JPH099103A - Noise reduction device - Google Patents

Abstract

PURPOSE: To reduce stripe noise sensed visually even under a condition of a deteriorated C/N or a weak input. CONSTITUTION: A clamp circuit 12 and an inverted addition section 13 are used to eliminate a dispersal signal. Till a synchronizing separator section 13a being a component of the inverted addition section 13 is mulfunctioned, a signal whose dispersal signal is eliminated by the inverted addition section 13 is used for an output signal, and a signal whose dispersal signal is eliminated by the clamp circuit 12 is used for an output signal under a limit of the performance of the synchronizing separator circuit 13a, and either of the output signals is selected depending on the quality of the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for reducing visual noise generated when removing dispersal from a video signal on which a dispersal signal is superimposed.

[0002]

2. Description of the Related Art Satellite (BS) broadcasting and communication satellite (CS)
In a television receiver for broadcasting, a triangular wave of 15 to 30 Hz, that is, a dispersal (energy diffusion) signal is superimposed and then modulated in order to avoid concentration of energy of transmitted radio waves. Since this dispersal signal has an adverse effect such as flicker on the receiving screen, it must be removed by the receiver.

FIG. 8 shows a conventional clamp circuit used for removing a dispersal signal. Transistor Q10 whose emitters are commonly connected from the input terminal 101 via the capacitor C101 for clamping.
1, Q102 connected to the base of the transistor Q101. The common emitter is connected to the current source I101 and the output terminal 102. Transistor Q101
Is connected to a constant voltage source V101. The base of the transistor Q102 is connected to the constant voltage source V102. The collector of the transistor Q102 is a resistor R101.
Is connected to the constant voltage source V101 via a collector, the collector is connected to the base of the transistor Q101, and the emitter is connected to the base of the transistor Q103 connected to the constant voltage source V101.

When an input signal that causes the base potential of the transistor Q101 to be lower than the potential of the constant voltage source V102 is input, the transistor Q103 becomes an active region and charges the capacitor C101 with a current, and the potential of the constant voltage source V102. It operates so that it becomes the same potential as. That is, when the input signal is the video signal shown in FIG. 9A, the sync tip level has the lowest potential. By optimizing the clamp capacitance, it is possible to obtain an output signal having a uniform sync tip potential as shown in FIG. 9B.

When the reception condition is good, a good operation is possible, but as shown in FIG. 10A, when the C / N (carrier power to noise power) ratio is low or when the input signal is weak, Not only is the noise component n superimposed on the sync chip to be clamped, but this noise component is not constant every horizontal period. Therefore, the output signal is as shown in FIG.
As shown in 0 (b), it appears as a variation a of the brightness level. This appears noticeably as streaky noise on a dark screen (a screen with a lot of gray), resulting in a visually difficult image.

[0006]

In the above-mentioned conventional device for removing the dispersal signal, when the C / N is low or the input is weak, the sync tip to be clamped is
Since a noise component is superimposed and this noise component is not constant every horizontal period, it appears as a variation in the brightness level as an output signal. This appears remarkably as streaky noise on a dark screen, resulting in a visually difficult image.
Had a problem.

The present invention provides a noise reduction device that visually reduces streak noise even under conditions of low C / N or weak input.

[0008]

According to the present invention, in order to solve the above-mentioned problems, first removing means for removing a dispersal signal from a video signal on which the dispersal signal is superimposed, and the first removing means. Second removing means for removing the dispersal signal based on the output signal of the means and the video signal, and selecting means for selecting and outputting the outputs of the first and second removing means according to the reception state of the video signal. It consists of and.

[0009]

