Sound wave sensor drive circuit, sound wave sensor, and vehicle

Abstract

To accurately calculate the distance from a plurality of sound wave transmission / reception units to a detection object.SOLUTION: In a sound wave sensor drive circuit (1) for driving a sound wave sensor (109), a control unit (3) causes the sound wave drive unit (4) to generate a first drive signal (DA1) consisting of a prescribed first number of pulses while a step-up circuit (9) is driven, maintains the step-up circuit (9) in a driven state, then causes the sound wave drive unit (4) to generate a second drive signal (DA2) consisting of a prescribed second number of pulses after elapse of a given period (Ta), and then causes the sound wave drive unit (4) to generate an antiphase signal (Iv) that is 180 degrees out of phase with the second drive signal (DA2) and consists of a prescribed third number of pulses.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to an ultrasonic sensor drive circuit, and to an ultrasonic sensor and a vehicle using the ultrasonic sensor drive circuit. [Background technology]

[0002] Conventionally, there has been known an acoustic wave sensor that measures the distance to an obstacle by generating an acoustic wave and measuring the wave reflected by the obstacle. Such an acoustic wave sensor is used, for example, in an acoustic wave sonar that is installed in a vehicle and measures the distance between the vehicles (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 004609

[0004] [overview] In the above-mentioned acoustic wave sensors, there is an increasing demand for further reduction in power consumption.

[0005] An ultrasonic sensor driving circuit according to one aspect of the present disclosure drives an ultrasonic sensor. The ultrasonic sensor driving circuit includes an ultrasonic driving unit configured to generate first and second drive signals for driving an ultrasonic wave transmitting and receiving element, and an inverse-phase signal having an inverse phase to the second drive signal, and a control unit. The control unit is configured to cause the ultrasonic driving unit to generate the first drive signal with a predetermined first pulse number, causing the ultrasonic wave transmitting and receiving element to transmit a first carrier wave, and then, after a certain period of time has elapsed, cause the ultrasonic driving unit to generate the second drive signal with a predetermined second pulse number, causing the ultrasonic wave transmitting and receiving element to transmit a second carrier wave, causing the ultrasonic driving unit to generate the inverse-phase signal with a predetermined third pulse number. The control unit is configured to determine the first pulse number of the first drive signal so that the first carrier wave includes sound waves generated by the operation of the ultrasonic wave transmitting and receiving element in response to the first drive signal and sound waves generated by reverberation in the ultrasonic wave transmitting and receiving element. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram showing the relative positions of an acoustic wave sensor and an object to be detected according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing the configuration of the acoustic wave sensor driving circuit. [Figure 3] FIG. 3 is a circuit diagram of an example of a damping circuit. [Figure 4] FIG. 4 is a timing chart showing the state of each part when the ultrasonic sensor detects an object to be detected. [Figure 5] FIG. 5 is a flowchart showing the operation of the acoustic wave sensor. [Figure 6] FIG. 6 is a schematic diagram of a vehicle, which is an example of a device in which an acoustic wave sensor is used.

[0007] [Detailed explanation] An embodiment of the present disclosure will be described below with reference to the drawings.

[0008] <Sonar Device> FIG. 1 is a schematic diagram showing the relative positions of an ultrasonic sensor 100 and a detection target 600 according to an embodiment of the present disclosure. FIG. 2 is a diagram showing the configuration of an ultrasonic sensor drive circuit 1. As shown in FIG. 1, the ultrasonic sensor 100 transmits a carrier wave in the ultrasonic range (a frequency band above the human audible range, generally 20 kHz or higher) to the outside and detects the reflected wave reflected by the detection target 600. The ultrasonic sensor 100 then measures the distance to the detection target 600 based on the time between the transmission of the carrier wave and the reception of the reflected wave. In other words, the ultrasonic sensor 100 measures the distance using a so-called TOF (Time of Flight) method. The ultrasonic sensor 100 includes an ultrasonic sensor drive circuit 1 and an ultrasonic wave transmitting and receiving element 2.

[0009] <Acoustic wave transmitting and receiving element 2> The ultrasonic wave transmitting and receiving element 2 is a so-called piezoelectric element. The ultrasonic wave transmitting and receiving element 2 has the property of generating mechanical displacement (vibration) in response to a voltage signal applied across its two ends, and can transmit and receive carrier waves. The ultrasonic wave transmitting and receiving element 2 also has the property of generating an electromotive force across its two ends in response to mechanical displacement (vibration) applied to it. The ultrasonic wave transmitting and receiving element 2 can use this property of generating an electromotive force to receive the ultrasonic waves Sd (see FIG. 2) that include waves reflected by the detection object 600.

[0010] As shown in Figures 1 and 2, the ultrasonic wave transmitting and receiving element 2 is configured to vibrate and transmit a first carrier wave WA1 and a second carrier wave WA2 in response to a first drive signal DA1 and a second drive signal DA2 from the ultrasonic wave driving unit 4 of the ultrasonic sensor driving circuit 1.

