Piezoelectric element control device, and ultrasonic sensor

Abstract

This piezoelectric element control device comprises a drive circuit configured to supply a drive current to a primary-side coil of a transformer in order to drive a piezoelectric element connected in parallel to a secondary-side coil of the transformer, and a control circuit configured to control the drive circuit, wherein the control circuit increases a value of the drive current over time in at least a portion of a supply period of the drive current.

Description

Piezoelectric element control device and ultrasonic sensor

[0001] The present disclosure relates to a piezoelectric element control device and an ultrasonic sensor.

[0002] By applying an AC voltage to the piezoelectric element, the piezoelectric element can generate sound waves.

[0003] JP 2018-96752 A

[0004] To drive a piezoelectric element, a method of applying a drive voltage to the piezoelectric element using a transformer has been considered. In this method, the piezoelectric element is connected in parallel to the secondary coil of the transformer, and a drive current is supplied to the primary coil of the transformer, thereby applying a transformed high drive voltage to the piezoelectric element. Increasing the voltage applied to the piezoelectric element can increase the output intensity of the sound waves.

[0005] However, a rated voltage is set for piezoelectric elements, and voltages exceeding the rated voltage cannot be applied to the piezoelectric element. Ingenuity is required to maximize the output strength of sound waves while keeping the applied voltage below the rated voltage.

[0006] An object of the present disclosure is to provide a piezoelectric element control device and an ultrasonic sensor that contribute to improving the output intensity of sound waves.

[0007] The piezoelectric element control device of the present disclosure comprises a drive circuit configured to drive a piezoelectric element connected in parallel to a secondary coil of a transformer by supplying a drive current to the primary coil of the transformer, and a control circuit configured to control the drive circuit, wherein the control circuit increases the value of the drive current over time during at least a portion of the supply period of the drive current.

[0008] According to the present disclosure, it is possible to provide a piezoelectric element control device and an ultrasonic sensor that contribute to improving the output intensity of sound waves.

[0009] FIG. 1 is a diagram illustrating the overall configuration of an ultrasonic sensor according to an embodiment of the present disclosure. FIG. 2 is a perspective view of the appearance of a piezoelectric element control IC according to an embodiment of the present disclosure. FIG. 3 is a diagram illustrating an overview of the operation of an ultrasonic sensor according to an embodiment of the present disclosure. FIG. 4 is a diagram illustrating transmission and reception operations by an ultrasonic sensor according to an embodiment of the present disclosure. FIG. 5 is a diagram illustrating the internal configuration of a drive circuit and the relationship between the drive circuit and a control circuit according to an embodiment of the present disclosure. FIG. 6 is a diagram illustrating the operation of a drive circuit according to an embodiment of the present disclosure. FIG. 7 is a diagram illustrating the operation of a drive circuit according to an embodiment of the present disclosure. FIG. 8 is a waveform diagram of control signals supplied to two switching elements in a transmission operation according to an embodiment of the present disclosure. FIG. 9 is a waveform diagram of drive current and element applied voltage in a basic transmission operation according to an embodiment of the present disclosure. FIG. 10 is a diagram illustrating an example of a change pattern of drive current in an improved transmission operation according to an embodiment of the present disclosure. FIG. 11 is a waveform diagram of drive current and element applied voltage in an improved transmission operation according to an embodiment of the present disclosure. Fig. 12 is a diagram showing an example of a change pattern of the drive current in an improved transmit operation according to a second example of an embodiment of the present disclosure. Fig. 13 is a diagram showing a state in which a receive-only piezoelectric element is connected to a receive circuit according to a fifth example of an embodiment of the present disclosure. Fig. 14 is a diagram showing a modified configuration of the drive circuit according to a sixth example of an embodiment of the present disclosure.

[0010] Hereinafter, examples of embodiments of the present disclosure will be described in detail with reference to the drawings. In each of the drawings, the same parts are designated by the same reference numerals, and duplicate descriptions of the same parts will be omitted as a general rule. In this specification, for the sake of simplicity, symbols or signs referring to information, signals, physical quantities, functional units, circuits, elements, or components may be used, and the names of the information, signals, physical quantities, functional units, circuits, elements, or components corresponding to the symbols or signs may be omitted or abbreviated.

[0011] First, some terms used in describing the embodiments of the present disclosure will be explained. IC is an abbreviation for Integrated Circuit. Ground refers to a reference conductive part having a reference potential of 0 V (zero volts), or refers to the potential of 0 V itself. The reference conductive part may be formed using a conductor such as metal. The potential of 0 V is sometimes referred to as ground potential. In the embodiments of the present disclosure, a voltage indicated without a particular reference represents a potential seen from ground.

[0012] A level refers to the level of potential, and for any given signal or voltage, a high level has a higher potential than a low level. For any given signal or voltage, when the signal or voltage is at a high level, strictly speaking, the signal or voltage level is at a high level, and when the signal or voltage is at a low level, strictly speaking, the signal or voltage level is at a low level. A level for a signal may be expressed as a signal level, and a level for a voltage may be expressed as a voltage level.

[0013] Unless otherwise specified, the connection between a plurality of parts forming a circuit, such as any circuit element, wiring, or node, may be understood to refer to an electrical connection.

[0014] 1 shows the overall configuration of an ultrasonic sensor 1 according to an embodiment of the present disclosure. The ultrasonic sensor 1 includes a piezoelectric element control IC 2 (hereinafter, may be referred to as IC2), which is an example of a piezoelectric element control device, a piezoelectric element 3, a transformer TR, and a resistor R T and capacitor C T , C1 and C2. IC2 includes a drive circuit 10, a receiving circuit 20, a control circuit 30 and a signal processing circuit 40. The drive circuit may be interpreted as a transmission circuit. The piezoelectric element 3 is a ceramic vibrator (ceramic piezoelectric element) formed from ceramic.

[0015] An MPU (Micro Processing Unit) 4 is connected to the IC 2. The MPU 4 may be understood as not being included in the components of the ultrasonic sensor 1, or as being included in the components of the ultrasonic sensor 1.

[0016] FIG. 2 is a perspective view of IC2. IC2 is an electronic component including a semiconductor chip having a semiconductor integrated circuit formed on a semiconductor substrate, a housing (package) that houses the semiconductor chip, and multiple external terminals exposed to the outside of IC2 from the housing. IC2 is formed by encapsulating the semiconductor chip in a housing (package) made of resin. Note that the number of external terminals of IC2 and the type of housing of IC2 shown in FIG. 2 are merely examples and can be designed as desired. FIG. 1 shows the power supply terminal PW, ground terminal PGND, output terminals DRV1 and DRV2, input terminal IN1, and input terminal IN2, which are included in the multiple external terminals. Other external terminals are also provided on IC2.

