JPS5979875A - Ultrasonic detection apparatus - Google Patents

Abstract

PURPOSE:To obtain an inexpensive ultrasonic detection apparatus, by changing over the impedance of the synchronous circuit of an amplifier corresponding to the input level of the amplifier. CONSTITUTION:Low voltage diodes 22, 33 are inserted in a synchronous circuit 31 in parallel in reverse connection. When the resonance voltage of the synchronous circuit 31 exceeds the Zener voltages of the low voltage diodes 32, 33, the diodes 32, 33 are brought to a continuity state and the impedance of the synchronous circuit 31 is abruptly reduced to reduce the size of resonance and, therefore, the amplification degree of an amplifier is lowered to a large extent. On the other hand, when the resonance voltage of the synchronous circuit 31 is equal to or less than the voltages of the diodes 32, 33, the synchronous circuit 31 is brought to such a state that almost infinite resistance are inserted in parallel and the amplification degree of the amplifier becomes large. As a result, the reduction of a dead zone is simply attained and an inexpensive ultrasonic detection apparatus can be obtained.

Description

Detailed Description of the Invention (1) Field of the Invention The present invention relates to an ultrasonic detection device that detects the presence of an object by transmitting ultrasonic waves to an object and receiving the reflected waves. This relates to reducing the area (dead zone).

(2) Prior art and its problems FIG. 1 shows the basic configuration of a conventional ultrasonic detection device, and FIG. 2 shows waveforms at various parts. In the figure, an ultrasonic transducer 1 receives an output excitation wave signal from an amplifier 2 and continuously sends out ultrahigh wave pulses toward a subject 3.

This excitation wave signal is obtained by superimposing a continuous wave signal of an appropriate frequency on the output pulse signal a of the pulse signal generating circuit 4 in the modulation circuit 5 and amplifying it.

On the other hand, the ultrasonic transducer 1 receives reflected ultrasonic pulses from the subject 3, and this received signal (b) is input to the amplifier 6 together with the transmitted signal (a) (input signal C ). The output signal d of the amplifier 6 is subjected to envelope detection in a detection circuit 7, and a gate circuit 8 extracts the wave receiver Qf contained in this detection signal.

Therefore, the received wave extraction signal e is input to the goo 1 circuit 8, and this signal e is generated based on the pulse signal a in the received wave extraction signal generation circuit 9, and is generated one hour after the fall of the pulse signal a. This is a level signal that rises to 1 lvl after the lapse of time. The distance covered corresponding to this time T1) ill is the subject 3
It shows the limit distance that can be detected, that is, the dead zone,
This occurs for the following reasons.

First, at the input of the amplifier 6, the transmission signal (A) is not the excitation wave signal itself, but has a waveform in which the trailing edge of the excitation wave signal is expanded exponentially. This is due to the characteristic characteristic of the ultrasonic transducer 1 that still carries out damped vibration even after the excitation wave signal disappears, and is called reverberation.

Next, the amplifier 6 is a narrowband type tuning amplifier in which the Q of the tuning circuit is increased to ensure a sufficient S/N ratio for low-level received signals. Therefore, when the transmission signal (a) is amplified by this amplifier 6, as shown in signal d, the part affected by the reverberation is compounded by the resonant damped vibration of the tuned circuit, and as a result, the part swells greatly as a whole, and the excitation wave signal This is equivalent to a wider width.

If the subject 3 is within this dead zone, the received signal at the output J of the amplifier 6 will be masked by the transmitted signal and cannot be extracted. Therefore, reducing this dead zone is an important research topic for this type of ultrasonic detection device, and it is necessary to selectively adopt ultrasonic transducers with low reverberation. Regarding amplifiers, the dead zone can be reduced by providing a gain control circuit that increases or decreases the gain of the amplifier depending on the arrival time of the received signal, that is, increases or decreases the gain of the amplifier in a short distance range and increases it in a long distance range. The reality is that we are trying to do so.

However, the ultrasonic detection device to which this invention is directed uses a single electroacoustic converter (ultrasonic transducer 1) for transmitting and receiving waves.
As can be inferred from the fact that the device is made smaller and lighter, it is an inexpensive and versatile device. In addition, the circuit configuration of the amplifier becomes complicated, resulting in an overall cost increase.

(3) Purpose of the Invention The purpose of the present invention is to provide an inexpensive ultrasonic detection device in which the dead zone can be easily reduced by switching the impedance of the amplifier's tuning circuit according to the input power level of the amplifier. It's about doing.

(4) Structure and Effect of the Invention In order to achieve the above object, the present invention provides a tuning circuit for an amplifier in which the impedance of the tuning circuit is set to a low impedance when the input level to the amplifier is high and to a high impedance when the input level is low. It is characterized by having impedance switching means for switching to impedance.

According to this configuration, when the input level of the amplifier is large,
That is, when a transmission signal is input, the impedance of the tuned circuit decreases and the gain of the amplifier decreases. Therefore, both the amplitude and width of the amplified transmission signal are smaller than those of the conventional one, and the dead zone is reduced compared to the conventional one without selecting the ultrasonic transducer. When the input level of the amplifier is low, that is, when a received signal is input, the impedance of the tuned circuit increases and the gain of the amplifier almost returns to its original value. Therefore, the -C amplified received signal can be made to have approximately the same amplitude as the above-mentioned transmitted signal, and a sufficient S/N ratio with respect to the received signal can be ensured.

Further, since the impedance switching means can be realized without using a complicated circuit configuration like a conventional gain control circuit, an inexpensive ultrasonic detection device can be provided.

