JPS6019389A - Signal converting circuit - Google Patents

Abstract

PURPOSE:To display an excellent black-and-white picture without color noise by constituting the circuit that the color killer of a television receiver receiving an SECAM signal is operated when a PAL signal is used as a black-and-white signal in a television signal converting circuit from the PAL system to the SECAM system. CONSTITUTION:A PAL signal detecting circuit 6 detects a color burst by synchronis detection at the color burst inserting period through a low pass filter while utilizing an output signal amplitude of the filter. When the PAL signal has a chrominance signal, an output signal is given from a chrominance signal detecting circuit and a cut-off circuit 7 is in the state passing the color modulated signal being an output of an SECAM modulating circuit 3. On the other hand, when no chrominance signal is included in the PAL signal, i.e., a black- and-white signal, no output signal exists in the chrominance signal detecting circuit 6, the cut-off circuit 7 cuts off the output of the color modulating circuit 3 thereby inhibiting the signal from being given to an adder 5. As a result, since no modulated chrominance signal exists in the SECAM signal and no non-modulation carrier signal exist, the color killer circuit of the television receiver is activated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a conversion circuit for converting television signals from PAL system to 5ECAAf system.

[Background of the invention]

The signal conversion circuit from the conventional pAL system to the SECAM system is as shown in Figure 1, and converts a luminance signal (hereinafter abbreviated as 'f'Y signal) and a modulated color signal (hereinafter abbreviated as C signal).
+', P, AL color demodulation circuit 2, SE
CAM color modulation circuit5. Y signal delay circuit 4. It is composed of an adder circuit 5.

The pAL signal input to the Y-C separation circuit 1 is as follows.

Y and CK are separated, and the C signal enters the PAL color demodulation circuit 2. After encircling, the signals become (R-Y) and (B-Y) color difference signals, which are input to the SECAM color change circuit B, and the FM-modulated SECAM color signal C is sent. One side separated Y
The signal passes through a Y signal delay circuit 4 that compensates for the delay caused by one telegraph signal passing through a demodulation circuit 2 and a modulation circuit 3, and is added to the modulated SECAM color signal in an adder 5 to produce a SECAM signal. He lives a long life.

In this configuration, if the pAL signal is a monochrome signal having no color information, the color difference signals (R-Y) and (B-)') output from the PAL color demodulation circuit 2 will have no signal. Then, only the unmodulated color carrier wave signal is outputted to the SECAM color modulation circuit, and is added to the Y signal to form the SECAM signal. As a result, the television receiver receives the SECAM signal.

The same operation as when detecting an unmodulated color carrier signal and receiving five color information is performed. In general, the display screen fS! The normal operation is black and white with no color. 1. If the color signal contains the same frequency component as the modulated color signal, or if noise is mixed into the input of the one-color modulation circuit 60 and a color modulation output is generated due to noise, color noise may appear in the monochrome display image. appears, resulting in an unsightly image.

As described above, the conventional configuration has the disadvantage that color noise occurs when a monochrome signal is used, resulting in an unsightly image.

[Purpose of the invention]

The object of the present invention is to provide a PA that eliminates the drawbacks of the prior art described above.
An object of the present invention is to provide a television signal conversion circuit from the L system to the SECAM system.

[Summary of the invention]

The present invention focuses on the fact that the SECAM television receiver performs a color killer operation, detects whether there is one electrical signal in the pAL signal, and if possible, cuts off the color carrier wave of the SECAM signal to make the television receiver color Characterized by operating a killer.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. Second
In the figure, 6 is a PAL color signal detection circuit, and 7 is a SECAM
1 shows a modulated color signal cutoff circuit, in which the same components as in FIG. 1 are given the same reference numerals.

The pAL color signal detection circuit 6 detects whether or not there is a color burst in the PAL signal. Color burst detection is performed by performing synchronous detection during the color burst insertion period, passing the signal through a low-pass filter, and using the output signal amplitude of the filter. Now, if the PAL signal contains a color signal, the color signal detection circuit 6 has an output signal,
The output signal causes the cutoff circuit 7 to pass the modulated color signal output from the 5ECAN color modulation circuit 6. On the other hand, if the PALK color signal is not included, that is, if it is a monochrome signal, there is no output signal to the color signal detection circuit 6, and the cutoff circuit 7 cuts off the output of the color modulation circuit 5, so that it does not pass through to the adder 5. As a result, according to this embodiment, SEC
Since the AM signal does not have a modulated color signal or even an unmodulated carrier wave signal, a color killer circuit operates in the TV receiver and it is possible to display a black and white image with one color and no sound for 1 second. .

