JPH031694A - Color signal eliminating circuit - Google Patents

Abstract

PURPOSE:To prevent a color signal from being left without losing a high frequency component of a luminance signal by providing a horizontal line discrimination circuit discriminating a horizontal line period of a composite video signal, plural filter circuits and a switching circuit. CONSTITUTION:The resonance frequency of filter circuits 5, 8 is set in matching with each subcarrier frequency of two kinds of color signals based on the SECAM system. Moreover, a collector and an emitter of a bipolar transistor(TR) 9 are inserted between the circuit 5 and a ground voltage VSS and a collector and an emitter of a bipolar TR 10 are inserted between the circuit 8 and the ground voltage VSS. Then a line discrimination circuit 11 discriminates the line of two kinds of color signals sent in line sequential state and supplies a discrimination signal whose level is inverted for each horizontal period to the base of the TR 9 and to the base of the TR 10 via an inverter 12. Thus, the TRs 9, 10 in the switching circuit 13 are switched by the output of the circuit 11 and the circuits 5, 8 are operated alternately, then the residual color signal is prevented without losing the high frequency component of a luminance signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a color signal removal circuit used in a SECAM type television receiver.

(Prior art) As is well known, the SECAM system, which is one of the television broadcasting systems, switches two types of color difference signals proportional to R-Y and B-Y line-sequentially (alternately for each scanning line). , after pre-emphasis and bandwidth limiting,
A method is adopted in which the frequency is modulated and multiplexed into the luminance signal (Y signal).

The subcarrier frequency of two types of color difference signals (hereinafter referred to as color signals) multiplexed with the luminance signal is approximately 4 for the R-Y signal.
．． 406MHz, approximately 4.250M for B-Y signal
It is different from Hz.

Composite SECAM in which two types of color signals are sent line-sequentially.
When demodulating a video signal on the receiver side, first, a luminance signal and a color signal are separated. Then, the carrier signal including the color signal is converted into a sequential signal using a delay line for one horizontal line time, and into a simultaneous signal by switching the signal that passes through the delay line and the signal that does not pass for each scanning line. . This results in
Two types of color signals are extracted and each is FM demodulated.

By the way, a color signal removal circuit is used to remove the color signal from the video signal and separate the luminance signal, and a conventional +M configuration thereof is shown in FIG.

In the figure, 2 [ is a video detection circuit, 22 is a delay circuit for aligning the luminance signal and chrominance signal on the screen of the television receiver, and the inductor 23 and capacitor 24 connected in series are the chrominance signal It constitutes a filter circuit 25 for trapping.

Further, 26 is a luminance signal processing circuit.

The composite SECAM video signal S output from the video detection circuit 21 passes through the delay circuit 22 and then passes through the filter circuit 25.
The color signal component is removed. That is, the inductor 23
A signal component of a frequency matching the resonant frequency fO set according to each part of the capacitor 24 is removed. Here, the frequency fO is the subcarrier frequency 4.4 of the two types of color signals.
The frequency is set to an intermediate value between 0.06 MHz and 4.250 MHz.

Then, by lowering the selectivity (sharpness) Q determined by the inductor 23 and capacitor 24 of the filter circuit 25 to some extent and widening the bandwidth of the color signal trap, two types of color signals having different subcarrier frequencies can be used together. I'm trying to remove it.

In this way, the color signal is removed from the composite SECAM video signal S, and the composite SECAM video signal S is transmitted to the luminance signal processing circuit 26. However, in such a configuration, the selectivity Q of the filter circuit 25
Since the value of is set low, high-frequency components of the luminance signal are also deleted, resulting in a disadvantage that the horizontal resolution of the television receiver is significantly reduced. Furthermore, as described above, the resonant frequency fO for trapping the color signal does not match the subcarrier frequencies of the two types of color signals, so the color signal is not completely removed and remains. As a result, the luminance signal is transmitted to the luminance signal processing circuit 26 while containing the residual subcarrier, and in this luminance signal processing circuit 26, a pedestal clamp circuit that uses the voltage level of the back porch as a reference for the black level is used. The drawback is that residual subcarriers cause malfunctions, making it difficult to reproduce accurate black levels.

