JPH06189330A - Television receiver - Google Patents

Abstract

PURPOSE:To obtain an excellent color picture even in the reception under a weak electric field strength by varying a passing frequency band of a primary color signal from a color demodulation circuit depending on a level of an AGC signal obtained by an AGC circuit. CONSTITUTION:When the television receiver is used at a slightly weak electric field, a level of an AGC detection signal outputted from an AGC detection circuit 35 is lower and a comparator 39 outputs a signal of an L level to LPFs 40-42. In this case, an RGB matrix circuit 14 obtains primary color signals R',G',B' enough to display a color picture regardless of being slightly weak and they are fed to the LPFs 40-42. Since a signal of an L level is inputted from the comparator 39 to the LPFs 40-42, the primary color signals R, G, B are generated and outputted based on the primary color signals R', G', B' by selecting the LPFs in which a time constant is large and an upper limit of a pass frequency band is set lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver having a color killer function, which is suitable for a liquid crystal television device used in a portable manner.

[0002]

2. Description of the Related Art Recently, a liquid crystal television device using a liquid crystal display panel for a display portion has been widely spread, including in a vehicle, because of its small size, light weight and excellent portability. This type of liquid crystal television device is often used while moving, and the reception radio wave environment changes from moment to moment. Therefore, it is desired to always perform good reception in a stable state.

In such a liquid crystal television device, as shown in FIG.
Shows an example of the configuration of a chroma signal processing circuit that creates R, G, B primary color signals from a video signal. In the figure, the video signal obtained by the video detection circuit (not shown) at the previous stage is sent to the chromatolap circuit 11 and the chroma band pass filter (chroma BPF) 12.

The chromatographic circuit 11 extracts only the luminance signal Y from the video signal and sends the extracted luminance signal Y to the pedestal clamp circuit 13. The pedestal clamp circuit 13 stabilizes the pedestal level of the luminance signal corresponding to the black portion of the image by clamping the pedestal level at a constant voltage, and sends it to the RGB matrix circuit 14.

On the other hand, the chroma bandpass filter 12 is
Only the chroma signal C in the video signal is extracted and sent to the ACC amplifier 15. The ACC amplifier 15 amplifies while controlling the gain according to the DC voltage level of a burst signal (not shown) so that the signal level of the transmitted chroma signal C becomes constant, and the amplified chroma signal C is APC circuit 16 R-through the color killer detection circuit 17 and the switch 18.
It is sent to the Y, BY detection circuit 19.

The APC circuit 16 phase-locks the chroma-processing subcarrier signal by the color burst of the chroma signal C, and the obtained subcarrier signal is subjected to the above-mentioned RY, B-
It is sent to the Y detection circuit 19 and the color killer detection circuit 17.

The color killer detection circuit 17 is an ACC amplifier.
The level of the color burst signal is detected by the chroma signal C from 15 and the subcarrier signal from the APC circuit 16, and the detection result is sent to the comparator 20. The comparator 20 compares the output from the color killer detection circuit 17 with a preset killer level voltage Vk, and turns on / off the switch 18 according to the comparison result.

However, the RY, BY detection circuit 19
Performs color demodulation detection using the chroma signal C sent from the ACC amplifier 15 via the switch 18 and the subcarrier signal from the APC circuit 16 to obtain color difference signals RY, B-.
Y is generated, and the generated color difference signals R-Y and B-Y are sent to the RGB matrix circuit 14 after removing unnecessary carrier components through the filters 21 and 22, respectively.

In the RGB matrix circuit 14, the luminance signal Y and the color difference signal RY from the pedestal clamp circuit 13,
By adding B-Y with appropriate amplitude and polarity, primary color signals RGB for display are obtained and output to a display drive circuit (not shown) in the subsequent stage.

