JPH03210492A - Noise removing circuit - Google Patents

Abstract

PURPOSE:To enhance the finding capacity of a school of fish by reading an output signal changing linearly or along a desired curve with respect to an input signal from a table ROM at every clutter level. CONSTITUTION:An output signal linearly proportional to an input signal is read from a table ROM 12 at every level of a signal desired to be removed. By this method, the areas of color display to the respective level widths in a detection signal can be made equal. When an output signal is read from the ROM 12 with respect to the input signal according to a predetermined curve characteristic, for example, the area of color display to the detection signal of an intermediate level can be made large.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a noise removal (clutter) circuit for removing noise signals in underwater detection devices.

[Conventional technology]

FIG. 3 shows the general configuration of a fish finding device. 1 is a transducer, which emits an ultrasonic electrical signal as a sound wave from the transmitter 2 applied via the transmitter/receiver switch S, and also receives an echo signal of the emitted sound wave and converts it into an electrical signal. . 3 is an amplifier, which amplifies the received signal from the transducer l. 4 is a detection circuit for extracting the echo component from the amplified signal from the amplifier 3; Reference numeral 5 denotes a recorder that records and reproduces the detected signal from the detection circuit 4. Reference numeral 6 denotes a clutter circuit for removing unnecessary noise components from the detection signal from the detection circuit 4 or the reproduced signal from the recorder 5. This clutter circuit 6 will be described in detail later. 7 is an A/D converter that outputs the intensity of the analog signal processed by the clutter circuit 6 as a 4-bit digital signal indicating 16 levels; 8 is a digital output from the A/D converter 7; V to store the signal as an image signal
This is RAM (video ram). 9 is a D/A converter that converts the 4-bit digital signal read from the VRAM 8 into an analog signal, and 10 is a D/A converter that converts the 4-bit digital signal read from the VRAM 8 into an analog signal. This is a display device for displaying analog signals as images by dividing them into eight colors according to their levels. Fig. 4 shows a conventional circuit diagram of the clutter circuit 6. 61 is an operational amplifier. A negative detection signal is input to the subtraction input section of the operational amplifier 61 via an input resistor VRI for variable gain, and a signal is input via a resistor R1 to a subtraction input section by a resistor R2 and a variable resistor VR2 for adjusting the club pitch. A divided voltage is applied.The addition input part of the operational amplifier 61 is grounded through a resistor R3.The resistor R4 is connected to the operational amplifier 61.
is the feedback resistance of In the clutter circuit 6 of FIG. 4, when the gain of the operational amplifier 61 is set to 1, that is, when the input resistance VR1 is made equal to the feedback resistance R4, the resistance value of the variable resistor VR2 is set to 0.
FIG. 5 shows the relationship between the input voltage and the output voltage of the operational amplifier 61 when the voltage is gradually increased from . When the variable resistor VR2 for clutter adjustment is 0, the line becomes a straight line (■), and as the resistance value increases, the line shifts to the right in the figure as shown in the lines (■, ■...■). For example, in the straight line (2), the signal is output when the input voltage is o, osv or more, and signals less than 0.06 V are removed as noise.

[Problems to be Solved by the Invention] However, since the level range of the input voltage to be handled is extremely wide, it is usually necessary to process the input voltage into a logarithm or decibel value using a logarithmic compression circuit. The graph in FIG. 6 is a redrawn version of the graph in FIG. 5, with the input voltage on the horizontal axis on a logarithmic scale (semi-logarithmic graph) and the output level on the vertical axis divided into 16 levels. On the vertical axis of FIG. 6, the output levels are divided into 16 stages and are color-coded every two steps using eight colors: eye, blue, . . . red, and brown. When no clutter is applied, the relationship between input voltage and output level is a straight line as shown in ■, so the input voltage range corresponding to each color from eye color to brown, which indicates the output level, is 0 to 7. They are equally spaced on a logarithmic scale of .68V. FIG. 7 shows an example of the seabed displayed on the display 10 in this case, and the area of each color displayed in the order of brown, red, . Noise appears at the top of the screen. On the other hand, when clutter is applied, the curves appear as shown in ■ to ■. For example, in the case of curve ■, the input voltage range corresponding to each color from eye color to brown is shown in the bar graph at the bottom of Figure 6. As such, the input voltage range for the low output levels of eye color and blue becomes narrow and dense. An example of the display in this case is shown in Figure 8. Although noise below 0.06V is removed, brown and red colors that indicate high output levels are displayed more frequently, and conversely, the eye color that indicates low output levels is displayed. However, the disadvantage was that the display area of the blue color was reduced, making it difficult to see important echo information from schools of fish and seabed tailings (sediment) detected at weak levels. This invention was made to eliminate the above-mentioned problems, and even when clutter is applied, the input signal, which is displayed in logarithmic or decibel format, is processed linearly or according to a desired curve characteristic. An object of the present invention is to provide a noise cancellation circuit that outputs a signal. [Means for Solving the Problems] A noise removal circuit of the present invention is a noise removal circuit used in an underwater detection device to remove noise below a desired level from an input signal. a clutter level selection means for input; and a clutter level selection means for each level selected by the clutter level selection means for the input signal to be displayed in logarithm or decibels.
The present invention is characterized by comprising a signal output means for converting the signal level to a desired signal level based on the data in the table ROM and outputting the signal.

[Effect]

In conventional noise removal circuits, if the level of the signal to be removed is set using the clutter level selection means, the output signal will no longer be linearly proportional to the input signal expressed in logarithm or decibels, and the level of the input signal will change. When displaying signals in different colors, the color display area for low-level detection signals decreases, making it difficult to see. If an output signal that is linearly proportional to
Furthermore, if the output signal is read out from the table ROM according to a predetermined curve characteristic with respect to the input signal, it is possible to increase the color display area for, for example, an intermediate level detection signal.

【Example】

FIG. 1 is a block diagram showing an embodiment of the noise canceling circuit of the present invention. Reference numeral 11 denotes an 8-bit A/D converter, which converts the detection signal output from the detection circuit 4 in FIG. 3 into 8-bit digital data (D, -D?
). 12 is a table ROM in which the digital data (D
o~D? ), the data stored internally as a table is read out and output buses O8-0. From 16(
= Output as 4-bit digital data indicating two levels. Details of this table data will be described later. The clutter level selection signals input to addresses A and A11 of the ROM 12 are OV, 0.03V, O, and 12V as shown in FIGS. 5 and 6. This is a signal for selecting five clutter levels of 0.24V. Reference numeral 13 denotes a latch circuit that outputs 4-bit digital data (indicated by M in the figure) output from the ROM 12 in response to an enable signal output from a pulse width discrimination circuit 15, which will be described later. 14 is a comparator which compares the digital data M with the digital data latched in the latch circuit 13 (previously latched data, indicated by N), and compares the current digital data M with the previous digital data. When the value exceeds the digital data N, the pulse width discrimination circuit 15
A predetermined signal is output to. Incidentally, the whisker-like noise shown in the display example of FIG. 7 is an extremely short signal in terms of time, and the pulse width discrimination circuit 15 is provided to prevent such noise from being output. , when the relationship of M>N continues for 1 μsec or more in the comparison in the comparator 14, an enable signal is sent to the latch circuit 13, determining that the signal is not a noise signal. Next, the operation of the noise canceling circuit having the above configuration will be explained. First, a clutter level selection signal that sets the clutter level to 0.06V, for example, is input to R and 0M12. After that, when the detection signal from the detection circuit 4 shown in FIG. 3 or the detection signal reproduced by the recorder 5 is input to the A/D converter 11, this detection signal is converted into 256 levels. Segmented 8-bit digital data (DO~D
, ) and input to the ROM 12 as address data. Here, the table stored in the ROM 12 will be described. In Figure 6 described in the conventional example, when clutter is applied, the relationship between the input voltage and the output voltage becomes a curve as shown in ■ to ■, so the display of eye color, blue, etc. for weak levels is reduced. However, in this invention, as shown in FIG. 2, the ROM is designed to make the output level linearly proportional to the input level regardless of the clutter level.
Predetermined table data is stored in I2. That is, in the graph of Fig. 2, the horizontal axis indicating the input level is 1 to 2 degrees), 2 (= 2 degrees), 3.4 (-2 degrees...255.2
In order to display signals with a wide range of input levels of 256 types of 5B (=2@), a logarithmic scale of 0 to 8 with base 2 is used, and the output level on the vertical axis is divided into 16 levels. Each straight line ■ to ■ in the figure represents the clutter level, OV,
The relationship between the output level and the Kino input level is shown for 0.03V, 006V, 0.12V, and 0.24V, and for the input level for each clutter level, ■～■
The 16 output levels output along the corresponding straight line are stored as 4-bit data in the ROM 12? I remember this table. For example, when the clutter level is o and osv, the successive data that is the output level with respect to the input level is the second
There is a relationship shown by the straight line ■ in the figure, and A/D converter 1! For input levels of 1 to 256 (0 to 8 on a logarithmic scale) that are input from 1 to 4 (0 to 2 on a logarithmic scale), input levels of 1 to 4 (0 to 2 on a logarithmic scale) are removed as noise. The output level is read for an input level of magnitude ~256 (2-8 on a logarithmic scale). As you can see from the bar graph at the bottom of Figure 2, the input level ranges for each color from eye color to brown are equally spaced on the logarithmic scale, and even when clutter is applied, In the display of the seabed on the display 10, the display area for each color is approximately equal, as shown in FIG. The 4-bit digital data M from the ROM 12 is taken into the latch circuit 13 in synchronization with the sampling clock SCK, and is also sent to the comparator 14. This comparator 14 compares the magnitude of the current digital data M and the digital data N latched last time in the latch circuit 13, and when M>N, it is assumed that there is a detection signal and the predetermined signal is pulsed. The signal is sent to the width discrimination circuit 15. In this pulse width discrimination circuit 15, as described above, only when a predetermined condition is satisfied, it is determined that the signal is not a noise signal and an enable signal is sent to the latch circuit I3, and the latched data is 1 to indicate the display color to the D converter 7
It is sent as pixel data for a dot. By repeating such control, once the pixel data for one screen is stored in the VRAM 8, the image data is read out, converted from a digital signal to an analog signal by the D/A converter 9, and sent to the display IO. Echo intensity is displayed in different colors. In addition, in the circuit shown in FIG. 1, in order to correspond to 16 display colors, the read data from the ROM 12 is set to 4 bits and 1
Although it is divided into 6 steps, if the display is performed in 8 colors as in this embodiment, the successive data may be 3 bits. Also, R
As a substitute for OM12, each straight line ■～■ shown in Figure 2
It may also be a function generator that stores a function representing . Further, as shown in FIG. 2, table data showing input-output characteristics as shown by curves ■′ and ■゛ with respect to straight lines ■ and ■ representing input-output characteristics is stored in the ROM 12. By doing so, it is possible to increase the color display area of intermediate colors of green and yellow for an input signal of an intermediate level.

