JPH045594A - Input signal noise removing device - Google Patents

Abstract

PURPOSE:To easily separate and extract an extremely fine target signal from noises by selectively removing a noise which has shorter width than the target signal to be extracted and preventing the target signal from dropping in level. CONSTITUTION:A resistance R and a capacitor C constitute a CR time constant circuit, and a transistor TRQ turns on when the output of a comparator 6 is 'L' to discharge the capacitor C or turns off when the output of the comparator 6 is 'H' to charge the capacitor C with the CR time constant. Therefore, while the output of the comparator 6 is 'H', the input signal (b) of a comparator 10 rises with the CR time constant and when the reference voltage of the comparator 10 is exceeded, the output signal of the comparator 10 goes up to 'H'. Thus, a gate circuit cuts a received signal for the time determined by the relation between the CR time constant and the reference voltage of the comparator to selectively remove short-width noises. Then the level of the target signal is made not to fall and then the fine target signal can easily by separated and extracted from noises.

Description

DETAILED DESCRIPTION OF THE INVENTION (Al Industrial Field of Application) The present invention relates to an input signal noise removal device that is applied to radar, sonar, etc. and effectively removes noise components contained in a signal.

(b) Conventional technology When displaying received images on a display device in radar, sonar, etc., when the sensitivity is high, external noise or noise generated in the receiving system mixes with the received signal, and fine dot-shaped noise is displayed. Such noise is not only unsightly, but can also be caused by, for example, automatic radar plotting equipment (
When a target object is automatically tracked in ARPA), etc., there is a problem that noise is erroneously tracked and the original target object is not tracked.

In order to solve this problem, - For boat fishing, the sensitivity is adjusted to be slightly lower to reduce unnecessary noise.

(e) Problems to be Solved by the Invention However, if noise is reduced by lowering the sensitivity, the level of the target signal also decreases, which may result in the inability to extract a very weak target signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide an input signal noise removal device that eliminates the above-mentioned conventional problems by effectively removing noise without reducing the level of a target signal.

(Means for Solving Problem d1) The input signal noise removal device of the present invention compares a target signal to be extracted and an input signal including a noise signal having a width shorter than the target signal with a certain threshold value. It consists of a signal start point detection means for detecting a point exceeding this threshold value, and a short time signal removal means for removing an input signal for a certain period of time shorter than the width of the target signal from the signal start point.

(e) Operation In the input signal noise removing device of the present invention, the signal starting point detection means compares the input signal with a certain threshold value and detects a point exceeding this threshold value as the input signal starting point. The short-time signal removing means removes the input signal for a certain period of time from the input signal starting point. Since this certain period of time is shorter than the width of the target signal, only a part of the target signal is removed by the signal removal process for this certain period of time, and most of it remains. On the other hand, since noise has a shorter time width than the target signal, most of the noise is removed by the signal removal process for a certain period of time. Therefore, a signal containing only the target signal from which most of the noise has been removed can be obtained.

(f) Embodiment FIG. 1 shows a block diagram of the main parts of a radar device according to an embodiment of the present invention, and FIG. 2 shows a waveform diagram of each part.

In FIG. 1, a control circuit 1 provides a transmission trigger signal to a transmission circuit 2. In FIG. The transmitting circuit 2 provides a transmitting signal to the antenna 3 in response to this trigger signal. The receiving circuit 4 amplifies the signal received by the antenna 3. The time setting circuit 5 operates only for a time corresponding to the range signal given from the control circuit 1.
Time setting control is performed so that a timer circuit 7, which will be described later, measures a certain period of time. A comparator 6 compares the signal received by the receiving circuit 4 with a constant reference voltage Vr and compares it with a constant reference voltage Vr.
become The timer circuit 7 measures a certain period of time (time set by the time setting circuit 5) from when the output signal of the comparator 6 rises. The gate circuit 8 forcibly sets the level of the received signal to 0 for the time measured by the timer circuit 7, and outputs the received signal as is during the other period. The display circuit 9 displays the received signal from which noise has been removed in this way on a screen.

(a) to (d) shown in Figure 2 are (a) shown in Figure 1.
It is an example of a waveform of each part of - (d). In the same figure (a), A
and B are the target signals to be extracted, and N is the noise signal.

Generally, a noise signal has a lower amplitude level and a shorter duration than a target signal. By comparing such received signals with a constant threshold value Vr lower than the noise level, a binarized signal is obtained as shown in FIG. 4(b). Further, by canting the received signal for a certain period of time from the rise of the binarized signal as shown in (c), a received signal from which noise has been removed can be obtained as shown in (d) of the figure.

Next, FIG. 3 shows a specific circuit example of a timer circuit for counting down a certain period of time from the point at which the received signal exceeds a certain threshold value, and FIG. 4 shows a waveform diagram of each part of the timer circuit.

