Signal processing device, acceleration sensor, and portable device

Abstract

This signal processing circuit is provided with an analog circuit, an analog / digital converter, and a plurality of detection circuits. The analog circuit is configured to be capable of connecting to a sensor element configured such that a property thereof changes in response to acceleration. The analog circuit is also configured to output an analog signal indicating said property change. The analog / digital converter is configured to convert the analog signal into a digital signal. The plurality of detection circuits are configured to detect the change in acceleration on the basis of the digital signal. The respective sampling periods of the plurality of detection circuits are different values.

Description

Signal processing device, acceleration sensor, and portable device

[0001] The invention disclosed in this specification relates to a signal processing device, and an acceleration sensor and a portable device using the same.

[0002] The acceleration sensor includes a sensor element configured such that its characteristics change in response to acceleration, and a signal processing device configured to determine acceleration based on the change in the characteristics of the sensor element.

[0003] Some acceleration sensors not only output the detected acceleration but also detect specific acceleration changes and notify an external host device of the detected acceleration changes. Acceleration sensors that have both the former and latter functions are used as motion sensors that detect the movement of objects such as people (see, for example, Patent Document 1).

[0004] Special Publication No. 2021-519936 (Paragraph 0091)

[0005] However, conventional acceleration sensors have room for improvement in terms of failing to detect changes in acceleration.

[0006] In the signal processing device disclosed herein, the signal processing circuit includes an analog circuit, an analog-to-digital converter, and a plurality of detection circuits. The analog circuit is configured to be connectable to a sensor element configured to change characteristics in response to acceleration and is configured to output an analog signal indicating the change in the characteristic. The analog-to-digital converter is configured to convert the analog signal into a digital signal. The plurality of detection circuits are configured to detect the change in acceleration based on the digital signal. Each of the plurality of detection circuits has a different sampling period.

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

[0008] The portable device disclosed in this specification has an acceleration sensor having the above-described configuration.

[0009] According to the invention disclosed in this specification, it is possible to prevent the acceleration sensor from failing to detect a change in acceleration.

[0010] Fig. 1 is a diagram showing a comparative example of an acceleration sensor. Fig. 2 is a diagram showing an example of sampling in a detection circuit. Fig. 3 is a diagram showing another example of sampling in a detection circuit. Fig. 4 is a diagram showing yet another example of sampling in a detection circuit. Fig. 5 is a diagram showing an embodiment of an acceleration sensor. Fig. 6 is a block diagram showing an example configuration of a smartphone.

[0011] <Acceleration Sensor (Comparative Example)> Fig. 1 is a diagram showing a comparative example of an acceleration sensor (= a general configuration to be compared with the embodiments described later). The acceleration sensor 101 of this comparative example includes a sensor element 1 and a signal processing device 2A. The acceleration sensor 101 is a capacitance-type three-axis acceleration sensor that can simultaneously measure acceleration in three mutually orthogonal axial directions. Note that the acceleration that can be simultaneously measured by the acceleration sensor 101 is not limited to acceleration in three mutually orthogonal axial directions, but may also be acceleration in two mutually orthogonal axial directions or acceleration in a single axial direction.

[0012] The sensor element 1 is a capacitance-type acceleration sensor element that uses MEMS (Micro Electro Mechanical System) technology. The sensor element 1 has a fixed electrode, a movable electrode, and a spring, each made of, for example, silicon. When no acceleration is applied to the sensor element 1, the distance between the fixed electrode and the movable electrode does not change. On the other hand, when acceleration is applied to the sensor element 1, the movable electrode is displaced relative to the fixed electrode, and the capacitance between the fixed electrode and the movable electrode changes. In other words, the capacitance of the sensor element 1 changes depending on the acceleration applied to the sensor element 1.

[0013] The sensor element 1 is not limited to a capacitance type acceleration sensor element, but may be, for example, a piezo-resistance type acceleration sensor element, a thermal detection type acceleration sensor element, etc. In other words, the sensor element 1 may be any sensor element whose characteristics change in response to the acceleration applied to the sensor element 1.

[0014] The signal processing device 2A determines the acceleration based on the change in capacitance of the sensor element 1. The signal processing device 2A includes an AFE (Analog Front End) 21, an ADC (Analog to Digital Converter) 22, a data correction circuit 23, a detection circuit 24, an interrupt generation circuit 25, a register 26, and a communication circuit 27.

