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DESCRIPTION JPWO2016167003

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DESCRIPTION JPWO2016167003
Abstract: An ultrasonic sensor capable of suppressing reverberation oscillation with a circuit
configuration simpler than that of the prior art is provided. The ultrasonic sensor (100) includes
a flat piezoelectric body (50) including an ultrasonic wave transmitting area (50A) and an
ultrasonic wave reflected wave receiving area (50B), and a transmitting area (50A) A common
electrode (30) provided in the reception area (50B), a transmission electrode (10) provided in the
transmission area (50A), and a reception provided in the reception area (50B) For the
transmission electrode (10), the transmission electrode (10) and the semiconductor element
(107) electrically connected to the reception electrode (20), and the transmission electrode (10)
and the reception electrode (20) And a semiconductor element (107) which switches the path
(109) between the conductive state and the non-conductive state. The semiconductor element
(107) turns on the path (109) after stopping the application of the alternating voltage, thereby
transmitting the reverberation signal output from the receiving area (50B) according to the
reverberation vibration of the ultrasonic wave to the transmission electrode Give feedback to
(10).
Ultrasonic sensor and control method thereof
[0001]
The present disclosure relates to an ultrasonic sensor provided with a piezoelectric element, and
more particularly, to control of the ultrasonic sensor.
[0002]
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1
Ultrasonic sensors provided with piezoelectric elements are known.
The ultrasonic sensor vibrates the piezoelectric element by applying an alternating voltage to the
piezoelectric element to emit an ultrasonic wave. The ultrasonic sensor detects an object based
on the reception of the ultrasonic wave reflected by the object.
[0003]
After the transmission of the ultrasonic waves, the vibration remains in the ultrasonic sensor. The
ultrasonic sensor is also referred to as this vibration (hereinafter, referred to as "reflex
vibration"). May be falsely detected as a reflected wave. In recent years, techniques for
suppressing reverberation vibration have been developed. For example, JP 2009-4916 A (Patent
Document 1) discloses an ultrasonic wave output device capable of suppressing reverberation
vibration.
[0004]
JP, 2009-4916, A
[0005]
The ultrasonic wave output device disclosed in Patent Document 1 includes a detection portion
that detects reverberation vibration and a transmission and reception portion that transmits and
receives ultrasonic waves.
The ultrasonic wave output device generates a signal for suppressing the reverberation vibration
according to the reverberation vibration detected in the detection part. After that, the ultrasonic
wave output device suppresses the reverberation vibration by returning the generated signal to
the transmitting and receiving part. In the ultrasonic output device, a detection portion for
detecting reverberation vibration is additionally provided, and therefore, a circuit configuration
for returning a signal for suppressing the reverberation vibration to the transmission / reception
portion is required. As a result, the circuit configuration becomes complicated.
[0006]
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The present disclosure has been made to solve the problems as described above, and an object in
one aspect is to provide an ultrasonic sensor capable of suppressing reverberation vibration with
a circuit configuration simpler than that of the prior art. It is. An object in another aspect is to
provide a control method of an ultrasonic sensor capable of suppressing reverberation vibration
with a circuit configuration simpler than the conventional one.
[0007]
According to an aspect, the ultrasonic sensor comprises a piezoelectric element. The piezoelectric
element includes a flat piezoelectric body including a transmitting area for transmitting an
ultrasonic wave when an AC voltage is applied and a receiving area for receiving a reflected wave
of the ultrasonic wave, a transmitting area, The common electrode provided in the reception area
and the transmission electrode are disposed so as to face the common electrode with the
transmission area interposed therebetween, and the transmission electrode provided in the
transmission area and the reception area provided therebetween. And a receiving electrode
which is disposed to face the common electrode and is provided in the receiving area. The
ultrasonic sensor is electrically connected to the transmission electrode and the reception
electrode, and is a semiconductor element that switches the electrical path between the
transmission electrode and the reception electrode between the conductive state and the
nonconductive state. Equipped with Preferably, the semiconductor element feeds back a
reverberation signal output from the reception area to the transmission electrode according to
the reverberation vibration of the ultrasonic wave by making the path conductive after stopping
the application of the alternating voltage.
[0008]
Preferably, the semiconductor element switches the path from the conductive state to the nonconductive state after feedback of the reverberation signal to the transmitting electrode.
[0009]
Preferably, the ultrasonic sensor further comprises an amplifier connected in series with the
semiconductor element in the path.
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The amplifier amplifies the reverberation signal and outputs the amplified reverberation signal to
the transmission electrode.
[0010]
Preferably, the ultrasonic sensor further comprises an I / V conversion circuit that converts
current to voltage. The I / V conversion circuit is provided on the path.
[0011]
Preferably, the I / V conversion circuit filters a signal in a frequency band that causes abnormal
oscillation of the ultrasonic sensor.
[0012]
Preferably, the I / V conversion circuit includes an operational amplifier and a capacitor.
The inverting input terminal of the operational amplifier is electrically connected to the receiving
electrode. The output terminal of the operational amplifier is electrically connected to the
amplifier. The capacitor is electrically connected to the inverting input terminal and the output
terminal.
[0013]
Preferably, the ultrasonic sensor further includes a receiving circuit electrically connected to the
I / V conversion circuit.
[0014]
Preferably, the ultrasonic sensor has a plurality of operation modes having different detection
distances.
The control conditions of the piezoelectric element are associated in advance with each of the
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plurality of operation modes according to the detection distance. The ultrasonic sensor switches
a plurality of operation modes in order, and controls the piezoelectric element under control
conditions corresponding to the current operation mode.
[0015]
Preferably, the ultrasonic sensor has a first operation mode and a second operation mode in
which the detection distance is longer than the first operation mode. The ultrasonic sensor
performs a process of feeding back the reverberation signal to the transmission electrode in the
first operation mode, and does not carry out a process of feeding back the reverberation signal to
the transmission electrode in the second operation mode.
[0016]
Preferably, the ultrasonic sensor further includes a step-up transformer provided on the path.
According to another aspect, a control method of an ultrasonic sensor is provided. The ultrasonic
sensor comprises a piezoelectric element. The piezoelectric element is a flat piezoelectric body
including a transmitting area for transmitting an ultrasonic wave when an alternating voltage is
applied, and a receiving area for receiving a reflected wave of the ultrasonic wave, a transmitting
area And a common electrode provided in the reception area, and the transmission electrode
provided in the transmission area, disposed so as to face the common electrode with the
transmission area interposed therebetween, and the reception area in between And a receiving
electrode disposed in the receiving area and disposed so as to face the common electrode. The
ultrasonic sensor is electrically connected to the transmission electrode and the reception
electrode, and is a semiconductor element that switches the electrical path between the
transmission electrode and the reception electrode between the conductive state and the
nonconductive state. Further comprising The control method includes the steps of making the
path nonconductive, applying the AC voltage to the transmission region after making the path
nonconductive, and making the path conductive after stopping the application of the AC voltage.
Feeding back a reverberation signal output from the reception area to the transmission electrode
according to the reverberation vibration of the ultrasonic wave.
[0017]
In one aspect, reverberant vibration can be suppressed with a circuit configuration simpler than
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that of the prior art. The above and other objects, features, aspects and advantages of the present
invention will become apparent from the following detailed description of the present invention
taken in conjunction with the accompanying drawings.
[0018]
It is a figure which shows an example of a circuit structure of the ultrasonic sensor according to
1st Embodiment. FIG. 7 is a conceptual diagram schematically showing an operation example of
the ultrasonic sensor according to the first embodiment. It is a flowchart showing a part of
process which the ultrasonic sensor according to 1st Embodiment performs. It is a figure which
shows each signal in case the ultrasonic sensor according to 1st Embodiment does not suppress
reverberation vibration. It is a figure which shows each signal in case the ultrasonic sensor
according to 1st Embodiment suppresses reverberation vibration. It is a figure which shows an
example of the circuit structure of the ultrasonic sensor according to a comparative example. It is
a figure which shows the noise signal produced by switching of a semiconductor element. It is a
figure which shows each signal of the ultrasonic sensor according to a comparative example. It is
a top view which shows the piezoelectric element according to 1st Embodiment. FIG. 1 is a
perspective view showing a piezoelectric element according to a first embodiment. FIG. 1 is a
perspective view showing a piezoelectric element according to a first embodiment and an
internal structure thereof. FIG. 3 is a perspective view showing a transmitting electrode, a
receiving electrode, and a common electrode provided in the piezoelectric element according to
the first embodiment. It is arrow sectional drawing along the XIII-XIII line in FIG. It is arrow
sectional drawing along the XIV-XIV line in FIG. It is arrow sectional drawing along the XV-XV
line in FIG. It is a figure which shows an example of a circuit structure of the ultrasonic sensor
according to 2nd Embodiment. It is a figure which shows an example of a circuit structure of the
ultrasonic sensor according to 3rd Embodiment. It is a figure which shows the parasitic
capacitance which arises in the ultrasonic sensor according to 3rd Embodiment. It is a figure
which shows an example of a circuit structure of the ultrasonic sensor according to 4th
Embodiment. It is a figure which shows an example of the circuit structure of the ultrasonic
sensor according to a comparative example. It is a figure which shows the simulation result in
case abnormal oscillation has arisen, and the simulation result in case abnormal oscillation has
not arisen. It is a figure which shows the relationship between the frequency of the signal which
flows into an ultrasonic sensor at the time of suppression of reverberation vibration, and the gain
of the ultrasonic sensor with respect to the said signal. It is a figure which shows the difference
of the reverberation time to the temperature in the ultrasonic sensor according to 4th
Embodiment, and the ultrasonic sensor according to a comparative example. It is a figure which
shows an example of a circuit structure of the ultrasonic sensor according to 5th Embodiment. It
is a figure which shows an example of a circuit structure of the ultrasonic sensor according to
6th Embodiment. It is a flowchart showing a part of process which the ultrasonic sensor
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according to 7th Embodiment performs. It is a figure which shows the content of the control
information in 7th Embodiment. It is a flowchart showing a part of process which the ultrasonic
sensor according to 8th Embodiment performs.