【Effect of the invention】

As explained above, the present invention allows the Crabtalepel turtle to read out from the table ROM an output signal that varies linearly or according to a desired curve with respect to the input signal, so that the received signal can be read out from the table ROM like a fish finder. When displaying colors according to intensity, the color display area for weak reception signals does not become smaller as in conventional devices, and the fish detection performance is improved. Furthermore, since the clutter level can be set arbitrarily, it is possible to set the clutter level sufficiently high, thereby narrowing the range of input signals to be displayed, and displaying only the received signal to be investigated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the noise removal circuit of the present invention, FIG. 2 is a graph showing the relationship between the input level and the output level of the noise removal circuit of FIG. FIG. 4 is a circuit diagram showing a conventional example of the clutter circuit in FIG. 3, and FIG. 5 is a block diagram showing the general configuration of
Fig. 4 is a graph showing the relationship between input voltage and output voltage of the clutter circuit, Fig. 6 is a graph when the scale of the graph in Fig. 5 is changed, and Figs. 7 and 8 are graphs showing the relationship between input voltage and output voltage of the clutter circuit. FIG. 7 is a diagram illustrating an example of a seabed displayed when clutter is not applied and when clutter is applied in a clutter circuit. 1... A/D converter, 2... ROM. 3...Latch circuit, 4...Comparator, 5...Pulse width discrimination circuit.

Claims (4)

[Claims] (1) A noise removal circuit used in an underwater detection device to remove noise below a desired level from an input signal, comprising a clutter level selection means for inputting the desired level, and a logarithmic display or decibel For each input signal to be displayed, for each level selected by the clutter level selection means,
1. A noise removal circuit comprising: signal output means for converting to a desired signal level based on data in a table ROM and outputting the signal. (2) The noise removal circuit according to claim 1, wherein said signal output means outputs a signal linearly proportional to said input signal. (3) The noise removal circuit according to claim 1, wherein the signal output means outputs a signal according to predetermined characteristics with respect to the input signal in order to emphasize a desired level in the input signal. (4) The noise removal circuit according to claim 1, further comprising pulse width discrimination means for removing a pulse-like signal that changes in a short time from the signal output from the output means.