Sensor device

Abstract

To provide a sensor device capable of improving dynamic range. [Solution] The sensor device includes a sensor unit 2, a switch circuit 4, an amplification circuit 5, and a control unit 8. The sensor unit 2 is equipped with a plurality of sensor elements 20. The switch circuit 4 is equipped with a plurality of switches 21, each connected to one of the plurality of sensor elements 20. Each of the plurality of switches 21 can be switched between a plurality of first paths and a plurality of second paths. The amplification circuit 5 is equipped with a plurality of amplifiers 22, each connected to one of the plurality of first paths of the plurality of switches 21, and an amplifier 24, which is commonly connected to the plurality of second paths of the plurality of switches 21. In the divided drive mode, the control unit 8 controls the switch circuit 4 to connect the plurality of sensor elements 20 and the plurality of amplifiers 22, respectively, and in the linked drive mode, it controls the switch circuit 4 to commonly connect the plurality of sensor elements 20 and the amplifiers 24.

Description

Technical Field

[0001] The present invention relates to a sensor device.

Background Art

[0002] Sensor devices that detect various pressures using the piezoelectric effect are used. A piezoelectric sensor as a sensor device changes the amount of charge according to pressure and detects this change in the amount of charge as an electrical signal. When the pressure or vibration is minute, the amount of charge is also small, and it is necessary to perform signal processing to a level that can be identified by a general electrical circuit in the subsequent stage or to improve the noise resistance against power supply noise and the like. In order to widen the dynamic range that a piezoelectric sensor can detect from a minute pressure to a large pressure, improvements are required in the detection method and the control method.

[0003] Patent Document 1 discloses a wristwatch having a function of measuring a pulse as biological information. In Patent Document 1, a band is attached to the artery part of the wrist, an air chamber is provided in the band, and the pulse is detected from the fluctuation of the air pressure. Patent Document 2 discloses a motion sensor that detects the movement of a tendon in the wrist by using a strain sensor provided with a plurality of sensors. In the detection methods according to Patent Documents 1 and 2, although the pulse (minute signal) and the movement of the tendon (large signal) can be detected individually, it is difficult to detect them within a dynamic range that covers from a minute signal to a large signal.

[0004] Patent Document 3 discloses a sensor device in which a sensor unit is attached to the front surface of the wrist and pressure fluctuations are detected from the blood vessels in the wrist via a transmission member. When measuring the pulse of an artery in the wrist, the pressure applied to the sensor unit is minute. Therefore, when the sensor unit and the measurement target (for example, an artery) are misaligned, it becomes difficult to detect the pressure. To accurately measure the pulse, it takes time to align the sensor unit with the position of the measurement target. Also, it is necessary to add a specific transmission member as in Patent Document 3.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-185631 [Patent Document 2] International Publication No. 2022 / 130684 [Patent Document 3] Japanese Patent Publication No. 2020-156659 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention provides a sensor device capable of improving the dynamic range. [Means for solving the problem]

[0007] According to a first aspect of the present invention, a sensor device is provided comprising: a sensor unit having a plurality of sensor elements; a switch circuit having a plurality of first switches each connected to the plurality of sensor elements, each of the plurality of first switches being switchable between a plurality of first paths and a plurality of second paths; an amplification circuit having a plurality of first amplifiers each connected to the plurality of first paths of the plurality of first switches, and a second amplifier commonly connected to the plurality of second paths of the plurality of first switches; and a control unit that performs a divided drive mode and a coupled drive mode, wherein the control unit controls the switch circuit to connect the plurality of sensor elements and the plurality of first amplifiers in the divided drive mode, and controls the switch circuit to commonly connect the plurality of sensor elements and the second amplifier in the coupled drive mode.

[0008] A sensor device according to the first embodiment is provided, wherein the control unit selects the divided drive mode when the voltage amplitude of at least one of the plurality of detection signals of the plurality of sensor elements is greater than a first threshold, and selects the coupled drive mode when the voltage amplitude of at least one of the plurality of detection signals is less than or equal to the first threshold.

[0009] According to a third aspect of the present invention, a sensor device according to the first aspect is provided, wherein the control unit switches between the split drive mode and the linked drive mode based on a request from an external device.

