microphone

Abstract

To provide a microphone capable of setting a correction value without need for a sound source.SOLUTION: A microphone includes a MEMS device 200, a driver 330 and a control section 320. The MEMS device outputs a first electric signal corresponding to an acoustic pressure. The driver vibrates the MEMS device through a driving signal. The control section computes a correction value for correcting the first electric signal on the basis of a second electric signal output from the MEMS device when being vibrated by the driving signal.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The disclosure provided herein relates to microphones. [Background technology]

[0002] As shown in Patent Document 1, an acoustic characteristic correction system having a sound emitting equalizing processing unit and a CPU is known. The sound emitting equalizing processing unit corrects a sound signal picked up by a microphone. The CPU sets correction parameters for the sound emitting equalizing processing unit based on an acoustic characteristic measurement signal emitted from a speaker and a desired acoustic characteristic stored in a memory. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-268257 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the acoustic characteristic correction system described in Patent Document 1, when setting the correction parameters, a test sound source for emitting sound from a speaker is required. Without a test sound source (sound source), it is not possible to set the correction parameters (correction values).

[0005] An object of the present disclosure is to provide a microphone that allows a correction value to be set even without a sound source. [Means for solving the problem]

[0006] A microphone according to one embodiment of the present disclosure includes a vibration device (200) that outputs a first electrical signal in response to an acoustic pressure; A drive unit (330) that vibrates the vibration device by a drive signal; a correction unit (320) that calculates a correction value for correcting the first electrical signal based on a second electrical signal output from the vibration device when the vibration device is vibrated by the drive signal; The correction unit is configured so that the vibration of the vibration device caused by acoustic pressure does not affect the correction value. Status The second electrical signal is used to calculate a correction value.

[0007] This makes it possible to calculate the correction value even without a sound source, and the correction value does not depend on the characteristics of the sound source.

[0008] It should be noted that the reference numbers in parentheses above merely indicate the corresponding relationship with the configurations described in the embodiments described below, and do not in any way limit the technical scope. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a piezoelectric MEMS microphone. [Diagram 2] FIG. 2 is a top view of a MEMS device. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 2 is a circuit diagram for explaining an equivalent circuit of a MEMS device. [Diagram 5] 1 is a graph showing sensitivity frequency characteristics of a MEMS device. [Figure 6] FIG. 1 is a block diagram for explaining a piezoelectric MEMS microphone. [Figure 7] 13 is a flowchart showing a correction value calculation process. [Figure 8] 4 is a schematic diagram showing sensitivity frequency characteristics stored in a storage unit. FIG. [Figure 9] 13 is a flowchart showing a correction process. [Figure 10] 5 is a schematic diagram for explaining correction values ​​stored in a storage unit. FIG. [Figure 11] 13 is a flowchart showing a correction value calculation process. [Figure 12]FIG. 1 is a cross-sectional view showing a piezoelectric MEMS microphone. [Figure 13] FIG. 1 is a block diagram showing a piezoelectric MEMS microphone. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, several embodiments for carrying out the present disclosure will be described with reference to the drawings. In each embodiment, the same reference numerals may be used to designate parts corresponding to matters described in the preceding embodiment, and duplicated descriptions may be omitted. In each embodiment, when only a part of the configuration is described, the other embodiment described previously may be applied to the other parts of the configuration.

[0011] It is possible to combine parts of each embodiment that are specifically indicated as being possible to combine with each other. In addition, even if it is not specifically indicated that the combination is possible, it is also possible to partially combine embodiments with each other, embodiments with variations, and variations with each other, as long as there is no particular problem with the combination.

[0012] (First embodiment) The piezoelectric MEMS microphone will be described with reference to FIGS.

[0013] <Piezoelectric MEMS microphone> 1, a piezoelectric MEMS microphone 100 includes a MEMS device 200, an ASIC 300, and a package 400. MEMS is an abbreviation for Micro Electro Mechanical Systems. ASIC is an abbreviation for Application Specific Integrated Circuit.

[0014] The MEMS device 200 and the ASIC 300 are electrically connected. The package 400 has a substrate 410 and a lid 420. The MEMS device 200 and the ASIC 300 are mounted on an inner surface 410a of the substrate 410. This inner surface 410a is covered by the lid 420. The MEMS device 200 and the ASIC 300 are housed in an internal space of the package 400 defined by the substrate 410 and the lid 420.

[0015] An introduction hole 410c that opens to an inner surface 410a and an outer surface 410b on the reverse side is formed in the substrate 410. The introduction hole 410c communicates the internal space of the package 400 with the external space on the outside. The opening of the introduction hole 410c on the internal space side is covered by the MEMS device 200.

[0016] Due to this configuration, when air vibrations (sound) occur in the external space, the vibrations act as acoustic pressure on the MEMS device 200. The MEMS device 200 outputs an electrical signal corresponding to the acoustic pressure to the ASIC 300. In this way, the sound generated in the external space is detected.

[0017] <MEMSデバイス> The MEMS device 200 will be described in detail below. In the following, the three mutually orthogonal directions will be referred to as the x-direction, the y-direction, and the z-direction. In the drawings, the directions are omitted and simply written as x, y, and z.

