Patent ID: 12241908

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some preferred embodiments of the present disclosure will hereinafter be described in detail using the drawings. It should be noted that the embodiments described below do not unreasonably limit the content of the present disclosure as set forth in the appended claims. Further, all of the constituents described below are not necessarily essential elements of the present disclosure.

1. First Embodiment

1-1. Structure of Sensor Module

First, an example of a structure of a sensor module according to a first embodiment will be described.

FIG.1is a perspective view of the sensor module1when viewed from a mounting target surface to which the sensor module1is fixed. In the following description, the description is presented defining a direction along a long side of the sensor module1forming a rectangular shape in a plan view as an X-axis direction, a direction perpendicular to the X-axis direction in the plan view as a Y-axis direction, and a thickness direction of the sensor module1as a Z-axis direction.

The sensor module1is a rectangular solid having a rectangular planar shape, and has long sides along the X-axis direction, and short sides along the Y-axis direction perpendicular to the X-axis direction. In two positions in the vicinities of end portions of one of the long sides, and one position in a central portion of the other of the long sides, there are formed screw holes103. The sensor module1is used in a state in which fixation screws are threaded into the respective screw holes103at the three positions to fix the sensor module1to the mounting target surface of a mounting target body of a structure such as a building, a bulletin board, or a variety of types of devices.

As shown inFIG.1, a surface of the sensor module1viewed from the mounting target surface is provided with an opening121. Inside the opening121, there is disposed a connector116of a plug type. The connector116has a plurality of pins arranged in two rows, and the plurality of pins is arranged in the Y-axis direction in each of the rows. To the connector116, there is coupled a connector of a socket type not shown from the mounting target body, whereby transmission and reception of an electrical signal such as a drive voltage or detection data of the sensor module1are performed.

FIG.2is an exploded perspective view of the sensor module1. As shown inFIG.2, the sensor module1is constituted by a container101, a lid102, a seal member141, a circuit board115, and so on. In a detailed description, the sensor module1has a configuration in which the circuit board115is attached inside the container101via a fixation member130, and an opening of the container101is covered with the lid102via the seal member141with cushioning properties.

The container101is a housing container for the circuit board115formed to have a box-like shape having an internal space using, for example, aluminum. An outer shape of the container101is a rectangular solid having a substantially rectangular planar shape similarly to the overall shape of the sensor module1described above, and fixation protrusions104are disposed at two positions in the vicinities of both end portions of one of the long sides and one position in a central portion of the other of the long sides. The screw holes103are provided to the fixation protrusions104, respectively.

The container101is shaped like a box having a rectangular solid outer shape, and an opening at one side. The inside of the container101is an internal space surrounded by a bottom wall112and a side wall111. In other words, the container101is shaped like a box having one face opposed to the bottom wall112as an opening face123, the outer edge of the circuit board115is arranged along an inner surface122of the side wall111, and the lid102is fixed so as to cover the opening. On the opening face123, there are erected the fixation protrusions104at the two positions in the vicinities of the both end portions of one of the long sides of the container101, and the one position in the central portion of the other of the long sides. Further, an upper surface, namely a surface exposed toward the −Z direction, of each of the fixation protrusions104projects from the upper surface of the container101.

Further, in the internal space of the container101, there is disposed a protrusion129protruding from the side wall111toward the internal space from the bottom wall112to the opening face123in a central portion of the one of the long sides opposed to the fixation protrusion104disposed in the central portion of the other of the long sides. An upper surface of the protrusion129is provided with an internal thread174. The lid102is fixed to the container101via the seal member141with a screw172inserted into a through hole176and the internal thread174. It should be noted that the protrusion129and the fixation protrusion104are disposed at positions opposed to constrictions133,134of the circuit board115described later, respectively.

In the internal space of the container101, there are disposed a first pedestal127and second pedestals125each protruding like a step raised toward the opening face123from the bottom wall112. The first pedestal127is disposed at a position opposed an arrangement area of the connector116of the plug type attached to the circuit board115. The first pedestal127is provided with an opening121shown inFIG.1, and the connector116of the plug type is inserted into the opening121. The first pedestal127functions as a pedestal for fixing the circuit board115to the container101.

The second pedestals125are located at an opposite side to the first pedestal127with respect to the fixation protrusion104and the protrusion129located in the central portions of the long sides, and are disposed in the vicinities of the fixation protrusion104and the protrusion129. The second pedestals125function as pedestals for fixing the circuit board115to the container101at the opposite side to the first pedestal127with respect to the fixation protrusion104and the protrusion129.

It should be noted that although the description is presented assuming that the outer shape of the container101is shaped like the box which is the rectangular solid having the substantially rectangular planar shape, and which does not have a lid, but this is not a limitation, and the planar shape of the outer shape of the container101can be a square, a hexagon, a octagon, or the like. Further, in the planar shape of the outer shape of the container101, corners of vertex portions of the polygon can be chamfered, and further, it is possible to adopt a planar shape in which any one of the sides is formed of a curved line. Further, the planar shape of the inside of the container101is not limited to the shape described above, and can also be another shape. Further, the planar shapes of the outer shape and the inside of the container101can be shapes similar to each other, or not required to be the shapes similar to each other.

The circuit board115is a multilayer board provided with a plurality of through holes and so on, and there is used, for example, a glass epoxy board, a composite board, or a ceramic board.

The circuit board115has a second surface115rat the bottom wall112side, and a first surface115fhaving an obverse-reverse relationship with the second surface115r. On the first surface115fof the circuit board115, there are mounted the vibration rectification error correction device2, three physical quantity sensors200, other electronic components not shown, and so on. Further, on the second surface115rof the circuit board115, there is mounted the connector116. It should be noted that although an illustration and an explanation thereof will be omitted, the circuit board115can be provided with other interconnections, terminal electrodes, and so on.

The circuit board115is provided with the constrictions133,134where the outer edge of the circuit board115is constricted in a central portion in the X-axis direction along the long sides of the container101in the plan view. The constrictions133,134are disposed at both sides in the Y-axis direction of the circuit board115in the plan view, and are constricted from the outer edges of the circuit board115toward the center thereof. Further, the constrictions133,134are disposed so as to be opposed to the protrusion129and the fixation protrusion104of the container101, respectively.

The circuit board115is inserted in the internal space of the container101with the second surface115rfacing to the first pedestal127and the second pedestals125. Further, the circuit board115is supported by the container101with the first pedestal127and the second pedestals125.

The three physical quantity sensors200are each a frequency variation sensor the output signal of which varies in frequency in accordance with a physical quantity to be applied. Among the three physical quantity sensors200, the physical quantity sensor200X detects a physical quantity in the X-axis direction, the physical quantity sensor200Y detects a physical quantity in the Y-axis direction, and the physical quantity sensor200Z detects a physical quantity in the Z-axis direction. Specifically, the physical quantity sensor200X is erected so that obverse and reverse surfaces of the package face to the X-axis direction, and so that a side surface thereof is opposed to the first surface115fof the circuit board115. Further, the physical quantity sensor200X outputs a signal corresponding to the physical quantity in the X-axis direction thus detected. The physical quantity sensor200Y is erected so that obverse and reverse surfaces of the package face to the Y-axis direction, and so that a side surface thereof is opposed to the first surface115fof the circuit board115. Further, the physical quantity sensor200Y outputs a signal corresponding to the physical quantity in the Y-axis direction thus detected. The physical quantity sensor200Z is disposed so that obverse and reverse surfaces of the package face to the Z-axis direction, namely the obverse and reverse surfaces of the package are opposed straight to the first surface115fof the circuit board115. Further, the physical quantity sensor200Z outputs a signal corresponding to the physical quantity in the Z-axis direction thus detected.

The vibration rectification error correction device2is electrically coupled to the physical quantity sensors200X,200Y, and200Z via interconnections and electronic components not shown. Further, the vibration rectification error correction device2generates physical quantity data reduced in vibration rectification error based on the output signals of the physical quantity sensors200X,200Y, and200Z.

1-2. Structure of Physical Quantity Sensor

Then, an example of a structure of each of the physical quantity sensors200will be described citing when the physical quantity sensor200is an acceleration sensor as an example. The three physical quantity sensors200shown inFIG.2, namely the physical quantity sensors200X,200Y, and200Z can be the same in structure as each other.

FIG.3is a perspective view of the physical quantity sensor200,FIG.4is a plan view of the physical quantity sensor200, andFIG.5is a cross-sectional view in a line P1-P1inFIG.4. It should be noted thatFIG.3throughFIG.5each illustrate only an inside of the package of the physical quantity sensor200. In each of the following drawings, an x axis, a y axis, and a z axis are illustrated as three axes perpendicular to each other for the sake of convenience of explanation. Further, a plan view viewed from the z-axis direction as a thickness direction of extending parts38a,38bis also referred to simply as a “plan view” in the following description for the sake of convenience of explanation.

As shown inFIG.3throughFIG.5, the physical quantity sensor200has a substrate part5and four weights50,52,54, and56.

