JPS6132873B2 - - 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 that operates at half the horizontal frequency (hereinafter referred to as fH/2) and is switched every 1H is used, and to drive it, two horizontal pulses are used.
A frequency-dividing flip-flop is used, fH/2
A line switching signal is generated. It is also well known to control flip-flops so that the phase of the fH/2 line switching signal has the proper relationship to the transmit line information carried by the color synchronization signal. In such a well-known circuit, the
-As stated in Publication No. 4566, in order to control the phase of the fH/2 line switching signal, the above
There was a drawback that the PAL switch would stop working permanently.

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 fH/2 line changeover switch. This is the purpose.

Therefore, in the present invention, the carrier color signal of the PAL color television signal is applied to the (RY) demodulator, and the first and third switches are switched in conjunction with each other for each horizontal scanning line. , a stationary type second and fourth switches that are switched in conjunction with each other. the third of them
The polarity of the color subcarrier of the (RY) demodulator is set to 1 by cascade-connecting the polarity inversion switching circuit using the switch
Invert each horizontal scan line. On the other hand, by using the first and second switches and the phase discriminator which are switched in conjunction with the third and fourth switches, it is possible to
It is detected whether the polarity of the color subcarrier applied to the demodulator matches the polarity of the burst signal in the PAL color television signal. If they do not match, the detected output switches the static second and fourth switches to opposite sides, inverting the polarity of the color subcarrier applied to the (R-Y) demodulator. Y) The polarity of the carrier color signal applied to the demodulator and the color subcarrier are made to match, so that the carrier color signal can be correctly demodulated.

As means for determining whether the color subcarrier and the burst signal match in polarity, a polarity inversion switching circuit using a first switch and a polarity inversion switching circuit phase discriminator using a second switch are connected in cascade. A circuit that applies a burst signal to the input terminal of the connection circuit and a fixed polarity color subcarrier to the phase discriminator.

A polarity inversion switching circuit using a second switch and a phase discriminator are connected in cascade, a burst signal is applied to the input terminal of the cascade connection circuit, and the polarity is inverted every horizontal scanning period via the first switch. This circuit adds the color subcarrier wave to the phase discriminator.

A polarity inversion switching circuit using a first switch and a phase discriminator are connected in cascade, a burst signal is applied to the input terminal of this cascade connection circuit, and a color subcarrier of fixed polarity is applied to the phase discriminator via a second switch. A circuit that adds

A polarity inversion switching circuit using a first switch, a polarity inversion switching circuit using a second switch, and a phase discriminator are connected in cascade, and a color subcarrier with a fixed polarity is added to the input terminal of the cascade connection circuit. A circuit that adds a burst signal to the phase discriminator.

can be used.

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 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, the (BY) axis carrier signal is obtained from the adder 3 and is added to the (BY) demodulator 5. on the other hand,
From the subtracter 4, the polarity is reversed every 1H.
Since the carrier color signal of the Y) axis is obtained, it is added to the (RY) demodulator 6. Such delay and addition/subtraction means are well known. 7 and 8 were demodulated (B-
This is an output terminal for the Y) signal and the (RY) signal. However, in this device, burst removal gates 9 and 10 are provided before adding the input carrier color signal and the delayed carrier color signal to the adder 3 and the subtracter 4.
The burst signal is removed in advance, and the adder 3 and subtracter 4
This prevents burst components from appearing in the output.

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 11. The polarity of this burst signal is also inverted by the inverting circuit 12, and the direct burst signal and the burst signal with the inverted polarity are transferred to the two terminals of the first switch 13.
are applied to two input terminals A and B, respectively. This first
The switch 13 is switched every 1H by a switching signal with a frequency of fH/2 from the flip-flop 15, which is inverted every 1H by a horizontal pulse (horizontal synchronization pulse or horizontal flyback pulse) applied from the horizontal pulse input terminal 14. Do it like this. As a result, the output signal of the first switch 13 has a (RY) axis component of + depending on whether the switch 3 is switched from the A side or from the B side.
A that becomes something special or something B that becomes something that nothing else
Do something. Its output is also inverted by an inverting circuit 16, and the direct output signal and the inverted output signal are applied to two input terminals a, b of a second switch 17. This second switch 17 is of a static type and is switched by a switching signal from a flip-flop 18 which is switched and inverted only once when matching the demodulation polarity of the (RY) signal. The output signal of the second switch 17 is applied to a phase discriminator 19 for controlling a flip-flop 18.