(Problem to be Solved by the Invention) As described above, conventionally, one filter circuit is used to remove the color signal of the matched SECAM video signal that includes the subcarrier frequencies of two types of color signals. The selectivity value of the filter circuit is set low. As a result, the high-frequency components of the luminance signal are also deleted, resulting in a drawback that the horizontal resolution of the television receiver is significantly reduced. Furthermore, since the resonance frequency for trapping the color signal does not match the subcarrier frequencies of the two types of color signals, the signal is transmitted to the luminance signal processing circuit while containing the residual subcarrier. Therefore, in the luminance signal processing circuit, a pedestal clamp circuit that uses the back porch voltage level as a black level reference malfunctions due to residual subcarriers, making it difficult to accurately reproduce the black level.

The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a color signal removal circuit that does not lose the high frequency components of the luminance signal and does not leave any color signals remaining.

[Configuration of the Invention (Means for Solving the Problems) The color signal removal circuit of the present invention has a first color signal component modulated on a first subcarrier and a second color signal component modulated on a second subcarrier. A processing circuit for a SECAM-based composite video signal including color signal components includes a horizontal line discrimination circuit for determining a horizontal line period of the composite video signal, and a horizontal line discrimination circuit for removing the first color signal component from the composite video signal. 1 filter circuit, a second filter circuit that removes the second color signal component from the composite video signal, and the first and second filter circuits are alternately operated based on the discrimination output of the horizontal line discrimination circuit. It consists of a control circuit that operates the device.

(Function) The first and second filter circuits for color signal trapping, which are matched to the subcarrier frequency of color signals of class 28, are operated alternately by a switching circuit controlled by a line discrimination signal, so that accurate color Remove the signal. Thereby, there is no need to lower the selectivity of each of the resonant circuits forming the first and second filter circuits, thereby preventing deletion of high-frequency components of the luminance signal.

(Examples) Hereinafter, the present invention will be explained by examples with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a color signal removal circuit according to the present invention. In the figure, ] is a video detection circuit, and 2 is a delay circuit that aligns the luminance signal and color signal on the screen of the television receiver. Also,
An inductor 3 and a capacitor 4 connected in series constitute a first filter circuit 5 for a first color signal trap, and an inductor 6 and a capacitor 7 connected in series constitute a second color signal trap. It constitutes a second fill circuit 8 for.

The resonance frequency of each of the filter circuits 5 and 8 is SEC
It is matched to each subcarrier frequency of two types of color signals based on the AM method, for example, the resonant frequency f1 of the filter circuit 5 is approximately 4.406 MHz, and the resonant frequency f2 of the filter circuit 8 is approximately 4.406 MHz.
are set at approximately 4.250 MHz.

Further, a collector-emitter of a bipolar transistor 9 is inserted between the filter circuit 5 and the ground voltage Vss, and a collector-emitter of a bipolar transistor 10 is inserted between the filter circuit 8 and the ground voltage Vss. There is. In addition, 11 is a line discrimination circuit, which accurately discriminates the lines of two types of color signals sent line sequentially.
A determination signal whose level is inverted every horizontal period is output.

The output of this line discrimination circuit [[ is supplied to the base of transistor 9 and also to the base of transistor 10 via inverter 12. This transistor 9
, 10 constitute a switching circuit 13 for alternately operating the filter circuits 5 and 8 in accordance with the discrimination output of the line discrimination circuit 11.

14 is a luminance signal processing circuit to which the signal from which the color signal has been removed is supplied.

Next, the operation of the circuit having the above configuration will be explained with reference to the waveform diagrams shown in FIGS. 2(a) to 2(c).