[0017] A power supply voltage VCC is supplied to the power supply terminal PW. Each circuit within IC2 is driven by the power supply voltage VCC. The power supply voltage VCC has a predetermined positive DC voltage value. An internal power supply circuit (not shown) that generates another internal power supply voltage from the power supply voltage VCC may be provided within IC2. The ground terminal PGND is connected to ground.

[0018] The transformer TR has a primary coil L1 and a secondary coil L2, which are magnetically coupled while being electrically insulated from each other. A first end of the primary coil L1 is connected to the output terminal DRV1, and a second end of the primary coil L1 is connected to the output terminal DRV2. A power supply terminal PW is connected to the midpoint (center tap) of the primary coil L1 via a resistor R0. More specifically, the power supply terminal PW is connected to one end of the resistor R0, and the other end of the resistor R0 is connected to the midpoint of the primary coil L1 and to ground via a capacitor C0.

[0019] The piezoelectric element 3 is connected in parallel to the secondary coil L2. That is, a first end of the secondary coil L2 is connected to a first end of the piezoelectric element 3, and a second end of the secondary coil L2 is connected to a second end of the piezoelectric element 3 and is also connected to ground. In addition, a capacitor C T and resistor R Tare connected. Furthermore, a first end of the secondary coil L2 and a first end of the piezoelectric element 3 are connected to the input terminal IN1 via a capacitor C1. That is, the first end of the secondary coil L2 and the first end of the piezoelectric element 3 are connected to the first end of the capacitor C1, and the second end of the capacitor C1 is connected to the input terminal IN1. Furthermore, a second end of the secondary coil L2 and a second end of the piezoelectric element 3 are connected to the input terminal IN2 via a capacitor C2. That is, the second end of the secondary coil L2 and the second end of the piezoelectric element 3 are connected to the first end of the capacitor C2, and the second end of the capacitor C2 is connected to the input terminal IN2. Note that the capacitors C1 and C2 may be built into the IC2. The voltage applied across the piezoelectric element 3 may be referred to as the element applied voltage V3 below. The element applied voltage V3 corresponds to the potential of the first end of the piezoelectric element 3 as viewed from the potential of the second end of the piezoelectric element 3.

[0020] An overview of the operation of the ultrasonic sensor 1 will be described with reference to Figure 3. Note that Figure 3 shows only the piezoelectric element 3 out of the components of the ultrasonic sensor 1. The ultrasonic sensor 1 uses the piezoelectric element 3 to transmit a transmission wave signal W1 in the ultrasonic band toward the space outside the ultrasonic sensor 1 (in a direction away from the ultrasonic sensor 1). The transmission wave signal W1 is reflected by the detection object OBJ, generating a reflected wave signal W2. The reflected wave signal W2 is received by the ultrasonic sensor 1 using the piezoelectric element 3.

[0021] The ultrasonic band refers to a frequency band that is higher than the frequency band of sound waves that can be heard by the human ear but is inaudible to the human ear, and generally refers to a band of 20 kHz or higher. For example, the transmitted wave signal W1 has a frequency in the range of 30 kHz to 80 kHz. Both the transmitted wave signal W1 and the reflected wave signal W2 belong to the ultrasonic signal category.

[0022] The piezoelectric element 3 generates a mechanical displacement (vibration) in response to a voltage signal applied between its first and second ends, and generates a transmission wave signal W1 through its own mechanical displacement. Therefore, the piezoelectric element 3 functions as a transmitter of the transmission wave signal W1. The piezoelectric element 3 also has the property of generating an electromotive force between its first and second ends in response to the mechanical displacement (vibration) applied to itself, and functions as a receiver of the reflected wave signal W2.

[0023] The IC2 transmits the transmission wave signal W1 and receives the reflected wave signal W2 using the piezoelectric element 3. Hereinafter, the combined operation of transmitting the transmission wave signal W1 and receiving the reflected wave signal W2 may be referred to as a transmission / reception operation.

[0024] The drive circuit 10 is connected to output terminals DRV1 and DRV2. The drive circuit 10 transmits a transmission wave signal W1 under the control of the control circuit 30. In transmitting the transmission wave signal W1, the drive circuit 10 drives the piezoelectric element 3 by supplying an AC drive current to the primary coil L1. More specifically, in transmitting the transmission wave signal W1, the drive circuit 10 supplies an AC drive current to the primary coil L1 via the output terminals DRV1 and DRV2, thereby generating an AC voltage in the secondary coil L2. The AC voltage generated in the secondary coil L2 is applied to the piezoelectric element 3 as an element applied voltage V3, thereby generating a transmission wave signal W1 in the piezoelectric element 3 and transmitting the transmission wave signal W1 from the piezoelectric element 3. The number of turns of the secondary coil L2 is greater than the number of turns of the primary coil L1, and an AC voltage having an amplitude greater than the amplitude of the AC voltage applied across the primary coil L1 is generated across the secondary coil L2.

[0025] The receiving circuit 20 is connected to the input terminals IN1 and IN2 and performs an operation of receiving the reflected wave signal W2. In the operation of receiving the reflected wave signal W2, the receiving circuit 20 receives the reflected wave signal W2 in the ultrasonic band using the piezoelectric element 3. That is, the receiving circuit 20 receives the reflected wave signal W2 by receiving the voltage signal applied across the piezoelectric element 3 via capacitors C1 and C2. The capacitors C1 and C2 remove the DC component of the voltage signal applied across the piezoelectric element 3, and only the AC component of the voltage signal applied across the piezoelectric element 3 is input to the receiving circuit 20 as an input signal Sin. The input signal Sin corresponds to the signal received by the receiving circuit 20 of the reflected wave signal W2.

