Signal processing device, ultrasonic sensor, and vehicle

Abstract

To provide a signal processing device that can offer improved capability of detecting nearby objects.SOLUTION: A signal processing device (10) is provided, comprising a transmission frequency control unit (12) configured to switch a transmission frequency of an ultrasonic sensor element (1), and a waveform change detection unit (13, 14) configured to detect changes in waveform of a reflected wave signal generated by combining a reverberation waveform caused by reverberation of the ultrasonic sensor element and that of a reflected wave reflected by a target object when the transmission frequency is switched.SELECTED DRAWING: Figure 13

Description

[Technical Field]

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

[0002] Conventionally, the time it takes for an ultrasonic wave to be emitted and for the reflected wave to return from an obstacle is called 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 thereof is known as an in-vehicle clearance sonar. [Prior art documents] [Patent documents]

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

[0004] [overview] When an ultrasonic sensor starts measuring, it drives the ultrasonic sensor element with high voltage to generate ultrasonic waves. At this time, even if the drive of the ultrasonic sensor element is stopped, the mechanical vibration of the ultrasonic sensor element continues. At this time, the generated voltage is input to the receiving circuit, and the voltage generated by the sensor and the signal from the received ultrasonic waves reflected by an obstacle are superimposed, resulting in a period of time when the receiving operation is not possible. This phenomenon is called reverberation, and this time is called reverberation time. Reverberation time is related to the performance of short-distance measurement (short-distance measurement limit distance).

[0005] It is desirable to detect obstacles at close range as much as possible under the influence of reverberation as described above.

[0006] In view of the above circumstances, an object of the present disclosure is to provide a signal processing device that can improve the performance of detecting a close-range object.

[0007] A signal processing device according to one aspect of the present disclosure includes: a driver circuit configured to drive the ultrasonic sensor element to transmit ultrasonic waves to the ultrasonic sensor element; a receiving circuit configured to output a receiving signal based on an output of the ultrasonic sensor element; a reflected wave signal generator configured to generate a reflected wave signal by detecting the received signal; a transmission frequency control unit configured to switch the transmission frequency of the ultrasonic sensor element; The ultrasonic wave sensor is configured to detect a change in the waveform of the reflected wave signal generated by combining a reverberation waveform due to reverberation of the ultrasonic sensor element and a reflected wave from an object when the transmission frequency is switched. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example in which an ultrasonic sensor is applied to a vehicle. [Figure 2] FIG. 2 is a diagram showing the configuration of an ultrasonic sensor according to a comparative example. [Figure 3] FIG. 3 is a waveform diagram showing an example of a reflected wave signal (when the reverberation waveform and the reflected wave waveform are separated). [Figure 4] FIG. 4 is a waveform diagram showing an example of a reflected wave signal (when the reverberation waveform and the reflected wave waveform are not separated). [Figure 5] FIG. 5 is a waveform diagram showing an example of a reference waveform and a reflected wave signal (when the reflected wave signal deviates from the reference waveform). [Figure 6] FIG. 6 is a waveform diagram showing an example of a reference waveform and a reflected wave signal (when the reflected wave signal does not deviate from the reference waveform). [Figure 7] FIG. 7 is a diagram showing an example of a reverberation sine wave W1, a reflected sine wave W2, and a composite waveform W3 obtained by combining the sine waves W1 and W2. [Figure 8] FIG. 8 is a schematic diagram showing a case where an ultrasonic wave is transmitted from an ultrasonic sensor. [Figure 9] FIG. 9 is a waveform diagram showing an example of a reflected wave signal obtained before the transmission frequency is changed. [Figure 10] FIG. 10 is a waveform diagram showing an example of a reflected wave signal obtained after changing the transmission frequency. [Figure 11] FIG. 11 is a waveform diagram showing an example of a reference waveform and a reflected wave waveform (before the transmission frequency is changed). [Figure 12] FIG. 12 is a waveform diagram showing an example of a reference waveform and a reflected wave waveform (after changing the transmission frequency). [Figure 13] FIG. 13 is a diagram illustrating a configuration of an ultrasonic sensor according to an exemplary embodiment of the present disclosure. [Figure 14] FIG. 14 is a flowchart relating to the operation of detecting the distance to an object. [Figure 15] FIG. 15 is a flowchart showing the operation of detecting the presence of a nearby object. [Figure 16] FIG. 16 is a diagram showing the configuration of an ultrasonic sensor according to a modified example.

[0009] [Detailed explanation] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.

[0010] <Ultrasonic sensors installed in vehicles> FIG. 1 shows a vehicle 200 equipped with an ultrasonic sensor 10X and an object (obstacle) 300. Ultrasonic waves transmitted from the ultrasonic sensor 10X are reflected by the object 300 and received as reflected waves by the ultrasonic sensor 10X. The ultrasonic sensor 10X measures distance by measuring the time between transmitting and receiving the ultrasonic waves. Various ultrasonic sensors described below can be used as the ultrasonic sensor 10X, but the application of ultrasonic sensors is not limited to vehicles.

[0011] <Comparative Example> 2 is a diagram showing the configuration of an ultrasonic sensor 100 according to a comparative example. The ultrasonic sensor 100 includes an ultrasonic sensor element (hereinafter referred to as a sensor element) 1 and a semiconductor device 100A. The semiconductor device 100A is an IC (integrated circuit) that integrates a drive circuit 2, a receiving circuit 3, an ADC 4, a reflected wave signal generator 5, a threshold generator 6, a comparator 7, and a communication terminal 8.

[0012] The sensor element 1 is made up of a piezoelectric element and is connected to the outside of the semiconductor device 100A.

[0013] The drive circuit 2 is a circuit that drives the sensor element 1. When the drive circuit 2 pulse-drives the sensor element 1, the sensor element 1 vibrates and ultrasonic waves are transmitted from the sensor element 1. When the sensor element 1 vibrates due to, for example, receiving a reflected ultrasonic wave, it outputs a sensor output signal SS.

[0014] The receiving circuit 3 is a circuit that receives and processes the sensor output signal SS. The receiving circuit 3 includes an LNA (low noise amplifier) ​​and an LPF (low pass filter). The LNA can amplify the weak sensor output signal SS. The receiving circuit 3 outputs a received signal RS as a result of processing the sensor output signal SS.

[0015] An ADC (AD converter) 4 converts the received signal RS, which is an analog signal, into a digital signal DS.

[0016] The reflected wave signal generator 5 performs detection processing on the digital signal DS to generate a reflected wave signal WS. The detection method may be, for example, envelope detection or quadrature demodulation.

[0017] The threshold generator 6 generates a threshold value TH to be input to the comparator 7. The comparator 7 compares the reflected wave signal WS with the threshold value TH and outputs a comparison signal CMP as the comparison result. The comparison signal CMP can be either high or low.

[0018] The comparison signal CMP is output to the outside via a communication terminal 8.

[0019] Figure 3 is a waveform diagram showing an example of a reflected wave signal WS. When an object is located close by and farther away than the distance proportional to the reverberation time, the reverberation waveform Rv and the reflected wave waveform Rf due to reflection from the object are separated, as shown in Figure 3. In this case, if it is detected that the reflected wave signal WS falls below the threshold value TH (time t0) by time t1, a predetermined time T1 after the start of measurement, and then subsequently rises above the threshold value TH (time t2), it can be determined that reverberation has ended and that an object is present in the vicinity. In this case, the distance can be measured based on the time from the start of measurement to time t2, for example.

[0020] FIG. 4 is a waveform diagram showing another example of a reflected wave signal WS. FIG. 4 shows a case where the target is closer to the ultrasonic sensor than in FIG. 3. In this case, the reverberation waveform and the reflected wave waveform overlap, and the reverberation waveform and the reflected wave waveform cannot be separated. As a result, the timing t3 at which the reflected wave signal WS falls below the threshold value TH is delayed compared to FIG. 3, and the reflected wave signal WS does not fall below the threshold value TH by the time t1 at which the predetermined time T1 has elapsed. Therefore, in such a case, distance cannot be measured.

[0021] There is also a method to detect the presence of an object in the vicinity by detecting the deviation (change) from the reference waveform as the reflected wave signal WS when it is not reflected by the object. This method cannot measure distance, but it can expand the detection range compared to the method of detecting the reflected wave waveform mentioned above.

[0022] FIG. 5 is a waveform diagram showing an example of a reflected wave signal WS. FIG. 5 shows a reference waveform WS1 and a reflected wave waveform WS2, which is a reflected wave signal WS based on reflection from a nearby object. The reference waveform includes a reverberation waveform. The reflected wave waveform appears as a composite waveform that combines the reverberation waveform and the waveform due to reflection. In the case of FIG. 5, the reflected wave waveform WS2 deviates significantly from the reference waveform WS1, allowing the presence of an object in the nearby distance to be detected.