[0011] In the ultrasonic sensor 100, each ultrasonic wave transmitting and receiving element 2 transmits a carrier wave twice, with the timing shifted. A first carrier wave WA1 and a second carrier wave WA2 are transmitted from the ultrasonic wave transmitting and receiving element 2. In terms of time series, the first carrier wave WA1 is transmitted at an earlier timing than the second carrier wave WA2.

[0012] In the ultrasonic sensor 100 according to this embodiment, the first carrier wave WA1 transmitted from the ultrasonic wave transmitting and receiving element 2 is used to measure the distance to the detection object 600 when the detection object 600 is located farther than a predetermined distance (referred to as a long distance) within the measurable range of the ultrasonic sensor 100. The second carrier wave WA2 is used to measure the distance to the detection object 600 when the detection object 600 is located closer than a predetermined distance (referred to as a short distance) within the measurable range of the ultrasonic sensor 100.

[0013] The first carrier wave WA1 and the second carrier wave WA2 are sound waves (ultrasonic waves) having multiple peaks. The first carrier wave WA1 is used to measure a detection target 600 located at a long distance. To ensure that the first carrier wave WA1 and its first reflected wave RA1 can be detected even if they are attenuated, the number of peaks of the first carrier wave WA1 is, for example, about 16 to 32, which is greater than the number of peaks of the second carrier wave WA2 (for example, 4 to 8). The second carrier wave WA2 is used to measure a detection target 600 located at a short distance. It is preferable that the time until the transmission of the second carrier wave WA2 is completed is short. Therefore, the number of peaks of the second carrier wave WA2 is, for example, 4 to 8, which is less than the number of peaks of the first carrier wave WA1 (for example, 16 to 32).

[0014] As described above, the ultrasonic wave transmitting and receiving element 2 is configured to transmit and receive sound waves by the vibration of the piezoelectric element. The piezoelectric element is configured to vibrate in response to the first drive signal DA1 and the second drive signal DA2, but continues to vibrate even after the first drive signal DA1 and the second drive signal DA2 are stopped. The vibration attenuates over time and eventually converges. This vibration of the ultrasonic wave transmitting and receiving element 2 after the signal input is stopped is called reverberation, and the state of the ultrasonic wave transmitting and receiving element 2 at this time is called a reverberation state. When the ultrasonic wave transmitting and receiving element 2 is in a reverberation state, the ultrasonic wave transmitting and receiving element 2 continues to transmit sound waves. Note that the amplitude of the sound waves transmitted in a reverberation state attenuates over time (see FIG. 4, described below).

[0015] <Sonic sensor drive circuit 1> The ultrasonic sensor driving circuit 1 controls the ultrasonic sensor 100 and controls the ultrasonic transmitting and receiving element 2 to transmit a carrier wave. The ultrasonic sensor driving circuit 1 is also configured to recognize the reflected wave reflected by the detection object 600 from the ultrasonic wave received by the ultrasonic transmitting and receiving element 2, and acquire the distance to the detection object 600.

[0016] 2, the ultrasonic sensor driving circuit 1 includes a control unit 3, an ultrasonic driving unit 4, a received wave signal generating unit 5, a reflected wave identifying unit 6, a damping circuit 7, a detection distance calculating unit 8, and a boosting circuit 9. The ultrasonic sensor driving circuit 1 may be configured as a single chip, or may be configured with multiple chips housed in a single package.

[0017] The control unit 3 is a control circuit for controlling the operation of the ultrasonic sensor driving circuit 1. The control unit 3 generates a transmission signal. For example, an MPU (Micro Processor Unit) is used as the control unit 3. The control unit 3 outputs the transmission signal at a predetermined timing. The control unit 3 is configured to control the ultrasonic driving unit 4 by supplying the first transmission signal PA1, the second transmission signal PA2, and the reverse phase transmission signal Pv to the ultrasonic driving unit 4.

[0018] As shown in Fig. 4, the first transmission wave signal PA1 and the second transmission wave signal PA2 are pulse signals. The acoustic wave driver 4 converts the first transmission wave signal PA1 and the second transmission wave signal PA2 into a first drive signal DA1 and a second drive signal DA2, respectively. The reverse phase transmission wave signal Pv is also a pulse signal. The acoustic wave driver 4 converts the reverse phase transmission wave signal Pv into a reverse phase signal Iv.

[0019] The acoustic wave driver 4 is connected to the acoustic wave transmitting and receiving element 2. The acoustic wave driver 4 supplies the acoustic wave transmitting and receiving element 2 with a first drive signal DA1, a second drive signal DA2, and a reverse phase signal Iv.