[0018] 2 and 3, the MEMS device 200 has a support base 210 and a vibrator 220. The vibrator 220 is integrally connected to the support base 210.

[0019] <Support stand> The support 210 has a base 211 and a design layer 212 that are stacked in the z-direction. The base 211 is made of silicon. The design layer 212 is made of silicon oxide.

[0020] The base portion 211 and the design layer 212 are integrally connected. Each of the base portion 211 and the design layer 212 has an open hole 210a that opens in the z direction. Each of the base portion 211 and the design layer 212 forms an annular shape in the circumferential direction around the z direction.

[0021] <Transducer> The MEMS device 200 has a plurality of vibrators 220. Each of the plurality of vibrators 220 is integrally connected to the design layer 212 of the support base 210. The plurality of vibrators 220 are cantilevered by the design layer 212. The plurality of vibrators 220 cover the opening of the open hole 210a on the design layer 212 side.

[0022] 2, one oscillator 220 forms a triangle on a plane perpendicular to the z-direction. One of the three sides of oscillator 220, a lower side 220a, is fixed to support base 210. The remaining two oblique sides 220b extend away from lower side 220a and then intersect to form tip 220c. Tip 220c of oscillator 220 is open from support base 210.

[0023] For ease of explanation, the bottom side 220a of the vibrator 220 will be referred to as the supporting end 221, and the tip 220c will be referred to as the open end 222. The direction in which the supporting end 221 and the open end 222 are aligned will be referred to as the extension direction.

[0024] The oscillator 220 extends in the extension direction. The oscillator 220 tapers away from the support base 210. A support end 221 on the side of the lower side 220a of the oscillator 220 forms a trapezoid in a plane perpendicular to the z direction. An open end 222 on the side of the tip 220c of the oscillator 220 forms a triangle in a plane perpendicular to the z direction.

[0025] The bottom side of the trapezoidal support end 221 is located in the projection area of ​​the support base 210 in the z direction. The top side of the support end 221 is located in the projection area of ​​the open hole 210a in the z direction. In Fig. 2, the boundary between the part of the vibrator 220 located in the projection area of ​​the support base 210 in the z direction and the part located in the projection area of ​​the open hole 210a is shown by a dashed dotted line. This dashed dotted line is between the bottom side and the top side of the support end 221.

[0026] The open end 222 is integrally connected to the upper side of the support end 221. The open end 222, together with the upper side of the support end 221, is located in a projection area of ​​the open hole 210a in the z direction. In Fig. 2, the boundary between the support end 221 and the open end 222 is indicated by a dashed line.

[0027] <Gap> As shown in Fig. 2, the MEMS device 200 has four oscillators 220. These four oscillators 220 are arranged in order in the circumferential direction around the z direction. Of two oscillators 220 arranged adjacent to each other in the circumferential direction, one of the two oblique sides 220b of one of the oscillators 220 faces one of the two oblique sides 220b of the other oscillator in the circumferential direction via a small gap. This gap is open on both the upper surface 220d side and the lower surface 220e side of the oscillators 220 arranged at a distance in the z direction.

[0028] The gaps between the hypotenuses 220b of each of the four oscillators 220 arranged in the circumferential direction form a cross on a plane perpendicular to the z direction. The center point of the MEMS device 200 is located on the central axis passing through the center of the cross gap in the z direction. In Figure 2, two guide lines passing through the center of the cross are shown by two-dot chain lines. One of the two guide lines runs along the x direction, and the other runs along the y direction.

[0029] <Vibration caused by acoustic pressure> 1 and 3, the portions of the support end 221 and the open end 222 of the transducer 220 that are located in the projection area of ​​the open hole 210a in the z direction cover the opening of the open hole 210a on the design layer 212 side. The portions of the support end 221 and the open end 222 that are located in the projection area of ​​the open hole 210a in the z direction and the portion that defines the open hole 210a of the support base 210 cover the opening of the introduction hole 410c on the internal space side.

[0030] Due to this configuration, when sound is generated in the external space, the sound vibrates the air in the open hole 210a. The vibration of the air acts on the vibrator 220 as acoustic pressure. This causes the supporting end 221 and the open end 222 of the vibrator 220 to vibrate. The supporting end 221 and the open end 222 are deflected.

[0031] Note that a part of the acoustic pressure escapes into the internal space of the package 400 through the above-mentioned gap. Due to this configuration, if the gap is wider than the design value, the acoustic pressure is more likely to escape into the internal space of the package 400. This makes it difficult for the transducer 220 to vibrate due to the acoustic pressure. To avoid such a problem, the gap is made very small.

[0032] <Material> The transducer 220 includes a piezoelectric element that converts pressure into voltage. As shown in Fig. 3, the transducer 220 has a piezoelectric layer 230 and an electrode layer 240. The piezoelectric layer 230 and the electrode layer 240 are laminated in the z direction.

[0033] The piezoelectric layer 230 includes a material having a piezoelectric constant higher than that of aluminum nitride (AlN). Examples of materials (piezoelectric materials) included in the piezoelectric layer 230 include scandium aluminum nitride (ScAlN), lead zirconate titanate (PZT), and potassium sodium niobate (KNN). The electrode layer 240 includes a conductive material such as molybdenum.

