Drive device, ultrasonic sensor, and vehicle

Abstract

To provide a drive device that can effectively shorten the reverberation time.SOLUTION: A drive device (101X) includes a switch circuit (1) having switching elements (QH1, QH2, QL1, QL2) and configured to drive a piezoelectric element (Pz) on the basis of the switching of the switching elements and a switch drive unit (2) configured to drive the switching elements on the basis of a pulsed drive signal (DS2) and a pulsed beat signal (BT). The drive signal is generated during a drive period and a trailing period after the drive period. The beat signal is generated during the trailing period at least. The frequencies of the drive signal and the beat signal are different.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a drive device. [Background technology]

[0002] Conventionally, the time it takes for an ultrasonic wave to be emitted and reflected back from an obstacle is called the Time of Flight (TOF). Ultrasonic sensors are known that measure the distance to an obstacle by measuring the distance of the obstacle. Such ultrasonic sensors are often mounted on vehicles, and an example of such sensors is an on-board clearance sonar. [Prior art documents] [Patent documents]

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

[0004] [overview] Even when the drive of a piezoelectric element used as an ultrasonic transducer is stopped, the vibration of the piezoelectric element continues. The time from when the drive is stopped until the vibration of the piezoelectric element stops is called the reverberation time, but if a reflected wave reflected by a nearby object is received during the reverberation time, the distance cannot be measured. Therefore, it is desirable to shorten the reverberation time as much as possible.

[0005] In view of the above circumstances, an object of the present disclosure is to provide a drive device that can effectively shorten the reverberation time.

[0006] A drive device according to one aspect of the present disclosure includes: a switch circuit having a switching element and configured to drive a piezoelectric element based on switching of the switching element; a switch driver configured to drive the switching element based on a pulsed drive signal and a pulsed beat signal; Equipped with The drive signal is generated during a drive period and a trailing end period following the drive period, the beat signal is generated at least in the trailing edge period, The drive signal and the beat signal have different frequencies. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example in which an ultrasonic sensor is applied to a vehicle. [Diagram 2] FIG. 2 is a diagram showing a configuration of an ultrasonic sensor according to a comparative example. [Diagram 3] FIG. 3 is a diagram showing an example of a vibration waveform of a piezoelectric element under various driving conditions. [Figure 4] FIG. 4 is a diagram showing an example of the waveforms of the drive signals DS1 and DS2, the beat signal BT, and the damping pulse DP. [Diagram 5] FIG. 5 is a diagram illustrating a configuration of an ultrasonic sensor according to the first embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram showing a modified example of a method for driving a piezoelectric element. [Figure 7] FIG. 7 is a diagram showing an example of a beat in the envelope of a vibration waveform. [Figure 8] FIG. 8 is a diagram illustrating a configuration of an ultrasonic sensor according to the second embodiment of the present disclosure. [Figure 9] FIG. 9 is a diagram illustrating a configuration of an ultrasonic sensor according to a third embodiment of the present disclosure. [Figure 10] FIG. 10 is a diagram showing an equivalent circuit on the secondary side in the third embodiment of the present disclosure.

[0008] [Detailed Description] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.

[0009] <Ultrasonic sensors installed in vehicles> 1 shows a vehicle 200 equipped with an ultrasonic sensor 10, and an object (obstacle) 300. Ultrasonic waves transmitted from the ultrasonic sensor 10 are reflected by the object 300 and received as reflected waves by the ultrasonic sensor 10. The ultrasonic sensor 10 measures distance by measuring the time from when the ultrasonic wave is transmitted to when it is received. Various ultrasonic sensors described below can be used as the ultrasonic sensor 10, but the application of ultrasonic sensors is not limited to vehicles.

[0010] <Comparative Example> 2 is a diagram showing the configuration of an ultrasonic sensor 100 according to a comparative example. The ultrasonic sensor 100 includes a driving device 100X and a piezoelectric element Pz (ultrasonic sensor element). The driving device 100X drives the piezoelectric element Pz, causing the piezoelectric element Pz to transmit ultrasonic waves.

