower than the first frequency to make the moving electrode <NUM> vibrate. The processing unit <NUM> includes a detection processor <NUM> and a diagnostic processor <NUM>. The detection processor <NUM> is configured to perform a detection processing of detecting the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM> based on a detection signal A2. The detection signal A2 corresponds to a component of an inertial force applied to the moving electrode <NUM>, of the electrical signal output from the moving electrode <NUM>. The diagnostic processor <NUM> is configured to perform a diagnostic processing of diagnosing abnormality of the detector <NUM> based on a diagnostic signal T2. The diagnostic signal T2 corresponds to a component of the second frequency, of the electrical signal output from the moving electrode <NUM>.

According to the present aspect, the abnormality of the detector <NUM> can be diagnosed. Furthermore, the fixed electrode <NUM> serves not only as an electrode to which the drive voltage D1 is applied but also as an electrode to which the test voltage T1 is applied. Thus, the inertial detection circuit <NUM> can realize further simplifying the configuration of the detector <NUM>, compared with that the detector <NUM> further includes an electrode to which the test voltage T1 is applied, separately from an electrode to which the drive voltage D1 is applied.

The inertial detection circuit <NUM> includes, for example, a microcontroller (e.g., a digital signal processor: DSP) as a main component. The microcontroller may be implemented as a computer system including one or more processors and one or more memories. That is to say, as least some functions of the inertial detection circuit <NUM> are performed by making the one or more processors execute one or more programs stored in the one or more memories. The program may be stored in advance in the one or more memories, or may be downloaded via a telecommunications line such as the Internet or distributed after having been stored in a non-transitory storage medium such as a memory card.

The inertial detection circuit <NUM> further includes an A/D converter <NUM> and a filter <NUM> in addition to the signal generator <NUM> and the processing unit <NUM>, but they are merely represented to explain some functions to be realized by the inertial detection circuit <NUM>. Accordingly, they do not necessarily represent components with entities.

The test voltage T1 has an amplitude larger than an amplitude of the drive voltage D1. Also, the test voltage T1 has a frequency lower than a frequency of the drive voltage D1. The test voltage T1 and the drive voltage D1 output from the signal generator <NUM> are applied to the fixed electrode <NUM>, thereby the moving electrode <NUM> being caused to vibrate with respect to the fixed electrode <NUM>.

Furthermore, the acceleration is applied to the moving electrode <NUM>, thereby the moving electrode <NUM> being caused to vibrate with respect to the fixed electrode <NUM>. If the acceleration, which is a measurement target, is considered as vibration, the vibration has a sufficiently low frequency. The vibration frequency of the moving electrode <NUM>, which is generated due to application of the acceleration (the measurement target) to the moving electrode <NUM>, is lower than the frequency of the test voltage T1.

The moving electrode <NUM> outputs a current signal corresponding to the vibration. The current signal is converted to a voltage signal by a CV conversion circuit <NUM> of the detector <NUM>, described later. That is to say, the detector <NUM> outputs the voltage signal corresponding to the vibration of the moving electrode <NUM>. The voltage signal is a superimposed signal including: a component (the diagnostic signal T2) derived from the test voltage T1; and a component (a drive output D2) derived from the drive voltage D1.

A change in distance between the fixed electrode <NUM> and the moving electrode <NUM>, due to the acceleration applied to the moving electrode <NUM>, is output from the moving electrode <NUM>, as an output that is in-phase with the drive voltage D1 (a clock signal). Therefore, the superimposed signal further includes a component (the detection signal A2) derived from the acceleration applied to the moving electrode <NUM>.

The diagnostic signal T2 has a frequency lower than a frequency of the drive output D2. The detection signal A2 has a frequency lower than the frequency of the diagnostic signal T2. In the present aspect, the detection signal A2 is assumed as a DC signal.

The diagnostic signal T2 has an amplitude larger than an amplitude of the drive output D2. The detection signal A2 has an absolute value smaller than the amplitude of the drive output D2.

The detector <NUM> outputs, to the inertial detection circuit <NUM>, the superimposed signal, which includes the diagnostic signal T2, the drive output D2 and the detection signal A2. The A/D converter <NUM> converts the above-mentioned superimposed signal from an analog signal to a digital signal. The superimposed signal (as the digital signal) from the A/D converter <NUM> is input to the filter <NUM>.

The filter <NUM> includes a low-pass filter and a band-pass filter. The filter <NUM> is configured as a digital filter. The above-mentioned superimposed signal (as the digital signal) from the A/D converter <NUM> is input to each of the low-pass filter and the band-pass filter. The low-pass filter of the filter <NUM> extracts the detection signal A2 from the superimposed signal (as the digital signal), output from the A/D converter <NUM>. On the other hand, the band-pass filter of the filter <NUM> extracts the diagnostic signal T2 from the superimposed signal (as the digital signal), output from the A/D converter <NUM>.

The detection processor <NUM> of the processing unit <NUM> is configured to perform a detection processing of detecting the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM> based on the detection signal A2. The diagnostic processor <NUM> is configured to perform a diagnostic processing of diagnosing abnormality of the detector <NUM> based on the diagnostic signal T2. Also, the diagnostic processor <NUM> is configured to perform a correction processing of correcting at least one of an output signal of the detector <NUM> or an output signal of the signal generator <NUM> based on the diagnostic signal T2. The detection processing, the diagnostic processing and the correction processing will be described in more detail later.

The detector <NUM> includes a detection module M1. The detection module M1 may be formed by the Micro Electro Mechanical Systems (MEMS) technology, for example. The detection module M1 includes the fixed electrode <NUM>, the moving electrode <NUM>, a fixed body <NUM>, a mover <NUM> and a support <NUM>.

The fixed body <NUM> and the mover <NUM> have electrical insulation. The fixed body <NUM> includes a semiconductor substrate, for example. The fixed body <NUM> is disposed to hold the fixed electrode <NUM>. The mover <NUM> is disposed to hold the moving electrode <NUM>. The support <NUM> is disposed to couple the fixed body <NUM> and the mover <NUM> to each other. The support <NUM> is provided to support the mover <NUM> such that the moving electrode <NUM> faces the fixed electrode <NUM> with the moving electrode <NUM> and the fixed electrode <NUM> being disposed at a prescribed interval. Thus, the moving electrode <NUM> is electrically insulated from the fixed electrode <NUM>.

