JP2008151537A - Object detection circuit and ultrasonic sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an object detection circuit or the like capable of supplying a linear detection signal regardless of distance from an object. <P>SOLUTION: An object detection circuit 10 comprises: a transmission means 110 for transmitting a detection signal (a) having a predetermined frequency to an object; a reception means 110 for receiving a reflected signal (b) reflected by the object; a signal amplification means 120 having a field effect transistor for amplifying a level of the reflected signal (b) received by the reception means 110; and an automatic level control means 140 for detecting the level of the reflected signal (c) amplified by the signal amplification means 120 and for superimposing the level on the signal (b) before amplification or on the signal (c) after amplification by the signal amplification means 120. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides an object detection circuit having a transmission means for transmitting a detection signal having a predetermined frequency to an object, a reception means for receiving a reflected signal reflected by the object, and such an object detection circuit. And an ultrasonic sensor device.

  The ultrasonic sensor device detects the presence or absence of an object and the distance from the object by transmitting an ultrasonic wave having a predetermined frequency such as 40 kHz or 200 kHz and receiving a reflected wave reflected from the object. The ultrasonic sensor device generates an electric signal by a reflected wave received from an object. The voltage level of this signal varies depending on the distance d between the ultrasonic sensor device and the object. For example, when a pipe made of polyvinyl chloride is experimentally detected, d = 300 mm and 2 to 3 mV. , D = 2,000 mm and 20 μV. In order to detect the presence or absence of an object and the distance from the object, it is necessary to amplify this electric signal to a level that can be handled by a processing device such as a CPU (Central Processing Unit). For example, when the electrical signal is 20 μV, an amplifier circuit having a gain of about 94 dB may be used to amplify this signal to 1 V. However, a simple amplifier circuit amplifies not only a desired signal but also noise, and as a result, the S / N (signal-to-noise ratio) may deteriorate.

  In recent years, ultrasonic sensor devices are often used as back sonar for automobiles. When used as a back sonar for an automobile, the ultrasonic sensor device detects the object as described above over a wide range from the proximity d = 300 mm to the distance d = 2,500 mm. The voltage level of the generated electrical signal can also vary over a wide range. In general, the power supply voltage of an ultrasonic sensor device used as a back sonar for an automobile is 8 to 12 V. If a high gain amplifier circuit as described above is used, the output is saturated when the proximity d = 300 mm. The input / output characteristics of the amplifier circuit are not linear.

For example, Japanese Patent Application Laid-Open No. 2001-221851 (Patent Document 1) discloses an ultrasonic sensor device that makes it easy to identify a reflected wave with respect to noise and that can expand the measurement range of the proximity distance.
Japanese Patent Laid-Open No. 2001-221851

  However, although the invention disclosed in Patent Document 1 makes it easy to identify any reflected wave without being buried in the noise even if noise is mixed, the distance between the ultrasonic sensor device and the object is close However, the problem that the output signal is saturated when the electrical signal generated by the ultrasonic sensor device is amplified remains unsolved.

  The present invention has been made to solve such a problem. An object detection circuit capable of supplying a linear detection signal regardless of a distance from an object, and such an object detection circuit are provided. It is an object of the present invention to provide an ultrasonic sensor device.

  In order to achieve the above object, an object detection circuit of the present invention includes a transmission unit that transmits a detection signal having a predetermined frequency to an object, and a reception unit that receives a reflected signal reflected by the object. The object detection circuit includes an automatic level adjustment unit that automatically adjusts the level of the reflected signal received by the reception unit in accordance with the level.

  Thereby, the object detection circuit which can supply a linear detection signal irrespective of the distance from a target object can be provided.

  In order to achieve the above object, an object detection circuit of the present invention includes a transmission unit that transmits a detection signal having a predetermined frequency to an object, and a reception unit that receives a reflected signal reflected by the object. An object detection circuit, comprising a field effect transistor, for amplifying the level of the reflected signal received by the receiving means, and detecting the level of the reflected signal amplified by the signal amplifying means And an automatic level adjusting means for superimposing the level on the signal before or after being amplified by the signal amplifying means.

  Thus, an object that can supply a linear detection signal regardless of the distance from the object and at the same time reduce the signal loss and improve the S / N by using a field effect transistor having a high input impedance. A sensing circuit can be provided.