[0023] On the other hand, Figure 6 is a waveform diagram showing another example of a reflected wave signal WS. In Figure 6, a reference waveform WS1 and a reflected wave waveform WS3 are shown, but the reflected wave waveform WS3 hardly deviates from the reference waveform WS1, and an object cannot be detected. As such, depending on how the reference waveform and the reflected wave waveform overlap, there may be almost no change from the reference waveform, making it impossible to detect an object.

[0024] <Embodiments of the present disclosure> <<Object detection method>> Here, a method for detecting an object according to an embodiment of the present disclosure will be described. Fig. 7 shows an example of a reverberation sine wave W1, a reflected sine wave W2, and a composite waveform W3 obtained by combining the sine waves W1 and W2. The left side of Fig. 7 shows a case where the sine waves W1 and W2 are in phase, while the right side of Fig. 7 shows a case where they are out of phase. In this way, the composite waveform W3 changes into various waveforms depending on the signal strength and phase of the two sine waves W1 and W2.

[0025] 8 is a schematic diagram showing the case where ultrasonic waves are transmitted from the ultrasonic sensor 10X. In Fig. 8, a transmission wave US1 is transmitted from the ultrasonic sensor 10X, and is reflected by an object OB, generating a reflected wave US2 that travels toward the ultrasonic sensor 10X. The object OB is placed on the ground G.

[0026] Changing the frequency (transmission frequency) of the transmission wave US1 changes the wavelength of the ultrasound. Figure 8 shows sine waves S1 and S2 with different transmission frequencies. Therefore, the wavelengths λ1 and λ2 of the sine waves S1 and S2 are different. Since the phase is the remainder when the distance L to the object OB is divided by the wavelength, a change in wavelength leads to a change in phase. In Figure 8, the phase of the sine wave S1 is the remainder of (L x 2) / λ1, and the phase of the sine wave S2 is the remainder of (L x 2) / λ2.

[0027] In this disclosure, detecting a nearby object is achieved by changing the phase by changing the transmission frequency, which changes the composite waveform obtained by combining a sine wave due to reverberation and a sine wave due to reflection. FIG. 9 is a waveform diagram showing an example of a reflected wave signal WS obtained before changing the transmission frequency. In this example, the reverberation waveform and the reflected wave waveform due to the reflected wave cannot be separated. FIG. 10 is a waveform diagram showing an example of a reflected wave signal WS obtained after changing the transmission frequency. In this way, changing the transmission frequency changes the composite waveform obtained by combining a sine wave due to reverberation and a sine wave due to reflection, and the reverberation waveform Rv and the reflected wave waveform Rf can be separated in the reflected wave signal WS. This makes it possible to detect the distance to a nearby object.

[0028] 11 and 12 respectively show a reference waveform WS1 and reflected wave waveforms WS11 and WS12, which are reflected wave signals WS based on reflection from a nearby object. The reflected wave waveform WS11 corresponds to the waveform before the transmission frequency was changed, and the reflected wave waveform WS12 corresponds to the waveform after the transmission frequency was changed. As can be seen, before the transmission frequency was changed, the reflected wave waveform WS11 deviates little from the reference waveform WS1, whereas after the transmission frequency was changed, the deviation of the reflected wave waveform WS12 from the reference waveform WS1 becomes greater. This makes it possible to detect the presence of an object in the nearby distance.

[0029] A more specific method for detecting a close-range object will be described later.

[0030] <<Ultrasonic sensor configuration>> 13 is a diagram illustrating a configuration of an ultrasonic sensor 101 according to an exemplary embodiment of the present disclosure. The ultrasonic sensor 101 includes a sensor element 1 and a signal processing device 10. The signal processing device 10 includes a semiconductor device 10A and a control device 10B.

[0031] The semiconductor device 10A differs from the comparative example (FIG. 2) described above in that it includes a communication unit 80 and a transmission frequency setting unit 9. The control device 10B is disposed outside the semiconductor device 10A and is configured as, for example, a microcomputer. The communication unit 80 is capable of bidirectional communication with the control device 10B. For example, the communication unit 80 transmits a comparison signal CMP to the control device 10B and receives a transmission frequency setting signal from the control device 10B. The transmission frequency setting unit 9 is configured as a register in which the transmission frequency is set.