[0019]
Hereinafter, embodiments according to the present invention will be described with reference to
the drawings. In the following description, the same parts and components are denoted by the
same reference numerals. Their names and functions are also the same. Therefore, detailed
description of these will not be repeated. In addition, the embodiments or modifications
described below may be selectively combined as appropriate.
[0020]
First Embodiment [Circuit Configuration of Ultrasonic Sensor 100] An ultrasonic sensor 100
according to a first embodiment will be described with reference to FIG. FIG. 1 is a view showing
an example of the circuit configuration of the ultrasonic sensor 100. As shown in FIG.
[0021]
The ultrasonic sensor 100 is mounted on, for example, a vehicle, a smartphone or the like. The
ultrasonic sensor 100 measures the distance from itself to an object according to the time from
emitting ultrasonic waves to receiving reflected waves. Alternatively, the ultrasonic sensor 100
detects the presence of an object based on the reception of the reflected wave.
[0022]
As shown in FIG. 1, the ultrasonic sensor 100 includes a control circuit 101, a memory 102, a
signal generation circuit 104, a power supply 105, a semiconductor element 107, an amplifier
108, a reception circuit 110, and a piezoelectric element 200. And.
[0023]
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Control circuit 101 is, for example, a microcomputer.
The semiconductor element 107 is, for example, a transistor. The control circuit 101 drives the
semiconductor element 107 to switch the electrical path 109 between the transmitting electrode
10 and the receiving electrode 20 between the conductive state and the non-conductive state.
The control circuit 101 also reads data stored in the memory 102 and outputs a control signal
suitable for driving the ultrasonic sensor 100 to the signal generation circuit 104. The power
supply 105 outputs, for example, a DC voltage of 12 V to the signal generation circuit 104. The
signal generation circuit 104 generates an AC voltage from the DC voltage based on the control
signal output from the control circuit 101. The AC voltage is supplied to the piezoelectric
element 200 in a state of being boosted by an amplifier circuit (not shown) as necessary.
[0024]
The piezoelectric element 200 includes a transmitting electrode 10, a receiving electrode 20, a
common electrode 30, and a piezoelectric body 50. The piezoelectric element 200 is, for
example, flat. The transmission electrode 10 is provided with a terminal DRV. The receiving
electrode 20 is provided with a terminal REC. The common electrode 30 is provided with a
terminal COM. The piezoelectric element 200 has a three-terminal structure including a terminal
DRV, a terminal REC, and a terminal COM. The terminal COM is grounded but does not have to
be grounded.
[0025]
The piezoelectric body 50 includes a transmitting area 50A for transmitting an ultrasonic wave
and a receiving area 50B for receiving a reflected wave of the ultrasonic wave. The transmission
electrode 10 is disposed to face the common electrode 30 with the transmission area 50A
interposed therebetween, and is electrically connected to the transmission area 50A. The
receiving electrode 20 is disposed to face the common electrode 30 with the receiving area 50B
interposed therebetween, and is electrically connected to the receiving area 50B. The common
electrode 30 is electrically connected to the transmission area 50A and the reception area 50B.
[0026]
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The amplifier 108 is connected in series to the receiving electrode 20 and the semiconductor
element 107. As an example, the amplifier 108 is an inverting amplification circuit configured of
a resistor and an operational amplifier.
[0027]
The receiving circuit 110 receives the reflected wave, detects a wave receiving signal generated
in the receiving area 50B as a voltage value, and outputs the voltage value to the control circuit
101.
[0028]
In addition, although the ultrasonic sensor 100 of 3 terminal structure is shown by FIG. 1, the
ultrasonic sensor 100 may have a structure which consists of four or more terminals.
In this case, for example, an electrode different from the transmission electrode 10 and the
reception electrode 20 may be disposed to face the common electrode 30 with the piezoelectric
body 50 interposed therebetween. The electrode is electrically connected to the piezoelectric
body 50.
[0029]
[Operation of Ultrasonic Sensor 100] The operation of the ultrasonic sensor 100 according to the
present embodiment will be described with reference to FIG. FIG. 2 is a conceptual view
schematically showing an operation example of the ultrasonic sensor 100. As shown in FIG. In
FIG. 2, the control circuit 101, the memory 102, the power supply 105, and the receiving circuit
110 shown in FIG.
[0030]
As shown in FIG. 2, the ultrasonic sensor 100 according to the present embodiment includes a
step (A) of transmitting an ultrasonic wave, a step (B) of suppressing reverberation vibration
generated by the transmission of the ultrasonic wave, and Step (C) of receiving the reflected wave
is sequentially performed. Hereinafter, steps (A) to (C) will be described in order.
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[0031]
In step (A), the control circuit 101 drives the semiconductor element 107 to make the path 109
nonconductive. Thereafter, the control circuit 101 outputs a control command to the signal
generation circuit 104, whereby the signal generation circuit 104 applies an alternating voltage
to the transmission area 50A of the piezoelectric element 200. Preferably, the period of the
alternating voltage is equal to the resonant frequency of the transmission area 50A of the
piezoelectric element 200. The transmission area 50A starts to vibrate due to the inverse
piezoelectric effect by applying an AC voltage, and transmits an ultrasonic wave toward air and
the like.
[0032]
In step (B), the control circuit 101 applies an AC voltage to the transmission area 50A after a
predetermined time (for example, several microseconds to several milliseconds) has elapsed since
transmission of ultrasonic waves is started. Stop. At this time, the vibration of the transmission
area 50A can not be corrected immediately. That is, even after the application of the AC voltage
is stopped, the transmission area 50A vibrates for a while. This vibration (i.e., reverberation
vibration) affects the reception area 50B, and the reception area 50B resonates with the
transmission area 50A.
[0033]
The control circuit 101 switches the path 109 from the nonconductive state to the conductive
state after the application of the AC voltage is stopped. As a result, a closed circuit configured of
the transmission electrode 10, the transmission region 50A, the common electrode 30, the
reception region 50B, the reception electrode 20, and the path 109 in this order is formed. As
described above, the transmission area 50A and the reception area 50B vibrate due to
reverberation vibration. The reverberation vibration of the transmission area 50A and the
reception area 50B is suppressed by giving a signal of an appropriate phase so that the
reverberation vibration is canceled. For example, in the present embodiment, a voltage whose
phase is shifted 180 degrees with respect to the vibration velocity of the reverberation vibration
on the path 109 is fed back to the transmission terminal, whereby the reverberation vibration is
suppressed in a short time. That is, the reverberation vibration of the piezoelectric element 200
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is suppressed by feeding back the reverberation signal output from the reception area 50B to the
transmission electrode 10 as a voltage according to the reverberation vibration.
[0034]
Preferably, the amplifier 108 amplifies the reverberation signal output from the reception area
50B, and outputs the amplified reverberation signal to the transmission electrode 10. The
amplification factor of the reverberation signal may be predetermined at the time of design, or
may be changed in accordance with the magnitude of the AC voltage applied to the transmission
area 50A.
[0035]
In step (C), the control circuit 101 switches the path 109 from the conductive state to the nonconductive state after feeding back the reverberation signal to the transmission electrode 10.
Thus, the receiving area 50B can receive the ultrasonic wave reflected by the object. As a result,
the ultrasonic sensor 100 can accurately detect the reflected wave. The receiving area 50B
vibrates by receiving an ultrasonic wave, and outputs a signal by the piezoelectric effect to the
control circuit 101 as a voltage value.
[0036]
[Control Structure of Ultrasonic Sensor 100] The control structure of the ultrasonic sensor 100
will be described with reference to FIG. FIG. 3 is a flowchart showing a part of the process
performed by the ultrasonic sensor 100. The process of FIG. 3 is realized by the control circuit
101 (see FIG. 1) of the ultrasonic sensor 100 executing a program. In another aspect, part or all
of the processing may be performed by a central processing unit (CPU) or other hardware.
[0037]
In step S10, the control circuit 101 drives the semiconductor element 107 (see FIG. 2) to make
the path 109 (see FIG. 2) nonconductive.
[0038]
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In step S12, the control circuit 101 applies an alternating voltage to the transmission area 50A of
the piezoelectric element 200, and transmits an ultrasonic wave from the transmission area 50A.
[0039]
In step S20, control circuit 101 determines whether or not a predetermined time (for example,
several microseconds to several milliseconds) has elapsed since an AC voltage is applied to
transmission region 50A.
The control circuit 101 switches the control to step S22 when it is determined that a
predetermined time has elapsed since application of the AC voltage to the transmission area 50A
(YES in step S20).
If not (NO in step S20), control circuit 101 executes the process of step S20 again.