[0011] The driving device 100X is a semiconductor device that integrates the internal configuration shown in Fig. 2. For convenience, Fig. 2 illustrates only the configuration related to driving the piezoelectric element Pz in the driving device 100X, and does not illustrate the configuration for processing the reflected wave received by the piezoelectric element Pz.

[0012] 2, the driving device 100X includes a switch circuit 1 and a switch driving unit 2. The driving device 100X also includes a power supply terminal T1, a first driving terminal T2, a second driving terminal T3, and a ground terminal T4 as external terminals for establishing an electrical connection with the outside.

[0013] The switch circuit 1 has half bridges HB1 and HB2. The half bridge HB1 has an upper switching element QH1 and a lower switching element QL1. The upper switching element QH1 is configured by a P-channel MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). The lower switching element QL1 is configured by an N-channel MOSFET. The upper switching element QH1 and the lower switching element QL1 are connected in series between a power supply terminal T1 and a ground terminal T4. A power supply voltage VH can be applied to the power supply terminal T1. A ground potential can be applied to the ground terminal T4.

[0014] More specifically, the source of the upper switching element QH1 is connected to the power supply terminal T1. The drain of the upper switching element QH1 is connected to the drain of the lower switching element QL1. The source of the lower switching element QL1 is connected to the ground terminal T4. The node at which the upper switching element QH1 and the lower switching element QL1 are connected is connected to the first drive terminal T2.

[0015] The half bridge HB2 has an upper switching element QH2 and a lower switching element QL2. The upper switching element QH2 is configured with a P-channel MOSFET. The lower switching element QL2 is configured with an N-channel MOSFET. The upper switching element QH2 and the lower switching element QL2 are connected in series between the power supply terminal T1 and the ground terminal T4.

[0016] More specifically, the source of the upper switching element QH2 is connected to the power supply terminal T1. The drain of the upper switching element QH2 is connected to the drain of the lower switching element QL2. The source of the lower switching element QL2 is connected to the ground terminal T4. The node at which the upper switching element QH2 and the lower switching element QL2 are connected is connected to the second drive terminal T3.

[0017] The piezoelectric element Pz is connected between the first drive terminal T2 and the second drive terminal T3.

[0018] The switch driving unit 2 drives the upper switching elements QH1, QH2 and the lower switching elements QL1, QL2 in the switch circuit 1. The switch driving unit 2 has a level shifter 21. An internal signal IS is input to the level shifter 21. The internal signal IS is a pulse signal. A power supply voltage VH is supplied to the level shifter 21 via a power supply terminal T1. The level shifter 21 shifts the level of the internal signal IS and outputs gate signals GH1, GH2 for driving the gates of the upper switching elements QH1, QH2. For example, when the power supply voltage VH=45V and the internal signal IS has a low level=GND and a high level=5V, the gate signals GH1, GH2 have a low level=(45-5)V and a high level=45V.

[0019] Furthermore, the level shifter 21 outputs gate signals GL1 and GL2 for driving the gates of the lower switching elements QL1 and QL2. For example, the low level of the gate signals GL1 and GL2 is GND, and the high level is 5V.

[0020] The level shifter 21 outputs gate signals GH1, GH2 and GL1, GL2 according to the level of the internal signal IS. For example, when the internal signal IS is at a high level, GH1=low level, GL1=low level, GH2=high level, and GL2=high level. That is, QH1=on state, QL1=off state, QH2=off state, and QL2=on state, the voltage of the first drive terminal T2 is at a high level, and the voltage of the second drive terminal T3 is at a low level.

[0021] On the other hand, when the internal signal IS is at a low level, GH1=high level, GL1=high level, GH2=low level, and GL2=low level. That is, QH1=off state, QL1=on state, QH2=on state, and QL2=off state, the voltage of the first drive terminal T2 is at a low level, and the voltage of the second drive terminal T3 is at a high level.

[0022] Next, a reverberation suppression process in a comparative example will be described. Fig. 3 is a diagram showing an example of the vibration waveform of the piezoelectric element Pz under various driving conditions. Fig. 4 is a diagram showing an example of each waveform of the driving signals DS1 and DS2, the beat signal BT, and the damping pulse DP.

