JPH0488778A - Satellite broadcast receiver picture quality improving device - Google Patents

Abstract

PURPOSE:To realize picture quality improvement efficiently by extracting a noise component from an FM demodulation output, detecting the component, and controlling automatically the noise reduction quantity of a video signal noise reduction circuit in response to the S/N of a reception signal. CONSTITUTION:A noise signal extracted by a BPF 4 is amplified by an amplifier 5 and inputted to a detector 6, in which the signal is detected. A high frequency component of a signal extracted by a high pass filter 10 after being distributed into two by a distributer 9 connecting to a video signal processing circuit 7 is amplified by an amplifier 11 and inputted to a limiter 12, the polarity is inverted by a polarity inverter 13 and the result is inputted to an attenuator 14. A DC voltage obtained by a detector 6 is used to apply variable control to a superimposing quantity at a high frequency in a superimposing circuit 15 by controlling the output amplitude limit of the limiter 12 and the attenuation of the attenuator 14 thereby improving the S/N of the video signal automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a satellite broadcast receiver, and relates to a satellite broadcasting receiver that automatically and variably controls the amount of noise reduction of a video signal noise reduction circuit by detecting the quality of received radio waves. The present invention relates to a broadcast receiver image quality improvement device.

As shown in Figure 8, conventional satellite broadcasting modulates microwave band radio waves with television signals and radiates the radio waves from a geostationary satellite.
After the radio waves are converged in step 1, the frequency is converted to the IGHz band 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. 9, the satellite broadcasting receiver applies de-emphasis to the FM demodulation output and uses a well-known video Equipped with a signal noise reduction circuit 45,
By controlling this to two states, ON and OFF, using an external control signal 47 from a controller such as a control switch, noise in the video signal can be reduced when the SN ratio of the video signal decreases. For example, it is possible to reduce the high-frequency noise component of the luminance signal that appears on the screen by a set amount, thereby improving the S/N ratio of the video signal.

Problem to be Solved by the Invention However, in the above configuration, the video signal noise reduction circuit operates under external control, so when this circuit is in the OFF state, the SN ratio of the video signal decreases. If the image quality deteriorates when the signal is turned on and the noise reduction amount is specified, conversely, when the signal-to-noise ratio of the video signal is good,
The problem was that the image quality changed due to the video signal noise reduction circuit.

The present invention is based on the above! In view of IH, the present invention aims to provide a satellite broadcasting image quality improvement device that detects the quality of radio waves received by a satellite broadcasting receiver and automatically controls the amount of noise reduction of a video signal noise reduction circuit using the detected signal. be.

Means for Solving the Problems In order to solve the above-mentioned "jiR", the satellite broadcasting image quality improvement device of the present invention takes a satellite TV signal as input and improves the TV signal components, that is, the video luminance component and the video carrier color, from the components of the demodulated output signal. a bandpass filter that removes the signal component and the modulated signal component of the audio subcarrier and extracts the noise component; a first amplifier that amplifies the extracted noise to a level necessary for detection; and a first amplifier that receives the amplified noise as input. A detection circuit that detects the magnitude of noise components by detection, a divider that is connected to the video signal processing circuit and divides the video signal into two, and a high-pass filter that is connected to the first output terminal of the divider and extracts high-frequency components. , a second amplifier connected to the high-pass filter to amplify high-frequency components, and an i# connected to the second amplifier to variably control the magnitude of the output amplitude of the output of the detector.
a limiter that is input to the 1ms output; a polarity inverter that inverts the polarity of the output of the limiter; an attenuator that is connected to the polarity inverter and that inputs the output of the detector to a control terminal that variably controls the amount of attenuation; and a video signal noise reduction circuit consisting of a superposition circuit that superimposes the output of the divider and the second output of the divider.

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 signal component that changes depending on the input level of a satellite broadcasting antenna, from the FM demodulator. The bandpass 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 system is generally called triangular noise, and is 11Fi! As the wave number increases, the noise voltage increases, so the higher the frequency of the bandpass filter, the greater the noise voltage can be obtained, and a bandpass filter with a center frequency higher than the highest frequency of the composite TV signal can more easily remove noise components. It can be taken out. Also, the noise voltage is
It will decrease as the input level of the satellite antenna increases. The noise component extracted by the bandpass filter is amplified to a sufficient level by the first amplifier and then input to the detection circuit, which detects the noise component.
It is possible to obtain a DC voltage according to the magnitude of the noise voltage. The high-frequency components of the video signal, which is connected to the video signal processing circuit and extracted by a high-pass filter after being divided into two, are amplified by a second amplifier and then input to a limiter that variably controls the magnitude of the signal. The amplitude below the amplitude limit value is output as a noise component. After the polarity of the output of the limiter is inverted by a polarity inverter, the level is adjusted by an attenuator. DC obtained by the detection circuit! Since the voltage corresponds to the S/N ratio of the demodulated signal, the output amplitude limit value of the limiter and the attenuation amount of the attenuator are controlled using the above DC voltage, and the output of the attenuator and the second output signal of the distributor are overlapped. It is possible to variably control the amount of superimposition in the high frequency range in the combining circuit, automatically control the amount of noise reduction by following changes in the S/N ratio of the demodulated signal, and automatically improve the S/N ratio of the video signal. .