[0040]
In step S22, the control circuit 101 stops the application of the AC voltage to the transmission
area 50A.
[0041]
In step S24, the control circuit 101 drives the semiconductor element 107 to switch the path
109 from the nonconductive state to the conductive state.
Thereby, the reverberation signal output according to the reverberation vibration is fed back
from the reception area to the transmission electrode. As a result, reverberation vibration of the
ultrasonic sensor 100 is suppressed.
[0042]
In step S30, the control circuit 101 determines whether or not a predetermined time (for
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example, several microseconds to several milliseconds) has elapsed since the path 109 was
turned on. If the control circuit 101 determines that the predetermined time has elapsed since
the path 109 was turned on (YES in step S30), the control circuit 101 switches the control to
step S32. If not (NO in step S30), control circuit 101 executes the process of step S30 again.
[0043]
In step S32, the control circuit 101 drives the semiconductor element 107 to switch the path
109 from the conductive state to the non-conductive state.
[0044]
In step S34, the control circuit 101 receives the reflected wave of the transmitted ultrasonic
wave, and outputs the reflected wave as a voltage value to the receiving circuit 110 (see FIG. 1).
[0045]
[Comparison Result 1] Referring to FIGS. 4 and 5, the output of the ultrasonic sensor 100 in the
case of suppressing the reverberation vibration is compared with the output of the ultrasonic
sensor 100 in the case of not suppressing the reverberation vibration.
FIG. 4 is a diagram showing an output waveform of the ultrasonic sensor 100 when the
reverberation vibration is not suppressed.
FIG. 5 is a diagram showing an output waveform of the ultrasonic sensor 100 when the
reverberation vibration is suppressed.
[0046]
The graph (A) of FIG. 4 shows a control signal that the control circuit 101 (see FIG. 1) outputs to
the signal generation circuit 104 (see FIG. 1). When receiving the control signal, the signal
generation circuit 104 applies an alternating voltage to the transmission area 50A (see FIG. 1) of
the piezoelectric element 200.
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[0047]
More specifically, the control circuit 101 outputs a control signal to the signal generation circuit
104 (see FIG. 1) from time T1 to time T2. Thereby, the signal generation circuit 104 applies an
alternating voltage to the transmission area 50A. After time T2, the control circuit 101 stops the
output of the control signal to the signal generation circuit 104. Thereby, the signal generation
circuit 104 stops applying the AC voltage to the transmission area 50A of the piezoelectric
element 200.
[0048]
The control signal which the control circuit 101 outputs to the semiconductor element 107 (refer
FIG. 1) is shown by the graph (B) of FIG. As shown in the graph (B) of FIG. 4, the control circuit
101 does not output a control signal to the semiconductor element 107 from the start to the end
of the control. That is, the path 109 (see FIG. 1) of the reverberation signal is maintained in the
non-conductive state, and the reverberation signal is not fed back to the transmission area 50A.
[0049]
The output waveform of the ultrasonic sensor 100 is shown in the graph (C) of FIG. In the control
example of FIG. 4, since the reverberation signal is not fed back, the piezoelectric element 200
vibrates also after time T2 when the application of the AC voltage is stopped. The reflected wave
received at time T4 is buried in reverberation vibration (see dotted line 301). Therefore, the
ultrasonic sensor 100 can not detect a reflected wave.
[0050]
The control signal that the control circuit 101 outputs to the signal generation circuit 104 is
shown in the graph (A) of FIG. 5. The graph (A) of FIG. 5 is the same as the graph (A) of FIG. 4
and thus the description thereof will not be repeated.
[0051]
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The control signal that the control circuit 101 outputs to the semiconductor element 107 is
shown in the graph (B) of FIG. 5. More specifically, the control circuit 101 makes the path 109
non-conductive from the start of control until time T2. From time T2 to time T3, the control
circuit 101 drives the semiconductor element 107 to make the path 109 conductive. That is, the
ultrasonic sensor 100 feeds back the reverberation signal output from the reception area 50B to
the transmission area 50A. After time T3, the control circuit 101 causes the path 109 to be
nonconductive.
[0052]
The graph (C) of FIG. 5 shows the output waveform of the ultrasonic sensor 100 when the
reverberation vibration is suppressed. The reverberation vibration is suppressed by feedback of
the reverberation signal to the transmission area 50A from time T2 to time T3 (see the dotted
line 303). Thereby, the ultrasonic sensor 100 can detect the reflected wave received at time T4.
[0053]
Thus, by suppressing the reverberation vibration, the ultrasonic sensor 100 can detect the
reflected wave without waiting for the reverberation vibration to naturally settle. As a result, the
ultrasonic sensor 100 can detect an object present closer to it, and can improve the detection
accuracy and the distance measurement accuracy of the object.
[0054]
[Comparison Result 2] Referring to FIG. 6, the ultrasonic sensor 100 according to the first
embodiment is compared with the ultrasonic sensor 100X according to the comparative example.
FIG. 6 is a diagram showing an example of the circuit configuration of the ultrasonic sensor 100X
according to the comparative example.
[0055]
(Circuit Configuration of Ultrasonic Sensor 100X) First, the circuit configuration of the ultrasonic
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sensor 100X according to the comparative example will be described. As shown in FIG. 6, the
ultrasonic sensor 100X includes a signal generation circuit 104, semiconductor elements 120
and 122, amplifiers 121A to 121C, 123A to 123C, and a piezoelectric element 200X.
[0056]
The piezoelectric element 200X includes a transmitting / receiving electrode 10X, a monitoring
electrode 20X, a common electrode 30X, and a piezoelectric body 50X. The transmission /
reception electrode 10X is provided with a terminal DRV. A terminal MON is provided on the
monitor electrode 20X. A terminal COM is provided on the common electrode 30X.
[0057]
The signal generation circuit 104 is connected to the terminal DRV and the terminal COM. The
amplifiers 121A to 121C are connected in series between the terminal MON and the
semiconductor element 120. The semiconductor element 120 is connected to the amplifier 121C
and the terminal DRV. The semiconductor element 122 is connected to the terminal DRV, and is
connected in parallel to the semiconductor element 120. The amplifiers 123 </ b> A to 123 </ b>
C are connected in series to the semiconductor element 122.
[0058]
(Operation of Ultrasonic Sensor 100X) The operation of the ultrasonic sensor 100X according to
the comparative example will be described with reference to FIG. When transmitting ultrasonic
waves, the ultrasonic sensor 100X outputs a control signal to the signal generation circuit 104 to
apply an alternating voltage between the terminal DRV and the terminal COM. At this time, the
ultrasonic sensor 100X drives the semiconductor element 120 to make the path 126
nonconductive, and drives the semiconductor element 122 to make the path 127 nonconductive.
[0059]
Next, the ultrasonic sensor 100X stops the application of the alternating voltage and switches the
path 126 from the non-conduction state to the conduction state. Thereby, the reverberation
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signal corresponding to the reverberation vibration of the piezoelectric element 200X is
amplified by the amplifiers 121A to 121C and then fed back to the transmission / reception
electrode 10X. As a result, reverberation vibration is suppressed.
[0060]
Thereafter, the ultrasonic sensor 100X switches the path 126 from the conductive state to the
non-conductive state, and switches the path 127 from the non-conductive state to the conductive
state. When receiving the reflected wave of the ultrasonic wave, the ultrasonic sensor 100X
amplifies the signal generated according to the reflected wave by the amplifiers 123A to 123C,
and outputs the amplified signal to the receiving circuit.
[0061]
(Advantage 1 of Ultrasonic Sensor 100) As described above, in the ultrasonic sensor 100X
according to the comparative example, the monitor electrode 20X for detecting reverberation
vibration and the transmission / reception electrode 10X for transmitting / receiving ultrasonic
waves. It is configured separately. Therefore, both a circuit configuration for feeding back a
reverberation signal and a circuit configuration for receiving a reflected wave are required. More
specifically, as a circuit configuration for feeding back a reverberation signal, the semiconductor
element 120, the amplifiers 121A to 121C, and the like are required. As a circuit configuration
for receiving a reflected wave, a semiconductor element 122, amplifiers 123A to 123C, and the
like are required. That is, the ultrasonic sensor 100X requires two semiconductor elements 120
and 122 and six amplifiers 121A to 121C and 123A to 123C.
[0062]
On the other hand, in the ultrasonic sensor 100 according to the first embodiment, an electrode
for detecting reverberation vibration and an electrode for receiving an ultrasonic wave are
provided as one reception electrode 20. . Therefore, the ultrasonic sensor 100 can share circuit
elements in the step of detecting reverberation vibration and the step of receiving a reflected
wave. More specifically, the ultrasonic sensor 100 can realize both the detection of the
reverberation vibration and the reception of the reflected wave by the same semiconductor
element 107 and the same amplifier 108. Similarly, in an ultrasonic sensor 100C according to a
fourth embodiment described later, both the detection of the reverberation vibration and the
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reception of the reflected wave are the same amplifier as that of the same semiconductor element
107 (amplifier 108, operational amplifier 141, buffer circuit 113).
[0063]
Thus, the ultrasonic sensor 100 can realize suppression of reverberation vibration with a circuit
configuration simpler than that of the ultrasonic sensor 100X. By simplifying the circuit
configuration of the ultrasonic sensor 100, downsizing of the ultrasonic sensor 100 is realized.