[0010] A fourth aspect of the present invention provides a sensor device according to the first aspect, further comprising a plurality of first load resistors connected to the inputs of the plurality of first amplifiers, and a second load resistor connected to the input of the second amplifier.

[0011] According to a fifth aspect of the present invention, a sensor device according to the first aspect is provided, further comprising: a plurality of first load resistors connected to the inputs of a plurality of first amplifiers, a second switch connected to the input of a second amplifier and switchable between a first path and a second path, a second load resistor connected to the first path of the second switch, and a third load resistor connected to the second path of the second switch and having a resistance value greater than that of the second load resistor, wherein the control unit controls the second switch based on the output voltage of the second amplifier.

[0012] According to a sixth aspect of the present invention, a sensor device according to the fifth aspect is provided, wherein the control unit controls the second switch to change from the second load resistor to the third load resistor when the output voltage of the second amplifier is lower than a second threshold.

[0013] According to a seventh aspect of the present invention, a sensor device according to the first aspect is provided, wherein each of the plurality of sensor elements is a piezoelectric element. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a sensor device that can improve the dynamic range. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a block diagram of a sensor device according to the first embodiment of the present invention. [Figure 2]FIG. 2 is a circuit diagram of the sensor unit, switch circuit, and amplifier circuit shown in FIG. 1. [Figure 3] FIG. 3 is a circuit diagram obtained by extracting the circuit portion connected to one sensor element. [Figure 4] FIG. 4 is a circuit diagram showing an example of one amplifier included in the amplifier circuit. [Figure 5] FIG. 5 is a flowchart for explaining the operation of the sensor device. [Figure 6] FIG. 6 is a diagram for explaining the operation of the switch circuit in the divided driving mode. [Figure 7] FIG. 7 is a diagram for explaining the operation of the switch circuit in the connected driving mode. [Figure 8] FIG. 8 is a diagram for explaining the measurement results in the embodiment. [Figure 9] FIG. 9 is a diagram showing an example of the measurement results in the divided driving mode using a load resistor of 10 MΩ. [Figure 10] FIG. 10 is a diagram showing an example of the measurement results in the connected driving mode using a load resistor of 10 MΩ. [Figure 11] FIG. 11 is a diagram showing an example of the measurement results in the connected driving mode using a load resistor of 20 MΩ. [Figure 12] FIG. 12 is a diagram showing an example of the measurement results in the connected driving mode using a load resistor of 100 MΩ. [Figure 13] FIG. 13 is a block diagram of the main parts of the sensor unit and signal processing unit according to the second embodiment of the present invention. [Figure 14] FIG. 14 is a circuit diagram of the main parts of the sensor unit and signal processing unit according to the third embodiment of the present invention. [Figure 15] FIG. 15 is a flowchart for explaining the operation of the sensor device. [Figure 16] FIG. 16 is a diagram for explaining an example of the output voltage of the amplifier.

Embodiments for Carrying Out the Invention

[0016] The embodiments will be described below with reference to the drawings. However, the drawings are schematic or conceptual, and the dimensions and proportions in each drawing are not necessarily the same as those in reality. Furthermore, even when the same part is represented between drawings, the relationship between dimensions and proportions may be represented differently. In particular, the embodiments shown below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not determined by the shape, structure, arrangement, etc. of the components. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] In the following embodiment, a piezoelectric sensor will be used as an example of the sensor device 1.

[0018] [1] First Embodiment [1-1] Configuration of Sensor Device 1 Figure 1 is a block diagram of a sensor device 1 according to the first embodiment of the present invention. The sensor device 1 comprises a sensor unit 2, a signal processing unit 3, a controller 7, and a voltage generation circuit 12.

[0019] Sensor unit 2 comprises multiple sensor elements. Each of the multiple sensor elements is composed of, for example, a piezoelectric element. A piezoelectric element is a sensor element that utilizes the piezoelectric effect and is capable of outputting an electrical signal in response to the pressure applied to the piezoelectric material. Sensor unit 2 outputs multiple detection signals corresponding to the multiple sensor elements.

[0020] The signal processing unit 3 receives multiple detection signals from the sensor unit 2 and performs signal processing on these multiple detection signals. The signal processing unit 3 includes a switch circuit 4, an amplification circuit 5, and a filter circuit 6, among others.

[0021] The switch circuit 4 switches the signal path according to the two drive modes described later. The switch circuit 4 is composed of, for example, an analog switch circuit.

[0022] The amplification circuit 5 receives multiple detection signals from the switch circuit 4. The amplification circuit 5 amplifies the electrical signals input to itself.

[0023] The filter circuit 6 receives multiple detection signals from the amplification circuit 5. The filter circuit 6 removes signals and noise in frequency bands other than the required frequency band. The filter circuit 6 includes a low-pass filter circuit.

[0024] The controller 7 comprehensively controls the operation of the sensor device 1. The controller 7 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processors included in the controller 7 realize various functions by executing programs stored in the memory unit 9. The controller 7 includes a mode control unit 8, a memory unit 9, an external interface 10, and a power supply control unit 11.

[0025] The mode control unit 8 controls multiple drive modes. The sensor device 1 can perform both a split drive mode and a linked drive mode. The split drive mode is a mode in which sensing is performed using multiple sensor elements individually. The split drive mode is used when the voltage amplitude of the detection signal detected by the sensor unit 2 is relatively large. The split drive mode can be used for motion sensors that detect muscle movement, etc. The linked drive mode is a mode in which sensing is performed by connecting multiple sensor elements in parallel. The linked drive mode is used when the voltage amplitude of the detection signal detected by the sensor unit 2 is relatively small. The linked drive mode can be used for pulse wave sensors that detect pulse rate, etc.

[0026] The memory unit 9 stores various data necessary for the operation of the sensor device 1 and also functions as a workspace for the processor included in the controller 7. The memory unit 9 includes volatile memory and non-volatile memory. The volatile memory includes RAM (Random Access Memory) and registers, etc. The non-volatile memory includes ROM (Read Only Memory), HDD (Hard Disk Drive), and SSD (Solid State Drive), etc.

[0027] The external interface 10 is connected to an external device by wire and / or wireless means and has the function of communicating with the external device. The external interface 10 performs interface processing with the external device based on a predetermined standard.

[0028] The power control unit 11 controls the operation of the voltage generation circuit 12. The voltage generation circuit 12 generates multiple voltages necessary for the operation of the sensor device 1. The voltage generation circuit 12 supplies voltage to the corresponding circuit.

[0029] Figure 2 is a circuit diagram of the sensor unit 2, switch circuit 4, and amplifier circuit 5 shown in Figure 1.

[0030] The sensor unit 2 comprises a plurality of sensor elements 20-1 to 20-n, where "n" is a natural number greater than or equal to 2. In this embodiment, the description common to reference numerals with sub-numbers is given using reference numerals without sub-numbers. As described above, the sensor element 20 is composed of a piezoelectric element. The piezoelectric element includes a lower electrode, an upper electrode, and a piezoelectric layer sandwiched between them.

[0031] The switch circuit 4 comprises multiple switches 21-1 to 21-n. Each of the switches 21-1 to 21-n is connected to a plurality of sensor elements 20-1 to 20-n. Switch 21 is composed of an SPDT (Single-Pole Double-Throw) switch capable of switching between two paths (one pole and two contacts).

[0032] Figure 3 is a circuit diagram showing the circuit portion connected to one sensor element 20 (sensor element 20-1). Switch 21 has one input terminal T1 and two output terminals T2 and T3. Switch 21 switches between a first path connecting input terminal T1 and output terminal T2, and a second path connecting input terminal T1 and output terminal T3. Input terminal T1 of switch 21 is connected to the output of sensor element 20. A control signal CNT1 is input to switch 21 from controller 7. Based on the control signal CNT1, switch 21 performs the switching operation of the two paths.

[0033] The amplification circuit 5 comprises multiple amplifiers 22-1 to 22-n and multiple load resistors 23-1 to 23-n. Amplifier 22 is composed of an operational amplifier. The inputs of each of the multiple amplifiers 22-1 to 22-n are connected to the output terminals T3 of the multiple switches 21-1 to 21-n. The multiple load resistors 23-1 to 23-n are each connected to the inputs of the multiple amplifiers 22-1 to 22-n. The multiple amplifiers 22-1 to 22-n and the multiple load resistors 23-1 to 23-n are used in a divided drive mode.