The support <NUM> is made of an elastic member. The moving electrode <NUM> and the mover <NUM> are movable together with elastic deformation of the support <NUM> to the fixed electrode <NUM> and the fixed body <NUM>. The movement directions of the moving electrode <NUM> and the mover <NUM> are restricted to be along a facing direction in which the fixed electrode <NUM> and the moving electrode <NUM> face each other (refer to an arrow Y1).

A signal line W1 extending from the signal generator <NUM> is connected to the fixed electrode <NUM>. Thus, the drive voltage D1 and the test voltage T1 are applied to the fixed electrode <NUM>, of the fixed electrode <NUM> and the moving electrode <NUM>. The potential of the moving electrode <NUM> is assumed as a reference potential of the drive voltage D1 and the test voltage T1.

When the drive voltage D1 and the test voltage T1 are applied to the fixed electrode <NUM>, the moving electrode <NUM> vibrates, and accordingly a distance between the fixed electrode <NUM> and the moving electrode <NUM> is changed. Also, the distance between the fixed electrode <NUM> and the moving electrode <NUM> is changed in accordance with the acceleration applied to the moving electrode <NUM> (mover <NUM>).

The capacitance C<NUM> is formed between the fixed electrode <NUM> and the moving electrode <NUM>. The capacitance C<NUM> is changed to be inversely proportional to the distance between the fixed electrode <NUM> and the moving electrode <NUM>. Thus, the capacitance C<NUM> is changed in accordance with the drive voltage D1, the test voltage T1, and the acceleration applied to the moving electrode <NUM>.

The inertial sensor <NUM> further includes a CV conversion circuit <NUM>. The CV conversion circuit <NUM> includes an operational amplifier <NUM> and a capacitor <NUM>.

The operational amplifier <NUM> has a non-inverting input terminal at which a voltage is kept to the reference voltage. In the present aspect, the non-inverting input terminal of the operational amplifier <NUM> is grounded.

The operational amplifier <NUM> further has an inverting input terminal, and a signal line W2 extending from the inverting input terminal is connected to the moving electrode <NUM>. Thus, the inverting input terminal of the operational amplifier <NUM> is electrically connected to the moving electrode <NUM>. The capacitor <NUM> has: a first end electrically connected to the inverting input terminal of the operational amplifier <NUM>; and a second end electrically connected to an output terminal of the operational amplifier <NUM>. The output terminal of the operational amplifier <NUM> is electrically connected to the inertial detection circuit <NUM>.

The AC voltage to be applied between the fixed electrode <NUM> and the moving electrode <NUM> is represented by "V = V<NUM> × exp (-jωt)," where "V<NUM>" denotes amplitude, "j" denotes imaginary unit, "ω" denotes angular velocity and "t" denotes time. The AC current flowing from the moving electrode <NUM> to the capacitor <NUM> is represented by "I = -jωC<NUM>V" The output voltage of the operational amplifier <NUM> is represented by "Vout = -jωC<NUM>ZV," where "Z" denotes impedance of the capacitor <NUM>. Thus, the operational amplifier <NUM> outputs a voltage with an amplitude that is proportional to the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM>. That is to say, the CV conversion circuit <NUM> converts the capacitance C<NUM> to the voltage.

As described above, the capacitance C<NUM> is changed in accordance with the drive voltage D1, the test voltage T1, and the acceleration applied to the moving electrode <NUM>. Therefore, the CV conversion circuit <NUM> (operational amplifier <NUM>) outputs the voltage depending on the drive voltage D1, the test voltage T1, and the acceleration applied to the moving electrode <NUM>. More specifically, the CV conversion circuit <NUM> (operational amplifier <NUM>) outputs a superimposed signal where the diagnostic signal T2, the drive output D2 and the detection signal A2 are superimposed, which respectively have frequencies different from one another. The superimposed signal may be a voltage signal.

The filter <NUM> extracts the detection signal A2 from the above-mentioned superimposed signal. The detection processor <NUM> performs the detection processing of detecting, based on the detection signal A2, the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM>. More specifically, the detection processor <NUM> obtains the capacitance C<NUM> by multiplying the absolute value of the detection signal A2 by a prescribed value (a first coefficient).

The detection processor <NUM> calculates the acceleration applied to the moving electrode <NUM>, from the capacitance C<NUM> obtained based on the detection signal A2. More specifically, the detection processor <NUM> calculates the acceleration by multiplying the capacitance C<NUM> obtained based on the detection signal A2 by a prescribed value (a second coefficient). Alternatively, the detection processor <NUM> may calculate the acceleration directly from the detection signal A2. Since the acceleration is proportional to the capacitance C<NUM>, calculating the acceleration can be also regarded as "obtaining the capacitance C<NUM>.

The filter <NUM> extracts the diagnostic signal T2 from the above-mentioned superimposed signal. The diagnostic processor <NUM> performs the diagnostic processing of diagnosing, based on the diagnostic signal T2, the abnormality of the detector <NUM>.

For example, when the acceleration with a certain magnitude is added to the moving electrode <NUM>, the displacement amount of the moving electrode <NUM> is preferably at a certain constant value. However, an abnormality that the structure of the detector <NUM> is mechanically changed may occur due to aging in the detector <NUM> or the like (e.g., an amount or a direction in the deflection of the support <NUM> may be changed). Thus, when the abnormality occurs at the detector <NUM>, the displacement amount of the moving electrode <NUM> may deviate from the certain constant value. Such the "deviation" may cause an offset error and an amplitude error or the like in the voltage signal output from the detector <NUM>, which may cause an error of the capacitance C<NUM> obtained based on the voltage signal.

In view of the above problem, the diagnostic processor <NUM> detects the offset error and the amplitude error or the like in the voltage signal to diagnose the abnormality of the detector <NUM> (i.e., the diagnostic processing). Furthermore, the diagnostic processor <NUM> corrects the offset error and the amplitude error or the like in the voltage signal (i.e., the correction processing).

