JP7820145B2 - Switch device, drive device, ultrasonic sensor, and vehicle - Google Patents

Description

The invention disclosed in this specification relates to a switch device, a drive device including the switch device, an ultrasonic sensor including the drive device, and a vehicle including the ultrasonic sensor.

Ultrasonic sensors transmit ultrasonic waves and receive reflected waves to detect the distance to an object, as well as the presence and status of the object. Ultrasonic sensors are widely used in obstacle detection devices for passenger cars, automatic parking systems, object detection on conveyor belts, automatic doors, intrusion prevention monitoring, and various types of displacement measurement.

In ultrasonic sensors that use a single transducer to transmit and receive ultrasonic waves, a phenomenon known as reverberation occurs, in which the vibration of the transducer gradually decreases immediately after the transducer is activated. This makes it difficult for ultrasonic sensors with this configuration to detect close-range objects where reflected waves can be obtained during the reverberation time. Therefore, as a countermeasure against reverberation, a challenge for ultrasonic sensors with this configuration is to quickly attenuate the vibration of the transducer that occurs immediately after transmitting ultrasonic waves (reverberation vibration).

Patent Document 1 discloses an ultrasonic sensor equipped with a reverberation vibration suppression circuit as an ultrasonic sensor with reverberation countermeasures. The circuit constants of the reverberation vibration suppression circuit are set to cancel the resonant frequency of the ultrasonic sensor.

JP 2019-12955 A (paragraph 0005)

When an ultrasonic sensor equipped with a reverberation vibration suppression circuit transmits and receives ultrasonic waves, a decrease in sensor sensitivity can be prevented by electrically disconnecting the drive circuit that drives the transducer from the reverberation vibration suppression circuit. Therefore, it is desirable for an ultrasonic sensor equipped with a reverberation vibration suppression circuit to be equipped with a switch device that switches between electrical connection and electrical disconnection between the drive circuit that drives the transducer and the reverberation vibration suppression circuit.

However, if the switching noise of the switch device is large, there is a risk that the ultrasonic sensor may detect the signal incorrectly due to the switching noise of the switch device.

The switch device disclosed in this specification includes a first switch, a second switch, and a control unit. The second switch is connected in series to the first switch and has a lower withstand voltage than the first switch. The control unit is configured to turn on the first switch and the second switch when turning on the switch device, and to turn on the first switch and the second switch when turning off the switch device.

The driving device disclosed in this specification includes a driving circuit configured to drive a vibrator, a reverberation vibration suppression circuit configured to suppress reverberation vibration of the vibrator, and a switch device configured as described above that is configured to switch between electrical connection and disconnection between the driving circuit and the reverberation vibration suppression circuit.

The ultrasonic sensor disclosed in this specification comprises a drive device having the above-described configuration and the vibrator.

The vehicle disclosed in this specification is equipped with an ultrasonic sensor having the above configuration.

The switch device, drive device, ultrasonic sensor, and vehicle disclosed in this specification can reduce switching noise.

FIG. 1 is a diagram showing a schematic configuration of an ultrasonic sensor according to an embodiment. FIG. 2 is an equivalent circuit of the vibrator, the drive circuit, and the reverberation vibration suppression circuit in a state where the drive circuit and the reverberation vibration suppression circuit are electrically connected. FIG. 3 is a diagram showing an example of the configuration of a pseudo inductor circuit. FIG. 4 is a diagram showing a schematic waveform of a received signal based on the reception of an ultrasonic wave. FIG. 5 is a diagram illustrating an example of the configuration of the second switch. FIG. 6 is a diagram showing another example of the configuration of the second switch. FIG. 7 is a diagram showing yet another example of the configuration of the second switch. FIG. 8 is an external view of the vehicle.

Figure 1 is a diagram showing the schematic configuration of an ultrasonic sensor according to an embodiment. The ultrasonic sensor 1 according to the embodiment shown in Figure 1 (hereinafter abbreviated as "ultrasonic sensor 1") includes a vibrator 2 and a driver 3.

The transducer 2 is driven (vibrates) by a voltage supply from the driver 3 to transmit ultrasonic waves. The transducer 2 also receives ultrasonic waves.