In such a configuration, when the color burst level in the chroma signal C is sufficiently high, the output of the comparator 20 is output according to the result of comparison between the output of the color killer detection circuit 17 and the killer level voltage Vk. By switch 18
Is turned on, the chroma signal C output from the ACC amplifier 15 is supplied to the RY, BY detection circuit 19, and the RGB matrix circuit 14 outputs R, G, B primary color signals to display a color image. Is executed.

On the contrary, when the level of the color burst in the chroma signal C is not so high, the switch 18 is activated by the output of the comparator 20 according to the comparison result between the output of the color killer detection circuit 17 and the killer level voltage Vk. When turned off, the chroma signal C output from the ACC amplifier 15 is RY,
It is no longer supplied to the BY detection circuit 19. Therefore, R
Only the luminance signal Y is output from the GB matrix circuit 14 in place of the R, G, B primary color signals, and a monochrome image is displayed.

[0012]

By the way, when the environment of use changes and the received television signal weakens, the level of the color burst is still at a sufficient level and the comparator.
Although the switch 18 is turned on by the output of 20 and the chroma signal C is supplied to the RY, BY detection circuit 19, the noise component ratio in the actual chroma signal C increases and color noise is displayed in the displayed image. Occurs and the level of the color burst decreases, and the switch 18 is turned off by the output of the comparator 20, and the chrominance signal RY, B
-While the supply to the Y detection circuit 19 is cut off and a monochrome image is displayed, it is more natural to display a lighter color image using the chroma signal C of a small level if color noise can be reduced. Can be.

Therefore, in the past, the comparator 20
The killer level voltage Vk is set to a high level to detect a decrease in the level of the chroma signal C early to switch to a monochrome image display, or the voltage Vk is set to a low level and some color noise including noise in the luminance signal system is also generated. Had adopted a method of choosing either to allow.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a television receiver capable of obtaining a good color image even when receiving under a weak electric field. is there.

[0015]

That is, the present invention provides an AGC circuit for detecting the signal level of a video signal of a television broadcast radio wave to perform AGC (automatic gain control) of the video signal, and a chroma signal in the video signal. A color difference signal generation circuit that generates a color difference signal from the color difference signal generation circuit, a color killer circuit that blocks the chroma signal input to the color difference signal generation circuit according to the level of the chroma signal, and the output of the color difference signal generation circuit. A color demodulation circuit for generating a primary color signal by a color difference signal and a luminance signal in the video signal;
A low-pass filter for varying and outputting the pass frequency band of the primary color signal from the color demodulation circuit according to the level of the AGC signal level obtained by the GC circuit is provided.

[0016]

With the above-mentioned structure, since the color noise at the time of a weak electric field can be reduced by the low-pass filter in the latter stage of the color demodulation circuit, the reference killer level voltage in the color killer circuit can be set low. It is possible to obtain a color image even when receiving under an electric field.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the circuit configuration. In the figure, television broadcast radio waves composed of high frequency signals for a plurality of channels received by an antenna 31 enter a tuner 32, a high frequency signal of only a desired channel is selected and converted into an intermediate frequency signal, and an intermediate frequency amplification circuit (IF amplification) ) 33.

The intermediate frequency amplifier circuit 33 amplifies this intermediate frequency signal to a voltage necessary for video detection, and sends the amplified intermediate frequency signal to the video detection circuit 34. The video detection circuit 34
The amplified intermediate frequency signal is detected to obtain a video signal, A
The signal is sent to the GC detection circuit 35, the chromatolap circuit 11 of the chroma signal processing circuit, and the chroma bandpass filter 12.

The AGC detection circuit 35 is the video detection circuit 34.
So that the level of the signal obtained at is always constant.
(Automatic gain control) Detection is performed, and the obtained detection signal is converted into a voltage signal through filters 36 and 37, respectively, and is fed back to the tuner 32 and the intermediate frequency amplifier circuit 33 to output AG.
At the same time as forming a C loop, it is converted into a voltage signal through the filter 38 and sent to the comparator 39.

The comparator 39 uses the voltage level Vth for judging the weak electric field in which the noise component ratio of the chroma signal C exceeds a predetermined value as a reference, and the level of the AGC detection signal sent through the filter 38. Of the low pass filter (LPF) 40-42
Output to. Each of the low-pass filters 40 to 42 has a configuration in which the time constant is switched by the output of the comparator 39 to change the upper limit of the pass frequency band.

Now, the configuration of the circuit portion for performing the chroma signal processing on the video signal output from the video detection circuit 34 is almost the same as that in FIG. 2 described above. Is omitted.

In this chroma signal processing circuit, however, the killer level voltage Vk 'set lower than the killer level voltage Vk shown in FIG. 2 is applied to the comparator 20, and the comparator 20 uses this killer level voltage Vk' as a reference. The detection level of the color burst signal sent from the color killer detection circuit 17 is compared and judged, and the ON / OFF control of the switch 18 is performed based on the result. Also,
The color difference signals R-Y and B-Y containing the unnecessary carrier component output from the R-Y and B-Y detection circuit 19 are directly read as R.
It is sent to the GB matrix circuit 14.

The RGB matrix circuit 14 adds the luminance signal Y from the pedestal clamp circuit 13 and the color difference signals R-Y and B-Y containing unnecessary carrier components with appropriate amplitudes and polarities to obtain a primary color signal. R ', G', B '
At least unnecessary carrier components are removed through the low-pass filters 40 to 42 to obtain primary color signals RGB for display, and then output to a display drive circuit (not shown) in the subsequent stage.

When the television receiver is used under the standard electric field with the above-mentioned structure, the level of the AGC detection signal output from the AGC detection circuit 35 becomes high, and the comparator 39 outputs the AGC detection signal. When it is judged that the signal level is higher than the voltage level Vth for weak electric field judgment, for example, an "H" level signal is sent to the low-pass filters 40-42.

At this time, the chroma signal processing circuit corresponds to the chroma signal C having a sufficiently high signal level, and the switch 18 is output by the output of the comparator 20 according to the comparison result of the output of the color killer detection circuit 17 and the killer level voltage Vk '. Is turned on, and the chroma signal C output from the ACC amplifier 15 becomes R-
It is supplied to the Y, BY detection circuit 19.

Therefore, the RGB matrix circuit 14 uses the luminance signals Y and RY from the pedestal clamp circuit 13,
Primary color signals R ', G', B'for displaying a color image are obtained by the color difference signals RY, BY containing an unnecessary carrier component from the BY detection circuit 19, and each of them is the low-pass signal. Send to filters 40-42.

Since the "H" level signal is input from the comparator 39 to the low-pass filters 40 to 42, the time constant is small enough to remove the unnecessary carrier component according to this signal. The circuit is switched to the side where the upper limit of the pass frequency band is set to be relatively high, and the primary color signals RGB are generated from the primary color signals R ', G', B'and output.

When the television receiver is used in a slightly weak electric field, the A output from the AGC detection circuit 35 is output.
The level of the GC detection signal becomes low, and the comparator 39 determines that the level of the AGC detection signal is lower than the voltage level Vth for weak electric field determination, and sends a signal of "L" level to the low pass filters 40 to 42, for example. .

At this time, in the chroma signal processing circuit, the output of the color killer detection circuit 17 and the killer level voltage Vk 'correspond to the chroma signal C having a slightly low but still sufficient signal level.
The switch 18 is turned on by the output of the comparator 20 in accordance with the result of comparison with, and the chroma signal C output from the ACC amplifier 15 is supplied to the RY and BY detection circuit 19.

Therefore, the RGB matrix circuit 14 uses the luminance signals Y and RY from the pedestal clamp circuit 13,
By the color difference signals RY and BY containing the unnecessary carrier component from the BY detection circuit 19, primary color signals R ', G', and B'for displaying a color image are obtained although they are slightly weak,
Each is sent to the low-pass filters 40-42.