If the abnormality occurs at the detector <NUM>, the displacement amount of the moving electrode <NUM> becomes an abnormal amount when the test voltage T1 with a certain constant amplitude is applied to the fixed electrode <NUM>. Accordingly, the diagnostic signal T2 shows an abnormal value. Therefore, the diagnostic processor <NUM> can diagnose the abnormality of the detector <NUM> based on the diagnostic signal T2.

More specifically, the diagnostic processor <NUM> compares a difference between the amplitude of the diagnostic signal T2 and a prescribed value (hereinafter, referred to as an "amplitude design value") with a first threshold. The amplitude design value is set so as to correspond to the amplitude of the diagnostic signal T2 while the detector <NUM> operates normally. When finding that the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is larger than or equal to the first threshold, the diagnostic processor <NUM> decides that an abnormality related to the amplitude of the voltage signal has occurred at the detector <NUM>. Furthermore, the diagnostic processor <NUM> corrects, based on the diagnostic signal T2, a magnitude of at least one of the diagnostic signal T2 or the detection signal A2. More specifically, when finding that the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is larger than or equal to the first threshold, the diagnostic processor <NUM> corrects, based on the difference between the amplitude of the diagnostic signal T2 and the amplitude design value, the magnitude of at least one of the diagnostic signal T2 or the detection signal A2. As the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is increased, the diagnostic processor <NUM> increases a correction amount about the magnitude of at least one of the diagnostic signal T2 or the detection signal A2. Correcting the magnitude of the detection signal A2 can enhance the detection accuracy in the capacitance C<NUM> of the detector <NUM>. Correcting the magnitude (amplitude) of the diagnostic signal T2 can cause the amplitude of the diagnostic signal T2 to be closer to the amplitude design value, which can suppress that the diagnostic processor <NUM> is kept in a state of continuously detecting the presence of the abnormality.

Also, the diagnostic processor <NUM> compares an absolute value of the offset (the average of the maximum and the minimum) of the diagnostic signal T2 with a second threshold. The second threshold is set so as to correspond to the offset of the diagnostic signal T2 while the detector <NUM> operates normally. When finding that the absolute value of the offset of the diagnostic signal T2 is larger than or equal to the second threshold, the diagnostic processor <NUM> decides that an abnormality related to the offset of the voltage signal has occurred at the detector <NUM>. Furthermore, the diagnostic processor <NUM> corrects, based on the diagnostic signal T2, the offset of at least one of the diagnostic signal T2 or the detection signal A2. More specifically, when finding that the absolute value of the offset of the diagnostic signal T2 is larger than or equal to the second threshold, the diagnostic processor <NUM> corrects, based on a difference between the offset of the diagnostic signal T2 and the second threshold, the offset of at least one of the diagnostic signal T2 or the detection signal A2. As the difference between the offset of the diagnostic signal T2 and the second threshold is increased, the diagnostic processor <NUM> increases a correction amount about the offset of at least one of the diagnostic signal T2 or the detection signal A2. The diagnostic processor <NUM> preferably decides the correction amount such that the offset of at least one of the diagnostic signal T2 or the detection signal A2 is caused to be zero. Correcting the offset of the detection signal A2 can enhance the detection accuracy in the capacitance C<NUM> of the detector <NUM>. Correcting the offset of the diagnostic signal T2 can suppress that the diagnostic processor <NUM> is kept in a state of continuously detecting the presence of the abnormality.

The signal generator <NUM> may correct, based on the diagnostic signal T2, the amplitude of at least one of the test voltage T1 or the drive voltage D1. More specifically, when finding that the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is larger than or equal to the first threshold, the signal generator <NUM> may correct, based on the difference between the amplitude of the diagnostic signal T2 and the amplitude design value, the amplitude of at least one of the test voltage T1 or the drive voltage D1. As the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is increased, the signal generator <NUM> may increase a correction amount about the amplitude of at least one of the test voltage T1 or the drive voltage D1. Correcting the amplitude of the drive voltage D1 can enhance the detection accuracy in the capacitance C<NUM> of the detector <NUM>. Correcting the amplitude of test voltage T1 can cause the amplitude of the diagnostic signal T2 to be closer to the amplitude design value, which can suppress that the diagnostic processor <NUM> is kept in a state of continuously detecting the presence of the abnormality.

Both correcting the amplitude of the diagnostic signal T2 by the diagnostic processor <NUM> and correcting the amplitude of the test voltage T1 by the signal generator <NUM> (the test voltage generator <NUM>) may be performed. Alternatively, only either correcting the amplitude of the diagnostic signal T2 or correcting the amplitude of the test voltage T1 may be performed. At least one of the amplitudes of the diagnostic signal T2 and the test voltage T1 is preferably corrected such that the difference between the amplitude of the diagnostic signal T2 and the amplitude design value is caused to be less than the first threshold.

Both correcting the magnitude of the detection signal A2 by the diagnostic processor <NUM> and correcting the magnitude (amplitude) of the drive voltage D1 by the signal generator <NUM> (the drive voltage generator <NUM>) may be performed. Alternatively, only either correcting the magnitude of the detection signal A2 or correcting the magnitude of the drive voltage D1 may be performed. At least one of the magnitudes of the detection signal A2 and the drive voltage D1 is preferably corrected such that the magnitude of the detection signal A2 is caused to be a value within a prescribed range when a certain constant acceleration is applied to the moving electrode <NUM>.

The signal generator <NUM> may correct the offset of at least one of the test voltage T1 or the drive voltage D1, based on the diagnostic signal T2. More specifically, when finding that the absolute value of the offset of the diagnostic signal T2 is larger than or equal to the second threshold, the signal generator <NUM> may correct the offset of at least one of the test voltage T1 or the drive voltage D1, based on the difference between the offset of the diagnostic signal T2 and the second threshold. As the difference between the offset of the diagnostic signal T2 and the second threshold is increased, the signal generator <NUM> may increase a correction amount about the offset of at least one of the test voltage T1 or the drive voltage D1. The signal generator <NUM> preferably decides the correction amount such that the offset of at least one of the diagnostic signal T2 or the detection signal A2 is caused to be zero. Correcting the offset of the drive voltage D1 can enhance the detection accuracy in the capacitance C<NUM> of the detector <NUM>. Correcting the offset of test voltage T1 can suppress that the diagnostic processor <NUM> is kept in a state of continuously detecting the presence of the abnormality.