Next, a section that generates color subcarriers for demodulation will be explained. First, only the burst signal is extracted from the input chroma signal applied to the input terminal 1 by the burst gate 20, and is applied to an oscillation phase control loop consisting of a phase discriminator 21, a local color subcarrier oscillator 22, and a 90° shifter 23. This circuit is well known, and the oscillator 22 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 24 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 22 is phase-shifted by a 90° phase shifter 23 to become a color subcarrier with a +(R-Y) axis phase, and is inverted by an inverting circuit 25 to have a −(R-Y) axis phase. The color subcarriers having the phase of the ±(RY) axis are applied to the two input terminals A and B of the third switch 26, respectively. This third switch 24 also receives a signal from the flip-flop 15.
The switch is switched every 1H in conjunction with the first switch 13 by a switching signal with a frequency of fH/2, and
The (RY) axis phase color subcarrier and the -(RY) axis phase color subcarrier are taken out alternately every 1H.

Therefore, the output color subcarrier of this third switch 26 also depends on whether the switch 26 is switched from the A side or from the B side.
Regarding the axis +, -, +, - (1st H, 2nd H, 3rd H
Is A in the order of th, 4th H, and so on) -,
Do B in the order of +, -, +. The output color subcarrier is also inverted by the inversion circuit 27, and the direct output color subcarrier and the inverted color subcarrier are transferred to the fourth switch 2.
8 to the two input terminals a and b. It is assumed that this fourth switch 28 is also switched in conjunction with the second switch 17 only once when matching the demodulation polarity of the (RY) signal by a switching signal from the flip-flop 18. Then, the ±(RY) axis color subcarrier output from the fourth switch 28 is applied to the (RY) demodulator 6 as a color subcarrier for demodulating the (RY) signal.

On the other hand, the −(RY) axis color subcarrier output from the inversion circuit 25 is added to the phase discriminator 19 as a color subcarrier for demodulation phase discrimination.

In this device, unlike conventional devices, the switching polarities of the first and third switches 13, 26 and the flip-flop 15 are not controlled in any way, so the switching signal output from the flip-flop 15 starts from which polarity. Accordingly, the polarity of the burst signal output from the first and third switches 13 and 26 and the color subcarrier differ, and the polarity becomes either A or B2 as shown in the figure. 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 added from the subtracter 4 and the fourth switch 2 must be
It is necessary that the polarity of the color subcarrier added from the third switch 26 matches correctly with the polarity of the color subcarrier added from the third switch 26.
If it is not known which of B2 will be the case, a situation may occur where the polarities of the two do not match.

Therefore, in this device, the phase discriminator 19 compares the color subcarrier polarity from the inversion circuit 25 and the polarity of the burst signal obtained from the second switch 17, and if the polarities of the two match, the phase One positive switching pulse is generated from the discriminator 19 to invert the flip-flop 18, and the second and fourth switches 17 and 28 are switched to the opposite side (RY) to output the color subcarrier to the demodulator 6. By switching the polarities, both polarities are matched and correct (RY) demodulation is performed. When the two polarities do not match and a negative pulse is being output, flip-flop 18 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, subtractor 4
The polarity of the carrier color signal applied to the (RY) demodulator 6 is +, -, +, - (1st H, 2nd H, 3rd H
4th H, and so on). Furthermore, the polarity of the (RY) axis component of the output burst signal of the second switch is determined when the first switch 13 is switched from the A side (or B side) first and the second switch 17 is switched from the A side (or the B side). If it has been switched to the side B (or side b), it will only be +, and if it has been switched from side B (or side A) first and then to side A (or side B), it will only be -. In conjunction with this, the polarity of the output color subcarrier for (RY) demodulation of the fourth switch 26 is determined by the fact that the third switch 26 is switched from the A side (or B side) first, and the fourth switch 26 If the switch 28 is switched to the a side (or b side), it will be +, -, +, -, and if it was switched from the B side or A side first and then switched to the a side (or b side). It becomes -, +, -, +. That is, if the polarity of the burst signal output from the second switch 17 is positive, it indicates that the phase of the color subcarrier from the fourth switch 28 to the (RY) demodulator 6 is correct; If it's old, it means it's wrong.