[0026] The signal processing circuit 40 performs predetermined signal processing on the reflected wave signal W2 received by the receiving circuit 20 to generate a detection signal S40 based on the reflected wave signal W2. For example, the receiving circuit 20 performs amplification processing to amplify the signal Sin between the input terminals IN1 and IN2, and sends a signal Sin', which is the amplified signal Sin, to the signal processing circuit 40. For example, the signal processing may include envelope detection processing to generate an envelope signal by detecting the envelope of the signal Sin', and comparison processing to compare the magnitude of the envelope signal with a predetermined threshold. The envelope signal has a voltage value proportional to the amplitude of the input signal Sin to the receiving circuit 20, and the signal processing circuit 40 can generate a detection signal S40 that indicates the magnitude relationship between the magnitude (voltage value) of the envelope signal and the threshold. The detection signal S40 is sent to the control circuit 30. The detection signal S40 generated by the signal processing circuit 40 based on the signal Sin' is a signal that indicates the magnitude relationship between the intensity of the signal Sin and a predetermined reference intensity, and the content of the signal processing is arbitrary as long as the signal can be generated. For example, instead of envelope detection, the detection signal S40 may be generated by performing quadrature detection or correlation processing on the signal Sin'. Both detection methods are well known as detection methods for ultrasonic sensors, so a detailed description will be omitted here.

[0027] 4 is a diagram showing the transmission and reception operation of the ultrasonic sensor 1. The detection signal S40 is a binary signal having a high or low signal level. Here, the detection signal S40 has a low level when the magnitude (voltage value) of the envelope signal is equal to or greater than the threshold value, and the detection signal S40 has a high level when the magnitude (voltage value) of the envelope signal is less than the threshold value.

[0028] The IC2 and MPU4 are connected to each other in a manner that allows bidirectional communication. The control circuit 30 communicates bidirectionally with the MPU4. The MPU4 can send a measurement instruction command to the IC2. When the IC2 receives the measurement instruction command, the control circuit 30 causes the drive circuit 10 to transmit a transmission wave signal W1, and in response to this transmission operation, transmits a detection signal S40 obtained by receiving a reflected wave signal W2 to the MPU4. The MPU4 performs object detection processing based on the detection signal S40.

[0029] The object detection process may be a distance detection process that detects the distance between the ultrasonic sensor 1 and the detection object OBJ (in other words, the distance between the piezoelectric element 3 and the detection object OBJ). The distance between the ultrasonic sensor 1 and the detection object OBJ can be derived by measuring the length of time from transmitting the transmission wave signal W1 at time t1 to receiving the reflected wave signal W2 at time t3 (i.e., the length between times t1 and t3). Time t1 represents the start time of transmission of the transmission wave signal W1 using the drive circuit 10 and the piezoelectric element 3, and time t3 represents the start time of reception of the reflected wave signal W2 using the reception circuit 20 and the piezoelectric element 3. Time t2 represents the end time of transmission of the transmission wave signal W1 using the drive circuit 10 and the piezoelectric element 3. Time t2 is a time before time t3. Before time t1, the detection signal S40 is at a high level. Between times t1 and t2, an AC voltage of sufficiently large amplitude is applied to the piezoelectric element 3, causing the detection signal S40 to go low, and then returning to high at time t2. Thereafter, the reflected wave signal W2 from the object detector OBJ is received at time t3, causing the detection signal S40 to switch from high to low. The detection signal S40 is maintained at low level as the reflected wave signal W2 continues to be received from time t3 to time t4, causing the detection signal S40 to switch from low to high at time t4. Ideally, the length between times t3 and t4 is equal to the length between times t1 and t2.

[0030] The object detection process may be an approach detection process. In the approach detection process, if the MPU 4 receives the reflected wave signal W2 within a predetermined time period after transmitting the transmission wave signal W1 at time t1, the MPU 4 determines that the detection object OBJ is approaching the ultrasonic sensor 1; otherwise, the MPU 4 determines that the detection object OBJ is not approaching the ultrasonic sensor 1. If the detection signal S40 switches from high level to low level within a predetermined time period after time t2 from time t1, the MPU 4 can determine that the detection object OBJ is approaching the ultrasonic sensor 1; otherwise, the MPU 4 can determine that the detection object OBJ is not approaching the ultrasonic sensor 1.

[0031] The ultrasonic sensor 1 is mounted on any device. For convenience, a device mounted with the ultrasonic sensor 1 is referred to as a sensor-mounted device. A typical example of a sensor-mounted device is a vehicle such as an automobile. It can also be said that the distance between the ultrasonic sensor 1 and the detection object OBJ corresponds to the distance between the sensor-mounted device and the detection object OBJ. It can also be said that the approach of the detection object OBJ to the ultrasonic sensor 1 corresponds to the approach of the detection object OBJ to the sensor-mounted device.

[0032] Here, it is assumed that the object detection process is performed by the MPU 4, but the object detection process may also be performed by the control circuit 30. In this case, the result of the object detection process by the control circuit 30 is transmitted to the MPU 4.

[0033] Even after the supply of drive current to the primary coil L1 is stopped after the start of supplying the drive current, the piezoelectric element 3 continues to vibrate for a while based on the mechanical energy accumulated during the supply of the drive current. The vibration of the piezoelectric element 3 after the supply of the drive current is stopped is called reverberation. If the reverberation continues for a long time, it becomes difficult to detect an object at close range. Capacitor C T and resistor R T is provided to reduce reverberation. Furthermore, for the purpose of improving EMC (electromagnetic compatibility) characteristics, a resistor may be inserted between the capacitor C1 and the input terminal IN1, a resistor may be inserted between the capacitor C2 and the input terminal IN2, and a capacitor may be inserted between the input terminals IN1 and IN2.

[0034] 5 shows the internal configuration of the drive circuit 10 and the relationship between the drive circuit 10 and the control circuit 30. The drive circuit 10 includes switching elements 11 and 12 and a current source 13. A first end (first electrode) of the switching element 11 is connected to the output terminal DRV1, and therefore to the first end of the primary coil L1. A second end (second electrode) of the switching element 11 is connected to the input end of the current source 13. A first end (first electrode) of the switching element 12 is connected to the output terminal DRV2, and therefore to the second end of the primary coil L1. A second end (second electrode) of the switching element 12 is connected to the input end of the current source 13. The current source 13 is a constant current source having an input end and an output end, and outputs a drive current I from its input end to its output end. DRV The output terminal of the current source 13 is connected to the ground. DRV flows from the input terminal of the current source 13 to the output terminal (and therefore to ground).

[0035] The control circuit 30 supplies a control signal CNT1 to the switching element 11 to control the state (on or off) of the switching element 11. The control circuit 30 supplies a control signal CNT2 to the switching element 12 to control the state (on or off) of the switching element 12. The control signals CNT1 and CNT2 each have a value of "1" or "0."

