KR940004604Y1 - Specific signal trap circuit for multi-tv system - Google Patents

Abstract

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Description

Color signal trap circuit

1 is a characteristic diagram showing frequency characteristics of a color signal trap circuit.

2 shows a resonator and its equivalent circuit.

3 is a block diagram showing a preferred embodiment of the color signal trap circuit according to the present invention.

The present invention relates to a color signal trap circuit for processing video signals by a plurality of broadcast methods, and more particularly, to a color signal trap circuit including a low pass filter whose blocking characteristics are adjusted according to a broadcast method of an input video signal.

The color signal trap circuit is for trapping color signals from a video signal in which a color signal and a luminance signal are combined. The color signal trap circuit is a filter having a center frequency of a color subcarrier. Such a color signal trap circuit is usually located at a rear end of a first video amplifier circuit of a television receiver and bypasses a color signal from a composite video signal amplified by the first video amplifier circuit to output only a luminance signal from which the color signal is removed. The luminance signal from which the color signal is removed is the second of the rear stages. Amplified by the fourth image amplification circuit and provided to the image output circuit. The image output circuit inputs the color difference signal from the color demodulation circuit and the luminance signal from the image amplification circuit to generate the primary color signal, and outputs it to the receiving tube so that the image is displayed.

Since the color signal is a quadrature amplitude modulated signal with a color subcarrier (for NTSC, PAL) or a frequency modulated signal (for SECOM), the color signal trap circuit includes a filter having the largest attenuation at the frequency of the color carrier. NTSC stands for National Television System Committee, PAL stands for Phase Alternation by Line, and SECOM stands for Sequentiel Couleur a Memoire.

1 shows the frequency characteristics of the color signal trap circuit and shows an example applied in the NTSC method. In the NTSC type television signal, the color signal is orthogonal amplitude modulated by a color carrier having a frequency of 3.579545 MHz. Thus, the color signal trap circuit becomes a filter having a center frequency of 3.579545 MHz.

As the color signal trap circuit, a resonator (correction filter) may be used in addition to the RC resonance circuit. 2 is a view showing a resonator and an equivalent circuit thereof.

In the color signal trap circuit corresponding to the plurality of broadcasting systems, since the frequency of the color subcarriers in each broadcasting system is different, a plurality of trap circuits having different center frequencies are provided to be replaced according to the broadcasting system.

For example, a television receiver corresponding to a broadcasting method having color subcarriers of 3.58 MHz and 4.43 MHz, respectively, includes a first color signal trap circuit having a center frequency of 3.58 MHz and a second color signal trap circuit having a center frequency of 4.43 MHz. It is equipped with and selects a suitable one according to each broadcasting system.

On the other hand, if the broadcast method is different, the occupied bandwidth of the video signal is also different, so the characteristics of the filter for filtering the video signal should be different according to the reception state of the broadcast method. For example, the bandwidth of video signal in NTSC system is 4.2MHz, but the bandwidth of video signal in PAL and SECOM system is 5MHz. Since it is 6MHz, in the NTSC reception mode, a low pass filter that blocks signals beyond the occupied band of the NTSC should be provided.

As described above, the separate installation of the color signal trap circuit and the low pass filter not only complicates the circuit configuration but also causes a cost increase due to the increase of the labor.

Accordingly, an object of the present invention is to provide a color signal trap circuit which also serves as a low pass filter having a different cutoff characteristic according to each broadcasting scheme, which was devised to overcome the above problems.

The color signal trap circuit according to the present invention for achieving the above object is a color signal for inputting a video signal having a first or second color carrier, and outputs a video signal from which the color signal is removed by trapping the color signal modulated to each color carrier A trap circuit, comprising: a first color signal trap circuit for trapping and outputting a color signal modulated by a first color carrier; A low pass filter connected in series with the first color signal trap circuit; A first color signal trap circuit connected in parallel to the first color signal trap circuit, for trapping and outputting a color signal modulated by a second color carrier; And a switch connected in parallel to the low pass filter to maintain a blocking state when an image signal having a first color carrier is input and to maintain a conduction state when an image signal having a second color carrier is input. It is characterized by. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

3 is a circuit diagram showing an embodiment of a color signal trap circuit according to the present invention. In Fig. 1, reference numeral X1 is a first color signal trap circuit having a center frequency of 3.58 MHz, and X2 is a second color signal trap connected in parallel to the first color signal trap circuit X1 and having a center frequency of 4.43 MHz. Circuit. Q1 Q3 is a switching transistor which performs a switching operation according to each broadcasting method, and R1. R6 is a bias resistor. Resistor R7 and capacitor C1 form a low pass filter.