  Desirably, the object detection circuit of the present invention has a plurality of amplification functions which are arranged at a subsequent stage of the signal amplification unit and filter the reflected signal amplified by the signal amplification unit so as to pass only a predetermined frequency range. The filter means can be further provided. The automatic level adjusting means detects a level corresponding to a signal level between the last and the last of the plurality of filters, and supplies the level to an input terminal of the signal amplifying means or an input terminal of the plurality of filter means. Supply.

  As a result, only a necessary signal component having a predetermined frequency can be extracted and amplified, so that the S / N can be further improved.

  More preferably, the object detection circuit of the present invention can further include external connection means that can output signals output from the plurality of filter means in a digital or analog manner.

  Thereby, a detection signal can be output in a format suitable for an external application to which the object detection circuit is connected.

  In order to achieve the above object, the present invention provides an ultrasonic sensor device having the object detection circuit as described above.

  According to the object detection circuit and the ultrasonic sensor device of the present invention, it is possible to supply a linear detection signal regardless of the distance from the object.

FIG. 1 is a block diagram showing a configuration example of an object detection circuit according to the present invention. The object detection circuit 10 in FIG. 1 is a circuit for detecting the presence / absence of an object and / or a distance from the object, and includes a transmission / reception unit 110, a signal amplification unit 120, and a plurality of filter units 130 arranged in series. ₁ ,. . . , 130 _n (n is a natural number), automatic level adjustment means 140, and external connection means 150.

  The transmission / reception means 110 is a means for transmitting a signal a having a predetermined frequency, such as an ultrasonic wave, to the object and receiving a reflected signal b reflected by the object. The transmission / reception unit 110 may be divided into a transmission unit that transmits a signal a having a predetermined frequency to an object and a reception unit that receives a reflected signal b reflected by the object.

The signal amplification unit 120 is a unit for amplifying the reflected signal b received by the transmission / reception unit 110. A plurality of filter means 130 ₁ ,. . . , 130 _n are means for filtering the reflected signal c amplified by the signal amplifying means 120 so as to pass only a predetermined frequency, and further amplifying only necessary signal components extracted by the filtering process.

Automatic level adjustment means 140, the signal supplied to the external connecting means 150, i.e., such that the filter means 130 the signal d output from the _n of the last stage is not saturated, the signal level adjustment signal e corresponding to the signal d This is a means for superimposing on the reflected signal b inputted to the amplifying means 120. Therefore, the signal amplification unit 120 amplifies the reflected signal b on which the level adjustment signal e supplied by the automatic level adjustment unit 140 is superimposed.

The external connection unit 150 is a unit for outputting a detection signal in a signal format corresponding to an external application connected to the object detection circuit 10. For example, when the external application requests a digital signal, the external connection unit 150 converts the signal d output from the filter unit 130 _n into a digital signal and outputs the digital signal, while the external application requests an analog signal. case, outputs a signal d which is output from the filter means 130 _n remains an analog signal.

The automatic level adjusting means 140 includes a plurality of filter means 130 ₁ ,. . . , 130 _n may be used to generate the level adjustment signal e. For example, when the gain characteristics from the filter means 130 _i (i = 1, 2,..., N) to 130 _n are fixed, according to the signal output from 130 _(i−1) , It is possible to generate a level adjustment signal e that does not saturate the signal supplied to the external connection means 150. The automatic level adjustment means 140 may be supplied to level adjustment signal e to the first filter means 130 ₁ inputs. In this case, the level adjustment signal e is superimposed on the reflected signal c amplified by the signal amplification means 120.

  The object detection circuit of the present invention will be specifically described below.

[Constitution]
FIG. 2 is a circuit diagram illustrating an example of the ultrasonic sensor device according to the present embodiment. Ultrasonic sensor device of FIG. 2 20 is a object detection circuit using an ultrasonic sensor, a transceiver circuit 210, the signal amplifier circuit 220, a first filter circuit 230 _1, the second filter circuit 230 ₂ And an automatic level adjustment circuit 240 and an external connection circuit 250.

