JPH0160988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal processing circuit used when color broadcasts of different systems are received by one color television receiver.

Conventionally, when receiving both the NTSC system (color broadcasting system in Japan, the United States, etc.) and the PAL system (color broadcasting system in Britain, West Germany, etc.) with a single color television receiver (hereinafter referred to as CTV), Video intermediate frequency, audio, video, and deflection signal processing can share the same circuit by switching constants, but color signal processing requires dedicated ICs for each, and cannot be shared. Therefore, the color signal processing section uses the NTSC method,
In addition to dedicated ICs for each PAL system, switching circuits and clamp circuits for both were required, making it quite large-scale.

FIG. 1 is a block diagram showing a conventional color signal processing circuit. In the figure, 1 is a color signal input terminal;
2 is an NTSC color signal processing circuit, 3 is a PAL color signal processing circuit, 4 is a control circuit consisting of an NTSC/PAL switching circuit, a color control circuit, a DC reproduction circuit, etc., and 5 is a color signal output terminal. be.

Next, the operation of the color signal processing circuit having the above configuration will be explained.

First, when an NTSC color signal is input to color signal input terminal 1, this NTSC color signal is
The signal is input to an NTSC color signal processing circuit 2 and a PAL color signal processing circuit 3. Here, PAL
Since the color signal of the NTSC system is input to the signal processing circuit 3 of the NTSC system, a killer circuit (not shown) (a circuit that turns off the output of the color signal processing circuit) is operated, so that no output signal appears. On the other hand, since the NTSC color signal processing circuit 2 receives the NTSC color signal, it operates normally, and after being demodulated, the control circuit 4
Color control, direct current reproduction, color signal output terminal 5
The demodulated output is output from. It should be noted that when a PAL color signal is input to the color signal input terminal 1, the PAL signal processing circuit 3 operates normally and a killer circuit (not shown) on the NTST side operates, contrary to the above description. Therefore, the demodulated output of PAL is output.

However, in conventional color signal processing circuits, a dedicated
In addition to requiring two IC-based color signal processing circuits, this method also required many additional circuits such as a switching circuit, a color control circuit, and a DC regeneration circuit, making it uneconomical.

Therefore, the object of the present invention is to provide a color signal processing circuit that can process both NTSC and PAL color signals with a small number of switching circuits, and that can have a configuration suitable for IC implementation with fewer external components. It is something to do.

In order to achieve such an object, the present invention converts an input reference subcarrier into a first reference subcarrier and a second reference subcarrier with a phase difference of approximately 90° using a first phase shifter and a second phase shifter. The first reference subcarrier is input to an automatic phase control detector, the second reference subcarrier is input to a killer detector, and the first reference subcarrier and second reference subcarrier are divided at an arbitrary ratio. After combining, the third and fourth phase shifters separate the third reference subcarrier and the fourth reference subcarrier with a phase difference of about 90°, and only in PAL, the third reference subcarrier is separated into one horizontal subcarrier. It is designed to be inverted every time it is scanned, and will be explained in detail below using an example.

FIG. 2 is a block diagram showing an embodiment of the color signal processing circuit according to the present invention. In the same figure, 6
7 is an input terminal into which the reference subcarrier is input, and 7 is a resistor 7, whose detailed circuit is shown in FIG. 3a.
For example, the detailed circuit of the first phase shifter 8 with a phase lag composed of a and a capacitor 7b is
As shown in figure b, capacitor 8a and resistor 8
9 is a first output terminal for outputting the first reference subcarrier 10 shown in FIG. 4a; 11 is a first output terminal as shown in FIG. 4a;
a second output terminal for outputting a second reference subcarrier 12 having a phase difference of about 90° with respect to the reference subcarrier 10;
3 is a phase control terminal to which a control voltage is applied, 14 is a hue controller, and 15 is a resistor 7a and a capacitor 7b, the detailed circuit of which is shown in FIG. 3a.
A third phase shifter 16 has a phase lag, and 16 is a fourth phase shifter 17, whose detailed circuit is shown in FIG. A PAL switch input terminal, 18 is a PAL switch, 19 is a third output terminal to which a reference subcarrier for BY-axis demodulation is output, and 20 is a fourth output terminal to which a reference subcarrier for R-Y axis demodulation is output.