Both correcting the offset of the diagnostic signal T2 by the diagnostic processor <NUM> and correcting the offset of the test voltage T1 by the signal generator <NUM> (the test voltage generator <NUM>) may be performed. Alternatively, only either correcting the offset of the diagnostic signal T2 or correcting the offset of the test voltage T1 may be performed. At least one of the offsets of the diagnostic signal T2 and the test voltage T1 is preferably corrected such that the offset of the diagnostic signal T2 is caused to be a value within a prescribed range.

Both correcting the offset of the detection signal A2 by the diagnostic processor <NUM> and correcting the offset of the drive voltage D1 by the signal generator <NUM> (the drive voltage generator <NUM>) may be performed. Alternatively, only either correcting the offset of the detection signal A2 or correcting the offset of the drive voltage D1 may be performed. At least one of the offsets of the detection signal A2 and the drive voltage D1 is preferably corrected such that the offset of the detection signal A2 is caused to be a value within a prescribed range.

The correction processing may be performed regardless of finding that the abnormality has occurred at the detector <NUM> based on the result obtained in the diagnostic processing by the diagnostic processor <NUM>.

According to the inertial sensor <NUM> of the present aspect, the abnormality of the detector <NUM> can be diagnosed. Furthermore, the fixed electrode <NUM> serves not only as an electrode to which the drive voltage D1 is applied but also as an electrode to which the test voltage T1 is applied. Thus, the inertial detection circuit <NUM> can realize further simplifying the configuration of the detector <NUM>, compared with that the detector <NUM> further includes an electrode to which the test voltage T1 is applied, separately from an electrode to which the drive voltage D1 is applied. For example, the detector <NUM> can be downsized.

Also, a voltage to be applied to a circuit(s) (the CV conversion circuit <NUM> or the like) provided on the following stage of the moving electrode <NUM> is further reduced, compared with that the test voltage T1 is applied to the moving electrode <NUM>. The reduction in the voltage therefore can loosen a requirement specification in the withstand voltage performance of the CV conversion circuit <NUM> or the like.

Furthermore, the test voltage T1 is applied to the fixed electrode <NUM>, but no test voltage T1 is applied to the moving electrode <NUM> displacing depending on the inertial force. Therefore, it can further reduce the chance that the test voltage T1 affects detecting the detection signal A2, compared with that the test voltage T1 is applied to the moving electrode <NUM>. Accordingly, it can reduce the chance that the detection accuracy in the capacitance C<NUM> (i.e., the inertial force applied to the detector <NUM>) between the fixed electrode <NUM> and the moving electrode <NUM> is deteriorated.

Hereinafter, variations of the first aspect will be listed. The following variations may be adopted in combination as appropriate.

The support <NUM> may support the moving electrode <NUM> without via the mover <NUM>. The support <NUM> may be connected to the fixed electrode <NUM> without via the fixed body <NUM>.

In the first aspect, the detection signal A2 is assumed as the DC signal, and the processing unit <NUM> corrects the magnitude of the detection signal A2 in the correction processing. On the other hand, when the detection signal A2 is assumed as an AC signal, the magnitude of the detection signal A2 may be the amplitude of the detection signal A2.

Instead of the capacitor <NUM>, the CV conversion circuit <NUM> may include: a resistor; a parallel circuit where a resistor and a capacitor <NUM> are connected in parallel; or a parallel circuit where a capacitor <NUM> and a switch for discharging the electric charge of the capacitor <NUM> are connected in parallel, for example.

The signal lines W1, W2 may include patterned conductors formed in the printed board. Also, the signal lines W1, W2 may include cables such as copper wires.

The detector <NUM> is configured such that the distance between the moving electrode <NUM> and the fixed electrode <NUM> is changed in accordance with the acceleration, but this configuration is merely an example and should not be construed as limiting. Another configuration may be adopted, as long as the detector <NUM> is configured such that the capacitance C<NUM> between the moving electrode <NUM> and the fixed electrode <NUM> is changed in accordance with the acceleration. For example, the detector <NUM> may be configured such that facing areas of the moving electrode <NUM> and the fixed electrode <NUM> facing each other are changed in accordance with the acceleration.

The inertial detection circuit <NUM> may be configured to notify the user of the diagnostic result about the abnormality of the detector <NUM>, obtained from the diagnostic processor <NUM>, by outputting a text message or a voice message and so on. The drive voltage generator <NUM> may be configured to stop outputting the drive voltage D1 when the diagnostic processor <NUM> has detected presence of the abnormality at the detector <NUM>.

The inertial detection circuit <NUM> may include an amplifier configured to amplify the output of the detector <NUM> and disposed on the front stage of the A/D converter <NUM>.

The functions of the inertial detection circuit <NUM> and the inertial sensor <NUM> may also be implemented as an inertial detection method, a (computer) program or a non-transitory storage medium on which the computer program is stored.

An inertial detection method according to one aspect includes a signal generating step and a processing step. The signal generating step includes generating a signal to be output to a detector <NUM>. The detector <NUM> is configured to convert an inertial force to an electrical signal. The processing step includes processing the electrical signal output from the detector <NUM>. The detector <NUM> includes a fixed electrode <NUM> and a moving electrode <NUM>. The moving electrode <NUM> is disposed to face the fixed electrode <NUM>. The moving electrode <NUM> is movable with respect to the fixed electrode <NUM> in a facing direction in which the moving electrode <NUM> and the fixed electrode <NUM> face each other.

As illustrated in <FIG>, the signal generating step includes a drive voltage generating step ST1 and a test voltage generating step ST2. The drive voltage generating step ST1 includes applying to the fixed electrode <NUM> a drive voltage D1 with a first frequency to make the moving electrode <NUM> vibrate. The test voltage generating step ST2 includes applying to the fixed electrode <NUM> a test voltage T1 with a second frequency lower than the first frequency to make the moving electrode <NUM> vibrate. More specifically, the signal generator <NUM> applies the superimposed voltage, where the drive voltage D1 and the test voltage T1 are superimposed, to the fixed electrode <NUM>.