With the above-mentioned means, the dispersal removal can be surely performed under good reception conditions, and the reception signal is deteriorated by using the output signal of the anti-phase addition method which does not generate streak noise. Since the output signal of the clamp circuit is used under the conditions, the presence of streak noise can be made visually inconspicuous without deteriorating the dispersal removal capability even under the receiving conditions.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit configuration diagram for explaining one embodiment of the present invention. The video signal on which the dispersal signal input from the input terminal 11 is superimposed is supplied to the clamp circuit 12, and is also supplied to one input of the triangular wave generation circuit 13b and the subtraction circuit 13c of the anti-phase adder 13. The output of the clamp circuit 12 is supplied to the input of the sync separation circuit 13a of the anti-phase adder 13 and
It is supplied to the fixed contact 14a of the switch circuit 14. The output of the sync separation circuit 13a is supplied to the triangular wave generation circuit 13b, and the output of the triangular wave generation circuit 13b is supplied to the other input of the subtraction circuit 13c. The output of the subtraction circuit 13c is the fixed contact 1 of the switch circuit 14 as the output of the anti-phase addition unit 13.
4b. Reference numeral 15 is an output terminal for selecting a signal supplied to the fixed contacts 14a and 14b and outputting the obtained signal to the movable contact 14c. 16 is a switch circuit 14
It is a switching signal generation circuit that generates a signal for switching the movable contact 13c.

The switching signal generation circuit 16 detects the reception state of the reception signal according to the electric field strength or the C / N ratio of the video signal on which the dispersal signal input to the input terminal 11 is superimposed, and outputs the switch circuit 14 from the output. A switching signal for switching is generated.

The operation of the noise reduction circuit thus configured will be described. When the video signal on which the dispersal signal is superimposed is input from the input terminal 11 to the clamp circuit 12 via the input terminal 11, the video signal from which the dispersal signal is removed can be obtained. From the video signal from which the dispersal signal has been removed, a sync signal component is extracted by the sync separation circuit 13a of the anti-phase adder 13. Only the dispersal signal component is extracted from the sync signal component and the video signal on which the dispersal signal is superimposed by using the triangular wave generation circuit 13b. A video signal from which the dispersal component has been removed can be obtained by performing anti-phase addition on the video signal in which the dispersal signal component and the dispersal signal are superimposed, using the subtraction circuit 13c.

By the way, both the video signal removed by the clamp circuit 12 and the video signal removed by the anti-phase adder 13 have exactly the same good characteristics under good reception conditions. As shown in FIG. 8, when the video signal obtained by the clamp circuit 12 has a low C / N or C / N of about 13 to 14 and the IF input signal level to the demodulator is a weak input of about -30 dBm, , Streak noise is generated.

However, the image does not collapse under the receiving condition where the image can be visually recognized. That is,
Under the reception conditions below the above-described level, truncation noise is generated by the PLL circuit generally used for demodulating the IF signal, and the streak noise is less visible to the eye. On the other hand, in the anti-phase adder 13, the clamp circuit 1
A lower level C than the dispersal removal signal obtained in 2
/ N or C / N is about 10 or 11, and the IF input signal level to the demodulator is a weak input of about -40 dBm, it is possible to obtain a video signal without observing streak noise. Under the receiving condition, the sync separation circuit malfunctions, and it is very difficult to see as an image, and a broken video signal is obtained.

Therefore, the switching signal generator 16 transmits the level-set signal to the switch circuit 14, and selects the above two dispersal-free video signals so that an optimum image can be supplied according to the reception conditions. Since it is output, a video signal can be supplied without observing streak noise on the screen and without visually impairing the reception level to the limit level.

FIG. 2 is a circuit configuration diagram for explaining another embodiment of the present invention. The same components as those of the embodiment shown in FIG. 1 will be described with the same reference numerals. Input terminal 1
1 supplies the detection output signal of the satellite broadcasting receiver. The detected output signal is supplied to the inputs of the video processing circuit 22 and the C / N detection circuit 23, respectively. The output signal of the video processing circuit 22 is supplied to the input of the clamp circuit 12 and one input of the triangular wave generation circuit 13b and the subtraction circuit 13c of the anti-phase addition section 13, respectively. The output signal of the clamp circuit 12 is
The sync separation circuit 13a and the switch circuit 1 of the anti-phase adder 13
4 fixed contacts 14a. The output of the sync separation circuit 13a is supplied to the triangular wave generation circuit 13b, and the output of the triangular wave generation circuit 13b is supplied to the other input of the subtraction circuit 13c. The output of the subtraction circuit 13c is supplied to the fixed contact 14b of the switch circuit 14 as an output signal of the anti-phase addition section 14. The output selected by the switch circuit 14 from the fixed terminal 14c is supplied to the output terminal 15. The switch circuit 14 is
Using the output signal of the C / N detection circuit 23 as a control signal, the output signal of the clamp circuit 14 or the output signal of the anti-phase adder 13 is selected.