[0020] A boost circuit 9 is connected to the acoustic wave driver 4. A drive voltage Vcp boosted by the boost circuit 9 is supplied to the acoustic wave driver 4. The acoustic wave driver 4 converts the first transmission wave signal PA1 and the second transmission wave signal PA2 output from the control unit 3 into a first drive signal DA1 and a second drive signal DA2 using the drive voltage Vcp from the boost circuit 9. For example, the acoustic wave driver 4 may be configured to amplify the amplitudes of the first transmission wave signal PA1, the second transmission wave signal PA2, and the reverse phase transmission wave signal Pv, to generate the first drive signal DA1, the second drive signal DA2, and the reverse phase signal Iv.

[0021] The boost circuit 9 is connected to the control unit 3 and operates based on a boost signal Sv from the control unit 3. The boost circuit 9 is, for example, a charge pump circuit, but is not limited to this, and any circuit capable of writing the drive voltage Vcp required for the acoustic wave drive unit 4 to output the first drive signal DA1 and the second drive signal DA2 can be widely used. A storage capacitor 91 is arranged in the wiring connecting the boost circuit 9 and the acoustic wave drive unit 4. As the boost circuit 9 operates, charge is accumulated in the storage capacitor 91. The drive voltage Vcp is supplied by discharging from the storage capacitor 91. In other words, the voltage across the storage capacitor 91 is the drive voltage Vcp.

[0022] As described above, the ultrasonic wave transmitting and receiving element 2 vibrates and outputs sound waves even when reverberation is occurring. In the ultrasonic wave sensor 100, the sound waves output by the vibration of the ultrasonic wave transmitting and receiving element 2 when reverberation is occurring are also used as the first carrier wave WA1. In other words, a portion of the latter half of the first carrier wave WA1 is a sound wave transmitted from the ultrasonic wave transmitting and receiving element 2 in a reverberant state, and the first drive signal DA1 is not input. Therefore, the first pulse number, which is the number of pulses of the first transmission signal PA1, may be smaller than the number of peaks of the first carrier wave WA1. If the number of peaks of the first carrier wave WA1 is, for example, 16 to 32, the first pulse number can be, for example, 10 to 24. Furthermore, since the first drive signal DA1 is a signal converted from the first transmission signal PA1 by the ultrasonic wave driver 4, the control unit 3 outputs the first transmission signal PA1 with the first pulse number.

[0023] On the other hand, the second carrier wave WA2 is used to detect a nearby detection object 600. When the detection object 600 is located in a short distance, the time from the end of transmission of the second carrier wave WA2 until the return of the second reflected wave RA2 may be short. It is preferable for the acoustic wave transmitting and receiving element 2 to converge the reverberation as soon as possible after reception of the second drive signal DA2 is stopped.

[0024] In other words, the second carrier wave WA2 does not utilize sound waves transmitted from the acoustic wave transmitting and receiving element 2 in a reverberant state. Therefore, the second pulse number, which is the number of pulses of the second drive signal DA2, is approximately the same as the number of peaks of the second carrier wave WA2. In other words, if the number of peaks of the second carrier wave WA2 is, for example, 2 to 8, the second pulse number can be, for example, 4 to 8. And, since the second drive signal DA2 is a signal converted from the second transmission wave signal PA2 by the acoustic wave driver 4, the control unit 3 outputs the second transmission wave signal PA2 with the second pulse number.

[0025] Furthermore, in order to converge the reverberation as quickly as possible, it is preferable that the reverse phase signal Iv be supplied to the acoustic wave transmitting and receiving element 2 immediately after the second drive signal DA2 is stopped. For this reason, the control unit 3 is configured to be able to output the reverse phase transmission signal Pv immediately after stopping the output of the second transmission signal PA2. The reverse phase transmission signal Pv is a signal that causes the acoustic wave driving unit 4 to output the reverse phase signal Iv that cancels the vibration of the acoustic wave transmitting and receiving element 2. The reverse phase signal Iv is a pulse signal that can generate vibrations in the acoustic wave transmitting and receiving element 2 that are in the opposite phase to the vibrations in the reverberation state. For this reason, when the reverse phase signal Iv is input to the acoustic wave transmitting and receiving element 2 in the reverberation state, the vibration of the acoustic wave transmitting and receiving element 2 in the reverberation state is attenuated. The reverse phase signal Iv is a signal that is in the opposite phase to the second drive signal DA2.

[0026] When the reverse-phase signal Iv is input to the ultrasonic wave transmitting and receiving element 2, the attenuation of reverberation is promoted. Note that when the reverse-phase signal Iv having many peaks is input, the ultrasonic wave transmitting and receiving element 2 may vibrate in the reverse phase, which attenuates the reverberation. Therefore, the number of peaks of the reverse-phase signal Iv may be less than the number of peaks of the second drive signal DA2, for example, about 1 to 2. Furthermore, since the reverse-phase signal Iv is a signal obtained by converting the reverse-phase transmission signal Pv by the ultrasonic wave driver 4, the control unit 3 outputs the reverse-phase transmission signal Pv with the third pulse number, which is the number of pulses of the reverse-phase transmission signal Pv, set to 1 to 2.

