JPS6130472B2 - - Google Patents

Description

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

In the PAL system, the modulation axis for one of the two color difference signals, that is, the (RY) color difference signal, is 180 pixels per horizontal scanning period (hereinafter referred to as 1H).
It is well known that the signal is sent with a phase shift of 1°. It is sent like this (R
-Y) In order to demodulate the color difference signal with the correct polarity, a frequency that is half the horizontal frequency (hereinafter referred to as H/
A switch is used that operates at 1H (referred to as 2) and is switched every 1H, and a flip-flop that divides the horizontal pulse frequency by 2 is used to drive this switch.
A line switching signal of H/2 is generated. It is also well known to control flip-flops so that the phase of the H/2 line switching signal has the proper relationship to the transmission line information transmitted by the color synchronization signal. In such a well-known circuit, the PAL switch is permanently stopped in order to control the phase of the H/2 line switching signal, as described in Japanese Patent Publication No. 49-4566. There were some drawbacks.

SUMMARY OF THE INVENTION Therefore, the present invention provides a color demodulation device for a PAL color television receiver that can accurately demodulate (RY) color difference signals without controlling the phase of the H/2 line changeover switch. The purpose is to

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

In the figure, 1 is an input terminal for a chroma signal extracted from a PAL color television signal. A carrier color signal (indicated by a broken line) and a burst signal (indicated by a solid line) whose polarity is reversed with respect to the (RY) axis every 1H are added here. This input carrier color signal is delayed by a 1H period in a 1H delay circuit 2, and is added together with the original input carrier color signal to an adder 3 and a subtracter 4, where they are added to and subtracted from each other. As a result, the (BY) axis carrier signal is obtained from the adder 3 and is added to the (BY) demodulator 5. On the other hand, the subtracter 4 obtains a ±(RY)-axis carrier color signal whose polarity is inverted every 1H, so it is applied to the (RY) demodulator 6 via a switching circuit to be described later. Such delay and addition/subtraction means are well known. 7 and 8 are (B-Y) signals and (R
-Y) signal output terminal. However, in this device, before adding the input carrier color signal and the delayed carrier color signal to the adder 3 and the subtracter 4, burst removal gates 9 and 10 are provided to remove the burst signal in advance, and the adder 3 and the output of the subtracter 4 so that no burst component appears.

Then, the polarity of the ±(RY) axis carrier color signal output from the subtractor 4 is inverted by the inverting circuit 11, and the direct carrier color signal and the inverted carrier color signal are transferred to the two terminals of the first switch 12. and the output carrier color signal is applied to the (RY) demodulator 6. This first switch 12 is a static switch that is switched only once when necessary by a switching signal from a flip-flop 13.

On the other hand, only the burst signal is extracted from the input carrier color signal applied to the input terminal 1 by the burst gate 14. The polarity of this burst signal is also inverted by the inverting circuit 15, and the direct burst signal and the burst signal with the inverted polarity are transferred to the second switch 16.
are applied to two input terminals A and B, respectively. This second
The switch 16 is switched by a switching signal from a flip-flop 26 which is switched every horizontal period. 25 is a horizontal pulse input terminal to which a horizontal pulse (horizontal synchronization pulse or horizontal flyback pulse) is applied. The output of the second switch 16 is applied to a phase discriminator 17.

Next, a section that generates color subcarriers for demodulation will be explained. First, only a burst signal is taken out by the burst gate 18 from the input chroma signal applied to the input terminal 1, and is applied to an oscillation phase control loop consisting of a phase discriminator 19, a local color subcarrier oscillator 20, and a 90° phase shifter 21. This circuit is well known, and the oscillator 20 is controlled to continuously oscillate at the average phase of the burst signal, and generates a -(BY) axis color subcarrier. Therefore, by inverting the polarity of this signal using the phase inverter 22 and adding it to the (BY) demodulator 5 as a color subcarrier of the (BY) axis, the (BY) signal can be demodulated.