[0034] The piezoelectric layer 230 includes a first piezoelectric layer 231 and a second piezoelectric layer 232. The electrode layer 240 includes a first electrode layer 241, a second electrode layer 242, and a third electrode layer 243.

[0035] 3, a first electrode layer 241, a first piezoelectric layer 231, a second electrode layer 242, a second piezoelectric layer 232, and a third electrode layer 243 are laminated in this order in the z direction. The first electrode layer 241 is connected to the support base 210. The first electrode layer 241 is located on the lower surface 220e side of the vibrator 220. The third electrode layer 243 is located on the upper surface 220d side of the vibrator 220.

[0036] A lower layer capacitor is formed by arranging the first electrode layer 241 and the second electrode layer 242 in the z direction with the first piezoelectric layer 231 in between. An upper layer capacitor is formed by arranging the second electrode layer 242 and the third electrode layer 243 in the z direction with the second piezoelectric layer 232 in between.

[0037] These two capacitors have the second electrode layer 242 as a common component. The two capacitors are electrically connected in series in the z-direction through this common component. The MEMS device 200 includes a plurality of composite capacitors each consisting of two capacitors electrically connected in series.

[0038] <Extraction electrode> A plurality of extraction electrodes 250 are formed on the supporting end 221 of the vibrator 220 to electrically connect the plurality of composite capacitors in series and to detect the voltages of the plurality of electrically connected composite capacitors.

[0039] Some of the multiple extraction electrodes 250 electrically connect the second electrode layer 242 of one of the two electrically connected composite capacitors to the first electrode layer 241 and the third electrode layer 243 of the other.

[0040] One of the remaining two extraction electrodes 250 is electrically connected to the first electrode layer 241 and the third electrode layer 243 of the composite capacitor located at the lowest potential. The first electrode layer 241 and the third electrode layer 243 are connected to ground. The last extraction electrode 250 is connected to the second electrode layer 242 of the composite capacitor located at the highest potential.

[0041] These remaining two extraction electrodes 250 are each connected to the ASIC 300 via a wire 510. As a result, both ends of the electrically connected composite capacitors are connected to the ASIC 300.

[0042] <Detection of acoustic pressure> When acoustic pressure is applied, the vibrator 220 vibrates in the z-direction. A tensile stress acts on one of the first piezoelectric layer 231 and the second piezoelectric layer 232 of the vibrator 220, and a compressive stress acts on the other.

[0043] Due to this difference in the acting stress, voltages of opposite polarity are generated in the first piezoelectric layer 231 and the second piezoelectric layer 232. This voltage is generated in the electrode layer 240 of the composite capacitor. A voltage obtained by adding up the voltages generated in each of the multiple composite capacitors is generated in the MEMS device 200. The capacitance changes of the multiple composite capacitors or the charge changes of the multiple composite capacitors corresponding to this voltage are output to the ASIC 300 as a first electrical signal. For ease of notation, hereinafter, the multiple electrically connected composite capacitors will be simply referred to as a capacitor as necessary.

[0044] <Detection area and vibration area> The transducer 220 of this embodiment has a detection area DA that generates a voltage by vibration due to the action of acoustic pressure, and a vibration area VA that is forcibly vibrated by input of a drive signal described below. In Fig. 2, the detection area DA is shown by hatching in one of the four transducers 220. The vibration area VA is shown surrounded by a two-dot chain line.

[0045] The detection area DA is located on the central side of the vibrator 220. The vibration area VA is located on the end side of the vibrator 220. One detection area DA is located between two vibration areas VA. One vibration area VA includes one oblique side 220b. Note that, unlike this embodiment, a configuration in which the detection area DA is located on the end side of the vibrator 220 and the vibration area VA is located on the central side of the vibrator 220 can also be adopted.

[0046] The detection area DA and the vibration area VA are electrically insulated. Although not shown, a drive electrode is formed on the vibrator 220, which electrically connects the electrode layer 240 of the capacitor included in the vibration area VA to the ASIC 300 by a wire 510 or the like. A drive signal, which will be described later, is input to this drive electrode. The MEMS device 200 corresponds to the vibration device. The detection area DA corresponds to the first detection unit. The vibration area VA corresponds to the second detection unit.

[0047] It is not necessary to divide the vibrator 220 into the detection area DA and the vibration area VA as described in this embodiment. In this configuration, the above-mentioned drive electrode is not formed on the vibrator 220. A drive signal is input to the above-mentioned extraction electrode 250. The case where a voltage is generated by vibration due to the action of acoustic pressure and the case where forced vibration is caused by input of a drive signal are executed at different times.

[0048] In this modified example, when a correction process described below is performed, no drive signal is input from the ASIC 300 to the extraction electrode 250. When a correction value calculation process described below is performed, a drive signal is input from the ASIC 300 to the extraction electrode 250.

[0049] <Equivalent circuit> As described above, when sound is generated in the external space, the air in the open hole 210a vibrates. The vibration of the air causes the vibrator 220 to vibrate. As a result, a voltage is generated in the vibrator 220.