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 broadcast reception image quality improvement apparatus in 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 tuning circuit that selects only one channel from many channels, and 3 is an FM modulated channel. 4 is a bandpass filter (4) for extracting only the noise component from the FM demodulated output signal without including the video luminance signal component, the video luminance signal component, and the modulation signal component of the audio subcarrier. B P F), 5 is a first amplifier for amplifying the extracted noise as necessary for detection, 6
7 is a detector for obtaining a DC output (detection output) according to the magnitude of the noise voltage, and 7 is a video signal processor for applying de-emphasis to the FM demodulation output and removing energy spread signals specific to satellite broadcasting. 8 is a video signal noise reduction circuit that reduces the noise component of the video signal; 9 is a distributor that is connected to the video signal processing circuit 7 and divides the video signal into two; 10 is connected to the first output terminal of the distributor 9; 11 is a high-pass filter 1 that extracts high-frequency components of the signal.
12 is a limiter that variably controls its output limit value based on the output of the detection circuit 6; 13 is a limiter of the limiter 12; A polarity inverter 14 inverts the polarity of the output; 14 is an attenuator that variably controls the amount of attenuation based on the output of the detection circuit 6; 15 is connected to the output of the attenuator 14 and the second output terminal of the distributor 9, and outputs two signals; A superimposition circuit 16 is an on-screen display circuit for superimposing information such as a channel on a video signal and displaying it on a television receiver 17.

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 in the channel selection circuit 2, FM demodulated in the FM demodulation circuit 3, and then de-emphasized and audio subcarrier in the video signal processing circuit 7. A video signal is obtained by removing the signal and the energy diffusion signal component, and after passing through the video signal noise reduction circuit 8, information such as channel display and volume is superimposed on the video signal in the on-screen display circuit 15. The signal is supplied to the television receiver 16.

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 FM demodulation consists of a video luminance component and a video carrier color signal (center frequency is 3.58M).
Hz), the modulation signal component of the audio subcarrier (center frequency is 5
．． 7272MHz). Also, the demodulated noise is generally called triangular noise, as shown in Figure 3.
The higher the frequency, the higher the noise power. 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 BPF4 to be 11MHz or higher means that
Although the demodulated signal component can be removed, the frequency band of the demodulated output of the FM demodulator 3 of the satellite broadcasting receiver is generally 50 Hz.
to about 8 MHz, and is not guaranteed at frequencies higher than that, so the output level of the noise component decreases, so it is necessary to increase the gain of the amplifier 5, and the variation in the level of the noise component increases. So I don't like it.

The noise extracted by the BPF 4 is amplified by the first amplifier 5 until it reaches a level sufficient to be detected by the detector 6, and is input to the detector 6 and detected. After being divided into two by a divider 9 connected to the video signal processing circuit 7, the high-frequency components of the signal taken out by a high-pass filter 10 are amplified by a second amplifier 11 and then passed through a limiter that limits the magnitude of the signal. 12, the amplitude below the amplitude limit value is output as a noise component, the polarity of which is inverted by a polarity inverter 13, and then input to an attenuator 14.

Since the DC voltage obtained by the detector 6 corresponds to the S/N ratio of the demodulated signal, the output amplitude limit value of the limiter 12 and the attenuation amount of the attenuator I4 are controlled by the DC voltage. The amount of superposition in the high frequency range of the output and the second output signal of the distributor 9 in the superposition circuit 14 is variably controlled, and the amount of noise reduction is automatically controlled in accordance with the change in the S/N ratio of the demodulated signal. However, the SN ratio of the video signal can be automatically improved.

Variable amplitude 1Ill! The limiter circuit with IN action is
This can be realized using a transistor differential amplifier circuit as shown in FIG. Here, 81 is a bias voltage source for transistor Q2, R1 and R2 are load resistances for transistors Ql and C2, R3 and R4 are emitter resistances for transistors Ql and C2, and I is a variable current source. Assuming that R1-R2=RL, the output characteristic of this differential amplifier circuit is as shown in FIG. 5, where the current value of the variable 1 current fII is i. , the maximum output amplitude is ±RLX+□, and when the current value of the variable current r is 1□, the maximum output amplitude is ±RLXimt*, and the limit value of the output amplitude changes depending on the current value of the variable current source ■.