When the drive voltage generating step ST1 and the test voltage generating step ST2 are performed and the inertial force (acceleration) is added to the moving electrode <NUM>, the detector <NUM> outputs to the inertial detection circuit <NUM> the superimposed signal, where the diagnostic signal T2, the drive output D2 and the detection signal A2 are superimposed (in Step ST3).

The processing step includes a detection processing ST4 and a diagnostic processing ST5. The detection processing ST4 includes detecting a capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM> based on a detection signal A2. The detection signal A2 corresponds to a component of an inertial force applied to the moving electrode <NUM>, of the electrical signal output from the moving electrode <NUM>. The diagnostic processing ST5 includes diagnosing abnormality of the detector <NUM> based on a diagnostic signal T2. The diagnostic signal T2 corresponds to a component of the second frequency, of the electrical signal output from the moving electrode <NUM>. If finding that the abnormality is present at the detector <NUM> based on the result obtained in the diagnostic processing ST5 (if the answer is Yes in Step S6), the processing unit <NUM> performs the correction processing to correct the offset error and the amplitude error or the like in the voltage signal output from the detector <NUM> (in Step ST7). While the inertial sensor <NUM> operates, the processes from the drive voltage generating step ST1 to the Step ST7 are repeatedly performed.

The flowchart shown in <FIG> is merely an example of the inertial detection method according to the present variation. The order of the processes in the flowchart may be modified as appropriate. Also, one or more processes may be newly added, or any of the processes in the flowchart may be omitted.

A program according to one aspect may be designed to cause one or more processors to execute the inertial detection method described above.

The inertial detection circuit <NUM> according to the present disclosure includes a computer system. The computer system includes a processor and a memory as hardware components. The functions of the inertial detection circuit <NUM> according to the present disclosure may be realized by making the processor execute a program stored in the memory of the computer system. The program may be stored in advance in the memory of the computer system. Alternatively, the program may also be downloaded through a telecommunications line or be distributed after having been recorded in some non-transitory storage medium such as a memory card, an optical disc, or a hard disk drive, any of which is readable for the computer system. The processor of the computer system may be implemented as a single or a plurality of electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). As used herein, the "integrated circuit" such as an IC or an LSI is called by a different name depending on the degree of integration thereof. Examples of the integrated circuits include a system LSI, a very large-scale integrated circuit (VLSI), and an ultra-large scale integrated circuit (ULSI). Optionally, a field-programmable gate array (FPGA) to be programmed after an LSI has been fabricated or a reconfigurable logic device allowing the connections or circuit sections inside of an LSI to be reconfigured may also be adopted as the processor. Those electronic circuits may be either integrated together on a single chip or distributed on multiple chips, whichever is appropriate. Those multiple chips may be integrated together in a single device or distributed in multiple devices without limitation. As used herein, the "computer system" includes a microcontroller including one or more processors and one or more memories. Thus, the microcontroller may also be implemented as a single or a plurality of electronic circuits including a semiconductor integrated circuit or a large-scale integrated circuit.

Also, the plurality of functions of the inertial detection circuit <NUM> are integrated together in a single housing, but this is not an essential configuration for the inertial detection circuit <NUM>. Alternatively, the plurality of functions of the inertial detection circuit <NUM> may be distributed in multiple different housings. Still alternatively, at least some functions of the inertial detection circuit <NUM> (e.g., some functions of the processing unit <NUM>) may be implemented as a cloud computing system as well.

In contrast, at least some functions of the inertial sensor <NUM> distributed in multiple different housings in an aspect may be integrated together in a single housing. For example, some functions of the inertial sensor <NUM> distributed in the inertial detection circuit <NUM> and the detector <NUM> may be integrated together in a single housing.

Hereinafter, an inertial sensor 1A according to a second aspect will be described with reference to <FIG>. Components similar to those of the first aspect are assigned with the same reference numbers and the explanations thereof are omitted.

The inertial sensor 1A of the present aspect is different from the inertial sensor <NUM> of the first aspect in the configuration of a detector 4A. The detector 4A is configured to output, to a processing unit <NUM>, a differential signal between an output signal of a moving electrode <NUM> and an output signal of a fixed electrode <NUM>.

The detector 4A includes a detection module M1, a switching unit <NUM>, a capacitor <NUM>, two CV conversion circuits <NUM> and a differential amplifier <NUM>.

The capacitor <NUM> includes a first electrode <NUM> and a second electrode <NUM>. The first electrode <NUM> is electrically connected to the fixed electrode <NUM>. The second electrode <NUM> is disposed to face the first electrode <NUM>. The second electrode <NUM> is electrically connected to the switching unit <NUM>. A capacitance C<NUM> between the first electrode <NUM> and the second electrode <NUM> may be a value corresponding to a capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM>. More specifically, the capacitor <NUM> is selected such that a difference between the capacitance C<NUM> and the capacitance C<NUM> is less than a prescribed value while the moving electrode <NUM> does not vibrate.

The configuration of each of the two CV conversion circuits <NUM> is substantially the same as that of the CV conversion circuit <NUM> of the first aspect. Hereinafter, the two CV conversion circuits <NUM> may be also respectively referred to as a first CV conversion circuit 7P and a second CV conversion circuit 7Q to distinguish those from each other for convenience of explanation. Output terminals of the two CV conversion circuits <NUM> are electrically connected to input terminals of the differential amplifier <NUM>, respectively.

The differential amplifier <NUM> is configured to output, to the inertial detection circuit <NUM>, a differential voltage between an output voltage of the first CV conversion circuit 7P and an output voltage of the second CV conversion circuit 7Q. The output voltage of the first CV conversion circuit 7P in <FIG> is a voltage depending on an output current from the moving electrode <NUM>. That is to say, the output voltage of the first CV conversion circuit 7P is a superimposed signal where a diagnostic signal T2, a drive output D2 and a detection signal A2 are superimposed. On the other hand, the output voltage of the second CV conversion circuit 7Q in <FIG> is a voltage depending on a current output from the fixed electrode <NUM> via the capacitor <NUM>. That is to say, the output voltage of the second CV conversion circuit 7Q is a reference signal to be compared with the output voltage of the first CV conversion circuit 7P and is also a superimposed signal where a diagnostic signal T2*, a drive output D2* and a detection signal A2* are superimposed.

