Acceleration sensor

Abstract

To accurately and easily acquire information necessary for detecting the state of an object.SOLUTION: An acceleration sensor (1B) comprises: a sensor element (11) configured to output a signal indicating a result of detection of the acceleration of an object; an envelope detection circuit (23) configured to perform envelope detection processing on an acceleration signal based on an output signal from the sensor element to generate an envelope signal; and a frequency analysis circuit (16) configured to extract a signal component of the envelope signal for each of a plurality of element bands, and derive intensity data of the signal component of the envelope signal for every element band.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present disclosure relates to an acceleration sensor.

Background Art

[0002] Various types of acceleration sensors are widely used. An acceleration sensor can detect the acceleration of an object using a sensor element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] [Summary] Depending on the state, an object may generate vibrations at a specific frequency. Therefore, it has been considered to detect (estimate) the state of the object through frequency analysis of the acceleration signal obtained using the sensor element. However, acceleration signals often contain various frequency components, and ingenuity is required for good frequency analysis.

[0005] An acceleration sensor according to an aspect of the present disclosure includes a sensor element configured to output a signal indicating a detection result of the acceleration of an object, an envelope detection circuit configured to generate an envelope signal by performing envelope detection processing on an acceleration signal based on the output signal of the sensor element, and a frequency analysis circuit configured to extract signal components of the envelope signal for each of a plurality of element bands and derive intensity data of the signal components of the envelope signal for each of the element bands.

Brief Description of the Drawings

[0006]

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[0007] [Detailed Description] Hereinafter, examples of embodiments of the present disclosure will be specifically described with reference to the drawings. In each of the drawings referred to, the same parts are denoted by the same reference numerals, and redundant descriptions regarding the same parts are omitted in principle. In this specification, for the sake of simplicity of description, the name of information, signal, physical quantity, functional unit, circuit, element, or component corresponding to a symbol or reference numeral may be omitted or abbreviated by writing the symbol or reference numeral for referring to the information, signal, physical quantity, functional unit, circuit, element, or component. Also, the connection between a plurality of parts forming a circuit, such as any circuit element, wiring, node, etc., may be understood to refer to an electrical connection unless otherwise specified.

[0008] Fig. 1 shows the overall configuration of the system according to an embodiment of the present disclosure. The system shown in Fig. 1 includes an acceleration sensor 1, an MPU (Micro Processing Unit) 2, a target device 3, and a bus 4.

[0009] The acceleration sensor 1 is an electronic component (semiconductor device) including a semiconductor chip having a semiconductor integrated circuit formed on a semiconductor substrate, a housing (package) accommodating the semiconductor chip, and a plurality of external terminals exposed from the housing to the outside of the acceleration sensor 1. The acceleration sensor 1 is formed by encapsulating the semiconductor chip in a resin-formed housing.

[0010] The acceleration sensor 1 is attached to a predetermined position in the target device 3. The target device 3 is an example of an object to which acceleration is to be detected. The target device 3 has a movable mechanism having a bearing or the like, and vibration is generated by the movement of the movable mechanism. The acceleration sensor 1 is attached to the location where the vibration occurs, and the acceleration due to the vibration is detected by the acceleration sensor 1. In the following description, the acceleration refers to the acceleration due to the vibration of the target device 3 (the acceleration of the target device 3 accompanying the vibration of the target device 3) unless otherwise specified.

[0011] The acceleration detection method by the acceleration sensor 1 is arbitrary. That is, for example, the acceleration sensor 1 may be a frequency change type acceleration sensor, a piezoelectric type acceleration sensor, a piezoresistive type acceleration sensor, or a capacitive type acceleration sensor.

[0012] The MPU 2 is connected to the acceleration sensor 1 through the bus 4. Bidirectional communication is possible between the acceleration sensor 1 and the MPU 2 via the bus 4. The bus 4 is composed of a plurality of signal wirings. The bus 4 may include a serial bus or a parallel bus. When the bus 30 includes a serial bus, the bidirectional communication between the acceleration sensor 1 and the MPU 2 is, for example, I 2 C (Inter-Integrated Circuit) communication or SPI (Serial Peripheral Interface) communication.