The internal structure of the video processing circuit 22 is such that LPF (low-pass
It is composed of a filter) and a de-emphasis circuit, and a de-emphasized video signal is obtained from its output.

The C / N detection circuit 23 has a function of detecting a ratio between a noise signal superimposed on a transmission line and a required broadcast signal, and generally, a constant detection output signal does not exist. The noise level distributed in the band is detected. The required band of the detection output signal is direct current even if MUSE broadcasting is considered.
It is 8.5 MHz. As described above, in order to perform C / N detection, it is necessary to detect frequency components outside the above band, so in a general satellite broadcast receiver, the frequency characteristics of the detection output are expanded to DC to 15 MHz. are doing. Therefore, the C / N detection is to extract any frequency band of 8.5 to 15 MHz by a filter, convert the noise amount into a voltage, and output the voltage. As shown in FIG. 5, the noise amount increases as the C / N value decreases.

The generation of the video signal from which the dispersal signal after the clamp circuit 12 has been removed will be described with reference to FIG.
Is exactly the same as. That is, in FIG. 2, the switching signal for switching the switch circuit 14 is the C / N detection signal.

In this embodiment, C / N of about 10 to 11 is used.
Since the switching signal is generated using the value as the threshold level, no streak noise is recognized, and an appropriate video signal can be obtained even in the reception area under further adverse conditions.

FIG. 3 is a circuit diagram for explaining a second embodiment of the present invention. The same components as those of the embodiment shown in FIG. 2 will be described with the same reference numerals. In FIG. 3, a second intermediate frequency signal (IF signal) is supplied from the input terminal 11. This second IF signal is supplied to the input of the AGC circuit 32 which is composed of the gain control amplifier 32a and the detection circuit 32b. The output signal of the AGC circuit 32 is supplied to the input of the demodulation circuit 33. The output signal of the demodulation circuit 33 is supplied to the input of the video processing circuit 22. The output signal of the video processing circuit 22 is the clamp circuit 12
Is supplied to the opposite phase addition section 13. The output signal of the clamp circuit 12 is supplied to the anti-phase adder 13 and the fixed contact 14a of the switch circuit 14 is supplied.
To supply. The output signal of the anti-phase adder 13 is supplied to the fixed contact 14b of the switch circuit 14. The AGC control voltage of the AGC circuit 32 is connected to the switching signal generation circuit 34. The output signal of the switching signal generation circuit 34 is supplied as the control signal of the switch circuit 14. The clamp circuit 12 is supplied to the output terminal 15 by the control signal.
A signal that selects either the output signal of 1 or the output signal of the anti-phase addition unit 13 is obtained from the movable contact 14c.

The second IF signal supplied to the input terminal 11 supplies a stable output signal to the demodulation circuit 33 by the AGC circuit 32 even if the input level changes. The demodulation circuit 33 performs FM demodulation and supplies the baseband signal to the video processing circuit 22. The function of the video processing circuit 22 is composed of the LPF and the de-emphasis circuit as in the previous embodiment, and the signal processing after the video processing circuit 22 is the same as that of the embodiment of FIG.

FIG. 6 is a characteristic diagram for explaining the relationship between the AGC control voltage and the input level of the second IF signal.
Since the input level of the IF signal can be recognized by the AGC control voltage, the information obtained by the AGC control voltage is supplied to the switching signal generation circuit 34 and detected as a switching signal of the switch circuit 14 when the weak input is detected. Due to the above, the clamp circuit reacts to the noise generated at the time of weak input, and the output signal obtained by the anti-phase adder is selected in the area where streak noise is visible, and below the area, the output signal of the clamp circuit is Since the selection is made, visually it is possible to obtain an adapted video signal even when the input is weak.

FIG. 4 is a circuit configuration diagram for explaining a third other embodiment of the present invention. This embodiment is shown in FIGS.
A part of the configuration of each embodiment is combined, and the same components as those of the embodiments of FIGS. 2 and 3 are denoted by the same reference numerals and described.