[0034] The amplification circuit 5 further comprises an amplifier 24 and a load resistor 25. The amplifier 24 is composed of an operational amplifier. The input of the amplifier 24 is connected in common to the output terminal T2 of a plurality of switches 21-1 to 21-n. The load resistor 25 is connected to the input of the amplifier 24. The amplifier 24 and the load resistor 25 are used in coupled drive mode.

[0035] Figure 4 is a circuit diagram showing an example of one amplifier 22 included in the amplification circuit 5. The configuration of amplifier 24 is the same as in Figure 4. Amplifier 22 is composed of, for example, a non-inverting amplifier.

[0036] The amplification circuit 5 comprises an amplifier 22, a load resistor 23, an input terminal 30, an output terminal 31, and resistors 32 and 33. The input terminal 30 is connected to the output terminal T3 of the switch 21. The output terminal 31 is connected to the filter circuit 6.

[0037] A positive power supply V+ (e.g., 5V) is supplied to the positive power supply terminal of amplifier 22. A negative power supply V- (e.g., -5V) is supplied to the negative power supply terminal of amplifier 22.

[0038] The non-inverting input terminal (+) of amplifier 22 is connected to input terminal 30. One end of load resistor 23 is connected to the non-inverting input terminal of amplifier 22, and the other end is connected to the ground terminal GND. 0V is supplied to the ground terminal GND.

[0039] The inverting input terminal (-) of amplifier 22 is connected to one end of resistor 32. The other end of resistor 32 is connected to the ground terminal GND. One end of resistor 33 is connected to the output of amplifier 22, and the other end is connected to the inverting input terminal of amplifier 22. The output of amplifier 22 is connected to output terminal 31.

[0040] The load resistor 23 converts the charge supplied from the sensor element 20 into a voltage. The amplifier 22 is capable of amplifying the input signal and outputting it. The amplification factor of the amplifier 22 is calculated by the following equation (1). Let Vi be the input voltage of the amplifier 22, Vo be the output voltage of the amplifier 22, R1 be the resistance value of resistor 32, and R2 be the resistance value of resistor 33. Vo = (1 + (R² / R¹))Vi ···(1) [1-2] Operation Next, we will explain the operation of the sensor device 1 configured as described above. Figure 5 is a flowchart illustrating the operation of the sensor device 1.

[0041] Multiple sensor elements 20 included in the sensor unit 2 detect pressure. That is, multiple sensor elements 20 included in the sensor unit 2 detect pressure and output a detection signal as a result of the detection.

[0042] The signal processing unit 3 receives multiple detection signals from multiple sensor elements 20 included in the sensor unit 2 (step S100).

[0043] Next, the mode control unit 8 selects a drive mode (step S101). The drive mode determination operation is performed in step S107, which will be described later. As an initial operation, for example, the mode control unit 8 may select a predetermined drive mode. Information on predetermined drive modes is stored in the memory unit 9.

[0044] If the split drive mode is selected in step S101, the mode control unit 8 switches the switch circuit 4 to the split drive mode path (step S102). That is, the mode control unit 8 sends a control signal CNT1 to the switch circuit 4 to switch to the split drive mode path.

[0045] Figure 6 illustrates the operation of the switch circuit 4 in the split drive mode. Figure 6 shows five sensor elements 20 as an example.

[0046] Each of the multiple switches 21 connects to multiple sensor elements 20 and multiple amplifiers 22. In the divided drive mode, the amplifier 24 is not connected to any of the multiple sensor elements 20.

[0047] Next, the signal processing unit 3 amplifies and filters the detection signal (step S104). That is, in the divided drive mode, the amplification circuit 5 amplifies each of the multiple detection signals from the multiple sensor elements 20, and the filter circuit 6 filters each of the multiple detection signals.

[0048] Next, the mode control unit 8 outputs the multiple detection signals transmitted from the signal processing unit 3 to an external device via the external interface 10 (step S105).

[0049] On the other hand, if the linked drive mode is selected in step S101, the mode control unit 8 switches the switch circuit 4 to the linked drive mode path (step S103). That is, the mode control unit 8 sends a control signal CNT1 to the switch circuit 4 to switch to the linked drive mode path.

[0050] Figure 7 illustrates the operation of the switch circuit 4 in the coupled drive mode. Figure 7 shows five sensor elements 20 as an example.

