Signal processing circuit, acceleration sensor, and electronic device

Abstract

To reduce time required for measuring the band of an accelerator sensor.SOLUTION: A signal processing device (2) can be connected to sensor elements (1x, 1Y, 1Z) including a first fixed electrode (E1), a first movable electrode (E2), a second movable electrode (E3), and a second fixed electrode (E4), and includes a drive circuit (22) configured so as to supply a first drive signal to a first variable capacitor between the first fixed electrode and the first movable electrode, and supply a second drive signal to a second variable capacitor between the second fixed electrode and the second variable electrode, and a detection circuit (24) configured so as to generate a detection signal corresponding to a difference between the first variable capacitor and the second variable capacitor. The drive circuit is configured so as to apply Coulomb force periodically between the first fixed electrode and the first variable electrode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention disclosed in this specification relates to a signal processing circuit, an acceleration sensor, and an electronic device. [Background technology]

[0002] It is known that the bandwidth of an acceleration sensor (the frequency range of detectable acceleration changes) can be broadened by increasing the resonant frequency of vibration of a movable part of the acceleration sensor (see Patent Document 1).

[0003] The bandwidth of an acceleration sensor is an important parameter for the acceleration sensor and is measured during shipping tests of the acceleration sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-49434 A

[0005] [overview] A common method for measuring the bandwidth of an acceleration sensor is to actually apply acceleration to the acceleration sensor and change the frequency of the acceleration change. However, this method has the problem that it takes a long time to measure.

[0006] The signal processing circuit disclosed in the present specification is a signal processing circuit connectable to a sensor element including a first fixed electrode, a first movable electrode, a second movable electrode, and a second fixed electrode, and includes a drive circuit configured to supply a first drive signal to a first variable capacitance between the first fixed electrode and the first movable electrode and a second drive signal to a second variable capacitance between the second fixed electrode and the second movable electrode, and a detection circuit configured to generate a detection signal according to a difference between the first variable capacitance and the second variable capacitance. The drive circuit is configured to periodically apply a Coulomb force between the first fixed electrode and the first movable electrode.

[0007] The acceleration sensor disclosed in this specification includes the signal processing circuit configured as above and the sensor element.

[0008] The electronic device disclosed in this specification includes an acceleration sensor having the above-described configuration. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of an acceleration sensor according to an embodiment. [Diagram 2] FIG. 2 is a timing chart of the trigger signal. [Diagram 3] FIG. 3 is a timing chart of various signals when the trigger signal TG is at a low level. [Figure 4] FIG. 4 is a schematic diagram showing the electrode structure of the sensor element. [Diagram 5] FIG. 5 is a timing chart of various signals when the trigger signal TG is at a high level. [Figure 6] FIG. 6 is an external view of the vehicle.

[0010] [Detailed Description] <Acceleration sensor> Fig. 1 is a diagram showing the configuration of an acceleration sensor according to an embodiment. The acceleration sensor 100 shown in Fig. 1 includes a sensor element 1X, a sensor element 1Y, a sensor element 1Z, and a signal processing device 2. The acceleration sensor 1010 is a capacitance-type three-axis acceleration sensor capable of measuring acceleration in three mutually orthogonal axial directions (X-axis, Y-axis, and Z-axis).

[0011] The sensor element 1X, the sensor element 1Y, and the sensor element 1Z are each a capacitance type acceleration sensor element using MEMS (Micro Electro Mechanical System) technology. The sensor element 1X has a first fixed electrode, a second fixed electrode, a movable electrode, and a spring made of, for example, silicon. When no acceleration in the X-axis direction is applied to the sensor element 1X, the first distance between the first fixed electrode and the movable electrode and the second distance between the second fixed electrode and the movable electrode do not change. On the other hand, when acceleration in the X-axis direction is applied to the sensor element 1, the movable electrode is displaced relative to the first fixed electrode and the second fixed electrode, and one of the first capacitance between the first fixed electrode and the movable electrode and the second capacitance between the second fixed electrode and the movable electrode increases and the other decreases. The sensor elements 1Y and 1Z each have the same structure as the sensor element 1X. The sensor elements 1X, the sensor elements 1Y, and the sensor elements 1Z are installed in different directions. The capacitance of the sensor element 1X changes depending on the acceleration in the X-axis direction applied to the sensor element 1X. The capacitance of sensor element 1Y changes in response to the acceleration applied to sensor element 1Y in the Y-axis direction, and the capacitance of sensor element 1Z changes in response to the acceleration applied to sensor element 1Z in the Z-axis direction.