[0013] The state of the target device 3 can be a specific state. The specific state is a state in which deterioration, damage, etc. have occurred in the movable mechanism. In the specific state, a specific frequency component is mixed into the vibration generated by the movable mechanism of the target device 3.

[0014] FIG. 2 shows the vibration waveform of the movable mechanism of the target device 3 in the normal state. The normal state refers to a state in which deterioration, damage, etc. have not occurred in the movable mechanism. FIG. 3 shows the vibration waveform of the movable mechanism of the target device 3 in the specific state. In both the normal state and the specific state, pulsed vibration occurs each time the movable mechanism moves. Only in the specific state, a vibration component having a specific frequency fx (see FIG. 5) is superimposed on the pulsed vibration component. The specific frequency fx depends on the structural characteristics of the movable mechanism, etc.

[0015] The use of the acceleration sensor 1 includes the maintenance of the target device 3, and the acceleration sensor 1 functions beneficially for detecting a specific abnormality. Depending on the vibration waveform of the movable mechanism of the target device 3 (for example, when the vibration waveform has a single-frequency sine wave shape), the amplitude and frequency in the output signal of the sensor element in the acceleration sensor 1 can be easily detected, and thus it can be easily determined whether the target device 3 is in a specific state. However, as shown in FIGS. 2 and 3, for the target device 3 in which pulsed vibration (and thus a pulsed acceleration signal) occurs, some ingenuity is required.

[0016] Hereinafter, among a plurality of embodiments, specific configuration examples, operation examples, application technologies, modification technologies, etc. of the acceleration sensor 1 will be described. The matters described above in this embodiment are applied to the following respective embodiments unless otherwise specified and without contradiction. In each embodiment, if there are matters conflicting with the above-described matters, the description in each embodiment may be given priority. Also, without contradiction, among the plurality of embodiments shown below, the matters described in any one embodiment can be applied to any other embodiment (that is, it is also possible to combine any two or more of the plurality of embodiments).

[0017] <<First Embodiment>> The first embodiment will be described. The acceleration sensor 1 in the first embodiment is the acceleration sensor 1A. Fig. 4 shows the configuration of the acceleration sensor 1A. The acceleration sensor 1A includes a sensor element 11, an AFE 12, an ADC 13, a correction circuit 14, an envelope detection circuit 15, and a frequency analysis circuit 16.

[0018] The sensor element 11 detects the acceleration due to the vibration of the target device 3 and generates and outputs a signal S11 indicating the detection result of the acceleration. The signal S11 is an analog acceleration signal representing the waveform of the detected acceleration, and thus may be referred to as the acceleration signal S11. The sensor element 11 may be able to detect accelerations in a plurality of directions along a plurality of axes, but here attention is paid only to the acceleration in one direction along a single axis (i.e., one-dimensional acceleration). The signal S11 is a voltage signal representing the direction and magnitude of the acceleration to be detected. As described above, the acceleration detection method in the present disclosure is arbitrary, but here, a capacitive sensor based on MEMS (Micro Electro Mechanical System) is used as the sensor element 11. The output signal S11 of the sensor element 11 is supplied to the AFE 12.

[0019] The AFE 12 is an analog front end and amplifies the output signal S11 of the sensor element 11. The signal S11 after amplification by the AFE 12 is referred to as the signal S12. The AFE 12 outputs the signal S12. The signal S12 is an analog acceleration signal representing the waveform of the detected acceleration, similar to the signal S11, and thus may be referred to as the acceleration signal S12. Note that the signal processing performed by the AFE 12 on the signal S11 may include operations other than amplification. The output signal S12 of the AFE 12 is supplied to the ADC 13.