The transmission / reception circuit 210 is a circuit for transmitting an ultrasonic wave having a predetermined frequency to an object and receiving a reflected wave reflected by the object, and an ultrasonic sensor S1 composed of a transmission / reception piezoelectric element; And a transformer T1 and an npn transistor Q1. One terminal of the primary winding of the transformer T1 is connected to power supply voltage V _D, and the other terminal is connected to the collector terminal of the transistor Q1. The emitter terminal of the transistor Q1 is connected to the ground, and the base terminal is connected to a control circuit (not shown). The ultrasonic sensor S1 is connected in parallel to the secondary winding of the transformer T1, and one terminal is connected to the input terminal of the signal amplification circuit 220 and the other terminal is connected to the ground.

  When a control signal is applied to the base terminal of the transistor Q1 by the control circuit, the transistor Q1 becomes conductive and current flows through the primary winding of the transformer T1. Thereby, on the secondary side of the transformer T1, the resonance circuit composed of the inductance of the secondary winding and the electrostatic capacitance of the ultrasonic sensor S1 resonates, and the ultrasonic sensor S1 emits ultrasonic waves. On the other hand, when the ultrasonic wave emitted from the ultrasonic sensor S1 is reflected by the object, the resonance circuit composed of the inductance of the secondary winding and the electrostatic capacitance of the ultrasonic sensor S1 resonates, so that the ultrasonic sensor S1 converts the reflected wave into an electric signal.

  The constant of each component of the transmission / reception circuit 210 is set so that the resonance frequency of the resonance circuit composed of the transformer T1 and the ultrasonic sensor S1 is equal to the nominal frequency of the ultrasonic sensor S1 used. Thereby, since the ultrasonic sensor S1 is used in the vicinity of the operating frequency of the maximum sensitivity of transmission and reception, it becomes possible to extract only a signal in the band near the reception signal, and the S / N is improved.

The signal amplification circuit 220 is a circuit for amplifying the electric signal output from the transmission / reception circuit 210, that is, the ultrasonic sensor S1, and includes an n-type field effect transistor (FET) Q2 and first, second, and second elements. 3 and a fourth resistor R _D , R _S , R _G1 , R _G2 . The gate terminal of the FET Q2 is connected to one terminal of the ultrasonic sensor S1 of the transmission / reception circuit 210, and is supplied with an electrical signal output from the ultrasonic sensor S1. The drain terminal of the FET Q2 is connected to the voltage source V _D via the first resistor R _D , and the source terminal is connected to the ground via the second resistor R _S. Third resistor _{R G1} is connected between the drain terminal and the gate terminal of the FET Q2, the fourth resistor _{R G2,} is connected between the ground and the gate terminal of the FET Q2. As is apparent from FIG. 2, in this embodiment, the signal amplifier circuit 220 constitutes a common source amplifier circuit using FETs. The signal amplifying circuit 220 is also provided with a series capacitor _CD at the output stage in order to cut off the DC component of the output signal.

  The FET has a characteristic that the input impedance is high with respect to a high-resistance signal source. Therefore, the equivalent impedance of an ultrasonic sensor is typically 2 kΩ, for example, an ultrasonic sensor with a nominal frequency of 40 kHz. Therefore, using an FET reduces signal loss and improves S / N. can do.

First filter circuit 230 ₁ and the second filter circuit 230 _2, in order to take out the band of the signal near the drive frequency of the ultrasonic sensor S1, a predetermined signal component of the frequency the amplified signal by the signal amplifying circuit 220 This is a circuit for further amplifying only necessary signal components extracted by the filtering process.

The first filter circuit 230 ₁ is a low-pass filter (LPF) non-inverting amplifier circuit, a first operational amplifier OP1, a resistor R31, R32 of the fifth and sixth, the first and second Capacitors C31 and C32. One terminal of the fifth resistor R31 is connected to the inverting terminal of the operational amplifier OP1, and the other terminal is connected to one terminal of the first capacitor C31. The other terminal of the first capacitor C31 is connected to ground. The sixth resistor R32 and the second capacitor C32 are arranged in parallel, and one terminal is connected to the inverting terminal of the operational amplifier OP1 and the other terminal is connected to the output terminal of the operational amplifier OP1. The non-inverting terminal of the operational amplifier OP1 is connected via a series capacitor _{C D} to the drain of the FETQ2 the signal amplifier circuit 220. Constant of the first component parts of the filter circuit 230 ₁ is set to have a higher gain than the preceding stage of the signal amplifier circuit 220.

