JPS6129592B2 - - 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 switch is used that operates at a frequency that is half the horizontal frequency (hereinafter referred to as H/2) and is initially switched every 1H. To drive this switch, a flip-flop that divides the horizontal pulse frequency by 2 is used. /2 line switching signals are generated. It is also well known to control flip-flops so that the phase of the H/2 line switching signal has a proper relationship to the transmission line information transmitted by the color synchronization signal.
In such well-known circuits, the
As stated in the publication, there was a drawback in that the PAL switch was permanently stopped in order to control the phase of the H/2 line switching signal.

Therefore, the present invention aims to provide 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. This is the purpose.

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 to an adder 3 and a subtracter 4 together with the original input carrier color signal, where they are added to and subtracted from each other. As a result, a carrier color signal of the (BY) axis is obtained from the adder 3 and is added to the (BY) demodulator 5. On the other hand, the polarity from subtracter 4 is reversed every 1H.
Since a carrier color signal of the (RY) axis is obtained, 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 output terminals for the (BY) signal and the (RY) signal. 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 an inverter 11, and the direct carrier color signal and the inverted carrier color signal are combined into the first carrier color signal.
switch 12 and two input terminals A and B, respectively, and the output carrier color signal is applied to the (RY) demodulator 6. This first switch is a static switch that is switched only once when necessary by a switching signal from flip-flop 13.

Next, a section that generates color subcarriers for demodulation will be explained. Only the burst signal is taken out by the burst gate 14 from the input chroma signal applied to the input terminal 1 and applied to an oscillation phase control loop consisting of a phase discriminator 15, a local color subcarrier oscillator 16, and a 90° phase shifter 17. This circuit is well known, and the oscillator 16 is controlled to continuously oscillate at its average phase in synchronization with the burst signal.
Y) axis color subcarrier is generated. Therefore, the (BY) signal can be demodulated by inverting the polarity of this signal using the inverter 18 and applying it to the (BY) demodulator 5 as a tone carrier wave of the (BY) axis.

On the other hand, the output of the oscillator 16 is phase-shifted by a 90° phase shifter 17 and applied to the phase discriminator 15 for oscillation phase control as a color subcarrier with a +(RY) axis phase, and the polarity is changed by a phase inverter 19. Invert -(R-
Y)-axis phase color subcarriers, and their ±(R-
The color subcarriers having the phase of the Y) axis and having opposite polarities are applied to the two input terminals a and b of the third and fourth switches 20 and 21, respectively. The third and fourth switches 20 and 21 are connected to the horizontal pulse input terminal 22.
The signal is switched every 1H by a switching signal with a frequency of H/2 from the flip-flop 23, which is inverted every 1H by a horizontal pulse (horizontal synchronization pulse or horizontal flyback pulse) applied from +(RY ) axis phase color subcarrier and −(R
-Y) axis phase color subcarriers are taken out alternately every 1H, and the ±(R-Y) axis color subcarriers taken out from the third switch 20 are used for (R-Y) demodulation. -Y) Add to demodulator 6.

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 24 and applied to the phase discriminator 25. and,
Synchronous detection is performed using the ±(RY) axis color subcarrier taken out from the fourth switch 21 ahead of this burst signal, and the polarity of the (RY) axis component is detected. At this time, if the polarity of the (RY) axis component of the burst signal and the polarity of the color subcarrier obtained from the fourth switch 21 match, a positive pulse is obtained, and if they do not match, a negative pulse is obtained. A pulse is obtained.
The polarity of this detection pulse is also inverted by the inverter 26, and the direct detection pulse and the detection pulse with the polarity inverted are applied to the two input terminals A and B of the second switch 27, respectively. The second switch 27 is also switched in conjunction with the first switch 12 by a switching signal from the flip-flop 13.

At this time, the first and second switches 1
Switching between switches 2 and 27 occurs when the polarity of the carrier color signal output from the first switch 12 and the polarity of the color subcarrier applied from the third switch 20 to the (RY) demodulator 6 do not match. 4th switch 27
Set so that a positive switching signal is output from. The flip-flop 13 that switches these first and second switches 12 and 27 is configured to invert only once when it detects that the demodulation polarity is incorrect, and when the demodulation polarity is correct, the flip-flop 13 switches the switches 12 and 27. cannot be switched.

However, in this device, unlike conventional devices, the switching polarity of the flip-flop 23 of the third and fourth switches 20 and 21 is not separated in any way, so the switching signal of the output of the flip-flop 23 starts from which polarity. The polarity of the color subcarrier output from the third and fourth switches 20 and 21 differs depending on the case, and has one of the polarities a and b2 as shown in the figure. It is unspecified which one will be. However, the (RY) demodulator 6 correctly outputs (R
-Y) First switch 1 to demodulate the signal
It is necessary that the polarity of the carrier color signal applied from the third switch 20 and the polarity of the color subcarrier applied from the third switch 20 match correctly. If it is not known whether the carrier wave will have polarity a or b2, there is a possibility that the two polarities will not match.

Therefore, in this device, the phase discriminator 25 compares the polarity of the color subcarrier applied from the third switch 20 to the (RY) demodulator 6 and the polarity of the burst signal obtained from the burst gate 24. If the two polarities do not match, a negative detection pulse is generated from the phase discriminator 25 and the flip-flop 1
3 and turn the first and second switches 12, 27
By switching to the opposite side and switching the polarity of the carrier color signal to the (RY) demodulator 6, the polarities of both are made to match and correct (RY) demodulation is performed.