The substrate part5is provided with a base10, a joint12, a movable part13, two support parts30a,30b, and a physical quantity detection element40, wherein the base10has principal surfaces10a,10bextending in the x-axis direction and facing to respective directions opposite to each other, the joint12extends from the base10in the y-axis direction, the movable part13extends from the joint12toward the opposite direction to the base10so as to form a rectangular shape, the two support parts30a,30bextend along the outer edges of the movable part13from the both ends in the x-axis direction of the base10, respectively, and the physical quantity detection element40is bridged from the base10to the movable part13and is bonded to the base10and the movable part13.

In the two support parts30a,30b, the support part30aextends along the y axis with a gap32awith the movable part13, and is provided with a bonding part36afor fixing the support part30a, and the extending part38aextending along the x axis with a gap32cwith the movable part13. In other words, the support part30aextends along the y axis with the gap32awith the movable part13, and is provided with the extending part38aextending along the x axis with the gap32cwith the movable part13, and is provided with the bonding part36adisposed between the support part30aand the extending part38a. Further, the support part30bextends along the y axis with a gap32bwith the movable part13, and is provided with a bonding part36bfor fixing the support part30b, and the extending part38bextending along the x axis with the gap32cwith the movable part13. In other words, the support part30bextends along the y axis with the gap32bwith the movable part13, and is provided with the extending part38bextending along the x axis with the gap32cwith the movable part13, and is provided with the bonding part36bdisposed between the support part30band the extending part38b.

It should be noted that the bonding parts36a,36bprovided respectively to the support parts30a,30bare for mounting the substrate part5of the physical quantity sensor200on an external member such as a package. Further, the base10, the joint12, the movable part13, the support parts30a,30b, and the extending parts38a,38bcan be formed integrally with each other.

The movable part13is surrounded by the support parts30a,30band the base10, and is coupled to the base10via the joint12to be in a cantilevered state. Further, the movable part13has principal surfaces13a,13bfacing to the directions opposite to each other, a side surface13cextending along the support part30a, and a side surface13dextending along the support part30b. The principal surface13ais a surface facing to the same side as the principal surface10aof the base10, and the principal surface13bis a surface facing to the same side as the principal surface10bof the base10.

The joint12is disposed between the base10and the movable part13to couple the base10and the movable part13to each other. The joint12is formed to have a thickness thinner than the thickness of the base10and the thickness of the movable part13. The joint12has grooves12a,12b. These grooves12a,12bare formed along the x axis, and when the movable part13is displaced with respect to the base10, the grooves12a,12bof the joint12each function as a pivot, namely an intermediate hinge. Such a joint12and such a movable part13function as a cantilever.

Further, to the surface continuing from the principal surface10aof the base10to the principal surface13aof the movable part13, there is fixed the physical quantity detection element40with a joining material60. The fixation positions of the physical quantity detection element40are two places, namely central positions in the x-axis direction of the principal surface10aand the principal surface13a, respectively.

The physical quantity detection element40has a base part42afixed to the principal surface10aof the base10with the joining material60, a base part42bfixed to the principal surface13aof the movable part13with the joining material60, and vibrating beams41a,41blocated between the base part42aand the base part42band configured to detect a physical quantity. In this case, the shape of each of the vibrating beams41a,41bis a prismatic shape, and when a drive signal as an alternating-current voltage is applied to excitation electrodes not shown respectively provided to the vibrating beams41a,41b, the vibrating beams41a,41bmake a flexural vibration along the x axis so as to get away from each other and come closer to each other. In other words, the physical quantity detection element40is a tuning-fork vibrator element.

On the base part42aof the physical quantity detection element40, there are disposed extraction electrodes44a,44b. These extraction electrodes44a,44bare electrically coupled to excitation electrodes not shown provided to the vibrating beams41a,41b. The extraction electrodes44a,44bare electrically coupled to coupling terminals46a,46bprovided to the principal surface10aof the base10with metal wires48. The coupling terminals46a,46bare electrically coupled respectively to external coupling terminals49a,49bwith interconnections not shown. The external coupling terminals49a,49bare disposed at the side of the principal surface10bof the base10as a surface at which the physical quantity sensor200is mounted on the package or the like so as to overlap package bonding parts34in the plan view. The package bonding parts34are for mounting the substrate part5of the physical quantity sensor200on the external member such as the package, and are disposed at two places, namely end portions at the both end sides in the x-axis direction of the base10.

The physical quantity detection element40is formed by patterning a crystal substrate, which has been carved out from a crystal raw stone at a predetermined angle, using a photolithography process and an etching process. In this case, it is desirable for the physical quantity detection element40to be formed of the same material as the material of the base10and the movable part13taking the reduction of the difference in linear expansion coefficient between the base10and the movable part13into consideration.

The weights50,52,54, and56each have a rectangular planar shape, and are provided to the movable part13. The weights50,52are fixed to the principal surface13aof the movable part13with a joining member62, and the weights54,56are fixed to the principal surface13bof the movable part13with a joining member62. Here, one side of the weight50fixed to the principal surface13a, namely a marginal side of the rectangular shape, is aligned in direction with the side surface13cof the movable part13in the plan view, and at the same time, another side thereof is aligned in direction with a side surface31dof the extending part38a. Due to such alignment in direction, the weight50is disposed at the side of the side surface13cof the movable part13, and the weight50and the extending part38aare disposed so as to overlap each other in the plan view. Similarly, one side of the weight52fixed to the principal surface13a, namely a marginal side of the rectangular shape, is aligned in direction with the side surface13dof the movable part13in the plan view, and at the same time, another side thereof is aligned in direction with a side surface31eof the extending part38b. Thus, the weight52is disposed at a side of the side surface13dof the movable part13, and the weight52and the extending part38bare disposed so as to overlap each other in the plan view. One side of the weight54having a rectangular shape fixed to the principal surface13bis aligned in direction with the side surface13cof the movable part13in the plan view, and at the same time, another side thereof is aligned in direction with the side surface31dof the extending part38a. Thus, the weight54is disposed at the side of the side surface13cof the movable part13, and the weight54and the extending part38aare disposed so as to overlap each other in the plan view. Similarly, one side of the weight56having a rectangular shape fixed to the principal surface13bis aligned in direction with the side surface13dof the movable part13in the plan view, and at the same time, another side thereof is aligned in direction with the side surface31eof the extending part38b. Thus, the weight56is disposed at a side of the side surface13dof the movable part13, and the weight56and the extending part38bare disposed so as to overlap each other in the plan view.

In the weights50,52,54, and56arranged in such a manner, the weights50,52are arranged symmetrically about the physical quantity detection element40, and the weights54,56are arranged so as to respectively overlap the weights50,52in the plan view. These weights50,52,54, and56are fixed to the movable part13with the joining members62disposed at respective barycentric positions of the weights50,52,54, and56. Further, since the weights50,54overlap the extending part38a, and the weights52,56overlap the extending part38bin the plan view, when an excessive amount of the physical quantity is applied, the weights50,52,54, and56have contact with the extending parts38a,38b, and thus, it is possible to suppress the displacements of the weights50,52,54, and56.

The joining members62are each formed of a silicone resin-based thermosetting adhesive or the like. The joining members62are applied in two places of each of the principal surface13aand the principal surface13bof the movable part13, and then heated to be cured after the weights50,52,54, and56are mounted thereon, to thereby fix the weights50,52,54, and56to the movable part13. It should be noted that the joining surfaces opposed to the principal surface13aand the principal surface13bof the movable part13of the weights50,52,54, and56are each a rough surface. Thus, when fixing the weights50,52,54, and56to the movable part13, the joining area in each of the joining surfaces increases, and thus, the joining strength can be increased.

As shown inFIG.6, when acceleration toward the +z direction indicated by an arrow α1is applied to the physical quantity sensor200configured as described above, a force acts on the movable part13toward the −z direction, and the movable part13is displaced toward the −z direction taking the joint12as a pivot point. Thus, a force in the direction in which the base part42aand the base part42bget away from each other along the y axis is applied to the physical quantity detection element40, and tensile stress is generated in the vibrating beams41a,41b. Therefore, a frequency with which the vibrating beams41a,41bvibrate rises.

In contrast, as shown inFIG.7, when acceleration toward the −z direction indicated by an arrow α2is applied to the physical quantity sensor200, a force acts on the movable part13toward the +z direction, and the movable part13is displaced toward the +z direction taking the joint12as a pivot point. Thus, a force in the direction in which the base part42aand the base part42bcome close to each other along the y axis is applied to the physical quantity detection element40, and compressive stress is generated in the vibrating beams41a,41b. Therefore, a frequency with which the vibrating beams41a,41bvibrate falls.

When the frequency with which the vibrating beams41a,41bvibrate varies in accordance with the acceleration, a frequency of a signal output from the external coupling terminals49a,49bof the physical quantity sensor200varies. The sensor module1is capable of calculate the value of the acceleration applied to the physical quantity sensor200based on the variation in frequency of the output signal of the physical quantity sensor200.

It should be noted that in order to increase the detection accuracy of the acceleration as the physical quantity, it is desirable for the joint12for coupling the base10as a stationary part and the movable part13to each other to be formed of quartz crystal as a material high in Q-value. For example, the base10, the support parts30a,30b, and the movable part13can be formed of a quartz crystal plate, and the grooves12a,12bof the joint12can be formed by performing a half-etching process from the both surfaces of the crystal plate.

