JP2843640B2 - Input signal noise eliminator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an input signal noise eliminator applied to a radar, a sonar, and the like, for effectively removing a noise component contained in a signal.

(B) Conventional technology When displaying a received image on a display device in a radar, a sonar, or the like, in a high sensitivity state, external noise or noise generated in a receiving system is mixed in a received signal, and fine dot-shaped noise is displayed. May be done.

Such noise is not only unsightly, but also has a disadvantage that, for example, when automatically tracking a target in an automatic radar plotting device (ARPA) or the like, the noise is erroneously tracked and the original target cannot be tracked. Occurs.

In order to solve such a problem, the sensitivity is generally adjusted so as to be slightly lowered to reduce unnecessary noise.

(C) Problems to be Solved by the Invention However, if the noise is reduced by lowering the sensitivity, the level of the target signal also decreases, so that a very weak target signal may not be extracted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an input signal noise elimination device which eliminates the above-mentioned conventional problems by effectively removing noise without lowering the level of a target signal.

(D) Means for Solving the Problems According to the invention of claim 1 of the present application, a target signal to be extracted and an input signal including a noise signal shorter in width than the target signal are compared with a certain threshold value. A signal start point detecting means for detecting a signal rising timing exceeding the threshold value, and an input signal being inputted simultaneously with the signal starting point detecting means, and the input signal having a fixed width shorter than a target signal width from the signal rising timing. And short-time signal removing means for masking the signal.

According to the invention of claim 2 of the present application, the target signal and the noise signal appear discretely at regular intervals on the input signal. It is characterized in that it is a means for processing a width that connects signals that appear in a random manner.

The invention according to claim 3 of the present application compares a target signal to be extracted and an input signal including a noise signal shorter in width than the target signal with a certain threshold value, and sets a signal rising timing exceeding the threshold value. And a short-time signal removing means for inputting an input signal at the same time as the signal starting point detecting means and masking the input signal by a constant width shorter than the width of the target signal from the signal rising timing. After removing the input signal by the short-time signal removing means, for the remaining signal exceeding the threshold,
Reproducing means for reproducing a signal width by adding a signal exceeding the threshold value by the predetermined width.

(E) Function In the input signal noise elimination device of the present invention, the signal start point detecting means compares the input signal with a certain threshold value and detects a point exceeding the threshold value as the input signal start point.

The short-time signal removing means removes the input signal by a fixed width from the input signal start point. Since the fixed width is shorter than the width of the target signal, only a part of the target signal is removed by the signal removal processing of the fixed width, and most of the target signal remains. On the other hand, noise is shorter than the target signal,
The signal is removed by the above-described signal removal processing of a fixed width. As a result, a signal including only the target signal from which noise has been removed is obtained. The target signal and the noise signal may be input as a continuous time signal, or may appear discretely at regular intervals on the input signal. The signal that appears discretely is, for example, a signal in which the input signal is a scanning signal and a target that exists across the main scanning direction is detected. In such a case, the signal start point detecting means and the short-time signal removing means may be processed with respect to the width connecting the discretely appearing signals.

Further, the short-time signal removing means according to claim 3 removes a signal whose area exceeding the threshold value is equal to or smaller than a predetermined width. Since the fixed width is shorter than the width of the target signal, the target signal is not removed by the signal removal processing of the fixed width. On the other hand, since the noise has a shorter width than the target signal, the noise is removed by this fixed width signal removal processing. As a result, a signal including only the target signal from which noise has been removed is obtained. Specifically, the noise signal is removed by removing only a fixed width from the signal exceeding the threshold, and a signal exceeding the fixed width threshold is added again to a part of the remaining target signal. By doing so, the entire target signal is reproduced.

(F) Embodiment FIG. 1 is a block diagram of a main part of a radar apparatus according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part thereof.

In FIG. 1, a control circuit 1 gives a transmission trigger signal to a transmission circuit 2. The transmission circuit 2 gives a transmission signal to the antenna 3 according to the trigger signal. The receiving circuit 4 amplifies a signal received by the antenna 3. The time setting circuit 5 performs time setting control so that a timer circuit 7 described later measures a certain time only for a time corresponding to the range signal given from the control circuit 1. The comparator 6 binarizes the signal received by the receiving circuit 4 by comparing the signal with a constant reference voltage Vr. The timer circuit 7 measures a predetermined time (time set by the time setting circuit 5) from the time when the output signal of the comparator 6 rises. The gate circuit 8 is a timer circuit 7
, The level of the received signal is forcibly set to 0 for the time counted by, and the received signal is output as it is during the other periods. The display circuit 9 displays the received signal from which noise has been removed in this manner on a screen.

(A) to (d) shown in FIG. 2 are waveform examples of respective parts (a) to (d) shown in FIG. In FIG. 3A, A and B are target signals to be extracted, and N is a noise signal. Generally, a noise signal has a lower amplitude level and a shorter duration than a target signal. By comparing such a received signal with a fixed threshold value Vr lower than the noise level, a binary signal is obtained as shown in FIG. Further, by cutting 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 as shown in FIG.

Next, FIG. 3 shows a specific circuit example of a timer circuit for measuring a fixed time from the point where the received signal exceeds a certain threshold value, and FIG. 4 shows a waveform diagram of each part thereof.

In FIG. 3, the resistor R and the capacitor C constitute a CR time constant circuit. When the output of the comparator 6 is at "L" level, the transistor Q is turned on and the charge of the capacitor C is discharged.
When the output of the comparator 6 is "H", the transistor Q is turned off and the capacitor C is charged with the CR time constant. Therefore, as shown in FIGS. 4 (a) and 4 (b), while the output of the comparator 6 is at the "H" level, the input signal (b) of the comparator 10 rises with the above CR time constant, When the voltage is exceeded, the output signal of the comparator 10 becomes "H" level as shown in FIG. 4 (c). In this way, the gate circuit cuts the received signal for the time T shown in FIG. 4 determined by the relationship between the CR time constant and the reference voltage of the comparator.