[0020] ADC13 is an AD conversion circuit that converts the analog signal S12 from AFE12 into a digital signal S13. The signal S13 is a digital acceleration signal representing the detected acceleration waveform, and thus may be referred to as the acceleration signal S13. The signal S13 is supplied from ADC13 to the correction circuit 14. Incidentally, a low-pass filter for suppressing the mixing of aliasing noise into the signal S13 may be provided in the previous stage of ADC13 (for example, AFE12).

[0021] The correction circuit 14 performs correction signal processing on the signal S13. The correction circuit 14 is a circuit for suppressing the influence of manufacturing variations of the acceleration sensor 1A. In the correction signal processing, the offset that may be included in the signal S13 is corrected, and the sensitivity of the signal S13 is also corrected. The signal S13 after the correction signal processing is supplied from the correction circuit 14 to the envelope detection circuit 15 as the signal S14. The signal S14, like the signal S13, is a digital acceleration signal representing the detected acceleration waveform, and thus may be referred to as the acceleration signal S14. Incidentally, the correction circuit 14 may be omitted in the acceleration sensor 1A. When the correction circuit 14 is omitted, the signal S13 and the signal S14 are regarded as the same.

[0022] The envelope detection circuit 15 performs envelope detection processing for extracting the envelope of the signal S14 in the digital signal domain (that is, performs envelope detection on the signal S14). The signal indicating the envelope extracted by the envelope detection circuit 15 is referred to as the signal S15. The signal S15 is a digital envelope signal representing the waveform of the extracted envelope, and thus may be referred to as the envelope signal S15. The signal S15 is supplied from the envelope detection circuit 15 to the frequency analysis circuit 16. The envelope detection circuit 15 can be formed by a known configuration for realizing envelope extraction (that is, envelope detection) in the digital signal domain. For example, the envelope detection circuit 15 may be composed of a Hilbert transform circuit, a peak detection circuit, or a low-pass filter. The low-pass filter in the envelope detection circuit 15 may be a FIR (Finite Impulse Response) type low-pass filter or an IIR (Infinite Impulse Response) type low-pass filter.

[0023] In FIG. 5, the solid-line waveform 610 is an example of the waveform of signal S14, and the dashed-line waveform 620 is the waveform of the envelope signal S15 obtained by performing envelope detection processing on the signal S14 having the waveform 610. In FIG. 5, the horizontal axis corresponds to time, and the vertical axis corresponds to the signal value. The waveforms of signal S11 and signal S12 are in a substantially similar relationship, and the waveforms of signal S13 and signal S14 are in a substantially similar relationship. Also, signals S12 and S13 only differ in whether the signal representation region is the analog region or the digital region, and represent the same thing for each other. Therefore, the waveform 610 can also be understood as the waveform of signal S11, S12, or S13.

[0024] The waveform 610 includes a pulse-like signal component corresponding to the above-described pulse-like vibration. The waveform 610 is a waveform observed when the target device 3 is in a specific state. For this reason, in the waveform 610, a signal component having a specific frequency fx is superimposed on the pulse-like signal component. The signal component having the specific frequency fx is extracted by the envelope detection processing. Here, for the sake of simplicity of explanation and illustration, a waveform 610 including only the pulse-like signal component and the signal component having the specific frequency fx is shown, but the waveform of the actual signal S14 may include signal components of various frequencies.

[0025] The frequency analysis circuit 16 performs frequency analysis on the envelope signal S15 and generates a signal S16 indicating the result of the frequency analysis. The acceleration sensor 1A can output (transmit) signals S14, S15, and S16 to the MPU 2 through the bus 4.

[0026] FIG. 6 shows the internal configuration of the frequency analysis circuit 16. The frequency analysis circuit 16 includes a band component main output circuit 161, an arithmetic circuit 162, and a storage circuit 163. In the frequency analysis circuit 16, first to nth element bands belonging to the entire band of the envelope signal S15 are set. The first to nth element bands are n different types of bands. n represents an arbitrary integer of 2 or more.