1-3. Functional Configuration of Sensor Module

FIG.8is a functional block diagram of the sensor module1according to the first embodiment. As described above, the sensor module1is provided with the physical quantity sensors200X,200Y, and200Z, and the vibration rectification error correction device2.

The vibration rectification error correction device2includes oscillation circuits201X,201Y, and201Z, frequency ratio measurement circuits202X,202Y, and202Z, a micro-control unit210, a storage220, and an interface circuit230.

The oscillation circuit201X amplifies the output signal of the physical quantity sensor200X to generate a drive signal, and then applies the drive signal to the physical quantity sensor200X. Due to the drive signal, the vibrating beams41a,41bof the physical quantity sensor200X vibrate with the frequency corresponding to the acceleration in the X-axis direction, and the signal with that frequency is output from the physical quantity sensor200X. Further, the oscillation circuit201X outputs a measurement target signal SIN_X as a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200X to the frequency ratio measurement circuit202X. The measurement target signal SIN_X is a signal based on the output signal of the physical quantity sensor200X.

Similarly, the oscillation circuit201Y amplifies the output signal of the physical quantity sensor200Y to generate a drive signal, and then applies the drive signal to the physical quantity sensor200Y. Due to the drive signal, the vibrating beams41a,41bof the physical quantity sensor200Y vibrate with the frequency corresponding to the acceleration in the Y-axis direction, and the signal with that frequency is output from the physical quantity sensor200Y. Further, the oscillation circuit201Y outputs a measurement target signal SIN_Y as a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200Y to the frequency ratio measurement circuit202Y. The measurement target signal SIN_Y is a signal based on the output signal of the physical quantity sensor200Y.

Similarly, the oscillation circuit201Z amplifies the output signal of the physical quantity sensor200Z to generate a drive signal, and then applies the drive signal to the physical quantity sensor200Z. Due to the drive signal, the vibrating beams41a,41bof the physical quantity sensor200Z vibrate with the frequency corresponding to the acceleration in the Z-axis direction, and the signal with that frequency is output from the physical quantity sensor200Z. Further, the oscillation circuit201Z outputs a measurement target signal SIN_Z as a rectangular wave signal obtained by amplifying the output signal of the physical quantity sensor200Z to the frequency ratio measurement circuit202Z. The measurement target signal SIN_Z is a signal based on the output signal of the physical quantity sensor200Z.

A reference signal generation circuit203generates and then outputs a reference signal CLK with a constant frequency. In the present embodiment, the frequency of the reference signal CLK is higher than the frequencies of the measurement target signal SIN_X, SIN_Y, and SIN_Z. It is preferable for the reference signal CLK to be high in frequency accuracy, and the reference signal generation circuit203can be, for example, a temperature-compensated crystal oscillator.

The frequency ratio measurement circuit202X counts the number of pulses of the reference signal CLK included in a predetermined period of the measurement target signal SIN_X as a signal based on the signal output from the oscillation circuit201X, and then outputs a count value CNT_X. The count value CNT_X is a reciprocal count value corresponding to a frequency ratio between the measurement target signal SIN_X and the reference signal CLK.

The frequency ratio measurement circuit202Y counts the number of pulses of the reference signal CLK included in a predetermined period of the measurement target signal SIN_Y output from the oscillation circuit201Y, and then outputs a count value CNT_Y. The count value CNT_Y is a reciprocal count value corresponding to a frequency ratio between the measurement target signal SIN_Y and the reference signal CLK.

The frequency ratio measurement circuit202Z counts the number of pulses of the reference signal CLK included in a predetermined period of the measurement target signal SIN_Z output from the oscillation circuit201Z, and then outputs a count value CNT_Z. The count value CNT_Z is a reciprocal count value corresponding to a frequency ratio between the measurement target signal SIN_Z and the reference signal CLK.

To each of the frequency ratio measurement circuits202X,202Y, and202Z, there is input a first frequency signal CLK1asynchronous with the reference signal CLK. The first frequency signal CLK1is a signal based on an external trigger signal EXTRG input from the outside of the sensor module1. The external trigger signal EXTRG is output from, for example, a processing device3outside the sensor module1. The first frequency signal CLK1can be, for example, the external trigger signal EXTRG itself, or can also be a signal obtained by buffering the external trigger signal EXTRG. Then, the frequency ratio measurement circuits202X,202Y, and202Z respectively output the count values CNT_X, CNT_Y, and CNT_Z in sync with the first frequency signal CLK1.

The storage220is for storing a program and data, and can include a volatile memory such as an SRAM or a DRAM. SRAM is an abbreviation of Static Random Access Memory, and DRAM is an abbreviation of Dynamic Random Access Memory. Further, the storage220can include a nonvolatile memory such as a semiconductor memory such as an EEPROM or a flash memory, a magnetic storage device such as a hard disk drive, or an optical storage device such as an optical disk drive. The EEPROM is an abbreviation of Electrically Erasable Programmable Read Only Memory.

The micro-control unit210operates in sync with the reference signal CLK, and executes a program not shown stored in the storage220to thereby perform predetermined arithmetic processing and control processing. For example, the micro-control unit210measures the physical quantities detected by the physical quantity sensors200X,200Y, and200Z based on the count value CNT_X output from the frequency ratio measurement circuit202X, the count value CNT_Y output from the frequency ratio measurement circuit202Y, and the count value CNT_Z output from the frequency ratio measurement circuit202Z, respectively. Specifically, the micro-control unit210converts the count value CNT_X, the count value CNT_Y, and the count value CNT_Z into the measurement value of the physical quantity in the X-axis direction, the measurement value of the physical quantity in the Y-axis direction, and the measurement value of the physical quantity in the Z-axis direction, respectively. For example, the storage220can store table information which defines a corresponding relationship between the count value and the measurement value of the physical quantity, or information of a relational expression between the count value and the measurement value of the physical quantity, and the micro-control unit210can convert the count value into the measurement value of the physical quantity with reference to such information.

It is possible for the micro-control unit210to transmit the measurement value of the physical quantity in the X-axis direction, the measurement value of the physical quantity in the Y-axis direction, and the measurement value of the physical quantity in the Z-axis direction to the processing device3via the interface circuit230. Alternatively, it is possible to adopt a configuration in which the micro-control unit210writes the measurement value of the physical quantity in the X-axis direction, the measurement value of the physical quantity in the Y-axis direction, and the measurement value of the physical quantity in the Z-axis direction into the storage220, and then the processing device3retrieves the measurement values via the interface circuit230.

It should be noted that since the frequency ratio measurement circuits202X,202Y, and202Z are the same in configuration and operation as each other, arbitrary one of the frequency ratio measurement circuits202X,202Y, and202Z will hereinafter be referred to as a frequency ratio measurement circuit202. Further, arbitrary one of the measurement target signals SIN_X, SIN_Y, and SIN_Z to be input to the frequency ratio measurement circuit202will be referred to as a measurement target signal SIN, and arbitrary one of the count values CNT_X, CNT_Y, and CNT_Z to be output from the frequency ratio measurement circuit202will be referred to as a count value CNT.

1-4. Vibration Rectification Error

The vibration rectification error corresponds to a DC offset caused when performing rectification due to nonlinearity of a response of the sensor module1with respect to the vibration, and is observed as an abnormal shift of an output offset of the sensor module1. In an application in which a DC output of the sensor module1directly becomes the measurement target such as a tiltmeter using the sensor module1, the vibration rectification error becomes a factor of a serious measurement error. As main mechanisms of causing the vibration rectification error, there can be cited three mechanisms, namely [1] a vibration rectification error due to an asymmetric rail, [2] a vibration rectification error due to nonlinearity in scale factor, and [3] a vibration rectification error due to a structural resonance of the physical quantity sensor200.

[1] Vibration Rectification Error Caused by Asymmetric Rail

When a sensitivity axis of the physical quantity sensor200is set in a gravitational acceleration direction, in the measurement value of the sensor module1, there occurs an offset corresponding to the fact that the gravitational acceleration is 1 g=9.8 m/s2. For example, when a dynamic range of the physical quantity sensor200is 2 g, the vibration which can be measured without clipping is up to a vibration of 1 g. When a vibration exceeding 1 g is applied in this state, the clipping occurs in an asymmetric manner, and therefore, the vibration rectification error is included in the measurement value as a result.

For example, when the dynamic range is as broad as 15 g, the clipping hardly matters in an ordinary use environment. On the other hand, the physical quantity sensor200incorporates a physical protection mechanism for the purpose of preventing breakage of the physical quantity detection element40, and since the protection mechanism works when the vibration level exceeds a certain threshold value, the clopping occurs. In order to prevent the above, it becomes necessary to devise the attachment for arranging the sensor module1to perform a countermeasure such as damping of a vibration in a resonance frequency band.

[2] Vibration Rectification Error Caused by Nonlinearity in Scale Factor

FIG.9is a diagram for explaining in principle that the vibration rectification error is caused by an output waveform distortion. InFIG.9, solid lines represent a vibration waveform of a sine wave and a waveform obtained by smoothing the vibration waveform, and dotted lines represent a vibration waveform vertically asymmetric about the vibration center and a waveform obtained by smoothing that vibration waveform. The smoothed waveform represented by the solid line takes 0 on the one hand, the smoothed waveform represented by the dotted line takes a negative value, and thus, an offset occurs when performing the smoothing.

