JPS6327919B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention is particularly applicable to television receivers capable of receiving multi-system color signals.
This invention relates to a detection device for automatically discriminating NTSC color signals. Conventional configurations and their problems In recent years, television receivers have become nearly 100% popular.
At the same time, video sources such as video tape recorders, video disk players, and personal computers have become more diverse, and there is a demand for multi-system television receivers capable of receiving a wide variety of broadcasts. Based on this demand, a television receiver that automatically detects input signals and switches the television receiver's system in accordance with the input signal, allowing the user of the television receiver to receive broadcasts without being aware of the type of broadcast. has been developed and is becoming popular. Multi-systems mainly include PAL and NTSC, or PAL and SECAM, or PAL/
It is NTSC/SECAM system. Conventionally, the vertical frequency of the PAL and NTSC systems is 50Hz for the PAL system and 60Hz for the NTSC system, so by detecting the vertical frequency,
NTSC was being determined. However, with the spread of video disc players, the vertical frequency has increased to 60Hz.
Now that PAL signals and NTSC signals with a vertical frequency of 50 Hz can be obtained, detection of PAL and NTSC systems must be performed using only burst signals. Figure 1 shows a block diagram of a color demodulation circuit for PAL and NTSC systems. The one-horizontal period inversion circuit 19, flip-flop 18, and line identification circuit 17 shown by broken lines in the figure are unique to the PAL system.
Not used in NTSC format. The case of the NTSC system will be explained with reference to FIG. The chroma signal that has passed through the bandpass filter enters the ACC circuit 2 and the color saturation adjustment circuit 21 from the terminal 1.
The ACC circuit 2 has the function of making the burst amplitude of its output 3 constant regardless of the magnitude of the input burst amplitude. The ACC output 3 is input to a color demodulator 4, an APC detector 11, and a killer detector 20. APC
The detector 11, voltage controlled oscillator 9, and low pass filter 10 constitute a PLL (phase locked loop), and the voltage controlled oscillator 9 generates color subcarriers 6 and 7 phase-locked to the input burst signal. The color subcarrier 6 has a phase of 90° (270°) with the NTSC burst phase being 180°, and is input to the APC detector 11. The color subcarrier 7 (7 and 8 are the same in the NTSC system) is input to the killer detector 20 with a phase of 0° (180°). The killer detector 20 synchronously detects the burst signal with a 180° phase using the color subcarrier 8 with a 0° (180°) phase, and if there is a burst signal, an output current flows from the killer detector 20 to charge the capacitor 13. The voltage at terminal 14 rises to a high level. On the other hand, when there is no burst signal, the capacitor 13 is discharged and the voltage at the terminal 14 decreases to a low level. Comparator 1
2 detects the high and low levels of the terminal 14, and if the level is low, it is regarded as a signal with no burst signal, that is, a black and white signal, and the color saturation adjustment circuit 21 removes only the chroma component to adjust the color of the black and white signal. Prevent noise generation. Figure 2 shows the relationship between the burst signal and killer detector output in the case of the NTSC system. What is shown in Figure 2A is the NTSC burst phase, which has a phase of 180°. Here, the period T indicates one horizontal period. FIG. 2B shows a color subcarrier (hereinafter abbreviated as CW) input to the killer detector 20, which may be at 0° or 180°, but for simplicity, it is assumed to be 180°. Reference numeral 11 denotes a killer detection output, which generates a signal output only in the burst signal portion, charging the killer capacitor 13 and raising it to a high level. The threshold value of the comparator 12 is set to a level slightly higher than the base level (0 level), as shown in FIG. The comparator 12 functions to determine that if the level is higher than the threshold value, it is a color broadcast, and if the level is lower than the threshold value, it is determined to be a monochrome signal. On the other hand, consider a case where a PAL burst signal is input to this NTSC system. Figure 3 shows the PAL burst phase A, killer detector CW phase Lo, and killer detection output C in that case. PAL
The burst signal is +135°, -135°, + for each horizontal period.
It changes to 135° and -135°, but killer detector 2
An output of 0 means that the output amplitude is NTSC.

[Formula] is generated, and the killer detection output becomes "High" level. That is, even if a PAL burst signal is input to the NTSC system, an output is generated even if an NTSC burst signal is input, so it is impossible to detect whether it is a PAL color signal or an NTSC color signal. Next, only the parts of the PAL color demodulation circuit that are different from the NTSC system will be explained using FIG. The difference between the PAL system and the NTSC system is that the phase of the color subcarrier (CW) 7 generated by the one-horizontal period inversion circuit 19, flip-flop 18, line identification circuit 17, and voltage controlled oscillator 19, shown by the broken line in FIG. or 270°. Color subcarrier 7 generated by voltage controlled oscillator 9
is inverted by the 1-horizontal-period inversion circuit 19 by the output of the horizontal pulse given for each horizontal period, which is divided by 1/2 by the flip-flop 18, and
The signal 8 has an alternating phase of 90° (270°) - 270° (90°) - 90° (270°). The line identification circuit 17 is +135°, -
The polarity of the PAL burst signal transmitted alternately at 135° and the color subcarrier 8 input to the killer detector 20
This is to match the polarity of the That is, +
This is to synchronize so that when a 135° burst signal is input, the phase of color subcarrier 8 is 90°, and when a -135° PAL burst signal is input, the phase of color subcarrier 8 is 270°. , if the polarity is reversed, it resets the flip-flop 18 to ensure the correct polarity. Figure 4 shows the PAL burst signal and killer detector 2.