[0027] FIG. 7 shows the relationship between the first to nth element bands. The (i + 1)th element band is higher than the ith element band. Here, i represents an arbitrary integer. In the example of FIG. 7, the upper limit frequency of the ith element band coincides with the lower limit frequency of the (i + 1)th element band. However, there may be another band with a certain size between the ith element band and the (i + 1)th element band. Alternatively, a part of the ith element band and a part of the (i + 1)th element band may overlap (in this case, at least, the lower limit frequency of the (i + 1)th element band is higher than the lower limit frequency of the ith element band, and the upper limit frequency of the (i + 1)th element band is higher than the upper limit frequency of the ith element band).

[0028] As shown in FIG. 8, the band component extraction circuit 161 includes n band-pass filters BPF161[1] to 161[n]. The envelope signal S15 is input to each of BPF161[1] to 161[n]. Each of BPF161[1] to 161[n] extracts and outputs the signal components within its set passband from the signal components of the envelope signal S15. The output signal of BPF161[i] is referred to as the band signal BS[i]. The passband in BPF161[i] is the ith element band. Therefore, BPF161[i] extracts the signal components within the ith element band from the signal components of the envelope signal S15 and outputs the band signal BS[i] composed of the extracted signal components.

[0029] The total number of band-pass filters provided in the band component extraction circuit 161 may be less than n. For example, only one band-pass filter may be provided for the band component extraction circuit 161, and a single band-pass filter may be used in a time-division manner to obtain the band signals BS[1] to BS[n]. In this case, with the acceleration signal S15 supplied to the single band-pass filter, the passband of the single band-pass filter is sequentially switched between the first to nth element bands, whereby the band signals BS[1] to BS[n] can be obtained. That is, the band signal BS[1] is acquired by setting the passband of the single band-pass filter to the first element band, and thereafter, the band signal BS[2] can be acquired by setting the passband of the single band-pass filter to the second element band. The same applies to the other element bands. When "n ≥ 3", only the first and second band-pass filters may be provided in the band component extraction circuit 161, and a part of the band signals BS[1] to BS[n] may be acquired using the first band-pass filter in a time-division manner, and the remainder of the band signals BS[1] to BS[n] may be acquired using the second band-pass filter in a time-division manner.

[0030] The band signals BS[1] to BS[n] are input to the arithmetic circuit 162. The arithmetic circuit 162 derives intensity data of the envelope signal S15 for each element band based on the band signals BS[1] to BS[n]. The intensity data represents the effective value or power. That is, the intensity data of the envelope signal S15 for each element band may be the effective value of the envelope signal S15 for each element band, or may be the power of the envelope signal S15 for each element band. The intensity data (effective value or power) of the envelope signal S15 in the ith element band is referred to as intensity data D[i]. The intensity data D[i] is derived based on the band signal BS[i]. Therefore, in the arithmetic circuit 162, the intensity data D[1] to D[n] are derived based on the band signals BS[1] to BS[n].

[0031] In FIG. 9, the waveform 630 shown above is an example of the frequency spectrum (power spectrum) of the envelope signal S15, and the plot group 640 shown below is an example of the intensity data D[1] to D[n] derived by the arithmetic circuit 162 (assuming "n = 5" in FIG. 9).

[0032] The memory circuit 163 stores the intensity data D[1] to D[n] derived by the arithmetic circuit 162. The memory circuit 163 may be a volatile memory such as a RAM (Random Access Memory), or may be a non-volatile memory such as a flash memory. The MPU 2 can read any data stored in the memory circuit 163 by transmitting necessary commands to the acceleration sensor 1A, and in this reading, the intensity data D[1] to D[n] is transmitted (output) to the MPU 2. The intensity data D[1] to D[n] corresponds to the signal S16.