On the other hand, the output of the oscillator 20 is phase-shifted by a 90° phase shifter 21 and applied to the phase discriminator 19 as a color subcarrier with a +(RY) axis phase for oscillation phase control, and the polarity is changed by an inversion circuit 23. Reverse -(R-
Y)-axis phase color subcarriers, and their ±(R-
The color subcarrier of the phase of the Y) axis is switched to the third switch 24.
are applied to the two input terminals a and b, respectively. This third switch 24 has a horizontal pulse input terminal 25.
The H/H signal from the flip-flop 26 is inverted every H by a horizontal pulse (horizontal synchronization pulse or horizontal flyback pulse) applied from the flip-flop 26.
The frequency is switched every 1H by the frequency switching signal of 2, and the color subcarrier of the phase of the + (RY) axis and the -
The color subcarrier of the phase of the (RY) axis is taken out alternately every 1H and applied to the (RY) demodulator 6.

Further, the output of the inverting circuit 23 is transferred to the fourth switch 27.
In addition to one input terminal B of the switch 27, the output of the 90° phase shifter 21 is applied to the other input terminal A of the switch 27.
This fourth switch 27 is switched in conjunction with the first switch by the output of the flip-flop 13. The output of this fourth switch is applied to the phase discriminator 17.

However, in this device, unlike the conventional device, a third switch 24 and a flip-flop 26 are used.
Since the switching polarity of the third switch 24 is not controlled in any way, the polarity of the color subcarrier output from the third switch 24 differs depending on which polarity the switching signal output from the flip-flop 26 starts from, as shown in the figure. The polarity can be either a or b2. It is unspecified which one will be. However, in order to correctly demodulate the (RY) signal with the (RY) demodulator 6, the polarity of the carrier color signal applied from the first switch 12 and the color subcarrier applied from the third switch 24 must be changed. However, as mentioned above, if it is not known whether the polarity of the color subcarrier from the third switch 24 will be a or b2, it is necessary that the polarities of the two match correctly. There is a risk that a situation may arise where the Therefore, in this device, the polarity of the color subcarrier from the fourth switch 27 and the polarity of the burst signal obtained from the second switch 16 are compared by the phase discriminator 17, and if the polarities of the two match, If not, one positive switching pulse is generated from the phase discriminator 17 and the flip-flop 1 is switched.
3 and turn the first and fourth switches 12, 27
By switching the polarity of the carrier color signal to the (RY) demodulator 6 to the opposite side, the polarities of both are made to match, and correct (RY) demodulation is performed. When both polarities match and a negative pulse is output from the phase discriminator 17, the flip-flop 13 is not inverted.

This operation will be explained in more detail. now,
As shown in the figure, +(R
-The chroma signal modulated on the -Y) axis, and on the 2nd H, the chroma signal modulated on the -(R-Y) axis...
...assumed to have been input. Then, if the first switch 12 is switched to the input terminal A side, the polarity of the carrier color signal applied from the first switch 12 to the (RY) demodulator 6 will be +, -, +, -( No.
1st H, 2nd H, 3rd H, 4th H, and so on)
So, if the input terminal is switched to the B side, -,
+, -, +. The polarity of the color subcarrier signal applied from the fourth switch 27 to the phase discriminator 17 is
If the fourth switch 27 is switched to the input terminal A side, the signals will be +, +, +, +, and if it is switched to the input terminal B side, the signals will be -, -, -, -. On the other hand, the polarity of the color subcarrier applied from the third switch 24 to the (RY) demodulator 6 is determined by the third switch 24.
If is switched from the input terminal a side first, +,
+, +, and if the input terminal b side is switched first, it becomes -, -, -, -. When the burst signal applied to the phase discriminator 17 from the second switch 16 is switched from the a side first, the signals are +, -, +, -, b.
If the side is switched first, it becomes -, +, -, +.

Therefore, in the first state, the first and fourth switches 12 and 27 are switched to the A side, and the second and third switches 16 and 24 are switched from the A side first. think of. At this time, the polarity of the carrier color signal output from the first switch 12 and the polarity of the color subcarrier output from the third switch 24 are both +, -, +, -, which are the same. At this time, the two inputs to the phase discriminator 17 are both +, +, +, +, so the phase discriminator 17
No switching pulse is generated from then on, and the correct (RY) demodulation operation is performed in the same switching state. Conversely, the first and fourth switches 12 and 27 are switched to the B side, and the second and third switches 1
Similarly, in the case of the second state in which signals 6 and 24 are switched from the b side first, their polarities match and correct (RY) demodulation is performed.