[0050] In this way, the conversion of sound generated in the external space into an electrical signal is related to three factors: the ease with which the air in open hole 210a vibrates, the ease with which oscillator 220 vibrates, and voltage conversion in oscillator 220. The ease with which the air in open hole 210a vibrates is determined by fluid dynamics. The ease with which oscillator 220 vibrates is determined by mechanical dynamics. Voltage conversion in oscillator 220 is determined by electromagnetism.

[0051] The conversion of sound into an electrical signal involves three different physical phenomena. These three physical phenomena are expressed by differential equations. These three differential equations can be expressed by equivalent circuits. Figure 4 shows the equivalent circuits of the differential equations that represent these three different physical phenomena.

[0052] The tendency of the air in the open hole 210a to vibrate is represented by a sound field SF. The tendency of the vibrator 220 to vibrate is represented by a force field FF. The voltage conversion in the vibrator 220 is represented by an electric field EF. These three fields are electrically connected.

[0053] As shown in Figure 4, the sound field SF, the force field FF, and the electric field EF each contain various parameters such as reactor, capacitance, and resistance. The parameters of the sound field SF include L1, C1, C2, and R1. The parameters of the force field FF include L2, C3, and R2. The parameters of the electric field EF include C4, C5, and R3.

[0054] Of these sound field SF, force field FF, and electric field EF, the parameters of the force field FF are easily changed by temperature, etc. For this reason, as described below, the ASIC 300 calculates a correction value for correcting the first electric signal output from the MEMS device 200 based on the parameters of the force field FF. For ease of notation, the parameters of the force field FF will be referred to as force field parameters below.

[0055] <Detection sensitivity> The detection sensitivity of MEMS device 200 to acoustic pressure can be expressed as the amount of voltage generated in response to acoustic pressure. Figure 5 shows the frequency dependency of detection sensitivity (sensitivity frequency characteristics). The vertical axis of Figure 5 shows detection sensitivity, and the horizontal axis shows frequency. The units of the vertical axis are V / Pa and the horizontal axis are Hz. The detection sensitivity gradually increases in the low frequency range, becomes constant without changing with frequency, and then gradually increases in the high frequency range.

[0056] In Fig. 5, the ideal sensitivity frequency characteristic (desired sensitivity frequency characteristic) is shown by a solid line. The uncorrected sensitivity frequency characteristic is shown by a dashed line. By the above-mentioned correction, the sensitivity in the low frequency region of the sensitivity frequency characteristic shown by this dashed line is amplified, and the sensitivity in the high frequency region of the sensitivity frequency characteristic is attenuated.

[0057] This correction narrows the region in which the detection sensitivity varies with frequency. The frequency band in which the detection sensitivity does not depend on frequency is moved from the first frequency band FB1 to the second frequency band FB2. The sensitivity-frequency characteristic is brought closer to the desired sensitivity-frequency characteristic. Such frequency band expansion is performed by the ASIC 300.

[0058] Note that the ASIC 300 may perform correction other than frequency band expansion. For example, the ASIC 300 may amplify or attenuate the sensitivity of a specific frequency band.

[0059] <asic> 6, the ASIC 300 includes a conversion unit 310, a control unit 320, and a driver 330. In the drawing, the conversion unit 310 is denoted as CS. The driver 330 is denoted as DR. Each component of the ASIC 300 executes the correction process and the correction value calculation process described below.

[0060] <Correction process> The conversion unit 310 converts a first electrical signal, which indicates a change in capacitance or a change in charge of a capacitor output from the MEMS device 200 vibrating due to acoustic pressure, into a voltage. The conversion unit 310 then outputs the converted first electrical signal (sound pickup signal) to the control unit 320.

[0061] The control unit 320 performs correction to expand the frequency band of the picked-up sound signal output from the conversion unit 310. Then, the control unit 320 outputs the corrected picked-up sound signal to a speaker or the like.

[0062] <Correction value calculation process> The control unit 320 outputs a vibration signal to the driver 330 to forcibly vibrate the MEMS device 200. The vibration signal is a pulse signal whose voltage level periodically changes between high and low levels. The amplitude of the vibration signal is constant. The high level is, for example, 2.5 V. The low level is, for example, −2.5 V. The frequency of the vibration signal is constant. Note that the frequency of the drive signal may change.

[0063] The driver 330 amplifies the input vibration signal. Then, the driver 330 outputs the amplified vibration signal (drive signal) to the vibrator 220 of the MEMS device 200. When the drive signal is input to the vibration area VA of the vibrator 220, a pressure is generated in the vibrator 220 whose acting direction periodically changes in the z direction. As a result, the vibrator 220 vibrates in the z direction. Note that the driver 330 does not need to amplify the vibration signal. For example, the driver 330 may be a voltage follower circuit with an amplification factor of 1. The driver 330 corresponds to a driving unit.

[0064] The conversion unit 310 converts the second electrical signal, which indicates a change in capacitance or a change in charge of the capacitor and is output from the MEMS device 200 vibrating due to the drive signal, into a voltage. The conversion unit 310 then outputs the converted second electrical signal (reference signal) to the control unit 320.

[0065] The control unit 320 uses the reference signal output from the conversion unit 310 to calculate a correction value for expanding the frequency band of the picked-up signal.