The processing unit <NUM> performs a detection processing, a diagnostic processing and a correction processing based on the differential voltage output from the differential amplifier <NUM>. More specifically, a differential voltage between the detection signals A2, A2* and a differential voltage between the diagnostic signals T2, T2* are extracted by the filter <NUM>. The detection processor <NUM> performs the detection processing to detect the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM> based on the differential voltage between the detection signals A2, A2*. The diagnostic processor <NUM> performs the diagnostic processing to diagnose the abnormality of the detector 4A based on the differential voltage between the diagnostic signals T2, T2*. The diagnostic processor <NUM> corrects magnitudes and offsets of the diagnostic signals T2, T2* and the detection signals A2, A2* based on the differential voltage between the diagnostic signals T2, T2*. Parameters (thresholds or the like) according to the detection processing, the diagnostic processing and the correction processing may be modified as appropriate from those of the first aspect.

The switching unit <NUM> includes switches <NUM> to <NUM>. The switches <NUM> to <NUM> may be semiconductor switches.

The switch <NUM> is connected between the moving electrode <NUM> and an inverting input terminal of an operational amplifier <NUM> of the first CV conversion circuit 7P. The switch <NUM> is connected between the moving electrode <NUM> and an inverting input terminal of an operational amplifier <NUM> of the second CV conversion circuit 7Q.

The switch <NUM> is connected between the second electrode <NUM> and the inverting input terminal of the operational amplifier <NUM> of the second CV conversion circuit 7Q. The switch <NUM> is connected between the second electrode <NUM> and the inverting input terminal of the operational amplifier <NUM> of the first CV conversion circuit 7P.

That is to say, an input terminal (inverting input terminal) of each of the first and second CV conversion circuits 7P, 7Q is electrically connected to the fixed electrode <NUM> or the moving electrode <NUM> via the switching unit <NUM>. An output terminal of each of the first and second CV conversion circuits 7P, 7Q outputs a voltage depending on the capacitance C<NUM> between the fixed electrode <NUM> and the moving electrode <NUM>.

The differential amplifier <NUM> outputs, to the processing unit <NUM>, the differential voltage between the voltage output from the output terminal of the first CV conversion circuit 7P and the voltage output from the output terminal of the second CV conversion circuit 7Q.

The switching unit <NUM> is configured to switch between a first state and a second state. The first state is a state where the switches <NUM>, <NUM> are turned OFF and the switches <NUM>, <NUM> are turned ON. That is to say, the first state is a state where the second electrode <NUM> is caused to be electrically connected to the input terminal of the first CV conversion circuit 7P, and the moving electrode <NUM> is caused to be electrically connected to the input terminal of the second CV conversion circuit 7Q. The second state is a state where switches <NUM>, <NUM> are turned ON and the switches <NUM>, <NUM> are turned OFF. That is to say, the second state is a state where the second electrode <NUM> is caused to be electrically connected to the input terminal of the second CV conversion circuit 7Q, and the moving electrode <NUM> is caused to be electrically connected to the input terminal of the first CV conversion circuit 7P.

The switching unit <NUM> alternately switches between the first state and the second state in accordance with a control signal output from the inertial detection circuit <NUM>. Thus, signal chopping is performed in the detector 4A, which therefore can reduce the error in the offset of signal output from the moving electrode <NUM>.

Hereinafter, an inertial sensor 1B according to a third aspect will be described with reference to <FIG>. Components similar to those of the second aspect are assigned with the same reference numbers and the explanations thereof are omitted.

The inertial sensor 1B of the present aspect includes a detection module M3 having the configuration different from that of the detection module M1 of the second aspect. Also, a detector 4B includes two capacitors <NUM>.

The detection module M3 includes two fixed electrodes <NUM>, a fixed body <NUM>, two moving electrodes <NUM>, a mover <NUM>, a support <NUM> and a rotational shaft <NUM>.

The two fixed electrodes <NUM> correspond to the two moving electrodes <NUM> one-to-one. Each moving electrode <NUM> is disposed to face a corresponding fixed electrode <NUM>. One of the two moving electrodes <NUM> and a corresponding fixed electrode <NUM> form a capacitance C<NUM> therebetween. The other of the two moving electrodes <NUM> and a corresponding fixed electrode <NUM> form a capacitance C<NUM> therebetween.

The two fixed electrodes <NUM> are held by the fixed body <NUM>. The two moving electrodes <NUM> are held by the mover <NUM>. The support <NUM> may be a rigid body. The mover <NUM> is turnable around the rotational shaft <NUM> with respect to the support <NUM> (refer to an arrow Y2). The mover <NUM> is turned by the acceleration being applied to the mover <NUM>, and accordingly, a distance between each moving electrode <NUM> and a corresponding fixed electrode <NUM> is changed, and the capacitances C<NUM> and C<NUM> between the moving electrodes <NUM> and the fixed electrodes <NUM> are also changed. When one of the two moving electrodes <NUM> comes closer to a corresponding fixed electrode <NUM>, the other of them is apart from a corresponding fixed electrode <NUM>. Therefore, when the capacitance C<NUM> (or Ci) corresponding to one of the two moving electrodes <NUM> is increased, the capacitance C<NUM> (or C<NUM>) corresponding to the other of them is reduced.

A drive voltage D1 and a test voltage T1 are applied to each of the two fixed electrodes <NUM>. The voltages to be input to one of the two fixed electrodes <NUM> corresponds to reversal voltages of the voltages to be input to the other of them. Each of the two moving electrodes <NUM> is connected to the switches <NUM>, <NUM>.

The drive voltage D1 and the test voltage T1 are applied to each of the two capacitors <NUM>. The voltages to be applied to the two capacitors <NUM> are in a reverse-phase relation to each other. The capacitances C<NUM> of the two capacitors <NUM> are equal to each other. Each capacitor <NUM> is selected such that a difference between each of the capacitances C<NUM>, C<NUM> and the capacitance C<NUM> is less than a prescribed value while the moving electrode <NUM> does not vibrate.

In accordance with the state of the switching unit <NUM>, the current corresponding to the capacitances C<NUM>, C<NUM> is input to one of the first and second CV conversion circuits 7P, 7Q, and the current corresponding to the capacitances C<NUM>, C<NUM> of the two capacitors <NUM> is input to the other of the first and second CV conversion circuits 7P, 7Q.

