KR0124970Y1 - The fixed level preservation circuit of color burst - Google Patents

Abstract

The present invention relates to a circuit that maintains a constant color burst for each broadcasting station when receiving a TV broadcast. More specifically, a color burst signal is extracted from a complex video signal and then directly converted to a color burst signal. By maintaining the signal at a constant amplitude, the amplitude fluctuation of the color burst signal generated by fluctuations in the received field strength, impedance mismatch in the antenna reception period, fluctuations in the local oscillation frequency, or the field loss of the CATV can be uniformly maintained for each broadcasting station. This ensures that you can always enjoy high quality images regardless of the channel of each station or external influences.

Description

Color Burst Constant Level Hold Circuit

1 is a block diagram of a conventional broadcast signal receiving circuit.

2 is a block diagram showing a color burst constant level maintaining circuit when receiving a broadcast signal according to the present invention;

* Explanation of symbols for main parts of the drawings

10 tuner 11: high frequency amplifier

12 local oscillation unit 13 mixer

20: demodulator 21: image IF amplifier

22: image detector 23: image amplifier

30: speech IF amplifier 50: high frequency automatic gain control unit

201: low pass filter 202: automatic level control

203: delay unit 204: band pass filter

205: Burst Gate Pulse Generator 206: Burst Gate

207: color level detector 208: burst level controller

209: clamp

The present invention relates to a circuit that maintains a constant color burst for each broadcasting station when receiving a television broadcast. More specifically, it extracts only a color burst signal from a composite video signal and converts it into a direct current (DC) and compares it with a reference signal. The present invention relates to a color burst constant level maintaining circuit which obtains the same chromaticity for each broadcasting station by keeping the color burst signal at a constant amplitude.

1 is a diagram illustrating a conventional broadcast signal receiving circuit, in which a high frequency (hereinafter referred to as RF) signal received from an antenna ANT is referred to as an intermediate frequency (hereinafter referred to as IF). Tuner 10 for converting to 45.75Mhz is a high frequency amplification unit 11 for amplifying the RF signal to a predetermined level, and the high frequency amplification by channel data or voltage output from a microcomputer (not shown). A local oscillator 12 for oscillating a frequency for converting the RF amplified by the unit 11 into IF, and the output of the high frequency amplifier 11 and the output of the local oscillator 12 are mixed and output as IF signals. It consists of the mixer 13.

In addition, the demodulator 20 that separates and demodulates only an image signal from an IF output from the tuner 10 uses an SAW filter to pass only the image IF signal from the IF signal and then amplifies the image IF amplifier. 21, an image detector 22 for detecting the amplified image IF, and an image amplifier 23 for amplifying the image signal detected by the image detector 22.

At the same time, the tuner 10 is connected to the voice IF amplifier 30 which amplifies the number of passages of only the IF signal from the IF signal by using a sooth filter and outputs the voice signal. On the other hand, the demodulator 20 is connected to the trap unit 40 for removing the audio signal of the noise component included in the amplified video signal.

In addition, an RF automatic gain control is provided at the output terminal of the image IF amplifier 21 of the demodulator 20 to increase the gain of the image signal and feed it back to the high frequency amplifier 11 when the input electric field is a weak electric field. (Hereinafter referred to as AGC)) 50 is connected.

In FIG. 1 configured as described above, the RF signal received from the antenna ANT is amplified to a predetermined level by the high frequency amplifier 11 of the tuner 10.

At this time, when the channel data or the voltage is applied from the microcomputer (not shown), the local oscillator 12 of the tuner 10 oscillates a local oscillation frequency corresponding to the channel and outputs it to the mixer 13.

That is, the local oscillator 12 oscillates at F _CH + 45.75Mhz. Here, F _CH is a broadcasting station channel frequency applied from the microcomputer.

For example, if the user wants to receive 6 channels (83.25Mhz), the local oscillator 12 oscillates at 83.25Mhz + 45.75Mhz and outputs it to the mixer 13.

In this case, the mixer 13 outputs a difference frequency between the RF amplified by the high frequency amplification unit 11 and the oscillation frequency of the local oscillator 12, which is determined by the local oscillation frequency of the local oscillator 12. It is the IF of the tuned channel.

On the other hand, the IF signal output from the mixer 13 is separated only the video IF signal by the image IF amplifier 21 of the demodulator 20, the audio IF signal separated only by the audio IF amplifier 30 After each is amplified.

The image IF signal amplified by the image IF amplifier 21 is detected by the image detector 22, amplified to a predetermined level by the image amplifier 23, and then input to the 4.5 MHz trap unit 40. This eliminates audio components that are noise components in the video signal.