The driving device 3 is a semiconductor integrated circuit device. It includes a processing device 4, a driving circuit 5, an LNA (Low Noise Amplifier) 6, an LPF (Low Pass Filter) 7, an ADC (Analog to Digital Converter) 8, switch devices 9 and 10, a reverberation vibration suppression circuit 11, and external terminals T1 to T5.

When the power supply voltage VCC is applied to the external terminal T1 and the external terminal T2 is connected to ground potential, the drive unit 3 becomes operable.

The processing device 4 generates the transmission signal. For example, an MPU (Micro Processor Unit) is used as the processing device 4.

The drive circuit 5 converts the transmission signal output from the processing device 4 into a high voltage and outputs a differential signal. The differential signal output from the drive circuit 5 is supplied to the vibrator 2 via external terminals T3 and T4. The drive circuit 5 drives the vibrator 2 by supplying the differential signal to the vibrator 2.

LNA 6 receives the output signal of vibrator 2 via external terminals T3 and T4. LNA 6 power amplifies the output signal of vibrator 2, which is a differential signal, and converts it to a single-ended signal.

The LPF 7 removes high-frequency noise components that may be contained in the single-ended signal output from the LNA 6, and supplies the signal after the high-frequency noise components have been removed to the ADC 8.

The ADC 8 converts the output signal of the LPF 7 from an analog signal to a digital signal and supplies the A/D converted signal to the processing device 4. The output signal of the ADC 8 is a received signal based on the reception of ultrasonic waves. The processing device 4 uses the received signal to detect reflected waves of the transmitted waves. For example, if the level of the received signal is equal to or higher than a predetermined level, the processing device 4 detects reflected waves of the transmitted waves (self-waves). The processing device 4 also measures the TOF (Time Of Flight), which is the time from transmitting ultrasonic waves to receiving the reflected waves reflected by an object. The processing device 4 may also use the TOF to determine the distance from the ultrasonic sensor 1 to the object. The processing device 4 supplies TOF information or information on the distance from the ultrasonic sensor 1 to the object via the external terminal T5 to the outside of the ultrasonic sensor 1.

The switch devices 9 and 10 are configured to switch between electrical connection and electrical disconnection between the drive circuit 5 and the reverberation vibration suppression circuit 11. The switch devices 9 and 10 are switched on and off in response to instructions from the processing device 4. The processing device 4 turns on the switch devices 9 and 10 during the period when reverberation vibration is expected to be generated, i.e., during the period from the completion of output of the transmission signal until a certain amount of time has elapsed. On the other hand, the processing device 4 turns off the switch devices 9 and 10 during the period when reverberation vibration is expected not to be generated. Details of the switch devices 9 and 10 will be described later.

The reverberation vibration suppression circuit 11 is configured to suppress reverberation vibration of the vibrator 2. The reverberation vibration suppression circuit 11 includes a resistor RD and a pseudo-inductor circuit LP. The reverberation vibration suppression circuit 11 is a parallel circuit of the resistor RD and the pseudo-inductor circuit LP. In this embodiment, a bias voltage (e.g., a voltage of 2 V) is applied to the connection node between the resistor RD and the pseudo-inductor circuit LP and the switch device 10.

The resistor RD is configured so that the resistance value Rd of the resistor RD is adjustable. The pseudo inductor circuit LP is configured so that the inductance value Lp of the pseudo inductor circuit LP is adjustable.

Figure 2 shows an equivalent circuit of the vibrator 2, drive circuit 5, and reverberation vibration suppression circuit 11 when the drive circuit 5 and reverberation vibration suppression circuit 11 are electrically connected.

The equivalent circuit shown in Figure 2 has the following circuit configuration: One end of resistor RD and one end of pseudo-inductor circuit LP are connected to one end of capacitor CP and one end of resistor RS. The other end of resistor RS is connected to one end of inductor LS via capacitor CS. The other end of capacitor CP and the other end of inductor LS are connected to the other end of resistor RD and the other end of pseudo-inductor circuit LP.

