阅读说明：本技术 信号处理装置、惯性传感器、信号处理方法和程序 (Signal processing device, inertial sensor, signal processing method, and program ) 是由 黑田启介 梶原拓也 中塚淳二 永井正昭 于 2020-01-30 设计创作，主要内容包括：本文公开了一种用于检查校正电路的工作的技术。一种信号处理装置(1)包括检测电路(11)、校正电路(12)和比较器电路(13)。检测电路(11)基于检测惯性力的电容检测元件(2、3、4)的输出信号(Sig1)产生第一检测信号(Sig2)。校正电路(12)校正第一检测信号(Sig2)的非线性,并输出经校正的第二检测信号(Sig3)。比较器电路(13)将第一检测信号(Sig2)和第二检测信号(Sig3)相互比较,并输出表示比较结果的比较信号(Sig4)。(Disclosed herein is a technique for checking the operation of a correction circuit. A signal processing apparatus (1) includes a detection circuit (11), a correction circuit (12), and a comparator circuit (13). A detection circuit (11) generates a first detection signal (Sig2) based on an output signal (Sig1) of a capacitance detection element (2, 3, 4) that detects an inertial force. The correction circuit (12) corrects the nonlinearity of the first detection signal (Sig2), and outputs a corrected second detection signal (Sig 3). The comparator circuit (13) compares the first detection signal (Sig2) and the second detection signal (Sig3) with each other, and outputs a comparison signal (Sig4) indicating the comparison result.)

1. A signal processing apparatus comprising:

a detection circuit configured to generate a first detection signal based on an output signal of a capacitance detection element configured to detect an inertial force;

a correction circuit configured to correct nonlinearity of the first detection signal and output a corrected second detection signal; and

a comparator circuit configured to compare the first detection signal and the second detection signal with each other and output a comparison signal representing a comparison result.

2. The signal processing apparatus of claim 1, further comprising:

a first determination circuit configured to determine a magnitude of the inertial force based on the first detection signal and output a first determination signal representing a determination result; and

a second determination circuit configured to determine whether the correction circuit operates normally based on the comparison signal and the first determination signal, and output a second determination signal indicating a result of the determination

The second determination circuit is configured to: the correction circuit is determined to be operating abnormally if the comparison result obtained by the comparator circuit satisfies a first condition and the determination result obtained by the first determination circuit satisfies a second condition.

3. The signal processing apparatus according to claim 1 or 2, further comprising:

a first determination circuit configured to determine a magnitude of the inertial force based on the first detection signal and output a first determination signal representing a determination result; and

a second determination circuit configured to determine whether the correction circuit operates normally based on the comparison signal and the first determination signal, and output a second determination signal indicating a result of the determination

The second determination circuit is configured to: the correction circuit is determined to be operating normally if the comparison result obtained by the comparator circuit does not satisfy a first condition and the determination result obtained by the first determination circuit satisfies a second condition.

4. A signal processing apparatus according to claim 2 or 3, wherein

The first condition is that an absolute value of a difference between respective values of the first detection signal and the second detection signal is equal to or smaller than a first threshold value, and

the second condition is that the magnitude of the inertial force determined based on the first detection signal is equal to or greater than a second threshold value.

5. The signal processing apparatus according to any one of claims 2 to 4, further comprising a storage unit configured to store and be able to rewrite a determination threshold value, the first determination circuit determining the magnitude of the inertial force based on the first detection signal using the determination threshold value.

6. The signal processing apparatus according to any one of claims 2 to 5, having a determination mode designed to cause the second determination circuit to determine whether the correction circuit operates normally based on an artificially generated inertial force.

7. An inertial sensor, comprising:

the signal processing apparatus of any one of claims 1 to 6; and

the capacitance detection element.

8. A signal processing method, comprising:

a detecting step including generating a first detection signal based on an output signal of a capacitance detecting element configured to detect an inertial force;

a correction step of correcting nonlinearity of the first detection signal and outputting a corrected second detection signal; and

a comparing step including comparing the first detection signal and the second detection signal with each other and outputting a comparison signal representing a comparison result.

9. A program designed to cause one or more processors to execute the signal processing method of claim 8.

Technical Field

The present disclosure generally relates to a signal processing apparatus, an inertial sensor, a signal processing method, and a program. More particularly, the present disclosure relates to a signal processing device, an inertial sensor, a signal processing method, and a program that process a signal supplied from a detection element for detecting an inertial force.

Background

Patent document 1 describes a capacitive acceleration sensor (inertial sensor). The acceleration sensor of patent document 1 includes a sensor chip (detection element) and an ASIC (signal processing device). The ASIC includes an automatic correction circuit (correction circuit) that corrects a deviation from an ideal output by subtracting a correction value from an input acceleration. The correction value is calculated by a polynomial using the input acceleration as a variable.

The acceleration sensor of patent document 1 cannot determine whether the automatic correction circuit operates normally.

Reference list

Patent document

Patent document 1: JP 2015-17819A

Disclosure of Invention

An object of the present disclosure is to provide a signal processing device, an inertial sensor, a signal processing method, and a program, each configured or designed to be able to perform an operation check on a correction circuit (i.e., determine whether the correction circuit is functioning normally).

A signal processing apparatus according to an aspect of the present disclosure includes a detection circuit, a correction circuit, and a comparator circuit. The detection circuit generates a first detection signal based on an output signal of a capacitance detection element that detects an inertial force. The correction circuit corrects the nonlinearity of the first detection signal and outputs a corrected second detection signal. The comparator circuit compares the first detection signal and the second detection signal with each other and outputs a comparison signal representing a comparison result.

An inertial sensor according to another aspect of the present disclosure includes the above-described signal processing device and the above-described capacitance detection element.