The physical quantity sensor200is a frequency variation sensor, and the count value CNT corresponding to the frequency ratio between the measurement target signal SIN and the reference signal CLK is a reciprocal count value. A relationship between the acceleration to be applied to the physical quantity sensor200and the reciprocal count value has nonlinearity. A dotted line shown inFIG.10represents nonlinearity between the acceleration to be applied and the reciprocal count value. Further, a dotted line shown inFIG.11represents nonlinearity between the acceleration to be applied and the oscillation frequency of the physical quantity sensor200. Further, a dotted line shown inFIG.12represents nonlinearity between the oscillation frequency of the physical quantity sensor200and the reciprocal count value. A dotted line shown inFIG.10is obtained by combining the dotted line shown inFIG.11and the dotted line shown inFIG.12.

Here, by correcting the relationship between the oscillation frequency and the reciprocal count value as represented by a solid line shown inFIG.12, it is possible to approximate the relationship between the acceleration and the reciprocal count value to a linear relationship as represented by a solid line shown inFIG.10. Specifically, it is possible for the micro-control unit210described above to correct the count value CNT using a correction function expressed by Formula (1).
Y={c−d}2(1)

In Formula (1), c represents the count value which has not been corrected, and which corresponds to the dotted line shown inFIG.10, Y represents the count value which has been corrected, and which corresponds to the solid line shown inFIG.10, and d represents a coefficient for deciding a degree of the correction shown inFIG.12. For example, the coefficient d is stored in the storage220, or is set by the processing device3.

[3] Vibration Rectification Error Caused by Cantilever Resonance

As a detection principle of acceleration, the physical quantity sensor200transmits a distortion in a cantilever attached with a weight due to the acceleration to the physical quantity detection element40as a double tuning-fork vibrator to thereby vary tensile force acting on the physical quantity detection element40, and thus, varies the oscillation frequency. Therefore, the physical quantity detection element40has the resonance frequency caused by a structure of the cantilever, and when the cantilever resonance is exited, an inherent vibration rectification error occurs. The cantilever resonance has a frequency higher than the frequency band corresponding to a range of detectable acceleration, and a vibration component of the cantilever resonance is removed by an internal low-pass filter of the vibration rectification error correction device2, but the vibration rectification error occurs as a bias offset reflecting the nonlinearity of the vibration. As an amplitude of the cantilever resonance increases, the nonlinearity in the output waveform of the physical quantity sensor200increases, and thus, the vibration rectification error also increases. Therefore, reducing the vibration rectification error caused by the cantilever resonance will be the key issue.

In the present embodiment, since the frequency ratio measurement circuit202is of the reciprocal count type which counts the number of pulses of the reference signal CLK included in the predetermined period of the measurement target signal SIN, the timing at which the count value is obtained is synchronized with the measurement target signal SIN. On the other hand, the count value CNT output from the frequency ratio measurement circuit202is required to be synchronized with the first frequency signal CLK1, and since the timing at which the count value of the number of pulses of the reference signal CLK is obtained and the first frequency signal CLK1are not synchronized with each other, resampling becomes necessary. In the frequency ratio measurement circuit202, by devising the configuration necessary for the resampling, it is possible to generate the count value CNT in which the vibration rectification error caused by the cantilever resonance is corrected.

1-5. Configuration of Frequency Ratio Measurement Circuit

The frequency ratio measurement circuit202measures a frequency ratio between the measurement target signal SIN and the reference signal CLK using the reciprocal count method.FIG.13is a diagram showing a configuration example of the frequency ratio measurement circuit202in the first embodiment. As shown inFIG.13, the frequency ratio measurement circuit202is provided with a frequency delta-sigma modulation circuit300, a first low-pass filter310, a latch circuit320, and a second low-pass filter330.

The frequency delta-sigma modulation circuit300performs the frequency delta-sigma modulation on the reference signal CLK using the measurement target signal SIN to generate a frequency delta-sigma modulation signal. The frequency delta-sigma modulation circuit300is provided with a counter301, a latch circuit302, a latch circuit303, and a subtractor304. The counter301counts rising edges of the reference signal CLK to output a count value CT0. The latch circuit302latches the count value CT0in sync with a rising edge of the measurement target signal SIN to hold the count value CT0. The latch circuit303latches the count value held by the latch circuit302in sync with a rising edge of the measurement target signal SIN to hold the count value. The subtractor304subtracts the count value held by the latch circuit303from the count value held by the latch circuit302to generate and then output a count value CT1. The count value CT1is the frequency delta-sigma modulation signal to be generated by the frequency delta-sigma modulation circuit300.

The frequency delta-sigma modulation circuit300is also called a first-order frequency delta-sigma modulator, and latches the count value of the number of pulses of the reference signal CLK twice with the measurement target signal SIN, and sequentially holds the count value of the number of pulses of the reference signal CLK using the rising edges of the measurement target signal SIN as the triggers. Here, there is presented the explanation assuming that the frequency delta-sigma modulation circuit300performs the latch action with the rising edge of the measurement target signal SIN, but it is possible to perform the latch action with a falling edge or both of the rising edge and the falling edge. Further, the subtractor304calculates a difference between the two count values respectively held by the latch circuits302,303to thereby output an increment of the count value of the number of pulses of the reference signal CLK measured during a transition corresponding to one cycle of the measurement target signal SIN with elapse of time without a dead period. When defining the frequency of the measurement target signal SIN as fx, and the frequency of the reference signal CLK as fc, the frequency ratio is obtained as fc/fx. The frequency delta-sigma modulation circuit300is for outputting the frequency delta-sigma modulation signal representing a frequency ratio as a digital signal string.

The first low-pass filter310is disposed in a posterior stage of the frequency delta-sigma modulation circuit300, and operates in sync with the measurement target signal SIN. The first low-pass filter310outputs a count value CT2obtained by removing or reducing a noise component included in the count value CT1as the frequency delta-sigma modulation signal. Although the first low-pass filter310is disposed immediately after the frequency delta-sigma modulation circuit300inFIG.13, it is sufficient for the first low-pass filter310to be disposed on a signal path from an output of the frequency delta-sigma modulation circuit300to an input of the second low-pass filter330.

The latch circuit320is disposed in a posterior stage of the first low-pass filter310, latches the count value CT2output from the first low-pass filter310in sync with the first frequency signal CLK1, and then holds the result as a count value CT3.

The second low-pass filter330is disposed in a posterior stage of the first low-pass filter310, and operates in sync with the first frequency signal CLK1asynchronous with the reference signal CLK. The second low-pass filter330outputs a count value obtained by removing or reducing a noise component included in the count value CT3held by the latch circuit320. The count value output from the second low-pass filter330is output to the micro-control unit210as the count value CNT. Since the first frequency signal CLK1is a signal based on the external trigger signal EXTRG, the count value CNT is a count value synchronized with the external trigger signal EXTRG.

As described above, the frequency ratio measurement circuit202measures the frequency ratio between the measurement target signal SIN and the reference signal CLK. However, since a reciprocal of a frequency is a period, it can be said that the frequency ratio measurement circuit202measures a period ratio between the measurement target signal SIN and the reference signal CLK.

FIG.14is a diagram showing a configuration example of the first low-pass filter310. In the example shown inFIG.14, the first low-pass filter310has a delay element311, an integrator312, an integrator313, a decimator314, a delay element315, a differentiator316, a delay element317, and a differentiator318. The constituents of the first low-pass filter310operate in sync with the measurement target signal SIN.

The delay element311outputs a count value obtained by delaying the count value CT1in sync with the measurement target signal SIN. The number of taps of the delay element311is n1. For example, the delay element311is realized by a shift register having n1registers coupled in series to each other.

The integrator312outputs a count value obtained by accumulating the count value output from the delay element311in sync with the measurement target signal SIN.

The integrator313outputs a count value obtained by accumulating the count value output from the integrator312in sync with the measurement target signal SIN.

The decimator314outputs a count value obtained by decimating the count value output from the integrator313into a rate of 1/R in sync with the measurement target signal SIN.

The delay element315outputs a count value obtained by delaying the count value output from the decimator314in sync with the measurement target signal SIN. The number of taps of the delay element315is n2. For example, the delay element315is realized by a shift register having n2registers coupled in series to each other.

The differentiator316outputs a count value obtained by subtracting the count value output from the delay element315from the count value output from the decimator314.

The delay element317outputs a count value obtained by delaying the count value output from the differentiator316in sync with the measurement target signal SIN. The number of taps of the delay element317is n3. For example, the delay element317is realized by a shift register having n3registers coupled in series to each other.

The differentiator318outputs the count value CT2obtained by subtracting the count value output from the delay element317from the count value output from the differentiator316.

FIG.15is a diagram showing another configuration example of the first low-pass filter310. In the example shown inFIG.15, the first low-pass filter310has an integrator401, a delay element402, a differentiator403, an integrator404, an integrator405, a decimator406, a delay element407, a differentiator408, a delay element409, and a differentiator410. The constituents of the first low-pass filter310operate in sync with the measurement target signal SIN.

The integrator401outputs a count value obtained by accumulating the count value CT1in sync with the measurement target signal SIN.