[0012] The signal processing device 2 determines the acceleration in the X-axis direction based on the change in capacitance of the sensor element 1X, determines the acceleration in the Y-axis direction based on the change in capacitance of the sensor element 1Y, and determines the acceleration in the Z-axis direction based on the change in capacitance of the sensor element 1Z. The signal processing device 2 includes a communication circuit 20, a control register 21, a drive circuit 22, a switching circuit 23, an AFE (Analog Front End) 24, an ADC (Analog to Digital Converter) 25, a data correction circuit 26, an output register 27, and an interrupt generation circuit 28.

[0013] The communication circuit 20 communicates with an external device. When a test is performed to measure the bandwidth of the acceleration sensor 100, the communication circuit 20 is connected to the measurement device 3 as shown in Fig. 1. When the communication circuit 20 receives a control command output from the external device, the communication circuit 20 writes the control command to the control register 21. When the external device requests the latest detection result, the communication circuit 20 reads the latest detection result from the output register 27 and transmits it to the external host device.

[0014] The control register 21 stores a control command.

[0015] The drive circuit 22 outputs a first drive signal D1 and a second drive signal D2 to the switching circuit 23 and outputs a trigger signal TG to the communication circuit 20 in accordance with the control command stored in the control register 21.

[0016] The switching circuit 23 switches the connections between the drive circuit 22 and the AFE 24 and the sensor elements 1X, 1Y, and 1Z in accordance with the control commands stored in the control register 21.

[0017] The AFE24 receives a detection signal (charge signal) DET indicating a change in the capacitance of any one of the sensor elements 1X, 1Y, and 1Z, and performs CV conversion on the detection signal DET to generate a voltage signal that is an analog signal. The AFE24 outputs the analog signal generated by the CV conversion to the ADC25. The analog signal output from the AFE24 is a detection signal corresponding to the difference between the first variable capacitance and the second variable capacitance. The first variable capacitance is the capacitance between the first fixed electrode and the first movable electrode of any one of the sensor elements 1X, 1Y, and 1Z, and the second variable capacitance is the capacitance between the second fixed electrode and the second movable electrode of any one of the sensor elements 1X, 1Y, and 1Z.

[0018] The ADC 25 converts the analog signal output from the AFE 24 into a digital signal. The ADC 25 outputs the digital signal generated by the AD conversion to the data correction circuit 26 and the interrupt generation circuit 28.

[0019] The data correction circuit 26 performs data adjustment such as gain adjustment and offset adjustment on the digital signal received from the ADC 25. The data correction circuit 26 outputs the digital signal after the data adjustment to the output register 27.

[0020] The output register 27 stores the latest detection result.

[0021] The interrupt generation circuit 28 transmits a data ready signal DR, which generates a pulse when switching from a sensing sequence period P1 (see FIG. 5 described later) to a Coulomb force application sequence period P2 (see FIG. 5 described later), to an external device via the communication circuit 20. The measuring device 3 can read out the detection results without missing any detection results or overlapping any detection results by reading out the latest detection results from the output register 27 via the communication circuit 20 in synchronization with the data ready signal DR.

[0022] Fig. 2 is a timing chart of the trigger signal TG. The acceleration image shown in Fig. 2 is an acceleration image when the acceleration sensor 100 is stationary. When a test for measuring the bandwidth of the acceleration sensor 100 is performed, the drive circuit 22 switches the trigger signal TG from a LOW level to a HIGH level in accordance with a control command stored in the control register 21.

[0023] When the trigger signal TG is at a low level, the acceleration sensor 100 repeats the sensing sequence period P1 as shown in FIG. 2. Specifically, when the trigger signal TG is at a low level, the acceleration sensor 100 repeatedly switches the sensor element to be driven in the order of the sensor element 1X, the sensor element 1Y, and the sensor element 1Z as shown in FIG. 3. The signal XD1 is a signal supplied to the first movable electrode of the sensor element 1X, and the signal XD2 is a signal supplied to the second movable electrode of the sensor element 1X. The signal YD1 is a signal supplied to the first movable electrode of the sensor element 1Y, and the signal YD2 is a signal supplied to the second movable electrode of the sensor element 1Y. The signal ZD1 is a signal supplied to the first movable electrode of the sensor element 1Z, and the signal ZD2 is a signal supplied to the second movable electrode of the sensor element 1Z. When the sensor element 1X and the AFE 24 are electrically connected by the switching circuit 23, the detection signal DET is output from the first fixed electrode and the second fixed electrode of the sensor element 1X. When the sensor element 1Y and the AFE24 are electrically connected by the switching circuit 23, the detection signal DET is output from the first fixed electrode and the second fixed electrode of the sensor element 1Y. When the sensor element 1Z and the AFE24 are electrically connected by the switching circuit 23, the detection signal DET is output from the first fixed electrode and the second fixed electrode of the sensor element 1Z.