[0036] When the control signal CNT1 has a value of "1", the switching element 11 is in an on state, and when the control signal CNT1 has a value of "0", the switching element 11 is in an off state. When the switching element 11 is in an on state, the first terminal and the second terminal of the switching element 11 are in a conductive state, and when the switching element 11 is in an off state, the first terminal and the second terminal of the switching element 11 are in a cut-off state (non-conductive state). Similarly, when the control signal CNT2 has a value of "1", the switching element 12 is in an on state, and when the control signal CNT2 has a value of "0", the switching element 12 is in an off state. When the switching element 12 is in an on state, the first terminal and the second terminal of the switching element 12 are in a conductive state, and when the switching element 12 is in an off state, the first terminal and the second terminal of the switching element 12 are in a cut-off state (non-conductive state).

[0037] The control circuit 30 never simultaneously sets the values ​​of the control signals CNT1 and CNT2 to "1." Therefore, if the value of the control signal CNT1 is "1," the value of the control signal CNT2 is "0," and if the value of the control signal CNT2 is "1," the value of the control signal CNT1 is "0."

[0038] When the control signal CNT1 has a value of "1", as shown in FIG. 6, the first end of the primary coil L1 is electrically connected to the current source 13 through the output terminal DRV1 and the switching element 11, and the driving current I is supplied from the first end of the primary coil L1 to the current source 13 through the output terminal DRV1 and the switching element 11 by the action of the current source 13. DRV When the control signal CNT1 has a value of "1", a driving current I DRV In particular, the driving current I DRV1 The driving current I DRV1 flows through a current path passing through the capacitor C0, the midpoint (center tap) of the primary coil L1, and the first end of the primary coil L1 (see also FIG. 1).

[0039] When the control signal CNT2 has a value of "1", as shown in FIG. 7, the second end of the primary coil L1 is electrically connected to the current source 13 through the output terminal DRV2 and the switching element 12, and the driving current I is supplied from the second end of the primary coil L1 to the current source 13 through the output terminal DRV2 and the switching element 12 by the action of the current source 13. DRV When the control signal CNT2 has a value of "1", a driving current I DRV In particular, the driving current I DRV2 The driving current I DRV2 flows through a current path passing through the capacitor C0, the midpoint (center tap) of the primary coil L1, and the second end of the primary coil L1 (see also FIG. 1).

[0040] Each of the switching elements 11 and 12 is configured, for example, by an N-channel metal-oxide-semiconductor field-effect transistor (MOSFET). In this case, the drains of the switching elements 11 and 12 are connected to the output terminals DRV1 and DRV2, respectively, while the sources of the switching elements 11 and 12 are connected to the input terminal of the current source 13. Then, the gate potentials of the switching elements 11 and 12 are controlled by the control signals CNT1 and CNT2, respectively. However, the switching elements 11 and 12 may also be configured by P-channel MOSFETs.

[0041] The current source 13 supplies a driving current I DRV The control circuit 30 supplies a control signal CNT3 to the current source 13. The current source 13 generates a drive current I DRV In other words, the control circuit 30 variably sets the value of the drive current I by supplying the control signal CNT3 to the current source 13. DRV 1, the control circuit 30 has an information holding unit 31, the function of which will be described later.

[0042] 8 shows the waveforms of the control signals CNT1 and CNT2 in one transmission operation (one transmission operation of the transmission wave signal W1). In one transmission operation, a unit operation in which the control signals CNT1 and CNT2 are alternately set to "1" is repeated m times (i.e., a unit operation in which the switching elements 11 and 12 are alternately turned on and off is repeated m times). In one unit operation, "(CNT1, CNT2) = (1, 0)" is set for a time ΔT, and then "(CNT1, CNT2) = (0, 1)" is set for a time ΔT. The reciprocal of the time (2 x ΔT) is the frequency of the control signals CNT1 and CNT2, and will be referred to as the drive frequency f hereinafter. DRVwhere m is an integer value of 2 or more. In one transmission operation, m periods of sound waves are transmitted from the piezoelectric element 3 as the transmission wave signal W1. For this reason, the value of m is referred to as the wave number (hereinafter, m will be referred to as the wave number m). Note that, during a period in which the transmission operation is not being performed, the primary coil L1 and the current source 13 are disconnected by setting "(CNT1, CNT2) = (0, 0)", and the drive current I from the current source 13 is DRV is not supplied to the primary coil L1.

[0043] Drive frequency f DRV is the driving current I supplied to the primary coil L1 DRV and the frequency of the AC voltage generated in the secondary coil L2, and is set to a frequency that matches or is close to the resonance frequency fr of the piezoelectric element 3. DRV is a frequency in the ultrasonic band. DRV is supplied to the primary coil L1, the piezoelectric element 3 outputs a driving frequency f DRV A transmission wave signal W1 having a drive frequency f DRV A reflected wave signal W2 having the following wave frequency is received.

[0044] FIG. 9 shows the drive current I DRV1 , I DRV2 , I DRV 9 shows the waveforms of the driving current I to the primary coil L1 and the voltage V2 applied to the element. As mentioned above, the voltage V3 applied to the element is the voltage applied across the piezoelectric element 3 (see FIG. 1). The basic transmission operation is provided for comparison with the improved transmission operation described later. In IC2, the basic transmission operation may or may not be performed. Note that in FIG. 9, it is assumed that "m=12", and for the sake of convenience in the illustration and simplification of the explanation, each waveform is shown schematically and it is assumed that there is almost no reverberation. In the basic transmission operation, the driving current I to the primary coil L1 is DRV During the entire supply period of the driving current I DRV The value of is fixed to a constant value.

[0045] In the configuration shown in FIG. 1 in which the transformer TR is used to drive the piezoelectric element 3, in order to measure a longer distance, the driving current I DRVIt is necessary to increase the driving current I. On the other hand, the ceramic vibrator used as the piezoelectric element 3 has a characteristic that the input impedance is lower when it is vibrating at the resonant frequency fr than when it is stationary. That is, the input impedance of the piezoelectric element 3 when the piezoelectric element 3 is not yet vibrating sufficiently immediately after the start of transmission of the transmission wave signal W1 is higher than the input impedance of the piezoelectric element 3 when the piezoelectric element 3 is vibrating sufficiently. For this reason, as in the basic transmission operation, DRV When the value of is fixed to a constant value, the amplitude of the element applied voltage V3 becomes relatively large immediately after the start of transmission of the transmission wave signal W1, and thereafter, as the vibration of the piezoelectric element 3 increases, the amplitude of the element applied voltage V3 decreases.