The delay element402outputs a count value obtained by delaying the count value output from the integrator401in sync with the measurement target signal SIN. The number of taps of the delay element402is n1. For example, the delay element402is realized by a shift register having n1registers coupled in series to each other.

The differentiator403outputs a count value obtained by subtracting the count value output from the delay element402from the count value output from the integrator401.

The integrator404outputs a count value obtained by accumulating the count value output from the differentiator403in sync with the measurement target signal SIN.

The integrator405outputs a count value obtained by accumulating the count value output from the integrator404in sync with the measurement target signal SIN.

The decimator406outputs a count value obtained by decimating the count value output from the integrator405into a rate of 1/R in sync with the measurement target signal SIN.

The delay element407outputs a count value obtained by delaying the count value output from the decimator406in sync with the measurement target signal SIN. The number of taps of the delay element407is n2. For example, the delay element407is realized by a shift register having n2registers coupled in series to each other.

The differentiator408outputs a count value obtained by subtracting the count value output from the delay element407from the count value output from the decimator406.

The delay element409outputs a count value obtained by delaying the count value output from the differentiator408in sync with the measurement target signal SIN. The number of taps of the delay element409is n3. For example, the delay element409is realized by a shift register having n3registers coupled in series to each other.

The differentiator410outputs the count value CT2obtained by subtracting the count value output from the delay element409from the count value output from the differentiator408.

InFIG.14orFIG.15, for example, a decimation ratio R is fixed, and the numbers of taps n1, n2, and n3are variable. The numbers of taps n1, n2, and n3are stored in the storage220, or are set by the processing device3.

The first low-pass filter310configured as shown inFIG.14orFIG.15functions as a CIC filter the group delay amount of which can be varied in accordance with the numbers of taps n1, n2, and n3. CIC is an abbreviation of Cascaded Integrator Comb.

FIG.16is a diagram showing a configuration example of the second low-pass filter330. In the example shown inFIG.16, the second low-pass filter330has an integrator331, a delay element332, a differentiator333, and a decimator334. The constituents of the second low-pass filter330operate in sync with the first frequency signal CLK1.

The integrator331outputs a count value obtained by accumulating the count value CT3in sync with the first frequency signal CLK1.

The delay element332outputs a count value obtained by delaying the count value output from the integrator331in sync with the first frequency signal CLK1. The number of taps of the delay element332is n4. For example, the delay element332is realized by a shift register having n4registers coupled in series to each other. The number of taps n4is variable. The number of taps n4is stored in the storage220, or is set by the processing device3.

The differentiator333outputs a count value obtained by subtracting the count value output from the delay element332from the count value output from the integrator331.

The decimator334outputs a count value CNT obtained by decimating the count value output from the differentiator333into a rate of 1/n4in sync with the first frequency signal CLK1.

The second low-pass filter330configured as described above accumulates the count value CT3while resampling the count value CT3with the first frequency signal CLK1, and therefore functions as a weighted moving average filter which weights the count value CT3with the duration thereof.

As described above, the first low-pass filter310operates in sync with the measurement target signal SIN, and the second low-pass filter330performs the resampling in sync with the first frequency signal CLK1, whereby there occurs the nonlinearity in the input and the output of the frequency ratio measurement circuit202. Therefore, the count value CNT output from the frequency ratio measurement circuit202includes the vibration rectification error caused by the nonlinearity. Further, by adjusting at least one of the number of taps n1of the delay element311or the delay element402provided to the first low-pass filter310, the number of taps n2of the delay element315or the delay element407provided to the first low-pass filter310, the number of taps n3of the delay element317or the delay element409provided to the first low-pass filter310, and the number of taps n4of the delay element332provided to the second low-pass filter330, it is possible to adjust the vibration rectification error.

FIG.17is a diagram for explaining that it is possible to adjust the vibration rectification error caused by the nonlinearity of the input and the output of the frequency ratio measurement circuit202. InFIG.17, there is shown an example when the period of the measurement target signal SIN is longer than the period of the reference signal CLK, and an updating cycle of the count value CNT is longer than the period of measurement target signal SIN, and the horizontal axis corresponds to elapse of time. InFIG.17, regarding the reference signal CLK, the timing of the rising edge is represented by a short vertical line. Further, regarding the count values CT1, CT2, the timing at which the value changes is represented by a short vertical line. It should be noted that inFIG.17, simplified numerical values are used for making the understanding easy for the purpose of describing the adjustment mechanism of the vibration rectification error. Further, there is presented the description as if the count value CT2is fixed before the count value CT1is fixed despite the count value CT2is not fixed until the count value CT1is fixed, but the actual calculation of the count value CT2is executed after the count value CT1is fixed.

InFIG.17, (A) shows an example when the period of the measurement target signal SIN is constant, and (B), (C), and (D) show examples when a frequency modulation is performed on the measurement target signal SIN. In (B), (C), and (D), the group delay amount of the first low-pass filter310is different therebetween. For the sake of simplification, it is assumed that the ratio between the period of the reference signal CLK and the period of the measurement target signal SIN is a simple integral ratio, and the count value CT1input to the first low-pass filter310is directly output with a constant group delay. The second low-pass filter330accumulates the count value CT3obtained by latching the count value CT2output from the first low-pass filter310in sync with the first frequency signal CLK1, and then outputs the accumulated value corresponding to four times of accumulation as the count value CNT.

In the example (A), the count value CT2is always 4, and the count value CNT becomes 4×4=16. In the example (B), since the frequency modulation is performed on the measurement target signal SIN, and the group delay of the first low-pass filter310is set to 0, the count value CT2repeats to take 5, 5, 3, and 3. Since the weighting with time is performed when performing the accumulation, the count value CNT becomes 5×3+3×1=18, which is larger than the count value CNT in (A). In the example (C), the count value CT2repeats to take 5, 5, 3, and 3 similarly to the example (B), but there is described when the group delay occurs in the first low-pass filter310. As a result of the weighting with time in the accumulation, the count value CNT becomes 5×2+3×2=16, which is the same as the count value CNT in (A). In the example (D), the count value CT2repeats to take 5, 5, 3, and 3 similarly to the examples (B) and (C), but there is described when the group delay occurring in the first low-pass filter310is larger compared to the example (C). In the example (D), the count value CNT becomes 5×1+3×3=14, which is smaller than the count value CNT in (A).

According to the consideration usingFIG.17, it can qualitatively be understood that the vibration rectification error caused by the nonlinearity in the input and the output of the frequency ratio measurement circuit202varies in accordance with the group delay amount of the first low-pass filter310. Similarly, the vibration rectification error caused by the nonlinearity of the input and the output of the frequency ratio measurement circuit202varies in accordance with the group delay amount of the second low-pass filter330. Therefore, by controlling the group delay amounts of the first low-pass filter310and the second low-pass filter330so that the vibration rectification error caused by the nonlinearity of the input and the output of the frequency ratio measurement circuit202becomes opposite in phase to the vibration rectification error caused by the cantilever resonance, it becomes possible to cancel out each other's vibration rectification error. The group delay amount of the first low-pass filter310can be controlled by the setting of the numbers of taps n1, n2, and n3shown inFIG.14orFIG.15. Further, the group delay amount of the second low-pass filter330can be controlled by the setting of the number of taps n4shown inFIG.16. Therefore, in the present embodiment, the storage220stores the numbers of taps n1, n2, n3, and n4as the information for controlling the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330.

As an example,FIG.18shows dependency of the vibration rectification error included in the measurement value by the vibration rectification error correction device2to the number of taps n1when fixing the numbers of taps n2, n3, and n4. InFIG.18, the horizontal axis represents the number of taps n1, and the vertical axis represents the vibration rectification error. It should be noted that VRE in the vertical axis is an abbreviation of Vibration Rectification Error. According toFIG.18, when, for example, appropriately setting the number of taps n1, it is possible to correct the vibration rectification error to approximate the vibration rectification error to 0.

In the first low-pass filter310having a configuration shown inFIG.14, since the delay element311is realized by a FIFO register using a shift register, when taking out the FIFO register to the outside of the first low-pass filter310, the frequency ratio measurement circuit202having the configuration shown inFIG.13becomes to have a configuration shown inFIG.19, and the first low-pass filter310having the configuration shown inFIG.14becomes to have a configuration shown inFIG.20. FIFO is an abbreviation of First In First Out.

FIG.21shows an example of a timing chart of the count value CT1input to the FIFO register340, and a count value CT1′ output from the FIFO register340. In the example shown inFIG.21, the count values CT1, CT1′ vary in sync with both edges of the measurement target signal SIN. In other words, in the example shown inFIG.21, the frequency delta-sigma modulation circuit300and the FIFO register340operate in sync with the both edges of the measurement target signal SIN. Case1represents when the number of stages of the FIFO register340is 2, and Case2represents when the number of stages of the FIFO register340is 4.

Also in the frequency ratio measurement circuit202having the configuration shown inFIG.19, by appropriately setting the number of stages of the FIFO register340which is equivalent to the number of taps n1of the delay element311, the group delay amount of the first low-pass filter310, and the group delay amount of the second low-pass filter330, it is possible to correct the vibration rectification error to approximate the vibration rectification error to 0.