Thus, a rotary-type of mover <NUM> (moving electrode <NUM>) is used in the present aspect. Therefore, each CV conversion circuit <NUM> outputs the voltage corresponding to the difference between the capacitances C<NUM>, C<NUM> of the two moving electrodes <NUM>, which accordingly can reduce the detection error in the acceleration applied to the mover <NUM>.

Similarly to the second aspect, the differential amplifier <NUM> outputs a differential voltage between an output voltage of the first CV conversion circuit 7P and an output voltage of the second CV conversion circuit 7Q, and the processing unit <NUM> performs the detection processing, the diagnostic processing and the correction processing based on the differential voltage output from the differential amplifier <NUM>. Parameters (thresholds or the like) according to the detection processing, the diagnostic processing and the correction processing may be modified as appropriate from those of the second aspect.

In the detection processing, the detection processor <NUM> detects the capacitance corresponding to at least one of the capacitances C<NUM>, C<NUM>. That is to say, when a plurality of sets (each of which includes a fixed electrode <NUM> and a moving electrode <NUM>) are provided as the present aspect, the detection processing means a processing of detecting the capacitance corresponding to at least one of the plurality of sets. Also, the detection processor <NUM> obtains the acceleration added to at least one moving electrode <NUM> based on the capacitance detected.

As can be seen from the foregoing aspects and the like, the following aspects are disclosed.

An inertial detection circuit (<NUM>) according to a first aspect includes a signal generator (<NUM>) and a processing unit (<NUM>). The signal generator (<NUM>) is configured to generate a signal to be output to a detector (<NUM>, 4A, 4B). The detector (<NUM>, 4A, 4B) is configured to convert an inertial force to an electrical signal. The processing unit (<NUM>) is configured to process the electrical signal output from the detector (<NUM>, 4A, 4B). The detector (<NUM>, 4A, 4B) includes a fixed electrode (<NUM>) and a moving electrode (<NUM>). The moving electrode (<NUM>) is disposed to face the fixed electrode (<NUM>). The moving electrode (<NUM>) is movable with respect to the fixed electrode (<NUM>) in a facing direction in which the moving electrode (<NUM>) and the fixed electrode (<NUM>) face each other. The signal generator (<NUM>) includes a drive voltage generator (<NUM>) and a test voltage generator (<NUM>). The drive voltage generator (<NUM>) is configured to apply to the fixed electrode (<NUM>) a drive voltage (D1) with a first frequency to make the moving electrode (<NUM>) vibrate. The test voltage generator (<NUM>) is configured to apply to the fixed electrode (<NUM>) a test voltage (T1) with a second frequency lower than the first frequency to make the moving electrode (<NUM>) vibrate. The processing unit (<NUM>) includes a detection processor (<NUM>) and a diagnostic processor (<NUM>). The detection processor (<NUM>) is configured to perform a detection processing of detecting a capacitance (C<NUM>) between the fixed electrode (<NUM>) and the moving electrode (<NUM>) based on a detection signal (A2). The detection signal (A2) corresponds to a component of an inertial force applied to the moving electrode (<NUM>), of the electrical signal output from the moving electrode (<NUM>). The diagnostic processor (<NUM>) is configured to perform a diagnostic processing of diagnosing abnormality of the detector (<NUM>, 4A, 4B) based on a diagnostic signal (T2). The diagnostic signal (T2) corresponds to a component of the second frequency, of the electrical signal output from the moving electrode (<NUM>).

According to the above configuration, the abnormality of the detector (<NUM>, 4A, 4B) can be diagnosed. Furthermore, the fixed electrode (<NUM>) serves not only as an electrode to which the drive voltage (D1) is applied but also as an electrode to which the test voltage (T1) is applied. Thus, the inertial detection circuit (<NUM>) can realize further simplifying the configuration of the detector (<NUM>, 4A, 4B), compared with that the detector (<NUM>, 4A, 4B) further includes an electrode to which the test voltage (T1) is applied, separately from an electrode to which the drive voltage (D1) is applied.

In an inertial detection circuit (<NUM>) according to a second aspect, which may be implemented in conjunction with the first aspect, the processing unit (<NUM>) is configured to correct, based on the diagnostic signal (T2), an offset of at least one of the diagnostic signal (T2) or the detection signal (A2).

According to the above configuration, the inertial detection circuit (<NUM>) can improve the accuracy of detection about the inertial force.

In an inertial detection circuit (<NUM>) according to a third aspect, which may be implemented in conjunction with the first or second aspect, the signal generator (<NUM>) is configured to correct, based on the diagnostic signal (T2), an offset of at least one of the test voltage (T1) or the drive voltage (D1).

In an inertial detection circuit (<NUM>) according to a fourth aspect, which may be implemented in conjunction with any one of the first to third aspects, the processing unit (<NUM>) is configured to correct, based on the diagnostic signal (T2), a magnitude of at least one of the diagnostic signal (T2) or the detection signal (A2).

In an inertial detection circuit (<NUM>) according to a fifth aspect, which may be implemented in conjunction with any one of the first to fourth aspects, the signal generator (<NUM>) is configured to correct, based on the diagnostic signal (T2), an amplitude of at least one of the test voltage (T1) or the drive voltage (D1).

Note that the constituent elements other than the constituent elements according to the first aspect are not essential constituent elements for the inertial detection circuit (<NUM>) but may be omitted as appropriate.

An inertial sensor (<NUM>, 1A, 1B) according to a sixth aspect includes the inertial detection circuit (<NUM>) according to any one of the first to fifth aspects and the detector (<NUM>, 4A, 4B).

According to the above configuration, the inertial sensor (<NUM>, 1A, 1B) can realize further simplifying the configuration of the detector (<NUM>, 4A, 4B), compared with that the detector (<NUM>, 4A, 4B) further includes an electrode to which the test voltage (T1) is applied, separately from an electrode to which the drive voltage (D1) is applied.

In an inertial sensor (1A, 1B) according to a seventh aspect, which may be implemented in conjunction with the sixth aspect, the detector (4A, 4B) is configured to output, to the processing unit (<NUM>), a differential signal between an output signal of the moving electrode (<NUM>) and an output signal of the fixed electrode (<NUM>).