[0046] In the basic transmission operation, it is necessary that the applied voltage V3 of the element does not exceed the rated voltage of the piezoelectric element 3 immediately after the start of transmission of the transmission wave signal W1. DRV In this case, the voltage V3 applied to the element during the period when the vibration of the piezoelectric element 3 becomes sufficiently large, that is, the voltage V3 applied to the element during the period when ultrasonic waves are efficiently generated, has an excessive margin with respect to the rated voltage, and the original rated voltage cannot be effectively used.

[0047] Taking this into consideration, the IC2 is capable of performing the following improved transmission operation as the transmission operation of the transmission wave signal W1. DRV When the IC2 receives a measurement instruction command from the MPU 4, the control circuit 30 causes the drive circuit 10 to perform an improved transmission operation as a transmission operation of the transmission wave signal W1, and in response to the improved transmission operation, the detection signal S40 obtained by the reception operation of the reflected wave signal W2 can be transmitted to the MPU 4.

[0048] In one improved transmission operation, time t A10 From time t A20 Drive current I DRV is supplied to the primary coil L1. At time t A10 From time t A20 During the period up to DRV This is the supply period of the driving current I DRVDuring the supply period, the driving current I DRV1 , I DRV2 are alternately supplied, and the driving current I DRV1 and I DRV2 Each value of the drive current I DRV In this embodiment, the driving current I DRV The value of the drive current I DRV This can also be interpreted as the size of

[0049] In the change pattern of FIG. 10, the control circuit 30 A10 The driving current I DRV The value of SET1 and at time t A10 From time t A11 Over time, the driving current I DRV The value of SET1 From the current value I SET2 (Therefore, the current value I SET2 is the current value I SET1 (greater than ). Time t A11 is time t A10 later than time t A20 In the change pattern of FIG. 10, the control circuit 30 A11 and t A20 Drive current I DRV The value of SET2 Fix it to.

[0050] FIG. 11 shows the drive current I DRV1 , I DRV2 , I DRV 11 shows waveforms of the voltage V1 and the voltage V2 applied to the element. In FIG. 11, it is assumed that "m=12", and for the convenience of illustration and simplification of explanation, each waveform is shown schematically and it is assumed that there is almost no reverberation. The improved transmission operation in FIG. 11 employs the change pattern in FIG. 10. In FIG. 10, at time t A10 and t A11 Between the driving current I DRV However, as shown in FIG. 11, the drive current I DRV It is advisable to increase it step by step.

[0051] That is, since "m=12" in FIG. 11, the improved transmission operation is made up of the first to twelfth unit operations. The execution start time of the first unit operation is the time t A10 The execution end time of the 12th unit operation corresponds to time t A20 In the example of FIG. 11, the control circuit 30 controls the drive current I DRV The value of SET1 Then, during the execution period of the first to sixth unit operations, the driving current I DRV Each time one unit operation is executed, the value of "(I SET2 -I SET1 ) / 5″. Then, the driving current I DRV The value of is the current value I SET2 In the example of FIG. 11, the control circuit 30 controls the driving current I DRV The value of SET2 The execution start time of the sixth unit operation is fixed at time t A11 is equivalent to

[0052] According to the improved transmission operation, immediately after the start of transmission of the transmission wave signal W1 (time t A10 When the input impedance of the piezoelectric element 3 is relatively high, the driving current I DRV is set relatively low, and then, as time passes, the driving current I DRV is increasing.

[0053] Therefore, the drive current I DRV The fluctuation range of the voltage V3 applied to the element can be suppressed throughout the entire supply period of the voltage V3, and ideally, the voltage V3 applied to the element can be kept roughly constant. As a result, according to the improved transmission operation, the piezoelectric element 3 can be used effectively up to the rated voltage, and the output intensity of the ultrasonic waves can be increased compared to the basic transmission operation.

[0054] In the example of FIG. 11, "m=12" is used, but as described above, m can be any integer equal to or greater than 2, and may be, for example, "m=32".

[0055] Below, several specific operational examples, application techniques, modification techniques, etc. related to the ultrasonic sensor 1 will be described in multiple examples. The matters described above in this embodiment apply to each of the following examples unless otherwise specified and unless there is a contradiction. If there are any matters in each example that contradict the matters described above, the description in that example may take precedence. Furthermore, unless there is a contradiction, matters described in any of the multiple examples shown below can also be applied to any other example (i.e., any two or more of the multiple examples can also be combined).

[0056] First Example A first example will be described. In the example of FIG. 11, the drive current I DRV During a part of the supply period of the drive current I DRV However, the drive current I DRV may be increased.

[0057] When "k=2", for example, the driving current I DRV The value of SET1 and the driving current I DRV The value of SET1 + (I SET2 -I SET1 ) × 1 / 3), and the driving current I DRV The value of SET1 + (I SET2 -I SET1 ) × 2 / 3), and the driving current I DRV The value of SET2 k may be an integer of 3 or more.

[0058] Second Embodiment A second embodiment will be described. In the improved transmission operation, as shown in FIG. 12, the drive current I DRV The drive current I DRV As described above, in one improved transmission operation, the time t A10 From time t A20 Drive current I DRVis supplied to the primary coil L1. In the change pattern of FIG. A10 The driving current I DRV The value of is the current value I SET1 and at time t A10 From time t A20 The driving current I DRV The value of is the current value I SET1 From the current value I SET2 It gradually increases towards

[0059] 11, if "m=12" is considered, the improved transmission operation is made up of the first to twelfth unit operations. The control circuit 30 according to the second embodiment calculates the driving current I DRV The value of SET1 Then, the drive current I DRV The value of "(I SET2 -I SET1 ) / 11”. Then, the driving current I DRV The value of is the current value I SET2 In the improved transmission operation according to the second embodiment, the drive current I DRV The value of may be increased each time a k unit operation is performed.

[0060] <<Third Embodiment>> A third embodiment will be described. In the improved transmission operation, the control circuit 30 controls the drive current I DRV During the supply period, the driving current I DRV The change pattern can be set in various ways.

[0061] As described above (see FIG. 1), the control circuit 30 is provided with the information holding unit 31. The information holding unit 31 receives the driving current I DRV During the supply period of the driving current I DRV The information specifying the change pattern of the driving current I (hereinafter referred to as current change pattern specification information) is stored. DRV During the supply period of the driving current I DRVBased on the contents of the setting command received from the MPU 4, the control circuit 30 can variably set the current change pattern designation information.