Meanwhile, when the input electric field is a weak electric field, the RF AGC unit 50 increases the AGC voltage of the image IF signal output from the image IF amplifier 21 to pad back to the high frequency amplifier 11 to obtain a good image. .

On the other hand, Korea has also been able to receive more than 30 channels of broadcasting at home, as the country of cable television (CATV) broadcasting has entered the multi-channel era.

In this case, when the first diagram described above is applied to the CATV, a color burst signal is generated due to a change in received field strength for each broadcasting station, a change in local oscillation frequency due to a change in temperature or environment, and an impedance mismatch between an antenna and a receiver. Amplitude fluctuations may cause the chromaticity signals to differ from station to station.

That is, since the amplitude of the color burst signal is different for each broadcasting station, the user must adjust the image for each broadcasting station in order to see a good screen.

The present invention is to solve the above problems, and the object of the present invention is to separate the DC color by only the color burst signal from the composite image signal, and then compare and amplify the amplitude signal of the color burst signal by amplifying and amplifying a predetermined level. The present invention provides a color burst constant level maintaining circuit which maintains the same chromaticity for each broadcasting station.

A feature of the color burst constant level maintaining circuit according to the present invention for achieving the above object is a tuner for tuning a predetermined channel to a medium frequency in the high frequency signal received from the antenna, and the intermediate frequency output from the tuner A broadcast signal receiving circuit comprising a demodulator for separating and detecting and amplifying an intermediate frequency of a video signal, the brightness signal separation for separating only a luminance signal from an image signal amplified by the demodulator and adjusting the separated luminance signal to a video output level. Means, delay means for delaying the luminance signal output from the luminance signal separation means for a predetermined time, chromaticity signal separation means for separating and outputting only the chroma signal from the image signal amplified by the demodulator, and in the chromaticity signal separation means A knife that extracts and outputs a color burst signal from the output chromaticity signal La burst output means, a color level detection means for converting the color burst signal output from the color burst output means into a direct current voltage, and the chromaticity signal separation means by comparing the direct current voltage and the reference voltage output from the color level detection means. A burst level control means for maintaining a constant level of the color signal and the color burst signal outputted from the < RTI ID = 0.0 > and < / RTI > the amplitude of the color burst signal by combining the luminance signal delayed by the delay means for a predetermined time and the chroma signal output from the burst level control means. The present invention provides a combination means for outputting a composite video signal having a constant size.

Hereinafter, a preferred embodiment of the color burst constant level maintaining circuit according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram of a color burst constant level holding circuit according to the present invention.

In FIG. 2, the tuner 10 and the demodulator 20 are the same as in FIG.

That is, a low pass filter (LPF) 201 for passing only a luminance signal in the amplified image signal is connected to an output terminal of the image amplifier 23 of the demodulator 20, and the LPF 201 An automatic level control (hereinafter referred to as ALC) unit 202 for maintaining a level of the luminance signal passed through is connected.

In addition, the ALC unit 202 is connected to a delay unit 203 for delaying the luminance signal for a predetermined time in order to match the time of the luminance signal maintained at a constant voltage and the color signal at which the amplitude of the color burst signal is kept constant.

On the other hand, the output terminal of the image amplifier 23 of the demodulator 20 is connected to the 3.58Mhz Band Pass Filter (BPF) 204 for passing only the chroma signal from the amplified video signal. Here, the chroma signal includes a color burst and a color component.

In addition, the burst gate pulse generator 205 which generates a gate signal based on a composite image synchronization signal (C-Sync) removes a color component from the chroma signal output from the BPF 204 by the gate signal, and performs a color. A burst gate portion 206 that outputs only a burst signal is connected.

In addition, a color level detector 207 is connected to the burst gate unit 206 to DC the color burst signal, and the color level detector 207 is connected to the BPF 204 using the DC voltage and a reference voltage. The output burst level control unit 208 is connected to keep the level of the color burst signal and the color signal constant.

The burst level controller 208 is connected with a clamp unit 209 for removing a level variation of a color burst signal that has become a constant level, and an output terminal of the clamp unit 209 is connected to an output terminal of the delay unit 203. Are combined to output a composite video signal with a constant magnitude of color burst.

According to the present invention configured as described above, the RF signal received through the antenna ANT is amplified to a predetermined level by the high frequency amplifier 11 of the tuner 10.

At this time, the local oscillator 12 of the tuner 10 oscillates a local oscillation frequency corresponding to the channel and outputs it to the mixer 13 when data or voltage indicating a channel is applied from a microcomputer (not shown). .

That is, the local oscillator 12 oscillates at F _CH + 45.75Mhz. Here, F _CH is a broadcasting station channel frequency applied from the microcomputer.

