JPS5842383A - Switching circuit for line synchronism - Google Patents

Abstract

PURPOSE:To eliminate the titled circuit from being affected with external noise, while the line switching operation is performed, by making correction when the line switching operation is not normally executed. CONSTITUTION:A burst signal S5 obtained from a color signal of the PAL system is given to an input (a) of a switch 33 switchingly controlled with the output of a flip-flop 22 and given to an input (b) with a delay for one horizontal scanning period through a 1H delay line 31. The flip-flop 22 controls the line switching. A phase of an output signal of a contact (c) is detected with a reference demodulation carrier wave S6 of B-Y axis. An output of a phase detection circuit 3 makes the flip-flop 22 inoperative when the line switching is correctly done. When the line switching is not done correctly, the flip-flop 22 is controlled for normal operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present WA relates to a line synchronization switching circuit, and is particularly applicable to a PAL type cutout television receiver.

The mountain man style is a country #l & many countries that have adopted it in the blasphemy! Similar to the 'FF8C method, two-phase color sub-carrier liquids with a phase difference of 90'' are amplitude-modulated separately using two independent color difference signals (RY@ signal and ml-Y signal). The color tone carrier wave a whose amplitude is modulated by one color difference signal (B-Y1 signal) is transmitted.
m for each adjacent scanning line (i.e. 1 adjacent on the time axis)
A contrivance has been made to alternately invert (every horizontal scanning period of a scanning line) to be advantageous against phase distortion of the transmission line.

For such television signals, the receiver side identifies the phase of the carrier wave that is alternately switched, and also uses the phase of the burst signal that is sent as a phase reference of the one-color subcarrier wave to the phase of the other carrier wave that is not switched. By rotating each adjacent scanning line by ±ζ with respect to the phase of the color carrier wave (hereinafter referred to as a phase-fixed carrier wave), a color difference signal is generated from a color carrier wave whose phase is inverted (hereinafter referred to as a phase-inverted carrier wave). (
5 to reproduce the R-Y signal).

Incidentally, for the n-th fin, as shown in the first picture, the phase of the phase-fixed carrier wave (my signal lI) is inverted, the phase of the carrier wave (RY signal side) is advanced by 90', and the burst signal is A phase relationship is created in which the phase of is further advanced by d. Regarding the next (n+1)th twin, as shown in the first till(B)K, the phase of the phase-inverted carrier wave is delayed by 90 degrees with respect to the phase-fixed carrier wave, and the phase of the burst signal is further delayed by 45 degrees. Then the nth
+11th line, nth + 3rd line, etc., in Figure 1 (as shown in 0, 5, the above-mentioned nth,
The same phase relationship as described above for the (n+11)th line is alternately obtained.

Therefore, in a PAL system receiver, when demodulating a color difference signal (RY signal) from a phase-inverted carrier wave, the phase of the demodulating subcarrier wave supplied to the demodulator is simply inverted for each scanning line. Rather, it is necessary to provide the correct displacement relationship as described above with respect to FIG. 1 (5) to ρ with respect to the phase of the color difference signal that is currently arriving. To do this P
In the AL method, in order to identify the phase inversion state of the phase-inverted carrier wave, the phase of the burst signal is alternately changed by ±6° symmetrically with respect to the phase axis orthogonal to the phase axis of the phase-inverted carrier wave. (for each adjacent scanning line), and transmits this burst signal to the receiver.The phase of this burst signal is detected when the receiver is turned sideways, and the phase switching operation of the demodulating carrier wave is synchronized with the transmitting side. configuration has been adopted.

By the way, in the conventional PAL receiver, K(
In other words, the burst signal whose phase rotates between adjacent horizontal scanning periods on the time axis is phase-discriminated using the reference color subcarrier to obtain an identification signal at frequency 4 of the line frequency (i.e., horizontal waterfall frequency fH). 5KL was used to synchronize the line switching operation directly with this identification signal.

However, in this conventional line switching synchronous circuit, the phase discrimination result of the burst signal was obtained as an AC voltage, so a simple integrating circuit could not be applied as a noise removal means, and a nine-phase It was necessary to prepare a high-Q resonant circuit that resonates at the repetition frequency (ie, 2'H) of the identification signal. However, such a resonant circuit that resonates at a relatively low frequency and has a high Q is expensive because it has a special configuration, and the synchronous circuit is still operating even when the line switching operation is performed correctly. It had the disadvantage of becoming unstable due to noise.

In consideration of the above points, the present invention provides a line switching synchronization circuit for a PAL color television receiver that can realize sufficiently stable line switching operation without using any special parts.5. It is something.

An example of the present invention will be described in detail below with reference to the drawings.
In order to correctly demodulate the PAL color signal described above for 4 to 0, it is sufficient to synchronize the phase of the reference carrier wave for synchronous demodulation with the phase of the carrier color signal sent from the transmission side and invert it for each scanning line. . In order to achieve synchronization at the time of reversal as described above, the second WA) C is constructed as shown in 5.