[0033] The MPU 2 can execute a state detection process for detecting whether the target device 3 is in a specific state based on the intensity data D[1] to D[n] read from the memory circuit 163. For example, when the above-mentioned specific frequency fx belongs to the second element band, in the state detection process, the MPU 2 compares the intensity data D[2] (effective value or power) with a predetermined determination threshold value. If the intensity data D[2] is higher than the determination threshold value, it is determined that the target device 3 is in a specific state. If the intensity data D[2] is equal to or lower than the determination threshold value, it is determined that the target device 3 is not in a specific state (that is, it is determined to be in a normal state). In the state detection process, intensity data other than the intensity data D[2] may also be referred to in order to improve the accuracy of these determinations.

[0034] In this way, by using the acceleration sensor 1A, it is possible to easily and accurately detect whether the target device 3 is in a specific state. Although a method of performing frequency analysis using FFT is also considered, the acceleration sensor 1A can realize the necessary frequency analysis with a simpler configuration than when performing frequency analysis using FFT.

[0035] Depending on the type and structure of the target device 3, the specific frequencies fx to be noted are various. In the acceleration sensor 1A, since a plurality of element bands are set and intensity data is generated for each element band, it can be adapted to various specific frequencies fx.

[0036] During the period when acceleration is detected by the sensor element 11, a plurality of analysis target periods arranged in time series are set. The frequency analysis circuit 16 performs frequency analysis for each analysis target period, and can derive intensity data D[1] to D[n] for each analysis target period.

[0037] Regarding the first and second analysis target periods included in the plurality of analysis target periods, the following operations are performed. That is, signals S12 to S15 in the first analysis target period are generated based on the signal S11 in the first analysis target period, and intensity data D[1] to D[n] in the first analysis target period are derived based on the envelope signal S15 in the first analysis target period. Signals S12 to S15 in the second analysis target period are generated based on the signal S11 in the second analysis target period, and intensity data D[1] to D[n] in the second analysis target period are derived based on the envelope signal S15 in the second analysis target period. The same applies to the third analysis target period and so on.

[0038] The intensity data D[1] to D[n] are referred to as an intensity data group. The memory circuit 163 stores the intensity data group for each analysis target period. The memory circuit 163 can accumulate and store a plurality of intensity data groups derived for a plurality of analysis target periods in time series order. By referring to the accumulated intensity data group, the MPU 2 can grasp whether the state of the target device 3 is maintained in the normal state, has shifted from the normal state to a specific state, or is maintained in the specific state.

[0039] When the memory circuit 163 stores the intensity data group, it may store the date and time information of the analysis target period corresponding to the intensity data group in association with the intensity data group. The date and time information of the analysis target period represents the date and time belonging to the analysis target period. That is, for example, when the intensity data D[1] to D[n] in the first analysis target period are obtained, the memory circuit 163 stores the intensity data D[1] to D[n] in the first analysis target period and the date and time information of the first analysis target period in association with each other. Subsequently, when the intensity data D[1] to D[n] in the second analysis target period are obtained, the memory circuit 163 may store the intensity data D[1] to D[n] in the second analysis target period and the date and time information of the second analysis target period in association with each other. When the MPU 2 reads out the intensity data group of the i-th analysis target period from the memory circuit 163, the MPU 2 can also read out the date and time information of the i-th analysis target period. Based on the read information, the MPU 2 can grasp in detail the time-series change of the state of the target device 3.

[0040] <<Second Embodiment>> The second embodiment will be described. The acceleration sensor 1 in the second embodiment is the acceleration sensor 1B. The configuration of the acceleration sensor 1B is shown in FIG. 10. The acceleration sensor 1B includes a sensor element 11, an AFE 12, an envelope detection circuit 23, an ADC 24, a correction circuit 25, and a frequency analysis circuit 16. Different from the acceleration sensor 1A, in the acceleration sensor 1B, the envelope detection circuit is arranged in front of the ADC. The acceleration sensor 1B is a deformation of a part of the acceleration sensor 1A, and the description of the first embodiment is applied to the second embodiment for matters not specifically described in the second embodiment.