In FIG. 4, the second IF signal is supplied to the input terminal 11. This IF signal is sent to the AGC circuit 32.
Supply to the input of. The output signal of the AGC circuit 32 is supplied to the input of the demodulation circuit 33. The output signal of the demodulation circuit 33 is supplied to the input of the video processing circuit 22 and the input of the C / N detection circuit 231. The output signal of the video processing circuit 22 is supplied to the input of the clamp circuit 12, and the anti-phase adder 1
Supply 3 The output signal of the clamp circuit 12 is supplied to the inputs of the anti-phase adder 13 and the switch circuit 14. The output signal of the anti-phase adder 13 is supplied to the input of the switch circuit 14. Control signal of AGC circuit 32 and C / N
The output signal of the detection circuit 231 is the switching signal generation circuit 341.
Of the switching signal generation circuit 341 is used as the control signal of the switch circuit 14. The output signal of the clamp circuit 12 and the anti-phase adder 1 are connected to the output terminal 15.
One of the three output signals obtains the selected signal.

The generation of the video signal from which the dispersal signal after the clamp circuit 12 is removed is exactly the same as in FIG. In this embodiment, since the control signal of the switch circuit 14 is generated by combining the AGC control signal and the C / N detection signal, it can be applied to both low C / N and weak input.

FIG. 7 is a circuit configuration diagram for explaining a specific example of the switching signal generation circuit 44. The C / N detection signal and the AGC control voltage signal are independent of the hysteresis circuits 71 and 72 and the comparator circuit 73, respectively.
It is input to the OR circuit 75 via 74. Therefore, the output signal of the OR circuit 75 generates a switching signal when at least one of low C / N and weak input is detected.

In this way, a video signal adapted to the quality of the input signal of the second IF signal can be obtained, line noise does not occur, and signal processing is performed so that the image does not break down. It is possible to prevent the influence from being reflected in the image as much as possible.

[0029]

As described above, according to the noise reducing apparatus of the present invention, the transmission line for signal processing is switched according to the quality of the IF signal, so that an adapted video signal can be obtained, and streak noise can be obtained. It is possible to prevent the occurrence of the occurrence of the image and also prevent the image from being damaged due to the noise.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram for explaining another embodiment of the present invention.

FIG. 3 is a circuit configuration diagram for explaining a second another embodiment of the present invention.

FIG. 4 is a circuit configuration diagram for explaining a third other embodiment of the present invention.

FIG. 5 is a characteristic diagram for explaining the relationship between C / N and noise amount.

FIG. 6 is a characteristic diagram for explaining a relationship between an IF input level and an AGC control voltage.

FIG. 7 is a circuit configuration diagram for explaining a specific example of a switching signal generation circuit used in the present invention.

FIG. 8 is a conventional clamp circuit diagram used for removing a dispersal signal.

9 is a signal waveform diagram for explaining removal of the dispersal signal in FIG.

FIG. 10 is a signal waveform diagram for explaining the problem of FIG.

[Explanation of symbols]

11 ... Input terminal, 12 ... Clamp circuit, 13 ... Anti-phase adder, 14 ... Switch circuit, 15 ... Output terminal, 16, 3
4, 341 ... Switching signal generation circuit, 23, 231 ... C / N
Detection circuit, 22 ... Image processing circuit, 33 ... Demodulation circuit, 32
... AGC circuit.

Claims (5)

[Claims] 1. A first removing means for removing a dispersal signal from a video signal on which a dispersal signal is superimposed, and a dispersal signal based on an output signal of the first removing means and the video signal. A noise reduction device comprising: a second removing unit; and a selecting unit that selects and outputs the outputs of the first and second removing units according to a reception state of the video signal. 2. The selecting means for outputting the first and second removing means detects the C / N ratio of the video signal on which the dispersal signal is superimposed, and selects based on the detection result of the C / N ratio. The noise reduction device according to claim 1, wherein 3. The noise according to claim 1, wherein the selecting means for outputting the first and second removing means is selected by a control signal of an AGC circuit for controlling the gain of the intermediate frequency signal. Reduction device. 4. The noise reduction device according to claim 1, wherein the switching means is configured by combining the features of claims 2 and 3. 5. A clamp circuit for clamping a video signal on which a dispersal signal is superimposed to remove the dispersal signal, and an inverse circuit for periodically separating the output signal of the clamp circuit and removing the dispersal signal from the video signal. A noise reduction device comprising: a phase addition unit; and a switch circuit for selecting whether to take out the output of the clamp circuit or the output of the anti-phase addition unit according to the reception state of the video signal.