[0064]
(Advantage 2 of Ultrasonic Sensor 100) The advantages of the ultrasonic sensor 100 according
to the first embodiment will be further described with reference to FIGS. 7 and 8. FIG. 7 is a
diagram showing a noise signal generated by switching of semiconductor elements. FIG. 8 is a
diagram showing an output waveform of the ultrasonic sensor 100X (see FIG. 6) according to the
comparative example.
[0065]
As described in FIG. 6, when suppressing the reverberation vibration, the ultrasonic sensor 100X
drives the semiconductor element 120 to make the path 126 conductive, and drives the
semiconductor element 122 to make the path 127 nonconductive Make it When receiving the
reflected wave, the ultrasonic sensor 100X drives the semiconductor element 120 to make the
path 126 non-conductive, and drives the semiconductor element 122 to make the path 127
conductive.
[0066]
Such switching between the semiconductor elements 120 and 122 generates a noise signal. The
noise signal is caused by circuit connection between different potentials, clock feedthrough of the
semiconductor element, charge injection of the semiconductor element, and the like. The cause of
such a noise signal will be described in more detail with reference to FIG.
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[0067]
The circuit example (A) of FIG. 7 shows a semiconductor element M1 as a PMOS (Positivechannel Metal Oxide Semiconductor) transistor and a semiconductor element M2 as a Negativechannel Metal Oxide Semiconductor (NMOS) transistor. In the semiconductor element M1,
parasitic capacitances C1 and C2 are generated. In the semiconductor element M2, parasitic
capacitances C3 and C4 are generated.
[0068]
The graph (B) of FIG. 7 shows the waveform of the control signal at the position P1. The control
signal is output by the control circuit CLK. The control signal is inverted by the element INV and
then output to the semiconductor element M1, and is also output to the semiconductor element
M2 without being inverted. In the example of the graph (B), the semiconductor elements M1 and
M2 are driven at times T11 and T12.
[0069]
The graph (C) of FIG. 7 shows the change of the voltage at the position P2. The graph (D) of FIG.
7 shows the change of the voltage at the position P3. As shown in the graphs (C) and (D), socalled potential jumps (ringing) due to the parasitic capacitances C1 to C4 occur at times T11
and T12 at which the semiconductor elements M1 and M2 are driven. reference). Further, a noise
signal from the control circuit CLK passes through the parasitic capacitances C1 to C4 and flows
into the signal line AZ (see the dotted line 305).
[0070]
The noise signal generated by switching of the semiconductor element is also generated in the
ultrasonic sensor 100X according to the comparative example. The control signal which the
ultrasonic sensor 100X outputs to the signal generation circuit 104 (refer FIG. 6) is shown by the
graph (A) of FIG. The control signal which the ultrasonic sensor 100X outputs to the
semiconductor element 120 is shown by the graph (B) of FIG. The graph (C) of FIG. 8 shows the
output waveform of the ultrasonic sensor 100X.
11-04-2019
19
[0071]
As shown in the graph (C) of FIG. 8, at times T2 and T3 when the semiconductor element 120 is
driven, jumps in potential occur as noise signals (see dotted lines 307 and 309). In general, since
the strength of a received signal generated by a reflected wave from an object is very weak, the
gain is increased by several thousand to several ten thousand in the receiving circuit. Therefore,
even if the noise signal itself is weak, the noise signal is amplified by several thousand to several
ten thousand times. The amplified noise signal flows to the receiving circuit 110 and appears in
the output waveform.
[0072]
On the other hand, the ultrasonic sensor 100 according to the first embodiment does not require
a semiconductor element for the receiving circuit 110, as shown in FIG. As a result, since the
noise signal generated by switching of the semiconductor element is not generated in the
receiving circuit 110, the above problem does not occur.
[0073]
[Structure of Piezoelectric Element 200] The structure of the piezoelectric element 200 provided
in the ultrasonic sensor 100 will be described with reference to FIGS. FIG. 9 is a plan view
showing the piezoelectric element 200. As shown in FIG. FIG. 10 is a perspective view showing
the piezoelectric element 200. As shown in FIG. FIG. 11 is a perspective view showing the
piezoelectric element 200 and its internal structure. FIG. 12 is a perspective view showing the
transmitting electrode 10, the receiving electrode 20, and the common electrode 30 provided in
the piezoelectric element 200. As shown in FIG. FIG. 13 is a sectional view taken along line XIIIXIII in FIG. FIG. 14 is a cross-sectional view taken along line XIV-XIV in FIG. FIG. 15 is a sectional
view taken along the line XV-XV in FIG.
[0074]
In the multilayer ultrasonic sensor, as the number of stacked piezoelectric elements increases,
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the sound pressure at the time of transmission of ultrasonic waves increases, but the sensitivity
at the time of reception of reflected waves decreases. On the contrary, the smaller the number of
stacked piezoelectric elements, the lower the sound pressure at the time of transmission of
ultrasonic waves, but the higher the sensitivity at the time of reception of reflected waves.
Focusing on this point, the ultrasonic sensor 100 is configured such that the number of stacked
piezoelectrics in the transmission region 50A is larger than the number of stacked piezoelectrics
in the reception region 50B.
[0075]
In FIG. 9 to FIG. 15, arrows X, Y and Z are shown for convenience of explanation. Arrows X, Y, Z
are orthogonal to one another. Hereinafter, each configuration of the piezoelectric element 200
may be described with reference to arrows X, Y, and Z. However, the arrangement relationship of
each configuration (feature related to orthogonal and parallel) is not limited to the arrangement
shown by arrows X, Y, and Z. It is not limited to the relationship.
[0076]
(Piezoelectric Element 200) As shown in FIGS. 9 to 15, the piezoelectric element 200 includes a
transmitting electrode 10, a receiving electrode 20, a common electrode 30, and a piezoelectric
body 50. The outer shape of the piezoelectric body 50 is a substantially rectangular
parallelepiped (see FIGS. 10 and 11), and the piezoelectric body 50 has an upper surface 51, side
surfaces 52 to 55, and a lower surface 56.
[0077]
The upper surface 51 is a surface of the piezoelectric body 50 located on the side of the arrow Z
direction, and the lower surface 56 is a surface of the piezoelectric body 50 located on the side
opposite to the direction of the arrow Z. The side surfaces 52 and 54 are surfaces of the
piezoelectric body 50 orthogonal to the arrow X direction, and have a positional relationship in
which they face each other. The side surfaces 53 and 55 are surfaces orthogonal to the arrow Y
direction in the piezoelectric body 50, and have a positional relationship in which they face each
other.
11-04-2019
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[0078]
(Transmission Electrode 10) The transmission electrode 10 includes a side wall 11, an upper
surface 12, and intermediate portions 13 and 14 (see FIG. 12). The side wall portion 11, the
upper surface portion 12, and the middle portions 13 and 14 all have a plate-like shape. The side
wall portion 11 faces the side surface 52 (see FIG. 10) of the piezoelectric body 50 and is
disposed in contact with the side surface 52. The side wall portion 11 has a surface shape that
covers the entire side surface 52 of the piezoelectric body 50 (see FIGS. 9, 14 and 15).
[0079]
The upper surface portion 12 is continuously provided at the end of the side wall portion 11 in
the direction of the arrow Z (and the side opposite to the arrow Y), and is disposed on the upper
surface 51 of the piezoelectric body 50. Assuming that the dimension in the arrow Y direction is
“width”, the top surface 12 is narrower than the side wall 11. The end of the upper surface 12
in the direction opposite to the arrow Y has a flush relationship with the side surface 53 of the
piezoelectric body 50. The upper surface portion 12 is provided with a terminal DRV. A wire (not
shown) is connected to the terminal DRV.
[0080]
The top surface portion 12 and the middle portions 13 and 14 have a parallel positional
relationship, and the middle portions 13 and 14 are located on the side opposite to the arrow Z
with respect to the top surface portion 12. The middle portion 13 is located between the upper
surface portion 12 and the middle portion 14. The middle portion 13 and the middle portion 14
face each other at an interval. The intermediate portions 13 and 14 are portions of the
transmission electrode 10 disposed inside the piezoelectric body 50, and when the piezoelectric
element 200 is completed, these are not visually recognized (see FIG. 10). Although details will
be described later, an intermediate portion 33 of the common electrode 30 is disposed between
the intermediate portion 13 and the intermediate portion 14 (see FIGS. 13 to 15 and the like).
[0081]
Inside the intermediate portions 13 and 14, hollow portions 13H and 14H (FIG. 12) having a
11-04-2019
22
circular shape are respectively provided. The size (outer diameter) of the cut out portions 13H
and 14H is larger than the size (outer diameter) of the disc portion 21 of the receiving electrode
20. The positions of the cutouts 13H and 14H correspond to the position of the disc portion 21
of the receiving electrode 20. The hollowed parts 13H and 14H are disposed at positions not
overlapping the projection image of the disk part 21 when the disk part 21 of the receiving
electrode 20 is projected in the direction opposite to the arrow Z (see FIGS. 13 and 15). ).
[0082]
The notches 13T and 14T are also provided inside the intermediate portions 13 and 14,
respectively. The notches 13T and 14T are arranged so as to extend from the side where the
hollows 13H and 14H are located toward the side where the side surface 52 of the piezoelectric
body 50 is located (in the direction opposite to the arrow X) Be done. The positions of the
notches 13T and 14T correspond to the position of the extension 22 of the receiving electrode
20. As shown in FIGS. 12 and 14, the ends of the intermediate portions 13 and 14 in the
direction opposite to the arrow X are connected to the side wall 11. On the other hand, the end
portions of the intermediate portions 13 and 14 in the arrow X direction are not connected to
the side wall portion 31 of the common electrode 30 and are separated from the side wall
portion 31.