[0066] <Control Unit> 6, the control unit 320 has a memory unit 321 and a calculation unit 322. In the drawing, the memory unit 321 is written as ME. The calculation unit 322 is written as OP. The control unit 320 corresponds to a correction unit.

[0067] The storage unit 321 is a non-transient substantial storage medium that non-temporarily stores data and programs that can be read by a computer or a processor. The storage unit 321 has a volatile memory and a non-volatile memory. The storage unit 321 stores various input information and the processing results of the calculation unit 322. The storage unit 321 stores various programs and various reference values ​​for the calculation unit 322 to perform calculation processing.

[0068] The calculation unit 322 includes a processor. The calculation unit 322 stores various pieces of input information in the storage unit 321. The calculation unit 322 executes various types of calculation processing based on the information stored in the storage unit 321.

[0069] <Correction value calculation process flow> Next, the correction value calculation process will be described in detail. Fig. 7 shows the process executed by the calculation unit 322 in the correction value calculation process. The calculation unit 322 executes the correction value calculation process as a cycle task.

[0070] In step S10, the calculation unit 322 determines whether the power supply that supplies power to the piezoelectric MEMS microphone 100 has changed from off to on. If the power supply has changed from off to on, the calculation unit 322 proceeds to step S20. If the power supply is in an on or off state, the calculation unit 322 proceeds to step S30.

[0071] When the piezoelectric MEMS microphone 100 is mounted on a vehicle, the calculation unit 322 may determine whether or not the vehicle's ignition switch has been turned on from off in step S10. If the ignition switch has been turned on from off, the calculation unit 322 proceeds to step S20. If the ignition switch has not been turned on from off, the calculation unit 322 proceeds to step S30.

[0072] Also, the calculation unit 322 may determine in step S10 whether the power source of the vehicle has been changed from off to on. If the power source has been changed from off to on, the calculation unit 322 proceeds to step S20. If the power source has not been changed from off to on, the calculation unit 322 proceeds to step S30.

[0073] As a further example, the calculation unit 322 may not execute step S10. In this case, the calculation unit 322 executes the process of step S30 at the beginning of the correction value calculation process.

[0074] When the process proceeds to step S30, the calculation unit 322 acquires a picked-up sound signal. The calculation unit 322 then detects the volume (sound level) of the sound in the external environment based on the picked-up sound signal. The calculation unit 322 determines whether the sound level is lower than the quiet level stored in the storage unit 321 as a reference value.

[0075] If the sound level is lower than the quiet level, it is expected that the vibration of the transducer 220 due to the sound in the external environment will not affect the correction value. In this case, the calculation unit 322 proceeds to step S40.

[0076] If the sound level is higher than the quiet level, it is assumed that the vibration of the transducer 220 due to the sound in the external environment affects the correction value. In this case, the calculation unit 322 ends the correction value calculation process.

[0077] When the process proceeds to step S40, the calculation unit 322 acquires the temperature from the physical quantity sensor 520 provided in the MEMS device 200. The calculation unit 322 then stores this temperature in the memory unit 321. The calculation unit 322 repeatedly executes the correction value calculation process as a cycle task. For this reason, the calculation unit 322 stores a plurality of temperatures detected at different times. The calculation unit 322 calculates the temperature change of the MEMS device 200 based on the most recent acquired temperature and the past temperatures stored in the memory unit 321.

[0078] The past temperature used in the calculation of the temperature change is, for example, the temperature when the correction value stored in the memory unit 321 at the time of this processing is calculated. The force field parameters of the MEMS device 200 depend on the temperature. Therefore, if there is a large change of, for example, about 10° C. from the temperature when the correction value was calculated, it is expected that the sensitivity frequency characteristic has changed. Conversely, if there is no large change from the temperature when the correction value was calculated, it is expected that the sensitivity frequency characteristic has not changed. Note that, for example, the past temperature used in the calculation of the temperature change can be the temperature when the power supply is switched from on to off or from off to on, or the temperature before the time when the temperature change is expected to occur.

[0079] In step S40, the calculation unit 322 determines whether the calculated temperature change is greater than a temperature judgment value stored as a reference value in the storage unit 321. If the temperature change is greater than the temperature judgment value, the calculation unit 322 proceeds to step S20. If the temperature change is lower than the temperature judgment value, the calculation unit 322 ends the correction value calculation process.

[0080] The order of steps S30 and S40 is not particularly limited, and may be reversed.

[0081] When the process proceeds to step S20 after only step S10 or after steps S30 and S40, the calculation unit 322 outputs a vibration signal to the driver 330. This causes the driver 330 to output a drive signal to the MEMS device 200. As a result, the oscillator 220 is forcibly vibrated. The oscillator 220 vibrates by itself. After this, the calculation unit 322 proceeds to step S50.

[0082] When the process proceeds to step S50, the calculation unit 322 determines whether or not a predetermined time has elapsed since the output of the vibration signal. If the predetermined time has elapsed, the calculation unit 322 considers that the vibration of the oscillator 220 has stabilized. The calculation unit 322 stops outputting the vibration signal. In this way, the vibration of the oscillator 220 is damped. The calculation unit 322 obtains the behavior of the vibration at the time of damping as a reference signal. The control unit 320 calculates the resonant frequency and Q value of the oscillator 220 from the behavior of this reference signal. After this, the calculation unit 322 proceeds to step S60.