Note that FIG. 2(a) shows the composite SECAM video signal S output from the video detection circuit 1, and FIG. 2(b) (
c) is the pulse signal P output from the line discrimination circuit 11
1 and the pulse signal P2 output from the inverter 12, respectively.

Now, when the composite SECAM video signal S output from the video detection circuit 1 contains one color signal component modulated by the 4.406 MHz subcarrier during the water=lZ period, the line discrimination circuit 1 outputs The pulse signal P1 to be output becomes "H" level, and the pulse signal P2 becomes "L" level.At this time, the transistor 9 in the switching circuit 13 becomes conductive, and one of the filter circuits 5 operates. Since the resonance frequency is set to 4.406 MHz, one color signal component included in the composite SECAM video signal S is removed by this filter circuit 5. At this time, the transistor IO in the switching circuit 3 is non-conductive. Since the other filter circuit 8 does not operate, the other signal components are not affected and are directly passed to the luminance signal processing circuit 1.
4.

Composite SECAM video f≦ output from video detection circuit 1
In the next horizontal period in which the signal S contains the other color signal component modulated by the 4.250 MHz subcarrier, the pulse signal P1 output from the line discrimination circuit 11 is at "L" level, and the pulse signal P2 becomes "H" level. At this time, the transistor 10 in the switching circuit 13
becomes conductive, and the other filter circuit 6 operates. Since the resonance frequency of this filter circuit 6 is set to 4.250 MHz, the other color signal component included in the composite SECAM video signal S is removed by this filter circuit 6. At this time, the transistor 91 in the switching circuit 13 is non-conductive, and the other filter circuit 5 does not operate.
Also at this time, other signal components are transmitted to the luminance signal processing circuit 14 as they are without being affected. Thereafter, similarly, based on the discrimination output from the line discrimination circuit 11, the transistors 9 and 9 in the switching circuit 13. By alternately conducting the IO and operating the filter circuits 5 and 6 alternately, one color signal component modulated by the 4,406 MHz subcarrier included in the composite SECAM video signal and the 4,25 MHz
The other color 1g component modulated by the 0MHz subcarrier is removed.

According to the embodiment described above, two filter circuits 5. whose resonance frequencies match the subcarrier frequencies of two types of color signals, respectively.
8, there is no need to lower the selectivity Q of the resonant circuit. As a result, it is possible to prevent the color signal from entering the luminance signal processing circuit 14 without significantly losing the high frequency components of the luminance signal. Furthermore, since the luminance signal processing circuit 14 does not include residual subcarriers, the luminance signal processing circuit 14 uses the back porch 15 (as shown in FIG. 2(a)).
A pedestal clamp circuit (not shown) that uses the voltage level of .

[Effects of the Invention] As explained above, according to the present invention, it is possible to provide a color signal removal circuit that can transmit a signal to a luminance signal processing circuit without losing high-frequency components of a luminance signal and without residual color signals. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a configuration according to the present invention, FIG. 2 is a waveform diagram of each part of the circuit of FIG. 1, and FIG. 3 is a circuit diagram showing the configuration of a conventional color signal removal circuit. 1... Video detection circuit, 2... Delay circuit, 3, 6...
・Inductor, 4.7...Capacitor, 5,8...
Filter circuit, 9.10...transistor, H...
Line discrimination circuit, 12... Inverter, 13... Switching circuit, 14... Luminance signal processing circuit. Applicant's agent Patent attorney Takehiko Suzue911Figure 3Figure 2

Claims (1)

[Claims] A first color signal component modulated on a first subcarrier and a second color signal component modulated on a first subcarrier.
SEC comprising a second color signal component modulated on a subcarrier of
A processing circuit for an AM type composite video signal, comprising: a horizontal line discrimination circuit that determines a horizontal line period of the composite video signal; a first filter circuit that removes the first color signal component from the composite video signal; a second filter circuit that removes the second color signal component from the composite video signal; and a second filter circuit that removes the second color signal component from the composite video signal;
A color signal removal circuit comprising: a control circuit that alternately operates the second filter circuit.