[0015] The AFE 21 is connected to the sensor element 1 and outputs an analog signal indicating a change in capacitance of the sensor element 1. The AFE 21 supplies a drive signal for driving the sensor element 1 to the sensor element 1, receives an analog signal indicating a change in capacitance of the sensor element 1 from the sensor element 1, and outputs the analog signal to the ADC 22.

[0016] The ADC 22 is configured to convert into a digital signal an analog signal indicating a change in capacitance of the sensor element 1. The ADC 22 outputs the digital signal generated by the AD conversion to the data correction circuit .

[0017] The data correction circuit 23 performs data adjustment such as gain adjustment and offset adjustment on the digital signal received from the ADC 22. The data correction circuit 23 outputs the digital signal after the data adjustment to the detection circuit 24.

[0018] The detection circuit 24 detects a change in acceleration based on the digital signal received from the data correction circuit 23 .

[0019] The interrupt generation circuit 25 transmits an interrupt signal to an external host device (not shown) when the latest detection result of the detection circuit 24 changes from the previous detection result of the detection circuit 24. There are two patterns, a first pattern and a second pattern, in which the latest detection result of the detection circuit 24 changes from the previous detection result of the detection circuit 24. In the first pattern, the latest detection result of the detection circuit 24 is a detection result, and the previous detection result of the detection circuit 24 is a no detection result. In the second pattern, the latest detection result of the detection circuit 24 is a no detection result, and the previous detection result of the detection circuit 24 is a detection result.

[0020] The external host device does not need to periodically communicate with the acceleration sensor 101, but can capture all changes in the detection results of the detection circuit 24 by communicating with the acceleration sensor 101 when an interrupt signal is received. By not having the external host device and the acceleration sensor 101 communicate periodically, it is possible to reduce the power required for communication between both the external host device and the acceleration sensor 101. Note that the interrupt generation circuit 25 may be removed from the acceleration sensor 101, and the external host device and the acceleration sensor 101 may communicate periodically.

[0021] The register 26 stores the latest detection result of the detection circuit 24 .

[0022] The communication circuit 27 communicates with an external host device. When the external host device requests the latest detection result of the detection circuit 24, the communication circuit 27 reads the latest detection result of the detection circuit 24 from the register 26 and transmits the latest detection result of the detection circuit 24 that has been read to the external host device.

[0023] The detection circuit 24 described above detects a change in acceleration based on the digital signal received from the data correction circuit 23, i.e., data corresponding to the acceleration. Specifically, the detection circuit 24 detects a change in acceleration if the difference between the previously sampled data corresponding to the acceleration and the currently sampled data corresponding to the acceleration is equal to or greater than a threshold. Therefore, the detection circuit 24 may fail to detect a change in acceleration depending on the sampling period. Specifically, if the sampling period of the detection circuit 24 is short, the detection circuit 24 may fail to detect a slow change in acceleration. Furthermore, if the sampling period of the detection circuit 24 is long, the detection circuit 24 may fail to detect a fast change in acceleration.

[0024] 2 to 4 are diagrams showing examples of sampling in the detection circuit 24. The input signal to the detection circuit 24, i.e., the output signal from the data correction circuit 23, is a digital signal and therefore a discrete value, but for convenience, is illustrated here as a continuous value. In addition, the sampling timing S1 in FIGS. 2 to 4 will be the most recent sampling timing, and the sampling timing S0 in FIGS. 2 to 4 will be the immediately preceding sampling timing. The variation width W1 of the input signal to the detection circuit 24 in FIGS. 2 to 4 is the "difference between the input signal value of the detection circuit 24 at sampling timing S0 and the input signal value of the detection circuit 24 at sampling timing S1," which corresponds to the change in acceleration.

[0025] If the sampling period of the detection circuit 24 is appropriate for the change in acceleration, the "difference between the input signal value of the detection circuit 24 at sampling timing S0 and the input signal value of the detection circuit 24 at sampling timing S1" corresponding to the change in acceleration, i.e., the variation width W1 of the input signal of the detection circuit 24, becomes relatively large as shown in Figure 2. As a result, the variation width W1 of the input signal of the detection circuit 24 becomes equal to or greater than the threshold value, and the change in acceleration is detected by the detection circuit 24.

[0026] If the sampling period of the detection circuit 24 is too short compared to the change in acceleration, the variation width W1 of the input signal to the detection circuit 24 becomes relatively small as shown in Fig. 3. As a result, the variation width W1 of the input signal to the detection circuit 24 becomes less than the threshold value, and the change in acceleration is not detected by the detection circuit 24.