Meanwhile, when the vibration component to be input to the physical quantity sensor200includes a frequency of the structural resonance decided by the structure of the physical quantity sensor200, there occurs the structural resonance of the physical quantity sensor200. As a result, the output signal of the physical quantity sensor200includes a signal component caused by the structural resonance. The signal component caused by the structural resonance is not a signal taken as a detection target by the physical quantity sensor200, and therefore, is not desirably included in the count value CNT output from the frequency ratio measurement circuit202. Therefore, in the present embodiment, a cutoff frequency based on the first low-pass filter310and the second low-pass filter330is lower than the frequency related to the structural resonance of the physical quantity sensor200. For example, it is possible to make a cutoff frequency of the first low-pass filter310higher than the frequency related to the structural resonance of the physical quantity sensor200, and a cutoff frequency of the second low-pass filter330lower than the frequency related to the structural resonance of the physical quantity sensor200. Alternatively, it is possible to make both of the cutoff frequency of the first low-pass filter310and the cutoff frequency of the second low-pass filter330lower than the frequency related to the structural resonance of the physical quantity sensor200. In the present embodiment, the structural resonance of the physical quantity sensor200is the cantilever resonance. It should be noted that the first low-pass filter310is an example of a “first filter,” and the second low-pass filter330is an example of a “second filter.”

1-6. Vibration Rectification Error Correction Method

FIG.22is a flowchart showing an example of a procedure of a vibration rectification error correction method by the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202having the configuration shown inFIG.13or the configuration shown inFIG.19.

As shown inFIG.22, first, in the step S10, the vibration rectification error correction device2performs the frequency delta-sigma modulation on the reference signal CLK using the measurement target signal SIN to generate the frequency delta-sigma modulation signal.

Then, in the step S20, the vibration rectification error correction device2performs first filter processing on a signal based on the count value CT1as the frequency delta-sigma modulation signal generated in the step S10in sync with the measurement target signal SIN. Specifically, the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202shown inFIG.13performs the first filter processing on the count value CT1in sync with the measurement target signal SIN. Further, the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202shown inFIG.19performs the first filter processing on the count value CT1′ in sync with the measurement target signal SIN. For example, the first filter processing is low-pass filter processing.

Then, in the step S30, the vibration rectification error correction device2performs second filter processing on the count value CT3as a signal based on the count value CT2as a signal obtained by the first filter processing in the step S20, in sync with the first frequency signal CLK1asynchronous with the reference signal CLK. The first frequency signal CLK1is a signal based on the external trigger signal EXTRG input from the outside of the sensor module1. For example, the second filter processing is low-pass filter processing.

Then, in the step S40, the vibration rectification error correction device2repeatedly performs the steps S10, S20, and S30until the measurement is terminated.

1-7. Functions and Advantages

As described hereinabove, in the sensor module1according to the first embodiment, by the frequency delta-sigma modulation circuit300performing the frequency delta-sigma modulation on the reference signal CLK using the measurement target signal SIN based on the output signal of the physical quantity sensor200, the count value CT1as the frequency delta-sigma modulation signal representing the frequency ratio between the measurement target signal SIN and the reference signal CLK is generated in the vibration rectification error correction device2. Further, in the vibration rectification error correction device2, the first low-pass filter310disposed in the posterior stage of the frequency delta-sigma modulation circuit300operates in sync with the measurement target signal SIN, and the second low-pass filter330disposed in the posterior stage of the first low-pass filter310operates in sync with the first frequency signal CLK1different from the measurement target signal SIN, and thus, the nonlinearity occurs in the relationship between the count value CT1and the count value CNT output from the second low-pass filter330. Further, the vibration rectification error caused by the nonlinearity varies in accordance with the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330. Therefore, according to the sensor module1related to the first embodiment, by setting the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330to appropriate values in the vibration rectification error correction device2, the vibration rectification error caused by the nonlinearity and the vibration rectification error caused by the asymmetry of the measurement target signal SIN are canceled out each other, and thus, the vibration rectification error included in the count value CNT as measurement data based on the output signal of the physical quantity sensor200is reduced. In particular, in the vibration rectification error correction device2, since the storage220stores information for controlling the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330, by appropriately setting that information, the vibration rectification error included in the count value CNT is reduced.

Further, in the sensor module1according to the first embodiment, since the count value CNT output from the second low-pass filter330is synchronized with the first frequency signal CLK1in the vibration rectification error correction device2, neither a synchronization circuit large in circuit scale disposed in the posterior stage of the second low-pass filter330nor calculation in post-processing heavy in load is required to obtain the data synchronized with the first frequency signal CLK1. Therefore, according to the sensor module1related to the first embodiment, in the vibration rectification error correction device2, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the count value CNT synchronized with the first frequency signal CLK1asynchronous with the reference signal CLK.

Further, in the sensor module1according to the first embodiment, since the first frequency signal CLK1is a signal based on the external trigger signal EXTRG in the vibration rectification error correction device2, the count value CNT output from the second low-pass filter330is synchronous with the external trigger signal EXTRG. Therefore, according to the sensor module1related to the first embodiment, in the vibration rectification error correction device2, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the count value CNT synchronized with the external trigger signal EXTRG.

Further, in the sensor module1according to the first embodiment, by making the cutoff frequency based on the first low-pass filter310and the second low-pass filter330lower than the frequency related to the structural resonance of the physical quantity sensor200, it is possible for the vibration rectification error correction device2to generate the count value CNT in which a conspicuous noise component generated by the structural resonance of the physical quantity sensor200is reduced.

2. Second Embodiment

Hereinafter, regarding the sensor module according to a second embodiment, substantially the same constituents as those in the first embodiment will be denoted by the same reference numerals, and different contents from those in the first embodiment are mainly described while omitting or simplifying the description duplicating the first embodiment.

In the first embodiment, an adjustment resolution of the group delay amount of the first low-pass filter310is decided by the period of the measurement target signal SIN, and an adjustment resolution of the group delay amount of the second low-pass filter330is decided by the period of the first frequency signal CLK1based on the external trigger signal EXTRG. Therefore, a correction resolution of the vibration rectification error is decided by shorter one of the period of the measurement target signal SIN and the period of the external trigger signal EXTRG. Therefore, when the period of the external trigger signal EXTRG is longer than the period of the measurement target signal SIN, the correction resolution of the vibration rectification error is decided by the period of the measurement target signal SIN, and therefore, there is a certain limit. Therefore, in the second embodiment, in order to improve the correction resolution of the vibration rectification error, the period of the first frequency signal CLK1for making the second low-pass filter330operate is shortened to thereby improve the correction resolution of the vibration rectification error.

FIG.23is a functional block diagram of the sensor module1according to the second embodiment. InFIG.23, substantially the same constituents as those shown inFIG.8are denoted by the same reference numerals. Similarly to the first embodiment, the sensor module1according to the second embodiment is provided with the physical quantity sensors200X,200Y, and200Z, and the vibration rectification error correction device2. Functions and configurations of the physical quantity sensors200X,200Y, and200Z are substantially the same as those in the first embodiment, and therefore the description thereof will be omitted.

The vibration rectification error correction device2includes the oscillation circuits201X,201Y, and201Z, the frequency ratio measurement circuits202X,202Y, and202Z, the micro-control unit210, the storage220, the interface circuit230, and a multiplier circuit240. Functions and configurations of the oscillation circuits201X,201Y, and201Z, the micro-control unit210, the storage220, and the interface circuit230are substantially the same as those in the first embodiment, and therefore the description thereof will be omitted.

The multiplier circuit240multiplies a second frequency signal CLK2asynchronous with the reference signal CLK. The second frequency signal CLK2is a signal based on the external trigger signal EXTRG input from the outside of the sensor module1. The second frequency signal CLK2can be, for example, the external trigger signal EXTRG itself, or can also be a signal obtained by buffering the external trigger signal EXTRG. A multiplying factor of the multiplier circuit240can be an integer no smaller than 2. The multiplying factor of the multiplier circuit240can be fixed. Alternatively, the multiplying factor of the multiplier circuit240can be variable, and can be stored in the storage220, or can be set by the processing device3.

To each of the frequency ratio measurement circuits202X,202Y, and202Z, there is input the first frequency signal CLK1asynchronous with the reference signal CLK. The first frequency signal CLK1is a signal based on an output signal of the multiplier circuit240. The first frequency signal CLK1can be, for example, the output signal of the multiplier circuit240itself, or can also be a signal obtained by buffering the output signal of the multiplier circuit240. Then, the frequency ratio measurement circuits202X,202Y, and202Z respectively output the count values CNT_X, CNT_Y, and CNT_Z in sync with the first frequency signal CLK1.

FIG.24is a diagram showing a configuration example of the frequency ratio measurement circuit202in the second embodiment. InFIG.24, substantially the same constituents as those shown inFIG.13are denoted by the same reference numerals. The frequency ratio measurement circuit202shown inFIG.24is provided with the frequency delta-sigma modulation circuit300, the first low-pass filter310, the latch circuit320, the second low-pass filter330, and a latch circuit350. Functions of the frequency delta-sigma modulation circuit300, the first low-pass filter310, the latch circuit320, and the second low-pass filter330are substantially the same as in the first embodiment, and therefore, the description thereof will be omitted. Further, a configuration and a function of the first low-pass filter310are substantially the same as shown inFIG.14orFIG.15, and therefore, the illustration and the description thereof will be omitted. Further, a configuration and a function of the second low-pass filter330are substantially the same as shown inFIG.16when the count value output from the decimator334is changed from CNT to CT4, and therefore, the illustration and the description thereof will be omitted. It should be noted that the second embodiment is different in the point that the first frequency signal CLK1to be input to the latch circuit320and the second low-pass filter330is the signal based on the output signal of the multiplier circuit240from the first embodiment in which the first frequency signal CLK1is the signal based on the external trigger signal EXTRG.