A signal processing method according to still another aspect of the present disclosure includes a detecting step, a correcting step, and a comparing step. The detecting step includes generating a first detection signal based on an output signal of a capacitance detecting element that detects the inertial force. The correcting step includes correcting the nonlinearity of the first detection signal and outputting a corrected second detection signal. The comparing step includes comparing the first detection signal and the second detection signal with each other and outputting a comparison signal representing a result of the comparison.

A program according to still another aspect of the present disclosure is designed to cause one or more processors to execute the above-described signal processing method.

Drawings

Fig. 1 is a schematic diagram showing a configuration of a signal processing apparatus and an inertial sensor according to an example embodiment of the present disclosure;

fig. 2 is an exploded perspective view of a detection element as a constituent element of an inertial sensor;

FIG. 3 is a cross-sectional view taken along the plane X1-X2 shown in FIG. 2;

fig. 4 is a graph showing the relationship between the input acceleration of the inertial sensor and the sensor output; and

fig. 5 is a sequence diagram showing how the signal processing apparatus operates.

Detailed Description

(examples)

Fig. 2 and 3 referred to in the following description of the embodiment and its variants are both schematic representations. Therefore, the ratio of the sizes (including thicknesses) of the respective constituent elements shown in the drawings does not always reflect their actual size ratio.

(1) Summary of the invention

An outline of the inertial sensor 10 according to this embodiment will be described with reference to fig. 1.

The inertial sensor 10 according to the present embodiment is a sensor for detecting an inertial force, and may be, for example, a three-axis acceleration sensor that detects acceleration in three axial directions perpendicular to each other. Specifically, the inertial sensor 10 according to the present embodiment can detect the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction. The inertial sensor 10 may be, for example, a surface-mounted acceleration sensor mounted on the surface of a printed wiring board. The inertial sensor 10 may be implemented as, for example, a capacitive acceleration sensor (see fig. 3).

As shown in fig. 1, an inertial sensor 10 according to the present embodiment includes a signal processing device 1 and a plurality of (three in the example shown in fig. 1) detection elements 2, 3, 4. The signal processing apparatus 1 may be, for example, an ASIC (application specific integrated circuit). The detection element 2 detects an inertial force (acceleration) in the X-axis direction. The detection element 3 detects an inertial force (acceleration) in the Y-axis direction. The detection element 4 detects an inertial force (acceleration) in the Z-axis direction.

In general, this type of inertial sensor 10 is designed to exhibit a response characteristic that ideally allows for linear changes in the magnitude of the inertial force and the magnitude of the sensor output. However, in practice, when the magnitude of the inertial force becomes equal to or greater than a certain value, the magnitude of the sensor output starts to vary to deviate from its ideal linear characteristic. To overcome this problem, acceleration sensors including a correction circuit for correcting a deviation of the sensor output have been provided in the related art. However, an acceleration sensor configured to be able to determine whether the correction circuit is operating normally has not been provided so far. The signal processing apparatus 1 according to the present embodiment employs the following configuration to determine whether the correction circuit operates normally.

As shown in fig. 1, the signal processing apparatus 1 according to the present embodiment includes a detection circuit 11, a correction circuit 12, and a comparator circuit 13. The detection circuit 11 generates a first detection signal Sig2 based on the output signal Sig1 of the capacitance detection elements 2, 3, 4 that detect the inertial force. The correction circuit 12 corrects the nonlinearity of the first detection signal Sig2, and outputs a corrected second detection signal Sig 3. The comparator circuit 13 compares the first detection signal Sig2 and the second detection signal Sig3 with each other, and outputs a comparison signal Sig4 indicating the comparison result. As used herein, the term "non-linear" refers to the degree of deviation from linearity in response characteristics that ideally allow for linear changes in the input and output of the sensor. In this context, the non-linearity increases with increasing degree of deviation from linearity, and the non-linearity decreases with decreasing degree of deviation from linearity. In other words, the greater the non-linearity, the worse the linearity, and the smaller the non-linearity, the higher the linearity.

The signal processing apparatus 1 according to the embodiment compares the first detection signal Sig2 supplied from the detection circuit 11 and the second detection signal Sig3 supplied from the correction circuit 12 with each other. Then, the signal processing apparatus 1 outputs a comparison signal Sig4 indicating the comparison result. In the present embodiment, the correction circuit 12 corrects the nonlinearity of the first detection signal Sig2 supplied from the detection circuit 11. Therefore, when an inertial force of a predetermined magnitude or more is generated, a difference of a predetermined value or more is generated between the respective values of the first detection signal Sig2 and the second detection signal Sig 3. Therefore, the signal processing device 1 can determine that the correction circuit 12 is operating abnormally when it is found that a difference of a predetermined value or more is not generated based on the result of comparison between the first detection signal Sig2 and the second detection signal Sig 3. That is, the signal processing apparatus 1 according to the present embodiment can determine whether the correction circuit 12 operates normally based on the comparison signal Sig4 supplied from the comparator circuit 13.

(2) Configuration of

Next, the configuration of the inertial sensor 10 according to the present embodiment will be described with reference to fig. 1, 2, and 3.

As shown in fig. 1, an inertial sensor 10 according to the present embodiment includes a signal processing device 1 and a plurality of (e.g., three in the example shown in fig. 1) detection elements 2, 3, 4.

(2.1) Signal processing device

The signal processing apparatus 1 includes a plurality of (e.g., three in the example shown in fig. 1) detection circuits 11, a plurality of (e.g., three in the example shown in fig. 1) correction circuits 12, a plurality of (e.g., three in the example shown in fig. 1) comparator circuits 13, a plurality of (e.g., three in the example shown in fig. 1) first decision circuits 14, and a plurality of (e.g., three in the example shown in fig. 1) second decision circuits 15. The signal processing apparatus 1 further includes a storage unit 16.

The plurality of detection circuits 11, the plurality of correction circuits 12, the plurality of comparator circuits 13, the plurality of first determination circuits 14, and the plurality of second determination circuits 15 are in one-to-one correspondence (or association) with the plurality of detection elements 2, 3, 4. That is, one detection circuit 11, one correction circuit 12, one comparator circuit 13, one first determination circuit 14, and one second determination circuit 15 are associated with each of the detection elements 2, 3, 4.