[0062] This allows the drive current I to be adjusted to match the characteristics of the piezoelectric element 3 incorporated in the ultrasonic sensor 1. DRV As a result, the change pattern of the driving current I can be adjusted according to the characteristics of the piezoelectric element 3. DRV Therefore, the fluctuation range of the voltage V3 applied to the element can be suppressed throughout the entire supply period of the voltage V3, and ideally, the voltage V3 applied to the element can be kept approximately constant.

[0063] The information storage unit 31 is configured with a nonvolatile memory that can rewrite information to be stored. The information storage unit 31 stores initial pattern designation information as current change pattern designation information in advance, and in the improved transmission operation in the initial state of the IC2, the control circuit 30 controls the drive current I according to the designation content of the initial pattern designation information. DRV Thereafter, when the control circuit 30 receives a setting command from the MPU 4 to rewrite the current change pattern designation information, the control circuit 30 rewrites the current change pattern designation information in the information holding unit 31 in accordance with the content of the setting command received from the MPU 4. Thereafter, in the improved transmission operation, the control circuit 30 controls the drive current I in accordance with the content of the rewritten current change pattern designation information. DRV The current change pattern designation information may be rewritten multiple times.

[0064] Alternatively, the information holding unit 31 may be configured with a volatile memory classified as a register. In this case, every time the IC2 is started up, the MPU 4 transmits a setting command including current change pattern designation information to the IC2, and the control circuit 30 writes the current change pattern designation information in the received setting command to the information holding unit 31. Thereafter, in the improved transmission operation, the control circuit 30 controls the drive current I in accordance with the designation content of the current change pattern designation information stored in the information holding unit 31. DRV Change the value of .

[0065] However, the information storage unit 31 may be configured as a non-volatile memory (one-time programmable memory) in which the information to be stored cannot be rewritten. In this case, appropriate current change pattern designation information in accordance with the characteristics of the piezoelectric element 3 incorporated in the ultrasonic sensor 1 can be written to the information storage unit 31, for example, during the manufacturing or shipping process of the IC 2.

[0066] The current value I SET1 and I SET2 That is, the current change pattern designation information is the current value I SET1 and I SET2 The control circuit 30 includes information specifying the current value I SET1 and I SET2 At least one of these can be changed.

[0067] In addition, the driving current I DRV During the supply period of the driving current I DRV The value of SET1 From the current value I SET2 The process of increasing the driving current I DRV The characteristics of the change in the value of the driving current I are also specified by the current change pattern specification information. DRV How the value of is changed is specified by the current change pattern specification information.

[0068] For example, the control circuit 30 increases the drive current I every time one unit operation or k unit operations are performed in the current increasing process. DRV In this case, the control circuit 30 executes the current increasing process P times in the current increasing process. SET2 =I SET1 +ΔI×P″ is established. The control circuit 30 can change at least one of the current value ΔI and the number of times P that the current increasing process is executed, based on a setting command from the MPU 4. The current value ΔI may be a fixed current value.

[0069] Alternatively, the drive current I DRVThe current change pattern designation information may include information designating the value of the driving current I in the first unit operation. DRV The value of is the current value I SET1 and the driving current I in the sixth to mth unit operations DRV The value of is the current value I SET2 In this case, the driving current I DRV The values ​​may be individually specified in the current change pattern specification information.

[0070] The information storage unit 31 stores the driving frequency f DRV The control circuit 30 also stores drive frequency designation information specifying the drive frequency f and wave number designation information specifying the wave number m. DRV Based on the contents of the setting command received from the MPU 4, the control circuit 30 can variably set the driving frequency designation information and the wave number designation information (i.e., the driving frequency f DRV and the wave number m can be variably set).

[0071] <<Fourth Example>> A fourth example will be described. Although not shown, in the change pattern of FIG. 10, at time t A11 After that, at time t A20 Before reaching the drive current I DRV The value of SET2 The current may be reduced to a value lower than the predetermined value.

[0072] <<Fifth Embodiment>> A fifth embodiment will now be described. In the ultrasonic sensor 1 of FIG. 1 , a single piezoelectric element 3 functions as a transmitter of the transmitted wave signal W1 and as a receiver of the reflected wave signal W2. However, in addition to the piezoelectric element 3 functioning as a transmitter, the ultrasonic sensor 1 may also be provided with a separate piezoelectric element 3R functioning as a receiver, as shown in FIG. 13 . In this case, the piezoelectric element 3 is not connected to capacitors C1 and C2. Instead, the first end of the piezoelectric element 3R is connected to the first end of the capacitor C1, the second end of the capacitor C1 is connected to the input terminal IN1, the second end of the piezoelectric element 3R is connected to the first end of the capacitor C2, and the second end of the capacitor C2 is connected to the input terminal IN2. The piezoelectric element 3R is positioned at a distance from the piezoelectric element 3 and receives the reflected wave signal W2 to generate a voltage signal across its ends.

[0073] The receiving circuit 20 is connected to input terminals IN1 and IN2 and receives the reflected wave signal W2. In receiving the reflected wave signal W2, the receiving circuit 20 according to the fifth embodiment receives the reflected wave signal W2 in the ultrasonic band using the piezoelectric element 3R. That is, the receiving circuit 20 receives the reflected wave signal W2 by receiving the voltage signal applied across the piezoelectric element 3R via capacitors C1 and C2. The DC component of the voltage signal applied across the piezoelectric element 3R is removed by capacitors C1 and C2, and only the AC component of the voltage signal applied across the piezoelectric element 3R is input to the receiving circuit 20 as the input signal Sin. The input signal Sin corresponds to the signal received by the receiving circuit 20 as the reflected wave signal W2. The same is true as described above, except that the piezoelectric element that generates the input signal Sin is the piezoelectric element 3R.

[0074] <<Sixth Example>> A sixth example will be described. The configuration of the drive circuit 10 is not limited to the configuration shown in FIG. 5, and any configuration is possible as long as it can supply AC current to the primary coil L1. For example, a drive circuit 10a shown in FIG. 14 may be used as the drive circuit 10. The drive circuit 10a includes switching elements 11a, 12a, and 14a, and a current source 13a. The configuration and operation of the drive circuit 10a will be described.

[0075] The current source 13a is a constant current source having an input terminal and an output terminal, and a drive current I is supplied from its input terminal to its output terminal. DRV The input terminal of the current source 13a is connected to a terminal to which a positive DC voltage is applied, and the output terminal of the current source 13a is connected to a first terminal of the switching element 14a. The second terminal of the switching element 14a is connected to the midpoint (center tap) of the primary coil L1. The first terminal of the switching element 11a is connected to a first terminal of the primary coil L1, and the first terminal of the switching element 12a is connected to a second terminal of the primary coil L1. The second terminals of the switching elements 11a and 12a are connected to ground.

