JPH0228951B2 - TAHOSHIKITE REBIJONJUZOKI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a comb-shaped filter circuit for a multi-system television receiver capable of receiving images in any of the NTSC, PAL, and SECAM broadcasting systems.

Conventional configurations and their problems In recent years, multi-system television receivers that can receive images from any of the NTSC, PAL, and SECAM broadcasting systems have been devised. On the other hand, NTSC
In order to improve cross color and resolution,
A comb filter circuit has been devised that utilizes the frequency interleaving principle of color television radio waves.

This will be explained below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a conventional multi-system television receiver. Here, the input video signal is
One takes out a luminance signal through a delay line 1 and a chroma trap circuit 5 and supplies it to a video control circuit 6. On the other hand, this video signal is passed through a bandpass filter circuit 2 for PAL signals depending on each system.
Alternatively, it passes through a bandpass filter circuit 3 for NTSC signals and is supplied to a PAL or NTSC chroma demodulation circuit 7. Further, on the other side, the signal passes through a bell filter circuit 4 for SECAM signals and is supplied to a SECAM chroma demodulation circuit 8. The luminance signal that has passed through the video control circuit 6 and the chroma signal that has passed through the chroma demodulation circuit 7 or 8 depending on each system are mixed in a video amplifier circuit 9 and supplied to the CRT 10.

Furthermore, FIG. 2 is a circuit diagram of a conventional example of a comb-shaped filter circuit for a television receiver that can only receive images of the NTSC system.

Here, the inputted video signal passes through an impedance conversion transistor 11 and is supplied from its emitter, and one from a capacitor 12 passes through a resistor 14 and a resistor 15 and is supplied to the collectors of transistors 18 and 19. On the other hand, a resistor 26 and a capacitor 2 are connected to the emitter of the transistor 11.
The video signal applied to the 1H delay line 13 via line 7 is delayed by one horizontal scanning period, and is supplied to the bases of transistors 18 and 19 in opposite phases. There, it is mixed with the video signal supplied without delay, and a video signal containing only the chroma signal component is generated at the collector of the transistor 18, which is applied to the base of the impedance conversion transistor 25, and from its emitter to the NTSC bandpass filter. It is supplied to circuit 3. On the other hand, a video signal containing only a luminance signal component is generated at the collector of the transistor 19, and is applied to the base of the impedance conversion transistor 24, and is supplied to the delay line 1 from its emitter. The above-mentioned comb filter circuit improves cross color and resolution when using the NTSC system. However, SECAM
In this method, the chroma signal is FM modulated, so even if the above circuit is used, it is theoretically impossible to separate the video signal into two video signals, one containing only the color signal component and the other containing only the luminance signal component.

Furthermore, since the interleaved positions in the PAL system are different from those in the NTSC system, it is necessary to allow a longer delay time for the video signal to be mixed than in the NTSC system. (Approximately 2 horizontal scanning periods) For this reason, discontinuity in color information components is noticeable in images that include parts with rapid color changes, resulting in a significant drawback in that the screen becomes even more difficult to view.

Purpose of the Invention The present invention utilizes the advantages of the comb-shaped filter circuit in the case of the NTSC system, and eliminates the influence of the comb-shaped filter circuit in the case of the PAL and SECAM systems, so that good image reception can be achieved with either system. The purpose of the present invention is to provide a multi-system television receiver.

Another object of the present invention is to provide a television receiver capable of performing compensation so that the DC level of a video signal does not change due to switching of a comb filter circuit in each broadcast system.

Structure of the Invention A multi-system television receiver according to the present invention is provided by adding a video signal to each collector of a differential amplifier to which a video signal delayed by one horizontal scanning period and having different phases is applied to the base through a resistor. A comb filter circuit is constructed at each collector output terminal of the amplifier to take out a video signal containing only a luminance signal component and a video signal containing only a chroma signal component, and the emitters of the differential amplifiers are connected to each other via a resistor. In addition to connecting the point to ground through a diode, a switching circuit is installed at the base of the differential amplifier to operate as a differential amplifier in the case of the NTSC system, and to shut off the differential amplifier in the case of the PAL and SECAM systems. This circuit has a circuit that is connected to each collector output terminal of the differential amplifier as a pseudo load in PAL and SECAM, and the DC level of the video in PAL and SECAM and NTSC is the same. PAL and
When using the SECAM method, the conventional performance is maintained and the NTSC
When using this method, it has the effect of improving cross color and resolution.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a circuit diagram of a multi-system television receiver according to an embodiment of the present invention. In the figure, the same elements and circuits as in FIGS. 1 and 2 are given the same numbers.