[0024] 4 is a schematic diagram showing the electrode structure of the sensor element 1X. The first fixed electrode E1 and the second fixed electrode E4 are electrodes that do not move in the X-axis direction even when the acceleration sensor 100 receives acceleration in the X-axis direction. The first movable electrode E2 and the second movable electrode E3 are electrodes that move in the X-axis direction when the acceleration sensor 100 receives acceleration in the X-axis direction. The first movable electrode E2 and the second movable electrode E3 are electrically insulated from each other by an insulating member M1. A structure formed by the first movable electrode E2, the second movable electrode E3, and the insulating member M1 is supported by an elastic member M2. The first movable electrode E2 faces the first fixed electrode E1, and the second movable electrode EE faces the second fixed electrode E4.

[0025] When the trigger signal TG is at a HIGH level, the acceleration sensor 100 alternates between a sensing sequence period P1 and a Coulomb force application sequence period P2 as shown in FIG. 2. Specifically, when the trigger signal TG is at a HIGH level, the acceleration sensor 100 alternates between a sensing sequence period P1 for sensing the electrode position of the sensor element 1X and a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1X as shown in FIG. 5. In the Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1X, the acceleration sensor 100 applies a constant potential between the first fixed electrode and the first movable electrode of the sensor element 1X, applies a Coulomb force between the first fixed electrode and the first movable electrode of the sensor element 1X, and moves the first movable electrode of the sensor element 1X toward the first fixed electrode of the sensor element 1X. As a result, in the Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1X, a pseudo acceleration is applied to the sensor element 1X.

[0026] It is desirable that the driving circuit 22 applies a Coulomb force between the first fixed electrode and the first movable electrode of the sensor element 1X at a predetermined frequency of 500 Hz to 50 kHz. By setting the frequency in this manner, it becomes easy to improve both the speed and accuracy of the band measurement of the acceleration sensor 100.

[0027] In the first half of the Coulomb force application sequence period P2, no Coulomb force is applied between the first fixed electrode and the first movable electrode of the sensor element 1X, and in the Coulomb force application period P3, which is the second half of the Coulomb force application sequence period P2, the Coulomb force is applied between the first fixed electrode and the first movable electrode of the sensor element 1X. This makes it possible to adjust the magnitude of the pseudo acceleration generated by the application of the Coulomb force by adjusting the length of the Coulomb force application period P3.

[0028] 5, the acceleration sensor 100 alternates between a sensing sequence period P1 for sensing the electrode position of the sensor element 1Y and a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1Y, and then alternates between a sensing sequence period P1 for sensing the electrode position of the sensor element 1Z and a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1Z. In other words, the driving circuit 22 shifts the period for periodically applying the Coulomb force between the sensor elements 1X, 1Y, and 1Z. This can improve the driving response of the sensor elements 1X, 1Y, and 1Z.

[0029] 5, when the trigger signal TG is at a high level, the acceleration sensor 100 may repeat in this order a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1X, a sensing sequence period P1 for sensing the electrode position of the sensor element 1X, a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1Y, a sensing sequence period P1 for sensing the electrode position of the sensor element 1Y, a Coulomb force application sequence period P2 for applying a Coulomb force to the sensor element 1Z, and a sensing sequence period P1 for sensing the electrode position of the sensor element 1Z. In other words, the drive circuit 22 may cause the periods for periodically applying the Coulomb force to overlap among the three sensor elements 1X, 1Y, and 1Z. In addition, two of the sensor elements 1X, 1Y, and 1Z may be overlapped, and after the repetition of the sensing sequence period P1 and the Coulomb force application sequence period P2 for the two sensor elements is completed, the repetition of the sensing sequence period P1 and the Coulomb force application sequence period P2 for the remaining sensor element may be executed.

[0030] The sensor element 1X, the sensor element 1Y, and the sensor element 1Z can be expressed by the second-order delay transfer function T(s) shown below. n is the resonant frequency of the sensor element, and ζ is the damping ratio of the sensor element. The design value of the damping ratio of the sensor element is used for ζ. T(s)=ω n 2 / (s 2 +ζω n s+ω n 2 )

[0031] Therefore, in the step response in the timing chart shown in FIG. 2, the measurement device 3 fits the detection result read from the output register 27 to the above-mentioned second-order lag system to obtain the resonant frequency ω n and estimate the resonant frequency ω nThe bandwidth of the acceleration sensor 100 is estimated from the above. According to this method, the bandwidth of the acceleration sensor can be measured (estimated) without changing the frequency of the acceleration change, so that the time required to measure (estimate) the bandwidth of the acceleration sensor 100 can be shortened.

[0032] <Application Examples> The acceleration sensor 100 described above is built into an electronic device Y mounted on a vehicle X shown in Fig. 6, for example. Note that the mounting position of the electronic device Y in Fig. 6 may differ from the actual position for convenience of illustration. Furthermore, the acceleration sensor 100 described above is not limited to use in the automotive field, but can be built into electronic devices used in all fields (such as the automotive field, industrial machinery field, and home appliance field).

