JPS6344775Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is suitable for underwater detection devices such as acoustic sounders,
The present invention relates to a receiving device used in a detector using sound waves such as a fish finder or a detector using radio waves, and particularly relates to an automatic gain control device.

For the sake of convenience, in the case of detecting underwater objects using ultrasonic waves, the level of echo signals from the seabed, fish schools, etc. fluctuates greatly when affected by pitting and rolling.

When tracking the seabed, if the level of the echo signal is low, tracking may not be possible, so it is necessary to keep the level as stable as possible.

Generally, receiver automatic gain control (abbreviated as AGC) is used to stabilize the level.
AGC is extremely difficult when dealing with echo signals of pulse modulated waves, such as in underwater detection equipment. That is, when rapid tracking is performed for waveform fluctuations, noise is also affected by AGC, resulting in poor S/N ratio.

Therefore, if the AGC time constant is made long, the S/N ratio will be good, but on the other hand, it will not be able to follow rapid fluctuations.

This idea overcomes the conflicting conditions mentioned above, performs AGC in an intermediate operating range, and improves S/
This suppresses the decrease in N and also tracks rapid fluctuations well.

Next, an explanation will be given based on an example. FIG. 1 is a block diagram of the embodiment, and FIG. 2 is an explanatory diagram of the operation, and the respective waveforms are shown in correspondence with the symbols written in each part in FIG.

When the received signal P is amplified by the receive amplifier 1 and rectified by the rectifier 2, the output becomes as shown in Fig. 2A, and is sent to the comparators 3 and 4 and the analog switch 7, as well as the diode. 10 is applied.

Here, the comparator 3 is set to a suitably high level A,
Since comparator 4 is set to level B, which is lower than A (see Figure 2 A), an output appears on the output side of comparator 3 only between times t ₂ and t ₃ (see Figure 2 B). ), and an output appears on the output side of the comparator 4 between times t ₁ and t ₄ and between t ₅ and t ₆ .

Next, the outputs of the two comparators are respectively applied to the exclusive OR circuit 5. In this case,
The output of comparator 3 is (0) and the output of comparator 4 is (1)
Since the output of the exclusive OR circuit 5 becomes (1) only when , the output is applied to the analog switch 6 for a short period of time as shown in FIG. 2D.

Next, the output of the rectifier 2 and the output of the comparator 3 are applied to the analog switch 7 which acts as an ON/OFF switch, and when the output of the comparator 3 is applied, the analog switch 7 is activated. , the output of the rectifier 2 included in the range t ₂ to _{t 3} above the high level A is charged to the capacitor C ₁ through the diode 8 and the resistor R ₁ . Here, the values of R ₁ and C ₁ are set to have small time constants so that they are charged quickly.

The terminal voltage of _C1 is applied to the analog switch 11, but on the other hand, the switch is activated only while the analog switch 6 is activated and turned ON, that is, while the exclusive OR circuit 5 is producing an output. The terminal voltage of _C1 is diode 9
It is discharged through the resistor R inserted outside the analog switch 6 with a short time constant by the circuit consisting of the resistor R2 _and the capacitor _C1 .

On the other hand, the output of the rectifier 2 (signal in Fig. 2 A)
are the diode 10 and the long time constant resistors R ₀ , R ₃
and a capacitor C ₀ , and the capacitor C ₀ is charged every moment.

This charging voltage is applied to the analog switch 11 that performs the switching action, and is passed through the analog switch 11 to the receiving amplifier 1.
It is fed back as AGC voltage.

When the output of the comparator 4 is applied to the analog switch 11, the analog switch 11 is thereby switched, and the terminal voltage of the capacitor _C1 is supplied as the AGC voltage of the receiving amplifier 1. The AGC voltage is controlled as shown in FIG.

In this way, even when the level of the received pulse signal fluctuates, the received level can be controlled to be substantially constant regardless of the fluctuation.

Note that when setting the high and low levels of the comparator, the high level may be set based on the required level determined as the capture target. The low level may be set to a value higher than the noise level, taking noise into consideration, and it is more suitable if the design is such that the high and low levels can be switched in multiple stages so that both high and low levels can be selected as appropriate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the embodiment. Second
The figure is an explanatory diagram of the operation. 1... Receive amplifier, 2... Rectifier, 3, 4...
Comparator, 5... exclusive OR circuit,
6, 7...Analog switch, 8, 9, 10...
Diode, 11...Analog switch.

Claims (1)

[Scope of utility model registration request] The level of the pulsed reception signal amplified by the reception amplifier 1 and rectified by the rectifier 2 is compared with the level of the comparators 3 and 4, which are set to two levels, high and low, respectively. The outputs of the circuits 3 and 4 are applied to an exclusive OR circuit 5, and the output of the circuit 5 is applied to an analog switch 6.
The output of the rectifier 2 and the output of the comparator 3 at a high level are applied to an analog switch 7, and the switch 7 is controlled, and the output of the rectifier 2 applied to the switch 7 is passed. A capacitor C ₁ connected through a diode 8 and a resistor R ₁ in the latter stage is charged, and the terminal voltage of the capacitor C ₁ is applied to an analog switch 11, and the output of the exclusive OR circuit 5 is applied to an analog switch 6. resistance R ₂ when applied to
The output of the rectifier 2 is connected to the diode 10 and the resistor _R0 ,
Both the terminal voltage charged to the capacitor C ₀ through the charging circuit consisting of R ₃ and the capacitor C ₀ and the terminal voltage of the capacitor C ₁ are fed back as the AGC voltage of the amplifier 1 via the analog switch 11. An AGC device for pulse reception signals, characterized in that the AGC voltage is controlled by the low level output of the comparator 4 applied to the analog switch 11.