The latch circuit350is disposed in the posterior stage of the second low-pass filter330, and operates in sync with the second frequency signal CLK2. Specifically, the latch circuit350latches the count value CT4output from the second low-pass filter330in sync with the second frequency signal CLK2, and then holds the result as the count value CNT. The count value CNT held by the latch circuit350is output to the micro-control unit210. Since the second frequency signal CLK2is a signal based on the external trigger signal EXTRG, the count value CNT is a count value synchronized with the external trigger signal EXTRG.

In the first low-pass filter310having the configuration shown inFIG.14, since the delay element311is realized by the FIFO register using the shift register, when taking out the FIFO register to the outside of the first low-pass filter310, the frequency ratio measurement circuit202having the configuration shown inFIG.24becomes to have a configuration shown inFIG.25, and the first low-pass filter310having the configuration shown inFIG.14becomes to have the configuration shown inFIG.20.

In the second embodiment, the adjustment resolution of the group delay amount of the first low-pass filter310is decided by the period of the measurement target signal SIN, and the adjustment resolution of the group delay amount of the second low-pass filter330is decided by the period of the first frequency signal CLK1based on the output signal of the multiplier circuit240. Therefore, by making the period of the first frequency signal CLK1shorter than the period of the measurement target signal SIN, the correction resolution of the vibration rectification error is decided by the period of the first frequency signal CLK1, and therefore, a higher correction resolution than in the first embodiment is realized. Therefore, in the second embodiment, the multiplying factor of the multiplier circuit240is set so that the frequency of the first frequency signal CLK1becomes higher than the frequency of the measurement target signal SIN. Further, since the frequency of the reference signal CLK is higher than the frequency of the measurement target signal SIN, it is preferable for the frequency of the first frequency signal CLK1to be higher than the frequency of the reference signal CLK in order to further raise the correction resolution of the vibration rectification error.

FIG.26is a flowchart showing an example of a procedure of a vibration rectification error correction method by the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202having the configuration shown inFIG.24or the configuration shown inFIG.25.

As shown inFIG.26, first, in the step S110, the vibration rectification error correction device2performs the frequency delta-sigma modulation on the reference signal CLK using the measurement target signal SIN to generate the frequency delta-sigma modulation signal.

Then, in the step S120, the vibration rectification error correction device2performs the first filter processing on the signal based on the count value CT1as the frequency delta-sigma modulation signal generated in the step S110, in sync with the measurement target signal SIN. Specifically, the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202shown inFIG.24performs the first filter processing on the count value CT1in sync with the measurement target signal SIN. Further, the vibration rectification error correction device2equipped with the frequency ratio measurement circuit202shown inFIG.25performs the first filter processing on the count value CT1′ in sync with the measurement target signal SIN. For example, the first filter processing is the low-pass filter processing.

Further, in the step S130, the vibration rectification error correction device2performs multiplying processing on the second frequency signal CLK2asynchronous with the reference signal CLK. The second frequency signal CLK2is a signal based on the external trigger signal EXTRG input from the outside of the sensor module1.

Then, in the step S140, the vibration rectification error correction device2performs the second filter processing on the count value CT3as the signal based on the count value CT2as the signal obtained by the first filter processing in the step S120, in sync with the first frequency signal CLK1asynchronous with the reference signal CLK. The first frequency signal CLK1is a signal based on a signal obtained by the multiplying processing in the step S130. It is preferable for the frequency of the first frequency signal CLK1to be higher than the frequency of the reference signal CLK. For example, the second filter processing is the low-pass filter processing.

Then, in the step S150, the vibration rectification error correction device2performs latch processing on a signal based on the count value CT4as a signal obtained by the second filter processing in the step S140, in sync with the second frequency signal CLK2.

Then, in the step S160, the vibration rectification error correction device2repeatedly performs the steps S110, S120, S130, S140, and S150until the measurement is terminated.

As described hereinabove, in the sensor module1according to the second embodiment, by the frequency delta-sigma modulation circuit300performing the frequency delta-sigma modulation on the reference signal CLK using the measurement target signal SIN based on the output signal of the physical quantity sensor200, the count value CT1as the frequency delta-sigma modulation signal representing the frequency ratio between the measurement target signal SIN and the reference signal CLK is generated in the vibration rectification error correction device2. Further, in the vibration rectification error correction device2, the first low-pass filter310disposed in the posterior stage of the frequency delta-sigma modulation circuit300operates in sync with the measurement target signal SIN, and the second low-pass filter330disposed in the posterior stage of the first low-pass filter310operates in sync with the first frequency signal CLK1different from the measurement target signal SIN, and thus, the nonlinearity occurs in the relationship between the count value CT1, and the count value CT4output from the second low-pass filter330and the count value CNT output from the latch circuit350. Further, the vibration rectification error caused by the nonlinearity varies in accordance with the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330. Therefore, according to the sensor module1related to the second embodiment, by setting the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330to appropriate values in the vibration rectification error correction device2, the vibration rectification error caused by the nonlinearity and the vibration rectification error caused by the asymmetry of the measurement target signal SIN are canceled out each other, and thus, the vibration rectification error included in the count value CNT as measurement data based on the output signal of the physical quantity sensor200is reduced. In particular, in the vibration rectification error correction device2, since the storage220stores the information for controlling the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330, by appropriately setting that information, the vibration rectification error included in the count value CNT is reduced.

In particular, in the sensor module1according to the second embodiment, by making the frequency of the first frequency signal CLK1based on the output signal of the multiplier circuit240higher than the frequency of the reference signal CLK in the vibration rectification error correction device2, the adjustment resolution of the group delay amount of the second low-pass filter rises, and thus, it is possible to raise the correction resolution of the vibration rectification error. Therefore, according to the sensor module1related to the second embodiment, in the vibration rectification error correction device2, by setting the group delay amount of the first low-pass filter310and the group delay amount of the second low-pass filter330to appropriate values, the vibration rectification error included in the count value CNT is further reduced.

Further, in the sensor module1according to the second embodiment, since the count value CNT output from the latch circuit350is synchronized with the second frequency signal CLK2in the vibration rectification error correction device2, neither a synchronization circuit large in circuit scale disposed in the posterior stage of the second low-pass filter330nor calculation in post-processing heavy in load is required to obtain the data synchronized with the second frequency signal CLK2. Therefore, according to the sensor module1related to the second embodiment, in the vibration rectification error correction device2, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the count value CNT synchronized with the second frequency signal CLK2asynchronous with the reference signal CLK.

Further, in the sensor module1according to the second embodiment, since the second frequency signal CLK2is a signal based on the external trigger signal EXTRG in the vibration rectification error correction device2, the count value CNT output from the latch circuit350is synchronous with the external trigger signal EXTRG. Therefore, according to the sensor module1related to the second embodiment, in the vibration rectification error correction device2, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the count value CNT synchronized with the external trigger signal EXTRG.

Further, in the sensor module1according to the second embodiment, by making the cutoff frequency based on the first low-pass filter310and the second low-pass filter330lower than the frequency related to the structural resonance of the physical quantity sensor200, it is possible for the vibration rectification error correction device2to generate the count value CNT in which a conspicuous noise component generated by the structural resonance of the physical quantity sensor200is reduced.

3. Modified Examples

The present disclosure is not limited to the present embodiments, but can be implemented with a variety of modifications within the scope or the spirit of the present disclosure.

For example, the first frequency signal CLK1is the signal based on the external trigger signal EXTRG in each of the embodiments described above, but is not required to be the signal based on the external trigger signal EXTRG. For example, as shown inFIG.27, it is possible for the vibration rectification error correction device2to be further provided with a frequency signal generation circuit250for generating the first frequency signal CLK1. Further, for example, as shown inFIG.28, it is possible to adopt a configuration in which the vibration rectification error correction device2is further provided with the frequency signal generation circuit250for generating the second frequency signal CLK2, and the multiplier circuit240outputs the first frequency signal CLK1obtained by multiplying the second frequency signal CLK2generated by the frequency signal generation circuit250.

Further, for example, in the second embodiment described above, when the updating cycle of the count value CT4output from the second low-pass filter330coincides with the period of the second frequency signal CLK2, the latch circuit350can be eliminated. Similarly, in the flowchart shown inFIG.26, when the updating cycle of the signal obtained by the second filter processing in the step S140coincides with the period of the second frequency signal CLK2, the step S150can be eliminated.

Further, for example, although the sensor module1has the three physical quantity sensors200and the three frequency ratio measurement circuits202in each of the embodiments described above, each of the number of the physical quantity sensors200provided to the sensor module1and the number of the frequency ratio measurement circuits202provided to the sensor module1can be one, two, or four or more.

