JPS6014557B2 - color demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color demodulation device for a PAL color television receiver.

In the PAL system, one of the two color difference signals,
For example, it is well known that the modulation axis for the (RY) signal is sent with the phase shifted by 180° every horizontal scanning period (hereinafter referred to as IH).

In order to demodulate, for example, the (RY) signal transmitted in this way with the correct polarity, the horizontal frequency (hereinafter referred to as IH
It is well known that a switch that operates at 1/2 of H/2 is used to drive the switch, and a multipipelator that divides the horizontal pulse frequency by 2 is used to generate a line switching signal of N/H/2. be. It is also well known to control the multipipelator so that the phase of the line switching signal of N/H/2 has an appropriate relationship with the transmission line information transmitted by the color synchronization signal.

In this well-known circuit, as described in Tsubaki Kosho No. 49-4566, the PAL switch is permanently stopped in order to control the phase of the line switching signal of NaH/2. There were some drawbacks. The present invention
It is an object of the present invention to provide a color demodulation device for a color television receiver that can demodulate a (R-Y) signal of the correct polarity without controlling the phase of a line switching signal of /2.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.
FIG. 1 is a block diagram of main parts showing one embodiment of the present invention. In the figure, a carrier color signal (it is well known that it is not processed in the simple PAL system) processed by a well-known delay line matrix circuit consisting of an IH delay line and a difference calculation circuit (both not shown) is sent from terminal 1. The burst signal is applied to one input terminal A of the first switch circuit 2, and the carrier color signal with inverted polarity is applied to the other input terminal B together with the burst signal through a 180° phase shifter 3. The first switch circuit 2 is switched and controlled by a control signal from a control circuit 4, and its output terminal C is supplied with one of two inputs. The output signal is passed through a burst planking circuit 5 to remove the burst signal and is applied to a (RY) demodulator 6. On the other hand, a second switch circuit 7 with two input terminals
(RY) is applied to terminal 8 on one input terminal of
If the reference subcarrier, that is, the average phase of the PAL alternating burst is 180o, then a subcarrier with a phase of 900 is added.

Further, to the other input terminal L, a subcarrier wave whose suitability has been inverted, that is, has a phase of -90 degrees, is applied through an 18-pi phase shifter 9. The second switch circuit 7 is switched by the output of a flip-flop circuit 11 which divides the frequency of the horizontal pulse applied to the terminal 10 into two to generate a line switching signal of . 180
o Generate (RY) reference subcarriers with different phases. However, the phase that changes for each line is not synchronized with the transmission line information transmitted by the alternating burst signal. The (R-Y) demodulator 6 demodulates the output of the first switch circuit 2 using the (R-Y) reference subcarrier from the second switch circuit 7 as described above. Y) In order to apply the signal to the terminal 14, the control circuit 4 combines the burst signal from the burst extraction circuit 12, which extracts only the burst signal with the horizontal pulse applied to the terminal 10', and the output of the third switch circuit 13. The phases are compared, and when the phases do not match, a control signal for switching the first switch circuit 2 is generated.

Said third switch circuit 13 also has two input terminals, L, one of which is connected to the output terminal of the 180o phase shifter 9, and the other input terminal L is connected to the terminal 8. As a result, as in the case of the second switch circuit 7, reference subcarriers having different phases are supplied to each input terminal L.

The third switch circuit 13 is also switched in conjunction with the second switch circuit 7 by the line switching signal output from the flip-flop circuit 11, and supplies the reference subcarrier from the output terminal C to the control circuit 4. Make a grandchild. In this case, the second switch circuit 7 and the third switch circuit 13 are in such a relationship that when one output terminal is connected, the other output terminal is connected to the output side of the 180o phase shifter 9. It is set. Further, an automatic color gain control signal and a color killer control signal are obtained from the control circuit 4 to the terminal 15.