[0083] In step S50, the calculation unit 322 may gradually change the frequency of the vibration signal output to the driver 330 from a low frequency to a high frequency over time. This changes the vibration of the vibrator 220. The calculation unit 322 acquires the behavior of the vibration when it changes as a reference signal. The vibrator 220 may calculate the resonant frequency and Q value of the vibrator 220 from the reference signal.

[0084] In step S60, the calculation unit 322 calculates force field parameters based on the calculated resonant frequency and Q value, and the equivalent circuit shown in Fig. 4. In this calculation process, the calculation unit 322 sets various parameters of the sound field SF and the electric field EF to fixed values. After calculating the force field parameters, the calculation unit 322 proceeds to step S70.

[0085] When the process proceeds to step S70, the calculation unit 322 reads out the sensitivity frequency characteristic corresponding to the calculated force field parameters from the storage unit 321. At the same time, the calculation unit 322 reads out the desired sensitivity frequency characteristic from the storage unit 321. In step S70, the calculation unit 322 reads out from the storage unit 321, for example, the desired sensitivity frequency characteristic shown by the solid line in FIG. 5 and the sensitivity frequency characteristic shown by the dashed line.

[0086] As shown in Fig. 8, the storage unit 321 stores, as reference values, a desired sensitivity frequency characteristic including an ideal frequency band. The storage unit 321 stores, as reference values, a first sensitivity frequency characteristic to an n-th sensitivity frequency characteristic corresponding to force field parameters. n is an integer equal to or greater than 2. The storage unit 321 stores a relationship between the force field parameters and the sensitivity frequency characteristics. The force field parameters are not shown in Fig. 8. Note that the force field parameters depend on temperature. For this reason, the relationship of each of the first sensitivity frequency characteristic to the n-th sensitivity frequency characteristic to temperature may be stored in the storage unit 321.

[0087] When the process proceeds from step S70 to step S80, the calculation unit 322 calculates a difference value between the read sensitivity frequency characteristic and the desired sensitivity frequency characteristic. The calculation unit 322 calculates the difference value for each frequency. After this, the calculation unit 322 proceeds to step S90.

[0088] In step S90, the calculation unit 322 calculates a correction value (correction gain) for reducing the difference value of each frequency. The calculation unit 322 stores this correction gain in the storage unit 321. After this, the calculation unit 322 ends the correction value calculation process.

[0089] <Correction process flow> Next, the correction process will be described in detail. Fig. 9 shows the process executed by the calculation unit 322 in the correction process. The calculation unit 322 performs the correction process every time a picked-up sound signal (input sound) is input. In other words, the calculation unit 322 constantly performs the correction process when the piezoelectric MEMS microphone 100 is in use.

[0090] In step S110, the calculation unit 322 performs a Fourier transform on the picked-up sound signal input from the conversion unit 310. The calculation unit 322 decomposes the picked-up sound signal into waves of a plurality of frequencies. After this, the calculation unit 322 proceeds to step S120.

[0091] In step S120, the calculation unit 322 multiplies each of the waves of the multiple frequencies included in the collected signal by the correction gain for each frequency. In this way, each of the waves of the multiple frequencies is corrected. After this, the calculation unit 322 proceeds to step S130.

[0092] In step S130, the calculation unit 322 performs an inverse Fourier transform on the corrected waves of the multiple frequencies to return them to a single picked-up sound signal, and outputs the corrected picked-up sound signal to a speaker or the like.

[0093] <Action and effect> As described above, the calculation unit 322 causes the vibrator 220 to self-oscillate by the vibration signal. The calculation unit 322 then calculates a correction value (correction gain) for correcting the picked-up signal by using the reference signal input from the conversion unit 310 during the self-oscillation of the vibrator 220.

[0094] In this way, the correction value can be calculated even without a sound source, and the correction value does not depend on the characteristics of the sound source.

[0095] The calculation unit 322 calculates the correction value when the sound level of the external environment is lower than the quiet level. This prevents the calculation of an inaccurate correction value due to the sound (acoustic pressure) of the external environment. This prevents the correction of the picked-up sound signal from becoming inappropriate.

[0096] The calculation unit 322 calculates the correction value when the temperature change amount of the vibrator 220 is greater than the temperature judgment value. In other words, the calculation unit 322 stops calculating the correction value when the temperature change amount of the vibrator 220 is equal to or less than the temperature judgment value. This reduces the processing load of the calculation unit 322.

[0097] A detection area DA and a vibration area VA are included in one vibrator 220. This makes it possible to suppress an increase in the size of the MEMS device 200.

[0098] A detection area DA is located at the center of one vibrator 220, and a vibration area VA is located at the end. This makes it difficult for a change in capacitance or charge to occur in the detection area DA even if the edge side including the oblique side 220b is warped or bent due to a temperature change or the like. This prevents a decrease in the detection accuracy of the acoustic pressure due to warping or bending of the edge side including the oblique side 220b.

[0099] Second embodiment Next, a second embodiment will be described with reference to FIGS.