[0027] The control unit 3 controls the acoustic wave driver 4 to output a first drive signal DA1 with a first pulse count while maintaining the drive of the boost circuit 9 by outputting a first wave transmission signal PA1. The control unit 3 also controls the acoustic wave driver 4 to output a second drive signal DA2 with a second pulse count while maintaining the drive of the boost circuit 9 by outputting a second wave transmission signal PA2. The control unit 3 also controls the acoustic wave driver 4 to output a reverse phase signal Iv with a third pulse count while maintaining the drive of the boost circuit 9 by outputting a reverse phase wave transmission signal Pv. The second pulse count is less than the first pulse count, and the third pulse count is not less than the second pulse count.

[0028] As described above, the ultrasonic wave transmitting and receiving element 2 has a configuration capable of receiving ultrasonic waves. The received wave signal generator 5 converts the ultrasonic waves received by the ultrasonic wave transmitting and receiving element 2 into a received wave signal RS. The ultrasonic wave transmitting and receiving element 2 also receives ultrasonic waves other than the first reflected wave RA1 and second reflected wave RA2 that are reflected by the detection object 600 of the first carrier wave WA1 and the second carrier wave WA2.

[0029] The reflected wave discrimination unit 6 receives the received signal RS output from the received signal generation unit 5. The reflected wave discrimination unit 6 discriminates the first reflected wave RA1 and the second reflected wave RA2 from the received signal RS, which are the first carrier wave WA1 and the second carrier wave WA2 reflected by the detection object 600. When the reflected wave discrimination unit 6 discriminates the first reflected wave RA1 or the second reflected wave RA2 from the received signal RS, it notifies the detection distance calculation unit 8 of the first reflected wave discrimination information Rd1 or the second reflected wave discrimination information Rd2.

[0030] The detection distance calculation unit 8 is connected to the control unit 3 and the reflected wave identification unit 6. The control unit 3 notifies the detection distance calculation unit 8 of the transmitted wave information Pd each time the first transmitted wave signal PA1 or the second transmitted wave signal PA2 is output. The detection distance calculation unit 8 calculates a TOF value from the time when the transmitted wave information Pd was acquired and the time when the first reflected wave identification information Rd1 or the second reflected wave identification information Rd2 was acquired. The detection distance calculation unit 8 calculates the distance from the acoustic wave transmitting and receiving element 2 to the detection target 600 based on the TOF value.

[0031] The ultrasonic sensor 100 uses the negative-phase signal Iv to attenuate the reverberation of the ultrasonic wave transmitting and receiving element 2. As described above, the negative-phase signal Iv is a signal that causes the ultrasonic wave transmitting and receiving element 2 to vibrate in the opposite phase to the vibration of the reverberation state. If the number of peaks in the negative-phase signal Iv becomes large, the ultrasonic wave transmitting and receiving element 2 may vibrate in the opposite phase to when transmitting the first carrier wave WA1 and the second carrier wave WA2. For this reason, it is difficult to converge the reverberation using only the negative-phase signal Iv. Therefore, the ultrasonic sensor driving circuit 1 is configured to converge the reverberation using a damping circuit 7.

[0032] Here, the damping circuit 7 will be described. Fig. 3 is a circuit diagram of an example of the damping circuit 7. As shown in Fig. 3, the damping circuit 7 is, for example, a GIC (Generalized Impedance Converter) circuit, and has four resistors R1, R2, R3, and R4, a capacitor C1, and two operational amplifiers Op1 and Op2.

[0033] As shown in Figure 3, resistors R1, R2, and R3 are connected in series. The side of resistor R1 opposite to the side connected to resistor R2 is the input terminal. Resistor R4 is connected to the ground terminal. Capacitor C1 is connected between resistors R3 and R4. Resistors R1, R2, R3, capacitor C1, and resistor R4 are connected in series in this order.

[0034] The voltage at the junction of capacitor C1 and resistor R4 is input to the non-inverting input terminal of operational amplifier Op1. The voltage at the junction of resistors R2 and R3 is input to the inverting input terminal of operational amplifier Op1. The output of operational amplifier Op1 is connected between resistors R1 and R2.

[0035] Furthermore, the voltage at the input end of resistor R1 is input to the non-inverting input terminal of operational amplifier Op2. The voltage at the junction of resistors R2 and R3 is input to the inverting input terminal of operational amplifier Op2. The output of operational amplifier Op2 is connected between resistor R3 and capacitor C1.