[0083]
(Receiver Electrode 20) The receiver electrode 20 includes a disk portion 21 and an extension 22
and has a plate-like shape as a whole (see FIG. 12). The extending portion 22 has a rectangular
outer shape, and has a shape extending outward from the outer edge of the disk portion 21. The
extending portion 22 is provided with a terminal REC. A wire (not shown) is connected to the
terminal REC.
[0084]
The receiving electrode 20 is disposed on the upper surface 51 such that the disc portion 21 is
positioned at the center of the upper surface 51 of the piezoelectric body 50. The extension
portion 22 is arranged to extend from the side where the disk portion 21 is located toward the
side where the side surface 52 of the piezoelectric body 50 is located (in the direction opposite to
the arrow X).
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23
[0085]
(Common Electrode 30) The common electrode 30 includes a side wall 31, an upper surface 32,
a middle 33, and a lower surface 34 (see FIG. 12). The side wall portion 31, the upper surface
portion 32, the middle portion 33 and the lower surface portion 34 all have a plate-like shape.
The side wall portion 31 is disposed to face the side surface 54 (FIG. 10) of the piezoelectric
body 50 and to be in contact with the side surface 54. The side wall portion 31 has a surface
shape that covers the entire side surface 54 of the piezoelectric body 50 (see FIGS. 9, 14 and 15).
The lower surface portion 34 is disposed to face the lower surface 56 of the piezoelectric body
50 and to be in contact with the lower surface 56. The lower surface portion 34 has a surface
shape that covers the entire lower surface 56 of the piezoelectric body 50.
[0086]
The upper surface portion 32 is continuously provided at the end of the side wall portion 31 in
the direction of the arrow Z, and is disposed on the upper surface 51 of the piezoelectric body
50. Assuming that the dimension in the arrow Y direction is “width”, the width of the upper
surface portion 32 is equal to the width of the upper surface 51 of the piezoelectric body 50.
Both end portions of the upper surface portion 32 in the arrow Y have a flush relationship with
the side surfaces 53 and 55 of the piezoelectric body 50, respectively. The upper surface portion
32 is provided with a terminal COM. A wire (not shown) is connected to the terminal COM.
[0087]
The upper surface portion 32, the middle portion 33 and the lower surface portion 34 have a
parallel positional relationship, and the intermediate portion 33 and the lower surface portion 34
are located on the side opposite to the arrow Z with respect to the upper surface portion 32. The
intermediate portion 33 is located between the upper surface 32 and the lower surface 34. The
middle portion 33 is a portion of the common electrode 30 disposed inside the piezoelectric body
50, and the middle portion 33 is not visually recognized in a state where the piezoelectric
element 200 is completed (see FIG. 10).
[0088]
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24
Inside the upper surface portion 32 and the middle portion 33, cut out portions 32H and 33H
(see FIG. 12) having a circular shape are respectively provided. The size (outer diameter) of the
hollow portions 32H and 33H is larger than the size (outer diameter) of the disc portion 21 of
the receiving electrode 20. The positions of the hollow portions 32H and 33H correspond to the
position of the disc portion 21 of the receiving electrode 20. The disk portion 21 of the receiving
electrode 20 is disposed inside the hollow portion 32H (see FIG. 10). The hollowed portion 33H
is disposed at a position not overlapping the projected image of the disk portion 21 when the
disk portion 21 of the receiving electrode 20 is projected in the direction opposite to the arrow Z
(see FIGS. 13 and 15).
[0089]
Notches 32T and 33T are also provided inside the upper surface 32 and the middle 33,
respectively. The notches 32T and 33T are arranged to extend from the side where the hollow
portions 32H and 33H are located toward the side where the side surface 52 of the piezoelectric
body 50 is located (in the direction opposite to the arrow X) Be done. The positions of the
notches 32T and 33T correspond to the position of the extension 22 of the receiving electrode
20. The extension 22 of the receiving electrode 20 is disposed inside the notch 32T (see FIG. 10).
A receding portion 32F is provided in a portion of the upper surface portion 32 in the direction
opposite to the arrow Y. The receding portion 32F is a portion for permitting the arrangement of
the upper surface portion 12 of the transmission electrode 10.
[0090]
As shown in FIGS. 12 and 14, ends of the upper surface portion 32, the middle portion 33 and
the lower surface portion 34 in the arrow X direction are connected to the side wall portion 31.
On the other hand, the end of the upper surface 32, the intermediate portion 33 and the lower
surface 34 in the direction opposite to the arrow X is not connected to the side wall 11 of the
transmission electrode 10 and is separated from the side wall 11.
[0091]
(Transmission Area 50A and Reception Area 50B) As shown in FIGS. 13 to 15, the transmission
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25
area 50A and the reception area 50B are formed inside the piezoelectric body 50. The
transmission area 50A has a four-layer structure including the piezoelectric layers A1 to A4. The
white arrows in FIG. 13 to FIG. 15 indicate the polarization directions of the respective
piezoelectric layers.
[0092]
The piezoelectric layers A1 to A4 are formed between the middle portion 13 of the transmission
electrode 10, the middle portion 33 of the common electrode 30, and the transmission electrode
10 between four piezoelectric layers made of thin piezoelectric ceramic having a strip shape.
These are laminated by interposing the middle part 14 of the above, and they are manufactured
by baking integrally. The piezoelectric layers A1 to A4 are electrically connected in parallel by
the transmission electrode 10 and the common electrode 30.
[0093]
The receiving area 50B has a single-layer structure of the piezoelectric layer B1. The
piezoelectric layer B1 is manufactured by laminating the four layers of piezoelectric layers made
of thin piezoelectric ceramic having a strip shape without interposing an electrode and firing the
layers integrally.
[0094]
The lower surface portion 34 of the common electrode 30 has a shape that extends over both the
transmission area 50A and the reception area 50B. The upper surface portion 12 of the
transmission electrode 10 faces the lower surface portion 34 of the common electrode 30 with
the transmission region 50A including the piezoelectric layers A1 to A4 interposed therebetween.
The disc portion 21 of the receiving electrode 20 is opposed to the lower surface portion 34 of
the common electrode 30 with the receiving area 50B including the piezoelectric layer B1
interposed therebetween. That is, in the piezoelectric body 50, the region located between the
upper surface portion 12 of the transmission electrode 10 and the lower surface portion 34 of
the common electrode 30 functions as the transmission region 50A and is shared with the disk
portion 21 of the reception electrode 20. A region located between the electrode 30 and the
lower surface portion 34 functions as a reception region 50B. As shown in FIGS. 13 and 15, in
the present embodiment, the transmission area 50A and the reception area 50B are formed
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26
adjacent to each other in the XY plane direction.
[0095]
[Summary] As described above, the ultrasonic sensor 100 according to the present embodiment
includes the semiconductor element 107 electrically connected to the transmission electrode 10
and the reception electrode 20 after the application of the alternating voltage is stopped. By
driving, the path 109 between the transmitting electrode 10 and the receiving electrode 20 is
brought into conduction. Thereby, the ultrasonic sensor 100 feeds back the reverberation signal
output from the receiving area 50B to the transmission electrode 10 according to the
reverberation vibration generated after the transmission of the ultrasonic wave.
[0096]
The closer the object is to the ultrasonic sensor 100, the shorter the time from the transmission
of the ultrasonic wave to the reception of the reflected wave. The ultrasonic sensor 100 can
detect the reflected wave without waiting for the reverberation vibration to settle, so that even if
the object is present nearby, the reflected wave from the object can be detected.
[0097]
Further, in the ultrasonic sensor 100 according to the first embodiment, an electrode for
detecting reverberation vibration and an electrode for receiving an ultrasonic wave are provided
as one reception electrode 20. Therefore, the ultrasonic sensor 100 can share circuit elements
with a detection circuit for detecting reverberation vibration and a reception circuit for receiving
a reflected wave. Thereby, the circuit configuration of the ultrasonic sensor 100 is simplified, and
the miniaturization of the ultrasonic sensor 100 is realized.
[0098]
In particular, in the present embodiment, it is not necessary to provide a semiconductor element
for the reception circuit 110. Therefore, in the ultrasonic sensor 100, the noise signal generated
by switching of the semiconductor element can be suppressed. As a result, the ultrasonic sensor
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100 can suppress the S / N (Signal / Noise) ratio.
[0099]
Although the example in which the semiconductor element 107 is configured as a transistor
driven by the control circuit 101 is described in the above embodiment, the semiconductor
element 107 is not limited to the transistor. For example, the semiconductor element 107 may be
configured by a diode as shown in FIG. 24 described later. In this case, the reverberation signal is
higher than a threshold voltage (for example, forward voltage) for driving the diode, and the
output signal accompanying the reflected wave of the ultrasonic wave is lower than the threshold
voltage. Therefore, in the step of suppressing the reverberation vibration, the reverberation
signal is fed back to the transmission electrode 10 as a voltage, but in the step of receiving the
reflected wave of the ultrasonic wave, the output signal is not fed back to the transmission
electrode 10. Therefore, even in this case, the same effect as the ultrasonic sensor 100 according
to the first embodiment can be obtained.