[0100] In the first embodiment, an example was shown in which the desired sensitivity frequency characteristic and the relationship between the force field parameter and the sensitivity frequency characteristic are stored in the storage unit 321. In contrast, in the present embodiment, the desired parameter and the relationship between the difference value between the desired parameter and the force field parameter and the correction gain are stored in the storage unit 321.

[0101] In Fig. 10, the reactance, capacitance, and resistance included in the desired force field parameters are denoted as L0, C0, and R0. Correction gains corresponding to the difference values ​​between the desired force field parameters and the actual force field parameters are denoted as G1...Gn. The desired force field parameters are the force field parameters for the desired sensitivity frequency characteristics. The difference values ​​are not shown in Fig. 10. The relationship of the correction gains to the temperature may be stored in the storage unit 321.

[0102] The calculation unit 322 of this embodiment executes the correction value calculation process shown in Fig. 11 instead of the correction value calculation process shown in Fig. 7. The difference between the correction value calculation process shown in Fig. 7 and the correction value calculation process shown in Fig. 11 is the process after step S60.

[0103] After calculating the force field parameters in step S60, the calculation unit 322 proceeds to step S210.

[0104] In step S210, calculation unit 322 reads out the desired force field parameters from storage unit 321. After that, calculation unit 322 proceeds to step S220.

[0105] In step S220, the calculation unit 322 calculates a difference between the calculated force field parameters and the read desired force field parameters, and then the calculation unit 322 proceeds to step S230.

[0106] In step S230, the calculation unit 322 reads out a correction value (correction gain) corresponding to the calculated difference value from the storage unit 321. After that, the calculation unit 322 ends the correction value calculation process.

[0107] The piezoelectric MEMS microphone 100 described in this embodiment includes components equivalent to those of the piezoelectric MEMS microphone 100 described in the first embodiment. Therefore, it goes without saying that the piezoelectric MEMS microphone 100 of this embodiment achieves the same effects as the piezoelectric MEMS microphone 100 described in the first embodiment. Therefore, the description thereof will be omitted. The description of the effects that overlap with the other embodiments and modified examples described below will be omitted.

[0108] Third embodiment Next, a third embodiment will be described with reference to FIGS.

[0109] In the first embodiment, an example was shown in which the vibrator 220 included in the MEMS device 200 has both a detection area DA and a vibration area VA. In contrast, in this embodiment, the MEMS device 200 has a first MEMS device 201 and a second MEMS device 202.

[0110] 13, the vibrator 220 included in the first MEMS device 201 has only the detection area DA of the detection area DA and the vibration area VA. The vibrator 220 included in the second MEMS device 202 has only the vibration area VA of the detection area DA and the vibration area VA.

[0111] The first MEMS device 201 and the second MEMS device 202 are each formed by microfabricating a semiconductor chip extracted from the same ingot. Therefore, the first MEMS device 201 and the second MEMS device 202 have the same physical properties. The basic configuration of each of the first MEMS device 201 and the second MEMS device 202 is the same as the basic configuration of the MEMS device 200 described in the first embodiment, although there is a difference in the presence or absence of the detection area DA and the vibration area VA described above.

[0112] 12, package 400 has a partition wall 430 in addition to substrate 410 and lid portion 420. The internal space of package 400 formed by substrate 410 and lid portion 420 is separated into a first internal space and a second internal space by partition wall 430. The first internal space and the second internal space are not connected to each other.

[0113] The package 400 corresponds to a storage section, the first internal space corresponds to a detection space, and the second internal space corresponds to a test space.

[0114] The introduction hole 410c opens in a portion of the inner surface 410a of the substrate 410 that defines the first internal space. Therefore, the introduction hole 410c communicates the first internal space with the external space. The introduction hole 410c does not communicate the second internal space with the external space. The second internal space is isolated from the external space. The second internal space is not communicated with the external space.

[0115] Due to the above-described configuration, the air in the first internal space is easily vibrated by sound generated in the external space. The air in the second internal space is less likely to vibrate by sound generated in the external space. A first MEMS device 201 is provided in this first internal space. A second MEMS device 202 is provided in the second internal space.

[0116] Due to this arrangement, the oscillator 220 included in the first MEMS device 201 is easily vibrated by sounds generated in the external space, whereas the oscillator 220 included in the second MEMS device 202 is less likely to vibrate by sounds generated in the external space.

[0117] Therefore, even if the sound level in the external environment is higher than the quiet sound level, the correction gain can be calculated by forcibly vibrating the second MEMS device 202. In the case of this embodiment, for example, step S30 shown in Figs. 7 and 11 can be omitted.

[0118] (First Modification) In the first embodiment, an example has been shown in which one MEMS device 200 is mounted on the substrate 410. However, a plurality of MEMS devices 200 may be mounted on the substrate 410 to configure an array microphone.

[0119] (Second Modification) In each embodiment, an example has been shown in which the calculation unit 322 performs the correction value calculation process as a cycle task. In addition, in step S10 of the correction value calculation process, if the power supply is in an on state or an off state, the calculation unit 322 proceeds to step S30. Before proceeding to step S30, the calculation unit 322 may determine whether the power supply is in an on state or an off state.