Therefore, in the first state, the first and third switches 13 and 26 are switched from the A side first, and the second and fourth switches 17 and 28 are switched from the A side.
Consider the case where the signal is switched to the side. At this time, since the polarity of the burst signal output from the second switch 17 is positive, no switching pulse is generated from the phase discriminator 19, and the correct (RY) demodulation operation is performed in the same switching state. It will be done. vice versa,
The first and third switches 13 and 26B are switched first, and the second and fourth switches 1
Similarly, in the second state where switches 7 and 28 are switched to the b side, the polarity of the burst signal output from the second switch 17 is +, and correct (RY) demodulation is performed.

However, in the third state, even though the first and third switches 13 and 26 are switched from the A side first, the second and fourth switches 17 and 2
6 is switched to the b side, the polarity of the carrier color signal to the (RY) demodulator 6 is +, -, +, -, but the output of the fourth switch 28 is Since the polarity of the color subcarrier becomes -, +, -, +, correct (RY) demodulation cannot be performed. Therefore, in this case, the phase discriminator 17 detects that the polarity of the burst signal from the second switch 17 is - in the first H, generates one switching pulse, and inverts the flip-flop 18. Switch the second and fourth switches 17 and 28 to the a side. Then, from the 2nd H onward, the carrier color signal output from the subtracter 4 and the polarity of the color subcarrier from the fourth switch 28 match -, +, -, +, and from then on, it is correct (R-Y ) Demodulation can be performed. After all, the polarity of the output of the fourth switch 28 at this time becomes -, -, +, - as shown in the figure. From the 2nd H onwards, since the polarities of the two match, the phase discriminator 19 no longer generates a switching pulse, and the correct (RY) demodulation operation continues as in the first state.

Conversely, as a fourth state, the second and fourth switches 17 and 28 are not switched to the A side even though the first and third switches 13 and 26 are switched from the B 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 19 at the 1H, the flip-flop 18 is inverted, and the second, fourth switch 17, 28 is switched to the b side, and from the 2nd H onward, correct (RY) demodulation is performed in the same manner as in the second state described above.

In this way, in this device, the polarity of the carrier color signal to the (RY) demodulator 6 and the When the polarities of the color subcarriers do not match, it is possible to match the polarities of the two by switching the second and fourth switches 17 and 28 only once, making it easy to perform correct (RY) demodulation. This is something that can be realized.

In the embodiment shown in FIG. 1, the phase discriminator 19 is provided on the output side of the burst gate 11 or on the output side of the first switch 13, so that a positive switching pulse is generated from the second switch 17. The flip-flop 18 may be inverted when the flip-flop is turned on.

In addition, the first switch 13 and the second switch 1
7 may be reversed, and furthermore, the order of the third switch 26 and fourth switch 28 may also be reversed.

Next, a second embodiment of the present invention is shown in FIG.
In this embodiment, the first switch 13 in the embodiment of FIG.
Y) It is moved to the color subcarrier supply side, and the inverting circuit 12 is shared with the inverting circuit 25. In this case, the basic demodulation polarity discrimination switching operation is the same as that in Figure 1, except that instead of switching the burst signal every 1H, the color subcarrier for the phase discriminator 19 is switched every 1H. Therefore, detailed explanation will be omitted.

In this embodiment as well, the phase discriminator 19 may be provided on the output side of the burst gate 11, and the order of the third and fourth switches 26 and 28 may be interchanged. Furthermore, the first switch 13 may be used in common with the third switch 26 to obtain the (RY) color subcarrier for the phase discriminator 19 from the output of the inversion circuit 27.

