JPS61121591A - Trap circuit - Google Patents

Abstract

PURPOSE:To remove automatically a dot interference, etc., by installing a detecting circuit to detect the size of a color sub-carrier component at the rear step from the trap of the luminance signal and controlling an attenuating quantity of the trap by the output of the detecting circuit. CONSTITUTION:A luminance signal component and a chrominance signal component are respectively outputted from a comb-shaped filter circuit 1. Out of these components, to the luminance signal component side, a variable attenuating trap 2 of a color sub-carrier frequency fSC is inserted. A detecting circuit 3 detects a fSC component inserted to a luminance signal line after the trap 2 passes, gives to a detecting comparing circuit 4, and the circuit 4, when the quantity of the fSC component goes to be constant or above, outputs the output signal to control the trap 2. Usually, in a receiving condition, a variable resistor 5 is set to the condition where the output of the circuit 4 is not executed. When a color TV signal dislocated extremely from the regular frequency relation is inputted, the output is generated from the circuit 4, thereby the trap 2 is operated and the component near fSC included in a luminance signal is attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a trap circuit used in a color television receiver equipped with a comb filter introduced for higher resolution.

Conventional technology In color television using the NTSC system, the luminance signal component and color signal component are transmitted in an interleaved form, and in order to maximize the performance of the receiver, it is necessary to separate them. A comb filter circuit is introduced.

The advantage of using a comb filter circuit is that one color subcarrier frequency fBc (3,58
The luminance component and the color signal component in the vicinity of MHz) are ideally separated.

In FIG. 2, a is fl! in the transmitted signal. . It represents a nearby spectrum, and in the figure, the solid line represents the color signal component, and the dotted line represents the luminance signal component. Further, in the figure, b indicates the characteristics of the comb filter, and c and d indicate the spectra of the color signal and luminance signal after passing through the comb filter.

For the luminance signal component, by using such a comb filter, high resolution can be achieved, and for the color signal component, cross color can be reduced because the luminance signal component leaks into the color signal component. is possible.

Problems to be Solved by the Invention The problem in this case is that since a delay line of 10,000 periods is normally used when constructing a comb filter, the frequency relationship of the transmitted signals cannot be maintained accurately. If so,
The effect as a comb filter is maintained, but if the frequency relationship is shifted (for example, when playing a color image on a VTR, etc.), the comb filter circuit will not be able to exhibit its original effect, and on the contrary, it will become extremely In such cases, a large amount of color signal components leak into the luminance signal side, resulting in extreme dot interference.

The present invention attempts to automatically eliminate inconvenient phenomena such as dot interference when the frequency relationship is shifted in a color television device or the like equipped with a comb filter circuit.

Panting--In order to check the closeness when looking at the camera, a circuit is installed that detects the magnitude of the color subcarrier component, and a circuit is installed to detect the magnitude of the color subcarrier component mixed into the luminance signal side. The feature is that the amount of attenuation of the trap is controlled.

With this configuration, if the frequency relationship in the transmitted color television signal is shifted and the comb filter circuit is unable to effectively separate the luminance signal and color signal, automatic Specifically, the trap in the luminance signal circuit can be activated to reduce the leakage of the color signal into the luminance signal.

Embodiment A block diagram of an embodiment of the present invention is shown in FIG. In the figure, 1 is a comb filter circuit, and the comb filter circuit 1 outputs a luminance signal component and a color signal component separately.

Of these, the color subcarrier frequency f sc is on the luminance signal component side.
(3.58MHz) variable attenuation trap 2 is inserted. In addition, 3 in the figure is a detection circuit for detecting the fIIC component inserted into the luminance signal line after passing through the variable trough 12, and 4 is the 1tac signal obtained from the detection circuit 3.
This is a component detection/comparison circuit.

When the amount of the detected fsc component exceeds a certain amount, an output signal for controlling the variable trap 2 is output. Also,
5 is a variable resistor for setting the reference voltage.The operation of this configuration is as follows.

In a normal reception state (a state in which a signal with regular interleaving is being received), the detection/comparison circuit 4
The setting variable resistor 5 is set in such a state that no output is produced. If this is done, the presence or absence of such a circuit does not matter at all in the normal reception state.

However, when a color telephoto signal that is extremely deviated from the normal frequency relationship is input, the detection/comparison circuit 4 generates an output, which activates the trap 2 and detects the f8c signal contained in the luminance signal. Attenuates nearby components.

Moreover, the amount of attenuation increases as the amount of the fsc component output from the comb filter circuit 1 increases.

Moreover, since the circuit is a closed loop, the fBC component output to the luminance signal line does not increase beyond a certain amount.

The situation is shown in Figure 3. The value of k can be freely set using the setting variable resistor 5, and this setting can be made while observing that no dot interference appears on the screen when the comb filter circuit 1 is killed.

Effects of the Invention As described above, according to the present invention, the comb filter circuit exhibits the original effect when receiving a regular signal, and traps when a non-interleaved signal is transmitted. It is possible to operate effectively and automatically remove dot interference, etc., and always obtain product quality images.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a block diagram of a trap circuit in one embodiment of the present invention, Figs. 2 a to d are waveform diagrams for explaining the operation of the comb-shaped filter circuit, and Fig. 3 is the same. FIG. 3 is a characteristic diagram for explaining the operation and effect of the circuit. 1... Comb filter circuit, 2...
3.68MHzl-lap, 3...3.5s
MHz detection circuit, 4...Detection/comparison circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2: Mizuju period Figure 3: M/Ilh or now

Claims (1)

[Claims] A comb filter is provided to separate a luminance signal and a color signal, and a trap whose attenuation amount of a color subcarrier component is variable is provided on a luminance signal line output from the comb filter, and a trap is provided at a stage subsequent to the trap on the luminance signal line. A trap circuit comprising: a detection circuit for detecting the magnitude of a color subcarrier component; and an output of the detection circuit to control the amount of attenuation of the trap.