JPS6118464Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic receiving device that combines received signals from adjacent receiver groups to form a beam and detects a target in the direction of direction of the received beam.

An example of a device equipped with this type of receiving device is a scanning sonar. FIG. 1 shows a block diagram of the general receiving circuit. In the same figure,
V ₁ to _{V o} are n transducers with wide directivity arranged in a circular shape at equal intervals, and act as a wave transmitter during transmission and as a wave transmitter during reception. S ₁ to S ₈ are changeover switches that select eight adjacent transducers among these transducers, and each sequentially selects transducers V ₁ to Vn for circular scanning. It is. A ₁ to _{A 8} are high frequency preamplifiers that amplify the received signals of the eight selected transducer groups. D ₁ to _{D 6} are transducer V ₁
This is a delay circuit connected to preamplifiers A ₂ to _{A 7} in order to align the phases of the sound waves reaching ~Vn so that the sound wave arrival surfaces are aligned. It is not inserted into preamplifiers A ₁ and A ₈ which connect to transducers V ₁ and V ₈ . 1 is the transducer V ₁ ~
This is a combining circuit that combines the amplified received signals from V ₈ with aligned sound wave arrival surfaces to form a beam with sharp directivity as shown by the solid line in Figure ₂ . Input the received signal from _A8 ,
and an operational amplifier capable of outputting these combined signals. 2 is a display device for displaying the composite signal in PPI, and includes a detector for detecting the high-frequency composite signal from the composite circuit 1, a video amplifier for amplifying the detection output, a spiral sweep circuit, a cathode ray tube, etc. .

In the scanning sonar as explained above, sound waves are emitted simultaneously from transducers V ₁ to Vn, and in the receiving state, the transducers
A suitable plurality of transducers, for example, three transducers from V ₁ to Vn are combined to form a receiving beam with sharp directivity, and this receiving beam is sequentially scanned to determine the direction of each receiving beam. The echo is received and the target object is displayed on the display 2 in the corresponding direction and distance. That is, the scanning is performed using the selected eight transducers V ₁ ~
Since each received signal of Vn is phase-adjusted and synthesized so that the sound wave arrival surfaces are aligned, it is equivalent to one planar transducer corresponding to eight of these transducers moving in a circular shape. Become. However, in such a receiving device, if there is a received signal of a high level due to interference from another ship, etc., when each received signal is combined, the level will become high, which is the limit for the combining circuit 1 to operate faithfully. It had reached a state of saturation. The circle indicated by the dotted line in Figure 2 shows an example of such a state. In this case, the composite signal of the received signal due to not only the main lobe of the directional characteristic but also some side lobes reaches the saturation level of the composite circuit 1. A, the directivity deteriorates, and furthermore, in the connected video amplifier, the signal level appearing on the cathode ray tube exceeds the limit point B, or reaches the saturation level of the video amplifier, and the directivity is completely lost. As a result, as shown in Figure 3, on the cathode ray tube CRT, a ring-shaped interference wave D appears not only when the direction of the receiving beam is in the direction of arrow C, which is the interference wave direction, but also when a target such as a school of fish appears on the CRT. If a substance exists, it becomes impossible to distinguish, and the appearance is also undesirable. Note that this phenomenon is not limited to the synthesis circuit 1 in Fig. 1, and even when the synthesis circuit itself is composed only of passive elements, the saturation level of the high frequency or video amplifier, etc., which will be discussed later, is not limited to the synthesis signal. The same thing happens when .

In view of this point, it is an object of the present invention to provide an ultrasonic receiving device of the type mentioned at the beginning, which can suppress interference with observation due to high-level received signals such as interference from other ships. The purpose of this invention is to make the maximum value of the composite signal in the main lobe of the directional characteristic approximately equal to or lower than the saturation level of the circuit after the composite circuit (the composite circuit itself or the circuit following it). This can be solved by providing an amplitude limiting circuit in each input circuit of the combining circuit.

Next, an embodiment in which the present invention is applied to the receiving circuit shown in FIG. 1 will be described with reference to the drawings.

FIG. 4 is an example of a preamplifier having an amplitude limiting circuit according to the present invention. In the figure, 3 is an operational amplifier that amplifies a high-frequency received signal, 4 is a pair of diodes connected in antiparallel, and 5 is a tuning circuit. This pair of diodes 4 is connected to resistor R ₁ and
Together with _R2 , it forms an amplitude limiting circuit that works for both the positive and one side polarities. The preamplifiers having such a configuration are respectively substituted for the preamplifiers A ₁ to A ₈ inserted in each input circuit of the combining circuit 1 in the receiving circuit shown in FIG. As a result, each preamplifier according to the present invention is supplied with the received signal of the transducer connected sequentially in the scanning process, and after being tuned and amplified, it is directly or
It is supplied to the synthesis circuit 1 through D ₁ to D ₆ .

In a receiving circuit equipped with such a preamplifier, if a high level interference wave is received from, for example, another ship, the output level of each operational amplifier 3 will correspondingly increase. However, the level of each received signal input to the combining circuit 1 is limited by the pair of anti-parallel diodes 4 on both the + and - sides corresponding to the forward voltage of the diodes. As shown in Fig. 5, this limit level is not reached even if the received signals that have reached the limit level of the eight preamplifiers are combined when the direction of the interference wave and the directivity direction of the received beam match. The combined signal level of circuit 1 is set to approximately reach its saturation level A. On the other hand, the combined signal level at the side lobe changes depending on the maximum level of the main lobe in Fig. 2 and the attenuation ratio in Fig. 5, that is, the attenuation amount of the normal directional characteristic based on the saturation level A. decreases only,
No deterioration of directional characteristics occurs. In other words, when the received beam direction, that is, the above-mentioned hypothetical planar transducer is located in the direction of arrow C, the combined signal level reaches the saturation level A. On the other hand, when this planar transducer moves by scanning, each received signal Even if the levels of both of them are limited by the diode 4, it corresponds to the sidelobe characteristics, that is, corresponds to the phase shift at the time of combining each received signal, which corresponds to the unevenness of the sound wave arrival surface for the planar transducer mentioned above. , the composite signal level is attenuated. Therefore, as shown in FIG. 5, the composite signal level due to the side lobe whose directivity direction has moved from the direction of arrow C in the subsequent video amplification circuit may be below the limit point B of the video signal level. On the other hand, the echo from the target object does not reach the limit level of diode 4 and becomes a video signal according to the regular directional characteristics without being attenuated.
As a result, the interference wave D appears only when the directivity direction is in the direction of arrow C, as shown in FIG. 6, and interference with echoes is significantly suppressed.

FIG. 7 shows another embodiment of the present invention, in which the saturation level of the preamplifiers A ₁ to A ₈ is set to the amplitude limit level by adjusting the voltages of the +B and -B power supplies of the operational amplifier 6. do. In this case, each preamplifier is also used as an amplitude limiting circuit.

The embodiment described above is a case in which the present invention is applied to the circuit shown in FIG. 1, but it may also be applied to a scanning sonar in which the input circuit of the synthesis circuit, the synthesis circuit itself, or the circuit following the synthesis circuit are different. Applicable. In addition, if the gain of the amplifier after the combining circuit is adjustable, the limiting level of each amplitude limiting circuit should be set so that the combined signal level can be approximately below the saturation level in at least a part of the gain adjustment range. Set to .

Furthermore, the present invention is also applicable to the type of medical ultrasound receiving apparatus mentioned at the beginning.

As is clear from the above explanation, by providing an amplitude limiting circuit in each input circuit of the high-frequency reception signal synthesis circuit according to the present invention, the reception sensitivity of echoes from the target is not affected at all, and interference waves can be eliminated. It is possible to suppress the reception level due to side lobes of the high-level signal source, and interference with target detection is extremely reduced.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a general receiving circuit of a scanning sonar, Figs. 2 and 3 are reception characteristics for interference waves in the receiving circuit shown in Fig. 1, and Fig. 4 is an embodiment of the present invention. 5 and 6 show reception characteristics for interference waves according to the present invention, and FIG. 7 shows another embodiment of the present invention. 1... Synthesis circuit, 2... Display, 3, 6... Operational amplifier, 4... Anti-parallel diode, V ₁ to Vn...
…transducer, A ₁ to A ₈ … preamplifier,
_D1 to _D6 ...Delay circuit.

Claims (1)

[Scope of utility model registration request] An amplitude limiting circuit is provided in each input circuit of a combining circuit that combines each received signal from the adjacent wave receiver group so as to form a directivity that is sharper than that of the individual wave receivers, and the signal is received in the directivity direction, and the limiting level of the limiting circuit is set so that the combined signal level of each of the received signals whose level has been limited by the limiting circuit is approximately equal to or lower than the saturation level of the circuits subsequent to the combining circuit. Ultrasonic receiver.