JPS6218085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an active sonar device that emit sound waves underwater and receive the echoes to locate underwater objects, for example. Cathode
This invention relates to AGC (Automatic Gain Control) circuits that are useful for facilitating display on Ray Tubes.

Active sonar devices emit sound waves that are pulse-modulated sine waves, measure the time delay of echoes from underwater objects, and determine the distance to underwater objects.
This method involves preparing a number of receiving directional beams in different directions and comparing and measuring which receiving directional beam has the highest output level regarding the echoes from underwater objects, thereby clarifying the position of the underwater object.

The signals received by this active sonar device include echoes from underwater objects, reverberations scattered by minute underwater objects, etc., underwater natural noise that exists in the underwater natural world, and the levels of these signals change from moment to moment. , the degree of change is usually 60 ~
It reaches as high as 150dB. In order to detect reverberant sounds from underwater objects among widely fluctuating reverberations and noise, it is necessary to suppress this reverberation and noise to a nearly constant level, and the receiving system of active sonar devices usually includes an AGC circuit. It is prepared. In other words, the AGC circuit of an active sonar device equalizes the level of interfering noise such as reverberation and underwater noise whose level changes are relatively gradual over time, without impairing the quality of echoes from underwater objects that have a short duration. output and facilitates its detection.

Conventionally, this sonar AGC circuit is comprised of a variable gain amplifier circuit 1 and a control signal generation circuit 2, as shown in FIG. Note that 3 and 4 are the AGC circuit input terminal and output terminal, respectively, 5 is the input of the control signal generation circuit, and 6 is the gain control signal of the output of the control signal generation circuit. Variable gain amplifier circuits include those that use the nonlinear effect of diodes and those that utilize multiplier circuits, and there are various types of control signal generation circuits that correspond to the types of variable gain amplifier circuits. As an example, the principle of operation of a method using a diode will be explained with reference to FIG. In Figure 2, 7 is an input resistor, 8 is a diode, 9 is an amplifier circuit, 10 and 11 are capacitors for direct current blocking, and 12 is an input resistor for gain control signals, which constitutes a variable gain amplifier circuit. , 13 is a detection circuit, 14 is an integration circuit, and 15 is an amplifier circuit, which constitute a control signal generation circuit.

When a signal whose level changes complexly over time is applied to the input terminal 3, the signal is transferred to the variable gain amplifier circuit 1.
The signal is amplified by the amplifier circuit and applied to the control signal generation circuit 2. In the control signal generation circuit, after the wave is detected, components that change rapidly over time are removed by an integrating circuit, and only components that change slowly are outputted and amplified to become a control signal. When the voltage of the control signal increases, the resistance of the diode 8 decreases, so the level of the signal input to the amplifier circuit 9 decreases, and conversely, when the control voltage decreases, the level of the signal input to the amplifier circuit 9 increases. .

As a result of the above-described operation, the signal applied to the input terminal 3 that changes complexly over time is outputted after its components that change slowly over time are removed and the signal is made uniform.

However, conventional AGC circuits for sonar that operate in this manner usually have the following problems. In general, the input signal to the AGC circuit of a sonar has the characteristics shown in Figure 3a. In this figure, the part indicated by Z is the reverberation, and the level decreases over time. The part indicated by H is the reverberation sound from the submarine, and the level is higher than the reverberation by A. When the signal shown in FIG. 3a is applied to the sonar AGC circuit shown in FIG. 2, the output will be as shown in FIG. 3b. As shown in FIG. 3a, the level of the reverberation portion that decreases over time is equalized, but the envelope of the reverberant sound indicated by H is distorted. This third
Distortion of the envelope of the reverberant sound, indicated by H in Figure b, is a defect in the conventional AGC circuit. In other words, when the distortion is severe, the level of A in the rising part is maintained, but its envelope becomes a steep triangle, and in a general sonar that detects and integrates this signal to generate a CRT brightness signal, the level of the brightness signal is significantly increased. This will result in a decline in In extreme cases, even if there is a reverberant sound as shown by H in Figure 3a at the input of the AGC circuit, depending on the characteristics of the AGC circuit, the reverberant signal may disappear in the CRT luminance signal. .

The distortion of the reverberant sound in the conventional AGC circuit shown above is mainly affected by the time constant in the integrating circuit shown in FIG. If the time constant is extremely short, the rectangular echo signal input to the integrating circuit will be output without being smoothed by the integrating circuit and will appear in the control signal. In such a state, the level of the signal is reduced by the diode 8 as described above, and the echo signal at the output section of the AGC circuit becomes a steep triangle. On the other hand, if the time constant of the integrating circuit is made extremely long, the distortion of the envelope of the reverberating sound will be reduced, but the reverberation part shown by Z in Fig. 3a, which changes slowly over time, cannot be made uniform. Therefore, in conventional AGC circuits, it is necessary to find the time constant of the integrating circuit so that the distortion of the echo envelope and the level of reverberation can be compromised, and this integral number is found by repeating trial and error experiments. It was customary.

The present invention solves the above drawbacks by limiting signals above a set level and sending only signals within the limit range to the integrating circuit before integrating in the control signal generation circuit, resulting in low distortion and response. A sonar with good performance and easy circuit design.
It provides an AGC circuit.

Next, embodiments of the present invention will be described with reference to the drawings. Referring to FIG. 4 showing the sonar AGC circuit according to the present invention, the output of the variable gain amplifier circuit 1 is a detection circuit 13, a level limiting circuit 16, and an integrating circuit 1.
4 and an amplifier circuit 15. After this input signal is detected, it is applied to a level limiting circuit 16 that limits signals exceeding a set level. Reverberation sounds from underwater objects that are higher in level than background noise such as reverberation and underwater noise are limited by this level limiting circuit. If the reflected sound exceeds the set level, the reflected sound is limited to the set level, and if it is below the set level, it is output as is to the integrating circuit 14.

In this way, the reverberant sound signal is limited to below the set level and input to the integrating circuit, so the reverberant sound signal component output from the integrating circuit will never exceed the level corresponding to the level set by the level limiting circuit. .
Therefore, the reverberant sound component in the gain control signal 6 generated by amplifying the output of the integrating circuit by the amplifier circuit 15 is limited, and the reverberant sound output of the sonar AGC circuit is at the level set by the level limiter circuit. The corresponding distortion is the maximum one, and the distortion is always below this certain value.

As described above, the time constant of the integrating circuit 14 in the control signal generating circuit 2 only needs to be set so that the distortion can be made sufficiently small only for the echo sound corresponding to the level set in the level limiting circuit. There is no need to take any consideration to high reverberant sounds.

As explained above, by including the level limiting circuit in the control signal generating circuit, the present invention can limit the distortion of the echo sound signal to a predetermined value or less, and the time constant of the integrating circuit can be easily calculated. Since there is no need to extend the time constant any further, a sonar AGC circuit with excellent response characteristics can be obtained.

[Brief explanation of the drawing]

Figure 1 is a basic principle block diagram of a sonar AGC circuit, Figure 2 is a conventional sonar AGC circuit.
Block diagram of the AGC circuit, Figure 3 a and b are the second
Signal waveforms of input terminal 3 and output terminal 4 in the figure, 4th
The figure is a block diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Variable gain amplifier circuit, 2...Control signal generation circuit, 3...Input terminal, 4...Output terminal, 5...Control signal generation circuit input, 6...Gain control signal, 7...Input resistance, 8...Diode, 9...Amplification Circuit, 10... DC blocking capacitor, 11... DC blocking capacitor, 1
2... Gain control signal input resistance, 13... Detection circuit, 1
4... Integrating circuit, 15... Amplifying circuit, 16... Level limiting circuit.

Claims (1)

[Claims] 1. A variable gain amplifier circuit whose gain is varied by a control signal, a level limiting circuit connected to receive the output signal of the variable gain amplifier circuit and limiting signals above a predetermined level, and a level limiting circuit of the level limiting circuit. An AGC circuit comprising: an integrating circuit connected to receive an output signal, and supplying the output signal of the integrating circuit as the control signal to the variable gain amplifier circuit.