[0033] <Other> In addition to the above-described embodiment, various modifications can be made to the configuration of the invention without departing from the spirit of the invention. The above-described embodiment should be considered to be illustrative in all respects and not restrictive, and the technical scope of the present invention is indicated by the claims, not the description of the above-described embodiment, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0034] For example, in the above-described embodiment, the bandwidth of the acceleration sensor 100 is measured (estimated) from the rising step response, but the bandwidth of the acceleration sensor 100 may be measured (estimated) from the falling step response, impulse response, square wave response, triangular wave response, sawtooth wave response, etc.

[0035] <Additional Notes> Regarding the present disclosure, specific configuration examples of which have been shown in the above-mentioned embodiments, additional notes will be provided.

[0036] The signal processing circuit (2) of the present disclosure is a signal processing circuit connectable to a sensor element (1X, 1Y, 1Z) including a first fixed electrode (E1), a first movable electrode (E2), a second movable electrode (E3), and a second fixed electrode (E4), and includes a drive circuit (22) configured to supply a first drive signal to a first variable capacitance between the first fixed electrode and the first movable electrode and to supply a second drive signal to a second variable capacitance between the second fixed electrode and the second movable electrode, and a detection circuit (24) configured to generate a detection signal corresponding to the difference between the first variable capacitance and the second variable capacitance, and the drive circuit is configured to periodically apply Coulomb force between the first fixed electrode and the first movable electrode (first configuration).

[0037] According to the signal processing circuit of the first configuration, the band of the acceleration sensor can be measured without changing the frequency of the acceleration change, so that the time required to measure the band of the acceleration sensor can be shortened.

[0038] In the signal processing circuit of the first configuration, the drive circuit may be configured to apply the Coulomb force at a predetermined frequency of 500 Hz or more and 50 kHz or less (second configuration).

[0039] In the signal processing circuit of the first or second configuration, the signal processing circuit may be connectable to a plurality of the sensor elements, and the driving circuit may be configured to shift the period for periodically applying Coulomb force for each of the plurality of sensor elements (third configuration).

[0040] In the signal processing circuit of the first or second configuration, the signal processing circuit may be connectable to a plurality of the sensor elements, and the driving circuit may be configured to overlap the period for periodically applying Coulomb force for at least two of the plurality of sensor elements (fourth configuration).

[0041] The signal processing circuit of any one of the first to fourth configurations may have a configuration (fifth configuration) configured to output a signal synchronized with a period for applying the Coulomb force.

[0042] An acceleration sensor (100) of the present disclosure has a configuration (sixth configuration) including the signal processing circuit of any one of the first to fifth configurations and the sensor element.

[0043] The electronic device (Y) of the present disclosure has a configuration (seventh configuration) including the acceleration sensor of the sixth configuration. [Explanation of symbols]

[0044] 1X, 1Y, 1Z sensor elements 2. Signal Processing Device 3. Measuring Equipment 20 Communication Circuits 21 Control Registers 22 Drive circuit 23 Switching circuit 24 AFE 25 ADC 26 Data correction circuit 27 Output Register 28 Interrupt Generation Circuit 100 Acceleration Sensor E1 1st fixed electrode E2 1st movable electrode E3 2nd movable electrode E4 2nd fixed electrode M1 Insulation material M2 Elastic member X Vehicle Y Electronic equipment

Claims

1. A signal processing circuit connectable to a sensor element including a first fixed electrode, a first movable electrode, a second movable electrode, and a second fixed electrode, a drive circuit configured to supply a first drive signal to a first variable capacitance between the first fixed electrode and the first movable electrode, and to supply a second drive signal to a second variable capacitance between the second fixed electrode and the second movable electrode; a detection circuit configured to generate a detection signal corresponding to a difference between the first variable capacitance and the second variable capacitance; Equipped with The drive circuit is configured to periodically apply a Coulomb force between the first fixed electrode and the first movable electrode.

2. 2. The signal processing circuit according to claim 1, wherein the drive circuit is configured to apply the Coulomb force at a predetermined frequency of 500 Hz to 50 kHz.

3. connectable to a plurality of said sensor elements; 2. The signal processing circuit according to claim 1, wherein the driving circuit shifts a period during which the Coulomb force is periodically applied to each of the plurality of sensor elements.

4. connectable to a plurality of said sensor elements; 2. The signal processing circuit according to claim 1, wherein the drive circuit causes periods during which the Coulomb force is periodically applied to overlap with each other for at least two of the plurality of sensor elements.

5. 2. The signal processing circuit according to claim 1, configured to output a signal synchronized with a period in which the Coulomb force is applied.

6. A signal processing circuit according to any one of claims 1 to 5; The sensor element; An acceleration sensor comprising:

7. An electronic device comprising the acceleration sensor according to claim 6.

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