The variable current source I can be realized using a current mirror circuit as shown in No. 60. l here? 1. R2 is an emitter-to-interresistance of transistors Ql and C2. Input control voltage Vc and transistor (collector t of 12
Base-emitter voltage V of file transistor Q2
The relationship between be and Ic-(Vc-17bez)/R2 holds true if the base current of transistor Q2 is ignored.
A variable current source that can control the collector current 1c of the transistor Q2 by the control voltage Vc can be configured.

If this differential amplifier circuit is used in a limiter circuit, the output amplitude limit value can be varied by controlling the current value of the variable current source using the voltage obtained by the detection circuit.

Further, the attenuator 14 having a variable control function for the amount of attenuation can be constructed of a PIN diode as shown in FIG.

Here, Ill is a PIN diode, R1 and R2 are PIN
The bias resistance of diode Di, CI, C2 is D
This is a C cant capacitor. The one-song direction current If of the PIN diode and the series resistance R1 have the following relationship.

I, ζ /R, (k is a proportionality constant) (1) Control voltage Vc and forward current of PIN diode D1 1. If the forward voltage of the PIN diode D1 is Vd, the relationship between the PIN diode D1 and the PIN diode D1 is expressed by the following equation.

1%=H(Vo-V, )/(R2+R1) ・--
---(2) From the above equations (1) and (2), the relationship between the series resistance R of the PIN diode D1 and the control voltage 1/C is as shown in the following equation.

111, K(R2+R1)/(V, -V,) Therefore,
As the control voltage VC increases, the series resistance Rs of the PIN diode [11] decreases, and the amount of attenuation decreases. If this attenuator is used, the voltage obtained by the detection circuit can be used to
By controlling the forward open current value of the diode, the amount of attenuation of the input signal of the attenuator can be variably controlled.

By using the above limiter circuit and attenuator, it is possible to change the amount of high-frequency component superposition of the signal in response to the voltage obtained by the detection circuit, so the amount of noise reduction can be automatically controlled. I can do it. Note that the limiter circuit having a variable amplitude uniform effect may be constructed of a circuit other than that shown in FIG. 4 as long as it has a variable amplitude limiting effect. Further, the variable current source may also be constructed from a circuit other than the circuit shown in FIG. 6, as long as the current value of the current source can be varied. Also,
The attenuator having a variable control function for the amount of attenuation may be constructed with a circuit other than that shown in FIG. 7, as long as it has a variable control function for the attenuation position.

Effects of the Invention As described above, the present invention extracts the noise component from the FMII output, detects the magnitude of the noise component, and reduces the noise reduction amount of the video signal noise reduction circuit according to the S/N ratio of the received signal. Since the image quality of the satellite broadcasting receiver is automatically controlled, 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 a demodulated signal at the demodulated output of the satellite broadcasting receiver, and FIG. 3 is a demodulated signal at the demodulated output. Noise spectrum diagram,
Fig. 4 is a circuit diagram showing an example of a limiter having a variable amplitude limiting action, Fig. 5 is an input/output characteristic diagram of the limiter, Fig. 6 is a circuit diagram showing an example of a current source, and Fig. 7 is a circuit diagram showing an example of a limiter having a variable amplitude limiting effect. FIG. 8 is a circuit diagram showing an example of an attenuator having a variable attenuation control function, FIG. 8 is a system diagram for satellite broadcast reception, and FIG. 9 is a block diagram of a satellite broadcast receiver. 3...FMIilFj, 4...Band pass filter (BPF), 5...Amplifier, 6...
...Detector, 9...Distributor, 10...
High-pass filter, 11...Amplifier, 12...
...Limiter, 13...Polarity inverter, 14
...Attenuator, 15...Superposition circuit. Name of agent: Patent attorney Shigetaka Awano and 1 other person

Claims (1)

[Claims] An FM demodulator for demodulating a satellite broadcast television signal;
a video signal processing circuit that receives an output signal from a demodulator; a bandpass filter that extracts only noise components that are not present; a first amplifier that is connected to the bandpass filter and amplifies the noise components; a detector that detects the magnitude of the output noise component of the first amplifier; a divider connected to a video signal processing circuit to divide the video signal into two; a high-pass filter connected to a first output terminal of the divider to take out high-frequency components of the video signal; and a high-pass filter connected to the high-pass filter to divide the video signal into two parts. a second amplifier that amplifies the high-frequency component of the limiter; a limiter that is connected to the second amplifier and inputs the output signal of the detector as an input to a control terminal that variably controls a limit value of the output signal amplitude; a polarity inverter connected to an output terminal to invert the polarity; an attenuator connected to the polarity inverter to input the output of the detector to a control terminal that variably controls the amount of attenuation; A satellite broadcasting receiver image quality improvement device comprising a video signal noise reduction circuit consisting of a superposition circuit that superimposes a second output of a distributor.