[0027] If the sampling period of the detection circuit 24 is too long compared to the change in acceleration, the change width W1 of the input signal to the detection circuit 24 may become small as shown in Fig. 4, even though the input signal value of the detection circuit 24 changes significantly between sampling timing S0 and sampling timing S1. As a result, the change width W1 of the input signal to the detection circuit 24 becomes less than the threshold value, and the change in acceleration is not detected by the detection circuit 24.

[0028] In view of the above considerations, a novel embodiment is proposed below that can suppress the failure of an acceleration sensor to detect a change in acceleration.

[0029] <Acceleration Sensor (Embodiment)> Fig. 5 is a diagram showing an embodiment of an acceleration sensor. In Fig. 5, the same parts as in Fig. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0030] The acceleration sensor 102 of this embodiment includes a sensor element 1 and a signal processing device 2B. The signal processing device 2B is an application-specific integrated circuit (ASIC). The sensor element 1 and the signal processing device 2B may be mounted on a single semiconductor device or on separate semiconductor devices.

[0031] The signal processing device 2B determines the acceleration based on the change in capacitance of the sensor element 1. The signal processing device 2B includes an AFE 21, an ADC 22, a data correction circuit 23, a first detection circuit 24A, a second detection circuit 24B, a synchronization circuit 24C, an interrupt generation circuit 25, a register 26, and a communication circuit 27.

[0032] The signal processing device 2B has a configuration in which the detection circuit 24 is removed from the signal processing device 2A, and a first detection circuit 24A, a second detection circuit 24B, and a synchronization circuit 24C are added.

[0033] The data correction circuit 23 outputs the digital signal after the data adjustment to the first detection circuit 24A and the second detection circuit 24B.

[0034] The first detection circuit 24A and the second detection circuit 24B each detect a change in acceleration based on the digital signal received from the data correction circuit 23. The first detection circuit 24A and the second detection circuit 24B each detect a change in acceleration if the difference between data corresponding to the previously sampled acceleration and data corresponding to the currently sampled acceleration is equal to or greater than a threshold value.

[0035] The sampling periods of the first detection circuit 24A and the second detection circuit 24B are different values. When the sampling period of the first detection circuit 24A is shorter than the sampling period of the second detection circuit 24B, the first detection circuit 24A can detect fast changes in acceleration that the second detection circuit 24B cannot detect, and the second detection circuit 24B can detect slow changes in acceleration that the first detection circuit 24A cannot detect.

[0036] Since the sampling periods of the first detection circuit 24A and the second detection circuit 24B are different values, the signal processing device 2B can prevent the acceleration sensor 102 from failing to detect a change in acceleration.

[0037] It is desirable that the sampling period of the ADC 22 be equal to or shorter than the sampling period of each of the first detection circuit 24A and the second detection circuit 24B. This makes it possible to prevent the acceleration sensor 102 from failing to detect a change in acceleration due to sampling by the ADC 22.

[0038] Furthermore, it is desirable that the sampling periods of the first detection circuit 24A and the second detection circuit 24B be changeable. The set values ​​of the sampling periods of the first detection circuit 24A and the second detection circuit 24B are stored in the register 26. When the communication circuit 27 is requested by an external host device to write the set value of the sampling period of the first detection circuit 24A, it writes the set value of the sampling period of the first detection circuit 24A to the register 26. This makes it possible to change the sampling period of the first detection circuit 24A. When the communication circuit 27 is requested by an external host device to write the set value of the sampling period of the second detection circuit 24B, it writes the set value of the sampling period of the second detection circuit 24B to the register 26. This makes it possible to change the sampling period of the second detection circuit 24B. Because the sampling periods of the first detection circuit 24A and the second detection circuit 24B are changeable, the signal processing device 2B can set sampling periods suitable for detecting a desired change in acceleration.

[0039] The synchronization circuit 24C synchronizes the detection results of the first detection circuit 24A and the second detection circuit 24B. Specifically, when the detection result of one of the first detection circuit 24A and the second detection circuit 24B indicates detection and the detection result of the other of the first detection circuit 24A and the second detection circuit 24B indicates no detection, the synchronization circuit 24C changes the detection result of the other of the first detection circuit 24A and the second detection circuit 24B from no detection to detection. Therefore, the signal processing device 2B can match the detection results of the first detection circuit 24A and the second detection circuit 24B. This allows the external host device to process data without being affected by a detection failure by the other of the first detection circuit 24A and the second detection circuit 24B.