In addition, as the timer circuit, a circuit that counts a predetermined time by an oscillation circuit and a counter, a monostable multivibrator, or the like can be used.

In addition, as shown in FIG. 2 (d), a part of the received signal is also cut by the cut of the received signal by the gate circuit for a certain period of time. 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, for example, one sweep, and the delay circuit 12 delays the data read from the memory 11 by a predetermined time by the timer circuit. The OR circuit 13 combines the signal read from the memory 11 and the signal delayed for a predetermined time. In addition, memory
11, the delay circuit 12 and the OR circuit 13 may be digital circuits or analog circuits.

Although the embodiments described above all relate to noise removal of signals within one sweep, the present invention can be similarly applied to the azimuth direction. An example will be described below.

FIG. 6 is a circuit diagram of a main portion for removing noise in the azimuth direction, and FIGS. 7 and 8 are waveform diagrams and explanatory diagrams of the respective portions. In FIG. 6, the comparator 6 binarizes the input received signal with a certain threshold value. The gate circuit 14 is a circuit for cutting off the signal for a fixed time from the rising of the binarized signal, similarly to the circuit shown in FIG. 1 or FIG. However, unlike the gate circuit 8, gate control is performed on a logic signal. Each of the memories 15 to 18 stores a one-sweep binarized received signal. The larger the number is, the more the previous (older) received signal is temporarily stored. The logic circuits denoted by 23 to 35 output the azimuth direction of the received signals in the azimuth direction from the output signal of the gate circuit 14 and the output signals of the memories 15 to 18 by a constant width (constant sweep) from the start point. (Number). Each of the counters 19 to 22 counts a certain period of time after the trigger signal is given in order to change the certain width (the number of constant sweeps) according to the distance.

Each of the memories 15 and 18 stores a received signal for one sweep, and each time a signal for one sweep is received, the stored content is transferred to a memory having a larger number. Therefore, for example, when the reception signal at point a shown in FIG. 8 is output from the gate circuit 14, the signal at point b from the memory 15 and the signal at point c from the memory 16 are simultaneously output.

For example, if the outputs of the counters 19 and 20 are both at the "H" level and the outputs of the other counters 21 to 22 are all at the "L" level, the outputs of the memories 15 and 16 are ORed only when the outputs are at the "H" level. The outputs of the gates 25 and 28 become "H" level. The other OR gates 31 to 34 are always at the "H" level because the outputs of the counters 21 to 22 are at the "L" level and the outputs of the inverters 30 to 33 are at the "H" level. Therefore, when the output of the gate circuit 14 becomes “H” level in this state, the AND gate 3
The output of 5 becomes "H" level, and the gate circuit 36 outputs the input signal as it is.

If the counters 19 to 22 satisfy the above conditions, the output of the AND gate 35 remains at the "L" level unless the received signal is continuous in the azimuth direction for three sweeps. Are removed as noise (see E1 in FIG. 8). Conversely, if the received signal is continuous in the azimuth direction for three sweeps or more, two seconds from the start of the continuous received signal
The remaining received signal removed by the sweep is extracted (see E2 in FIG. 8).

As shown in FIG. 7, the counters 19 to 22 are kept at "H" level for a predetermined period of time after the trigger signal is given, and thereafter set at "L" level. The counter is configured so that the duration of the “H” level is shortened. As a result, a signal received from a long distance has a shorter removal time (the number of sweeps to be removed decreases), and a reception signal from a short distance has a longer removal time (the number of sweeps removed). Many). In this manner, a similar noise removing effect can be obtained regardless of the distance.

(G) Effects of the Invention According to the present invention, noise having a width shorter than that of a target signal to be extracted is selectively removed, and the level of the target signal does not decrease, so that a weak target signal is separated from noise. And can be easily extracted. Therefore, if this is applied to, for example, a radar or a sonar, the detection capability at a long distance is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a main part of a radar apparatus according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part. Third
FIG. 4 is a circuit diagram of a timer circuit, and FIG. 4 is a waveform diagram of each part. FIG. 5 is a block diagram of a main part of a radar device according to another embodiment. FIG. 6 is a circuit diagram of a main part of the radar apparatus for removing noise in the azimuth direction, FIG. 7 is a waveform diagram of each part, and FIG. 8 is a diagram for explaining the operation.

Claims (3)

(57) [Claims] A signal start for comparing a target signal to be extracted and an input signal including a noise signal shorter in width than the target signal with a predetermined threshold value, and detecting a signal rising timing exceeding the threshold value. An input signal noise comprising a point detecting means and a short-time signal removing means for inputting an input signal simultaneously with the signal start point detecting means and masking the input signal by a fixed width shorter than the width of a target signal from the signal rising timing. Removal device. 2. The method according to claim 1, wherein the target signal and the noise signal appear discretely at regular intervals on the input signal. 2. The input signal noise eliminator according to claim 1, wherein the input signal noise eliminator is means for processing the connected width. 3. A signal start for comparing a target signal to be extracted and an input signal including a noise signal shorter in width than the target signal with a predetermined threshold value to detect a signal rising timing exceeding the threshold value. Point detection means, short-time signal removal means for inputting an input signal simultaneously with the signal start point detection means, and masking the input signal by a fixed width shorter than the width of the target signal from the signal rising timing; An input signal, comprising, after removal of the input signal by the removing means, a reproducing means for reproducing a signal width by adding a signal exceeding the threshold for the fixed width to the remaining signal exceeding the threshold. Noise removal device.