The operation of the circuit by the configuration of FIG. 3 will be described in detail. Switching transistor (Q1) The switching operation of Q3) is determined by the broadcasting method of the video signal input through the input terminal 30 and Q1. Q3 control signal input terminal (SW1) Table 1 shows the signal applied to SW3).

TABLE 1

In Table 1, NTSC 3.58 is a standard NTSC method and a broadcast method having a color signal modulated by a 3.58 MHz color subcarrier, whereas NTSC 4.43 refers to a broadcast method having a color signal modulated by a 4.43 MHz color subcarrier.

In addition, "H" means a logic signal in a high state, and "L" means a logic signal in a low state. As is known, the occupied band of the NTSC broadcast signal is about 6 MHz and the occupied bands of PAL and SECOM are about 8 MHz.

First, when the video signal of NTSC 3.58 is input, as shown in Table 1, 'H' signal is applied to SW1, 'L' signal is applied to SW2 and SW3, so Q1 is conducting and Q2 and Q3 are not conducting. do.

When Q1 is turned on, the color signal around 3.58MHz of the input video signal is removed through X1, Q1 and C1, and only the luminance signal is output through the output terminal 32. At this time, since the low pass filter is formed by R7 and C1 and the high pass is blocked, the bandwidth of the luminance signal output through the output terminal 32 is reduced. As is known, this is because the bandwidth of the video signal in the NTSC system is about 2 MHz less than that in the PAL and SECOM, so that the filtering characteristics of the color signal trap circuits are adjusted to the 6 MHz characteristics of the NTSC system.

Since the video signal of NTSC 4.43 method is input, as shown in Table 1, 'H' signal is applied to SW2, 'L' signal is applied to SW1 and SW3, so Q2 is conducting and Q1 and Q3 are non-conducting. do.

When Q2 is conducted, the color signal around 4.4358MHz in the input video signal is removed through X2, Q2, and C1, and only the luminance signal is output through the output terminal 32. At this time, since the low pass filter is formed in R7 and C1 and the high pass is blocked, the bandwidth of the luminance signal output through the output terminal 32 is reduced. As is well known, this is because the bandwidth of the video signal in NTSC system is about 2MHz less than the bandwidth in PAL and SECOM, so that the filtering characteristic of the color signal trap circuit is adjusted to the 6MHz characteristic of NTSC system.

Finally, when PAL or SECOM video signal is input, 'H' signal is applied to SW2 and SW3 and 'L' signal is applied to SW1 as shown in Table 1, so Q2 and Q3 are conducting. It is not conducting.

When Q2 and Q3 are conducted, the color signal around 4.4358MHz among the input video signals is removed through X2, Q2 and Q3, and only the luminance signal is output through the output terminal 32. At this time, since the low pass filter is not formed by R7 and C1, bandwidth attenuation does not occur.

As described above, the color signal trap circuit according to the present invention has an effect that the color signal trap processing with improved frequency characteristics can be performed by performing low pass filtering suitable for each broadcasting method in color signal trap processing corresponding to a plurality of broadcasting methods.

In addition, the color signal trap circuit according to the present invention has the advantage of contributing to the cost savings by reducing the work maneuver by performing a low pass filtering suitable for each broadcasting method.

Claims (3)

A color signal trap circuit for inputting a video signal having a first or second color carrier and outputting a video signal from which color signals have been removed by trapping a color signal modulated to each color carrier, wherein the first or second color carrier is An input terminal for introducing a video signal having a; A first color signal trap circuit for trapping and outputting a color signal modulated by the first color part carrier when the image signal having the first color part carrier is input through the input terminal; A low pass filter connected to the first color signal trap circuit in series; A second color signal trap circuit connected to the first color signal trap circuit in parallel and trapping and outputting a color signal modulated by the second color carrier by inputting a video signal having a second color carrier from the input terminal; ; Connected to the low pass filter in parallel, and maintain a blocking state when an image signal having the first color carrier is input through the input terminal, and a conduction state when an image signal having the second color carrier is input A switch to maintain; And an output terminal for outputting an image signal from which the color signal output from the low pass filter is removed. 2. The color signal trap circuit according to claim 1, wherein the frequency of the first color carrier is 3.58 MHz and the frequency of the second color carrier is 4.43 MHz. 3. The color signal trap circuit according to claim 2, wherein the passband of the low pass filter is an occupied bandwidth of an NTSC video signal.