[0036] The input terminal of the damping circuit 7 is connected to the wiring connecting the acoustic wave transmitting and receiving element 2 and the receiving signal generating unit 5 via the switch SW1. The switch SW1 is, for example, an N-channel MOS (Metal Oxide Semiconductor) transistor, and is turned on when the gate signal Sg from the control unit 3 is at a high level at its gate. Note that the switch SW1 is not limited to an N-channel MOS transistor, but may be a P-channel MOS transistor, or a wide variety of semiconductor switch elements such as a bipolar transistor or an IGBT (Insulated Gate Bipolar Transistor) can be used. The damping circuit 7 is a pseudo-inductance circuit that converts the capacitance of the capacitor C1 into inductance, and acts as an inductor to promote attenuation of reverberation in the acoustic wave transmitting and receiving element 2.

[0037] The ultrasonic sensor driving circuit 1 is configured so that processing by the damping circuit 7 is performed after the reverberation level (here, the amplitude of the vibration of the piezoelectric element) falls below a predetermined level due to the reverberation damping operation by the negative phase signal Iv. The operation of damping reverberation by the negative phase signal Iv is sometimes referred to as the first damping operation, and the operation of damping reverberation using the damping circuit 7 is sometimes referred to as the second damping operation. The ultrasonic sensor driving circuit 1 has the configuration shown above.

[0038] <Operation example of the ultrasonic sensor 100> In the ultrasonic sensor 100, when the ultrasonic wave transmitting and receiving element 2 is vibrating due to reverberation, it is not possible to receive ultrasonic waves. In other words, the ultrasonic sensor 100 cannot detect the detection target 600 when the ultrasonic wave transmitting and receiving element 2 is in a reverberation state.

[0039] As described above, the first carrier wave WA1 is used to detect a distant detection object 600. When the detection object 600 is far from the ultrasonic sensor 100, the time it takes for the first carrier wave WA1 to reach the detection object 600 and the time it takes for the first reflected wave RA1 reflected by the detection object 600 to reach the ultrasonic wave transmitting and receiving element 2 are longer than when the detection object 600 is close. Therefore, after the first drive signal DA1 is stopped, the reverberation of the ultrasonic wave transmitting and receiving element 2 converges by the time the first reflected wave RA1 reaches the ultrasonic wave transmitting and receiving element 2. Therefore, when outputting the first wave transmission signal PA1, the control unit 3 does not need to perform an attenuation operation to attenuate the reverberation. The ultrasonic sensor driving circuit 1 uses the sound waves transmitted by the vibration of the ultrasonic wave transmitting and receiving element 2 in a reverberant state as part of the first wave transmission signal PA1.

[0040] Furthermore, the ultrasonic sensor 100 transmits the first carrier wave WA1 and the second carrier wave WA2 consecutively. After the transmission of the first carrier wave WA1 is completed, the second carrier wave WA2 is transmitted after a certain time has elapsed. At this time, the control unit 3 outputs the first transmission signal PA1 and the second transmission signal PA2 so that the second carrier wave WA2 is transmitted after the reverberation of the ultrasonic wave transmitting and receiving element 2 when the first carrier wave WA1 is transmitted has converged.

[0041] On the other hand, the second carrier wave WA2 is used to detect a detection target 600 located near the ultrasonic sensor 100. When the detection target 600 is near the ultrasonic sensor 100, the time it takes for the second carrier wave WA2 to reach the detection target 600 and the time it takes for the second reflected wave RA2, which is reflected by the detection target 600 from the second carrier wave WA2, to reach the ultrasonic wave transmitting and receiving element 2, are shorter than when the detection target 600 is far away. Therefore, it is preferable that the reverberation of the ultrasonic wave transmitting and receiving element 2 converge as quickly as possible after the transmission of the second carrier wave WA2 is completed. Therefore, in the ultrasonic sensor 100, the control unit 3 outputs the second wave transmission signal PA2 and then controls the ultrasonic wave driver 4 and the switch SW1 to perform the first and second attenuation operations.

[0042] 4 is a timing chart showing the state of each part when the ultrasonic sensor 100 detects the detection target 600. FIG.

[0043] The control unit 3 switches the boost signal Sv being sent to the boost circuit 9 from low level to high level (step S101). When the boost circuit 9 operates, an electric charge is stored in the storage capacitor 91. This causes the ultrasonic sensor 100 to enter a standby state so that it can detect the detection object 600. When the ultrasonic sensor 100 is in the standby state, the voltage across the storage capacitor 91, i.e., the drive voltage Vcp, is set to a first voltage V1. In other words, when the boost circuit 9 causes the voltage across the storage capacitor 91 to reach the first voltage V1, the control unit 3 determines that the ultrasonic sensor 100 is in a state where it can detect the detection object 600, i.e., it has entered a standby state.