[0040] The synchronization circuit 24C outputs the detection results of the first detection circuit 24A and the second detection circuit 24B after the above-mentioned synchronization process to the interrupt generation circuit 25 and the register 26. Note that, if the detection result of the first detection circuit 24A received from the first detection circuit 24A and the detection result of the second detection circuit 24B received from the second detection circuit 24B match, the synchronization circuit 24C outputs the detection result of the first detection circuit 24A received from the first detection circuit 24A and the detection result of the second detection circuit 24B received from the second detection circuit 24B as they are to the interrupt generation circuit 25 and the register 26.

[0041] It is desirable that the synchronization circuit 24C be switchable between enabled and disabled. When the synchronization circuit 24C is disabled, the synchronization circuit 24C always outputs the detection result of the first detection circuit 24A received from the first detection circuit 24A and the detection result of the second detection circuit 24B received from the second detection circuit 24B as is to the interrupt generation circuit 25 and the register 26. By disabling the synchronization circuit 24C, the signal processing device 2B can output the detection result of the first detection circuit 24A output from the first detection circuit 24A and the detection result of the second detection circuit 24B output from the second detection circuit 24B as is to an external host device. By analyzing the detection result of the first detection circuit 24A output from the first detection circuit 24A and the detection result of the second detection circuit 24B output from the second detection circuit 24B, the external host device can determine whether the change in acceleration detected by at least one of the first detection circuit 24A and the second detection circuit 24B is a fast change or a slow change.

[0042] The interrupt generation circuit 25 transmits an interrupt signal to an external host device (not shown) when at least one of the following events occurs: the latest detection result of the first detection circuit 24A changes from the previous detection result of the first detection circuit 24A; or the latest detection result of the second detection circuit 24B changes from the previous detection result of the second detection circuit 24B.

[0043] The register 26 stores the latest detection result of the first detection circuit 24A and the latest detection result of the second detection circuit 24B.

[0044] The communication circuit 27 communicates with an external host device. When the external host device requests the latest detection result of the first detection circuit 24A and the latest detection result of the second detection circuit 24B, the communication circuit 27 reads the latest detection result of the first detection circuit 24A and the latest detection result of the second detection circuit 24B from the register 26 and transmits the latest detection result of the first detection circuit 24A and the latest detection result of the second detection circuit 24B that it has read to the external host device.

[0045] <Application Example> Here, an example in which the acceleration sensor 102 is applied to a smartphone will be described. Note that a smartphone is an example of a portable device. Naturally, the acceleration sensor 102 may also be applied to portable devices other than smartphones. Examples of portable devices other than smartphones include a wearable watch and a wearable camera.

[0046] 6 is a block diagram showing an example of the configuration of a smartphone 200. The smartphone 200 includes a communication unit 201, a camera unit 202, a display unit 203, an audio input / output unit 204, an acceleration sensor 205, an operation unit 206, a storage unit 207, and a control unit 208.

[0047] The communication unit 201 performs wireless communication with a base station in a mobile communication network, and uses this wireless communication to send and receive audio data, video data, e-mail data, etc., and to receive web data, streaming data, etc.

[0048] The camera unit 202 electronically captures images using an image sensor such as a CMOS image sensor, and can compress the captured images in, for example, JPEG format and store the compressed data in the storage unit 207 .

[0049] The display unit 203 is, for example, a liquid crystal display device or an organic EL (Electro Luminescence) display device. The display unit 203 displays various images. The audio input / output unit 204 includes a microphone that collects input ambient audio and converts it into an electrical signal, and a speaker that converts the input audio signal into audio and outputs it to the outside.

[0050] The acceleration sensor 205 is a motion sensor that detects the movement of the person carrying the smartphone 200, and the acceleration sensor 102 described above can be used.

[0051] The operation unit 206 includes keys arranged on the housing of the smartphone 200 for various operations such as power operation and volume operation, a touch panel arranged on the display screen of the display unit 203, and the like.

[0052] The storage unit 207 stores control programs and control data for the control unit 208, address data that associates names and telephone numbers of communication partners, sent and received e-mail data, web data downloaded by web browsing, downloaded content data, etc., and also temporarily stores streaming data, etc. The storage unit 207 is configured by, for example, a flash memory, RAM, ROM, etc.

[0053] The control unit 208 operates in accordance with the control program and control data stored in the storage unit 207, and controls all the units of the smartphone 200. The control unit 208 also operates as the host device described above.

[0054] Such a smartphone 200 can use the detection results of the acceleration sensor 205, for example, as a pedometer.