The diode 29 has its anode connected to the bases of the transistors 18 and 19 through the resistors 16 and 17, and its cathode connected to the system switching circuit 30.
3, the cathode is connected to ground.

In the case of the NTSC system, a high level voltage is output from the system switching circuit 30, so the diode 29 is cut off, the differential amplification transistors 18 and 19 forming the comb filter circuit operate, and the impedance conversion transistor 24 is turned off. A video signal containing only a luminance signal component is supplied from the emitter of the impedance converting transistor 25, and a video signal containing only a chroma signal component is supplied from the emitter of the other impedance conversion transistor 25, and is guided to the NTSC bandpass filter circuit 3.

On the other hand, when using the PAL or SECAM method, a low level voltage is output from the method switching circuit, so diode 29 is turned on and transistors 18 and 19 are cut off, so that the original signal input to the base of transistor 26 is The same is supplied from the emitters of transistor 24 and transistor 25, from transistor 24 the luminance signal is supplied through the delay line 1 and the chroma trap 5 of PAL and SECAM, and from transistor 25 the luminance signal is supplied.
PAL bandpass filter circuit 2 or
It is supplied to SECAM bell filter circuit 4.
Note that the diode 28 is inserted so that the transistors 18 and 19 are completely cut off in the PAL and SECAM systems.

However, the DC level of the video signal changes between the PAL and SECAM formats and the NTSC format.
There are problems with PAL and SECAM synchronization signals being corrupted and the screen being adversely affected the moment the broadcasting system is switched.

Therefore, in this circuit, the collector of the transistor 18 is connected to the system switching circuit 30 through a pseudo load resistor 31 and a diode 32 so that the pseudo load 31 is inserted in the PAL and SECAM systems, and a pseudo load resistor is also connected to the collector of the transistor 19. 33, a circuit in which a diode 34 is connected in the same manner as above is provided, and compensation is performed so that the DC level of the video signal does not change in each broadcasting system.

Effects of the Invention As described above, according to the present invention, when configuring a multi-system television receiver, PAL and SECAM
When using this method, the comb filter circuit is cut off and the video signal passes through as is, ensuring the original performance.
In the case of the NTSC system, a comb filter circuit is operated, which has the effect of improving cross color and resolution.

Furthermore, it has the effect of performing compensation so that the DC level of the video signal does not change due to switching of the comb filter circuit in each broadcasting system.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional multi-system television receiver, Fig. 2 is a circuit diagram of a comb filter circuit of a conventional television receiver that can only receive images in the NTSC system, and Fig. 3 is a circuit diagram of the present invention. 1 is a circuit diagram of a multi-system television receiver in one embodiment; FIG. 1... Delay line, 2... PAL band pass filter circuit, 3... NTSC band pass filter circuit, 4... SECAM bell filter circuit, 5...
Chroma trap circuit, 6... Video control circuit, 7
...PAL and NTSC chroma demodulation circuit, 8...
SECAM chroma demodulation circuit, 9...video amplifier circuit, 10...CRT, 11, 18, 19, 24,
25...Transistor, 12,27...Capacitor, 13...1H delay line, 14,15,
16, 17, 21, 22, 23...Resistance, 28,
29... Diode, 30... Method switching circuit, 3
1, 32... pseudo load resistance, 32, 34... diode.

Claims (1)

[Claims] 1. A differential amplifier is provided to each collector to which a video signal is applied via a resistor, and to a base to which a video signal delayed by one horizontal scanning period and whose phases differ by 180 degrees from the video signal is applied to the base. A comb-shaped filter circuit is configured at each collector output terminal to take out a video signal containing only a luminance signal component and a video signal containing only a chroma signal component, and the emitters of the differential amplifiers are connected to each other via a resistor, and this connection point is is connected to ground through a diode, and the base of the differential amplifier is operated as a differential amplifier when using the NTSC system, and the PAL
For PAL and SECAM methods, a switching circuit that acts to cut off the differential amplifier is connected, and a circuit connected as a pseudo load for PAL and SECAM methods is installed at each collector output terminal of the differential amplifier. system television receiver.