[0044] As shown in FIG. 4, at time T1, the control unit 3 outputs a first transmission wave signal PA1 (step S102). The first transmission wave signal PA1 is input to the acoustic wave driver 4 and converted into a first drive signal DA1 by the acoustic wave driver 4. The first drive signal DA1 is then supplied to the acoustic wave transmitting and receiving element 2, causing the acoustic wave transmitting and receiving element 2 to start transmitting the first carrier wave WA1. The control unit 3 outputs the first transmission wave signal PA1 including a pulse signal with a first pulse number (10 to 24). After outputting all the pulses, the output of the first transmission wave signal PA1 is stopped at time T2 (see FIG. 4) (step S103). As described above, the acoustic wave driver 4 amplifies the first transmission wave signal PA1 using the drive voltage Vcp and outputs the first drive signal DA1. Therefore, while the first transmission wave signal PA1 is being output, the drive voltage Vcp drops from the first voltage V1 over time. Then, at time T2, the driving voltage Vcp becomes the second voltage V2.

[0045] After this, from time T2 to time T21, the acoustic wave transmitting and receiving element 2 enters a reverberation state. In other words, the first carrier wave WA1 due to the reverberation state continues to be transmitted until time T21 (see FIG. 4). Note that the convergence of the reverberation state does not only mean that the acoustic wave transmitting and receiving element 2 has completely stopped, but may also include, for example, a state in which vibrations have attenuated to the extent that sound waves can be received. In other words, the acoustic wave sensor 100 transmits the first carrier wave WA1 from time T1 to time T21. At time T2, the first wave transmission signal PA1 is stopped, and the operation of the acoustic wave driver 4 is stopped. This stops the discharge of the storage capacitor 91. This allows the storage capacitor 91 to store electricity by the boost circuit 9. The voltage Vcp across the storage capacitor 91 becomes the first voltage V1 before time T3 (see FIG. 4).

[0046] Then, when the control unit 3 confirms that the first time Ta has elapsed since time T2 (step S104), it starts outputting the second transmission signal PA2 at time T3 (step S105).

[0047] The first time Ta is longer than the time required for the acoustic wave transmitting and receiving element 2 to naturally converge after entering a reverberation state. This makes it possible to prevent the second drive signal DA2 from being supplied to the acoustic wave transmitting and receiving element 2 vibrating in a reverberation state.

[0048] Then, the control unit 3 outputs the second transmission wave signal PA2 including a pulse signal with a second pulse number (4 to 8). After all the pulses have been output, the control unit 3 stops outputting the second transmission wave signal PA2 at time T4 (see FIG. 4) (step S106).

[0049] Thereafter, when the control unit 3 confirms that the second time Tb has elapsed since time T4 (step S107), it starts outputting the reverse phase transmission signal Pv at time T5 (step S108). Note that the control unit 3 may transmit the reverse phase transmission signal Pv without waiting for the second time Tb to elapse.

[0050] Then, the control unit 3 executes a first attenuation operation to output a reverse-phase transmission signal Pv including a pulse signal with a third pulse number (1 to 2). After all pulses have been output, the control unit 3 stops outputting the reverse-phase transmission signal Pv at time T6 (see FIG. 4) (step S109). After the reverberation of the ultrasonic wave transmitting and receiving element 2 is converged, the ultrasonic wave transmitting and receiving element 2 receives a reflected wave. If the boost circuit 9 is operating when the ultrasonic wave transmitting and receiving element 2 receives the sound wave, noise generated when the boost circuit 9 is operating may affect the received wave signal RS. Therefore, after stopping output of the reverse-phase transmission signal Pv at time T6, the control unit 3 switches the boost signal Sv to low level to stop the boost circuit 9 (step S110).

[0051] Between time T3 and time T6, the acoustic wave driver 4 is operating, causing the drive voltage Vcp to drop from the first voltage V1 over time. The number of pulses of the drive signal DA2 and the reverse phase signal Iv is less than the number of pulses of the first drive signal DA1, so at time T6 the drive voltage Vcp becomes a voltage between the first voltage V1 and the second voltage V2.

[0052] Then, when the first attenuation operation ends at time T6, the control unit 3 switches the gate signal Sg from low level to high level. This switches the switch SW1 on (step S111). As a result, the damping circuit 7 is connected to the wiring between the acoustic wave transmitting and receiving element 2 and the received wave signal generating unit 5. The damping circuit 7 is a circuit configured to act as an inductor, and uses pseudo inductance to attenuate reverberation.

[0053] Then, when the control unit 3 detects that the reverberation level (amplitude) has fallen below a predetermined level (step S112), it switches the gate signal Sg to low level at time T7. This switches the switch SW1 off (step S113). After that, the sound waves received by the acoustic wave transmitting and receiving element 2 are converted into a received wave signal RS by the received wave signal generating unit 5, and the reflected wave identifying unit 6 identifies the first reflected wave RA1 and the second reflected wave RA2 from the received wave signal RS (step S114). After the identification of the first reflected wave RA1 and the second reflected wave RA2 is completed, the process returns to step S101 and continues.