Second filter circuit 230 _2, a bandpass filter (BPF) non-inverting amplifier circuit, a second operational amplifier OP2, a resistor R33, R34 of the seventh and eighth, third and fourth capacitor C33 and C34. The third and fourth capacitors C33 and C34 are arranged in series. The seventh resistor R33 is arranged in parallel with the capacitors C33 and C34 arranged in series, and one terminal is connected to the inverting terminal of the operational amplifier OP2, and the other terminal is connected to the output terminal of the operational amplifier OP2. One terminal of the eighth resistor R34 is connected between the third and fourth capacitors C33 and C34 arranged in series, and the other terminal is connected to the ground. The non-inverting terminal of the operational amplifier OP2 is connected to the output terminal of the first operational amplifier OP1 of the first filter circuit 230 ₁ through a capacitor. Constant of the second of each component of the filter circuit 230 ₁ is set based on the gain required for the entire ultrasonic sensor system.

Automatic level adjusting circuit 240, the signal supplied to the external connection circuit 250, i.e., so that the signal output from the second filter circuit 230 ₂ is not saturated, the signal amplifying circuit level adjustment signal corresponding to the signal 220 Is a circuit for superimposing the signal from the ultrasonic sensor input to the first and second diodes D41 and D42, the fifth and sixth capacitors C41 and C42, and the ninth and tenth diodes. There are resistors R41 and R42. One terminal of the fifth capacitor C41 is connected to the output terminal of the _second filter circuit 2302, and the other terminal is connected to the cathode of the first diode D41 via the ninth resistor R41. The cathode of the first diode D41 is further connected to the anode of the second diode D42, and the cathode of the second diode D42 is connected to the ground. The anode of the first diode D41 is connected to the gate terminal of the FET Q2 of the signal amplification circuit 220 through the tenth resistor R42. The sixth capacitor C42 is connected between the anode of the first diode D41 and the ground.

  As is apparent from FIG. 2, in this embodiment, the automatic level adjustment circuit 240 forms a detection circuit and outputs a DC voltage corresponding to the level of the input signal. Therefore, this DC voltage is applied to the gate terminal of the FET Q2 of the signal amplification circuit 220 so as to be superimposed on the signal from the ultrasonic sensor.

External connection circuit 250 is a circuit for outputting a detection signal with a signal format corresponding to an external application that is connected to the ultrasonic sensor 20, in this embodiment, output from the second filter circuit 230 ₂ The comparator is configured to convert the received signal into a digital signal and output it. That is, the external connection circuit 250, a second filter circuit 230 ₂ signal output from comparison with a reference voltage, and outputs the comparison result by the voltage of the binary High / Low. The external connection circuit 250 includes a third operational amplifier OP3 and eleventh, twelfth and thirteenth resistors R51, R52 and R53. Inverting input of the operational amplifier OP3 is connected to the second output terminal of the filter circuit 230 _2, the non-inverting input, twelfth and 11 via a resistor R51 to the supply voltage V _D of which is and connected in series The thirteenth resistors R52 and R53 are connected to the ground. Accordingly, the power supply voltage V _D is divided by the eleventh resistor R51 and the twelfth and thirteenth resistors R52 and R53, and the reference voltage Vref = V _D × (R52 + R53) is applied to the non-inverting input of the operational amplifier OP3. / (R51 + R52 + R53) is applied.

As shown in FIG. 2, the ultrasonic sensor device 20 of this embodiment may further include a transmission signal limiting circuit 260 and a detection / smoothing circuit 270. The transmission signal limiting circuit 260 is disposed between the output stage of the transmission / reception circuit 210 and the input stage of the signal amplification circuit 220, and wraps around the input stage of the signal amplification circuit 220 when an ultrasonic signal is transmitted from the transmission / reception circuit 210. It is a circuit for limiting a signal. Detection / smoothing circuit 270 is disposed between the second filter circuit 230 ₂ and the external connection circuit 250 is a circuit for detecting a signal output from the second filter circuit 230 _2.

[Operation]
Next, the operation of the ultrasonic sensor device 20 of FIG. 2 will be described.