Further, a third embodiment of the present invention is shown in FIG. In this embodiment, the second switch 17 in the embodiment of FIG.
-Y) It is moved to the color subcarrier supply side, and the inverting circuit 16 is shared with the inverting circuit 25. In this case as well, the basic demodulation polarity discrimination switching operation is performed by simply switching the color subcarrier for the phase discriminator 19 instead of switching the burst signal when matching the (RY) demodulation polarity. Since it is the same as that shown in FIG. 1, detailed explanation will be omitted.

In this embodiment as well, the phase discriminator 19 may be provided on the output side of the burst gate 11, and the order of the third and fourth switches 26 and 28 may be reversed. Furthermore, when the order of the third and fourth switches 26 and 28 is reversed, the second switch 17 and the fourth switch 28 are used in common, and the (RY) color subcarrier for the phase discriminator is transferred to the inverting circuit 2.
It may be obtained from the output of 7.

Further, a fourth embodiment of the present invention is shown in FIG. In this embodiment, both the first and second switches 13 and 17 of the embodiment in FIG. It is shared with the inverting circuit 25. In this case as well, instead of switching the burst signal every 1H, the (R-
Y) The color subcarrier is switched every 1H, and the color subcarrier for the phase discriminator 19 is switched once instead of switching the burst signal once when matching the (RY) tone polarity. Since the demodulation polarity discrimination switching operation is the same as that shown in FIG. 1, detailed explanation will be omitted.

In this embodiment as well, the phase discriminator 19 to which the burst signal is added may be provided on the input side or the output side of the first switch 13. Further, the first switch 13 may be used in common with the third switch 26 so that the output signal is obtained from the inverting circuit 16 and the input signal of the second switch 17 is obtained from the inverting circuit 27. Furthermore, the order of the first switch 13 and the second switch 17 may be interchanged, or the order of the third switch 26 and the fourth switch 28 may be interchanged. If the order of both switches is changed, the second switch 17 and the fourth switch 2
8 may be used in common, and input signals for the first switch 13 and the inverting circuit 16 may be obtained from the inverting circuit 27.

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 fH/2 line switching signal whose phase is not controlled. A demodulation circuit can be realized.

[Brief explanation of the drawing]

FIGS. 1, 2, 3, and 4 are block diagrams of color demodulation devices according to embodiments 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...burst gate, 12...burst gate, 13...first Switch, 14...Horizontal pulse input terminal, 15...Flip-flop,
16...Inverting circuit, 17...Second switch, 1
8...Flip-flop, 19...Phase discriminator,
20...burst gate, 21...phase discriminator,
22... Color subcarrier oscillator, 23... 90° phase shifter, 24... Inverting circuit, 25... Inverting circuit, 26
...Third switch, 27...Inverting circuit, 28...
...The fourth switch.

Claims (1)