[0054] As described above, in the ultrasonic sensor 100, the ultrasonic sensor driving circuit 1 uses the sound waves transmitted when the ultrasonic transmitting and receiving element 2 is in a reverberant state as part of the first carrier wave WA1 for long distances, which has a large number of peaks, to reduce the number of pulses in the first transmission signal PA1 output from the control unit 3. In other words, when transmitting the first carrier wave WA1, the number of pulses in the first transmission signal PA1 converted by the ultrasonic driving unit 4 is reduced, making it possible to suppress a drop in the drive voltage Vcp. This makes it possible to reduce power consumption.

[0055] With the above configuration, even an ultrasonic sensor 100 that does not have a step-up transformer can stably transmit a carrier wave and accurately detect an object to be detected. Note that by applying the configuration of the present disclosure to an ultrasonic sensor that has a step-up transformer instead of a step-up circuit, it is possible to reduce power consumption.

[0056] In the above embodiment, an ultrasonic system that transmits ultrasonic waves (sound waves with a high frequency exceeding audible sound) has been described, but the ultrasonic system may transmit sound waves other than ultrasonic waves.

[0057] <Application> 6 is a schematic diagram of a vehicle 200, which is an example of a device that uses the ultrasonic sensor 100. As shown in FIG. 6, an ultrasonic sonar sensor 300 including an ultrasonic wave transmitting and receiving element 2 is attached to the front of the vehicle 200.

[0058] The computer 400 mounted on the vehicle 200 is connected to the ultrasonic sensor driving circuit 1, and acquires the distance between the ultrasonic sonar sensor 300 and the detection object 600 calculated by the detection distance calculation unit 8 of the ultrasonic sensor driving circuit 1. The computer 400 acquires the position and distance of the detection object relative to the vehicle 200 based on the distance. Then, the computer 400 controls the vehicle 200 so that the vehicle 200 does not come into contact with the detection object.

[0059] <Other> The above-described embodiments should be considered to be illustrative in all respects and not restrictive. The technical scope of the present disclosure is defined by the claims, not by the description of the above-described embodiments. Furthermore, it should be understood that all modifications within the meaning and scope of the claims are included.

[0060] <Additional Notes> The ultrasonic sensor driving circuit (1) described above is a circuit that drives the ultrasonic sensor (109). an acoustic wave driving unit (4) configured to generate a first driving signal (DA1) and a second driving signal (DA2) for driving the acoustic wave transmitting and receiving element (2), and an inverse phase signal (Iv) having an inverse phase to the first driving signal (DA1) and the second driving signal (DA2); A control unit (3), The control unit (3) is configured to cause the acoustic wave driving unit (4) to generate a first driving signal (DA1) having a predetermined first pulse number, causing the acoustic wave transmitting and receiving element (2) to transmit a first carrier wave (WA1), and then, after a certain period of time has elapsed, cause the acoustic wave driving unit (4) to generate a second driving signal (DA2) having a predetermined second pulse number, causing the acoustic wave transmitting and receiving element (2) to transmit a second carrier wave (WA2), and then cause the acoustic wave driving unit (4) to generate a reverse phase signal (Iv) having a predetermined third pulse number; The control unit (3) is configured (first configuration) to determine the number of first pulses of the first drive signal (DA1) generated by the acoustic wave driving unit (4) so ​​that the first carrier wave (WA1) includes acoustic waves generated by the operation of the acoustic wave transmitting and receiving element (2) by the first drive signal (DA1) and acoustic waves generated by the reverberation of the acoustic wave transmitting and receiving element (2).

[0061] In the ultrasonic sensor driving circuit (1) of the first configuration, the control unit (3) is configured (second configuration) to control the ultrasonic driving unit (4) so ​​that the second pulse number is less than the first pulse number and the third pulse number is less than the second pulse number.

[0062] In the ultrasonic sensor driving circuit (1) of the first or second configuration, a damping circuit (7) is connected to the ultrasonic wave transmitting and receiving element (2), can be switched between an on state and an off state, and operates to limit vibration of the ultrasonic wave transmitting and receiving element (2) when in the on state, The control unit (3) is configured to control the damping circuit (7) to be in an on state for a predetermined period after generating the reverse phase signal (Iv) (third configuration).

[0063] In the ultrasonic sensor driving circuit (1) of the third configuration, the damping circuit (7) is configured (fourth configuration) by a pseudo inductance circuit that operates as an inductance.

[0064] In the ultrasonic sensor driving circuit (1) of any of the second to fourth configurations, the control unit (3) is configured to switch the damping circuit (7) to an off state when the reverberation level of the ultrasonic transmitting and receiving element (2) falls below a predetermined level (fifth configuration).