[0055] <Others> In addition to the above-described embodiments, various modifications can be made to the configuration of the invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0056] For example, the acceleration sensor 102 has two detection circuits (the first detection circuit 24A and the second detection circuit 24B), but the acceleration sensor 102 may be provided with three or more detection circuits.

[0057] Furthermore, for example, the acceleration sensor 102 has a configuration including the synchronization circuit 24C, but may have a configuration without the synchronization circuit 24C.

[0058] Furthermore, for example, the acceleration sensor 102 is configured not to externally output the data-adjusted digital signal output from the data correction circuit 23, but may be configured to externally output the data-adjusted digital signal output from the data correction circuit 23.

[0059] The signal processing device (2B) described above is configured to be connectable to a sensor element (1) configured to change its characteristics in response to acceleration, and includes an analog circuit (21) configured to output an analog signal indicating the change in the characteristics, an analog / digital converter (22) configured to convert the analog signal into a digital signal, and a plurality of detection circuits (24A, 24B) configured to detect the change in acceleration based on the digital signal, and is configured (first configuration) such that the sampling periods of the plurality of detection circuits are different values.

[0060] The signal processing device having the first configuration can suppress failure to detect a change in acceleration in the acceleration sensor.

[0061] In the signal processing device of the first configuration, the sampling period of the analog / digital converter may be equal to or shorter than each sampling period of the plurality of detection circuits (second configuration).

[0062] The signal processing device of the second configuration can suppress failure to detect acceleration changes in the acceleration sensor due to sampling by the analog / digital converter.

[0063] In the signal processing device of the first or second configuration, the sampling period of each of the plurality of detection circuits may be changeable (third configuration).

[0064] The signal processing device of the third configuration allows the setting of a sampling period suitable for detecting a desired change in acceleration.

[0065] The signal processing device of any of the first to third configurations may have a configuration (fourth configuration) that includes a synchronization circuit (24C) configured to change the detection results of the remaining plurality of detection circuits from no detection to detection when the detection results of some of the plurality of detection circuits are detection and the detection results of the remaining plurality of detection circuits are no detection.

[0066] The signal processing device having the fourth configuration can make the detection results of the plurality of detection circuits coincide with each other.

[0067] The fourth signal processing device may have a configuration (fifth configuration) in which the synchronization circuit can be switched between enabled and disabled.

[0068] In the signal processing device of the fifth configuration, the synchronization circuit is disabled, so that the detection results of the plurality of detection circuits can be output to the outside as they are.

[0069] The acceleration sensor (102) described above has a configuration (sixth configuration) including a signal processing device of any one of the first to fifth configurations and the sensor element.

[0070] The acceleration sensor having the sixth configuration can suppress failure to detect changes in acceleration.

[0071] The portable device (200) described above has a configuration (seventh configuration) that includes the acceleration sensor of the sixth configuration.

[0072] The portable device having the seventh configuration can suppress the failure of the acceleration sensor to detect a change in acceleration.

[0073] REFERENCE SIGNS LIST 1 Sensor element 2A, 2B Signal processing device 21 AFE 22 ADC 23 Data correction circuit 24 Detection circuit 24A First detection circuit 24B Second detection circuit 24C Synchronization circuit 25 Interrupt generation circuit 26 Register 27 Communication circuit 101, 102 Acceleration sensor 200 Smartphone 201 Communication unit 202 Camera unit 203 Display unit 204 Audio input / output unit 205 Acceleration sensor 206 Operation unit 207 Memory unit 208 Control unit

Claims

1. an analog circuit configured to be connectable to a sensor element configured to change a characteristic in response to acceleration, and configured to output an analog signal indicative of the change in the characteristic; an analog to digital converter configured to convert the analog signal into a digital signal; a plurality of sensing circuits configured to sense changes in the acceleration based on the digital signal; having A signal processing device, wherein the sampling periods of the plurality of detection circuits are different values.

2. 2. The signal processing device according to claim 1, wherein the sampling period of the analog / digital converter is equal to or shorter than each sampling period of the plurality of detection circuits.

3. The signal processing device according to claim 1 , wherein the sampling period of each of the plurality of detection circuits is variable.

4. 2. The signal processing device according to claim 1, further comprising a synchronization circuit configured to change the detection results of the remaining detection circuits from no detection to detection when the detection results of some of the detection circuits are detection and the detection results of the remaining detection circuits are no detection.

5. The signal processing device according to claim 4 , wherein the synchronization circuit can be switched between enabled and disabled.

6. A signal processing device according to any one of claims 1 to 5, The sensor element; The acceleration sensor has

7. A portable device comprising the acceleration sensor according to claim 6.