[0041] In the acceleration sensor 1B, the sensor element 11 and the AFE 12 are the same as those in the acceleration sensor 1A. However, in the acceleration sensor 1B, the output signal S12 of the AFE 12 is supplied to the envelope detection circuit 23 instead of the ADC.

[0042] The envelope detection circuit 23 performs envelope detection processing for extracting the envelope of the signal S12 in the analog signal region (that is, performs envelope detection on the signal S12). A signal indicating the envelope extracted by the envelope detection circuit 23 is referred to as signal S23. The signal S23 is an analog envelope signal representing the waveform of the extracted envelope, and thus may be referred to as the envelope signal S23. The signal S23 is supplied from the envelope detection circuit 23 to the ADC 24. The envelope detection circuit 23 can be formed with a known configuration for realizing envelope extraction (that is, envelope detection) in the analog signal region. For example, the envelope detection circuit 23 may be configured with a peak detection circuit or a low-pass filter.

[0043] In the second embodiment, the solid line waveform 610 shown in FIG. 5 is an example of the waveform of the signal S12, and the broken line waveform 620 shown in FIG. 5 is the waveform of the envelope signal S23 obtained by performing envelope detection processing on the signal S12 having the waveform 610.

[0044] The ADC 24 is an AD conversion circuit that converts the analog signal S23 from the envelope detection circuit 23 into a digital signal S24. The signal S24 is a digital envelope signal representing the waveform of the envelope extracted by the envelope detection circuit 23, and thus may be referred to as the envelope signal S24. The envelope signal S24 is supplied to the correction circuit 25.

[0045] The correction circuit 25 performs signal processing for correction on the envelope signal S24. The correction circuit 25 is a circuit for suppressing the influence of manufacturing variations of the acceleration sensor 1B. The offset that may be included in the envelope signal S24 is corrected by the signal processing for correction, and the sensitivity of the envelope signal S24 is also corrected. The envelope signal S24 after the signal processing for correction is supplied from the correction circuit 25 to the frequency analysis circuit 16 as the signal S25. The signal S25 is a digital envelope signal representing the waveform of the envelope extracted by the envelope detection circuit 23, similar to the signal S24, and thus may be referred to as the envelope signal S25. Note that the correction circuit 25 may be omitted in the acceleration sensor 1B. When the correction circuit 25 is omitted, the signal S24 and the signal S25 are regarded as the same.

[0046] In the acceleration sensor 1B, the frequency analysis circuit 16 performs frequency analysis on the envelope signal S25 and generates a signal S16 indicating the result of the frequency analysis. The acceleration sensor 1B can output (transmit) the signals S25 and S16 to the MPU 2 through the bus 4.

[0047] FIG. 11 is an internal configuration diagram of the frequency analysis circuit 16 in the acceleration sensor 1B. The frequency analysis circuit 16 in the acceleration sensor 1B includes a band component extraction circuit 161, an arithmetic circuit 162, and a storage circuit 163, similar to the frequency analysis circuit 16 in the acceleration sensor 1A. In the acceleration sensor 1B, the difference from the acceleration sensor 1A is that the frequency analysis is performed on the envelope signal S25 (see FIG. 11) instead of the envelope signal S15 (see FIG. 6). Except for this point, the configuration and operation of the frequency analysis circuit 16 in the acceleration sensor 1B are the same as those of the frequency analysis circuit 16 in the acceleration sensor 1A, and the description of the frequency analysis circuit 16 in the first embodiment is also applicable to the frequency analysis circuit 16 in the second embodiment. When applying this, it is sufficient to replace the symbol "S15" in the first embodiment with "S25" in the second embodiment.

[0048] Therefore, in the acceleration sensor 1B, the band component extraction circuit 161 generates and outputs the band signals BS[1] to BS[n] by extracting the signal components within the first to nth element bands from the signal components of the envelope signal S25, respectively. The band signal BS[i] is obtained by extracting the signal components within the ith element band from the signal components of the envelope signal S25. In the acceleration sensor 1B, the arithmetic circuit 162 derives the intensity data of the envelope signal S25 for each element band based on the band signals BS[1] to BS[n]. In the second embodiment, the intensity data (effective value or power) of the envelope signal S25 in the ith element band is the intensity data D[i]. The intensity data D[i] is derived based on the band signal BS[i]. In the arithmetic circuit 162, the intensity data D[1] to D[n] are derived based on the band signals BS[1] to BS[n].

[0049] Then, the memory circuit 163 stores the intensity data D[1] to D[n] derived by the arithmetic circuit 162. The MPU 2 can read any data stored in the memory circuit 163 by transmitting necessary commands to the acceleration sensor 1B, and in this reading, the intensity data D[1] to D[n] is transmitted (output) to the MPU 2. The intensity data D[1] to D[n] corresponds to the signal S16. The state detection process for detecting whether the target device 3 is in a specific state based on the intensity data D[1] to D[n] can be executed by the MPU 2 in the same manner as in the first embodiment.

[0050] Here, the superiority of the second embodiment as seen from the first embodiment will be described. The output signal S11 of the sensor element 11 includes a pulsed signal component based on the pulsed vibration component. The pulsed signal component includes signal components in a band sufficiently higher than a specific frequency fx (for example, a frequency in the range of several tens of Hz to several kHz). In the first embodiment (see FIG. 4), in order to transmit the signal component of the specific frequency fx to the envelope detection circuit 15, it is necessary to accurately convert the pulsed signal component into a digital signal in the ADC 13 on the previous stage side, so a high sampling frequency is required. On the other hand, in the second embodiment (see FIG. 10), since the envelope detection process is performed before the ADC 24, the sampling frequency of the ADC 24 only needs to be sufficiently high with respect to the signal band of the envelope. That is, in the second embodiment, the sampling frequency of the ADC can be made lower than that in the first embodiment (the AD conversion can be slowed down). Slowing down the AD conversion contributes to reducing power consumption.

[0051] In addition, since the envelope signal S23 does not include a pulsed signal component, the output signal (S24) of the ADC 24 does not include aliasing noise based on the pulsed signal component (the increase in noise is suppressed or is likely to be suppressed compared to the first embodiment).

[0052] <<Third Embodiment>> The third embodiment will be described.

[0053] A state detection circuit (not shown) that performs the above-described state detection process may be provided in the acceleration sensor 1 (1A or 1B). In this case, a signal indicating the detection result of the state detection process by the state detection circuit (that is, a signal indicating whether the target device 3 is in a specific state) may be transmitted from the acceleration sensor 1 (1A or 1B) to the MPU 2.

[0054] In the embodiments of the present disclosure, various modifications can be appropriately made within the scope of the technical idea shown in the claims. The above embodiments are merely examples of the embodiments of the present disclosure, and the meanings of the terms of the present disclosure or each component are not limited to those described in the above embodiments. The specific numerical values shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

[0055] <<Supplementary Note>> A supplementary note is provided for the present disclosure in which specific configuration examples are shown in the above embodiments.

[0056] An acceleration sensor (1, 1A, 1B) according to one aspect of the present disclosure includes a sensor element (11) configured to output a signal indicating a detection result of the acceleration of an object (3), an envelope detection circuit (15, 23) configured to generate an envelope signal by performing envelope detection processing on an acceleration signal based on the output signal of the sensor element, and a frequency analysis circuit (16) configured to extract signal components of the envelope signal for each of a plurality of element bands and derive intensity data (D[1] to D[n]) of the signal components of the envelope signal for each element band.

[0057] Thereby, information necessary for state detection of the object can be accurately and easily acquired.