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 it is switched to the input terminal B side, +,
-, +, -. In conjunction with this, the polarity of the burst signal applied from the burst gate 24 to the phase discriminator 25 becomes +, -, +, -. On the other hand, the third
The polarity of the color subcarrier applied from the fourth switch 20, 21 to the (RY) demodulator 6 and phase discriminator 25 is changed by the third and fourth switches 20, 21 first from the input terminal a side. If it is -, +,
-, + and +, -, +, -, and if the input terminal b side is switched first, it becomes +, -, +, - and -, +, -, +.

Therefore, in the first state, the first and second switches 12 and 27 are switched to the A side, and the third and fourth switches 20 and 21 are switched from the A side first. think of. At this time, the polarities of the carrier color signal output from the first switch 12 and the color subcarrier output from the third switch 20 are both -, +, -, +, and therefore match, so the phase discriminator A positive detection pulse is generated from the switch 25, inverted by the inverter 26, and outputted as a negative detection pulse from the second switch, so that correct (RY) demodulation can be performed in the same switched state. Conversely, the first and second switches 12 and 27 are
Correct (RY) demodulation is similarly performed in the case of the second state in which the third and fourth switches 24 are switched from the b side first.

However, in the third state, even though the first and second switches 12 and 27 are switched to the A side, the third and fourth switches 20 and 21 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 20 is changed. The polarity becomes +, -, +, -, and correct (RY) demodulation cannot be performed. Therefore, in this case, the phase discriminator 25 detects that the polarity of the burst signal in the first H is + and the polarity of the color subcarrier from the fourth switch 21 is -, and that the two polarities do not match. A negative detection pulse is generated, which is inverted by the inverter 26 and taken out from the fourth switch 27 as a positive detection pulse, inverting the flip-flop 13 and switching the first and second switches 12 and 27 to the B side. Switch. Then,
From the 2nd H onward, 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 20, and from then on This means that 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.
From the 2nd H onwards, since the polarities of the two match, a positive detection pulse is no longer generated from the fourth switch 27, and the correct (RY) demodulation operation continues as in the case of the second state described above. .

Conversely, in a fourth state, even though the first and second switches 12 and 27 are switched to the B side, the third and fourth switches 20 and 21 are switched from the A side first. In this case as well, the polarities of the two signals do not match, but in this case as well, a positive detection pulse is generated from the phase discriminator 25 at the 1st H, and this time it is not inverted and is sent from the flip-flop 13 from the fourth switch 27. This is reversed and the first and second switches 12, 27 are switched to the A side, so that from the 2nd H onwards, the state is the same as in the first state above and is correct (R-
Y) Demodulation is performed.

In this way, in this device, the polarity of the carrier color signal to the (RY) demodulator 6 can be changed without any control over the switching polarity of the third and fourth switches 20 and 21, which are switched every 1H. When the polarity of the color subcarrier and 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 correct (RY) demodulation operation can be performed. This can be easily realized.

In the above embodiment, the color subcarrier of the output of the third switch 21 is added to the phase discriminator 25 for detecting polarity coincidence, but the fourth switch 21 is omitted and the color subcarrier of the output of the third switch 20 is added. The polarity of the output may be inverted and applied to the phase discriminator 25 for comparison with the polarity of the burst signal.

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... (RY) demodulator, 7...
(B-Y) signal output terminal, 8... (R-Y) signal output terminal, 9, 10... burst removal gate, 11... phase inverter, 12... first switch, 13... Flip-flop, 14...Burst gate, 15...Phase discriminator, 16...Local color subcarrier oscillator, 17...90° phase shifter, 18,1
9... Phase inverter, 20... Second switch, 2
1... Third switch, 22... Horizontal pulse input terminal, 23... Flip-flop, 24... Burst gate, 25... Phase discriminator, 26... Inverter, 27... Fourth switch.

Claims (1)

[Claims] 1 A static first and second switch each having two input terminals and switched in conjunction only when the demodulation polarity is matched is provided, and a PAL color television signal is directly connected to the input terminal of the first switch. Add the carrier color signal to the other input terminal (RY)
Add a carrier color signal whose polarity is reversed with respect to the axis,
The output carrier color signal of this first switch is (R-
Y) In addition to the demodulator, a third switch having two input terminals and switched every horizontal scanning line is provided,
A color subcarrier on the (RY) axis is applied to one input terminal of the third switch from a color carrier wave oscillator that oscillates at a constant phase in synchronization with the burst signal, and the -(RY) axis is applied to the other input terminal. The color subcarrier of the output of this third switch is added to the color subcarrier of the above (R
-Y) In addition to the demodulator, the carrier color signal is demodulated, and the color subcarrier of the output of the third switch or the color subcarrier with its polarity inverted is added to the phase discriminator to produce the PAL color television. The polarity of the burst signal extracted from the input signal is detected, and the detected output and the output obtained by inverting the polarity of the detected output are applied to one and the other input terminals of the second switch, and the (RY) demodulator When the polarity of the color subcarrier added to the color subcarrier and the polarity of the burst signal do not match, the second switch generates a switching signal of a specific polarity to switch the first and second switches. A color demodulation device characterized by: