JPH02179033A - Device for improving picture quality of satellite broadcast receiver - Google Patents

Abstract

PURPOSE:To realize the improvement of picture quality of a satellite broadcast receiver effectively by detecting an amplified noise component only included in a satellite broadcast TV signal and activating a video signal noise reduction circuit in response to a detection signal. CONSTITUTION:A reception signal inputted to an input terminal 1 is selected by a channel selection circuit 3, FM-modulated by a demodulation circuit 3 and fed to a video signal processing circuit 7. The processed video signal passes through a video signal noise reduction circuit 9 and information such as channel display and sound volume is superimposed on the video signal by an on-screen display circuit 10, and the resulting signal is fed to a TV receiver 11. The noise extracted by a BPF 4 is amplified hy an amplifier 5 to have a sufficient level by the detection of a detector 6, the resulting noise is inputted to the detector 6 and detected therein and the resulting signal is inputted to a comparator circuit 8, from which a control signal is outputted. The video signal noise reduction circuit 9 is operated by using the control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a satellite broadcast receiver, which automatically controls the operation of a video signal noise reduction circuit by detecting the quality of received radio waves. ! It is used for image quality improvement equipment.

Conventional satellite broadcasting technology modulates microwave band radio waves with a television signal, radiates the radio waves from a geostationary satellite, and focuses the radio waves on the ground using a satellite broadcasting antenna 31 such as a parabolic antenna, as shown in Figure 6. Thereafter, the frequency is converted to 1G seven bands using a satellite broadcast converter 32 including an ultra-low noise amplifier. The output signal from the satellite broadcast converter 32 is sent to an indoor satellite broadcast receiver 34 using a coaxial cable 33 to perform signal processing such as channel selection and FM demodulation, and outputs a video signal and an audio signal. Receiver 3
5 is input.

By the way, the SN ratio (signal level to noise level ratio) of the demodulated video signal is proportional to the CN ratio (carrier level to input noise level) of the received signal, so if the CN ratio of the received signal decreases, the SN ratio of the video signal decreases. will also decrease. In order to cope with this, as shown in FIG. 7, the satellite broadcasting receiver is equipped with a well-known video signal noise reduction circuit 45 in the video signal processing circuit system 48, and this is controlled by an external control signal from a controller such as a control switch. 46 is always ON and always 0FF (
When the S/N ratio of the video signal decreases, noise components in the video signal, such as high-frequency noise components of the luminance signal that appear on the screen, are This makes it possible to improve the signal-to-noise ratio of the video signal.

Problems to be Solved by the Invention However, in the above configuration, the video signal noise reduction circuit operates under external control, so if this circuit is always OFF, the SN ratio of the video signal will decrease. There is a problem in that the image quality deteriorates when the signal is degraded, and when the signal is always on, the image quality changes due to the image signal noise reduction circuit when the signal-to-noise ratio of the image signal is good.

In view of the above-mentioned problems, the present invention provides a means for detecting the quality of radio waves received by a satellite broadcasting receiver and solving the problems using this detection signal. , a bandpass filter that takes a satellite television signal as input, removes television signal components, that is, a video luminance component, a video carrier color signal component, and a modulation signal component of an audio subcarrier from the components of the demodulated output signal, and extracts a noise component; An amplifier that amplifies the extracted noise to the level required for detection, a detection circuit that manually detects the amplified noise and detects the size of the noise component, a comparator that receives the detection output as input, and a comparison thereof. It consists of a video signal noise reduction circuit that operates according to the output level of the device.

According to the above-described configuration, the present invention outputs a demodulated output component consisting of a television signal consisting of a video signal and a modulated signal of an audio subcarrier, and a demodulated noise component that changes depending on the input level of a satellite broadcasting antenna, from the FM demodulator, and The pass filter makes it possible to extract only the noise components in the frequency band where there is no television signal. The demodulation noise component at the signal detection output end of the FM method is generally called triangular noise.
As the demodulation frequency increases, the noise voltage increases, so the higher the frequency of the bandpass filter, the greater the noise voltage will be obtained, and a bandpass filter with a center frequency higher than the highest frequency of the composite TV signal will more easily remove the noise component. can be taken out. Also, the noise voltage will decrease as the human power level of the antenna for satellite broadcasting increases.

The noise component extracted by the bandpass filter is amplified to a sufficient level by an amplifier and then input to a detection circuit, where the noise component is detected and a DC output voltage corresponding to the magnitude of the noise voltage can be obtained. Since this DC output voltage corresponds to the S/N ratio of the video signal, by inputting the output of this detection circuit to a comparator circuit whose output changes between two states with a certain DC1l voltage as the input threshold,
When the SN ratio of the video signal changes, the video signal noise reduction circuit can be controlled to be automatically switched between the ON state and the OFF state.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a satellite broadcasting receiver image quality improvement device according to an embodiment of the present invention.

In Figure 1, 1 is a 1st IF input terminal to which a coaxial cable from a satellite broadcasting converter is connected and a signal is input, 2 is a selection circuit that selects only one channel from many channels, and 3 is an FM modulated terminal. 4 is an FM demodulation circuit for demodulating the signal; 4 is a bandpass filter (BPF) for extracting noise components from the FMulii output signal;
), 5 is an amplifier for amplifying the extracted noise to the extent necessary for detection, and 6 is a DC output corresponding to the magnitude of the noise voltage (
7 is a video signal processing circuit for applying de-emphasis to the FM demodulation output and removing energy spread signal components peculiar to satellite broadcasting; 8;
9 is a well-known video signal noise reduction circuit that is controlled by the control signal; 10 is a comparison circuit that receives the output of the wave detector 6 as an input and outputs a control signal; 10 superimposes information such as a channel on the video signal, and transmits it to a television receiver; This is an on-screen display circuit for displaying on 11.

