JPH0580146A - Underwater sonic signal receiver - Google Patents

Abstract

PURPOSE:To provide high fidelity echo envelope retaining characteristics by using a non-linear amplifier circuit to produce gain control signals, and suppressing change of the sensed envelope due to changing level of the input signal. CONSTITUTION:A received signal I is fed to an amplifier circuit 1, amplified with a gain set by the level of a gain control signal C, and emitted as an output signal 0. The signal 0 is fed to a detector circuit 2, converted into a DC signal, and fed to a time constant circuit 4 as a detection output signal D. The time constant circuit 4 decides the response speed of an AGC circuit, and the output therefrom is fed to a logarithmic amplifier circuit 3 of non-linear type, amplified logarithmically. yielded as a signal C to serve for controlling the gain of the amplifier circuit 1. The output signal 0 of the circuit 1 is converted into audio signal by a frequency converting circuit 5, amplified by an AC amplifier circuit 6, and emitted as an audio signal A. The signal D from the detection circuit 2 is amplified by a DC amplifier circuit 7 and emitted as an image signal B.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to underwater acoustic signal probes, and more particularly to active underwater acoustic signal probes.

[0002]

2. Description of the Related Art Reflected sound (echo) of sound transmitted by oneself
In an active underwater acoustic signal detection observing system that detects the presence or absence of an underwater target object or obstacle, the dynamic range of the received signal reaches 120 dB (1 million times).
Therefore, dynamic range compression is essential for efficient processing of received signals. As one of the means, an AGC circuit having a variable gain amplifier circuit, a linear amplifier circuit, a reference signal and an adder circuit as main constituent elements has been used.

FIG. 2 is a block diagram showing an example of a receiving circuit of a conventional underwater acoustic signal detecting instrument.

As shown in FIG. 2, the conventional underwater acoustic signal detecting instrument is gain-controlled by a gain control signal C and a received signal I is received.
A variable gain amplifier circuit 1 for amplifying a signal, a detector circuit 2 for detecting the output of the amplifier circuit 1, a time constant circuit 4 to which a detection output signal D, which is the output of the detector circuit 2, is input, and a time constant circuit 4
The amplifier circuit 8 that linearly amplifies the output signal of 1 and the adder circuit 9 that adds the output signal of the amplifier circuit 8 and the reference signal R to generate the gain control signal C are configured.

Next, the operation of the conventional underwater acoustic signal detecting instrument will be described.

First, the received signal I is input to the amplifier circuit 1, amplified by the gain set by the level of the gain control signal C, and output as the output signal O. Next, the output signal O is input to the detection circuit 2, converted into a DC signal, and input to the time constant circuit 4 as the detection output signal D. The time constant circuit 4 is for determining the response speed of the AGC circuit, and its output is input to the width circuit 8 and linearly amplified. The output of the amplifier circuit 8 is subtracted from the reference signal R, which is a fixed DC signal, in the adder circuit 9, and a gain control signal C is generated to control the gain of the amplifier circuit 1.

Assuming that the level of the output signal O is V _O , the level of the input signal I is V _I , and the gain control characteristic of the amplifier circuit 1 is G (c), the input / output characteristic of the amplifier circuit 1 is as follows. Indicated by.

V _O = G (c) · VI …………………………………………………… (1) Further, the detection circuit 2, the amplification circuit 8, the time constant circuit 4 and the gain of the adder circuit 9 are G _D , G _L , G _T , and G _A , respectively, and the level of the reference signal R is V _R , the control signal C
The level V _{C of} is expressed by the following equation.

[0009]

Here, τ is the time constant of the time constant circuit 4. Further, b ₀ is the output level of the time constant circuit 4 when the time t is negative, and is expressed by the following equation in the stable state.

[0011]

As an example, the characteristic of G (c) can be expressed by the following equation when it is represented by an analog multiplier which is widely used at present.

G (c) = G · V _C …………………………………………………………… (3) From the formulas (1) to (3), V _O If it asks, it will become like the following formula.

[0014]

However,

[0016]

Here, the gain G · G _A = 60 dB, the gain G
_{When L} = G _D = G _T = 0 dB, the reference signal level V _R = 2, the time constant τ = 1, and the input signal level V _I changes by 20 dB, two examples, that is, from 0.01 to 0.1 FIG. 3 shows changes in the respective output levels V _O when they change and when they change from 0.02 to 0.2.
The time required to reach 3.6, which is about twice the stable level of the output level, is 0.0854 and 0.2, respectively.
42, and the ratio is calculated to be 2.8 times.

In the active type underwater acoustic signal detector,
The echo envelope from the target or the like also plays an important role in determining what kind of echo the received sound is from. However, as described above, since there is a large difference in response time depending on the input signal level, it is difficult to maintain the echo envelope of high fidelity.

[0019]

The above-mentioned conventional underwater acoustic signal detecting instrument has a linear amplifying circuit and an adding circuit in the feedback circuit of the AGC of the receiver, so that the response time depends on the level of the input signal. Since a large difference occurs, even if echoes of the same envelope are detected by the level of the input signal, the envelopes of echoes with high fidelity are difficult to maintain.

[0020]

In the underwater acoustic signal detecting instrument of the present invention, a variable gain amplifying circuit which amplifies a received signal and whose gain is controlled by a gain control signal, and detects an output signal of the variable gain amplifying circuit. A detection circuit, a time constant circuit that delays the output signal of the detection circuit by a predetermined time, and a non-linear amplification circuit that amplifies the output signal of the time constant circuit with predetermined non-linear characteristics to generate the gain control signal. It is equipped with.

[0021]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the underwater acoustic signal detecting instrument of the present invention.

As shown in FIG. 1, the underwater acoustic signal detecting instrument of the present embodiment includes an amplifying circuit 1 having a variable gain as in the conventional example,
In addition to the detection circuit 2 and the time constant circuit 4, the time constant circuit 4
Logarithmic amplification circuit 3 for logarithmically amplifying the output signal of 1 to generate gain control signal C, and further as a peripheral circuit, frequency conversion circuit 5 for converting output signal O into an audio signal, and amplifying the output of frequency conversion circuit 5. Amplifier circuit 6 for outputting audio signal A
And an amplifier circuit 7 that amplifies the detection signal and outputs a video signal B.

Next, the operation of this embodiment will be described.

First, the received signal I is input to the amplifier circuit 1, amplified by the gain set by the level of the gain control signal C, and output as the output signal O. Next, the output signal O is input to the detection circuit 2, converted into a DC signal, and input to the time constant circuit 4 as the detection output signal D. The time constant circuit 4 is for determining the response speed of the AGC circuit, and its output is input to the logarithmic width circuit 3, logarithmically amplified, and is generated as a gain control signal C to control the gain of the amplifier circuit 1. As is well known, the logarithmic amplifier circuit is one of the nonlinear amplifier circuits, and the output signal has a logarithmic relationship with the input signal.

On the other hand, the output signal O of the amplifier circuit 1 is converted into an audio signal in the frequency conversion circuit 5, amplified by the AC amplifier circuit 6 and output as the audio signal A. Also,
The detection signal D from the detection circuit 2 is amplified by the DC amplification circuit 7 and output as the video signal B.

When the level of the output signal O is V _O , the level of the input signal I is V _I , and the gain control characteristic of the amplifier circuit 1 is G (c), the input / output characteristic of the amplifier circuit 1 is as described above. Like the conventional example, it is expressed by the following equation.

V _O = G (c) · VI ……………………………………………… (1) In addition, the gains of the detection circuit 2 and the time constant circuit 4 are G respectively
_D, and G _T, the gain characteristics of the logarithmic amplification circuit 3 -Nlog
Assuming that x is the input signal level of the logarithmic amplifier circuit 3, the level V _C of the control signal _C is given by the following equation.

[0029]

Here, τ is the time constant of the time constant circuit 4. Further, b ₀ is the output level of the time constant circuit 4 when the time t is negative, and is expressed by the following equation in the stable state.

[0031]

Here, as an example, it is assumed that the characteristic of G (c) is expressed by the equation (3) as in the conventional example.

[0033] G (c) = G · V C ..................................................................... (3) Then, the gain n · G = 60 dB, the gain G _D · G _T = -6
Two examples in which the input signal level V _I changes by 20 dB as in the conventional example with dB and time constant τ = 1, that is,
From the respective changes in the output level V _O when changing from 0.01 to 0.1 and when changing from 0.02 to 0.2, it is about twice the stable level of the output level V _O 3. Calculate the time to reach .6. The calculation results are 0.134 and 0.245, respectively,
The ratio is 1.8 times. This can be said to be a considerable improvement in comparison with 2.8 times that of the conventional example.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made.

For example, as a nonlinear amplifier circuit, instead of a logarithmic amplifier circuit, as long as it is a circuit that can express a function having a derivative in the use range without passing through the origin, any circuit is effective, as is clear from the mathematical expression. Of course, the present invention can be applied without departing from the gist of the present invention.

[0036]

As described above, the underwater acoustic signal probe according to the present invention can suppress the change of the detection envelope due to the change of the level of the input signal by using the non-linear amplification circuit for the generation of the gain control signal, and thus the high fidelity can be achieved. This has the effect that the envelope holding characteristic of the echo of each degree can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an underwater acoustic signal detecting pedestal of the present invention.

FIG. 2 is a block diagram showing an example of a conventional underwater acoustic signal detecting rig.

FIG. 3 is an input / output characteristic diagram showing an example of an operation in a conventional underwater acoustic signal detecting observatory.

[Explanation of symbols]

 1, 6, 7, 8 amplification circuit 2 detection circuit 3 logarithmic amplification circuit 4 time constant circuit 5 frequency conversion circuit 9 addition circuit

Claims (1)

[Claims] 1. A variable gain amplifier circuit in which a received signal is amplified and a gain is controlled by a gain control signal, a detection circuit for detecting an output signal of the variable gain amplifier circuit, and an output signal of the detection circuit is predetermined. An underwater acoustic signal detecting instrument comprising: a time constant circuit that delays time; and a non-linear amplification circuit that amplifies an output signal of the time constant circuit with a predetermined non-linear characteristic to generate the gain control signal.