  In response to the control signal output from the control circuit, the transmission / reception circuit 210 transmits the ultrasonic wave having a predetermined frequency such as 40 kHz to the target and the inductance of the secondary winding of the transformer T1 and the ultrasonic sensor. A resonance circuit composed of the capacitance of S1 is resonated at a resonance frequency of 40 kHz. Thereby, the ultrasonic sensor S1 emits a 40 kHz ultrasonic wave.

  When the ultrasonic wave emitted from the ultrasonic sensor S1 is reflected on an object and the reflected wave is received by the ultrasonic sensor S1, the inductance of the secondary winding of the transformer T1 and the capacitance of the ultrasonic sensor S1 are used. The resonant circuit is resonated at a resonant frequency of 40 kHz and generates an electrical signal corresponding to the reflected wave.

The electric signal generated in the transmission / reception circuit 210 is sent to the signal amplification circuit 220. The signal amplifier circuit 220 amplifies the electric signal. The electric signal amplified by the signal amplifying circuit 220 is input to the _first filter circuit 2301, and is filtered so that only a signal component of a predetermined frequency is extracted, and only the necessary signal component extracted by the filtering process is obtained. Is further amplified. Then, the electric signal is inputted the second to the filter circuit 230 _2, only the signal component of a predetermined frequency is further filtered so as to be taken out, is further amplified only necessary signal components extracted by the filtering process The

The electric signal thus amplified and filtered is then input to the automatic level adjustment circuit 240. As described above, the automatic level adjustment circuit 240 is a detection circuit composed of a diode. In this embodiment, the automatic level adjustment circuit 240 detects an input electric signal and converts a negative DC voltage corresponding to the level to a level adjustment signal. Output as. The level adjustment signal output from the automatic level adjustment circuit 240 is applied to the gate terminal of the FET Q2 of the signal amplification circuit 220. The level adjustment signal corresponds to the gate bias voltage of the FET Q2, and the amplification gain of the signal amplification circuit 240 changes according to the level of this voltage. Accordingly, the signal output from the second filter circuit 230 ₂ is adjusted to a level that does not saturate.

Then, the signal output from the second filter circuit 230 ₂ is input to the detection / smoothing circuit 270. In this embodiment, the detection / smoothing circuit 270 is configured to output a positive DC voltage according to the level of the input signal.

  The external connection circuit 250 compares the level of the positive DC voltage output from the detection / smoothing circuit 270 with the level of the reference voltage, and outputs the comparison result as a binary voltage of High / Low. The digital signal corresponding to the reflected wave received by the acoustic wave sensor S1 is output to an external application.

[Constitution]
FIG. 3 is a circuit diagram illustrating an example of the ultrasonic sensor device according to the present embodiment. Ultrasonic sensor device 30 of FIG. 3 is a object detection circuit using an ultrasonic sensor, a transmission circuit 310 _1, a receiving circuit 310 _2, a signal amplifying circuit 320, a first filter circuit 330 _1, has a second filter circuit 330 _2, the automatic level adjusting circuit 340, and an external connection circuit 350.

Transmission circuit 310 ₁ is a circuit for transmitting the object to ultrasonic waves having a predetermined frequency, a first ultrasonic sensor S11 in a transmission, a first transformer T11, an npn transistor Q11 Have One terminal of the primary winding of the transformer T11 is connected to power supply voltage V _D, and the other terminal is connected to the collector terminal of the transistor Q11. The emitter terminal of the transistor Q11 is connected to the ground, and the base terminal is connected to a control circuit (not shown). The ultrasonic sensor S11 is connected in parallel to the secondary winding of the transformer T11, and one terminal is connected to the ground.

  When a control signal is applied to the base terminal of the transistor Q11 by the control circuit, the transistor Q11 becomes conductive and current flows through the primary winding of the transformer T11. Thereby, on the secondary side of the transformer T11, the resonance circuit composed of the inductance of the secondary winding and the capacitance of the ultrasonic sensor S11 resonates, and the ultrasonic sensor S11 emits ultrasonic waves.

Receiving circuit 310 _2, when the ultrasonic wave transmitted from the transmitting circuit 310 ₁ is reflected by the object, a circuit for receiving a reflected wave, a second ultrasonic sensor S12 in reception And a second transformer T12. The primary winding of the transformer T12 is open, and the secondary winding of the transformer T12 has one terminal connected to one terminal of the ultrasonic sensor S12 via a resistor and the other terminal to ground. It is connected. The other terminal of the ultrasonic sensor S12 is connected to the ground.

Ultrasound emitted from the first ultrasonic sensor S11 in the transmission circuit 310 ₁ is reflected on the object, the second ultrasonic sensor S12 in the reception circuit 310 ₂ receives the reflected wave, the ultrasonic sensor S12 The ultrasonic sensor S12 converts the reflected wave into an electric signal by resonating the resonance circuit composed of the capacitance and the inductance of the secondary winding of the transformer T12.

The constants of the components of the transmitting circuit 310 ₁ and the receiving circuit 310 ₂ are such that the resonant frequency of the resonant circuit consisting of the respective transformer and ultrasonic sensor is equal to the nominal frequency of each ultrasonic sensor used. Is set. Accordingly, since any ultrasonic sensor is used in the vicinity of the operating frequency with the maximum sensitivity of transmission and reception, it becomes possible to extract only a signal in a band near the reception signal, and S / N is improved.

  In addition, in the combined type in which transmission and reception are performed by one element, the transmission frequency and the reception frequency are made compatible by operating at a frequency approximately halfway between the series resonance frequency at the time of transmission and the parallel resonance frequency at the time of reception. In fact, neither transmission nor reception is used at the highest sensitivity operating frequency. Therefore, a device including both transmission and reception sensors has higher sensitivity than a device using a transmission / reception sensor. On the other hand, the size of the apparatus can be reduced by using a transmission / reception sensor.

Signal amplifier circuit 320 is a circuit for amplifying the electric signal output from the receiving circuit 310 _2, and n-type field effect transistor (FET) Q21, first, second, third and fourth resistors R _D , R _S , R _G1 , R _G2 . The third resistor _{R G1} and the fourth resistor _{R G2} are arranged in series, one terminal of the third resistor _{R G1} is connected to the receiving circuit 310 ₂ to the ultrasonic sensor S12, a fourth resistor _{R G2} One terminal of is connected to ground. The gate terminal of FETQ21 is connected to the third movable terminal of the resistor R _G1 is a variable resistor, it is supplied with electrical signals outputted from the ultrasonic sensor S12 via a third resistor R _G1. The drain terminal of the FET Q21 is connected to the voltage source V _D through the first resistor R _D , and the source terminal is connected to the ground through the second resistor R _S. As is apparent from FIG. 3, in this embodiment, the signal amplifier circuit 320 constitutes a common source amplifier circuit using FETs. The signal amplifying circuit 320 is also provided with a series capacitor _CD at the output stage in order to cut off the direct current component of the output signal.

As shown in FIG. 3, the ultrasonic sensor system 30 of the present embodiment may further be provided a buffer circuit 360 between the signal amplifying circuit 320 and the first filter circuit 330 _1. The buffer circuit 360 is a circuit for buffering the signal amplified by the signal amplifier circuit 320, and is configured by an emitter follower in this embodiment.

First filter circuit 330 ₁ and the second filter circuit 330 _2, in order to take out the band of the signal near the drive frequency of the received ultrasonic sensor S12, the signal amplifying circuit 320 signals the predetermined frequency amplified by This is a circuit for performing a filter process so as to pass only a signal component and further amplifying only a necessary signal component extracted by the filter process.

The first filter circuit 330 ₁ is a wideband BPF inverting amplifier circuit, a first operational amplifier OP31, the fifth and sixth resistors R331, R332, and first and second capacitors C331, C332 Have. One terminal of the fifth resistor R331 is connected to the inverting terminal of the operational amplifier OP31, and the other terminal is connected to one terminal of the first capacitor C331. The other terminal of the first capacitor C331 is connected to the output terminal of the buffer circuit 360. The sixth resistor R332 and the second capacitor C332 are arranged in parallel, and one terminal is connected to the inverting terminal of the operational amplifier OP31 and the other terminal is connected to the output terminal of the operational amplifier OP31. A predetermined reference voltage is applied to the non-inverting terminal of the operational amplifier OP31. Constant of the first component parts of the filter circuit 330 ₁ is set to have a higher gain than the preceding stage of the signal amplifier circuit 320.