[0076] The switching elements 11a, 12a, and 14a can be configured as P-channel or N-channel MOSFETs, and the control circuit 30 can individually control the on / off of the switching elements 11a, 12a, and 14a by controlling the gate potentials of the switching elements 11a, 12a, and 14a.

[0077] Drive current I DRV to the primary coil L1, the control circuit 30 alternately turns on and off the switching elements 11a and 12a while keeping the switching element 14a on. When the switching element 14a is on, if the switching elements 11a and 12a are on and off, respectively, the driving current I from the current source 13a DRV flows from the midpoint of the primary coil L1 to the first end of the primary coil L1 through the switching element 11a. When the switching element 14a is on, if the switching elements 11a and 12a are off and on, respectively, the driving current I from the current source 13a DRV flows from the midpoint of the primary coil L1 to the second end of the primary coil L1 through the switching element 12a.

[0078] The current source 13a, like the current source 13, generates a drive current I DRV The current source 13a is a variable constant current source configured to be able to change the value of the drive current I DRV The method for variably setting the value of is the same as that for the current source 13.

[0079] The driving circuit according to the present disclosure is DRV and a current source (13, 13a) configured to generate a drive current I DRV The control circuit 30 may include a switch circuit configured to supply the drive current I in the first direction or the second direction. DRV During the supply period, the switch circuit is controlled to supply a drive current I DRV is supplied alternately in the first direction and the second direction, thereby generating an AC voltage in the secondary coil L2.

[0080] In the drive circuit 10 of Fig. 5, the switch circuit is configured to include switching elements 11 and 12. In the drive circuit 10a of Fig. 14, the switch circuit is configured to include switching elements 11a and 12a. Of the first and second directions, one is a direction from the first end to the second end of the primary coil L1, and the other is a direction from the second end to the first end of the primary coil L1.

[0081] <<Seventh Example>> A seventh example will be described.

[0082] The above description deals with an example in which the piezoelectric element 3 is a ceramic vibrator. However, the piezoelectric element 3 may be any type of piezoelectric element as long as it satisfies the condition that the input impedance of the piezoelectric element 3 when vibrating is lower than the input impedance of the piezoelectric element 3 when it is at rest. The input impedance of the piezoelectric element 3 when it is at rest refers to the input impedance of the piezoelectric element 3 when it is at rest (i.e., not vibrating). The input impedance of the piezoelectric element 3 when it is vibrating refers to the input impedance of the piezoelectric element 3 when it is vibrating at its own resonant frequency fr.

[0083] In the above example, each of the switching elements 11 and 12 is configured as a MOSFET. However, the switching elements 11 and 12 may be any type of switching element. For example, each of the switching elements 11 and 12 may be configured as a junction FET, a bipolar transistor, or an IGBT (Insulated Gate Bipolar Transistor).

[0084] With respect to any signal or voltage, the relationship between the high level and the low level thereof may be reversed without prejudice to the above-mentioned gist.

[0085] The embodiments of the present disclosure can be modified in various ways as appropriate within the scope of the technical ideas set forth in the claims. The above-described embodiments are merely examples of the present disclosure, and the meanings of the terms of the present disclosure and each constituent element are not limited to those described in the above-described embodiments. The specific numerical values ​​shown in the above description are merely examples, and as a matter of course, they can be changed to various numerical values.

[0086] <<Supplementary Notes>> Supplementary notes are provided for the present disclosure, the specific configuration examples of which have been shown in the above-described embodiments.

[0087] A piezoelectric element control device (2) according to one aspect of the present disclosure supplies a driving current (I DRV a drive circuit (10) configured to drive a piezoelectric element (3) connected in parallel to a secondary coil (L2) of the transformer by supplying a current (L3) to the drive circuit, and a control circuit (30) configured to control the drive circuit, wherein the control circuit is configured to increase the value of the drive current over time during at least a portion of the supply period of the drive current (first configuration).

[0088] This makes it possible to suppress fluctuations in the voltage applied to the piezoelectric element over the entire period of supply of the drive current, and ideally to keep the voltage applied to the piezoelectric element roughly constant. As a result, for example, the piezoelectric element can be used effectively up to its rated voltage, and the output strength of the sound wave can be increased.

[0089] In the piezoelectric element control device according to the first configuration, the control circuit may be configured (second configuration) to vary the change pattern of the drive current during the supply period of the drive current.

[0090] This allows the change pattern of the drive current to be adjusted to match the characteristics of the piezoelectric element, thereby reducing the fluctuation range of the voltage applied to the piezoelectric element over the entire period of supply of the drive current depending on the characteristics of the piezoelectric element, and ideally keeping the voltage applied to the piezoelectric element roughly constant.

[0091] In the piezoelectric element control device according to the second configuration, the control circuit may be provided with an information storage unit (31) configured to store current change pattern designation information that specifies the change pattern of the drive current, and may be configured (third configuration) in which the current change pattern designation information in the information storage unit is rewritable.

[0092] This allows the change pattern of the drive current to be adjusted to match the characteristics of the piezoelectric element, thereby reducing the fluctuation range of the voltage applied to the piezoelectric element over the entire period of supply of the drive current depending on the characteristics of the piezoelectric element, and ideally keeping the voltage applied to the piezoelectric element roughly constant.

[0093] In the piezoelectric element control device according to the third configuration, the control circuit controls the value of the drive current to a first current value (I SET1 ) to the second current value (I SET2 ), the first current value and the second current value are specified by the current change pattern specification information, and characteristics of change in the value of the driving current in the process of increasing the value of the driving current from the first current value to the second current value during the supply period of the driving current are specified (fourth configuration).

[0094] In the piezoelectric element control device according to any of the first to fourth configurations, the drive circuit may have a current source (13, 13a) configured to generate the drive current, and a switch circuit (11 and 12, or 11a and 12a) configured to supply the drive current to the primary coil in a first direction or a second direction, and the control circuit may be configured (fifth configuration) to control the switch circuit during the supply period of the drive current to supply the drive current to the primary coil alternately in the first direction and the second direction, thereby generating an AC voltage in the secondary coil.

[0095] More specifically, for example, in a piezoelectric element control device according to any of the first to fourth configurations, the drive circuit may have a current source (13) configured to generate the drive current, a first switching element (11) inserted between a first end of the primary coil and the current source, and a second switching element (12) inserted between a second end of the primary coil and the current source, wherein the drive current flows from the first end of the primary coil to the current source during an on period of the first switching element, and the drive current flows from the second end of the primary coil to the current source during an on period of the second switching element, and the control circuit may be configured to generate an AC voltage in the secondary coil by alternately turning on and off the first switching element and the second switching element during the supply period of the drive current.