Each of the plurality of detection circuits 11 generates a first detection signal Sig2 based on the output signal Sig1 of an associated one of the detection elements 2, 3, 4. Each of the plurality of correction circuits 12 corrects the nonlinearity of the first detection signal Sig2 supplied from an associated one of the plurality of detection circuits 11, and outputs a corrected second detection signal Sig 3. Each of the plurality of comparator circuits 13 compares the first detection signal Sig2 supplied from the associated one of the plurality of detection circuits 11 and the second detection signal Sig3 supplied from the associated one of the plurality of correction circuits 12 with each other. Then, each of the plurality of comparator circuits 13 outputs a comparison signal Sig4 representing the comparison result.

Each of the plurality of first decision circuits 14 determines the magnitude of the inertial force based on the first detection signal Sig2 supplied from an associated one of the plurality of detection circuits 11. Then, each of the plurality of first decision circuits 14 outputs a first decision signal Sig5 indicating a result of the decision. Each of the plurality of second decision circuits 15 determines whether the associated correction circuit 12 is functioning normally based on the comparison signal Sig4 supplied from the associated one of the plurality of comparator circuits 13 and the first decision signal Sig5 supplied from the associated one of the plurality of first decision circuits 14. Then, each of the plurality of second determination circuits 15 outputs a second determination signal Sig6 indicating a determination result.

(2.1.1) detection Circuit

As shown in fig. 1, each of the plurality of detection circuits 11 includes a CV converter circuit 111 and an a/D converter circuit 112.

The CV converter circuit 111 converts a change in capacitance caused by each of the detection elements 2, 3, 4 into a voltage. The CV converter circuit 111 includes an amplifier 113, a capacitor 114, and a switch 115. The inverting input of the amplifier 113 is electrically connected to a connection node between two capacitors C1, C2, which form part of each of the detecting elements 2, 3, 4, C1, C2. The capacitor 114 and the switch 115 are connected in parallel between the inverting input terminal and the output terminal of the amplifier 113. In addition, a reference voltage is input to the non-inverting input terminal of the amplifier 113.

The a/D converter circuit 112 generates a digital first detection signal Sig2 based on an analog output signal Sig supplied from each of the detection elements 2, 3, 4 via the CV converter circuit 111. The digital first detection signal Sig2 converted by the a/D converter circuit 112 is supplied to the correction circuit 12, the comparator circuit 13, and the first decision circuit 14.

(2.1.2) correction Circuit

As shown in fig. 1, each of the plurality of correction circuits 12 includes a subtractor 121 and a multiplier 122.

The multiplier 122 multiplies the first detection signal Sig2 supplied from the detection circuit 11 by any one of the correction coefficients a1, a2, or A3, and outputs the calculation result to the subtractor 121. The subtractor 121 subtracts the first detection signal Sig2 multiplied by any one of the correction coefficients a1, a2, or A3 from the first detection signal Sig2 supplied from the detection circuit 11. This allows the second detection signal Sig3 to be generated by correcting for the non-linearity of the first detection signal Sig 2. Specifically, each of the correction coefficients a1, a2, and A3 used by the multiplier 122 is a coefficient associated with the difference between the theoretical value and the actual measurement value of the first detection signal Sig 2. The second detection signal Sig3 generated by the subtractor 121 is supplied not only to the comparator circuit 13 but also to a control circuit mounted on the printed wiring board. The control circuit detects the magnitude of the inertial force (acceleration) based on the second detection signal Sig3 supplied from the correction circuit 12.

(2.1.3) comparator Circuit

As shown in fig. 1, each of the plurality of comparator circuits 13 includes a subtractor 131 and a comparator 132.

The subtractor 131 subtracts the first detection signal Sig2 supplied from the detection circuit 11 from the second detection signal Sig3 supplied from the correction circuit 12. That is, the subtractor 131 calculates the difference between the respective values of the first detection signal Sig2 and the second detection signal Sig 3.

For example, the comparator 132 may be implemented as a comparator. The comparator 132 receives the signal (differential signal) from the subtractor 131 at one input terminal thereof, and also receives the first threshold TH1 at the other input terminal thereof. The first threshold TH1 is stored in the storage unit 16. The comparator 132 compares the value of the differential signal supplied from the subtractor 131 and the first threshold TH1 with each other, and outputs a comparison signal Sig4 indicating the comparison result. If the value of the differential signal is equal to or less than the first threshold value TH1, the comparator 132 outputs a comparison signal Sig4 in a logic "1" state. Meanwhile, if the value of the differential signal is greater than the first threshold TH1, the comparator 132 outputs the comparison signal Sig4 in a logic "0" state. The comparison signal Sig4 is input to the second determination circuit 15.

(2.1.4) first decision circuit

Each of the plurality of first determination circuits 14 is configured to output a first determination signal Sig5 representing the magnitude of the inertial force (acceleration). Each of the plurality of first decision circuits 14 determines the magnitude of the inertial force (acceleration) based on the first detection signal Sig2 provided by the associated one of the plurality of detection circuits 11. The first determination circuit 14 determines the magnitude of the inertial force (acceleration) by comparing the value of the first detection signal Sig2 with the second threshold value stored in the storage unit 16, and outputs a first determination signal Sig5 indicating the determination result. If the value of the first detection signal Sig2 is equal to or greater than the second threshold value, the first decision circuit 14 outputs a first decision signal Sig5 that is in a logic "1" state. Meanwhile, if the value of the first detection signal Sig2 is less than the second threshold value, the first decision circuit 14 outputs the first decision signal Sig5 in a logic "0" state. The first determination signal Sig5 is input to the second determination circuit 15.