[0058] In the acceleration sensor according to the first configuration (see FIG. 10), the envelope detection circuit (23) generates an analog envelope signal (S23) by performing the envelope detection process on an analog acceleration signal based on the output signal of the sensor element. An AD conversion circuit (24) is provided between the envelope detection circuit (23) and the frequency analysis circuit (16). The AD conversion circuit converts the analog envelope signal into a digital envelope signal, and the frequency analysis circuit may be configured to derive each intensity data based on the digital envelope signal (second configuration).

[0059] By providing an envelope detection circuit on the front stage side of the AD conversion circuit, the speed requirement for the AD conversion circuit can be relaxed.

[0060] In the acceleration sensor according to the first configuration (see FIG. 4), an AD conversion circuit (13) is provided between the sensor element (11) and the envelope detection circuit (15). The AD conversion circuit converts an analog acceleration signal based on the output signal of the sensor element into a digital acceleration signal. The envelope detection circuit (15) generates a digital envelope signal by performing the envelope detection process on the digital acceleration signal, and the frequency analysis circuit may be configured to derive each intensity data based on the digital envelope signal (third configuration).

[0061] In the acceleration sensor according to any one of the first to third configurations, the frequency analysis circuit may be configured to include a storage circuit (163) configured to store each derived intensity data (fourth configuration).

[0062] In the acceleration sensor according to the fourth configuration, a group of the intensity data based on the output signal of the sensor element during the analysis target period is derived by the frequency analysis circuit, and the storage circuit may be configured to accumulatively store a group of a plurality of intensity data derived for a plurality of different analysis target periods (fifth configuration).

[0063] In the acceleration sensor according to any one of the first to fifth configurations, the intensity data may be a configuration (sixth configuration) representing an effective value or power.

Explanation of symbols

[0064] 1, 1A, 1B Acceleration sensor 2 MPU 3 Target device 4 Bus 11 Sensor element 12 AFE 13, 24 ADC 14, 25 Correction circuit 15, 23 Envelope detection circuit 16 Frequency analysis circuit 161 Band component extraction circuit 161[1]~161[n] BPF 162 Arithmetic circuit 163 Memory circuit BS[1]~BS[n] Band signal D[1]~D[n] Intensity data

Claims

1. A sensor element configured to output a signal indicating a detection result of the acceleration of an object, An envelope detection circuit configured to generate an envelope signal by performing envelope detection processing on an acceleration signal based on the output signal of the sensor element, A frequency analysis circuit configured to extract signal components of the envelope signal for each of a plurality of element bands and derive intensity data of the signal components of the envelope signal for each element band, and comprising an acceleration sensor.

2. The envelope detection circuit generates an analog envelope signal by performing the envelope detection processing on an analog acceleration signal based on the output signal of the sensor element, An AD conversion circuit is provided between the envelope detection circuit and the frequency analysis circuit, The AD conversion circuit converts the analog envelope signal into a digital envelope signal, The frequency analysis circuit derives each intensity data based on the digital envelope signal The acceleration sensor according to claim 1.

3. An AD conversion circuit is provided between the sensor element and the envelope detection circuit, The AD conversion circuit converts an analog acceleration signal based on the output signal of the sensor element into a digital acceleration signal, The envelope detection circuit generates a digital envelope signal by performing the envelope detection processing on the digital acceleration signal, The frequency analysis circuit derives each intensity data based on the digital envelope signal The acceleration sensor according to claim 1.

4. The frequency analysis circuit includes a storage circuit configured to store each derived intensity data The acceleration sensor according to any one of claims 1 to 3.

5. A group of the intensity data based on the output signal of the sensor element during an analysis target period is derived by the frequency analysis circuit, The storage circuit stores in an accumulated manner a group of a plurality of intensity data derived for a plurality of different analysis target periods The acceleration sensor according to claim 4.

6. The intensity data represents an effective value or power The acceleration sensor according to any one of claims 1 to 3.

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