In FIG. 2, a television signal received by an antenna (1) is detected in a receiving circuit (2) after being converted into an intermediate frequency signal, and sent out as a composite video signal S1 and an audio intermediate frequency signal 82. The intermediate frequency signal S2 is demodulated by the audio circuit (3) and given to the speaker (4).

On the other hand, [the composite video signal 81 is first suppressed by the trap circuit 2], the color subcarrier signal component (4, 48 pm) is suppressed, and the luminance fIe signal 83 is processed by the luminance signal processing circuit (6). It is given to the rear matrix circuit (7).

In addition to this, [the composite video signal 81 is given to a second band pass filter (8) K, the luminance signal S3 is removed [ ACC amplifier circuit)-) k is given. From that output burst game) II path (10) K
Therefore, the burst signal Ss on the back porch of the horizontal synchronization signal is extracted, and the level of the burst signal S5 is detected in the λCC detection circuit (11), and the detection output is used to detect the burst signal Ss in the CACC amplifier circuit (by controlling the gain of the signal). The level of signal 85 is controlled to be constant.

In addition, the burst signal S60 level obtained from the burst goo II path (10) is detected by the killer counting circuit (12), and when the detection level becomes lower than the expected level, it is determined by the detection signal of the circuit detection circuit (12). The killer amplifier circuit (13) is controlled, thus the ACC amplifier circuit-
) The ecJ two-key operation is performed so that the conveyed color No. 1 S4 obtained at the output terminal of

Furthermore, the burst signal 85 obtained from the burst gate circuit (l) is transmitted to the phase detection circuit (1
6) k is given and the phase is compared with the output of a continuous wave oscillator (17) that generates a continuous wave for demodulation. The output of this phase detection circuit (16) is smoothed by a low-pass filter (18) with a relatively long time constant, and the smoothed output is provided as a control signal to the continuous wave oscillator (17).

Here, the phase of the burst signal rotates by soo for each scanning line, but the time constant of the low-pass filter (18) is
If the period is sufficiently long compared to the horizontal period, the phase of the burst signal will be averaged, and thus the phase of the phase-locked carrier wave B-
A -(B-Y) signal having an opposite phase to the Y signal is sent out from the low-pass filter (1g). And this - (B
-Y) signal controls the continuous wave oscillator (17) so that when this continuous wave oscillator (17) is oscillating at the phase of the R-Y signal, the output of the phase detector (10) becomes O. Automatic phase control (APC) control is performed.

The output 86 of this continuous wave oscillator (17) is phase-shifted by the phase shift circuit (east) 90@ and then supplied to the BY signal demodulation circuit COD') as a demodulation reference-transmission wave. More continuous show m
The output of (17) is applied to one fixed contact (b) of the line changeover switch (inside) and is also applied to the other fixed contact (b) via the phase inverter circuit (14), and thus the line changeover switch When (21) is switched to the movable contact (contact (II) or C) by the switching signal generation circuit consisting of 7 lip-flop circuits (2), the movable contact (c) is switched to the R-Y signal demodulation circuit ( 23) K4
) The reference carrier wave for demodulation whose phase is inverted between scanning and R-
It is supplied to the Y signal demodulation circuit (23).

On the other hand, the output of the aforementioned killer amplifier (13) is delayed by one horizontal period in the IH delay line (25), and then
It is added to the non-delayed output in the adder circuit (26) and subtracted from the non-delayed output in the subtraction circuit (5). Thus, the addition circuit (26) and the subtraction circuit (5
), the B-Y axis color signal component and the R-Y axis color signal component are obtained, and these signals are sent to the B-Y demodulation circuit (20) and the R-Y demodulation circuit (23), respectively.
) is given to

In this way, the B-Y signal and R-Y signal obtained from the B-Y demodulation circuit (2o) and the R-Y demodulation circuit (23) are given to the matrix circuit σ), and the red, green, and blue signals are reproduced, respectively. be done.

The above configuration is the basic configuration of a conventional PAL signal demodulation circuit, and the flip-flop circuit (22) that controls the line changeover switch (2I) is simply inverted by an H pulse. Therefore, there is no guarantee that the setting and resetting operations of the flip-flop circuit (22) will be performed in synchronization with the inverted state of the RY axis of the color signal that is currently arriving.

However, in addition to the above configuration, the present invention allows the burst signal S5 obtained by the burst gate circuit (10) to be switched to one side of the burst changeover switch (33) which is controlled by the output of the clip 2 wrap circuit (22). Fixed contact (a) I
At the same time as cII contact, the kite is connected for one horizontal scanning period through the IH delay line (31) to the other constant contact point.
give to Then, the output 89 obtained at the movable contact (C) is phase detected in the phase detection circuit (34) using the BY-axis reference demodulation carrier wave S6 obtained at the output end of the above-mentioned continuous wave generation II circuit (17). do.