[Claims] 1. A carrier color signal of a PAL color television signal is applied to a (RY) demodulator, each of which has two input terminals and which is switched in conjunction with each horizontal scanning line. , a third switch is provided, and two
a second, which has two input terminals and is switched in conjunction;
a fourth switch is provided, and a path for directly applying the input signal and a path for inverting the input signal are connected to the two input terminals of the first switch to form a switching circuit;
A switching circuit is constructed by connecting a path for directly applying the input signal and a path for applying the input signal in reverse to the two input terminals of the second switch, and the two switching circuits and a phase discriminator are connected in cascade. The burst signal included in the PAL color television signal is added to the input terminal of the cascade connection circuit of
A switching circuit is constructed by connecting the input signal to the two input terminals of the fourth switch, and a switching circuit is constructed by connecting a path for directly applying the input signal and a path for applying the input signal by inverting the input signal to the two input terminals of the fourth switch. , a color width carrier wave whose polarity is fixed every horizontal scanning period is added to the input terminal of a second cascaded circuit in which these two switching circuits are cascaded, and the phase discriminator is connected to the output terminal of the second cascaded circuit. A color subcarrier is added to the (RY) demodulator, and the second and fourth switches are controlled by the output of the first cascaded circuit to output the carrier color signal and the second cascaded circuit. A color demodulating device characterized in that the polarities of the output color subcarriers are matched. 2. The carrier color signal of the PAL color television signal is applied to the (RY) demodulator, and first and third switches, each having two input terminals, are switched in conjunction with each other for each horizontal scanning line. and a second and fourth switch each having two input terminals and switching in conjunction, and a path for directly applying the input signal and a path for applying the input signal in reverse to the two input terminals of the second switch. The burst signal included in the PAL color television signal is applied to the input terminal of the first cascade connection circuit in which the switching circuit and the phase discriminator are connected in cascade to form a switching circuit, and the burst signal included in the PAL color television signal is applied every horizontal scanning period. A color subcarrier whose polarity is fixed and a color subcarrier whose polarity is inverted are applied to the two input terminals of the first switch.
The output color subcarrier of the third switch is added to the phase discriminator, and a path for directly applying the input signal and a path for inverting the input signal are connected to the two input terminals of the third switch to form a switching circuit. A switching circuit is constructed by connecting a path for applying the signal directly and a path for applying the signal in reverse to the two input terminals of the fourth switch, and a second cascade connection circuit in which these two switching circuits are connected in cascade. A color subcarrier whose polarity is fixed every horizontal scanning period is added to the input terminal, and this second
The output color subcarrier of the cascade connection circuit of (R-
Y) In addition to the demodulator, the output of the first cascade circuit controls the second and fourth switches to control the polarity of the color width carrier wave output from the carrier color signal and the second cascade circuit. A color demodulator characterized in that the color demodulation device matches the color. 3. The carrier color signal of the PAL color television signal is added to the (RY) demodulator, and the first and third switches each have two input terminals and are switched in conjunction with each other for each horizontal scanning line. a second and a fourth switch each having two input terminals and switching in conjunction; a path for directly applying the input signal and a path for inverting the input signal to the two input terminals of the first switch; The switching circuit and the phase discriminator are connected in series to form a switching circuit.
The burst signal included in the above PAL color television signal is added to the input terminal of the cascade connection circuit of In addition to the two input terminals of the switch, this first switch output color subcarrier is applied to the phase discriminator;
A switching circuit is constructed by connecting a path for directly applying the input signal and a path for applying the input signal in reverse to the two input terminals of the third switch, and a path for directly applying the input signal and a path for applying the input signal in reverse. A color sub circuit is connected to the two input terminals of the switch No. 4 to form a switching circuit, and the polarity is fixed for each horizontal scanning period to the input terminal of a second cascade connection circuit in which these two switching circuits are connected in cascade. adding a carrier wave and the output color subcarrier of this second cascaded circuit to the (RY) demodulator, and controlling the second and fourth switches by the output of the first cascaded circuit. A color demodulating device characterized in that the polarity of the carrier color signal and the output color subcarrier of the second cascade connection circuit are made to match. 4 The carrier color signal of the PAL color television signal is added to the (R-Y) demodulator, and first and third switches, each having two input terminals, are switched in conjunction with each other for each horizontal scanning line. a second and a fourth switch each having two input terminals and switching in conjunction; a path for directly applying the input signal and a path for inverting the input signal to the two input terminals of the first switch; A path for directly applying the input signal and a path for inverting the input signal are connected to the two input terminals of the second switch to form a switching circuit, and the two switching circuits and the phase A discriminator is connected in cascade to form a first cascade connection circuit, and a path for directly applying the input signal and a path for inverting and applying the input signal are connected to two input terminals of the third switch to form a switching circuit, A switching circuit is constructed by connecting the path for directly applying the input signal and the path for applying the input signal in reverse to the two input terminals of the fourth switch, and the two switching circuits are connected in cascade to form a second switching circuit.
A color subcarrier whose polarity is fixed in each horizontal scanning period is added to the input terminals of the first and second cascade connection circuits, and the output color subcarrier of the second cascade connection circuit (R -Y) In addition to the demodulator, the burst signal included in the PAL color television signal is added to the phase discriminator, and the first and fourth switches are activated by the output of the first cascaded circuit. A color demodulating device characterized in that the polarity of the carrier color signal and the output color subcarrier of the second cascaded circuit are controlled to match.