KR19980023272A - Noise Reduction Device for Television Receiver - Google Patents

Abstract

The present invention relates to a noise reduction device of a television receiver so as to provide a better image by differentially controlling the gain ratio for each frequency band of the video signal according to the level of noise included in the video signal. A noise reduction device of a television receiver of the present invention is a television receiver which separates a luminance signal and a color signal from a composite video signal and then processes them appropriately to reproduce the image on a CRT. Means for detecting a plurality of bandpass filters for separating the luminance signals by predetermined frequency bands and a plurality of gain variations for determining gains of luminance signals (section luminance signals) passing through the respective bandpass filters, respectively. A control voltage generator for generating a plurality of control voltages whose magnitude increases in proportion to the level of noise detected by the amplifier and the noise detection means and decreases as the frequency band increases, thereby differentially controlling the gain of the variable gain amplifier. Characterized in that provided.

Description

Noise Reduction Device for Television Receiver

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device of a television receiver, and more particularly, to provide a higher quality image by differentially controlling a gain ratio for each frequency band of a video signal according to a noise level included in the video signal. A noise reduction device.

1 is a block diagram showing an image processing system of a general television receiver. As shown in Fig. 1, in a typical television receiver, the antenna 1 picks up a broadcast wave signal of a plurality of channels transmitted from the transmitting station to the air, and the tuner 2 of the plurality of channels picked up by the antenna 1 Among the broadcast wave signals, only a broadcast wave signal for a channel selected by the user is selectively passed and mixed with the locally generated frequency generated by itself to generate a predetermined intermediate frequency signal (hereinafter referred to as IF signal).

The IF amplification section 3 amplifies the IF signal generated by the tuner 2 to an appropriate size for processing. The P / S separation unit 4 includes a surface acoustic wave filter (SAW) filter, and the like, and separates the image intermediate frequency signal (PIF) and the audio intermediate frequency signal (SIF) from the amplified IF signal, The detector 5 detects the image intermediate frequency signal PIF separated by the P / S separation unit 4 and generates a composite image signal CV.

The Y / C separation unit 8 includes, for example, a comb filter or the like, and the luminance signal Y and the color signal (i) in the composite image signal CV output from the image detection unit 5 are included. C), and the sync separator 10 separates the horizontal sync signal Hs and the vertical sync signal Vs from the composite video signal CV detected by the image detector 5.

Next, the image processing unit 11 includes the luminance signal Y and the color signal C provided from the Y / C separation unit 8, and the horizontal synchronization signal Hs and the vertical synchronization signal provided from the synchronization separation unit 10. Vs) is appropriately processed to output R (Red), G (Green), and B (Blue) signals, and the CRT driving unit 14 outputs the CRT based on the R, G, and B signals output from the image processing unit 11. 15 is driven.

In FIG. 1, reference numeral 7 selectively receives only one video signal of the video signal CV detected by the image detector 5 and a baseband video signal provided by an external video device 6, for example, a VCR. A switching unit provided to the Y / C separation unit 8, 12 is a key input unit for receiving a key signal commanded by a channel selection key, a volume control key, a mode switching key, an image control key, etc., and 13 is a key input unit. A control unit for controlling each part of the receiver circuit to perform a corresponding operation after determining the key signal inputted through (12).

On the other hand, in the above-described configuration, since the Y / C separation unit 8 obtains the luminance signal through the low pass filter having 4.2 (MHz) as the cutoff frequency, noise of 4.2 or more is inevitably included in the luminance signal. Further, even in the lower frequency bands, there is a weak noise component. The noise component level below 4.2 (MHz) is known to increase as the frequency band increases.

However, in the conventional television receiver, as described above, since the luminance signal including the noise component is amplified as it is and restored to an image, there is a problem that the restored image quality is deteriorated due to the influence of noise.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and the television receiver can provide a higher quality image by differentially controlling the gain ratio for each frequency band of the video signal according to the level of noise included in the video signal. To provide a noise reduction device of the object.

A noise reduction device of a television receiver of the present invention for achieving the above object is a television receiver for separating the luminance signal and the color signal from the composite video signal, and then appropriately processing the same to reproduce the image on a CRT. Means for detecting high frequency noise exceeding a band, a plurality of band pass filters for separating the luminance signals by predetermined frequency bands, and gains of luminance signals (section luminance signals) passing through the respective band pass filters. The gain of the variable gain amplifier is generated by generating a plurality of control voltages each of which increases in proportion to the level of noise detected by the plurality of gain variable amplifiers and the noise detection means, and decreases as the frequency band increases. And a control voltage generator for differential control.

1 is a block diagram illustrating a video processing system of a general television receiver;

2 is a circuit diagram of a noise reduction device of a television receiver according to the present invention;

3 is a waveform diagram illustrating a gain ratio curve for each frequency band according to a noise level in FIG. 2;

*** Explanation of symbols for main parts of drawing ***

1 antenna, 2 tuner,

3: IF amplification part, 4: P / S separation part,

5: image detector, 6: external video device,

7: switching part, 8: Y / C separation part,

10: synchronization separator, 11: image processor,

12: key input unit, 13: control unit,

14: CRT drive unit, 15: CRT,

20-23: band pass filter, 24-27: gain variable amplifier,

28: delay line, 29: noise detector,

30: control voltage generator, 31: addition circuit section

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the noise reduction device of the television receiver of the present invention.

FIG. 2 is a circuit diagram of a noise reduction device of a television receiver according to the present invention. The same reference numerals are given to the same parts as those of FIG. As shown in Fig. 2, the noise reduction device of the television receiver of the present invention is added between the Y / C separation section 8 and the image processing section 11, the main configuration of which is included in the luminance signal Y. A noise detector 29 for detecting a noise component of a specific band, a plurality of band pass filters 20 to 23 for selectively passing only a predetermined frequency band from the luminance signal Y, and the respective band pass filters 20 to 23. Each gain variable amplifier 24 according to a plurality of gain variable amplifiers 24 to 27 determining the gain of a luminance signal (hereinafter referred to as an interval luminance signal) and the detected voltage of the noise detector 29. A control voltage generator 30 which differentially controls the gain of < RTI ID = 0.0 > 27. < / RTI >

In the above-described configuration, the noise detector 29 is composed of a high pass filter for detecting a noise component exceeding 4.2 MHz, which is a frequency band of the luminance signal Y, and a smoothing circuit for smoothing and directing the detected noise.

The control voltage generator 30 can be preferably implemented by a plurality of transistor circuits in which the DC-detected detection voltage is commonly connected to a base terminal, and a collector resistor and an emitter resistor are inserted into the collector terminal and the emitter terminal, respectively. As a result, the ratio of the emitter resistor and the collector resistor is properly set and the output is drawn from the collector terminal, thereby generating a large control voltage in the low frequency band and a small control voltage in the high frequency band. The control voltage thus generated is provided to the control input terminals of the respective gain variable amplifiers 24 to 27. In FIG. 2, reference numeral 28 denotes the original luminance signal Y by the time delay of the interval luminance signal generated in the process of passing through each of the band pass filters 20-23 and the variable gain amplifiers 24-27 described above. An addition circuit section for synthesizing the luminance signal passing through the delay line 28 and the interval luminance signal whose gain is appropriately adjusted via each of the variable gain amplifiers 24 to 27. Indicates. The resistor R and the variable resistor VR represent a division resistor for appropriately lowering the amplitude of the luminance signal whose level is increased through the addition circuit section 31.

Hereinafter, the operation of the noise reduction device of the television receiver of the present invention having the above-described configuration will be described in detail.

FIG. 3 is a waveform diagram illustrating a gain ratio curve for each frequency band according to the amount of noise in FIG. 2. First, the composite video signal CV is separated into a luminance signal Y and a color signal C by the Y / C separator 8, and the separated luminance signal Y is slightly noise over the entire frequency band. The component is present. Furthermore, these noise components become larger as frequency bands increase. Therefore, in the present invention, after detecting the level of the high-frequency noise of 4.2 (MHz) or more, the gain of the section luminance signal is differentially controlled based on this.

In more detail, the noise detector 29 detects the noise included in the luminance signal Y by a high pass filter having the cutoff frequency of 4.2 (MHz), which is the upper limit frequency of the luminance signal Y. This is smoothed to direct the DC, and the DC voltage VT thus produced is increased in proportion to the level of noise, as shown in FIG.

Meanwhile, each band pass filter 20 to 23 selectively passes only luminance signals belonging to the 1 (MHz), 2 (MHz), 3 (MHz), and 4 (MHz) bands to form interval luminance signals, respectively. To the variable gain amplifiers 24-27. Next, the control voltage generator 30 generates control voltages V1-V4 that determine the gain of each of the variable gain amplifiers 24-27 based on the detected voltage VT from the noise detector 29. . 3B to 3E show control voltages V1 to V4 output from the control voltage generator 30. As shown in FIG. 3, gains are increased from a low frequency band to a high frequency band. The slope of the non-curve is reduced. That is, the control voltages V1-V4 for the same noise detection voltage VT decrease as the frequency band increases.

Therefore, when the control voltages V1-V4 are applied to the respective control input terminals of the variable gain amplifiers 24-27, the gain of the section luminance signal belonging to the low frequency band where the noise level is relatively small decreases relatively little. On the other hand, the gain of the section luminance signal belonging to the high frequency band where the noise component is relatively large is relatively reduced, so that the noise is effectively removed.

Then, the respective luminance signals obtained in this manner are combined together with the original luminance signals delayed by a predetermined time through the delay line 28 in the addition circuit section 31, and then are separated by the resistor R and the variable resistor VR. The level is appropriately lowered to be provided to the image processor 11. As a result, when the luminance signal thus obtained is processed by the image processing section 11, a clear image is obtained rather than the noise over the entire frequency band of the luminance signal uniformly reduced.

The noise reduction device of the television receiver of the present invention is not limited to the embodiment described above, and can be implemented in various modifications within the range permitted by the technical idea of the present invention.

According to the noise reduction apparatus of the television receiver of the present invention as described above, the noise over the entire frequency band of the luminance signal by differentially controlling the gain ratio for each frequency band of the video signal according to the noise level included in the video signal. Is uniformly removed, thereby providing an effect of providing a better image.

Claims (1)

A television receiver for separating a luminance signal and a color signal from a composite video signal, and then appropriately processing the same to reproduce an image on a CRT, comprising: means for detecting noise of a high frequency exceeding a band of the luminance signal; Noise detected by the noise detection means and a plurality of gain variable amplifiers for determining a gain of a luminance signal (section luminance signal) passing through each of the band pass filters, respectively. Noise of a television receiver having a control voltage generator for generating a plurality of control voltages whose magnitude increases in proportion to the level of the signal and decreases as the frequency band increases, thereby differentially controlling the gain of the variable gain amplifier. Reduction device.