Figure 4b shows the phase relationship between the burst and the reference subcarrier when a PAL signal is input. In particular, 21 and 22 change at +45° and -45° (centered on 180°) for each horizontal scan. This shows a PAL burst with changing phase. Therefore, the first reference subcarrier 10 shown in FIG.
APC) is used as a carrier wave for detection, and is used as a second
The reference subcarrier 12 is input to the killer detector of the hue controller 14 and is used as a carrier for killer detection. The hue controller 14 is used for phase adjustment of the color demodulator during PAL, and for hue adjustment during NTSC. That is, in order to adjust the phase of the reference subcarrier input to the demodulator, the amount of synthesis of the first and second reference subcarriers having a phase difference of 90 degrees is changed. Figure 4c shows burst 23 of the NTSC system.
and a first reference subcarrier 10 and a second reference subcarrier 12
This burst 23 has a phase relationship of 90° with the first reference subcarrier 10,
It is in phase with the second reference subcarrier 12. Therefore, in both cases, the killer detection output is present and the color is displayed on the screen. (Conventionally, PAL-dedicated ICs used killer detectors, so during NTSC, the detection output was 0, which was equivalent to no input, so the killer circuit was activated.) Next, the color signal processing circuit with the above configuration. The signal processing operation of the reference subcarrier will be explained. First, the reference subcarrier (its frequency is approximately 3.58MHz or 4.43MHz) input to the input terminal 6 is transmitted to the first phase shifter 7.
The second phase shifter 8 decomposes the wave into a first reference subcarrier 10 and a second reference subcarrier 12 having a phase difference of approximately 90°, as shown in FIG. The signal is output from the terminal 9 and the second output terminal 11, and is also input to the hue controller 14. This hue controller 14 synthesizes the input first reference subcarrier 10 and second reference subcarrier 12 having a 90° phase difference, and controls the synthesis ratio by a control voltage applied to a phase control terminal 13. By being changed, a carrier wave having an arbitrary phase between the input first reference subcarrier 10 and second reference subcarrier 12 can be created. This combined carrier wave is transmitted through the third phase shifter 15 and the fourth phase shifter 1.
6, it is again decomposed into a third reference subcarrier and a fourth reference subcarrier with a phase difference of approximately 90°, and the PAL
input to switch 18. Therefore, when the input signal is a PAL signal, the phase of the reference subcarrier for R-Y axis demodulation is inverted by 180 degrees every horizontal scanning period (however, the reference subcarrier for B-Y axis demodulation remains unchanged). , is output to the second output terminal 20. On the other hand, when the input signal is NTSC, no operation is performed on the PAL switch 18, and the carrier wave is output as is. In this way, NTSC/PAL color signal processing can be easily performed.

The first phase shifter 7 and the third phase shifter 15 are shown in FIG.
Although the phase shifter 16 is shown in FIG. 3b, it is needless to say that it is not limited to this circuit. Furthermore, by optimizing the configuration for IC implementation, due to the small variation in the relative values of each element due to the IC, the variation in the absolute phase at the first output terminal 9 and the second output terminal 11 seen from the input terminal 6 is large. but,
The 90° phase is almost maintained. Moreover, after combining these phases, by decomposing the phases again using phase shifters of the same type, the phase shifter 7 and the third phase shifter 15, the second phase shifter 8 and the fourth phase shifter Phase shift due to phase shifters of the same type between the phase shifters 16 can be reduced.

As explained in detail above, the color signal processing circuit according to the present invention has a simple configuration and can perform NTSC
In addition to being able to easily receive both PAL and PAL color broadcasting, it also has the advantage of providing a configuration suitable for IC implementation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional color signal processing circuit, FIG. 2 is a block diagram showing an embodiment of the color signal processing circuit according to the present invention, and FIGS. 3a and 3b are respectively shown in FIG. 4a to 4c are diagrams showing the phase relationship between the reference subcarrier and the burst in FIG. 2. 1... Color signal input terminal, 2... NTSC color signal processing circuit, 3... PAL color signal processing circuit, 4... Control circuit, 5... Color signal output terminal, 6
...Input terminal, 7...First phase shifter, 8...Second phase shifter, 9...First output terminal, 10...First reference subcarrier, 11...Second output terminal, 12... ...Second reference subcarrier, 13...Phase control terminal, 14...Hue controller, 15...Third phase shifter, 16...Fourth phase shifter, 17...PAL switch input terminal, 18...
...PAL switch, 19...Third output terminal, 20
...Fourth output terminal. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An input reference subcarrier is decomposed into a first reference subcarrier and a second reference subcarrier with a phase difference of about 90° by a first phase shifter and a second phase shifter, and the first reference subcarrier is The subcarrier is input to an automatic phase control detector, this second reference subcarrier is input to a killer detector, the first reference subcarrier and the second reference subcarrier are combined at an arbitrary ratio, and then the third phase The third reference subcarrier and the fourth reference subcarrier are separated into a third reference subcarrier and a fourth reference subcarrier with a phase difference of approximately 90° by a phase shifter and a fourth phase shifter, and the third reference subcarrier is inverted every horizontal scan only during PAL. A color signal processing circuit featuring: 2. The first phase shifter and the third phase shifter are phase lead circuits having substantially the same value of resistance and capacitance, and the second phase shifter and the fourth phase shifter are phase delay circuits having substantially the same value of resistance and capacitance. A color signal processing circuit according to claim 1.