According to the above configuration, the inertial sensor (1A, 1B) can reduce the noise and the offset error in the detection signal (A2).

In an inertial sensor (1A, 1B) according to an eighth aspect, which may be implemented in conjunction with the seventh aspect, the detector (4A, 4B) includes a first CV conversion circuit (7P) and a second CV conversion circuit (7Q), a differential amplifier (<NUM>), a capacitor (<NUM>) and a switching unit (<NUM>). Each of the first CV conversion circuit (7P) and the second CV conversion circuit (7Q) includes an input terminal to be electrically connected to the fixed electrode (<NUM>) or the moving electrode (<NUM>), and an output terminal outputting a voltage depending on the capacitance (C<NUM>) between the fixed electrode (<NUM>) and the moving electrode (<NUM>). The differential amplifier (<NUM>) is configured to output, to the processing unit (<NUM>), a differential voltage between a voltage output from the output terminal of the first CV conversion circuit (7P) and a voltage output from the output terminal of the second CV conversion circuit (7Q). The capacitor (<NUM>) includes a first electrode (<NUM>) and a second electrode (<NUM>). The first electrode (<NUM>) is electrically connected to the fixed electrode (<NUM>). The second electrode (<NUM>) is disposed to face the first electrode (<NUM>). The switching unit (<NUM>) is configured to switch between a first state and a second state. The first state is a state where the second electrode (<NUM>) is caused to be electrically connected to the input terminal of the first CV conversion circuit (7P), and the moving electrode (<NUM>) is caused to be electrically connected to the input terminal of the second CV conversion circuit (7Q). The second state is a state where the second electrode (<NUM>) is caused to be electrically connected to the input terminal of the second CV conversion circuit (7Q), and the moving electrode (<NUM>) is caused to be electrically connected to the input terminal of the first CV conversion circuit (7P).

Note that the constituent elements other than the constituent elements according to the sixth aspect are not essential constituent elements for the inertial sensor (<NUM>, 1A, 1B) but may be omitted as appropriate.

An inertial detection method according to a ninth aspect includes a signal generating step and a processing step. The signal generating step includes generating a signal to be output to a detector (<NUM>, 4A, 4B). The detector (<NUM>, 4A, 4B) is configured to convert an inertial force to an electrical signal. The processing step includes processing the electrical signal output from the detector (<NUM>, 4A, 4B). The detector (<NUM>, 4A, 4B) includes a fixed electrode (<NUM>) and a moving electrode (<NUM>). The moving electrode (<NUM>) is disposed to face the fixed electrode (<NUM>). The moving electrode (<NUM>) is movable with respect to the fixed electrode (<NUM>) in a facing direction in which the moving electrode (<NUM>) and the fixed electrode (<NUM>) face each other. The signal generating step includes a drive voltage generating step (ST1) and a test voltage generating step (ST2). The drive voltage generating step (ST1) includes applying to the fixed electrode (<NUM>) a drive voltage (D1) with a first frequency to make the moving electrode (<NUM>) vibrate. The test voltage generating step (ST2) includes applying to the fixed electrode (<NUM>) a test voltage (T1) with a second frequency lower than the first frequency to make the moving electrode (<NUM>) vibrate. The processing step includes a detection processing (ST4) and a diagnostic processing (ST5). The detection processing (ST4) includes detecting a capacitance (C<NUM>) between the fixed electrode (<NUM>) and the moving electrode (<NUM>) based on a detection signal (A2). The detection signal (A2) corresponds to a component of an inertial force applied to the moving electrode (<NUM>), of the electrical signal output from the moving electrode (<NUM>). The diagnostic processing (ST5) includes diagnosing abnormality of the detector (<NUM>, 4A, 4B) based on a diagnostic signal (T2). The diagnostic signal (T2) corresponds to a component of the second frequency, of the electrical signal output from the moving electrode (<NUM>).

According to the above configuration, the inertial detection method can realize further simplifying the configuration of the detector (<NUM>, 4A, 4B), compared with that the detector (<NUM>, 4A, 4B) further includes an electrode to which the test voltage (T1) is applied, separately from an electrode to which the drive voltage (D1) is applied.

Claim 1:
An inertial sensor (<NUM>, 1A, 1B), comprising:
a detector (<NUM>, 4A, 4B) configured to convert an inertial force to an electrical signal;
an inertial detection circuit (<NUM>) comprising:
a signal generator (<NUM>) configured to generate a signal to be output to the detector (<NUM>, 4A, 4B); and
a processing unit (<NUM>) configured to process the electrical signal output from the detector (<NUM>, 4A, 4B),
the detector (<NUM>, 4A, 4B) including:
a fixed electrode (<NUM>); and
a moving electrode (<NUM>) disposed to face the fixed electrode (<NUM>), the moving electrode (<NUM>) being configured to vibrate with respect to the fixed electrode (<NUM>) in a facing direction in which the moving electrode (<NUM>) and the fixed electrode (<NUM>) face each other and being configured to output the electrical signal corresponding to vibration thereof,
the signal generator (<NUM>) including:
a drive voltage generator (<NUM>) configured to apply to the fixed electrode (<NUM>) a drive voltage (D1) with a first frequency to make the moving electrode (<NUM>) vibrate; and
a test voltage generator (<NUM>) configured to apply to the fixed electrode (<NUM>) a test voltage (T1) with a second frequency lower than the first frequency to make the moving electrode (<NUM>) vibrate,
the processing unit (<NUM>) including:
a detection processor (<NUM>) configured to perform a detection processing of detecting a capacitance between the fixed electrode (<NUM>) and the moving electrode (<NUM>) based on a detection signal (A2) of the electrical signal output from the moving electrode (<NUM>), the detection signal (A2) corresponding to a component of an inertial force applied to the moving electrode (<NUM>) and
a diagnostic processor (<NUM>) configured to perform a diagnostic processing of diagnosing abnormality of the detector (<NUM>, 4A, 4B) based on a diagnostic signal (T2) of the electrical signal output from the moving electrode (<NUM>), the diagnostic signal (T2) corresponding to a component of the second frequency,
the signal generator (<NUM>) is configured to correct, based on the diagnostic signal (T2), at least one of an offset or an amplitude of the drive voltage (D1).