Shows the output interval of 0. A is a PAL burst signal with a phase of +135° and -135° for each horizontal period.
B is the color subcarrier (CW) to the killer detector 20
The phase is adjusted to the correct polarity by the line identification circuit 17. C is the killer detector output. Killer detector output is killer capacitor 13
However, since it is at a higher level than the killer threshold, it is considered a color signal. During black and white, the voltage of the killer capacitor 13 becomes 0, which is lower than the killer threshold and is considered to be a low level. Consider the case where an NTSC signal is input to this PAL system. Figure 5 shows the NTSC burst signal and
Indicates the color subcarrier phase of PAL killer detection. In Figure 5, A is NTSC burst phase, B is PAL
The killer detection color subcarrier input phase in the system, C is the killer detector output. In this case, the burst phase is 180° and the killer detection color subcarrier phase is 90° or 270°, so the output is E=I _B・I _CW cos(180°−90°)=0 or E= I _B · I _CW cos (180° - 270°) = 0 I _B : Burst amplitude I _CW : CW amplitude, and since no output is generated, its smoothed voltage becomes 0 and is lower than the killer threshold. Therefore, the output of comparator 12 is at a low level and is regarded as a black and white signal. That is, even if an NTSC color signal or a black-and-white signal is input to the PAL system, the killer detection output will be 0, and it will not be possible to determine whether the NTSC color signal is a black-and-white signal. As mentioned above, the current PAL color demodulation system or NTSC color demodulation system has the disadvantage that it is not possible to determine whether an input signal burst is a PAL color signal, an NTSC color signal, or a monochrome signal. It was hot. OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks and to provide a detection circuit that can automatically discriminate between PAL color broadcasting, NTSC color broadcasting, and black and white signals. Structure of the Invention The present invention distinguishes PAL and NTSC systems not by vertical frequency or color subcarrier frequency, but by the essential difference between PAL and NTSC systems, that is, the PAL signal (burst signal) has a period of one horizontal period. By focusing on the property that the signals are sent alternately at +135° and -135°, PAL/NTSC format can be detected and discriminated. For this purpose, PAL method or
0° or 180° (hereinafter referred to as 0° (180°)) and 90° or
a color subcarrier generation circuit that generates a color subcarrier with a phase of 270° (hereinafter referred to as 90° (270°)); and a first color subcarrier generating circuit that synchronously detects the burst signal with the color subcarrier of 0° (180°). detector and the above burst signal, the above 90° (270°) color subcarrier is 90° (270°) every horizontal period.
,
a second detector that performs synchronous detection while switching between 270° (90°), a first detector that determines the presence or absence of a signal output of the first detector, and a signal output of the second detector. It is equipped with a second detector that detects the presence or absence, and when both the first and second detectors detect the presence of a signal, it is regarded as a PAL color signal, and the first detector detects that the signal is present. Detect the second
When the detector detects that there is no signal,
It is assumed that the signal is an NTSC color signal, and when both the first and second detectors detect that there is no signal, it is detected as a black and white signal. DESCRIPTION OF THE EMBODIMENTS FIG. 6 shows a block diagram of an embodiment of the present invention. In the figure, the same parts as in FIG. 1 are given the same numbers. In Figure 6, the chroma signal applied to terminal 1 is
Passes through the ACC circuit 2 and color saturation adjustment circuit 21,
A chroma signal having a constant amplitude burst signal is output from the output terminal 3. Output signal 3 is the first
The signal is input to the killer detector 47, the second killer detector 48, and the color subcarrier generation circuit 56, respectively. The color subcarrier generation circuit 56 is the APC detector 1 shown in FIG.
1. Voltage controlled oscillator 9, low pass filter 10
PLL (phase locked loop) consisting of
This circuit generates a color subcarrier with the same phase as the input burst signal, and also generates a color subcarrier with a phase of 0° (180°) and
Generates color subcarriers with a phase of 90° (270°). The color subcarrier 51 with a phase of 0° is input to the first killer detector 47 . Similarly, the color subcarrier 55 with a phase of 90°
is input to the second killer detector 48 via the inverting circuit 53. The first killer detector 47 was explained in FIG.
This is the killer detector 20 in the NTSC system, and the second killer detector 48, line identification circuit 49, flip-flop 54, and inverting circuit 53 are the killer detector 20 in the PAL system shown in FIG.
Line identification circuit 17, flip-flop 18, 1
This is the same as the horizontal period inversion circuit 19. 1st
The killer detector 47 is the “first detector” in the claims.