(5) Description of Embodiments FIG. 3 shows a circuit configuration of a receiving amplifier of an ultrasonic detection device according to the present invention. In the figure, this amplifier amplifies the input signal V1 to two stages using a transistor Q1 having a tuning circuit 31 and a one-herald transistor Q2 electromagnetically coupled to the tuning circuit 31, and outputs the signal to the detection circuit 7 in the next stage. .

The tuned circuit 31 is a parallel resonant circuit consisting of a coil L and a capacitor C, and low voltage diodes 32 and 33 connected in reverse are inserted in parallel in this tuned circuit 31.

With this configuration, when the resonant voltage of the tuned circuit 31 exceeds the Zener voltage of the low voltage diodes 32 and 33,
The low voltage diodes 32, 33 become conductive. Therefore, the impedance of the tuning circuit 31 is drastically reduced and the magnitude of resonance is reduced, so that the input voltage of the transistor Q2 is reduced, and the amplification degree of the amplifier is significantly reduced. At this point, the resonance damped vibration in the tuned circuit 31 when the input to the transistor Q1 disappears also becomes small.

On the other hand, the resonant voltage of the tuned circuit 31 is
．． If the Zener voltage is below the '33, the tuning circuit 31 will
This means that an infinitely large resistor is inserted in parallel, and the magnitude of resonance becomes the original value defined by coil L and capacitor C. The input of transistor Q2 increases, and the amplification degree of the amplifier increases. becomes larger than in the case described above.

Therefore, when the transmitting signal (c) and the receiving signal (d) are close to each other as shown in FIG. 4(A), according to the amplifier according to the present invention, as shown in FIG. 4(B), It is amplified as follows. That is, the transmitted signal (C) with a large amplitude is amplified a little to become (E), and the received signal (D) with a small amplitude is greatly amplified to become (E). At this time, the amplitude of the received signal (b) can be made approximately equal to the amplitude of the transmitted signal (b).

What should be noted here is that the bulge at the trailing edge of the transmitted signal (e) is small.

This is because the above-mentioned resonance damping vibration is not added to the reverberation-affected portion when the transmission signal (c) is amplified, and according to the present invention, this reverberation influence can also be suppressed.

For example 1. Conventionally, as shown in Fig. 4 (A), there is a received signal (d) immediately after the transmitted signal (c), and when this is amplified, the trailing edge of the transmitted signal swells greatly and the received signal is The received wave signal could not be extracted because it enveloped the wave signal.

However, according to the present invention, the width of the received signal is almost the same before and after amplification, and the width of the received signal after amplification is actually smaller, so that the width of the received signal (e) and the received signal (e) are different, as shown in FIG. 4(B). ) the boundaries become clear. In other words, the dead zone is smaller than before.

Next, FIG. 5 is a schematic diagram showing an amplifier according to another embodiment of the present invention, mainly showing a tuning circuit. The impedance switching means according to the second embodiment includes two resistors R+ and R2 having sufficiently different magnitudes, and a switching element 81 . S2, switching element S+.

A control circuit 51 that issues a switching command signal PI (R2> to S2)
It consists of

The control circuit 51 sets the switching command signal P1 to 1 level or U level depending on whether the input level of the amplifier is at a predetermined level or not. At this time, the signal P2 is transferred to the inverter 52.
Invert by.

Switching elements 81 and 82 receive switching command signals P1 and R2.
In response to this, it performs an inversion operation and inserts one of the resistors R1 and R2 in parallel to the tuning circuit 31.

With the above configuration, the same effects as in the first embodiment can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram showing the basic configuration of a conventional ultrasonic detection device, and Fig. 2 shows waveforms of each part of the conventional device.
3 is a schematic circuit diagram showing an ultrasonic detection device according to an embodiment of the present invention, centering on a receiving amplifier, FIG. 4 is a diagram illustrating the reduction of the dead zone, and FIG. FIG. 7 is a schematic circuit diagram showing another embodiment of the invention, mainly showing an impedance switching means. 1・・・・・・・・・・・・・・・・・・Ultrasonic transducer 6・・・・・・・・・・・・・・・・・・Amplifier 31
................................................... Tuned circuit 32.33.
・・・・・・Low voltage diode 51・・・・・・・・・・
...Control circuit R+, R2...Resistor SL, S2...Switching element PI (R2)
...Switching command signal A......Transmission/reception signal B input to the amplifier...
・Transmission/reception signal T after amplification...
...Dead Zone Patent Applicant Tateishi Electric Co., Ltd. Figure 2 (f) - Icchoto Figure 3 Figure 4) Figure 5

Claims (3)

[Claims] (1) Send out ultrasonic pulses from one ultrasonic receiver, receive reflected waves with the ultrasonic transducer, amplify the transmitted and received signals with one amplifier, and extract the received signals. In the ultrasonic detection device, the tuning circuit of the amplifier is provided with impedance switching means for switching the impedance of the tuning circuit to a low impedance when the input level to the amplifier is high and to a high impedance when the input level is low. Features of ultrasonic detection device. (2) The ultrasonic detection device according to claim 1, wherein the ultrasonic switching means comprises two reversely connected low voltage diodes inserted in parallel in the tuning circuit. (3) The impedance switching means includes two resistors having sufficiently different values, a switching means for inserting one of these two resistors in parallel into the tuning circuit, and switching to this switching means. 2. The ultrasonic detection device according to claim 1, further comprising a control signal generating means for generating a command signal.