[0100]
Second Embodiment [Ultrasonic Sensor 100A] An ultrasonic sensor 100A according to a second
embodiment will be described with reference to FIG. FIG. 16 is a diagram showing an example of
the circuit configuration of the ultrasonic sensor 100A.
[0101]
The ultrasonic sensor 100A differs from the ultrasonic sensor 100 according to the first
embodiment in that the ultrasonic sensor 100A further includes a phase adjuster 111. The
configuration other than the phase adjuster 111 is as described above, and therefore the
description will not be repeated.
[0102]
As shown in FIG. 16, the ultrasonic sensor 100A includes a signal generation circuit 104, a
semiconductor element 107, an amplifier 108, a reception circuit 110, a phase adjuster 111, and
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a piezoelectric element 200. The phase adjuster 111 is electrically connected to the
semiconductor element 107 and the amplifier 108 in the path 109.
[0103]
The reverberation signal may deviate more than intended depending on the circuit
characteristics and the surrounding environment (eg, temperature).
[0104]
The phase adjuster 111 adjusts the phase of the reverberation signal from the receiving area 50B
so that the reverberation vibration can be suppressed best, and feeds back the adjusted
reverberation signal to the transmission electrode 10.
The magnitude of the phase shifted by the phase adjuster 111 may be predetermined at the time
of design, or may be changed according to the surrounding environment (for example,
temperature etc.), circuit characteristics, and the like.
[0105]
[Summary] As described above, the ultrasonic sensor 100A according to the second embodiment
feeds back the reverberation signal to the transmission electrode 10 in the phase-adjusted state.
Thus, the ultrasonic sensor 100A can more reliably suppress the reverberation vibration.
[0106]
Third Preferred Embodiment Ultrasonic Sensor 100B An ultrasonic sensor 100B according to a
third preferred embodiment will be described with reference to FIG. FIG. 17 is a diagram showing
an example of the circuit configuration of the ultrasonic sensor 100B.
[0107]
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29
The ultrasonic sensor 100B differs from the ultrasonic sensor 100A according to the second
embodiment in that the ultrasonic sensor 100B further includes a buffer circuit 113. The
configuration other than buffer circuit 113 is as described above, and therefore the description
will not be repeated.
[0108]
As shown in FIG. 17, the ultrasonic sensor 100B includes a signal generation circuit 104, a
semiconductor element 107, an amplifier 108, a reception circuit 110, a phase adjuster 111, a
buffer circuit 113, and a piezoelectric element 200. Prepare. The buffer circuit 113 is electrically
connected to the phase adjuster 111 and the semiconductor element 107 in the path 109.
[0109]
By providing the buffer circuit 113, the ultrasonic sensor 100B prevents the noise signal from
flowing into the receiving circuit 110 from the transmission electrode 10 through the path 109.
Thereby, the SN ratio in the receiving circuit 110 can be lowered.
[0110]
[Summary] As described above, in the ultrasonic sensor 100B according to the third embodiment,
the buffer circuit 113 is provided with the path 109 provided for reducing reverberation
vibration, and for receiving ultrasonic waves. And the path 114 provided in the circuit are more
electrically separated. Thereby, the ultrasonic sensor 100B can prevent the noise signal from
flowing into the receiving circuit 110.
[0111]
Fourth Embodiment [New Finding] With reference to FIG. 18, a finding newly found in an
ultrasonic sensor 100B according to the third embodiment will be described. FIG. 18 is a diagram
showing parasitic capacitance generated in the ultrasonic sensor 100B.
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30
[0112]
The inventors newly discovered that a parasitic capacitance 115 is generated between the
transmitting electrode 10 and the receiving electrode 20. As far as the inventors are aware, there
is no prior art document showing that parasitic capacitance 115 is generated between the
transmitting electrode 10 and the receiving electrode 20. As a reason why this has not been
discovered so far, it is conceivable that the ultrasonic sensor itself of the three-terminal structure
consisting of the transmission electrode 10, the reception electrode 20, and the common
electrode 30 is novel.
[0113]
The reverberation signal output from the transmission area 50A and the reverberation signal fed
back from the reception area 50B may pass through the parasitic capacitance 115 and flow into
the path 109. As a result, the piezoelectric element 200 may oscillate abnormally. The ultrasonic
sensor 100C according to the fourth embodiment can prevent such abnormal oscillation as
described below.
[0114]
[Ultrasonic Sensor 100C] An ultrasonic sensor 100C according to the fourth embodiment will be
described with reference to FIG. FIG. 19 is a diagram showing an example of the circuit
configuration of the ultrasonic sensor 100C.
[0115]
The ultrasonic sensor 100C differs from the ultrasonic sensor 100B according to the third
embodiment in that the ultrasonic sensor 100C further includes a filter circuit 140 as an I / V
conversion circuit and a protection circuit 160. The configuration other than filter circuit 140
and protection circuit 160 is as described above, and therefore the description will not be
repeated.
[0116]
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31
(Filter Circuit 140) As shown in FIG. 19, the ultrasonic sensor 100C includes a signal generation
circuit 104, a semiconductor element 107, an amplifier 108, a reception circuit 110, a phase
adjuster 111, and a buffer circuit 113. A filter circuit 140 and a protection circuit 160 are
provided.
[0117]
The filter circuit 140 filters a signal in a frequency band that causes the ultrasonic sensor 100C
to abnormally oscillate.
The filter circuit 140 is provided on the path 109. Thereby, the filter circuit 140 can filter the
noise signal flowing from the parasitic capacitance 115 into the path 109, and abnormal
oscillation of the ultrasonic sensor 100C can be prevented.
[0118]
In the example of FIG. 19, the filter circuit 140 is configured as an I / V conversion circuit
including an operational amplifier 141, a resistor 143, and a capacitor 145. The filter circuit 140
may have any function of cutting a specific frequency by converting current to voltage. For
example, a charge amplifier may be used instead of the operational amplifier 141.
[0119]
The inverting input terminal of the operational amplifier 141 is electrically connected to the
receiving electrode 20 (terminal REC). The noninverting input terminal of the operational
amplifier 141 is grounded. The output terminal of the operational amplifier 141 is electrically
connected to the amplifier 108.
[0120]
The resistor 143 is electrically connected to the inverting input terminal of the operational
amplifier 141 and the output terminal of the operational amplifier 141. The capacitor 145 is
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32
electrically connected to the inverting input terminal of the operational amplifier 141 and the
output terminal of the operational amplifier 141. The operational amplifier 141, the resistor 143,
and the capacitor 145 are connected in parallel to one another.
[0121]
With such a configuration, the filter circuit 140 functions as a low pass filter which is determined
by the ratio of the parasitic capacitance 115 and the capacitance of the capacitor 145. The ratio
is expressed, for example, as a value obtained by dividing the parasitic capacitance 115 by the
capacitance of the capacitor 145. Preferably, the capacitance of capacitor 145 is greater than
parasitic capacitance 115. As a result, the filter circuit 140 can reduce the gain response to the
signal component of the abnormal oscillation frequency band, and can stably operate the
ultrasonic sensor 100C.
[0122]
Although the filter circuit 140 is shown as an I / V conversion circuit that functions as a low pass
filter in the example of FIG. 19, the filter circuit 140 is not limited to the I / V conversion circuit.
For example, the filter circuit 140 may be a band pass filter or a charge amplifier circuit. The
band pass filter is configured to pass a frequency band including the resonance frequency of the
piezoelectric element 200. That is, the band pass filter is configured to cut a signal in a frequency
band other than the resonance frequency of the piezoelectric element 200.
[0123]
With reference to FIG. 20, circuit examples (A) and (B) which may cause abnormal oscillation of
the ultrasonic sensor will be described. FIG. 20 is a diagram showing an example of the circuit
configuration of each of the ultrasonic sensors 100Y and 100Z according to the comparative
example.
[0124]
As shown in the circuit example (A) of FIG. 20, the ultrasonic sensor 100Y includes a voltage
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33
follower circuit 170 instead of the filter circuit 140 (see FIG. 19). The voltage follower circuit
170 includes an operational amplifier 171. When a noise signal flows through the parasitic
capacitance 115 of the ultrasonic sensor 100Y, the noise signal flows directly to the inverting
input terminal of the operational amplifier 171. Due to this noise signal, the ultrasonic sensor
100Y may oscillate abnormally.
[0125]
As shown in the circuit example (B) of FIG. 20, the ultrasonic sensor 100Z includes an inverting
amplification circuit 180 instead of the filter circuit 140 (see FIG. 19). The inverting amplification
circuit 180 includes a capacitor 181, an operational amplifier 183, and resistors 184 and 185.
When a noise signal flows through the parasitic capacitance 115 of the ultrasonic sensor 100Z,
the noise signal flows directly to the inverting input terminal of the operational amplifier 183.
Due to this noise signal, the ultrasonic sensor 100Z may oscillate abnormally.
[0126]
(Protection Circuit 160) Referring back to FIG. 19, the protection circuit 160 will be described. A
voltage higher than the power supply voltage may be applied to the operational amplifier 141
due to the resonance characteristic of the ultrasonic sensor 100C. The protection circuit 160
prevents such an excessive voltage from being applied to the operational amplifier 141.