[0065] The ultrasonic sensor driving circuit (1) of the second or fifth configuration further comprises a boost circuit (9) configured to boost the voltage (Vcp) supplied to the ultrasonic driving unit (4), The control unit (3) is configured to drive the boost circuit (9), output the first drive signal (DA1), the second drive signal (DA2), and the reverse phase signal (Iv) from the acoustic wave drive unit (4), and then stop the boost circuit (9) (sixth configuration).

[0066] In the ultrasonic sensor driving circuit (1) having any one of the first to sixth configurations, a reflected wave discrimination unit (8) configured to discriminate reflected waves (RA1, RA2) reflected by a detection object (600) of sound waves transmitted in response to a first drive signal (DA1) and a second drive signal (DA2), The control unit (3) is configured (seventh configuration) to start driving the boost circuit (9) after the reflected wave discrimination unit (8) discriminates the reflected waves (RA1, RA2).

[0067] The ultrasonic sensor (100) described above comprises an ultrasonic sensor driving circuit (1) having any one of the first to seventh configurations described above, and an acoustic wave transmitting and receiving element (2) configured to be capable of transmitting carrier waves (WA1, WA2) and receiving reflected waves (RA1, RA2).

[0068] The vehicle (200) described above has a configuration (ninth configuration) including the ultrasonic sensor (100) of the eighth configuration. [Explanation of symbols]

[0069] 100 ultrasonic sensor 1. Ultrasonic sensor driver circuit 2. Ultrasonic wave transmitting and receiving element 3. Control Unit 4 Sonic drive unit 5 Received signal generation section 6 Reflected wave identification unit 7 Damping Circuit 8. Detection distance calculation unit 9. Boost circuit 91 Storage capacitor 200 vehicles 300 ultrasonic sonar sensor 400 computers 600 Detection target C1 capacitor Op1, Op2 operational amplifiers R1, R2, R3, R4 resistance SW1 switch

Claims

1. An ultrasonic sensor drive circuit for driving an ultrasonic sensor, an acoustic wave driving unit configured to generate a first drive signal and a second drive signal for driving the acoustic wave transmitting and receiving element, and an inverse phase signal having an inverse phase to the second drive signal; a control unit; the control unit is configured to cause the acoustic wave driver to generate the first drive signal having a predetermined first pulse number, causing the acoustic wave transmitting and receiving element to transmit a first carrier wave, and then, after a certain period of time has elapsed, cause the acoustic wave driver to generate the second drive signal having a predetermined second pulse number, causing the acoustic wave transmitting and receiving element to transmit a second carrier wave, causing the acoustic wave driver to generate the reverse phase signal having a predetermined third pulse number, The control unit is an acoustic sensor drive circuit configured to determine the first pulse number of the first drive signal so that the first carrier wave includes acoustic waves generated by the operation of the acoustic wave transmitting and receiving element by the first drive signal and acoustic waves generated by reverberation of the acoustic wave transmitting and receiving element.

2. The ultrasonic sensor driving circuit according to claim 1 , wherein the control unit is configured to control the ultrasonic driving unit so that the second number of pulses is smaller than the first number of pulses and the third number of pulses is smaller than the second number of pulses.

3. a damping circuit connected to the ultrasonic wave transmitting and receiving element, switchable between an on state and an off state, and configured to operate to limit vibration of the ultrasonic wave transmitting and receiving element when in the on state; The acoustic wave sensor drive circuit according to claim 1 , wherein the control unit is configured to control the damping circuit to be in an on state for a predetermined period after the generation of the opposite-phase signal.

4. 4. The acoustic wave sensor driving circuit according to claim 3, wherein the damping circuit is configured by a pseudo-inductance circuit that operates as an inductance.

5. 4. The ultrasonic sensor driving circuit according to claim 3, wherein the control unit is configured to switch the damping circuit to an off state when a reverberation level of the ultrasonic wave transmitting and receiving element falls below a predetermined level.

6. a boost circuit configured to boost the voltage supplied to the sound wave driver; The ultrasonic sensor driving circuit of claim 1, wherein the control unit is configured to stop the boost circuit after driving the boost circuit and outputting the first drive signal, the second drive signal, and the reverse phase signal from the ultrasonic driving unit.

7. a reflected wave discrimination unit configured to discriminate, from the received sound waves, the reflected waves of the sound waves transmitted in response to the first drive signal and the second drive signal, reflected by a detection object; 7. The ultrasonic sensor driving circuit according to claim 6, wherein the control unit is configured to start driving the boost circuit after the reflected wave identifying unit identifies the reflected wave.

8. The ultrasonic sensor drive circuit according to any one of claims 1 to 7; An acoustic wave sensor configured to include an acoustic wave transmitting and receiving element configured to be capable of transmitting a carrier wave and receiving a reflected wave.

9. A vehicle configured to include the sonic wave sensor of claim 8.

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