Second filter circuit 330 _2, a narrow band BPF non-inverting amplifier circuit, a second operational amplifier OP32, the seventh, the resistance of the eighth and 9 R333, R334, and R335, third, fourth And fifth capacitors C333, C334, and C335. The third and fourth capacitors C333 and C334 are arranged in series. The seventh resistor R333 is arranged in parallel with the capacitors C333 and C334 arranged in series, and one terminal is connected to the inverting terminal of the operational amplifier OP32 and the other terminal is connected to the output terminal of the operational amplifier OP32. One terminal of the eighth resistor R334 is connected between the third and fourth capacitors C333 and C334 arranged in series, and the other terminal is connected to the ground. The inverting terminal of the operational amplifier OP32 is further connected to one terminal of the ninth resistor R335. The other terminal of the ninth resistor R335 is connected to one terminal of the fourth capacitor, and the other terminal of the fourth capacitor is connected to the ground. The non-inverting terminal of the operational amplifier OP32 is connected to the output terminal of the first operational amplifier OP31 of the first filter circuit 330 ₁ through a capacitor. Constant of the second of each component of the filter circuit 330 ₁ is set based on the gain required for the entire ultrasonic sensor system.

Automatic level adjustment circuit 340, the signal supplied to the external connection circuit 350, i.e., such that the second signal output from the filter circuit 330 ₂ is not saturated, the signal amplifying circuit level adjustment signal corresponding to the signal 320 Is a circuit for superimposing the signal from the ultrasonic sensor input to the first and second diodes D341 and D342, the sixth and seventh capacitors C341 and C342, and the tenth and eleventh electrodes. There are resistors R341 and R342. One terminal of the sixth capacitor C341 is connected to the output terminal of the _second filter circuit 3302, and the other terminal is connected to the cathode of the first diode D341 via the tenth resistor R341. The cathode of the first diode D341 is further connected to the anode of the second diode D342, and the cathode of the second diode D342 is connected to the ground. The anode of the first diode D341 is connected to the gate terminal of the FET Q21 of the signal amplifier circuit 320 via the eleventh resistor R342. The seventh capacitor C342 is connected between the anode of the first diode D341 and the ground.

  As is apparent from FIG. 3, the automatic level adjustment circuit 340 of the present embodiment is a detection circuit having the same configuration as the automatic level adjustment circuit 240 shown in FIG.

External connection circuit 350 is a circuit for outputting a detection signal with a signal format corresponding to an external application that is connected to the ultrasonic sensor 30, in this embodiment, output from the second filter circuit 330 ₂ Output the signal as an analog signal. The external connection circuit 350 of this embodiment is a buffer circuit composed of an emitter follower. Further, the external connection circuit 350 may be further configured to adjust the signal level as necessary.

[Operation]
Next, the operation of the ultrasonic sensor device 30 of FIG. 3 will be described.

Transmission circuit 310 _1, in response to the control signal outputted from the control circuit, for example, to send the object to ultrasonic waves having a predetermined frequency such as 40 kHz, the inductance of the secondary winding of the first transformer T11 And a resonance circuit composed of the capacitance of the first ultrasonic sensor S11 are resonated at a resonance frequency of 40 kHz. Thereby, the first ultrasonic sensor S11 emits ultrasonic waves of 40 kHz.

The ultrasonic wave emitted from the first ultrasonic sensor S11, is reflected by the object, when the reflected wave is the second ultrasonic sensor S12 in the reception circuit 310 ₂ receives, secondary winding of the second transformer T12 A resonance circuit composed of the inductance of the line and the capacitance of the second ultrasonic sensor S12 resonates at a resonance frequency of 40 kHz, and generates an electric signal corresponding to the reflected wave.

Electric signal generated by the receiving circuit 310 ₂ is sent to the signal amplifier circuit 320. The signal amplifier circuit 320 amplifies the electric signal. The electric signal amplified by the signal amplifying circuit 320 is input to the _first filter circuit 3301 via the buffer circuit 360, and is filtered so that only a signal component having a predetermined frequency is extracted, and is extracted by the filtering process. Only the necessary signal components are further amplified. Then, the electric signal is inputted second to the filter circuit 330 _2, only the signal component of the predetermined frequency are filtered to be taken out, it is further amplified only necessary signal components extracted by the filtering process .