[0096] In the piezoelectric element control device relating to any of the above first to fifth configurations, there may be a configuration (sixth configuration) in which the input impedance of the piezoelectric element when the piezoelectric element is vibrating at a resonant frequency is lower than the input impedance of the piezoelectric element when the piezoelectric element is stationary.

[0097] In the piezoelectric element control device according to any of the first to sixth configurations, the device may further include a receiving circuit (20) configured to receive, using the piezoelectric element, a reflected wave signal (W2) from an object of a transmitted wave signal (W1) transmitted from the piezoelectric element based on the driving current, and a signal processing circuit (40) configured to generate a detection signal (S40) based on the reflected wave signal received by the receiving circuit (7th configuration).

[0098] An ultrasonic sensor (1) according to one aspect of the present disclosure includes a piezoelectric element control device (2) according to the seventh configuration, the piezoelectric element (3), and the transformer (TR), wherein the drive circuit supplies the drive current in the ultrasonic band to the primary coil of the transformer to cause the piezoelectric element to transmit the transmission wave signal in the ultrasonic band, and the receiving circuit receives the reflected wave signal in the ultrasonic band (eighth configuration).

[0099] According to this ultrasonic sensor, the piezoelectric element can be effectively used up to its rated voltage, and the output strength of the ultrasonic waves can be increased, which contributes to an increase in the measurable distance of the ultrasonic sensor.

[0100] In the piezoelectric element control device according to any of the first to sixth configurations, the device may further include a receiving circuit (20) configured to receive a reflected wave signal (W2) from an object of a transmitted wave signal (W1) transmitted from the piezoelectric element based on the driving current using another piezoelectric element (3R) different from the piezoelectric element, and a signal processing circuit (40) configured to generate a detection signal (S40) based on the reflected wave signal received by the receiving circuit (9th configuration).

[0101] An ultrasonic sensor (1) according to one aspect of the present disclosure may include a piezoelectric element control device (2) according to the ninth configuration, the piezoelectric element (3), the other piezoelectric element (3R), and the transformer (TR), and the drive circuit may be configured to transmit the transmission wave signal in the ultrasonic band from the piezoelectric element by supplying the drive current in the ultrasonic band to the primary coil of the transformer, and the receiving circuit may be configured to receive the reflected wave signal in the ultrasonic band (tenth configuration).

[0102] According to this ultrasonic sensor, the piezoelectric element can be effectively used up to its rated voltage, and the output strength of the ultrasonic waves can be increased, which contributes to an increase in the measurable distance of the ultrasonic sensor.

[0103] REFERENCE SIGNS LIST 1 ultrasonic sensor 2 piezoelectric element control IC 3, 3R piezoelectric element 4 MPU 10, 10a drive circuit 11, 12, 11a, 12a, 14a switching element 13, 13a current source 20 receiving circuit 30 control circuit 31 information storage unit 40 signal processing circuit TR transformer L1 primary coil L2 secondary coil C0, C1, C2, C T Capacitor R0, R T Resistor OBJ Object to be detected W1 Transmitted wave signal W2 Reflected wave signal VCC Power supply voltage Sin Input signal S40 Detection signal V3 Applied voltage to element I DRV Drive current CNT1, CNT2, CNT3 Control signal

Claims

1. A drive circuit configured to drive a piezoelectric element connected in parallel to a secondary coil of a transformer by supplying a drive current to a primary coil of the transformer; a control circuit configured to control the drive circuit; The control circuit increases the value of the drive current over time during at least a portion of a period during which the drive current is supplied. , Piezoelectric element control device.

2. The control circuit is configured to vary a change pattern of the drive current during a period in which the drive current is supplied. The piezoelectric element control device according to claim 1 .

3. The control circuit includes an information storage unit configured to store current change pattern designation information that designates a change pattern of the drive current, and the current change pattern designation information in the information storage unit is rewritable. The piezoelectric element control device according to claim 2 .

4. the control circuit increases a value of the drive current from a first current value to a second current value during a period in which the drive current is supplied; The current change pattern designation information designates the first current value and the second current value, and also designates characteristics of a change in the value of the drive current in a process of increasing the value of the drive current from the first current value to the second current value during a supply period of the drive current. The piezoelectric element control device according to claim 3 .

5. The drive circuit includes a current source configured to generate the drive current, and a switch circuit configured to supply the drive current to the primary coil in a first direction or a second direction; The control circuit controls the switch circuit during a period in which the drive current is supplied to alternately supply the drive current to the primary coil in the first direction and the second direction, thereby generating an AC voltage in the secondary coil. The piezoelectric element control device according to claim 1 .

6. The input impedance of the piezoelectric element is lower when the piezoelectric element is vibrating at a resonant frequency than when the piezoelectric element is stationary.

6. A piezoelectric element control device according to claim 1.

7. a receiving circuit configured to receive, by using the piezoelectric element, a reflected wave signal of a transmission wave signal transmitted from the piezoelectric element based on the driving current, the reflected wave signal being reflected by an object; and a signal processing circuit configured to generate a detection signal based on the reflected wave signal received by the receiving circuit.

6. A piezoelectric element control device according to claim 1.

8. The piezoelectric element control device according to claim 7 ; The piezoelectric element; The transformer, The drive circuit supplies the drive current in an ultrasonic band to a primary coil of the transformer to cause the piezoelectric element to transmit the transmission wave signal in the ultrasonic band, and the reception circuit receives the reflected wave signal in the ultrasonic band. , ultrasonic sensors.

9. a receiving circuit configured to receive, by using another piezoelectric element different from the piezoelectric element, a reflected wave signal of a transmission wave signal transmitted from the piezoelectric element based on the driving current, the reflected wave signal being reflected by an object; and a signal processing circuit configured to generate a detection signal based on the reflected wave signal received by the receiving circuit.

6. A piezoelectric element control device according to claim 1.

10. The piezoelectric element control device according to claim 9 , The piezoelectric element; The other piezoelectric element; The transformer, The drive circuit supplies the drive current in an ultrasonic band to a primary coil of the transformer to cause the piezoelectric element to transmit the transmission wave signal in the ultrasonic band, and the reception circuit receives the reflected wave signal in the ultrasonic band. , ultrasonic sensors.