In another embodiment, instead of the cutoff circuit 70, the modulation function of the color modulation circuit 5 is stopped in the case of a monochrome signal, thereby blocking the SECAM-modulated color signal and color carrier wave.

A specific example thereof is shown in FIG. In FIG. 6, an emitter-coupled multivibrator frequency modulation circuit is shown as the SECAM color modulation circuit 8 having a modulation stop function, and 61 is a current source transistor for frequency control;
Reference numeral 52 denotes a switch transistor which turns off VCm when a black and white signal is applied and stops the modulation function. Also, the same elements as in FIG. 2 are given the same reference numerals. In the configuration shown in Figure 3,
In the case of a black and white signal, the switch transistor 52 is turned off by the output of the color signal detection circuit 6, and the current source transistor 51 is also turned off.

This stops the modulation function. The configuration of this embodiment also has the advantage that the output of the modulation circuit 6 can be input directly to the addition circuit 5 without using the cutoff circuit 7 to cut it off.

FIG. 4 shows still another embodiment of the signal conversion circuit according to the present invention. The same components as in FIG. 2 are given the same reference numerals. In the configuration shown in FIG. 4, a transistor switch is used as the cutoff circuit 7 for the 2181st SECAM-modulated color signal. Reference numeral 61 denotes an inverter for differentially operating the transistors 701 and 702 using the output signal of the color signal detection circuit 6. The operation of the embodiment shown in FIG. 4 will be explained. Color change? ,
The collector currents of the differential pair transistors 710 and 711 whose bases are connected to the output of the Q circuit 5 and the collector currents of the differential pair transistors 708 and 709 through which direct current flows are connected to the differential pair transistors 706 and 707. By switching, the pressure drop of the resistors 712 and 7130 is changed. That is, when the current of the transistor 705 operating at a constant current flows through the transistor 707, the differential pair transistors 710 and 7N operate, and a signal similar to the output signal of the color modulation circuit 3 appears at the resistor 715. On the other hand, when current flows through transistor 705 (transistor OFF 061), a DC voltage appears across resistor 713, and the modulated color signal and color carrier wave are cut off. Switching of the current of transistor 705 to transistors 706 and 707 is performed by differentially bringing transistors 701 and 702 into conduction and connection states. The transistors 701 and 702 are controlled using the output signal of the PAL color signal detection circuit 6. In other words, if the PAL signal is a black and white signal, the detection circuit 6
By the output of .

Transistor 701 is cut off, transistor 702 is turned on, and the emitter potential of transistor 705 is set to transistor 7.
It becomes higher than the emitter potential of 04. Note that transistor 7
05 and 704 are operating as emitter lowers. Therefore, in the differential pair of transistors 706' and 707, transistor 707 becomes conductive.

Therefore, as described above, since only direct current appears in the resistor 715, the signal from the one-color modulation circuit 3 can be blocked. Also in this configuration.

No matter which transistor 706 or 707 is conductive, the DC current (average current) flowing through the resistors 715 and 712 is constant, and the DC voltage across the resistor 715 is also advantageously constant. Therefore, it is easy to connect to the next stage (for example, an add-on circuit), which has the advantage of being suitable for IC implementation.

〔Effect of the invention〕

According to the present invention, as described above, when the pAL signal is a black and white signal, the SECAM-modulated color signal and the color carrier are cut off and only the Y signal is made into a 5ECAM signal, so that the SECAM signal is received. The TV has the effect of being able to display good black and white images with a lot of color when the color killer works.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional signal conversion circuit from PAL system to SECAM system, Fig. 2 is a circuit diagram showing one embodiment of a signal conversion circuit according to the present invention, and Fig. 5 is a circuit diagram showing another embodiment of the present invention. FIG. 4 is a circuit diagram showing still another embodiment of the present invention. 2...pAL color demodulation circuit, 5...5ECAAf color change circuit, 6...PAL color signal detection circuit, 7...S/
! 'c', -tM modulated color signal cutoff circuit, 8.
...SECAM color modulation circuit with modulation stop 1'ζ capability. Figure 2 Cause Figure 3

Claims (1)

[Claims] t A signal conversion circuit from a PAL system to a SECAM system, comprising a PAL color signal detection circuit and means for controlling and blocking a color signal or a color carrier signal modulated in the 5ECAAf system using an output signal of the color signal detection circuit. A signal conversion circuit comprising: