JPH0412471Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a video waveform shaping circuit used in a display device of a sonar device.

Description of the Prior Art In active sonar devices that display PPI using a split beam reception method that determines the direction of reverberated sound, the video waveform after detection is a very important element.

This will be explained using FIGS. 1, 2, and 3.

FIG. 1 shows a block diagram of a reception display section of a sonar device.

Here, 1 is a reverberation sound direction detection section, 2 is a video detection section, 3 is a video waveform shaping circuit, 4 is a display section, and 5 is a video waveform shaping circuit.
is a received signal, 6 is an azimuth signal, 7 is a detection signal, and 8 is a video level signal.

FIG. 2 shows the signal waveforms of each part of the circuit shown in FIG. It is a signal waveform. FIG. 3 is an example of a display displayed on the display section 4 shown in FIG. Further, in FIGS. 2 and 3, A is a noise signal section, B is a target signal section, and C is an extension section of the video level signal. The received signal 5 is input to the direction detection section 1 and the video detection section 2. Direction detection unit 1
inputs the direction signal 6 to the display section. A received signal 5 inputted to the video detection section 2 is detected, shaped as a detected signal 7 by a video waveform shaping circuit 3, and inputted as a video level signal 8 to the display section 4.

In order to improve the S/N ratio, the video level signal waveform 38 passes through the video waveforming circuit 3 composed of a filter circuit having a time constant corresponding to the pulse width of the signal used in the sonar device. As shown in , compared to the detected signal waveform 37, the section B
In section C, where the received signal 5 becomes a noise signal, there is a temporal elongation. The extension time is determined by the time constant of the filter circuit.

Here, section B is a target signal section, and since the azimuth signal waveform 36 shows a constant value, it is displayed in a constant azimuth in FIG. However, section C is an elongated section, and while the video level signal waveform 38 has a temporal elongation, the azimuth signal waveform 36 has an uneven value due to noise. The display will sway significantly in the direction.

For this reason, in a sonar device that performs PPI display by using a split beam reception method to determine the direction of the echo sound, it is important to shorten the section C in which the direction fluctuates greatly.

A wave-forming circuit conventionally used as a method for shortening section C shown in FIG. 3 will be described with reference to FIGS. 4 and 6.

FIG. 4 shows a conventional waveform shaping circuit, in which 11 is a diode, 12 is a resistor, and 13 is a capacitor.

The sonar reception signal 5 is detected, and the detected signal 7 is
Therefore, ideally, the detected signal waveform 3 shown in Figure 6 is
It becomes 7a. The detection signal 7 is input to a diode 11 and a resistor 12, but since the diode 11 is in a reverse bias state, the current passes through the resistor 12, and as shown in the video level signal waveform 38 of FIG. Charge the capacitor 13. The charging time constant is the product of the resistance value of the resistor 12 and the capacitance value of the capacitor 13.

When the detection signal 7 falls to a low level, the diode 11 becomes forward biased and the current flows through the diode 1.
1 and resistor 12, and is discharged as shown in output waveform 38a of FIG. The discharge time constant is
It is the product of the forward resistance value of the diode 11, the parallel value of the resistance value of the resistor 12, and the capacitance value of the capacitor 13. Therefore, the discharging time constant becomes shorter than the charging time constant, and the section C in FIG. 3 becomes shorter.

Here, the forward rising voltage of diode 11 is
Since the voltage is about 0.6 to 0.7 V and the forward resistance tends to increase as the potential difference decreases, there is a drawback that the shortening rate of section C becomes small at a small signal level.

Description of the purpose of the invention The present invention solves the above drawbacks by using a transistor and a constant voltage power supply instead of a diode, and it is possible to suppress the temporal expansion of a video level signal to a small level even at a small signal level. The purpose is to provide circuits.

Structure of the Invention The present invention includes a charging circuit including a resistor and a capacitor, and a discharging circuit including a transistor, a constant voltage power source for biasing the base of the transistor, and a bias circuit including at least two resistors.

Explanation of an embodiment of the invention Next, an embodiment of the invention is shown in Figs. 5 and 6.
This will be explained with reference to the figures.

FIG. 5 shows an embodiment of the present invention. 21 is a transistor, 12 and 13 are resistors and capacitors, 22 is a diode, 23 is a constant voltage power supply, 24 is a resistor, 25 and 26 are resistors, and the output of the constant voltage power supply 23 is connected to the resistor 26 and It is applied to the base of transistor 21 through diode 22. The resistance values of the resistors 25 and 26 and the voltage value of the constant voltage power supply 23 vary depending on the characteristics of the transistor 21 and the diode 22, and the detected signal 7
When the level of the video level signal 8 is lower than the level of the video level signal 8, the transistor 21 is turned on, and when the opposite is true, the transistor 21 is turned off.