However, in the third state, even though the first and fourth switches 12 and 27 are switched to the A side, the second and third switches 16 and 24 are switched to the b side.
If the switch is switched from the side first, the polarity of the carrier color signal output from the first switch 12 is +, -, +, -, but the color subcarrier signal output from the third switch 24 is changed. The polarity becomes -, +, -, +, and correct (RY) demodulation cannot be performed. Therefore, in this case, the phase discriminator 17 determines that in the first H, the polarity of the burst signal from the second switch 16 is 1, the polarity of the color subcarrier from the fourth switch 27 is +, and both polarities match. It detects that the switch is not active, generates one positive switching pulse, inverts the flip-flop 13, and switches the first and fourth switches 1.
2, 27 to the B side. Then, from the 2nd H onwards, the polarity of the carrier color signal output from the first switch 12 becomes +, -, +, which matches the polarity of the color subcarrier from the third switch 24 +, -, +. , thereafter, correct (RY) demodulation can be performed. Eventually, the polarity of the output of the first switch 12 at this time becomes +, +, -, + as shown in C. After the 2nd H, the polarities of both match, so it is no longer the phase discriminator 1.
No positive switching pulse is generated from 7 and the second
The correct (RY) demodulation operation continues as in the case of state.

Conversely, in a fourth state, even though the first and fourth switches 12 and 27 are switched to the B side, the second and third switches 16 and 24 are switched from the A side first. In this case, the polarities of the two signals also do not match, but in this case as well, a switching pulse is generated from the phase discriminator 17 at the 1H, the flip-flop 13 is inverted, and the first and fourth switches 12, 27 are switched. is switched to the A side, and from the 2nd H onward, correct (RY) demodulation is performed in the same manner as in the first state.

In this way, in this device, the (RY) demodulator 6
When the polarity of the carrier color signal and the polarity of the color subcarrier do not match, it is possible to match the polarities of the two by switching the first and fourth switches 12 and 27 only once, and the polarity of the color subcarrier is correct ( RY) demodulation operation can be easily realized.

Note that the phase discriminator 17 may be provided immediately after the burst gate 14, and the flip-flop 13 may be directly controlled by the output of the switch 16.

As described above, according to the present invention, a completely new PAL color television receiver can obtain a (RY) color difference signal of the correct polarity simply by generating an H/2 line switching signal whose phase is not controlled. A demodulation circuit can be realized.

[Brief explanation of the drawing]

The figure is a block diagram of a color demodulator according to an embodiment of the present invention. 1... Chroma signal input terminal, 2... 1H delay circuit, 3... Adder, 4... Subtractor, 5... (B-Y) demodulator, 6... (R-Y) demodulator, 7... (B-Y) ) signal output terminal, 8...(RY) signal output terminal,
9, 10... Burst removal gate, 11... Inverting circuit, 12... First switch, 13... Flip-flop, 14... Burst gate, 15... Inverting circuit,
16...Second switch, 17...Phase discriminator, 18
...burst gate, 19...phase discriminator, 20...90
゜Phase shifter, 22... Phase discriminator, 23... Inversion circuit,
24...Third switch, 25...Horizontal pulse input terminal, 26...Flip-flop, 27...Fourth switch.

Claims (1)

[Claims] 1. A first and a fourth switch each having two input terminals and being switched in conjunction are provided; a second and third switch each having two input terminals and being switched in conjunction; The carrier color signal of the PAL color television signal is directly applied to one input terminal of the switch, and the carrier color signal whose polarity is reversed with respect to the (RY) axis is added to the other input terminal of the switch. The output carrier chrominance signal of this first switch is applied to the (RY) demodulator, and the chrominance subcarrier of the (RY) axis is applied to one input terminal of each of the third and fourth switches. The -(R-Y) axis color subcarrier is added to the other input terminal of the switch, and the output color subcarrier of the third switch is changed to (R-
Y) inverting the input signal to the other input terminal of a path that applies the output color subcarrier of the fourth switch to the demodulator and to the phase discriminator and applies the input signal directly to one input terminal of the second switch; A switching circuit is formed by connecting an inverting circuit, the phase discriminator and the switching circuit are connected in cascade, a burst signal included in the PAL color television signal is applied to the input terminal of the cascade circuit, and the second The switch and the third switch are controlled to switch in conjunction with each other for each horizontal scanning line, and the third switch and the fourth switch are controlled so that the polarities of both inputs of the phase discriminator match. 1. A color demodulation device characterized in that switching is performed in conjunction with a switching signal generated when the color demodulator is not in use.