[0127]
The protection circuit 160 includes diodes 161 and 163. The cathode of the diode 161 is
connected to the path 109. The anode of the diode 161 is grounded. The cathode of the diode
163 is grounded. The anode of the diode 163 is connected to the path 109. The protection
circuit 160 does not have to be provided in the ultrasonic sensor 100C.
[0128]
[Simulation Result 1] The simulation result using the ultrasonic sensor 100C according to the
fourth embodiment will be described with reference to FIG. 21 while continuously referring to
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34
FIG. FIG. 21 is a diagram showing a simulation result in the case where abnormal oscillation
occurs and a simulation result in the case where abnormal oscillation does not occur.
[0129]
More specifically, the control signals that the ultrasonic sensor 100C outputs to the signal
generation circuit 104 are shown in the graphs (A1) and (B1) of FIG. Control signals which the
ultrasonic sensor 100C outputs to the semiconductor element 107 are shown in the graphs (A2)
and (B2) of FIG.
[0130]
The graph (A3) of FIG. 21 shows the output waveform of the ultrasonic sensor 100C when the
parasitic capacitance 115 is assumed to be 50 pF (picoFarad) and the capacitance of the
capacitor 145 is assumed to be 10 pF. As shown in the graph (A3), a noise signal that has passed
through the parasitic capacitance 115 appears as an output waveform from time T2 to time T3
in which the reverberation vibration is suppressed (see dotted line 311). The ultrasonic sensor
100C abnormally oscillates after time T3 due to the noise signal. Therefore, the ultrasonic sensor
100C can not detect the reflected wave received at time T4 (see the dotted line 313).
[0131]
The graph (B3) of FIG. 21 shows the output waveform of the ultrasonic sensor 100C when the
parasitic capacitance 115 is assumed to be 50 pF and the capacitance of the capacitor 145 is
assumed to be 100 pF. As shown in the graph (B3), the noise signal from the parasitic
capacitance 115 does not appear as an output waveform from time T2 to time T3 in which the
reverberation vibration is suppressed (see the dotted line 311). Therefore, the ultrasonic sensor
100C can detect the reflected wave received at time T4 without abnormal oscillation after time
T3.
[0132]
[Simulation Result 2] Referring to FIG. 22 again with reference to FIG. 19, another simulation
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result using the ultrasonic sensor 100C according to the fourth embodiment will be described.
FIG. 22 also refers to the relationship between the frequency of a signal flowing to the ultrasonic
sensor 100C at the time of suppression of reverberation vibration and the gain of the ultrasonic
sensor 100C with respect to the signal (hereinafter, also referred to as “open loop
characteristic” FIG.
[0133]
The graph (A) of FIG. 22 shows the open loop characteristics when the parasitic capacitance 115
is 0.1 pF, 1 pF, 10 pF, and 100 pF when the filter circuit 140 is not provided. When the filter
circuit 140 is not provided, the gain is 0 dB or more in a frequency band other than the
resonance frequency (see the dotted line 321). A signal in this frequency band causes abnormal
oscillation.
[0134]
The graph (B) of FIG. 22 shows the open loop characteristics when the parasitic capacitance 115
is 0.1 pF, 1 pF, 10 pF, and 100 pF when the filter circuit 140 is provided. In the example of graph
(B), the capacitance of the capacitor 145 of the filter circuit 140 is 100 pF. In the graph (B), the
gain of the signal in the frequency band other than the resonance frequency is suppressed by the
filter circuit 140.
[0135]
[Summary] As described above, the ultrasonic sensor 100C includes the filter circuit 140 that
filters the signal of the frequency band that causes abnormal oscillation. Thus, the ultrasonic
sensor 100C can prevent abnormal oscillation.
[0136]
[Experimental Result 1] The advantages of the ultrasonic sensor 100C according to the fourth
embodiment will be further described with reference to FIG. FIG. 23 is a diagram showing a
difference in reverberation time to temperature in an ultrasonic sensor 100C according to the
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fourth embodiment and an ultrasonic sensor 100Z according to a comparative example.
[0137]
From the experimental results shown in FIG. 23, it can be seen that the ultrasonic sensor 100C
according to the fourth embodiment has less variation in reverberation time with respect to
temperature than the ultrasonic sensor 100Z according to the comparative example. The reason
for such a result is that the input of the I / V conversion circuit is ideally in a state of virtual
short, so that the vibration speed of the ultrasonic sensor is not affected by the influence of the
braking capacity of the ultrasonic sensor. It can be considered that it is possible to take out the
signal which is not influenced by the temperature characteristic of the braking capacity.
[0138]
Fifth Embodiment [Ultrasonic Sensor 100D] An ultrasonic sensor 100D according to the fifth
embodiment will be described with reference to FIG. FIG. 24 is a diagram showing an example of
the circuit configuration of the ultrasonic sensor 100D.
[0139]
In the ultrasonic sensor 100 according to the first embodiment, the semiconductor element 107
is configured as a transistor. On the other hand, in the ultrasonic sensor 100D according to the
fifth embodiment, the semiconductor element 107 is configured as the diodes 191 and 192. The
configuration other than the semiconductor element 107 is as described above, and therefore the
description will not be repeated.
[0140]
The diodes 191 and 192 are provided on the path 109 and are connected in parallel to each
other. The cathode of the diode 191 is connected to the amplifier 108. The anode of the diode
191 is connected to the terminal DRV. The cathode of the diode 192 is connected to the terminal
DRV. The anode of the diode 192 is connected to the amplifier 108.
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[0141]
[Summary] As described above, in the ultrasonic sensor 100D according to the fifth embodiment,
the semiconductor element 107 is configured as the diodes 191 and 192. The reverberation
signal is higher than the threshold voltage (for example, forward voltage) driving the diodes 191
and 192, and the output signal accompanying the reflected wave of the ultrasonic wave is lower
than the threshold voltage. Therefore, in the step of suppressing the reverberation vibration, the
reverberation signal is fed back to the transmission electrode 10 as a voltage, but in the step of
receiving the reflected wave of the ultrasonic wave, the output signal is not fed back to the
transmission electrode 10. Therefore, even in this case, the same effect as the ultrasonic sensor
100 according to the first embodiment can be obtained.
[0142]
Sixth Embodiment [Ultrasonic Sensor 100E] An ultrasonic sensor 100E according to the sixth
embodiment will be described with reference to FIG. FIG. 25 is a diagram showing an example of
the circuit configuration of the ultrasonic sensor 100E.
[0143]
In an ultrasonic sensor 100E according to the sixth embodiment, a step-up transformer 106 is
further provided on an electrical path 109 connecting the transmitting electrode 10 and the
receiving electrode 20 in the ultrasonic sensor 100 according to the first embodiment. Provided.
More specifically, the step-up transformer 106 is connected to the position on the terminal DRV
side of the transmission electrode 10, that is, to the front stage of the transmission electrode 10.
The configuration other than step-up transformer 106 is as described above, and therefore the
description will not be repeated.
[0144]
The step-up transformer 106 includes a primary coil and a secondary coil. The primary coil of
the step-up transformer 106 is connected to the signal generation circuit 104 and the
semiconductor element 107. The secondary coil of the step-up transformer 106 is connected to
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the terminal DRV. The ratio of the voltage on the primary coil side to the voltage on the
secondary coil side is, for example, 1:10. By being configured as described above, the
reverberation signal is amplified by the step-up transformer 106 when being fed back from the
receiving electrode 20 to the transmission terminal. As a result, even if the reverberation signal is
minute, the reverberation oscillation is suppressed.
[0145]
Seventh Embodiment [Overview] An overview of an ultrasonic sensor 100F according to a
seventh embodiment will be described. An ultrasonic sensor 100F according to the seventh
embodiment is different from the ultrasonic sensor 100A according to the first embodiment in
that the ultrasonic sensor 100F has a plurality of operation modes having different detection
distances. The ultrasonic sensor 100F sequentially switches a plurality of operation modes
having different detection distances, and controls the piezoelectric element 200 (see FIG. 1)
under control conditions according to the current operation mode. This broadens the range of
detectable distances. In addition, the ultrasonic sensor 100F can detect an object located
anywhere. The ultrasonic sensor 100F may have at least two operation modes.
[0146]
The hardware configuration and the like of the ultrasonic sensor 100F according to the seventh
embodiment are the same as the ultrasonic sensor 100 according to the first embodiment, and
therefore the description thereof will not be repeated below.
[0147]
[Control Structure of Ultrasonic Sensor 100F] An ultrasonic sensor 100F according to the
seventh embodiment will be described with reference to FIGS. 26 and 27.
FIG. 26 is a flowchart showing a part of the process performed by the ultrasonic sensor 100F
according to the seventh embodiment. The process of FIG. 26 is implemented by executing a
program by the control circuit 101 (see FIG. 1) for controlling the ultrasonic sensor 100F. In
another aspect, part or all of the processing may be performed by the CPU or other hardware.
[0148]
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In step S2, the control circuit 101 reads the control information 124 shown in FIG. FIG. 27 shows
the contents of control information 124. As shown in FIG. Control information 124 is stored in
advance in, for example, a storage area of control circuit 101. As shown in FIG. 27, control
conditions of the piezoelectric element 200 (see FIG. 1) are associated with each of the operation
modes of the ultrasonic sensor 100F in accordance with the detection distance of the ultrasonic
sensor 100F.
[0149]
In step S4, the control circuit 101 acquires, from the control information 124, control conditions
corresponding to the current operation mode of the ultrasonic sensor 100F.