Detection signal waveform 3 with the signal waveform shown in Figure 6
7a is input to resistors 12 and 25. Then, since the level of the video level signal waveform 38 becomes lower than the level of the detected signal waveform 37a, the diode 22 and the base-emitter of the transistor 21 are reverse biased, and the transistor 21 is turned off. Here, the diode 22 is the transistor 2
This is for protection to prevent destruction due to reverse bias between the base and emitter of 1. Detection signal waveform 37a
passes through resistor 12 and charges capacitor 13 as shown in video level signal waveform 38 of FIG. The charging time constant at this time is the product of the resistance value of the resistor 12 and the capacitance value of the capacitor 13, as in the conventionally used circuit.

On the other hand, when the detected signal waveform 37a falls to a low level, the level of the video level signal waveform 38 becomes higher in voltage than the level of the detected signal waveform 37a, so that the base and emitter of the transistor 1 are forward biased, and the transistor 21 becomes ON, and the current is discharged through the resistor 12, and also passes through the resistor 24 and the transistor 21.
is discharged from the collector.

Here, the resistor 24 is connected to the transistor 2 during discharging.
This is to prevent large current from flowing through 1.
By selecting a value that is sufficiently smaller than the resistance value of the resistor 12, the discharge time constant is the value obtained by connecting the resistance value of the resistor 24 and the resistance value during conduction between the emitter and collector of the transistor 21 in series, and the capacitor. 1
It is the product of the capacitance values of 3.

The saturation voltage between the collector and emitter of the transistor 21 is normally about 0.2V, which is smaller than the rising voltage of the speed-up diode 11 shown in FIG. 4, so the discharge waveform is similar to the video level signal waveform 38b in FIG. 6. The video signal is discharged as shown in FIG. 1, and the time-wise extension section C of the video signal becomes shorter than in the conventional circuit.

The above explanation has been made for cases in which the input signal to the waveform shaping circuit has positive polarity, but for signals with negative polarity, the circuit shown in FIG. The same effect can be obtained by the same function as the circuit described above. The names and functions of the various parts of the circuit shown in FIG. 7 are the same as those shown in FIG. 5, so their explanations will be omitted. The use of the diode 22 and resistor 24 for protecting the transistor 21 can be omitted if the transistor 21 is a transistor with a high reverse withstand voltage between the emitter and base, or a transistor that can flow a large current through the collector. is clear.

Explanation of the effect of the invention As explained above, this invention has the effect of suppressing the temporal expansion of the video level signal even at a small signal level by using a transistor and a constant voltage power supply instead of the conventionally used diode. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the reception display section of the sonar device, FIG. 2 is a diagram showing input/output signal waveforms of the circuit shown in FIG. 1, and FIG. 3 is a block diagram showing the display section 4 shown in FIG. FIG. FIG. 4 is a circuit diagram showing a conventional waveform shaping circuit. 5 and 7 are circuit diagrams showing an embodiment of the present invention. FIG. 6 is an input/output signal waveform diagram of the circuit shown in FIGS. 4 and 5. FIG. 1...Azimuth detection section, 2...Video detection section, 3...
...Video waveform shaping circuit, 4...Display section, 5...Received signal, 6...Direction signal, 7...Detection signal, 8...
...Video level signal, 11...Diode, 12
...Resistor, 13 ... Capacitor, 21 ... Transistor, 22 ... Diode, 23 ... Constant voltage power supply, 24 ... Resistor, 25, 26 ... Resistor,
35...Received signal waveform, 36...Direction signal waveform,
37...Detection signal waveform, 38...Video level signal waveform.

Claims (1)

[Scope of utility model registration request] In a video waveform shaping circuit used for display control of a sonar device, a video input terminal; a waveform shaping output terminal; a capacitor connected between the waveform shaping output terminal and a reference potential point; a charging circuit including a first resistor connected between the waveform shaping output terminal and setting a charging time constant by the first resistor and the capacitor; a constant voltage power supply; and the video input terminal. and a bias circuit including second and third resistors connected in series between the constant voltage power supply and the constant voltage power supply;
a transistor whose collector is connected to the reference potential point; means for connecting the base of the transistor to the connection point of the second and third resistors; and means for connecting the emitter of the transistor to the waveform shaping output terminal. and a discharge circuit that turns on and off the transistor depending on the difference between the signal level of the video input terminal and the signal level of the waveform shaping output terminal, and discharges the charge of the capacitor. Video waveform shaping circuit.