[0051] Each of the multiple switches 21 connects multiple sensor elements 20 and amplifiers 24 in common. That is, the multiple sensor elements 20 are connected in parallel, and the charges of the multiple sensor elements 20 are added together and supplied to the amplifiers 24. This makes it possible to increase the voltage amplitude and dynamic range of the detection signal. In the linked drive mode, the multiple sensor elements 20 are not connected to the multiple amplifiers 22.

[0052] Next, the signal processing unit 3 amplifies and filters the detection signal (step S104). That is, in the coupled drive mode, the amplification circuit 5 amplifies a single detection signal obtained by adding the charges of multiple sensor elements 20, and the filter circuit 6 filters the single detection signal.

[0053] Next, the mode control unit 8 outputs the detection signal transmitted from the signal processing unit 3 to an external device via the external interface 10 (step S105).

[0054] Next, the mode control unit 8 determines the voltage amplitude of the detection signal (step S106). In this case, if it is a divided drive mode, the voltage amplitude may be determined for any one of the multiple detection signals, or the voltage amplitude may be determined for each of the multiple detection signals. The mode control unit 8 compares the determined voltage amplitude with a threshold and determines whether the determined voltage amplitude is greater than the threshold. A voltage amplitude of less than or equal to the threshold means that the dynamic range is small. A voltage amplitude greater than the threshold means that the dynamic range is large.

[0055] Next, the mode control unit 8 determines whether or not to switch the drive mode based on the voltage amplitude determination result (step S107). Specifically, if the determined voltage amplitude is greater than the threshold, the mode control unit 8 selects the split drive mode. If the determined voltage amplitude is less than or equal to the threshold, the mode control unit 8 selects the coupled drive mode.

[0056] The mode control unit 8 may also select a drive mode requested by an external device via the external interface 10. The mode control unit 8 may also select a drive mode based on a button operation by the user, a wrist gesture input by the user, or a signal indicating that an external force has been applied to an artery at the measurement site.

[0057] [1-3] Examples Next, we will describe specific examples. The experimental conditions in the examples are as follows: • Detection target: In split drive mode, the detection target is motion caused by wrist movement. In linked drive mode, the detection target is the pulse rate at the wrist. • Sensor section: Uses 12 sensor elements corresponding to 12 channels (CH). • Fixation method: The sensor part was fixed to the wrist with an elastomer. At this time, pressure was applied to the wrist to make the pulse easier to understand. In this case, three fingers were lightly placed on the artery of the wrist, as in pulse diagnosis. Other methods include placing the wrist on a mouse pad, wrapping a wristband over the elastomer, or applying air pressure to the wrist like a blood pressure monitor. • Signal processing unit: 10MΩ, 20MΩ, and 100MΩ were used as load resistors to convert electric charge into voltage. The signal was amplified 11 times by an amplifier. • Mode control unit: The drive mode was switched using an external changeover switch. • Result measurement: Voltage waveforms were observed using an oscilloscope.

[0058] Figure 8 illustrates the measurement results in the embodiment. Figure 8 shows the detection target, drive mode, load resistance (Ω), amplifier amplification factor, and voltage amplitude (V). The voltage amplitude is the voltage amplitude of the detection signal output from the signal processing unit.

[0059] In motion detection using the split drive mode, the voltage amplitude ranges from 1V to 5V depending on the motion. Motion can be detected according to the voltage of 12 channels.

[0060] In pulse detection using the split drive mode, the voltage amplitude is small, at 0.6V. Therefore, it is preferable to detect minute signals such as pulses using the coupled drive mode. By detecting pulses in coupled drive mode, the voltage amplitude is more than double that of the split drive mode. As a result, it can be identified with a voltage amplitude similar to that of motion detection, thus increasing the dynamic range.

[0061] Furthermore, when detecting pulse in split drive mode, it is necessary to determine in advance which channel of the sensor unit is detecting the pulse. In contrast, in linked drive mode, it is not necessary to match the pulse measurement location with the position of the sensor unit's channel. Therefore, pulse can be easily measured using linked drive mode.

[0062] Figure 9 shows an example of measurement results in a divided drive mode using a load resistance of 10 MΩ. Figure 9 shows the voltage waveform of the channel in which a pulse wave was detected out of 12 channels. Figure 10 shows an example of measurement results in a linked drive mode using a load resistance of 10 MΩ. Figure 11 shows an example of measurement results in a linked drive mode using a load resistance of 20 MΩ. Figure 12 shows an example of measurement results in a linked drive mode using a load resistance of 100 MΩ. In Figures 9 to 12, the horizontal axis is time (arbitrary unit), and the vertical axis is voltage (V). In Figures 9 to 12, the raw data is averaged over 50 points to remove the effects of power supply noise. Figures 9 to 12 show waveforms corresponding to 5 pulses.

[0063] As shown in Figure 9, in the split drive mode, the voltage amplitude is small, making it difficult to distinguish between pulse and noise. As shown in Figure 10, by switching to the linked drive mode, the voltage amplitude can be increased, allowing for easy and accurate measurement of the pulse.

[0064] Furthermore, as can be seen from Figures 11 and 12, the voltage amplitude in the coupled drive mode can be increased by increasing the load resistance. The load resistance can be set appropriately according to the specifications of the sensor device 1.

[0065] [1-4] Effects of the first embodiment According to the first embodiment, the sensor device 1 can perform a divided drive mode in which multiple sensor elements 20 are driven separately, and a linked drive mode in which multiple sensor elements 20 are driven in a linked manner. In the divided drive mode, the sensor device 1 can output multiple detection signals from multiple sensor elements 20. In the linked drive mode, the sensor device 1 can output a single detection signal that combines the multiple sensor elements 20.

[0066] Furthermore, the system can select a split drive mode when the voltage amplitude of the detection signal is relatively large, and a coupled drive mode when the voltage amplitude of the detection signal is relatively small.

[0067] Furthermore, by executing the linked drive mode, the voltage amplitude and dynamic range of the detection signal can be increased. This allows for more accurate pressure detection. Consequently, it is possible to improve the dynamic range of the sensor device 1 in both the split drive mode and the linked drive mode.

[0068] Furthermore, in the split drive mode, the sensor device 1 can detect pressure in each of the multiple regions where the multiple sensor elements 20 are arranged. In the linked drive mode, the sensor device 1 can detect pressure in the entire region of the multiple sensor elements 20 as if they were a single sensor.

[0069] Furthermore, when detecting a pulse from an artery in the wrist, for example, the artery may be narrow, resulting in a limited detection range. Even in this case, by changing the detection area of ​​the sensor unit 2, it is possible to detect a pulse from the target artery.

[0070] Furthermore, if the voltage amplitude of the detection signal is relatively large, the sensor device 1 can be used as a motion sensor.

[0071] [2] Second embodiment In the second embodiment, the sensor unit 2 has a plurality of blocks 40, and the divided drive mode and linked drive mode are switched on a block 40 basis.

[0072] Figure 13 is a block diagram of the main parts of the sensor unit 2 and signal processing unit 3 according to the second embodiment of the present invention. The sensor device 1 comprises the sensor unit 2, a plurality of switch circuits 4, and a plurality of amplification circuits 5.

[0073] The sensor unit 2 comprises multiple blocks 40. In this embodiment, four blocks 40-1 to 40-4 are shown as an example. Each block 40 comprises multiple sensor elements 20. In this embodiment, a configuration in which one block 40 comprises three sensor elements 20 is shown as an example. The number of blocks 40 and the number of sensor elements 20 can be set arbitrarily. The arrangement of the sensor elements 20 can also be set arbitrarily. The number of sensor elements 20 included in multiple blocks 40 may be the same or different.

[0074] Multiple switch circuits 4 are connected to each of the multiple blocks 40. In this embodiment, four switch circuits 4-1 to 4-4 are shown as an example. In Figure 13, the wiring between the multiple blocks 40 and the multiple switch circuits 4 is omitted. The configuration of each switch circuit 4 is the same as in the first embodiment.

[0075] Multiple switch circuits 4 are each connected to multiple amplifier circuits 5. In this embodiment, four amplifier circuits 5-1 to 5-4 are shown as an example. The configuration of each amplifier circuit 5 is the same as in the first embodiment.

[0076] The operation of each block 40 is the same as in the first embodiment. The mode control unit 8 executes the processing shown in Figure 5 for each block.

[0077] According to the second embodiment, the divided drive mode and the linked drive mode can be switched in units of 40 blocks. This allows the sensor device 1 to be optimally configured according to the body part to be measured.

[0078] [3] Third embodiment In the third embodiment, multiple load resistors 25 are provided that are connected to the amplifier 24 for the linked drive mode, and one of the multiple load resistors 25 is selected to be used.

[0079] Figure 14 is a circuit diagram of the main parts of the sensor unit 2 and signal processing unit 3 according to the third embodiment of the present invention. The configuration of the switch and amplifier for the divided drive mode is the same as in the first embodiment.

[0080] The amplification circuit 5 includes an amplifier 24 for coupled drive mode, a switch 41, and a plurality of load resistors 25. The plurality of load resistors 25 have different resistance values. In this embodiment, three load resistors 25-1 to 25-3 are shown as an example. The number of load resistors 25 may be two or four or more.

[0081] A switch 41 is connected to the input of amplifier 24. Switch 41 is a single-pole, triple-throw switch capable of switching between three paths (one pole and three contacts).

[0082] The input terminal (pole) of switch 41 is connected to the input of amplifier 24. The three output terminals (three contacts) of switch 41 are each connected to one end of load resistors 25-1 to 25-3. The other ends of load resistors 25-1 to 25-3 are connected to the ground terminal GND.

[0083] A control signal CNT2 is input to the control terminal of switch 41 from the mode control unit 8. Based on the control signal CNT2, switch 41 switches between three paths. That is, based on the control signal CNT2, switch 41 switches the load resistor connected to the amplifier 24 from among the multiple load resistors 25. For example, load resistor 25-1 is 10MΩ, load resistor 25-2 is 50MΩ, and load resistor 25-3 is 100MΩ.

[0084] The operation of the sensor device 1 configured as described above will now be explained. Figure 15 is a flowchart illustrating the operation of the sensor device 1. The following operations are always performed in coupled drive mode.

[0085] The mode control unit 8 obtains the output voltage of the amplifier 24 for the coupled drive mode (step S200).

[0086] Next, the mode control unit 8 determines whether the output voltage of the amplifier 24 is lower than the lower threshold or higher than the upper threshold (step S201). The lower threshold and upper threshold are threshold voltages for setting the output voltage of the amplifier 24 to an optimal range. They have the relationship "lower threshold < upper threshold". It is desirable that the output voltage of the amplifier 24 is in a range that is greater than or equal to the lower threshold and less than or equal to the upper threshold. The lower threshold and upper threshold are set appropriately according to the specifications of the sensor device 1.

[0087] If the output voltage of amplifier 24 is lower than the lower threshold or higher than the upper threshold (step S201 = Yes), the mode control unit 8 determines whether a certain time T has elapsed (step S202). The process in step S202 allows control to be made so as not to detect voltage fluctuations due to noise, etc.

[0088] If a certain time T has elapsed (step S202 = Yes), the mode control unit 8 changes the load resistance (step S203). Specifically, if the output voltage of the amplifier 24 is lower than the lower threshold, the mode control unit 8 changes the load resistance so that the resistance value of the load resistance increases. The mode control unit 8 supplies a control signal CNT2 to the switch 41 and changes the load resistance to 50MΩ if the current load resistance is 10MΩ, and changes the load resistance to 100MΩ if the current load resistance is 50MΩ. By increasing the resistance value of the load resistance 25, the output voltage of the amplifier 24 can be increased.

[0089] Furthermore, the mode control unit 8 changes the load resistance so that the resistance value of the load resistor decreases when the output voltage of the amplifier 24 is higher than the upper threshold. The mode control unit 8 supplies a control signal CNT2 to the switch 41 and changes the load resistance to 50MΩ if the current load resistance is 100MΩ, and changes the load resistance to 10MΩ if the current load resistance is 50MΩ. By reducing the resistance value of the load resistor 25, the output voltage of the amplifier 24 can be lowered.

[0090] Figure 16 illustrates an example of the output voltage of amplifier 24. In Figure 16, the horizontal axis represents time (in arbitrary units), and the vertical axis represents the output voltage of amplifier 24 (in arbitrary units). Figure 16 includes graphs of the voltage input to amplifier 24 (input voltage), the voltage amplified by amplifier 24 (amplified voltage), and the voltage output by amplifier 24 (output voltage).

[0091] The maximum output voltage of amplifier 24 is called Vom. If the voltage calculated by "input voltage * amplification factor" exceeds the maximum output voltage Vom, the output voltage of amplifier 24 is capped and becomes a constant voltage.