The second killer detector 48 is the "second detector". Explanatory diagrams of the operations of the first killer detector 47 and the second killer detector 48 are shown in FIGS. 7 and 8. FIG. 7 is for explaining the operation when receiving a PAL color signal, and FIG. 8 is for explaining the operation when receiving an NTSC color signal. FIG. 7A shows a PAL burst signal having phases of +135° and -135° for each horizontal period. T represents the horizontal period. The phase of the color subcarrier input 51 of the first killer detector 47 is shown in FIG. The synchronous detection output of the signals A and B, which have a phase of 180°, is shown in C. The output of the first killer detector 47 is smoothed by a capacitor 44. The first detector 41 is a comparator, and the first
The smoothed output of the killer detector 47 is compared with the threshold value of the first detector 41 shown in FIG. 7C, and if (voltage of the capacitor 44>threshold voltage of the first detector), a high level is output. In this case, the output 39 of the first detector 41 is at a high level. On the other hand, the color subcarrier input 50 of the second killer detector 48 is shown in D. Each horizontal period has a phase of 90° and 270°. In this case, the line identification circuit 49 is operating, so for the +135° PAL burst signal, the color subcarrier is at 90° phase, and the PAL signal is at -135° phase.
For burst signals, this is a 270° color subcarrier. The output of the second killer detector 48 is smoothed by a capacitor 46, as shown in FIG. 7E. The second detector 42 also constitutes a comparator, and as shown in E, (voltage of capacitor 46 > threshold voltage of second detector 42), the second detector 42 constituted by a comparator output will be at a high level. FIG. 8 shows the functions of the first killer detector 47 and the second killer detector 48 when receiving an NTSC burst signal. As in FIG. 7, the output of the first killer detector 47 is (voltage of the capacitor 44>threshold voltage of the first detector 41), so the output 39 of the first detector 41 is at the "HIGH" level. . However, the color subcarrier 50 input to the second killer detector 48
is 90° or 270°, and the NTSC burst signal has a phase of 180°, so the phase difference is ±90°, and the second
There is no output from the killer detector 48. Therefore, the voltage of the capacitor 46<the threshold voltage of the second detector 42, and the output 40 of the second detector 42 is at a low level. Also, when receiving a black and white signal, the first killer detector 4
7. Since there is no output from the second killer detector 48, both the output 39 of the first detector 41 and the output 40 of the second detector 42 are at the "LOW" level. 31,3
2 and 33 are AND circuits, and 37 and 38 are NOT circuits. The outputs of the first and second detectors 41 and 42 are applied as they are to the input of the AND circuit 31, the output of the first detector 41 is applied as is to the input of the AND circuit 32, and the output of the second detector 42 is applied to the NOT circuit. 38, and the AND circuit 33 receives the outputs of the first and second detectors 41, 42 through NOT circuits 37, 38.
Added via. Therefore, AND circuit 31
The outputs 34, 35, and 36 of 33 are as shown in the following table.

[Table] When the detection output 34 is at a high level, the input signal of the television receiver is a PAL color signal, when the detection output 35 is at a high level, the input signal is an NTSC color signal, and when the detection output 36 is at a high level. It is a black and white signal. As described above, according to this configuration, a PAL color signal, an NTSC color signal, and a monochrome signal can be detected just by monitoring the burst signal. Effects of the Invention As explained above, according to the present invention, it is possible to detect PAL color signals, NTSC color signals, and monochrome signals only by inputting burst signals, and to switch between PAL and NTSC systems in a multi-system television receiver. can be done automatically.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional color demodulation circuit, Figures 2 and 3 are vector/waveform diagrams for explaining the relationship between the input burst phase and detection output of a killer detector in an NTSC system, and Figure 4. , Figure 5 is
A vector/waveform diagram for explaining the relationship between the input burst phase and the detection output of the killer detector in a PAL system. FIG. 6 is a block diagram of a color demodulation circuit including a detection device in an embodiment of the present invention.
The figure is a vector/waveform diagram showing the relationship between the burst phase and the first and second killer detection outputs in the PAL system. Figure 8 is the vector/waveform diagram showing the relationship between the burst phase and the first and second killer detection outputs in the NTSC system. It is a diagram. 31, 32, 33...AND circuit, 37, 38
...NOT circuit, 41...First detector, 42...
Second detector, 44, 46... Capacitor, 47
...First killer detector, 48...Second killer detector, 49...Line identification circuit, 54...Flip-flop, 53...Inverting circuit, 56...Color subcarrier generation circuit.

Claims (1)

[Claims] 1 A color subcarrier generation circuit that generates a color subcarrier with a phase of 0° or 180° and a phase of 90° or 270° that is phase-synchronized with a PAL or NTSC burst signal; A first detector performs synchronous detection with a color subcarrier of , and detects the burst signal with a color width carrier of 90° or 270° every horizontal period at 90° (270°), 270° (90°)... a second detector that performs synchronous detection while switching between the first and second detectors; a first detector that determines the presence or absence of a signal output from the first detector; the first and second detectors;
When both detectors detect that there is a signal, it is a PAL color signal, and when the first detector detects that there is a signal and the second detector detects that there is no signal, it is a PAL color signal. , an NTSC color signal, and when both the first and second detectors detect the absence of a signal, the detection device detects a monochrome signal.