(2.1.5) second determination circuit

As shown in fig. 1, each of the plurality of second determination circuits 15 is implemented as, for example, an AND circuit. Each of the plurality of second decision circuits 15 receives the comparison signal Sig4 from an associated one of the plurality of comparator circuits 13 and the first decision signal Sig5 from an associated one of the plurality of first decision circuits 14. Then, the second determination circuit 15 outputs the second determination signal Sig6 based on the comparison signal Sig4 and the first determination signal Sig 5. For example, if the value of the first determination signal Sig5 is "1" and the value of the comparison signal Sig4 is "1", the value of the second determination signal Sig6 is "1". On the other hand, if the value of the first determination signal Sig5 is "0" and/or the value of the comparison signal Sig4 is "0", the value of the second determination signal Sig6 is "0". The second determination signal Sig6 is input to the control circuit. If the value of the second determination signal Sig6 is "1", the control circuit determines that the correction circuit 12 is operating abnormally. Meanwhile, if the value of the second determination signal Sig6 is "0", the control circuit determines that the correction circuit 12 is operating normally.

In other words, if the comparison result of the comparator circuit 13 satisfies the first condition and the determination result of the first determination circuit 14 satisfies the second condition, the second determination circuit 15 determines that the correction circuit 12 operates abnormally. Meanwhile, if the comparison result of the comparator circuit 13 does not satisfy the first condition and the determination result of the first determination circuit 14 satisfies the second condition, the second determination circuit 15 determines that the correction circuit 12 operates normally.

In the present embodiment, the first condition is satisfied if the absolute value of the difference between the respective values of the first and second detection signals Sig2 and Sig3 is equal to or smaller than the first threshold TH 1. In other words, if the absolute value of the difference between the respective values of the first detection signal Sig2 and the second detection signal Sig3 is equal to or smaller than the first threshold TH1, the comparison result of the comparator circuit 13 satisfies the first condition. On the other hand, if the magnitude of the inertial force determined based on the first detection signal Sig2 is equal to or greater than the second threshold value, the second condition is satisfied. In other words, if the magnitude of the inertial force determined based on the first detection signal Sig2 is equal to or larger than the second threshold value, the determination result of the first determination circuit 14 satisfies the second condition.

(2.1.6) memory cell

The memory unit 16 may be a register of, for example, an ASIC. The storage unit 16 stores the correction coefficients a1, a2, A3, the first threshold TH1, and the second threshold. In the present embodiment, the second threshold value is a determination threshold value used by the first determination circuit 14 to determine the magnitude of the inertial force based on the first detection signal Sig 2. The storage unit 16 is configured to be able to overwrite at least the second threshold. Accordingly, the memory cell 16 may be configured to be able to rewrite at least one of the correction coefficient a1, a2, A3, or the first threshold TH 1.

(2.2) detection element

The detection element 2 detects an inertial force (acceleration) in the X-axis direction. The detection element 3 detects an inertial force (acceleration) in the Y-axis direction. The detection element 4 detects an inertial force (acceleration) in the Z-axis direction. That is, the inertial sensor 10 according to the present embodiment is a three-axis acceleration sensor, and can detect acceleration in the X-axis direction, acceleration in the Y-axis direction, and acceleration in the Z-axis direction.

As shown in fig. 2, the inertial sensor 10 according to the present embodiment further includes a housing 5, an upper cover 6, and a lower cover 7. Each of the housing 5, the upper cover 6, and the lower cover 7 is formed in a rectangular parallelepiped shape elongated in the Y-axis direction, and their outer dimensions (the dimension in the X-axis direction and the dimension direction in the Y-axis direction) are substantially the same when viewed in the Z-axis direction.

The detection element 2 includes a weight 21, a pair of fixed electrodes 22, and a pair of moving electrodes 23, 23. The weight 21 is formed in a rectangular shape when viewed in the Z-axis direction. Both ends of the weight 21 in the Y-axis direction are fixed to the housing 5 via a pair of beams 24, 24. A pair of moving electrodes 23, 23 are mounted on the upper surface (the surface facing the upper cover 6) of the weight 21 in a state where the pair of moving electrodes 23, 23 are juxtaposed in the X-axis direction. A pair of fixed electrodes 22, 22 is mounted on the lower surface (the surface facing the housing 5) of the upper cover 6 in a state where the pair of fixed electrodes 22, 22 are juxtaposed in the X-axis direction. The pair of fixed electrodes 22, 22 and the pair of moving electrodes 23, 23 face each other with a predetermined gap left therebetween in a state where the housing 5 and the upper cover 6 are superposed on each other. The detection element 2 is configured to swing within the ZX plane with the pair of beams 24, 24 as fulcrums when acceleration is applied in the X-axis direction.

The detection element 3 includes a weight 31, a pair of fixed electrodes 32, and a pair of moving electrodes 33, 33. The weight 31 is formed in a rectangular shape when viewed in the Z-axis direction. Both ends of the weight 31 in the X-axis direction are fixed to the housing 5 via a pair of beams 34, 34. A pair of moving electrodes 33, 33 are mounted on the upper surface (the surface facing the upper cover 6) of the weight 31 in a state where the pair of moving electrodes 33, 33 are juxtaposed in the Y-axis direction. A pair of fixed electrodes 32, 32 is mounted on the lower surface (the surface facing the housing 5) of the upper cover 6 in a state where the pair of fixed electrodes 32, 32 are juxtaposed in the Y-axis direction. The pair of fixed electrodes 32, 32 and the pair of moving electrodes 33, 33 face each other with a predetermined gap left therebetween in a state where the housing 5 and the upper cover 6 are superposed on each other. The detection element 3 is configured to swing within the YZ plane with the pair of beams 34, 34 as fulcrums when acceleration is applied in the Y-axis direction.