The electric signal thus amplified and filtered is then input to the automatic level adjustment circuit 340. The automatic level adjustment circuit 340 is a detection circuit composed of a diode as described above. In this embodiment, the automatic level adjustment circuit 340 detects an input electric signal and applies a negative DC voltage corresponding to the level to the level adjustment signal. Output as. The level adjustment signal output from the automatic level adjustment circuit 340 is applied to the gate terminal of the FET Q21 of the signal amplification circuit 320. The level adjustment signal corresponds to the gate bias voltage of the FET Q21, and the amplification gain of the signal amplification circuit 340 changes according to the level of this voltage. Accordingly, the signal output from the second filter circuit 330 ₂ is adjusted to a level that does not saturate.

Then, the signal output from the second filter circuit 330 ₂ is input to the external connection circuit 350. The external connection circuit 350 buffers the input signal and outputs it to an external application.

  As described above, the object detection circuit according to the present invention can output a linear detection signal with respect to an input voltage changing in a wide range by providing the automatic level adjustment means. Further, the S / N can be further improved by using the FET as the signal amplifying means. Therefore, stable sensor output processing can be realized regardless of an external application.

[Modification]
Although the best mode for carrying out the invention has been described above, the present invention is not limited to the embodiment described in the best mode. Modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the automatic adjustment circuit generates the level adjustment signal based on the output signal of the second filter circuit that is the latter stage of the two filter circuits, but the gain characteristic of the second filter circuit is If it is fixed, the level adjustment signal may be generated based on the output signal of the first filter circuit. In addition, the level adjustment signal output from the automatic adjustment circuit is input to the input terminal of the signal amplifier circuit, but may be input to the input terminal of the first filter circuit.

  Furthermore, the object detection circuit is not limited to the circuit configurations shown in FIGS. 2 and 3, and may have other circuit configurations, and can be applied to sensor circuits other than the ultrasonic sensor device.

It is a block diagram showing the example of a structure of the object detection circuit according to this invention. 1 is a diagram illustrating an example of a circuit of an ultrasonic sensor device according to a first embodiment. 6 is a diagram illustrating an example of a circuit of an ultrasonic sensor device according to Embodiment 2. FIG.

Explanation of symbols

10 Object detection circuit 20, 30 Ultrasonic sensor device 110, 210 Transmission / reception means / circuit 120, 220, 320 Signal amplification means / circuit 130, 230, 330 Filter means / circuit 140, 240, 340 Automatic level adjustment means / circuit 150, 250, 350 External connection means / circuit 310 ₁ transmitting circuit 310 ₂ receiving circuit Q2, Q21 FET

Claims (5)

An object detection circuit having a transmission means for transmitting a detection signal having a predetermined frequency to an object and a reception means for receiving a reflected signal reflected by the object,
An object detection circuit comprising automatic level adjustment means for automatically adjusting the level of the reflected signal received by the reception means in accordance with the level. An object detection circuit having a transmission means for transmitting a detection signal having a predetermined frequency to an object and a reception means for receiving a reflected signal reflected by the object,
A signal amplifying means having a field effect transistor for amplifying the level of the reflected signal received by the receiving means;
Automatic level adjusting means for detecting the level of the reflected signal amplified by the signal amplifying means and superimposing the level on the signal before or after being amplified by the signal amplifying means. Characteristic object detection circuit. A plurality of filter means having an amplifying function, which is disposed after the signal amplifying means and filters the reflected signal amplified by the signal amplifying means so as to pass only in a predetermined frequency range;
The automatic level adjusting means detects a level corresponding to a signal level between the last and the last of the plurality of filters, and supplies the level to an input terminal of the signal amplifying means or an input terminal of the plurality of filter means. The object detection circuit according to claim 2, wherein the object detection circuit is supplied.   4. The object detection circuit according to claim 3, further comprising an external connection unit that enables a signal output from the plurality of filter units to be output in a digital or analog manner.   An ultrasonic sensor device comprising the object detection circuit according to claim 1.

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