JPS62221291A - Deciding circuit - Google Patents

Abstract

PURPOSE:To surely decide both broadcasting systems with a simple constitution by detecting the level of a burst signal available at the output of a comb-line filter and discriminating a broadcasting signal made by a PAL-M system from a one made by an NTSC system. CONSTITUTION:A subtractor circuit 6 subtracts a video signal supplied to a terminal 1 and a video signal before 2H that is supplied through delay circuits 2 and 4, thereby obtaining a chroma signal included in the broadcasting signal made by the PAL-M system. After a burst flag circuit 8 removes only burst signals appearing at every H from the signal, a detector 11 detects a signal obtained in such a way that a ceramic filter 9 extracts a signal close to the frequency of a subcarrier. If the extracted signal is a one made by the PAL-M system, a signal with the prescribed amplitude appears at every H. Whereas it is a one made by the NTSC system, a signal with a slight amplitude can be obtained. Accordingly the signal is level-detected by a level detector 16 through a resonance circuit and a DC modulation circuit 15, whereby both systems can be discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discrimination circuit that discriminates between a PAL-M color television broadcast signal and an NTSC color television broadcast signal.

[Summary of the invention]

The present invention detects the level of the burst signal of both broadcast signals obtained at the output of a comb filter in a discrimination circuit that discriminates between a PAL-M color television broadcast signal and an NTSC color television broadcast signal. By making the distinction between the two broadcasting systems, it is possible to reliably distinguish between the two broadcasting systems with a simple configuration.

[Conventional technology]

There are various types of color television broadcast signal systems, and conventional color television receivers and video TESO recorders require dedicated devices for each broadcast signal system. For this reason, for example, color television receivers have been made compatible with the broadcasting system of the country in which the receiver is used, thereby making it possible to view color television broadcasts. However, with the spread of video tape recorders in recent years,
Video tapes with broadcasting systems different from those of the country are now readily available, and there is a need to be able to receive the video tapes on the same receiver.

Broadcasting systems that require the same receiver to receive images include, for example, the NTSC system and the PAL-M system.

[Problem that the invention seeks to solve]

By the way, when considering a television receiver capable of receiving images using a plurality of broadcasting systems as described above, it is necessary to distinguish between each broadcasting system. However, for example, the above-mentioned NTS
Since the C system signal and the PAL and -M system signals are very similar signals, it has been difficult to distinguish between the systems.

That is, according to the standard, the luminance signal is the same for the fi NTSC system and the PAL-M system, and the subcarrier frequency of the chroma signal is slightly 3.579545 MHz.
and 3.575611 MHz, which is only about 4 kHz different. For this reason, it has been impossible to use a general discrimination circuit that discriminates based on differences in frequency.

In view of these points, the present invention reliably supports NTSC with a simple configuration.
It is an object of the present invention to provide a discrimination circuit that can discriminate between the PAL-M method and the PAL-M method.

[Problems and means for solving them] The discriminating circuit of the present invention, for example, as shown in FIG.
Comb filters (2) and (3) are used in a discrimination circuit that discriminates between an M system color television broadcast signal and an NTSC system color television broadcast signal.

(6) The determination is made by detecting the levels of the burst signals of both broadcast signals obtained at the output.

[Effect]

According to the discrimination circuit of the present invention, the burst signal of the PAL-M system is offset by 7 fH (fH is one horizontal scanning frequency) from the fundamental frequency, and the burst signal of the NTSC system is offset by Σ from the fundamental frequency. Comb filter (2) l (3), (6) By sorting out this difference in offset frequency, we can create a comb filter (2).
), (3), and (6), the levels of the burst signals obtained in the outputs of the PAL-M system and the NTSC system are significantly different, and both systems can be easily distinguished.

〔Example〕

Hereinafter, one embodiment of the discrimination circuit of the present invention will be described with reference to the accompanying drawings.

Figure 1 is a diagram showing the configuration of one example discriminator circuit.
) indicates a video signal input terminal. This video signal input terminal (
The video signal obtained in step 1) is supplied to a first delay circuit (2), a first subtraction circuit (3), and a second subtraction circuit (6). The output signal of this wcl delay circuit (2) is supplied to a second delay circuit (4) and a second subtraction circuit (6).

Then, the output signal of the first subtraction circuit (3) is sent to the output terminal (
5), the output signal of the second subtraction circuit (6) is connected to the output terminal (
7) respectively. Note that the first and second delay circuits (
2) and (4) are circuits that respectively delay the video signal by IH (t is one horizontal scanning period).

With this configuration, a comb filter is configured that separates the chroma signal from the composite video signal. That is,
The first subtraction circuit (3) subtracts the video signal supplied to the terminal (1) and the video signal before IH, so that a good ROMA signal of the NTSC broadcasting signal is obtained at the output terminal (5). , the second subtraction circuit (6) subtracts the video signal supplied to the terminal (1) and the video signal 2H before, thereby producing PAL,
- If the M system broadcast signal is good or the Roma signal is output from the output terminal (7
) can be obtained.

Here, the discrimination circuit of this example supplies the output signal of the second subtraction circuit (6) to the burst flag circuit (8).