The detection element 4 includes a weight 41, a pair of fixed electrodes 42, and a pair of moving electrodes 43, 43 (only the upper moving electrode 43 is shown in fig. 2). The weight 41 is formed in a rectangular shape when viewed in the Z-axis direction. The weight 41 is fixed to the housing 5 via four beams 44, each of which is formed in an L-shape. A pair of moving electrodes 43, 43 are mounted on both surfaces of the weight 41 in the Z-axis direction. One fixed electrode 42 of a pair of fixed electrodes 42, 42 is mounted on the lower surface of the upper cover 6. Meanwhile, the other fixed electrode 42 of the pair of fixed electrodes 42, 42 is mounted on the upper surface of the lower cover 7. In a state where the case 5, the upper cover 6, and the lower cover 7 are superposed on each other, one fixed electrode 42 of the pair of fixed electrodes 42, 42 and one moving electrode 43 of the pair of moving electrodes 43, 43 face each other with a predetermined gap left therebetween. Meanwhile, in a state where the case 5, the upper cover 6, and the lower cover 7 are superposed on each other, the other fixed electrode 42 of the pair of fixed electrodes 42, 42 and the other moving electrode 43 of the pair of moving electrodes 43, 43 face each other with a predetermined gap left therebetween. The detection element 4 is configured to be movable in the Z-axis direction with the four beams 44 as fulcrums when acceleration is applied in the Z-axis direction.

Fig. 3 is a sectional view taken along the plane X1-X2 shown in fig. 2, and shows the detecting element 2. One fixed electrode 22 (shown on the left side of fig. 3) of the pair of fixed electrodes 22, 22 and one moving electrode 23 (shown on the left side of fig. 3) of the pair of moving electrodes 23 form a capacitor C1. In addition, the other fixed electrode 22 (shown on the right side in fig. 3) of the pair of fixed electrodes 22, 22 and the other moving electrode 23 (shown on the right side in fig. 3) of the pair of moving electrodes 23. The moving electrodes 23, 23 form a capacitor C2. It is assumed that acceleration acts on the structure in the direction indicated by the arrow X3 in fig. 3 (hereinafter referred to as "X3 direction"). In this case, the weight 21 of the detection element 2 swings within the ZX plane with the pair of beams 24, 24 as fulcrums due to the acceleration thus applied. In the example shown in fig. 3, when acceleration is applied in the X3 direction, the gap between one fixed electrode 22 and one moving electrode 23 becomes wider, and the gap between the other fixed electrode 22 and the other moving electrode 23 becomes narrower. This results in a decrease in the capacitance of the capacitor C1 and an increase in the capacitance of the capacitor C2 as compared with the case where no acceleration is applied in the X3 direction. Therefore, the inertial sensor 10 according to the present embodiment can detect the acceleration applied in the X3 direction based on the capacitance values of the two capacitors C1 and C2.

In the present embodiment, it is assumed that the surface area of each of the pair of fixed electrodes 22, 22 and the pair of moving electrodes 23, 23 as viewed in the Z-axis direction is Sa, the relative dielectric constant thereof is ∈ 0, and the inter-electrode distances of the capacitors C1, C2 are d1, d2, respectively. In this case, the capacitance values Ca, Cb of the capacitors C1 and C2 are given by the following equations (1) and (2), respectively:

[ equation 1]

Ca＝ε0×(Sa/d1)…(1)

[ formula 2]

Cb＝ε0×(Sa/d2)…(2)

If the inter-electrode distance d1 increases with increasing acceleration, the inter-electrode distance d2 decreases. In contrast, if the inter-electrode distance d1 decreases as the acceleration increases, the inter-electrode distance d2 increases. Therefore, the acceleration is proportional to the difference (Ca-Cb) between the capacitance values Ca, Cb of the capacitors C1 and C2.

Fig. 4 is a diagram showing the relationship between the input acceleration and the sensor output of the inertial sensor 10 of the present embodiment. In fig. 4, the abscissa represents the input acceleration, and the ordinate represents the sensor output. Specifically, in fig. 4, a solid line a1 represents the relationship between the input acceleration to be corrected and the sensor output, a broken line b1 represents the relationship between the corrected input acceleration and the sensor output, and a dashed-dotted line c1 represents the difference between the two curves respectively representing the characteristics before and after correction. The acceleration is proportional to the difference (Ca-Cb) between the capacitance values Ca, Cb of the capacitors C1 and C2 forming part of the detection element 2. The difference (Ca-Cb) between the capacitance values Ca, Cb is proportional to (1/d1-1/d 2). Further, as the acceleration increases, the nonlinearity in which the inter-electrode distances d1 and d2 change as the acceleration increases. Therefore, the nonlinearity is significant in a range where the input acceleration is high (see fig. 4).

For example, assume that the non-linearity of the inertial sensor 10 causes an error of at least 1% with 10G of acceleration applied. In this case, the value of the first detection signal Sig2 as the signal to be corrected is equal to or greater than 10.1G. If the value of the first detection signal Sig2 is equal to or greater than 10.1G, the value of the second detection signal Sig3 is 10G. This makes the difference between the respective values of the first and second detection signals Sig2 and Sig3 0.1G. In this case, for example, by setting the first threshold TH1 to 0.05G, if the difference is larger than the first threshold TH1, it is determined that the correction circuit 12 is operating normally. Meanwhile, if the first threshold TH1 is smaller than the difference, it is determined that the correction circuit 12 is operating abnormally.

In this case, as shown in fig. 4, when the input acceleration is low, the nonlinear error is also not significant. Therefore, it is preferably determined whether the correction circuit 12 operates normally only in a range where the nonlinear error is significant to some extent (e.g., 4G or more in fig. 4).

In addition, in the example shown in fig. 4, the determination threshold value (second threshold value) used by the first determination circuit 14 to determine the magnitude of the inertial force is preferably set to about 4G when the nonlinearity of the acceleration starts to be significant.

(3) Operation of

Next, with reference to a sequence diagram shown in fig. 5, the operation of the signal processing apparatus 1 according to the present embodiment is described. The following description will be given taking as an example a case where acceleration acts in the X-axis direction. However, almost the same description applies to the other two cases where the acceleration acts in the Y-axis and Z-axis directions, respectively, and therefore the description thereof will be omitted here.

Upon detecting the acceleration in the X-axis direction, the detection element 2 supplies an output signal Sig1 to an associated one of the detection circuits 11 (in the first step Si). The detection circuit 11 generates a first detection signal Sig2 based on the output signal Sig1 supplied from the detection element 2 (in a second step S2). The detection circuit 11 outputs the generated first detection signal Sig2 to its associated correction circuit 12, comparator circuit 13, and first determination circuit 14 (in third step S3).

The correction circuit 12 corrects the nonlinearity of the first detection signal Sig2 supplied from the detection circuit 11, and generates a corrected second detection signal Sig3 (in a fourth step S4). Specifically, the correction circuit 12 subtracts the product of the first detection signal Sig2 and the correction coefficient a1 from the value of the first detection signal Sig 2. The correction circuit 12 outputs the generated second detection signal Sig3 to the control circuit and comparator circuit 13 described above (in a fifth step S5).

The first determination circuit 14 determines the magnitude of the inertial force (acceleration) based on the first detection signal Sig2 supplied from the detection circuit 11 (in a sixth step S6). Specifically, the first determination circuit 14 compares the value of the first detection signal Sig2 and the first threshold TH1 with each other, and generates a first determination signal Sig5 indicating the comparison result. Then, the first determination circuit 14 outputs the generated first determination signal Sig5 to the second determination circuit 15 (in a seventh step S7).

The comparator circuit 13 compares the first detection signal Sig2 supplied from the detection circuit 11 and the second detection signal Sig3 supplied from the correction circuit 12 with each other (in an eighth step S8). Specifically, the comparator circuit 13 calculates a difference between the respective values of the second detection signal Sig3 and the first detection signal Sig2, and compares the difference with the first threshold TH 1. Then, the comparator circuit 13 generates a comparison signal Sig4 indicating the comparison result, and outputs the generated comparison signal Sig4 to the second decision circuit 15 (in a ninth step S9).

The second decision circuit 15 determines whether the correction circuit 12 operates normally based on the comparison signal Sig4 supplied from the comparator circuit 13 and the first decision signal Sig5 supplied from the first decision circuit 14 (in a tenth step S10). Specifically, if the value of the comparison signal Sig4 is "1" and the value of the first determination signal Sig5 is "1", the second determination circuit 15 generates the second determination signal Sig6 having a value of "1". On the other hand, if the value of the comparison signal Sig4 is "0" and/or the value of the first determination signal Sig5 is "0", the second determination circuit 15 generates the second determination signal Sig6 having a value of "0". The second determination circuit 15 outputs the generated second determination signal Sig6 to the control circuit described above (in an eleventh step S11).

(4) Advantages of the invention

The signal processing apparatus 1 according to the embodiment compares the first detection signal Sig2 supplied from the detection circuit 11 and the second detection signal Sig3 supplied from the correction circuit 12 with each other. Then, the signal processing apparatus 1 outputs a comparison signal Sig4 indicating the comparison result. In the present embodiment, the correction circuit 12 corrects the nonlinearity of the first detection signal Sig2 supplied from the detection circuit 11. This causes a difference of a predetermined value or more between the respective values of the first detection signal Sig2 and the second detection signal Sig 3. Therefore, the signal processing device 1 can determine that the correction circuit 12 is operating abnormally when it is found that a difference of a predetermined value or more is not generated based on the result of comparison between the first detection signal Sig2 and the second detection signal Sig 3. That is, the signal processing apparatus 1 according to the present embodiment can determine whether the correction circuit 12 operates normally based on the comparison signal Sig4 supplied from the comparator circuit 13.

In addition, in the signal processing apparatus 1 according to the present embodiment, if the comparison result of the comparator circuit 13 satisfies the first condition and the determination result of the first determination circuit 14 satisfies the second condition, the second determination circuit 15 determines that the correction circuit 12 operates abnormally. Meanwhile, if the comparison result of the comparator circuit 13 does not satisfy the first condition and the determination result of the first determination circuit 14 satisfies the second condition, the second determination circuit 15 determines that the correction circuit 12 operates normally. That is, the signal processing apparatus 1 according to the present embodiment can determine whether the correction circuit 12 operates normally based on the comparison result of the comparator circuit 13 and the determination result of the first determination circuit 14.

In addition, the signal processing device 1 according to the present embodiment determines that the correction circuit 12 is operating abnormally if the magnitude of the inertial force determined based on the first detection signal Sig2 is equal to or greater than the second threshold value and the absolute value of the difference between the respective values of the first detection signal Sig2 and the second detection signal Sig3 is equal to or less than the first threshold value TH 1. Therefore, if the absolute value of the difference between the respective values of the first detection signal Sig2 and the second detection signal Sig3 is equal to or smaller than the first threshold TH1, it can be determined that the correction circuit 12 is operating abnormally.

In addition, in the signal processing apparatus 1 according to the present embodiment, the storage unit 16 is configured to be able to rewrite the determination threshold value (second threshold value) that the first determination circuit 14 uses to determine the magnitude of the inertial force based on the first detection signal Sig 2. Therefore, even if the magnitude of the inertial force at the time when the sensor output starts to change nonlinearly changes, it is possible to cope with this by rewriting the determination threshold value.

(5) Variants

Note that the above-described embodiment is only one example embodiment among various embodiments of the present disclosure, and should not be construed as a limitation. Rather, the embodiments may be readily modified in various ways depending on design choices or any other factors without departing from the scope of the present disclosure. For example, the functions of the signal processing apparatus 1 according to the above-described embodiments may also be implemented as a signal processing method, a computer program, or a non-transitory storage medium storing a computer program.