[0032] The control device 10B has a measurement control unit 11, a transmission frequency control unit 12, a distance detection unit 13, and a short-distance object detection unit 14. The measurement control unit 11 controls the measurement operation by the ultrasonic sensor 101. The transmission frequency control unit 12 controls switching of the transmission frequency. The distance detection unit 13 detects the distance to an object. The short-distance object detection unit 14 detects the presence of an object in the short distance.

[0033] <<Distance detection operation>> 14 is a flowchart relating to the operation of detecting the distance to an object in the ultrasonic sensor 101 configured as described above. Explaining with reference to FIG. 14, first, in step S1, the transmission frequency control unit 12 sends a setting signal for the transmission frequency to the transmission frequency setting unit 9 via the communication unit 80, and an initial value of the transmission frequency is set in the transmission frequency setting unit 9. Then, proceeding to step S2, the measurement operation is started by the measurement control unit 11. At this time, the drive circuit 2 drives the sensor element 1 based on the transmission frequency set in the transmission frequency setting unit 9, causing the sensor element 1 to transmit ultrasonic waves at the set transmission frequency (here, the initial value).

[0034] Then, in step S3, the distance detection unit 13 determines whether the reverberation waveform and the reflected wave waveform are separated in the obtained reflected wave signal WS. Here, for example, as shown in Figures 9 and 10, it determines whether the reflected wave signal WS falls below the threshold value TH by time t11, when a predetermined time T11 has elapsed since the start of measurement, and whether the reflected wave signal WS thereafter becomes equal to or greater than the threshold value TH. As shown in Figures 9 and 10, the distance detection unit 13 makes this determination based on the comparison signal CMP obtained from the communication unit 80.

[0035] 9 and 10, if the reflected wave signal WS is equal to or greater than the threshold value TH, the comparison signal CMP is at a low level, and if it is lower than the threshold value TH, the comparison signal CMP is at a high level. In the case of FIG. 9, the comparison signal CMP is maintained at a low level until timing t11, so it is detected that the reflected wave signal WS has not fallen below the threshold value TH by timing t11. In the case of FIG. 10, the comparison signal CMP switches from a low level to a high level at timing t10, before timing t11, and then switches from a high level to a low level at timing t13. As a result, it is detected that the reflected wave signal WS fell below the threshold value TH by timing t11, and then became equal to or greater than the threshold value TH.

[0036] If the reverberation waveform and the reflected wave waveform are separated in the reflected wave signal WS (Y in step S3), the process proceeds to step S4, where the distance detection unit 13 calculates the distance. Here, the distance is calculated based on the elapsed time from the start of measurement at timing t13 (the timing when the reflected wave signal WS becomes equal to or greater than the threshold) shown in Fig. 10. After step S4, the detection result in step S5 indicates detection.

[0037] On the other hand, if the reverberation waveform and the reflected wave waveform are not separated in the reflected wave signal WS (N in step S3), the process proceeds to step S6, where the transmission frequency control unit 12 sets the transmission frequency changed from the initial value in the transmission frequency setting unit 9. As an example, the initial value may be 50 kHz, and the frequency may be increased by 1 kHz each time the transmission frequency is switched. Then, in step S7, the distance detection unit 13 determines whether the transmission frequency has been switched a specified number of times. If the specified number of times has not been reached (N in step S7), the process returns to step S2, and measurement is resumed. Here, measurement operation is performed at the changed transmission frequency.

[0038] If the transmission frequency is switched a specified number of times without the reverberation waveform and the reflected wave waveform being separated (Y in step S7), the detection result in step S8 is no detection.

[0039] <<Detection of close-range objects>> 15 is a flowchart showing the operation of detecting the presence of a nearby object in the ultrasonic sensor 101 having the above-described configuration. Explaining with reference to FIG. 15, first, in step S11, the transmission frequency is set to an initial value, and in step S2, the measurement operation is started. Steps S11 and S12 are the same as steps S1 and S2 described above.

[0040] Then, the process proceeds to step S13, where the short-distance object detection unit 14 determines whether the waveform of the obtained reflected wave signal WS deviates from the reference waveform. Here, as shown in FIGS. 11 and 12, for example, integration of the reflected wave signal WS begins at timing t21, a predetermined time T21 after the start of measurement, and the integration is performed for a predetermined period T22 from timing t21. If the difference between the obtained integral value and the reference value is greater than a predetermined value, it is determined that the waveform of the reflected wave signal WS deviates from the reference waveform; otherwise, it is determined that the waveform of the reflected wave signal WS does not deviate from the reference waveform. The reference value is the integral value obtained when integration is performed for the predetermined period T22 on the reference waveform WS1.