[0092] When the load resistance 25 is 100 MΩ, the output voltage of the amplifier 24 is higher than the upper threshold (e.g., Vom). At this time, the mode control unit 8 determines that a certain time T has elapsed. Therefore, the mode control unit 8 changes the load resistance 25 to 50 MΩ. Furthermore, when the load resistance 25 is 50 MΩ, the output voltage of the amplifier 24 is higher than the upper threshold (e.g., Vom). At this time, the mode control unit 8 determines that a certain time T has elapsed. Therefore, the mode control unit 8 changes the load resistance 25 to 10 MΩ. In this way, the output voltage of the amplifier 24 is set to a range that is above the lower threshold and below the upper threshold.

[0093] As a variation, the amplification factor of amplifier 24 may be changed according to the output voltage of amplifier 24. The amplification factor of amplifier 24 can be adjusted by changing the resistance value R1 of resistor 32 and / or the resistance value R2 of resistor 33 in Figure 4. Specifically, multiple resistors with different resistance values ​​are prepared for one or both of resistors 32 and resistor 33, and these multiple resistors are switched using a switch. The mode control unit 8 sets the amplification factor high when the output voltage of amplifier 24 is lower than the lower threshold, and sets the amplification factor low when the output voltage of amplifier 24 is higher than the upper threshold.

[0094] According to the third embodiment, optimal detection signals can be obtained in both the split drive mode and the linked drive mode.

[0095] Although the above embodiments were described using the case where the sensor device 1 is a piezoelectric sensor as an example, they can also be applied to other types of sensors. For example, the above embodiments can also be applied to pyroelectric sensors and the like.

[0096] The present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of symbols]

[0097] 1...Sensor device, 2...Sensor unit, 3...Signal processing unit, 4...Switch circuit, 5...Amplifier circuit, 6...Filter circuit, 7...Controller, 8...Mode control unit, 9...Memory unit, 10...External interface, 11...Power supply control unit, 12...Voltage generation circuit, 20...Sensor element, 21...Switch, 22...Amplifier, 23...Load resistor, 24...Amplifier, 25...Load resistor, 30...Input terminal, 31...Output terminal, 32,33...Resistors, 40...Block, 41...Switch.

Claims

1. A sensor unit equipped with multiple sensor elements, A switch circuit comprising a plurality of first switches connected to each of the plurality of sensor elements, each of the plurality of first switches capable of switching between a plurality of first paths and a plurality of second paths, An amplification circuit comprising: a plurality of first amplifiers connected to the plurality of first paths of the plurality of first switches, and a second amplifier commonly connected to the plurality of second paths of the plurality of first switches, A control unit that performs split drive mode and linked drive mode, It is equipped with, The control unit, In the divided drive mode, the switch circuit is controlled to connect the plurality of sensor elements and the plurality of first amplifiers, respectively. In the linked drive mode, the switch circuit is controlled to connect the plurality of sensor elements and the second amplifier in common. Sensor device.

2. The control unit selects the split drive mode when the voltage amplitude of at least one of the multiple detection signals of the multiple sensor elements is greater than a first threshold, and selects the coupled drive mode when the voltage amplitude of at least one of the multiple detection signals is less than or equal to the first threshold. The sensor device according to claim 1.

3. The control unit switches between the split drive mode and the coupled drive mode based on a request from an external device. The sensor device according to claim 1.

4. A plurality of first load resistors connected to the inputs of the plurality of first amplifiers, The second load resistor connected to the input of the second amplifier, It further comprises The sensor device according to claim 1.

5. A plurality of first load resistors connected to the inputs of the plurality of first amplifiers, A second switch connected to the input of the second amplifier and switchable between a first path and a second path, The second load resistor connected to the first path of the second switch, A third load resistor is connected to the second path of the second switch and has a resistance value greater than the second load resistor, Furthermore, it is equipped with, The control unit controls the second switch based on the output voltage of the second amplifier. The sensor device according to claim 1.

6. The control unit controls the second switch to change from the second load resistor to the third load resistor when the output voltage of the second amplifier is lower than the second threshold. The sensor device according to claim 5.

7. Each of the aforementioned plurality of sensor elements is a piezoelectric element. The sensor device according to claim 1.

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