Note that the first, second, and third switch circuits 2, 7, 1
3 may use a well-known semiconductor switch circuit such as a transistor circuit. FIG. 2 is a block diagram showing an example of the configuration of the control circuit 4. As shown in FIG. To explain this, 16 is a phase discrimination circuit, which converts the alternating burst signal from the burst extraction circuit 12 in FIG.
Synchronous detection is performed using the (RY) reference subcarrier whose sacrifice is inverted every time. In this case, the phase of the alternating burst signal is 1135°
When the line , the phase of the (R-Y) reference subcarrier is
0o, or in the IA period of the line where the phase of the alternating burst signal is -1350, the phase of the reference subcarrier (R-Y) is -1350.
900 (this case is assumed to have a correct phase relationship with the transmission line information), the burst detection output of the phase discrimination circuit 16 will have positive polarity, and conversely, if the phase of the alternating burst signal is 11
During the IH period of the line 350, the phase of the (R-Y) reference subcarrier is -900, or during the IH period of the line where the phase of the alternating burst signal is -1350, the phase of the (R-Y) reference subcarrier is -900. If the angle is 190° (this case is assumed to be an incorrect phase relationship), the burst detection output of the phase discrimination circuit 16 will have negative polarity. The DC component detection circuit 17 that follows the phase discrimination circuit 16 is a circuit that detects the DC component of the burst detection output realized by a low-pass filter or a peak holding circuit, and when it has a correct phase relationship with the line information, A DC signal that is more positive than the reference level is obtained, and if the phase relationship is wrong, a DC signal that is more negative than the reference level. In order to control the state of the first switch circuit 2 based on this information, a trigger circuit 18 and a flip-flop circuit 19 are connected in cascade to the DC component detection circuit 17 as shown in FIG. The trigger circuit 18 operates as a flip-flop circuit 19 only when the output of the DC component detection circuit 17 is negative.
A trigger signal for changing the state of the flip-flop circuit 19 is generated and supplied to the flip-flop circuit 19. When positive, the state of the flip-flop circuit 19 does not change. By switching and controlling the first switch circuit 2 using the output of the flip-flop circuit 19, a correct phase relationship can always be obtained.
The trigger circuit 18 has a horizontal pulse, a vertical pulse, and a H/2 line switching signal which is applied to the flip-flop circuit 19 as a trigger signal only when a signal indicating a negative output from the DC component detection circuit 17 is generated. This can be realized using a sum circuit. Further, since the output of the DC component detection circuit 17 corresponds to the level of the burst signal, the well-known automatic color gain control signal (AC
C signal). Furthermore, when the output of the DC component detection circuit 17 is below a certain level positive than the reference level, a so-called killer operation is activated, which stops the operation of the color demodulation layer. The killer circuit also operates when the state of the switch circuit 2 is incorrect and the polarity of the (R-Y) signal output is incorrect, causing inappropriate colors to appear on the screen of a color television receiver equipped with this device. Prevent reproduction from occurring. As is clear from the above description, according to the present invention, a completely new PAL color television receiver can obtain an R-Y color difference signal of the correct polarity simply by generating an H/2 line switching signal whose phase is not controlled. This color demodulation device can be realized, and its effects are very large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a main part of an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the configuration of a control circuit that can be used in the present invention.

2...First switch circuit, 3...1
800 phase shifter, 4... control circuit, 5... burst planking circuit, 6... (RY) demodulator, 7... second switch circuit , 9...
180.

Phase shifter, 11...Flip-flop circuit, 12...
... Burst extraction circuit, 13 ... Third switch circuit, 16 ... Phase discrimination circuit, 17 ...
...DC component detection circuit, 18...Trigger circuit,
19...Flip-flop circuit. Figure 1 Figure 2

Claims (1)

[Claims] 1 has an input terminal to which a carrier color signal and a burst signal of a PAL color television signal are supplied, and an input terminal to which a carrier color signal and a burst signal whose polarity is reversed with respect to the (RY) axis are supplied; a first switch circuit that can select and obtain one of the signals applied to the input terminal; a (R-Y) demodulator to which the output carrier color signal of the first switch circuit is supplied; It has an input terminal to which the reference subcarrier of the Y) axis is supplied, and an input terminal to which the reference subcarrier of the −(R−Y) axis is supplied, and is linked to each input terminal for each horizontal scanning line. second and third switch circuits that can select and obtain one of the given signals; a burst signal obtained from the output of the first switch circuit; and a reference subcarrier obtained from the third switch circuit. a control circuit that compares the phases and switches the first switch circuit when the phases do not match, and sends a reference subcarrier obtained from the second switch circuit to the (R-Y) demodulator; A color demodulating device characterized in that the color demodulating device is configured to supply the carrier color signal and demodulate the carrier color signal.