[0120] When the power is on, it is assumed that the piezoelectric MEMS microphone 100 is in use and the sound level of the external environment is higher than the quiet level, so in this case, the calculation unit 322 may determine to lengthen the cycle period of the correction value calculation process.

[0121] When the power is off, the piezoelectric MEMS microphone 100 is not in use, and it is expected that the sound level of the external environment is lower than the quiet level. Therefore, in this case, the calculation unit 322 may decide to shorten the cycle period of the correction value calculation process.

[0122] In addition, it is difficult to imagine that the physical parameters of the MEMS device 200 will change immediately after the correction values ​​are calculated. For this reason, the calculation unit 322 may be configured not to newly execute the correction value calculation process unless a predetermined time has elapsed since the correction values ​​were calculated. This reduces the processing load on the calculation unit 322.

[0123] (Third Modification) In each embodiment, an example has been shown in which the calculation unit 322 proceeds to step S20 when the power is turned on from off in step S10 of the correction value calculation process. In this case, the calculation unit 322 calculates a correction value regardless of the sound level of the external environment. Therefore, this correction value may be inappropriate. In this way, when the process of step S20 is executed through only step S10, the calculation unit 322 may compare the calculated correction value with the correction value stored in the storage unit 321. Then, when the difference between the two exceeds a threshold value stored as a reference value in the storage unit 321, the calculation unit 322 may determine that the calculated correction value is inappropriate.

[0124] (Other variations) In each embodiment, an example has been shown in which a gap is formed between a plurality of transducers 220. However, a defining portion may be supported on support base 210 together with transducers 220. A gap may be formed between this defining portion and transducer 220.

[0125] In each embodiment, an example in which the transducer 220 forms a tapered triangle has been shown. However, there is no particular limitation on the shape of the transducer 220. For example, the transducer 220 may form a rectangle.

[0126] In each embodiment, an example in which the number of transducers 220 is four has been shown. However, the number of transducers 220 is not particularly limited. The number of transducers 220 may be one.

[0127] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, although various combinations and forms are shown in the present disclosure, other combinations and forms including only one element, more than one element, or less than one element are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0128] Reference Signs List 100: piezoelectric MEMS microphone, 200: MEMS device, 201: first MEMS device, 202: second MEMS device, 220: transducer, 300: ASIC, 320: control unit, 321: storage unit, 322: calculation unit, 330: driver, 400: package, DA: detection area, VA: vibration area< / asic>

Claims

1. A vibration device (200) that outputs a first electrical signal in response to an acoustic pressure; A drive unit (330) that vibrates the vibration device by a drive signal; a correction unit (320) that calculates a correction value for correcting the first electrical signal based on a second electrical signal output from the vibration device when the vibration device is vibrated by the drive signal, The correction unit calculates the correction value using the second electrical signal in a state in which vibration of the vibration device due to the acoustic pressure does not affect the correction value.

2. The microphone according to claim 1 , wherein the correction unit has a calculation unit (322) that calculates parameters of an equivalent circuit that indicates characteristics of the vibration device from the second electrical signal.

3. The correction unit has a storage unit (321) in which a relationship between the parameter and the sensitivity frequency characteristic of the vibration device, and a desired sensitivity frequency characteristic of the vibration device are stored, The microphone according to claim 2, wherein the calculation unit reads out from the memory unit the sensitivity frequency characteristic and the desired sensitivity frequency characteristic corresponding to the calculated parameters, and calculates the correction value based on a difference value between the read sensitivity frequency characteristic and the desired sensitivity frequency characteristic.

4. the correction unit has a storage unit (321) in which a desired parameter of the equivalent circuit and the correction value corresponding to a difference between the parameter and the desired parameter are stored; The microphone according to claim 2 , wherein the calculation unit reads out the desired parameter from the memory unit, calculates the difference value based on the calculated parameter and the read out desired parameter, and reads out the correction value corresponding to the difference value from the memory unit.

5. The microphone according to any one of claims 1 to 4, wherein the driving section outputs the driving signal to the vibration device when a sound level indicated by the first electrical signal is lower than a quiet sound level.

6. The microphone according to any one of claims 1 to 5, wherein the driving section outputs the driving signal to the vibration device when an amount of change in temperature of the vibration device is greater than a temperature determination value.

7. The microphone described in any one of claims 1 to 6, wherein the vibration device has a vibrator (220) that outputs the first electrical signal in response to the acoustic pressure and outputs the second electrical signal when vibrated by the drive signal.

8. The microphone described in any one of claims 1 to 6, wherein the vibration device has a first detection unit (DA) that outputs the first electrical signal corresponding to the acoustic pressure, and a second detection unit (VA) that is vibrated by the drive signal.

9. The microphone of claim 8 , wherein the vibration device includes a vibrator (220) having the first and second detection portions, respectively.

10. A storage section (400) having a detection space communicating with an external space and a test space not communicating with the external space and the detection space, The first detection portion is provided in the detection space, The microphone according to claim 8 , wherein the second detection portion is provided in the test space.

11. The microphone according to any one of claims 1 to 10, wherein the vibration device includes a piezoelectric material having a piezoelectric constant higher than that of aluminum nitride.

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