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DESCRIPTION JPH0775198

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DESCRIPTION JPH0775198
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic transmitting and receiving apparatus for transmitting and receiving ultrasonic waves
in the air as a medium.
[0002]
2. Description of the Related Art Heretofore, as shown in FIG. 4, an ultrasonic transmitting and
receiving apparatus 3 in which a cylindrical piezoelectric ceramic 1 is fixed to a reflector 2, a
transmitting circuit 20 and a receiving circuit 23 are shown in FIG. The ultrasonic transducer 3 is
connected to the second winding 41 b of the transformer 41 by the two-core shield wire 5, and
the first winding 41 a and the second winding 41 b are connected to each other. The outer shield
6 of the core shield wire 5 is connected to the ground line (OV line) 22 of the transmission circuit
20 and the reception circuit 23. One end of the terminal of the second winding 41 b of the
transformer 41 is connected in common to the ground line (OV line) 22. However, in such a
configuration of the ground line (OV line) 22, noise received by the ultrasonic transducer 3 is
also superimposed on the ground line (OV line) 22, which adversely affects the reception circuit
23, and noise processing is required. Have the following disadvantages. Furthermore,
conventionally, this type of reception circuit 23 is configured to amplify the reception signal of
the ultrasonic transducer 3 by the amplifiers 7 and 9 as shown in FIG. 5, but as shown in FIG. 6A,
the amplifier 7 amplifies the signal to the amplitude Vb as shown in FIG. 6B, and the amplifier 9
amplifies the signal to the amplitude Vc of FIG. 6C. . For example, as shown in FIG. 6 (d), the
output of the amplifier 9 shown in FIG. 6 (c) and the DC component (V1 in FIG. 6 (c)) are detected
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by the capacitor 11 of FIG. It cuts and sets a certain detection level V2 for a signal of amplitude
Vd1 = Vc / 2, and has a function to determine the presence or absence of an obstacle by
comparing the detection levels V2 and Vd1. However, in such a configuration, as described
above, the signal amplified to 20 log Vc / Va (dB) by the amplifiers 7 and 9 is halved as in Vd1 of
FIG. There was a drawback that it decreased.
[0003]
SUMMARY OF THE INVENTION In the conventional ultrasonic transmitting and receiving
apparatus, since the terminal of the circuit of the ultrasonic transducer and the input terminal of
the receiving circuit are directly connected, the ultrasonic wave is transmitted through the
ground line. The noise of the transmitter-receiver mixes in the receiving circuit, which
deteriorates the performance of the ultrasonic transmitter-receiver. Further, since the direct
current component is cut by the output circuit of the receiving circuit, the signal is also reduced
to 1/2.
[0004]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to
the present invention, a transmitter circuit of an ultrasonic receiver, a receiver circuit, and an
ultrasonic transmitter-receiver are transformers each having three independent windings.
Coupling is made, and the ultrasonic transducer and the transformer are connected using a shield
wire, and the shield of the sheath of the shield wire is connected to the ground side ground line
of the transmission circuit and the reception circuit. Furthermore, the receiving circuit is
constituted by a cascade connection of an amplifier, a waveform shaping circuit and a detection
circuit.
[0005]
In the present invention, the ultrasonic transducer 3 is electrically isolated since it is connected
to the receiving circuit 21 by the transformer in the present invention, and the cylindrical
piezoelectric ceramic 1 and the shield are produced. The noise picked up by the line 5 does not
directly enter the receiving circuit 21 and the noise level can be attenuated by several tens of dB.
[0006]
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2
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a circuit block diagram of an ultrasonic transmitting and receiving apparatus showing an
embodiment of the present invention. The ultrasonic transducer 3 in which the cylindrical
piezoelectric ceramic 1 is formed at the center of the reflector 2 is connected to the second
winding 4 b of the transformer 4 by the shield wire 5. The transmission circuit 20 is connected
to and coupled to the first winding 4 a of the transformer 4, and the receiving circuit 21 is
connected to and coupled to the third winding 4 c of the transformer 4. Furthermore, the ground
line of the transmission circuit 20, the ground line of the reception circuit 21, and the outer
shield 6 of the shield line 5 are connected in common. FIG. 2 is a circuit block diagram of the
receiving circuit 21 showing an embodiment of the present invention. A first amplifier 7 is
connected to the third winding 4 c of the transformer 4, and a waveform shaping circuit 8
composed of a capacitor 11, a diode 12 and a resistor 13 is connected to the output of the
amplifier 7. Further, the second amplifier 9 is connected to the subsequent stage. Further, a
detection circuit 10 including a diode 14 and a capacitor 15 and 17 resistors 16 and 18 is
connected to the subsequent stage. The signal received by the ultrasonic transducer 3 is
transmitted through the shield wire 5 from the second winding 4b of the transformer 4 to the
third winding 4c, and the amplitude Va around the OV as shown in FIG. 3A. It appears as a signal.
Noise N is included here. The signal of this amplitude Va is amplified by an amplifier 7 having a
band pass filter inside, amplified to a signal of amplitude Vb including a DC component V1 as
shown in FIG. 3 (b), and noise shown in FIG. 3 (a) N disappears here. Furthermore, the DC
component V1 is cut off by the capacitor 11 by passing the waveform shaping circuit 8
consisting of the output of the amplifier 7 and the amplitude Vb through the capacitor 11, the
diode 12 and the resistor 13, and the amplitude of the amplitude Vb Is shaped as it is into a
waveform of positive side amplitude, that is, the amplitude Vc shown in FIG. 3 (c). The signal of
amplitude Vc shown in FIG. 3C is further amplified by a second amplifier 9 which amplifies a
signal of OV or more (+ side) by an operational amplifier for single power supply or the like.
Compared with the conventional method in which the direct current is cut only by the capacitor
11 shown in FIG. 5, the signal is halved and only the positive amplitude is taken out, and only a
signal of substantially half can be used. As described above, since the amplitude Vb = the
amplitude Vc and all the amplitude amplified by the first amplifier 7 can be used as a signal, the
amplification degree of the amplifiers 7 and 9 is improved by 6 dB as it is. Furthermore, the
signal amplified by the second amplifier 9 passes through the detection circuit 10 including the
diode 14, the capacitors 15, 17 and the resistors 16, 18 to obtain the frequency component f of
the amplitude Vc shown in FIG. Is detected in the form of an envelope and becomes a signal
having an amplitude Vd shown in FIG. 3 (d).
At the same time, the detection circuit 10 has a large amount of attenuation when the input
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signal level is small as in the graph shown in FIG. 7, so noise and signals can be separated to gain
an S / N ratio.
[0007]
As described above, a transformer having three windings is used for an ultrasonic transducer, a
transmitter circuit and a receiver circuit, and a receiver circuit including a waveform shaping
circuit and a detector circuit. Thus, it is possible to provide an ultrasonic transmitting and
receiving apparatus having low noise and high signal level.
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