The operation of the satellite broadcasting receiver image quality improvement device configured as described above will be explained below.

First, the received signal input to the 1st IF input terminal 1 of the satellite broadcasting receiver is tuned by the tuning circuit 2, and then sent to the demodulation circuit 3
After being subjected to M modulation, a video signal is obtained by performing de-emphasis, removal of audio subcarrier signals, and removal of energy spread signal components in a video signal processing circuit 7, and after passing through a video signal noise reduction circuit 9, a channel display is performed. and information such as volume in the on-screen display circuit 10,
After being superimposed on the video signal, it is supplied to the television receiver 11.

The circuit operation to date is included in the functionality of a normal satellite broadcast receiver.

Now, as shown in Figure 2, the signal after FMfi modulation includes an image luminance component, an image carrier color signal component (center frequency is 3.58M
Hz), the modulated signal component of the audio subcarrier (center frequency is 5°7272 MHz), and the demodulated noise is generally called triangular noise, as shown in Figure 3, and the higher the frequency, the higher the noise power. increases. For this reason, a bandpass filter (BPF) 4 for extracting only the noise component and excluding the demodulated signal component is used to remove the demodulated signal component and extract only the noise component. It is desirable to select a center frequency of about 8 MHz and a band of about IMHz in consideration of the generation of double harmonic components.

Choosing the center frequency of the BPF to be 11 MHz or higher can remove demodulated signal components, but generally the frequency band of the demodulated output of the FM demodulator of a satellite broadcasting receiver is from about 50 Hz to 8 MHz, and frequencies higher than that can be removed. Since this is not guaranteed, the output level of the noise component will decrease, so it is necessary to increase the gain of the amplifier 5, and
This is not preferable because it increases the variation in the level of the noise component.

The noise extracted by the BPF 4 is amplified by the amplifier 5 until it reaches a level sufficient to be detected by the detector 6, and is then input to the detector 6, where it is detected, input to the comparison circuit 8, and outputted as a control signal.

By using this control signal, the video signal noise reduction circuit 9 is automatically controlled to be in an ON state and an OFF state.

The comparison circuit 8 includes a comparator rc2 as shown in FIG.
This can be achieved using 0. Here, 2I and 22 are resistors that determine the threshold value of the comparator rc20. The input/output characteristics of this circuit are as shown in Figure 5.
If the value is greater than or equal to the threshold value determined by , the output goes high; otherwise, the output goes low.

Therefore, by setting this threshold value, it is possible to set the value at which the S/N ratio of the video signal starts to operate the video signal noise reduction circuit 9.

In addition to the above-described embodiments, the present invention can be modified in various ways without changing the gist thereof.

For example, the comparison circuit 8 uses a comparator IC 20 as shown in FIG. 4, but it may be configured in any manner as long as it has input/output characteristics as shown in FIG.

Also, BPF4 is twice the video carrier color signal in the demodulator,
The center frequency and band were selected taking into consideration the occurrence of three times the harmonic component and twice the harmonic component of the audio subcarrier modulation signal, but if these do not occur, the BPF4 The center frequency and band may be configured without considering harmonic components.

Effects of the Invention As described above, the present invention extracts the noise component from the FM demodulation output, detects it to detect the magnitude of the noise component, and compares it in the comparison circuit, thereby adjusting the S/N ratio of the video signal. Since the video signal noise reduction circuit is automatically controlled to the ON state and OFF (through) state according to the situation, the image quality of the satellite broadcasting receiver can be improved even more effectively, and its practical effects are significant. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a satellite broadcasting receiver image quality improvement device according to an embodiment of the present invention, FIG. 2 is a spectrum diagram of the demodulated output of the satellite broadcasting receiver, and FIG. 3 is a spectrum diagram of the demodulated output of the satellite broadcasting receiver. 11 Noise spectrum diagram, Figure 4 is a circuit diagram showing an example of a comparison circuit, Figure 5 is an input/output characteristic diagram of the comparison circuit, Figure 6 is a diagram of a satellite broadcasting receiving system, and Figure 7 is a diagram of a satellite broadcasting system. FIG. 2 is a block diagram of a receiver. 3...FM [l unit, 4...Band pass filter (BPF), 5...Amplifier, 6...
...Detection circuit, 8...Comparison circuit, 9...
...Video signal noise reduction circuit. Name of agent: Patent attorney Shigetaka Awano 1 guest A fist 1 sound Spectra, mu Diagram output ZS -- Kazumasa t 7t, fmh child A - power purchase W, M child Diagram Diagram 8ka

Claims (1)

[Claims] an FM demodulator for demodulating a satellite broadcast television signal;
A bandpass filter that extracts only a noise component that does not include a video luminance signal component and a video carrier color signal component and does not include a modulation signal component of an audio subcarrier from the output signal component of the demodulator, and is connected to the bandpass filter. an amplifier that amplifies the noise component of the output signal, a detection circuit that detects the magnitude of the output noise component of the amplifier, a comparison circuit that receives the output of the detection circuit as an input, and operates in accordance with the output level of the comparison circuit. A satellite broadcasting receiver image quality improvement device equipped with a video signal noise reduction circuit.