[0150]
In step S10, the control circuit 101 drives the semiconductor element 107 (see FIG. 2) to make
the path 109 (see FIG. 2) nonconductive.
[0151]
In step S12A, the control circuit 101 applies an alternating voltage to the transmission area 50A
of the piezoelectric element 200 (see FIG. 1) based on the control condition acquired in step S4.
More specifically, the drive voltage of the piezoelectric element 200 and the drive frequency of
the piezoelectric element 200 are defined in the control condition acquired in step S4, and the
control circuit 101 determines the drive voltage and the drive frequency. Drive the piezoelectric
element 200.
Thereby, an ultrasonic wave is emitted from the transmission area 50A of the piezoelectric
element 200.
[0152]
In step S20, control circuit 101 determines whether or not a predetermined time (for example,
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several microseconds to several milliseconds) has elapsed since an AC voltage is applied to
transmission region 50A. The control circuit 101 switches the control to step S22 when it is
determined that a predetermined time has elapsed since application of the AC voltage to the
transmission area 50A (YES in step S20). If not (NO in step S20), control circuit 101 executes the
process of step S20 again.
[0153]
In step S22, the control circuit 101 stops the application of the alternating voltage to the
transmission area 50A of the piezoelectric element 200.
[0154]
In step S23, the control circuit 101 determines whether to suppress the reverberation vibration
based on the control condition acquired in step S4.
More specifically, in the control condition acquired in step S4, a suppression mode indicating
whether to suppress the reverberation vibration is defined is defined. If the suppression mode
specified in the control condition acquired in step S4 is ON, the control circuit 101 determines to
suppress the reverberation vibration. When the suppression mode is OFF under the control
condition acquired in step S4, the control circuit 101 determines not to suppress the
reverberation vibration. When control circuit 101 determines that the reverberation vibration is
to be suppressed (YES in step S23), control is switched to step S24. If not (NO in step S23),
control circuit 101 switches control to step S34A.
[0155]
In step S24, the control circuit 101 drives the semiconductor element 107 to switch the path
109 from the nonconductive state to the conductive state. Thereby, the reverberation signal
output according to the reverberation vibration is fed back from the reception area 50B (see FIG.
2) of the piezoelectric element 200 to the transmission electrode 10 (see FIG. 2). As a result,
reverberation vibration of the ultrasonic sensor 100F is suppressed.
[0156]
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In step S30A, control circuit 101 determines whether or not a predetermined time has elapsed
since path 109 was turned on. The predetermined time is defined by the control condition
acquired in step S4. That is, the control circuit 101 causes the path 109 to be conductive only for
the time defined by the control condition acquired in step S4. When the control circuit 101
determines that the predetermined time has elapsed since the path 109 was turned on (YES in
step S30A), the control circuit 101 switches the control to step S32. If not (NO in step S30A),
control circuit 101 executes the process of step S30A again.
[0157]
In step S32, the control circuit 101 drives the semiconductor element 107 to switch the path
109 from the conductive state to the non-conductive state.
[0158]
In step S34A, the control circuit 101 controls the reception area 50B of the piezoelectric element
200 based on the control condition acquired in step S4.
In the control condition acquired in step S4, the waiting time from the generation of the
ultrasonic wave to the reception of the reflected wave and the gain of the reception signal to be
output upon receiving the reflected wave are defined. The control circuit 101 outputs the
reflected wave received from the emission of the ultrasonic wave to the lapse of the waiting time
to the receiving circuit 110 (see FIG. 1) as a voltage value corresponding to the gain. The control
circuit 101 switches the control to step S40 based on the elapse of the waiting time after
emitting the ultrasonic wave.
[0159]
In step S40, control circuit 101 determines whether or not control processing according to the
present embodiment has been performed for all the operation modes of ultrasonic sensor 100F.
When control circuit 101 determines that the control process according to the present
embodiment has been performed for all the operation modes of ultrasonic sensor 100F (YES in
step S40), the control process according to the present embodiment ends. If not (NO in step S40),
control circuit 101 switches control to step S50.
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[0160]
In step S50, the control circuit 101 switches the operation mode of the ultrasonic sensor 100F
from the current operation mode to another operation mode. By the processes of steps S40 and
S50, the process shown in FIG. 26 is repeated by the number of operation modes of the
ultrasonic sensor 100F.
[0161]
[Summary] As described above, the ultrasonic sensor 100F sequentially switches the plurality of
operation modes having different detection distances, and controls the piezoelectric element 200
under the control condition according to the current operation mode. This broadens the range of
detectable distances. In addition, the ultrasonic sensor 100F can detect an object located
anywhere.
[0162]
Eighth Embodiment [Summary] An outline of an ultrasonic sensor 100G according to an eighth
embodiment will be described. The ultrasonic sensor 100G according to the eighth embodiment
is at least also referred to as an operation mode (first operation mode) (hereinafter, referred to as
"short-distance mode") for detecting a short distance. And an operation mode (second operation
mode) for detecting a long distance (hereinafter, also referred to as “long distance mode”). And
the ultrasonic sensor 100F according to the seventh embodiment is different from the ultrasonic
sensor 100F according to the seventh embodiment.
[0163]
When the object to be detected is separated from the ultrasonic sensor 100G, the reverberation
vibration is naturally contained. Therefore, when the object to be detected is separated from the
ultrasonic sensor 100G, it is not necessary to suppress the reverberation vibration. Focusing on
this point, the ultrasonic sensor 100G does not execute the process of suppressing the
reverberation signal when the operation mode is the long distance mode. That is, in this case, the
process of suppressing the reverberation signal is stopped. Thereby, the power consumption of
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the ultrasonic sensor 100G is suppressed.
[0164]
The other points such as the hardware configuration are as described above, and therefore the
description thereof will not be repeated.
[0165]
[Control Structure of Ultrasonic Sensor 100G] An ultrasonic sensor 100G according to the eighth
embodiment will be described with reference to FIG.
FIG. 28 is a flowchart showing a part of the process performed by the ultrasonic sensor 100G
according to the eighth embodiment. The process of FIG. 28 is realized by the control circuit 101
(see FIG. 1) for controlling the ultrasonic sensor 100G executing a program. In another aspect,
part or all of the processing may be performed by the CPU or other hardware.
[0166]
The processes other than step S23A are the same as described in FIG. 3, and therefore the
description thereof will not be repeated below.
[0167]
In step S23A, the control circuit 101 determines whether the operation mode of the ultrasonic
sensor 100G is the short range mode.
The operation mode of the ultrasonic sensor 100G is arbitrarily set by the user, for example.
When the control circuit 101 determines that the operation mode of the ultrasonic sensor 100G
is the short distance mode (YES in step S23A), the control circuit 101 switches the control to step
S24. If not (NO in step S23A), control circuit 101 switches control to step S34.
[0168]
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When the operation mode of the ultrasonic sensor 100G is the short distance mode by the
process of step S23A, the control circuit 101 executes the processes of steps S24 to S32 for
suppressing reverberation vibration. That is, in this case, the control circuit 101 executes a
process of feeding back the reverberation signal to the transmission electrode 10 of the
piezoelectric element 200 (see FIG. 1). When the operation mode of the ultrasonic sensor 100G is
the long distance mode, the control circuit 101 does not execute the processing of steps S24 to
S32 for suppressing reverberation vibration. That is, in this case, the control circuit 101 stops the
process of feeding back the reverberation signal to the transmission electrode 10 of the
piezoelectric element 200.
[0169]
[Summary] As described above, when the operation mode is the long distance mode, the
ultrasonic sensor 100G according to the present embodiment does not execute the process for
suppressing the reverberation vibration. Thus, the power consumption of the ultrasonic sensor
100G is suppressed.
[0170]
As mentioned above, although each embodiment based on the present invention was described,
the above-mentioned disclosure content is illustration in all points, and is not restrictive. The
technical scope of the present invention is shown by the claims, and is intended to include all
modifications within the meaning and scope equivalent to the claims.
[0171]
DESCRIPTION OF SYMBOLS 10 Transmission electrode, 10X transmission / reception electrode
11, 31 side wall part 12, 32, upper surface part 13, 14, 33 middle part, 13H, 14H, 32H, 33H
hollow part, 13T, 14T, 32T, 33T part, 20 Receiving electrode, 20X monitoring electrode, 21 disk
portion, 22 extending portion, 30, 30X common electrode, 32F retreating portion, 34 lower
surface portion, 50, 50X piezoelectric body, 50A transmitting region, 50B receiving region, 51
upper surface , 52 to 55 side surface, 56 lower surface, 100, 100A to 100C, 100X to 100Z
ultrasonic sensor, 101, CLK control circuit, 102 memory, 104 signal generation circuit, 105
power supply, 106 step-up transformer, 107, 120, 122, M1 Semiconductor devices, 108, 121A
to 121C, 123A to 123C Amplifiers, 109, 114, 126, 127 , 110 reception circuits, 111 phase
adjusters, 113 buffer circuits, 115, C1 to C4 parasitic capacitances, 124 control information, 140
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filter circuits, 141, 171, 183 op amps, 143, 184, 185 resistors, 145, 181 capacitors, 160
Protection circuit, 161, 163, 191, 192 diode, 170 voltage follower circuit, 180 circuit, 200, 200X
piezoelectric element, 301, 303, 305, 307, 309, 311, 313, 321 dotted line.
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