The output 811 of the 10th phase phase detection circuit 34) is smoothed in the x filter (A) and converted into a DC level voltage to provide the operation control signal 8 of the flip-flop circuit (22).
It is used as 12. Here, the DC voltage level of the output 812 of the four-bass filter (■) is selected to be such that it forces the flip 70 two-way ('t) into the inactive state when properly synchronized switching operation is performed. On the other hand, if it is incorrect, the size is selected to control the flip-flop and correct it to the correct operating state.

The above configuration operates as follows. If the current switching operation of the burst selection switch (0) is correct, the inversion operation of the flip-flop circuit C22) is in phase with the phase switching operation of the incoming burst signal Ss, so the twin switching is performed. during switching) also switches correctly. At this time, the burst signal S5 obtained at the contact (C) of the changeover switch (33) is transmitted at time 1 in FIG. 3 (6) for each scanning line.
1 e t2...K occurs at a phase position d advanced from the R-Y axis as shown. Incidentally, when the burst signal shown in the first garden is obtained from the contact (I&) to the contact (c) at time tl, the burst signal at this time is the IH delay twin (
31), and at the next time t2, when the contact (C) switches to the contact 伽), it becomes the contact (C) again, and at the next time t3, the contact (<1) changes to the contact (1). This is because the burst signal shown as Ok in FIG. 1 has already arrived when the switch is made.

This burst signal is passed through the phase detection circuit (34) to R-
When phase detection is performed using the Y-axis carrier wave (FIG. 3 @), a continuous positive pulse is obtained at each time point as a detection output 811 as shown at 311qK. Therefore, the low-pass filter (35)
As shown in FIG. 3, the control signal SL2 is, for example, a positive DC level voltage. However, this positive DC level control signal 812 allows the flip-flop circuit (22) to operate freely, and therefore, the flip-flop circuit (22) operates inverted by the H pulse.

Next, if the operating state of the flip 70 tube circuit (22) is incorrect, the switching states of the line changeover switch (21) and the burst changeover switch (33) will change at the 411th (A) time point t.
The burst signal is -(R-Y
) occurs at a phase position l behind the axis. Incidentally, this is because the operation is the same as in the correct case described above except for the phase of the burst signal.

This burst signal is passed through the phase detection circuit (34) to R-
When phase detection is performed using the Y-axis carrier wave 86 (Fig. 4 @), the detection output 811 is obtained as the detection output 811 at time 00 in Fig. 4 t□1 e tig
-...K negative pulse outputs all as shown are continuously obtained. Therefore, the four-bass filter 05) smoothes this negative pulse and sends out a control signal S12 which is a negative DC level voltage output as shown in FIG. 4 ρ. However, this negative DC level control signal 812 puts the flip-flop circuit (22) in an inoperable state, and prevents the input of the H pulse to the 7-rip 70-tube link (22), for example, so that the flip-flop circuit (22) is turned off. Do not allow the trio of road (7)). Follower [frig 7W tube circuit (2
2) stops in the set or reset state.

When the flip-flop circuit (22) stops in this way, the burst changeover switch (33) switches to the contact (a) connected to the input end of one switching state (for example, IH delay line C31). ) to maintain. Therefore, at this time, the burst changeover switch (33).

4c) The resulting burst signal is at time t! in FIG. 5(g). 1@tg ・・・・・・ As shown in 5, R-Y
It will alternately switch between a state in which it is d ahead of the axis and a state in which it is delayed by d from the -(RY) axis. Therefore, 1 in this state is the carrier wave of the phase detection circuit (34) on the R-Y axis -5l
The phase detection output 811 from a@y becomes a pulse that alternately changes to positive or negative every 6 scanning lines as shown in FIG.
2 becomes OK as shown in FIG. 5 Φ.

When this state occurs, the flip-flop circuit (22
) in the correct switching state and start the trigger again.5
tC, the edge will operate in the correct switching state.

As described above, according to the configuration shown in FIG. 2, the switching output generated by the phase switching operation of the burst signal based on the H pulse formed in the receiver is transferred by the currently arriving R-Y axis carrier wave. By performing phase detection, if an error occurs in the switching operation, it can be easily corrected.

Furthermore, as mentioned above, when the flip-flop circuit (22) is forced into a non-operating state, it is possible to prevent the negative shadow from occurring in the color circuit. Incidentally, in a one-stage KPAL type cup television receiver (not shown), for example, the output of a flip-flop circuit (22) is used to control a color killer when the switching operation is interrupted. This is because when flip 7a (2) is inactive, the cutter is activated and becomes 5 without any color.