In FIG. 3, the resistor R and the capacitor C constitute a CR time constant circuit, and when the output of the comparator 6 is at L'' level,
When transistor Q is turned on and the charge in capacitor C is discharged, and the output of comparator 6 is "H", transistor Q
is turned off and capacitor C is charged with the CR time constant. Therefore, as shown in FIGS. 4(a) and 4(b), during the period when the output of the comparator 6 is at "H" level, the input signal (b) of the comparator 10 rises with the above CR time constant, and the reference signal of the comparator 10 When the voltage exceeds the voltage, the output signal of the comparator 10 becomes “H” as shown in FIG. 4(C).
In this way, the gate circuit cants the received signal for the time T shown in FIG. 4, which is determined by the relationship between the CR time constant and the reference voltage of the comparator.

As the timer circuit, it is also possible to use a circuit that counts a certain period of time using an oscillation circuit and a counter, a monostable multi-by-break circuit, or the like.

Note that by cutting the received signal for a certain period of time by the gate circuit, a part of the received signal is also cut, as shown in (d) in Figure 2. It is possible to return to the original target signal time width. In FIG. 5, the memory 11 stores the output signal of the gate circuit 8, for example, for l sweeps, and the delay circuit 12 stores the output signal of the gate circuit 8.
The data read from 1 is delayed by a certain amount of time by the timer circuit. The OR circuit 13 combines the signal read from the memory 11 and the signal delayed for a certain period of time. Note that the memory 11, delay circuit 12, and OR circuit 13 may be digital circuits or analog circuits.

Although all of the embodiments described above have been concerned with signal noise removal within one sweep, the present invention can be similarly applied to the azimuth direction. An example will be described below.

The circuit diagram of the main part that removes noise in the azimuth direction is shown in Part 6.
In addition, waveform diagrams and explanatory diagrams of each part are shown in FIGS. 7 and 8. In FIG. 6, a comparator 6 binarizes the input received signal using a certain threshold. The gate circuit 14 is a circuit similar to the one shown in FIG. 1 or FIG. 3, which controls the signal for a certain period of time from the rise of the binary signal. However, unlike the gate circuit 8, logic signals are gate-controlled. The memories 15 to 18 each store one switch's worth of binary received signals, and the larger the number, the earlier (older) the received signal is temporarily stored. Logic circuits 23 to 35 are gate circuits 14
From the output signal of and each output signal of memories 15 to 18,
This is a circuit for removing continuous reception signals in the azimuth direction by a certain width (a certain number of sweeps) from the starting point of the reception signals in the azimuth direction. Further, the counters 19 to 22 count a certain period of time after a trigger signal is applied in order to change the above-mentioned fixed width (fixed number of sweeps) according to the distance.

Each of the memories 15 to 18 stores 8 signals corresponding to one sweep, and is configured such that each time a signal corresponding to one sweep is received, the stored contents are transferred to a memory with a higher number. For this reason, for example, when the received signal at point a shown in FIG.

Now, for example, the outputs of counters 19 and 20 are both at the "H" level, and the outputs of the other counters 21 and 22 are all at "L" level.
” level, the output of memory 15.16 is “
Only when the level is “H”, the output of the OR gate 25.28 is “H” level.
It becomes H'' level.

The other OR gates 31-34 are always at the "H" level because the outputs of the counters 21-22 are at the "L" level and the outputs of the inverters 30-33 are at the "H" level. Therefore, in this state, the output of the gate circuit 14 is “H”.
When the signal reaches the "H level," the output signal of the AND gate 35 becomes the H level, and the gate circuit 36 outputs the input signal as it is.

If the counters 19 to 22 are under the above conditions, if the received signals are not continuous in the azimuth direction for 3 sweeps, the output of the AND gate 35 will remain at "L" level, and as a result, for 2 sweeps. Continuous received signals are removed as noise (see E1 in FIG. 8). Conversely, if the received signals are continuous in the azimuth direction for three sweeps or more, the remaining received signals are extracted by removing two sweeps from the start of the consecutive received signals (8th (See E2 in the figure).

As shown in FIG. 7, the counters 19 to 22 are kept at the "H" level for a predetermined period of time after the trigger signal is applied, and then set to the "L" level, and the counters with a large number are The duration of the "H" level is shortened. By this,
The farther away the signal is received, the shorter the time it takes to be removed (
The fewer sweeps are removed), and the closer the received signal is, the longer it takes to remove the signal (more sweeps are removed). In this way, the same level of noise removal effect can be obtained regardless of the distance.

(g1 Effect of the invention According to this invention, noise that is shorter in width than the target signal to be extracted is selectively removed, and the level of the target signal does not decrease. Therefore, a weak target signal can be separated from the noise. Therefore, if this is applied to radar, sonar, etc., the detection ability over long distances will be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of a radar device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part thereof. Third
The figure is a circuit diagram of the timer circuit, and FIG. 4 is a waveform diagram of each part thereof. FIG. 5 is a block diagram of the main parts of a radar device according to another embodiment. FIG. 6 is a circuit diagram of the main parts of a radar device that removes noise in the azimuth direction, FIG. 7 is a waveform diagram of each part thereof, and FIG. 8 is a diagram for explaining its operation.

Claims (1)

[Claims] (1) Signal starting point detection means for comparing a target signal to be extracted and an input signal including a noise signal with a width shorter than the target signal with a certain threshold value and detecting a point exceeding this threshold value; and short-time signal removing means for removing the input signal for a certain period of time shorter than the width of the target signal from the signal starting point.