[0041] If the waveform of the reflected wave signal WS deviates from the reference waveform (Y in step S13), the process proceeds to step S14, where the close-distance object detection unit 14 detects the presence of a close-distance object. On the other hand, if the waveform of the reflected wave signal WS does not deviate from the reference waveform (N in step S13), the process proceeds to step S15, where the transmission frequency is changed. Thereafter, in step S16, it is determined whether the transmission frequency has been switched a specified number of times. If the specified number of times has not been reached (N in step S16), the process returns to step S12, and measurement is resumed.

[0042] Then, if the transmission frequency is switched a specified number of times while the waveform of the reflected wave signal WS remains the same as the reference waveform (Y in step S16), the detection result in step S17 is no detection.

[0043] It is preferable that the resonant frequency of the sensor element 1 is included in the range in which the transmission frequency is changed as described above.

[0044] <<Modifications>> FIG. 16 is a diagram showing the configuration of an ultrasonic sensor 102 according to a modified example. The ultrasonic sensor 102 includes a sensor element 1 and a semiconductor device 10C. In the ultrasonic sensor 102, the functions of the control device 10B (FIG. 13) described above are incorporated into the semiconductor device 10C as a control unit 15. That is, the measurement control unit 11, transmission frequency control unit 12, distance detection unit 13, and short-distance object detection unit 14 are incorporated into the semiconductor device 10C. Here, the semiconductor device 10C functions as a signal processing device. According to this modified example, an external control device or the like is not required to detect the distance to an object or the presence of a short-distance object.

[0045] <Other> In addition to the above-described embodiments, the 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-described embodiments 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-described embodiments, but should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0046] <Additional Notes> As described above, the signal processing device (10) according to one aspect of the present disclosure includes: a drive circuit (2) configured to drive the ultrasonic sensor element (1) to transmit ultrasonic waves to the ultrasonic sensor element; a receiving circuit (3) configured to output a receiving signal (RS) based on the output of the ultrasonic sensor element; a reflected wave signal generator (5) configured to generate a reflected wave signal (WS) by detecting the received signal; a transmission frequency control unit (12) configured to switch the transmission frequency of the ultrasonic sensor element; The ultrasonic wave sensor is configured to include a waveform change detection unit (13, 14) configured to detect a change in the waveform of the reflected wave signal generated by combining a reverberation waveform due to reverberation of the ultrasonic sensor element and a reflected wave from an object when the transmission frequency is switched (first configuration).

[0047] With this configuration, it is possible to more reliably detect a target at close range even under the influence of reverberation.

[0048] In addition, in the first configuration, the waveform change detection unit may be a distance detection unit (13) configured to calculate the distance to the object when it detects that the waveform of the reflected wave signal reflected by the object has been separated from the waveform due to the reverberation (second configuration).

[0049] In addition, in the second configuration, the distance detection unit may be configured to detect that the reflected wave signal has been separated from the waveform due to reverberation by detecting that the reflected wave signal has fallen below a predetermined threshold (TH) and then rises above the threshold (third configuration).

[0050] In addition, in the third configuration, the device further includes a comparator (7) configured to compare the reflected wave signal with the threshold value, The distance detection unit may be configured to perform detection based on the output of the comparator (fourth configuration).

[0051] Furthermore, in any of the second to fourth configurations, if the transmission frequency is switched a specified number of times without the reflected waveform being separated from the reverberation waveform, the detection result may be deemed undetected (fifth configuration).

[0052] Furthermore, in the first configuration, the waveform change detection unit may be configured as a close-range object detection unit (14) that detects deviations in the waveform of the reflected wave signal from a reference waveform and determines that the object is present in the close range when such deviations are detected (sixth configuration).

[0053] In addition, in the above sixth configuration, the short-distance object detection unit may be configured to perform integration processing of the reflected wave signal for a predetermined period starting from a timing when a predetermined time has elapsed since the start of measurement, and determine whether or not there is a deviation based on the obtained integral value (seventh configuration).

[0054] In the sixth or seventh configuration, if the transmission frequency is switched a predetermined number of times without any deviation, the detection result may be regarded as undetected (eighth configuration).