[0023] Suppose that the piezoelectric element Pz is driven during the drive period Tdrv by the drive signal DS1 shown in Fig. 4, the drive is stopped at drive stop timing t0 when the drive period Tdrv ends, and the drive stop state is maintained thereafter. The drive signal DS1 is input to the level shifter 21 as the internal signal IS. In this case, the vibration waveform of the piezoelectric element Pz becomes the vibration waveform A shown in Fig. 3. In this way, reverberation occurs as the piezoelectric element Pz vibrates even after the drive stop timing t0, and the reverberation ends at the reverberation end timing t4. With the vibration waveform A, the reverberation time TA from the drive stop timing t0 to the reverberation end timing t4 becomes longer.

[0024] Therefore, in the comparative example, as shown in Fig. 4, a damping pulse DP is added after the drive signal DS1 to become an internal signal IS, which is input to the level shifter 21. Basically, the damping pulse is added in reverse phase to the drive signal DS1. That is, the damping pulse DP is raised to a high level at the drive stop timing t0 when the drive signal DS1 falls to a low level. The frequency of the damping pulse DP is equal to the frequency of the drive signal DS1.

[0025] However, as shown in Fig. 4, in practice, due to the characteristics of the piezoelectric element Pz or the influence of the environmental temperature, etc., it is necessary to adjust the start timing of the damping pulse DP to a timing tα that is slightly shifted from the drive stop timing t0. If the timing tα is adjusted appropriately, the vibration waveform of the piezoelectric element Pz will become like the vibration waveform C shown in Fig. 3, and the reverberation will end at timing t1 immediately after the drive stop timing t0, making it possible to significantly shorten the reverberation time TC.

[0026] However, if the timing tα is not appropriate, the result will be the vibration waveform D shown in Figure 3, the reverberation end timing will be timing t3, the reverberation time TD will increase, and the effect of shortening the reverberation time will be suppressed. It was not easy to appropriately adjust the timing tα.

[0027] Furthermore, when the amplitude of the reverberation decreased, the damping pulse itself sometimes became a cause of the reverberation.

[0028] First Embodiment 5 is a diagram showing a configuration of an ultrasonic sensor 101 according to a first embodiment of the present disclosure. The ultrasonic sensor 101 includes a driving device 101X and a piezoelectric element Pz.

[0029] The driving device 101X differs from the comparative example in that the switch driving unit 2 includes an OR circuit 22. A driving signal DS2 and a beat signal BT are input to the OR circuit 22. The OR circuit 22 outputs the logical sum of the inputs to the level shifter 21.

[0030] In this embodiment, as shown in FIG. 4, the piezoelectric element Pz is driven in the drive period Tdrv by the drive signal DS2. In the drive signal DS2, a drive pulse Pd is added even after the drive stop timing t0. In the beat signal BT, pulse generation starts in synchronization with the drive pulse Pd. Specifically, the beat signal BT rises at the falling timing tβ of the drive pulse Pd. The beat signal BT is a signal with a different frequency from the drive pulse Pd (drive signal DS2). That is, the drive pulse Pd and the beat signal BT are generated in the trailing end period Te after the drive stop timing t0. Note that the beat signal BT may rise at the rising timing of the drive pulse Pd, but the canceling effect can be obtained as soon as possible by raising the beat signal BT at the falling timing of the drive pulse Pd as described above.

[0031] In this way, by generating the drive pulse Pd and beat signal BT after the drive stop timing t0, a beat is generated in the envelope Ev of the vibration waveform, as shown in the vibration waveform B in Fig. 3, and the amplitude of the vibration waveform can be quickly reduced. This causes the reverberation to end at timing t2, and shortens the reverberation time TB from the drive stop timing t0 to timing t2. The frequency of the beat is the difference between the frequency of the drive pulse Pd and the frequency of the beat signal BT.

[0032] According to this embodiment, there is no need to fine-tune the timing as in the comparative example, and the beat signal BT can be generated in synchronization with the drive pulse Pd, which allows stable reverberation suppression that is not dependent on the characteristics of the piezoelectric element Pz or the surrounding environment.