Furthermore, when the correct switching operation is performed as described above, a gate circuit is provided on the output side of the 1-phase horizontal tILWA path (34), and this gate circuit is connected to, for example, the 00 pulse signal 811 in FIG.
By performing the gate operation according to the above, the possibility of malfunction occurring can be further reduced.

Furthermore, in the above example *, the phase of the reference carrier wave for demodulation for the RY signal was inverted between the scanning line and the scanning line, but instead of this, the reference carrier wave for demodulation was fixed and the phase was subtracted. A phase inverter and a line changeover switch may be inserted in the path of the color signal obtained at the output end of the circuit (27) to switch the phase of the color signal.

Furthermore, in the above description, the burst signal s5 is detected in the AcC detection circuit (11) and the killer detection circuit (l) to control the NΣ amplifier circuit (9) and the killer amplifier circuit (dog), respectively. Side paths <11) and (12) are omitted; instead, the phase detection circuit (34
) is obtained by smoothing the output 811 of the low-pass filter (
35) may be used for control using the output S12.

Furthermore, in the above description, the inversion operation of the flip-flop circuit (22) is forcibly suppressed when an incorrect switching operation is performed, but instead of this, the flip-flop circuit (22) is forcibly suppressed.
)) It may be possible to control the reversal operation of the switch itself and not to send out the switching output. In this case, if the correct switching operation is restored, the low-pass filter (
Since the voltage level of 35) is inverted, it is possible to automatically cancel the prohibition of switching output.

FIG. 6 shows another embodiment of the present invention, in which parts corresponding to those in FIG.
H delay line (31) is omitted and the changeover switch (3
Contacts (a) and (b) of 3) are connected to the BY signal and RY signal demodulation circuit @) and the 1-day lay-in (23) of
5) Even if you connect it to both ends, it will not work.

In this way, one IH delay-in can be omitted.

N: J40) is a burst gate circuit for increasing the accuracy of operation. At this time, the person (9) and the amplification circuit (
9) and as a control signal for the killer amplifier circuit (13).

As described in 5 above, according to the present invention, it is possible to correctly switch the phase of a burst signal based on the carrier wave arriving at IIK. By using a circuit and a four-pass filter, the configuration can be simplified compared to the conventional configuration. In addition, by setting 5 so that the line switching operation is corrected based on the currently arriving signal only when the line switching operation is incorrect, and not corrected when the line switching operation is correct, it is possible to prevent external noise from occurring while the line switching operation is being performed correctly. It is possible to avoid shadow change, and the operation can be made more stable than in the conventional case.

[Brief explanation of the drawing]

FIG. 1 is a vector diagram for explaining a burst signal included in a PAL color television signal, FIG. 2 is a block diagram showing an example of a line synchronization switching circuit according to the present invention, and FIGS. 4 and 5 are explanations of the operation of FIG. 2, and FIG. 6 is a block diagram showing another embodiment of the present invention. (2)...Reception circuit, (5)...Trap circuit, (
6)...Brightness processing circuit, (7)...Matrix circuit, (8)...Band pass filter, (9)...AC
C increase @ circuit, (10) ... burst gate circuit, (1
1)...ACC detection circuit, (12)...Killer detection circuit, (13)...Killer amplification circuit, (15)...
Automatic phase control circuit, (16)...detection circuit, (17)
Continuous wave oscillator, (18) Low pass filter, (19) -90' phase shift circuit, (20) -B-Y signal demodulation circuit, (21) Line selection switch, ( 2
2) :...Flip-flop circuit, (23)...R
-Y signal demodulation circuit, (25)...IH delay line, (26)...addition circuit, (27)...subtraction circuit,
(31)...IH delay line, (33)...Burst selection switch, (34)...Phase detection circuit, (
35)...Low pass filter, (40)...Burst gate circuit.

Claims (1)

[Claims] The first and third color subcarriers having a phase difference are then modulated by the first and third independent color difference signals, and each scan line is 1st
At the same time as inverting the phase of the tone carrier wave and transmitting it to the receiver, the receiver receives the above-mentioned first O transport! The phase of the burst signal is also used as a reference for identifying the phase state of the liquid, and the phase of the burst signal is made to correspond to the inverted state of the phase of the first carrier wave. 'f) Since the axis of the carrier wave is changed as a target, there is an IH delay twin that makes the above burst signal continuously fly for the IH time, and El! on both ends of this IH delay twin. Selective input and output of Todoroki IH delay twin
a phase detection circuit that detects the phase of the output of the pulse F signal switching circuit using the second carrier wave; Line synchronization characterized by comprising a switching signal generation circuit that synchronizes the line switching circuit that switches the phase of color 414# and generates a switching signal that causes switching operation to be performed or not to be performed between the Ichitaki pot and the other. Switching path.