JPS6246392Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal processing circuit in a multi-system color television receiver capable of receiving at least both PAL and NTSC color television broadcasts.

Currently, color television broadcasting in Japan is carried out using the NTSC system, but with this NTSC system, hue shifts tend to occur due to the effects of phase distortion in the transmission path, so in order to prevent this hue shift, PAL
A method has been developed. In this PAL method, the phase of one subcarrier for color signal transmission is +90% for each scan.
According to this, due to the above-mentioned inversion, the hue error due to the influence of the differential phase of the transmission system is reversed for each scanning line, and the two scanning lines are The lines will cancel each other out.

As mentioned above, the PAL system is an improvement over the NTSC system, and therefore the circuit configuration on the receiver side is also different.For example, in the PAL system, in addition to the NTSC system, there are also ) delay circuit etc. is required, so
In order to realize a color television receiver that supports both PAL and NTSC systems, a circuit that is compatible with both systems is required, and it is also necessary to ensure that there is no difference in hue, etc. no matter which system broadcasts are received. There is.

For this reason, conventionally, as shown in Figure 1,
PAL on the output side of PAL/NTSC common chromaticity signal circuit A
NTSC correction circuit B and NTSC correction circuit C were connected separately, and one of the outputs of both correction circuits B and C was selected by system switch circuit D and added to color difference demodulation circuit E. .

However, this conventional circuit requires correction circuits B and C for each method, which is disadvantageous in terms of cost.

The present invention was developed in consideration of this point, and its purpose is to provide a hue correction circuit within the PAL/NTSC common chromaticity signal circuit, and to switch this circuit using a diode switch circuit when selecting PAL or NTSC. Therefore, it is an object of the present invention to provide a color signal processing circuit that solves the above-mentioned problems.

The present invention will be explained below with reference to examples. Second
The figure shows an embodiment of some circuits in one common color signal processing circuit, in which a transistor 1 constitutes a color signal amplification circuit for amplifying a color signal applied to an input terminal 2, and its emitter The output signal appearing on the side passes through a diode 3 and a coupling capacitor 4, or a resistor 5, a diode 6, and the capacitor 4 that constitute a color signal level (saturation) correction circuit, and is applied to the midpoint of the coil 7. Also, the output signal appearing on the collector side is applied to a 1H delay line 10 via a coupling capacitor 8 and a diode 9. Further, on the base side, a capacitor 11, a diode 12, and a switch 13 forming a hue (color signal phase) correction circuit are arranged.
It is designed to be connected to ground through. Diodes 3, 6, 9, and 12 are connected to switching DC voltages of +12V, +24V, etc. through current-limiting resistors 14 to 17, which have relatively large values that do not affect the color signal. There is. These diodes 3, 6, 9, 12 and resistor 14~
17 constitutes a diode switch circuit.
A parallel circuit consisting of a capacitor 19, a resistor 20 and a coil 21 is used for matching, a series circuit consisting of a capacitor 22 and a variable resistor 23 is used for negative feedback, and capacitors 24 and 25 are used for an RY demodulation circuit 26, B
28 is a matrix for coupling to the -Y demodulation circuit 27;

Next, the operation will be explained. When switch 13 is switched to the side shown by the solid line, it is for PAL system selection;
When switched to the side shown by the broken line, it is for selecting the NTSC system. First, switch to the side shown by the solid line.
When inputting a PAL color signal, diodes 6 and 9 conduct, and diodes 3 and 1
2 is blocked. Therefore, in this case, the signal extracted from the emitter of the color signal amplified by the transistor 1 is applied to the coil 7 via the resistor 5, diode 6 and capacitor 4, and the color signal is amplified by the resistor 5. Level is attenuated. Further, the signal obtained at the collector of the transistor 1 is input to a 1H delay line 10 via a capacitor 8 and a diode 9, where it is delayed by 1H and output to the coil 7 side. Coil 7 part is PAL
It constitutes a matrix circuit, and on the side, the signal that has passed through the capacitor 4 and the 1H delay line 10
The 1H-delayed signal outputted from The signal that has passed and the signal delayed by 1H are vector-added, and a color signal with a constant phase is sent to the capacitor 25.
The signal is input to the BY demodulation circuit 27 via the . At this time R
-Y demodulation circuit 26 has a subcarrier added every 1H.
Since the subcarrier is added directly to the B-Y demodulation circuit 27, the R-Y demodulation output from the R-Y demodulation circuit 26 is Above B-Y
A BY demodulation output is obtained from the demodulation circuit 27.

Next, when switch 13 is switched to the side shown by the broken line and an NTSC color signal is input, diodes 6 and 9 are cut off and diodes 3 and 12 are conductive. Therefore, in this case, the signal extracted from the emitter of the color signal amplified by transistor 1 is applied to the midpoint of coil 7 via diode 3 and capacitor 4. That is, unlike the case of PAL selection, the level is not attenuated by the resistor 5. Also, transistor 1
On the base side, a capacitor 11 is connected to ground via a diode 12 and a switch 13, so that hue correction is performed. Furthermore, since the diode 9 is cut off, the 1H delay line 10 is removed from the color signal circuit. Therefore, in this case, the color signal applied to the midpoint of the coil 7 via the capacitor 4 is applied to the coil 7.
The signal is shunted at and input to the RY demodulation circuit 26 and the BY demodulation circuit 27. At this time, the PAL switch remains switched to one side and functions as a +90 degree (or -90 degree) phase shift circuit, so that the subcarrier has a 90 degree phase difference between the R-Y demodulator circuit 2 and
6 and the BY demodulation circuit 27.

As explained above, the diode switch circuit corrects the level difference and phase difference (hue difference) of color signals that occur when the PAL system is selected and when the NTSC system is selected.

Therefore, the color signal circuit according to the present invention is characterized in that the hue correction circuit can be realized extremely simply and at low cost.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional color signal circuit, Figure 2 is a block diagram of a conventional color signal circuit.
The figure is a circuit diagram of a color signal circuit according to an embodiment of the present invention.

Claims (1)

[Claims for Utility Model Registration] (1) One color signal processing circuit enables NTSC and
In a multi-system color television receiver that has a function of selectively processing color signals of the PAL system and has a hue correction circuit connected to the chromaticity signal path, there is a connection between the chromaticity signal path in the hue correction circuit and ground. A hue correction circuit and a diode are connected in series, the voltage applied to the diode is controlled to be positive or negative depending on the method of the received signal, and the hue correction circuit is connected to ground by cutting off conduction of the diode,
Or a color signal processing circuit characterized by floating from ground. (2) The color signal processing circuit according to claim 1, wherein the hue correction circuit comprises a capacitor.