[0033] When the frequency of the drive signal DS2 is set to the anti-resonance (parallel resonance) frequency of the piezoelectric element Pz, it is desirable to set the frequency of the beat signal BT to the resonant (series resonance) frequency of the piezoelectric element Pz. The receiving sensitivity of the piezoelectric element Pz is maximized at the anti-resonant frequency, and the transmitted sound pressure of the piezoelectric element Pz is maximized at the resonant frequency. On the other hand, when the frequency of the drive signal DS2 is set to the resonant frequency of the piezoelectric element Pz, it is desirable to set the frequency of the beat signal BT to the anti-resonant frequency of the piezoelectric element Pz.

[0034] Moreover, the driving device 101X according to this embodiment is provided with switches SW1 and SW2, an inductor L1, and a resistor R1. The switch SW1 is connected between the first driving terminal T2 and a first end of the inductor L1. The switch SW2 is connected between the second driving terminal T3 and a second end of the inductor L1. The resistor R1 is connected in parallel with the inductor L1. The inductor L1 is a variable inductor. The resistor R1 is a variable resistor. Note that the resistor R1 is not essential.

[0035] At the timing (timing tβ) when the generation of the beat signal BT starts, the switches SW1 and SW2 are switched from the OFF state to the ON state. As a result, the inductor L1 and the resistor R1 are connected to the piezoelectric element Pz, and resonance occurs between the inductor L1 and the piezoelectric element Pz, causing the energy of the piezoelectric element Pz to move to the inductor L1 side. Also, the energy of the piezoelectric element Pz is consumed by the resistor R1. This makes it possible to suppress the vibration of the piezoelectric element Pz after the generation of the beat signal BT. The adjustment of the inductor L1 and the resistor R1 will be described later.

[0036] 6, the beat signal BT may start to be generated when the generation of the drive signal DS2 starts. Specifically, at the timing ts when the first pulse of the drive signal DS2 falls to a low level, the beat signal BT rises to a high level and starts to be generated. Then, during the drive period Tdrv, the drive signal DS2 and the beat signal BT are generated, and the drive signal DS2 and the beat signal BT are also generated in the trailing end period Te after the drive stop timing t0. Note that the beat signal BT may start to be generated at the timing ts when the first pulse of the drive signal DS2 rises to a low level.

[0037] This allows the envelope of the vibration waveform Wv to pulsate from the start of driving, and the timing at which the envelope drops, i.e., the timing at which the amplitude of the vibration waveform Wv drops, to be set as the reverberation end timing tre. Therefore, the reverberation time Tr from the drive stop timing t0 to the reverberation end timing tre can be shortened.

[0038] As shown in Fig. 7, the envelope EV of the vibration waveform may be generated for two periods by generating a beat signal BT from the start of driving. This makes it possible to deal with cases where the driving period is long. The envelope of the vibration waveform Wv shown in Fig. 6 described above corresponds to one period. Also, the envelope may be generated for three or more periods.

[0039] <Second embodiment> 8 is a diagram showing a configuration of an ultrasonic sensor 102 according to the second embodiment of the present disclosure. The ultrasonic sensor 102 includes a driving device 102X and a piezoelectric element Pz.

[0040] The difference between the configuration of the driving device 102X and that of the first embodiment (FIG. 2) is that the switch circuit 1 has one half bridge. That is, the switch circuit 1 has only a half bridge HB1. A node to which the upper switching element QH1 and the lower switching element QL1 are connected is connected to a first end of the piezoelectric element Pz via a driving terminal T2. A second end of the piezoelectric element Pz is connected to a ground terminal T4. This configuration makes it easier for the switch driving unit 2 to control the driving of the switch circuit 1.

[0041] <Third embodiment> 9 is a diagram showing a configuration of an ultrasonic sensor 103 according to a third embodiment of the present disclosure. The ultrasonic sensor 103 includes a piezoelectric element Pz, a transformer Trs, and a driving device 103X. In addition, the configurations according to the first and second embodiments described above are direct drive systems that drive the piezoelectric element without using a transformer, in contrast to this embodiment.

[0042] The driving device 103X has, integrated therewith, a switch circuit 3 and a switch driving section 4. The driving device 103X also has, as external terminals, a first driving terminal T11, a second driving terminal T12, and a ground terminal T13.

[0043] The switch circuit 3 has a first switching element 31, a second switching element 32, and a constant current source 33. The first switching element 31 and the second switching element 32 are both configured by N-channel MOSFETs. The drain of the first switching element M1 is connected to a first drive terminal T11. The drain of the second switching element M2 is connected to a second drive terminal T12. The constant current source 33 is connected between a node at which the source of the first switching element M1 and the source of the second switching element M2 are connected, and a ground terminal T13. A ground potential can be applied to the ground terminal T13.

[0044] The transformer Trs has a primary winding w1 and a secondary winding w2. The primary winding w1 is connected between the first drive terminal T11 and the second drive terminal T12. A power supply voltage Vcc is applied to a midpoint tap of the primary winding w1. A piezoelectric element Pz is connected between both ends of the secondary winding w2.

[0045] The switch driver 4 includes a gate driver 41 and an OR circuit 42. A drive signal DS2 and a beat signal BT are input to the OR circuit 42. The gate driver 41 complementarily switches and drives the first switching element M1 and the second switching element M2 in accordance with the output level of the OR circuit 42. As a result, the power supply voltage Vcc is boosted and applied to the piezoelectric element Pz.

[0046] Here, in this embodiment, a damping resistor Rt and a damping capacitance Ct are provided on the secondary side of the transformer Trs. The damping resistor Rt and the damping capacitance Ct are connected in parallel to the piezoelectric element Pz, respectively. FIG. 10 is a diagram showing an equivalent circuit on the secondary side of the transformer Trs. The equivalent circuit of the piezoelectric element Pz is represented by a series inductance Ls, a series capacitance Cs, a series resistance Rs, and a parallel capacitance Cp. More specifically, the series inductance Ls, the series capacitance Cs, and the series resistance Rs are connected in series, and the parallel capacitance Cp is connected in parallel to the series connection configuration. The secondary inductance Lsec shown in FIG. 10 corresponds to the inductance of the secondary winding w2. The series resonance frequency of the piezoelectric element Pz is set to fr, and the damping capacitance Ct is adjusted so that fr coincides with the resonance frequency of the parallel capacitance Cp, the damping capacitance Ct, and the secondary inductance Lsec. That is, the damping capacity Ct is adjusted so as to satisfy the following formula (A). fr=1 / (2π×√(Lsec×(Cp+Ct))) (A) Moreover, the damping resistance Rt is adjusted so as to satisfy the following formula (B). Rt = π × fr × √(Lsec × Ls) (B) The damping resistance Rt may be set to, for example, more than twice the value that satisfies the above formula (B).

[0047] In the case of the first embodiment (FIG. 5) described above, an inductor L1 is provided instead of the secondary inductance Lsec, and no damping capacitance Ct is provided. Therefore, the value of the inductor L1 is adjusted to satisfy the above formula (A) when Ct=0. Also, the resistor R1 in the first embodiment corresponds to the damping resistor Rt.

[0048] <Other> In addition to the above-mentioned embodiment, various technical features disclosed in this specification can be modified in various ways without departing from the spirit of the technical creation. In other words, the above-mentioned embodiment should be considered to be illustrative and not restrictive in all respects, and the technical scope of the present invention should not be limited to the above-mentioned embodiment, but should be understood to include all modifications that fall within the meaning and scope equivalent to the scope of the claims.

[0049] <Additional Notes> As described above, the drive device (101X) according to one aspect of the present disclosure has: a switch circuit (1) having switching elements (QH1, QH2, QL1, QL2) and configured to drive a piezoelectric element (Pz) based on switching of the switching elements; a switch driver (2) configured to drive the switching element based on a pulsed drive signal (DS2) and a pulsed beat signal (BT); Equipped with The drive signal is generated during a drive period and a trailing end period following the drive period, the beat signal is generated at least in the trailing edge period, The drive signal and the beat signal have different frequencies (first configuration).

[0050] In the above first configuration, the beat signal may start to be generated in the rear end period (second configuration).

[0051] In the first configuration, the beat signal may start to be generated at the start of the driving period (third configuration).

[0052] In addition, in any of the above first to third configurations, one of the frequency of the drive signal and the frequency of the beat signal may be an anti-resonance frequency of the piezoelectric element, and the other may be a resonant frequency of the piezoelectric element (fourth configuration).