The signal processing method according to an aspect includes a detection step (second step S2), a correction step (fourth step S4), and a comparison step (eighth step S8). The detecting step comprises generating a first detection signal Sig2 based on the output signal Sig1 of the capacitive sensing element 2, 3, 4 detecting the inertial force. The correcting step includes correcting the non-linearity of the first detection signal Sig2 to output a corrected second detection signal Sig 3. The comparing step includes comparing the first detection signal Sig2 and the second detection signal Sig3 with each other to output a comparison signal Sig4 indicating a result of the comparison.

A program according to another aspect is designed to cause one or more processors to execute the above-described signal processing method.

Next, modifications of the above-described exemplary embodiments will be enumerated one by one. The modifications described below may be employed in appropriate combinations.

The signal processing apparatus 1 according to the present disclosure includes a computer system. The computer system includes a processor and memory as the main hardware components. The functions of the signal processing apparatus 1 according to the present disclosure may be performed by causing a processor to execute a program stored in a memory of a computer system. The program may be stored in advance in the memory of the computer system. Alternatively, the program may be downloaded via a telecommunication line, or may be recorded in a non-transitory storage medium readable by a computer system such as a memory card, an optical disk, or a hard disk drive and distributed. The processor of the computer system may be implemented as a single or multiple electronic circuits including a semiconductor Integrated Circuit (IC) or a large scale integrated circuit (LSI). As used herein, an "integrated circuit" such as an IC or an LSI is referred to by different names according to its degree of integration. Examples of the integrated circuit include a system LSI, a Very Large Scale Integration (VLSI), and a very large scale integration (ULSI). Alternatively, a Field Programmable Gate Array (FPGA) which is programmed after manufacturing an LSI or a reconfigurable logic device which allows reconfiguration of connections or circuit portions inside the LSI may also be employed as the processor. These electronic circuits may be integrated together on a single chip or distributed over multiple chips, as appropriate. The multiple chips may be integrated together in a single device or distributed among multiple devices, without limitation. As used herein, a "computer system" includes a microcontroller (including one or more processors) and one or more memories. Thus, a microcontroller may also be implemented as a single or multiple electronic circuits including a semiconductor integrated circuit or a large scale integrated circuit.

In addition, in the above-described embodiment, a plurality of constituent elements of the signal processing device 1 are integrated in a single housing. However, this is not a necessary configuration of the signal processing apparatus 1. Alternatively, these constituent elements of the signal processing device 1 may be distributed in a plurality of different housings. Still alternatively, at least some functions of the signal processing apparatus 1 (for example, functions of the correction circuit 12) may also be implemented as a cloud computing system.

Alternatively, the signal processing apparatus 1 may have a determination mode designed to cause the second determination circuit 15 to determine whether the correction circuit 12 operates normally based on an artificially generated inertial force (acceleration). In this case, for example, a fixed electrode is provided on the upper surface of the above-described lower cover 7 and a moving electrode is provided on the lower surface of the weight 21 to form at least one capacitor. Then, the fixed electrode and the moving electrode are energized to generate an electrostatic force between the two electrodes. This causes the weight 21 to tilt and thus to generate an artificial acceleration. Finally, the signal processing apparatus 1 causes the second determination circuit 15 to determine whether the correction circuit 12 operates normally based on the acceleration artificially generated in this manner. This allows determining whether the correction circuit 12 is functioning properly, not only at the time of pre-shipment inspection of the inertial sensor 10, but even when the inertial sensor 10 is being used.

In the above-described embodiment, the inertial sensor 10 is implemented as a three-axis acceleration sensor. However, the inertial sensor 10 may also be, for example, a biaxial acceleration sensor.

In the above embodiment, the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction are individually detected by three different detection circuits 11, respectively. However, for example, the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction may be detected by a single detection circuit. In this case, for example, the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction may be sequentially detected in time using a multiplexer.

In the above embodiments, the inertial sensor 10 is a surface mount sensor. However, the inertial sensor 10 may also be, for example, a through-hole mount sensor.

In the above embodiment, the inertial sensor 10 is an acceleration sensor. However, the inertial sensor 10 is not necessarily an acceleration sensor, but may be, for example, an angular velocity sensor (gyro sensor).

In the above-described embodiment, the signal processing apparatus 1 is an ASIC. However, the signal processing apparatus 1 is not limited to an ASIC, but may be, for example, an FPGA (field programmable gate array), or be composed of one or more processors and one or more memories.

In the above embodiment, the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction are individually detected by the three different detecting elements 2, 3, 4, respectively. However, for example, the acceleration in the X-axis direction, the acceleration in the Y-axis direction, and the acceleration in the Z-axis direction may be detected by a single detection element. Specifically, the detection element may also be realized as a MEMS (micro electro mechanical system) element in which the functions of detecting the X-axis directional acceleration, the Y-axis directional acceleration, and the Z-axis directional acceleration are integrated in a single chip.

In the above-described embodiment, the second determination circuit 15 is implemented as an AND circuit. However, the second determination circuit 15 is not limited to the AND circuit, AND may be, for example, a NAND circuit. In addition, the second determination circuit 15 may have any other configuration as long as the second determination circuit 15 is configured to determine whether the correction circuit 12 operates normally based on the comparison signal Sig4 and the first determination signal Sig 5.

In the above-described embodiment, the first threshold TH1 and the second threshold (determination threshold) are fixed values. However, at least one of the first threshold TH1 or the second threshold may be adjustable.

(general)

As can be seen from the above description, the signal processing apparatus (1) according to the first aspect includes a detection circuit (11), a correction circuit (12), and a comparator circuit (13). A detection circuit (11) generates a first detection signal (Sig2) based on an output signal (Sig1) of a capacitance detection element (2, 3, 4) that detects an inertial force. The correction circuit (12) corrects the nonlinearity of the first detection signal (Sig2), and outputs a corrected second detection signal (Sig 3). The comparator circuit (13) compares the first detection signal (Sig2) and the second detection signal (Sig3) with each other, and outputs a comparison signal (Sig4) indicating the comparison result.

This aspect allows checking the operation of the correction circuit (12) based on the comparison signal (Sig4) representing the result of comparison between the first detection signal (Sig2) supplied from the detection circuit (11) and the second detection signal (Sig3) supplied from the correction circuit (12).

The signal processing apparatus (1) according to the second aspect, which can be implemented in combination with the first aspect, further includes a first determination circuit (14) and a second determination circuit (15). The first determination circuit (14) determines the magnitude of the inertial force based on the first detection signal (Sig2), and outputs a first determination signal (Sig5) indicating the determination result. The second determination circuit (15) determines whether the correction circuit (12) is operating normally based on the comparison signal (Sig4) and the first determination signal (Sig5), and outputs a second determination signal (Sig6) indicating the determination result. The second determination circuit (15) determines that the correction circuit (12) operates abnormally if the comparison result of the comparator circuit (13) satisfies the first condition and the determination result of the first determination circuit (14) satisfies the second condition.

This aspect allows determination of an abnormality in operation of the correction circuit (12) based on the comparison result of the comparator circuit (13) and the determination result of the first determination circuit (14).

The signal processing apparatus (1) according to the third aspect, which may be implemented in combination with the first aspect or the second aspect, further includes a first determination circuit (14) and a second determination circuit (15). The first determination circuit (14) determines the magnitude of the inertial force based on the first detection signal (Sig2), and outputs a first determination signal (Sig5) indicating the determination result. The second determination circuit (15) determines whether the correction circuit (12) is operating normally based on the comparison signal (Sig4) and the first determination signal (Sig5), and outputs a second determination signal (Sig6) indicating the determination result. The second determination circuit (15) determines that the correction circuit (12) is operating normally if the comparison result of the comparator circuit (13) does not satisfy the first condition and the determination result of the first determination circuit (14) satisfies the second condition.

This aspect allows the correction circuit (12) to be determined to be functioning properly based on the comparison result of the comparator circuit (13) and the determination result of the first determination circuit (14).

In a signal processing apparatus (1) according to a fourth aspect that may be realized in combination with the second or third aspect, the first condition is that an absolute value of a difference between respective values of the first detection signal (Sig2) and the second detection signal (Sig3) is equal to or smaller than a first threshold value (TH 1). The second condition is that the magnitude of the inertial force determined based on the first detection signal (Sig2) is equal to or greater than a second threshold value.

This aspect allows the determination that the correction circuit 12 is operating abnormally if the magnitude of the inertial force determined based on the first detection signal (Sig2) is equal to or greater than the second threshold value and the absolute value of the difference between the respective values of the first detection signal (Sig2) and the second detection signal (Sig3) is equal to or less than the first threshold value TH 1. Therefore, if the absolute value of the difference between the respective values of the first detection signal (Sig2) and the second detection signal (Sig3) is equal to or smaller than the first threshold value (TH1), it can be determined that the correction circuit (12) is operating abnormally.

The signal processing apparatus (1) according to the fifth aspect, which may be implemented in combination with any one of the second to fourth aspects, further includes a storage unit (16). The storage unit (16) stores and can overwrite a determination threshold value used by the first determination circuit (14) to determine the magnitude of the inertial force based on the first detection signal (Sig 2).

According to this aspect, even if the magnitude of the inertial force at the time when the sensor output starts to change nonlinearly changes, it is possible to cope with this by rewriting the determination threshold value.

The signal processing apparatus (1) according to the sixth aspect, which can be implemented in combination with any one of the second to fifth aspects, has a determination mode. The determination mode is designed such that the second determination circuit (15) determines whether the correction circuit (12) is operating normally based on the artificially generated inertial force.

This aspect allows checking the operation of the correction circuit (12) based on artificially generated inertial forces.

An inertial sensor (10) according to a seventh aspect comprises a signal processing device (1) according to any one of the first to sixth aspects and a capacitive detection element (2, 3, 4).

This aspect allows checking the operation of the correction circuit (12) based on a comparison signal (Sig4) representing the result of comparison between the first detection signal (Sig2) supplied by the detection circuit (11) and the second detection signal (Sig3) supplied by the correction circuit (12).

The signal processing method according to the eighth aspect includes a detection step (S2), a correction step (S4), and a comparison step (S8). The detecting step (S2) includes generating a first detection signal (Sig2) based on an output signal (Sig1) of a capacitance detecting element (2, 3, 4) that detects the inertial force. The correcting step (S4) includes correcting the nonlinearity of the first detection signal (Sig2) and outputting a corrected second detection signal (Sig 3). The comparing step (S8) includes comparing the first detection signal (Sig2) and the second detection signal (Sig3) with each other and outputting a comparison signal (Sig4) indicating a result of the comparison.

This aspect allows the operation of the correction circuit (12) to be checked based on the comparison signal (Sig4) indicating the result of comparison between the first detection signal (Sig2) generated in the detection step (S2) and the second detection signal (Sig3) output in the correction step (S4).

A program according to a ninth aspect is designed to cause one or more processors to execute the signal processing method according to the eighth aspect.

This aspect allows the operation of the correction circuit (12) to be checked based on the comparison signal (Sig4) indicating the result of comparison between the first detection signal (Sig2) generated in the detection step (S2) and the second detection signal (Sig3) output in the correction step (S4).

Note that the constituent elements according to the second to sixth aspects are not essential constituent elements of the signal processing apparatus (1), but may be omitted as appropriate.

List of reference numerals

1 a signal processing device;

11 a detection circuit;

12 a correction circuit;

13 a comparator circuit;

14 a first decision circuit;

15 a second decision circuit;

16 a storage unit;

2, 3, 4 detection element;

10 an inertial sensor;

sig1 output signal;

sig2 first detection signal;

sig3 second detection signal;

sig4 compares the signals;

sig5 first decision signal;

sig6 second decision signal;

s2 second step (detection step);

s4 fourth step (correction step);

an eighth step (comparison step) of S8;

TH1 first threshold.