[0055] In any of the first to eighth configurations, the range in which the transmission frequency is switched may include the resonance frequency of the ultrasonic sensor element (ninth configuration).

[0056] In addition, in any one of the first to ninth configurations, a semiconductor device (10A) having the drive circuit, the receiving circuit, and the reflected wave signal generating unit; a control device (10B) having the transmission frequency control unit and the waveform change detection unit, The semiconductor device may have a communication section (80) configured to be able to communicate bidirectionally with the control device (tenth configuration).

[0057] Furthermore, in any of the first to ninth configurations, the semiconductor device (10C) may be configured to have the drive circuit, the receiving circuit, the reflected wave signal generating unit, the transmission frequency control unit, and the waveform change detection unit (eleventh configuration).

[0058] Moreover, an ultrasonic sensor (101) according to one embodiment of the present disclosure includes a signal processing device (10) having any one of the first to eleventh configurations and the ultrasonic sensor element (1) (twelfth configuration).

[0059] Moreover, a vehicle (200) according to an aspect of the present disclosure includes the ultrasonic sensor of the twelfth configuration (thirteenth configuration). [Industrial Applicability]

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

[0061] 1. Sensor element 2. Drive circuit 3. Receiving circuit 4 ADC 5 Reflected wave signal generation section 6 Threshold Generation Unit 7 Comparators 8 Communication terminal 9 Transmission frequency setting section 10. Signal Processing Device 10A Semiconductor Device 10B Control device 10C Semiconductor Devices 10X Ultrasonic Sensors 11 Measurement control section 12 Transmission frequency control section 13 Distance detection unit 14. Short-distance object detection unit 15 Control Unit 80 Communications Department 100 ultrasonic sensors 100A Semiconductor Device 101 Ultrasonic Sensor 102 Ultrasonic Sensor 200 vehicles 300 Objects G ground L distance OB Objects

Claims

1. a driver circuit configured to drive the ultrasonic sensor element to transmit ultrasonic waves to the ultrasonic sensor element; a receiving circuit configured to output a receiving signal based on an output of the ultrasonic sensor element; a reflected wave signal generator configured to generate a reflected wave signal by detecting the received signal; a transmission frequency control unit configured to switch the transmission frequency of the ultrasonic sensor element; a waveform change detection unit configured to detect a change in the waveform of the reflected wave signal generated by combining a reverberation waveform due to reverberation of the ultrasonic sensor element and a reflected wave from an object when the transmission frequency is switched; A signal processing device comprising:

2. 2. The signal processing device according to claim 1, wherein the waveform change detection unit is a distance detection unit configured to calculate a distance to the object when it detects that a waveform reflected by an object has been separated from a waveform due to reverberation in the reflected wave signal.

3. The signal processing device according to claim 2 , wherein the distance detection unit detects that the reflected wave signal has fallen below a predetermined threshold and then rises to or above the threshold, thereby detecting that the reflected waveform has been separated from the waveform due to reverberation.

4. a comparator configured to compare the reflected wave signal with the threshold; The signal processing device according to claim 3 , wherein the distance detection unit performs detection based on an output of the comparator.

5. The signal processing device according to claim 2 , wherein if the transmission frequency is switched a predetermined number of times while the reflected waveform is not separated from the reverberation waveform, the detection result is determined to be undetected.

6. The signal processing device according to claim 1 , wherein the waveform change detection unit is a short-distance object detection unit that detects a deviation of the waveform of the reflected wave signal from a reference waveform and determines that the object is present in a short distance when the deviation is detected.

7. The signal processing device according to claim 6, wherein if the transmission frequency is switched a specified number of times without the deviation, the detection result is determined to be undetected.

8. The signal processing device according to claim 1 , wherein the range in which the transmission frequency is switched includes a resonance frequency of the ultrasonic sensor element.

9. a semiconductor device including the driver circuit, the receiver circuit, and the reflected wave signal generator; a control device having the transmission frequency control unit and the waveform change detection unit, The signal processing device according to claim 1 , wherein the semiconductor device includes a communication unit configured to be able to communicate bidirectionally with the control device.

10. 2. The signal processing device according to claim 1, configured as a semiconductor device having the drive circuit, the receiving circuit, the reflected wave signal generating section, the transmission frequency control section, and the waveform change detecting section.

11. An ultrasonic sensor comprising: the signal processing device according to claim 1; and the ultrasonic sensor element.

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

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