Further, although the sensor module1provided with the acceleration sensors as the physical quantity sensors200is cited as an example in each of the embodiments described above, it is possible for the sensor module1to be provided with a sensor such an angular velocity sensor, a pressure sensor, or an optical sensor as the physical quantity sensor200. Further, it is possible for the sensor module1to be provided with two or more types of physical quantity sensors out of the variety of sensors such as the acceleration sensor, the angular velocity sensor, the pressure sensor, and the optical sensor.

Further, although in each of the embodiments described above, there is cited the element configured using quartz crystal as the physical quantity detection element40provided to the physical quantity sensor200as an example, the physical quantity detection element40can be configured using a piezoelectric element other than quartz crystal, or can also be an MEMS element of a capacitance type. MEMS is an abbreviation of Micro Electro Mechanical Systems.

Further, although in each of the embodiments described above, the first low-pass filter310is cited as an example of the first filter, and the second low-pass filter330is cited as an example of the second filter, the first filter and the second filter can each be a high-pass filter, a band-pass filter, or a smoothing filter. Similarly, the first filter processing and the second filter processing can each be high-pass filter processing, band-pass filter processing, or smoothing filter processing besides the low-pass filter processing.

The embodiments and the modified examples described above are illustrative only, and the present disclosure is not limited to the embodiments and the modified examples. For example, it is also possible to arbitrarily combine any of the embodiments and the modified examples with each other.

The present disclosure includes configurations substantially the same as the configuration described as the embodiment such as configurations having the same function, the same way, and the same result, or configurations having the same object and the same advantage. Further, the present disclosure includes configurations obtained by replacing a non-essential part of the configuration described as the embodiment. Further, the present disclosure includes configurations providing the same functions and advantages, and configurations capable of achieving the same object as those of the configuration described as the embodiment. Further, the present disclosure includes configurations obtained by adding a known technology to the configuration described as the embodiment.

The following contents derive from the embodiments and the modified examples described above.

A vibration rectification error correction device according to an aspect of the present disclosure is provided with a reference signal generation circuit configured to output a reference signal, a frequency delta-sigma modulation circuit configured to perform a frequency delta-sigma modulation on the reference signal using a measurement target signal to generate a frequency delta-sigma modulation signal, a first filter which is disposed in a posterior stage of the frequency delta-sigma modulation circuit, and operates in sync with the measurement target signal, and a second filter which is disposed in a posterior stage of the first filter, and operates in sync with a first frequency signal asynchronous with the reference signal.

In this vibration rectification error correction device, the frequency delta-sigma modulation circuit performs the frequency delta-sigma modulation on the reference signal using the measurement target signal to thereby generate the frequency delta-sigma modulation signal representing a frequency ratio between the measurement target signal and the reference signal. Further, in this vibration rectification error correction device, the first filter disposed in the posterior stage of the frequency delta-sigma modulation circuit operates in sync with the measurement target signal, and the second filter disposed in the posterior stage of the first filter operates in sync with the first frequency signal different from the measurement target signal, and thus, the nonlinearity occurs in the relationship between the frequency delta-sigma modulation signal and the output signal of the second filter. Further, the vibration rectification error caused by the nonlinearity varies in accordance with the group delay amount of the first filter and the group delay amount of the second filter. Therefore, according to this vibration rectification error correction device, by setting the group delay amount of the first filter and the group delay amount of the second filter to appropriate values, the vibration rectification error caused by the nonlinearity and the vibration rectification error caused by the asymmetry of the measurement target signal are canceled out each other, and thus, the vibration rectification error included in output data of the second filter is reduced.

Further, in this vibration rectification error correction device, since the output data of the second filter is synchronized with the first frequency signal, neither a synchronization circuit large in circuit scale disposed in the posterior stage of the second filter nor calculation in post-processing heavy in load is required to obtain the data synchronized with the first frequency signal. Therefore, according to this vibration rectification error correction device, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the data synchronized with the first frequency signal asynchronous with the reference signal.

In the vibration rectification error correction device according to the aspect described above, the first frequency signal may be a signal based on an external trigger signal.

According to this vibration rectification error correction device, since the output data of the second filter is synchronized with the external trigger signal, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the data synchronized with the external trigger signal.

The vibration rectification error correction device according to the aspect may further be provided with a multiplier circuit configured to multiply a second frequency signal asynchronous with the reference signal, wherein the first frequency signal may be a signal based on an output signal of the multiplier circuit, and a frequency of the first frequency signal may be higher than a frequency of the reference signal.

In this vibration rectification error correction device, since the frequency of the first frequency signal based on the output signal of the multiplier circuit is higher than the frequency of the reference signal, the adjustment resolution of the group delay amount of the second filter rises, and thus, it is possible to raise the correction resolution of the vibration rectification error. Therefore, according to this vibration rectification error correction device, by setting the group delay amount of the first filter and the group delay amount of the second filter to appropriate values, the vibration rectification error included in the output data of the second filter is further reduced.

The vibration rectification error correction device according to the aspect may further be provided with a latch circuit which is disposed in a posterior stage of the second filter, and operates in sync with the second frequency signal.

According to this vibration rectification error correction device, it is possible to generate the data synchronized with the second frequency signal asynchronous with the reference signal without requiring neither the synchronization circuit large in circuit scale nor the calculation heavy in load.

In the vibration rectification error correction device according to the aspect described above, the second frequency signal may be a signal based on the external trigger signal.

According to this vibration rectification error correction device, since the output data of the latch circuit is synchronized with the external trigger signal, neither the synchronization circuit large in circuit scale nor the calculation heavy in load is necessary to generate the data synchronized with the external trigger signal.

The vibration rectification error correction device according to the aspect may further be provided with a storage configured to store information used to control the group delay amount of the first filter and the group delay amount of the second filter.

According to this vibration rectification error correction device, by appropriately setting the information for controlling the group delay amount of the first filter and the group delay amount of the second filter stored in the storage, the vibration rectification error included in the output data is reduced.

In the vibration rectification error correction device according to the aspect described above, the measurement target signal may be a signal based on an output signal of a physical quantity sensor.

According to this vibration rectification error correction device, it is possible to reduce the vibration rectification error in measurement data based on the output signal of the physical quantity sensor.

In the vibration rectification error correction device according to the aspect described above, a cutoff frequency based on the first filter and the second filter may be lower than a frequency related to a structural resonance of the physical quantity sensor.

According to this vibration rectification error correction device, it is possible to reduce the conspicuous noise component caused by the structural resonance of the physical quantity sensor with the first filter and the second filter.

A sensor module according to an aspect of the present disclosure is provided with the vibration rectification error correction device according to the aspect, and the physical quantity sensor.

According to this sensor module, since the vibration rectification error correction device is provided, it is possible to generate the measurement data with the vibration rectification error reduced.

A vibration rectification error correction method according to an aspect of the present disclosure is provided with performing a frequency delta-sigma modulation on a reference signal using a measurement target signal to generate a frequency delta-sigma modulation signal, performing first filter processing on a signal based on the frequency delta-sigma modulation signal in sync with the measurement target signal, and performing second filter processing on a signal based on a signal obtained by the first filter processing, in sync with a first frequency signal asynchronous with the reference signal.

In this vibration rectification error correction method, by performing the frequency delta-sigma modulation on the reference signal using the measurement target signal, the frequency delta-sigma modulation signal representing a frequency ratio between the measurement target signal and the reference signal is generated. Further, in this vibration rectification error correction method, by performing the first filter processing in sync with the measurement target signal, and performing the second filter processing in sync with the first frequency signal different from the measurement target signal, nonlinearity occurs in the relationship between the frequency delta-sigma modulation signal and the signal obtained by the second filter processing. Further, the vibration rectification error caused by the nonlinearity varies in accordance with the group delay amount in the first filter processing and the group delay amount in the second filter processing. Therefore, according to this vibration rectification error correction method, by setting the group delay amount in the first filter processing and the group delay amount in the second filter processing to appropriate values, the vibration rectification error caused by the nonlinearity and the vibration rectification error caused by the asymmetry of the measurement target signal are canceled out each other, and thus, the vibration rectification error included in the signal obtained by the second filter processing is reduced.

Further, in this vibration rectification error correction method, since the signal obtained by the second filter processing is synchronized with the first frequency signal, calculation in post-processing heavy in load is not required after the second low-pass filter processing in order to obtain the data synchronized with the first frequency signal. Therefore, according to this vibration rectification error correction method, the calculation heavy in load is not necessary to generate the data synchronized with the first frequency signal asynchronous with the reference signal.

The vibration rectification error correction method according to the aspect may further include performing multiplying processing on a second frequency signal asynchronous with the reference signal, wherein the first frequency signal may be a signal based on a signal obtained by the multiplying processing, and a frequency of the first frequency signal may be higher than a frequency of the reference signal.

In this vibration rectification error correction method, since the frequency of the first frequency signal based on the signal obtained by the multiplying processing is higher than the frequency of the reference signal, the adjustment resolution of the group delay amount in the second filter processing rises, and thus, it is possible to raise the correction resolution of the vibration rectification error. Therefore, according to this vibration rectification error correction method, by setting the group delay amount in the first filter processing and the group delay amount in the second filter processing to appropriate values, the vibration rectification error included in the signal obtained by the second filter processing is further reduced.