The burst flag circuit (8) extracts the burst signal from the supplied signal and supplies the extracted burst signal to the ceramic filter (9). This ceramic filter (9) is a pandonosas filter that passes signals around 3-58 Ml (z), and supplies the output signal of this ceramic filter (9) to the detector α power via the amplifier α. This detector αυ is a circuit that performs envelope detection of the input signal, and the detected output signal of this detector aυ is N
It is supplied to the pace of the PN type transistor 0a. Also,
The emitter of this transistor α2 is grounded through the capacitor (to) and inductance α4, and this transistor (6), capacitor 0, and inductance α are connected to 1
fH1, or approximately 15.75 kHz, constitutes a resonant circuit. Then, the collector of the transistor (6) is connected to the DC conversion circuit (B), and the output signal of the detector H is supplied to the DC conversion circuit (G) via this resonance circuit.

Then, the output signal of this DC conversion circuit αQ is supplied to a level detector αQ, and the level of the supplied signal is detected. Then, a determination signal indicating whether the level is above a certain level is supplied to the output terminal αη.

Next, the discrimination operation by the discrimination circuit of this example will be explained below.

First, when a video signal is supplied to the video signal input terminal (1), the output signal characteristic of the second subtraction circuit (6) is a comb shape in which the signal attenuates every Σ8, as shown by waveform C in Figure 2. This is a signal characteristic unique to the filter. Here, when the video signal obtained at the input terminal (1) is a PAL-M broadcast signal, the chroma of this video signal is placed at a position offset by 7 fH from the fundamental frequency, as shown by P in Fig. 2, for example. A burst signal of the signal appears.Also, the input terminal (1)
When the video signal obtained is an NTSC broadcast signal, a burst signal of the chroma signal of the video signal appears, for example, at the second position W (shifted by 19 from the PAL-M system).

However, due to the output signal characteristics of the second subtraction circuit (6) as described above, what is actually obtained as the output signal of this subtraction circuit (6) is only a burst signal of the PAL-M chroma signal, and the NTSC Almost no burst signal of the chroma signal can be obtained using this method. This means that the subcarrier frequency of the chroma signal of both methods is 3.575611 MJ (z
(PAL-M method) and 3.5795454 MHz (
NTSC system), there is a difference of approximately 3.934 kHz,
This difference of about 3.934 kHz is a frequency corresponding to a difference in shift of approximately LfH, and is because it is the peak and valley of the output waveform C of the comb filter.

Therefore, after extracting only the burst signal generated every filH by the burst flag circuit (8) from the output signal of the second subtraction circuit (6), the frequency signal near the subcarrier frequency of this chroma signal is filtered through the ceramic filter. The signal extracted in step (9) is subjected to envelope detection by the detector 0p, resulting in a signal as shown in FIG. That is, P.A.
In the case of the LM system, a signal with a predetermined amplitude appears every 1 as shown in Figure 3A, but in the case of the NTSC system, a signal with a small amplitude appears every 1 as shown in Figure 3B. , or only a signal with no amplitude at all. Then, the detected signal of the detector α power is resonated for each 1) I in a resonant circuit consisting of a transistor αa, a capacitor (6), and an inductance α, and the resonant signal is converted into a DC current by a DC converting circuit (6). After that, the level is detected by a level detector αQ. This level detector 0→ is, for example, a PA
The intermediate value between the LM system resonance signal and the NTSC system resonance signal is set as a reference point, and a determination signal indicating whether the input signal is above or below this reference point is output to the output terminal αη. By obtaining the discrimination signal in this way, it is possible to know that the signal obtained at the input terminal (1) is a PAL-M broadcasting signal when the discrimination signal indicating that the reference point is above the reference point is output. When the determination signal indicating that the reference point is also below the reference point is output, it can be seen that the signal obtained at the input terminal (1) is an NTSC broadcasting signal.

According to the discrimination circuit of this example, by detecting the output signal of the comb filter that separates the chroma signal from the composite video signal, it is possible to reliably distinguish between the PAL-M system and the NT system with a simple configuration.
Can distinguish SC broadcast signals.

Therefore, by incorporating this discrimination circuit into a television receiver that can receive both PAL-M broadcast signals and NTSC broadcast signals, the broadcast system can be automatically switched based on the discrimination signal. becomes possible. Also,
Similarly, by incorporating this discrimination circuit into a video tape recorder capable of recording broadcast signals of both types, it becomes possible to automatically switch the recording system based on the discrimination signal.

Note that the present invention is not limited to the above-described embodiments, and it goes without saying that various other configurations can be made without departing from the gist of the present invention.

〔Effect of the invention〕

According to the discrimination circuit of the present invention, a comb filter (2).

(3) # By detecting the level of the burst signal obtained from the output of (6) and distinguishing between PAL-M and NTSC broadcasting signals, it is possible to reliably use both broadcasting systems with a simple configuration. There is a discernible benefit.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the discrimination circuit of the present invention, and FIG.
The figure and FIG. 3 are diagrams for explaining the example in FIG. 1. (2) is the first delay circuit, (4) is the 8g2 delay circuit,
(6) is a second subtraction circuit.

Claims (1)

[Claims] PAL-M color television broadcast signal and NT
1. A discrimination circuit for discriminating between an SC color television broadcast signal and an SC color television broadcast signal, the discrimination circuit being characterized in that the discrimination is made by detecting the level of a burst signal of both of the broadcast signals obtained at the output of a comb filter.