Since the "L" level signal is input from the comparator 39 to the low-pass filters 40 to 42, a large time constant is passed so that sudden color noise can be sufficiently reduced according to this signal. The circuit is switched to the side where the upper limit of the frequency band is set lower, and the primary color signals RGB are generated from the primary color signals R ', G', B'and output.

Further, when this television receiver is used under a completely weak electric field, the level of the AGC detection signal output from the AGC detection circuit 35 becomes low, and the comparator
At 39, it is judged that the level of this AGC detection signal is lower than the voltage level Vth for weak electric field judgment, and a signal of "L" level is sent to the low-pass filters 40-42.

At this time, the chroma signal processing circuit responds to the chroma signal C having a completely low signal level, and switches it by the output of the comparator 20 according to the comparison result between the output of the color killer detection circuit 17 and the killer level voltage Vk '. 18 is turned off, and the chroma signal C output from the ACC amplifier 15 becomes R-
The supply to the Y, BY detection circuit 19 is cut off.

Therefore, the RGB matrix circuit 14 uses only the luminance signal Y from the pedestal clamp circuit 13 to output the primary color signals R ', G', for displaying a monochrome image.
B'are obtained and sent to the low pass filters 40 to 42, respectively.

Since the "L" level signal is input from the comparator 39 to the low-pass filters 40 to 42, a large time constant is passed so that sudden color noise can be sufficiently reduced in accordance with this signal. The circuit is switched to the side where the upper limit of the frequency band is set lower, and primary color signals RGB are generated from the primary color signals R ', G', B'for monochrome images and output.

[0037]

As described above, according to the present invention, an AGC circuit for detecting the signal level of a video signal of a television broadcast wave and performing AGC (automatic gain control) of the video signal, and the above-mentioned video signal A color difference signal generating circuit for generating a color difference signal from the chroma signal, a color killer circuit for cutting off the chroma signal input to the color difference signal generating circuit according to the level of the signal level of the chroma signal, and the color difference signal generating circuit. And a color demodulation circuit for generating a primary color signal by the color difference signal output from the video signal and a luminance signal in the video signal, and the passage of the primary color signal from the color demodulation circuit according to the level of the AGC signal level obtained by the AGC circuit. Since it has a low-pass filter that outputs by changing the frequency band, color noise at the time of a weak electric field can be eliminated by the low-pass filter in the latter stage of the color demodulation circuit. Since it can be reduced, the killer level voltage, which is the reference in the color killer circuit, can be set low, and to a certain extent, a television receiver capable of obtaining a color image with sufficiently reduced color noise even when receiving under a weak electric field. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional chroma signal processing circuit.

[Explanation of symbols]

11 ... Chromatolap circuit, 12 ... Chroma band pass filter (Chroma BPF), 13 ... Pedestal clamp circuit, 14
… RGB matrix circuit, 15… ACC amplifier, 16… A
PC circuit, 17 ... Color killer detection circuit, 18 ... Switch,
19 ... RY, BY detection circuit, 20, 39 ... Comparator,
21, 22, 36 to 38 ... Filter, 31 ... Antenna, 32 ... Tuner, 33 ... Intermediate frequency amplification circuit, 34 ... Video detection circuit, 35 ... A
GC detection circuit, 40 to 42 ... Low-pass filter (LPF).

Claims (1)

[Claims] 1. A detection means for detecting a signal level of a video signal of a television broadcast radio wave, a color difference signal generation circuit for generating a color difference signal from a chroma signal in the video signal, and a color difference signal generation circuit for controlling the signal level of the chroma signal. A color killer circuit that blocks a chroma signal input to the color difference signal generation circuit, a color demodulation circuit that generates a primary color signal by the color difference signal output from the color difference signal generation circuit and the luminance signal in the video signal, A television receiver comprising: a filter for varying and outputting the pass frequency band of the primary color signal from the color demodulation circuit according to the level of the signal level obtained by the detecting means.