[0053] In addition, in any of the first to third configurations, the switch driving unit may have an OR circuit (22) configured to receive the driving signal and the beat signal, and may be configured to drive the switching element based on the output of the OR circuit (fifth configuration).

[0054] In the fifth configuration, the switch circuit may have only one half bridge (HB1) including the switching element (sixth configuration).

[0055] In addition, in any one of the first to sixth configurations, the switch circuit has at least one half bridge including the switching element, The piezoelectric element can be directly connected to the half bridge, The driving device may be configured to include an inductor (L1), and switches (SW1, SW2) connected between the inductor and the piezoelectric element (seventh configuration).

[0056] In the seventh configuration, a resistor (R1) may be connected in parallel with the inductor (eighth configuration).

[0057] In any one of the first to sixth configurations, the switch circuit (3) may be configured to be connectable to the piezoelectric element via a transformer (Trs) (ninth configuration).

[0058] Moreover, an ultrasonic sensor (101) according to an aspect of the present disclosure includes a driving device (101X) having any one of the first to ninth configurations and the piezoelectric element (Pz) (tenth configuration).

[0059] Moreover, a vehicle (200) according to an embodiment of the present disclosure includes the ultrasonic sensor (10) of the tenth configuration (eleventh configuration). [Industrial Applicability]

[0060] The present disclosure can be used in ultrasonic sensors, for example, for in-vehicle use. [Explanation of symbols]

[0061] 1 Switch circuit 2 Switch drive unit 3 Switch Circuit 4 Switch drive unit 10 Ultrasonic Sensor 21 Level Shifter 22 OR Circuit 31 First switching element 32 Second switching element 33 Constant current source 41 Gate driver 42 OR Circuit 100 Ultrasonic Sensor 100X Drive Unit 101 Ultrasonic Sensor 101X Drive Unit 102 Ultrasonic Sensor 102X Drive Unit 103 Ultrasonic Sensor 103X Drive Unit 200 vehicles 300 Objects Cp parallel capacitance Cs series capacitance Ct Damping Capacity L1 Inductor Ls Series inductance Lsec Secondary inductance M1 First switching element M2 Second switching element Pz Piezoelectric element QH1, QH2 Upper switching element QL1, QL2 Lower switching element R1 Resistor Rs Series resistance Rt Damping resistor SW1, SW2 switches T1 power terminal T11 First drive terminal T12 Second drive terminal T13 Ground terminal T2 First drive terminal T3 Second drive terminal T4 Ground terminal Trs Transformer w1 Primary winding w2 Secondary winding

Claims

1. a switch circuit having a switching element and configured to drive a piezoelectric element based on switching of the switching element; a switch driver configured to drive the switching element based on a pulsed drive signal and a pulsed beat signal; Equipped with The drive signal is generated during a drive period and a trailing end period following the drive period, the beat signal is generated at least in the trailing edge period, The driving signal and the beat signal have different frequencies.

2. The driving device according to claim 1 , wherein generation of the beat signal starts in the trailing edge period.

3. The driving device according to claim 1 , wherein the beat signal starts to be generated at the start of the driving period.

4. 2. The driving device according to claim 1, wherein one of the frequency of the driving signal and the frequency of the beat signal is an anti-resonance frequency of the piezoelectric element, and the other is a resonant frequency of the piezoelectric element.

5. 2. The drive device according to claim 1, wherein the switch drive section has an OR circuit configured to receive the drive signal and the beat signal, and drives the switching element based on an output of the OR circuit.

6. The drive device according to claim 5 , wherein the switch circuit has only one half bridge including the switching element.

7. the switch circuit has at least one half bridge including the switching element; The piezoelectric element can be directly connected to the half bridge, The drive device according to claim 1 , comprising: an inductor; and a switch connected between the inductor and the piezoelectric element.

8. The drive device of claim 7 , further comprising a resistor connected in parallel with the inductor.

9. The driving device according to claim 1 , wherein the switch circuit is connectable to the piezoelectric element via a transformer.

10. 10. An ultrasonic sensor comprising: the driving device according to claim 1; and the piezoelectric element.

11. A vehicle comprising the ultrasonic sensor according to claim 10.

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