For example, if the user wants to receive 6 channels (83.25Mhz), the local oscillator 12 oscillates at 83.25Mhz + 45.75Mhz and outputs it to the mixer 13.

In this case, the mixer 13 outputs a difference frequency between the RF amplified by the high frequency amplification unit 11 and the oscillation frequency of the local oscillator 12, which is determined by the local oscillation frequency of the local oscillator 12. It is the IF of the tuned channel.

Meanwhile, the IF signal output from the mixer 13 is separated and amplified only by the image IF signal by a low pass filter (not shown) of the image IF amplifier 21 of the demodulator 20, and an audio IF amplifier unit. Only the negative IF signal is separately amplified by the high pass filter and the band filter (not shown) of (30).

The image IF signal amplified by the image IF amplifier 21 is detected by the image detector 22 and amplified to a predetermined level by the image amplifier 23.

At this time, when the input electric field is a weak electric field, the RF AGC unit 50 increases the AGC voltage of the image IF signal output from the image IF amplifier 21 to feed back to the high frequency amplifier 11 to obtain a good image. .

On the other hand, the image signal amplified by the image amplifier 23 is separated only the luminance signal in the LPF 201, the separated luminance signal is adjusted to the video output level in the ALC unit 202 to maintain a constant voltage.

The delay unit 203 is output from the ALC unit 202 to match the time of the luminance signal adjusted to the video output level from the ALC unit 202 and the color signal including the color burst maintained at a constant level. Delay the luminance signal for a predetermined time.

On the other hand, the BPF 204 is a filter that passes only the 3.58Mhz band, and separates only the chroma signal including the color burst and the color component from the image signal amplified by the image amplifier 23.

In addition, since the color burst signal is input after a predetermined time after the composite image synchronization signal, the burst gate pulse generator 205 generates a gate signal based on the composite image synchronization signal (C-Sync), and the burst gate unit 206 Only the color burst signal is extracted from the chroma signal output from the BPF 204 by the generated gate signal and outputs the color burst signal.

In addition, the color burst signal output from the burst gate unit 208 is DCized by the color level detection unit 207 and then output to the burst level control unit 208.

The burst level control unit 208 compares the DC voltage output from the color level detection unit 207 with a reference voltage to maintain a constant level of the color signal and the color burst signal output from the BPF 204.

In addition, the color burst signal having a predetermined level in the burst level control unit 208 removes the level variation in the clamp unit 209 to make the amplitude constant.

The chroma signal with constant amplitude in the clamp unit 209 is combined with the luminance signal delayed by the predetermined time in the delay unit 203 to be output as a composite image signal having a constant color burst.

Therefore, each broadcasting station maintains a constant amplitude variation of the color burst signal generated by variations in the received field strength, impedance mismatch in the antenna reception period, variations in the local oscillation frequency, and electric field loss of the CATV. You can always enjoy high quality images regardless of the channel or external influences.

On the other hand, the present invention can be applied to demodulation such as a video cassette recorder, a television, etc., which receives an air broadcast or a CATV broadcast.

Claims (3)

In a broadcast signal receiving circuit comprising a tuner for tuning a predetermined channel to an intermediate frequency from a high frequency signal received from an antenna, and a demodulator for separating, detecting, and amplifying an image intermediate frequency from an intermediate frequency output from the tuner. Luminance signal separation means for separating only the luminance signal from the image signal amplified by the demodulator and adjusting the separated luminance signal to a video output level, delay means for delaying the luminance signal output from the luminance signal separation means for a predetermined time; Chromaticity signal separation means for separating and outputting only the chromaticity signal from the image signal amplified by the demodulator, color burst output means for extracting and outputting a color burst signal from the chromaticity signal output from the chromaticity signal separation means, and the color; Directly outputs the color burst signal output from the burst output means. Burst level control for comparing the color level detection means for converting the voltage with the direct current voltage output from the color level detection means and the reference voltage to maintain a constant level of the color signal and the color burst signal output from the chromaticity signal separation means. And a combining means for combining the luminance signal delayed by the delay means for a predetermined time with the chromaticity signal output from the burst level control means to output a composite video signal having a constant magnitude of the color burst signal. 2. The color burst of claim 1, wherein the luminance signal separating means comprises a low pass filter for passing only the luminance signal through the demodulator and an automatic level control unit for adjusting the luminance signal passed through the low pass filter to a video output level. Constant level holding circuit. 2. The apparatus of claim 1, wherein the color burst output means comprises: a burst gate pulse generator for generating a gate signal based on a composite video synchronization signal, and the chroma signal separation means by a gate signal generated by the burst gate pulse generator; A color burst constant level maintaining circuit comprising a burst gate portion that removes a color component from a chroma signal output from a color signal and outputs only a color burst signal.