If the following formulas (1) and (2) are satisfied in the equivalent circuit shown in Figure 2, the reverberation vibration suppression circuit 12 can cancel the resonance frequency of the ultrasonic sensor 1 and appropriately suppress reverberation vibration. Note that Cp is the capacitance value of the capacitor CP, Rs is the resistance value of the resistor RS, Cs is the capacitance value of the capacitor CS, and Ls is the inductance value of the inductor LS.
Lp=Ls*Cs/Cp...(1)
Rd=(1/2)*√(Ls/Cp)...(2)

Figure 3 shows an example configuration of a pseudo-inductor circuit LP. The pseudo-inductor circuit LP of the example configuration shown in Figure 3 includes a capacitor C0, resistors R1 to R4, and operational amplifiers OP1 and OP2. Resistors R1 and R2 are fixed resistors, and resistors R3 and R4 are variable resistors.

The pseudo inductor circuit LP of the configuration example shown in FIG. 3 has the following circuit configuration. The connection node between one end of resistor R1 and the non-inverting input terminal of operational amplifier OP1 forms one end of the pseudo inductor circuit LP. The other end of resistor R1 is connected to one end of resistor R4 and the output terminal of operational amplifier OP2. The other end of resistor R4 is connected to the inverting input terminals of operational amplifiers OP1 and OP2 and one end of resistor R2. The other end of resistor R2 is connected to the output terminal of operational amplifier OP1 and one end of capacitor C0. The other end of capacitor C0 is connected to the non-inverting input terminal of operational amplifier OP1 and one end of resistor R3. The inductance value Lp of the pseudo inductor circuit LP of the configuration example shown in FIG. 3 is expressed by the following equation (3). Note that _C0 is the capacitance value of capacitor C0, _R1 is the resistance value of resistor R1, _R2 is the resistance value of resistor R2, and _R3 is the resistance value of resistor R3. _R4 is the resistance value of resistor R4.
Lp=C ₀ *R ₁ *R ₂ *R ₃ /R ₄ (3)

Next, we will explain the details of switch devices 9 and 10.

The switch device 9 includes a first switch SW1A, a second switch SW2A, and a control unit CNT1A. The second switch SW2A is connected in series with the first switch SW1A and has a lower withstand voltage than the first switch SW1A. The control unit CNT1A is configured to turn on the first switch SW1A and turn on the second switch SW2A when turning on the switch device 9, and to turn on the first switch SW1A and turn off the second switch SW2A when turning off the switch device 9.

The switch device 10 includes a first switch SW1B, a second switch SW2B, and a control unit CNT1B. The second switch SW2B is connected in series with the first switch SW1B and has a lower withstand voltage than the first switch SW1B. The control unit CNT1B is configured to turn on the first switch SW1B and turn on the second switch SW2B when turning on the switch device 10, and to turn on the first switch SW1B and turn off the second switch SW2B when turning off the switch device 10.

The control units CNT1A and CNT1B may each be included in the processing device 4. Furthermore, the control units CNT1A and CNT1B may be separate control units, or the control units CNT1A and CNT1B may be shared and formed as a single control unit.

In this embodiment, high-voltage N-channel MOS transistors (e.g., 80 V or higher) are used as the first switches SW1A and SW1B. The first switches SW1A and SW1B may each be a conventional NMOSFET (Negative-Channel Double-Diffused Metal Oxide Semiconductor Field Effect Transistor) or an NDMOSFET (Negative-Channel Double-Diffused Metal Oxide Semiconductor Field Effect Transistor). In this specification, a MOSFET refers to a field-effect transistor whose gate structure consists of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with low resistance, an insulating layer, and a P-type, N-type, or intrinsic semiconductor layer. In other words, the gate structure of a MOSFET is not limited to a three-layer structure of metal, oxide, and semiconductor. High-voltage MOS transistors have large gate capacitance, drain capacitance, and gate-drain parasitic capacitance, resulting in large switching noise. On the other hand, the second switches SW2A and SW2B have a lower withstand voltage than the first switches SW1A and SW1B, and therefore generate less switching noise than the first switches SW1A and SW1B.

In addition, in this embodiment, the first switch SW1A is an N-channel MOS transistor, and is configured to clamp the voltage at the connection node between the first switch SW1A and the second switch SW2A, i.e., the source voltage of the N-channel MOS transistor that is the first switch SW1A, when the first switch SW1A is on. The gate voltage of the first switch SW1A when it is on is adjusted so as not to exceed the withstand voltage of the second switch SW2A. This prevents the second switch SW2A from being destroyed by a high voltage being applied to the second switch SW2A. Similarly, in this embodiment, the first switch SW1B is an N-channel MOS transistor, and is configured to clamp the voltage at the connection node between the first switch SW1B and the second switch SW2B, i.e., the source voltage of the N-channel MOS transistor that is the first switch SW1B, when the first switch SW1B is on. The gate voltage of the first switch SW1B when it is on is adjusted so as not to exceed the withstand voltage of the second switch SW2B. This prevents the second switch SW2A from being destroyed by applying a high voltage to the second switch SW2B.

The switch device 9 ensures a high withstand voltage by using the first switch SW1A. Therefore, the switch device 9 can be installed in a location where a high voltage is applied. Furthermore, the switch device 9 switches the second switch SW2A without switching the first switch SW1A, thereby suppressing switching noise. Similarly, the switch device 10 ensures a high withstand voltage by using the first switch SW1B. Therefore, the switch device 10 can be installed in a location where a high voltage is applied. Furthermore, the switch device 10 switches the second switch SW2B without switching the first switch SW1B, thereby suppressing switching noise.

Figure 4 shows the schematic waveform of the output signal of ADC 8, i.e., the received signal based on the received ultrasonic waves. The horizontal axis of Figure 4 represents time, and the vertical axis represents signal level. The schematic waveform W1, indicated by a thin solid line, is the schematic waveform of the received signal at ultrasonic sensor 1. On the other hand, the schematic waveform W2, indicated by a thick dotted line, is the schematic waveform of the received signal when the second switch is removed from ultrasonic sensor 1 and the first switch is switched on. In the schematic waveform W2, indicated by the thick dotted line, a first peak PK1 due to the transmitted wave and reverberation vibration, a second peak PK2 due to switching noise of the switch device, and a third peak PK3 due to the received wave appear. On the other hand, in the schematic waveform W1, indicated by a thin solid line, the first peak PK1 due to the transmitted wave and reverberation vibration and the third peak PK3 due to the received wave appear, but the second peak PK2 due to switching noise of the switch device does not appear. Therefore, ultrasonic sensor 1 can suppress false detection caused by the second peak PK2.

The specific configuration of the second switches SW2A and SW2B is not particularly limited.

The second switches SW2A and SW2B may each be, for example, a single MOS transistor.

Furthermore, the second switches SW2A and SW2B may each be a parallel circuit of an N-channel MOS transistor Q1 and a P-channel MOS transistor Q2, as shown in FIG. 6, and the on/off of the N-channel MOS transistor Q1 may be synchronized with the on/off of the P-channel MOS transistor Q2. In this case, the switching noise of the second switches SW2A and SW2B can be reduced.

Furthermore, the second switches SW2A and SW2B may each be a parallel circuit of an N-channel MOS transistor Q3 and a dummy N-channel MOS transistor Q4, as shown in FIG. 7, for example, and may turn on/off the non-dummy N-channel MOS transistor Q3 and turn off the dummy N-channel MOS transistor Q4. In this case, too, the switching noise of the second switches SW2A and SW2B can be reduced.

Furthermore, unlike this embodiment, when the output terminal of the amplifier is connected to the source of the N-channel MOS transistor that serves as the first switch, the amplifier's output stage can be used as the second switch by switching between the enabled and disabled states of the amplifier. In this case, there is no need to provide a second switch between the first switch and the amplifier, which contributes to lower costs and space savings. The amplifier's output stage is, for example, a series circuit of a P-channel MOS transistor Q5 and an N-channel MOS transistor Q6 provided within amplifier AMP1, as shown in FIG. 7. The connection node between P-channel MOS transistor Q5 and N-channel MOS transistor Q6 becomes the output terminal TOUT of amplifier AMP1, and is connected to the first switch (not shown in FIG. 7).

The ultrasonic sensor 1 described above can be used, for example, as an on-board clearance sonar mounted on vehicle X shown in Figure 8. Furthermore, the drive device that drives the piezoelectric element can be mounted not only in ultrasonic sensors that sense the distance to a measurement object, but also in ultrasonic flowmeters that measure the velocity of a fluid, for example.

In addition to the above-described embodiments, various modifications can be made to the configuration of the present invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

For example, in the above embodiment, the switch device was mounted on an ultrasonic sensor, but the above-described switch device can also be mounted on products other than ultrasonic sensors. The above-described switch device is suitable for situations where high voltage resistance and reduced switching noise are required.

The switch device (9, 10) described above is configured (first configuration) to include a first switch (SW1A, SW1B), a second switch (SW2A, SW2B) connected in series to the first switch and having a lower withstand voltage than the first switch, and a control unit (CNT1A, CNT1B) configured to turn on the first switch and the second switch when the switch device is turned on, and to turn on the first switch and the second switch when the switch device is turned off.

The switch device having the first configuration described above can reduce switching noise.

In the switch device having the first configuration described above, the first switch may be configured to clamp the voltage of the connection node between the first switch and the second switch when the first switch is on (second configuration).

The switch device having the second configuration described above can prevent the second switch from being destroyed by applying a high voltage to the second switch.

In the switch device having the first or second configuration described above, the second switch may be configured as a parallel circuit of an N-channel MOS transistor and a P-channel MOS transistor (third configuration).

The switch device having the third configuration described above can reduce the switching noise of the second switch.

In the switch device having the first or second configuration described above, the second switch may be configured as a parallel circuit of an N-channel MOS transistor and a dummy N-channel MOS transistor (fourth configuration).

The switch device having the fourth configuration described above can reduce the switching noise of the second switch.

In the switch device having the first or second configuration described above, the second switch may be an output stage of an amplifier, and the output end of the amplifier may be configured to be connected to the first switch (fifth configuration).

The switch device having the fifth configuration described above eliminates the need for a second switch between the first switch and the amplifier, thereby reducing costs and space.

The drive device (3) described above is a configuration (sixth configuration) that includes a drive circuit (5) configured to drive the vibrator (2), a reverberation vibration suppression circuit (11) configured to suppress reverberation vibration of the vibrator, and a switch device having any of the first to fifth configurations described above that is configured to switch between electrical connection and electrical disconnection between the drive circuit and the reverberation vibration suppression circuit.

The drive device with the sixth configuration described above can reduce the switching noise of the switch device.

The ultrasonic sensor (1) described above has a configuration (seventh configuration) that includes the drive device of the sixth configuration and the vibrator.

The ultrasonic sensor having the seventh configuration described above can reduce the switching noise of the switch device, thereby suppressing false detections caused by the switching noise of the switch device.

The vehicle (X) described above has a configuration (eighth configuration) that includes an ultrasonic sensor, which is the seventh configuration described above.

A vehicle with the eighth configuration described above can reduce switching noise from the switch device, thereby suppressing false detections by the ultrasonic sensor caused by switching noise from the switch device.

REFERENCE SIGNS LIST 1 Ultrasonic sensor according to embodiment 2 Transducer 3 Driving device 4 Processing device 5 Driving circuit 6 LNA
7 LPF
8 ADC
9, 10 Switching device 11 Reverberation vibration suppression circuit AMP1 Amplifier C0, CP, CS Capacitor CNT1A, CNT1B Control unit R1 to R4, RD, RS Resistor LP Pseudo inductor circuit LS Inductor OP1, OP2 Operational amplifier Q1, Q3, Q4, Q6 N-channel MOS transistor Q2, Q5 P-channel MOS transistor SW1A, SW1B First switch SW2A, SW2B Second switch T1 to T5 External terminal TOUT Output end X Vehicle

Claims (5)

A first switch;
a second switch connected in series to the first switch and having a lower withstand voltage than the first switch;
A switch device comprising:
a control unit configured to turn on the first switch and the second switch when the switch device is turned on, and to turn on the first switch and the second switch when the switch device is turned off ,
The second switch is a parallel circuit of an N-channel MOS transistor and a P-channel MOS transistor . The switch device of claim 1, wherein the first switch is configured to clamp the voltage of a connection node between the first switch and the second switch when the first switch is on. a drive circuit configured to drive the transducer;
a reverberation vibration suppression circuit configured to suppress reverberation vibration of the vibrator;
a switch device according to claim 1 or 2 , configured to switch between electrical connection and electrical disconnection between the drive circuit and the reverberation vibration suppression circuit;
A drive device comprising: The drive device according to claim 3 ;
The vibrator;
An ultrasonic sensor comprising: A vehicle comprising the ultrasonic sensor according to claim 4 .