JPH033990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line synchronous switching circuit, and particularly to a line synchronous switching circuit.
It is applied to PAL color television receivers.

The PAL system is a color television system adopted by many countries in Europe. Similar to the NTSC system, the PAL system uses two-phase color subcarriers with a phase difference of 90 degrees to produce two mutually independent color difference signals (R-Y signals). and B-Y signal) and are separately amplitude-modulated and transmitted. Then, the phase of the color subcarrier that is amplitude-modulated by one color difference signal (R-Y signal) is alternated for each adjacent scanning line (that is, for each horizontal scanning period of one adjacent scanning line on the time axis). A contrivance has been devised to be advantageous for the phase distortion of the transmission line by inverting the signals.

For such a television signal, the receiver side identifies the phase of the carrier wave which is alternately switched and is sent as a phase reference for the color subcarrier wave. The phase of the burst signal is adjusted ± for each adjacent scanning line based on the phase of the other color carrier wave whose phase is not switched (hereinafter referred to as phase-locked carrier wave).
By rotating it by 45 degrees, a color difference signal (RY signal) is reproduced from a color carrier wave whose phase is inverted (hereinafter referred to as a phase-inverted carrier wave). By the way, for the nth line, Figure 1A
Phase-locked carrier wave (B-Y signal side) as shown in
The phase of the phase-inverted carrier wave (RY signal side) is advanced by 90 degrees with respect to the phase of , and the phase of the burst signal is further advanced by 45 degrees. Regarding the next (n+1)th line, as shown in FIG. 1B, 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. After that, as shown in FIG.
A phase relationship similar to that described above for the 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 supplied to the demodulator is simply inverted for each scanning line. Instead, it is necessary to provide the correct phase relationship as described above with respect to FIGS. 1A to 1D with respect to the phase of the currently arriving color difference signal. In order to do this, in the PAL system,
In order to identify the phase inversion state of the phase inverted carrier wave, the phase of the burst signal is symmetrically ±± with respect to the phase axis orthogonal to the phase axis of the phase inverted carrier wave.
Rotate by 45 degrees alternately (for each adjacent scan line),
A configuration is adopted in which this burst signal is transmitted to the receiver, the receiver side detects the phase of the burst signal, and the phase switching operation of the demodulating carrier wave is synchronized with the transmission side.

By the way, in conventional PAL receivers, as a line switching synchronization circuit for switching the phase of the demodulating carrier wave in synchronization with the transmitting side,
A burst signal whose phase rotates for each adjacent scanning line (i.e., for each adjacent horizontal scanning period on the time axis) is phase-discriminated using a reference color subcarrier, and is converted to 1/1 of the line frequency (i.e., horizontal scanning frequency f _H ). A device was used in which an identification signal with a frequency of 2 was created and line switching operations were directly synchronized using this identification signal.

However, in this conventional line switching synchronous circuit, the phase discrimination result of the burst signal is obtained as an alternating current voltage, so a simple integrating circuit cannot be used as a noise removal means.
Instead, it was necessary to prepare a high-Q resonant circuit that resonates at the repetition frequency (ie, 1/2f _H ) of the phase 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. The drawback was that it became unstable due to noise.

Considering the above points, the present invention can realize sufficiently stable line switching operation without using any special parts.
The present invention attempts to provide a line switching synchronization circuit for PAL color television receivers.

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 with reference to Figures 1A to D, the phase of the reference carrier wave for synchronous demodulation is synchronized with the phase of the carrier color signal sent from the transmission side, and the phase is inverted for each scanning line. That's fine. In order to achieve synchronization at the time of reversal in this way, the configuration is as shown in FIG. 2.

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

On the other hand, the composite video signal S1 is first processed in the trap circuit 5 by the color subcarrier signal component (4.43M
Hz), and the luminance signal S3 is processed by the luminance signal processing circuit 6 and then supplied to the Strix circuit 7.

In addition, the composite video signal S1 is secondly applied to a bandpass filter 8, where the luminance signal S3 is removed and a chromaticity signal containing a carrier color signal S4 and a burst signal S5 is output to an automatic color control amplifier circuit (ACC amplifier). circuit) given to 9. The burst signal S5 in the back porch of the horizontal synchronizing signal is extracted from the output by the burst gate circuit 10, and the ACC
The level of the burst signal S5 is detected in the detection circuit 11, and the burst signal is detected by controlling the gain of the ACC amplifier circuit 9 based on the detected output.
The level of S5 is controlled to be constant.

Further, the level of the burst signal S5 obtained from the burst gate circuit 10 is detected by the killer detection circuit 12, and when the detection level becomes below a predetermined level, the killer amplifier circuit 13 is controlled by the detection signal of the killer detection circuit 12. And thus
Carrier color signal obtained at the output end of the ACC amplifier circuit 9
Execute color killer operation so as not to apply S4 to the subsequent demodulation circuit.

Furthermore, the burst signal S5 obtained from the burst gate circuit 10 is given to the phase detection circuit 16 of the automatic phase circuit 15, and its phase is compared with the output of a continuous wave oscillator 17 that generates a continuous wave for demodulation. The output of the phase detection circuit 16 is smoothed by a low-pass filter 18 having 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 is determined for each scanning line.
Although it rotates by 90 degrees, if the time constant of the low-pass filter 18 is made sufficiently long compared to one horizontal period, the phase of the burst signal is equivalently averaged, and thus the phase is opposite to that of the B-Y signal of the phase-fixed carrier wave. -(B-
Y) signal will be sent out from the low pass filter 18. This -(B-Y) signal controls the continuous wave oscillator 17 so that when the continuous wave oscillator 17 is oscillating with the phase of the R-Y signal, the output of the phase detection circuit 16 becomes 0. Perform phase control (APC) control.

The output S6 of the continuous wave oscillator 17 is phase-shifted by a 90° phase shift circuit 19 and then supplied to a BY signal demodulation circuit 20 as a reference carrier wave for demodulation. Further, the output of the continuous wave oscillator 17 is applied to one fixed contact a of the line changeover switch 21, and is applied to the other fixed contact b via the phase inversion circuit 14, so that the line changeover switch 21 is formed by a flip-flop circuit 22. As the movable contact c is alternately switched to contact a or b by the switching signal generation circuit, a demodulation reference carrier wave whose phase is inverted for each scanning line is sent from the movable contact c to the R-Y signal demodulation circuit 23. The signal is supplied to the Y signal demodulation circuit 23.

On the other hand, the output of the killer amplifier 13 described above is delayed by one horizontal period in the 1H delay line 25, and then added to the non-delayed output in the addition circuit 26 and subtracted from the non-delayed output in the subtraction circuit 27. In this way, the B-Y axis color signal component and the R-Y axis color signal component are obtained at the output ends of the adder circuit 26 and the subtracter circuit 27, respectively, and these signals are sent to the B-Y demodulation circuit 20 and the R-Y axis, respectively.
−Y demodulation circuit 23;

In this way, the B-Y demodulation circuit 20 and the R-Y
B-Y signal and R-Y obtained from demodulation circuit 23
The signals are applied to the matrix circuit 7, and red, green, and blue signals are reproduced, respectively.

The above configuration is the basic configuration of a conventional PAL signal demodulation circuit, and the line selection switch 21
The flip-flop circuit 22 which controls the flip-flop circuit 22 was designed to perform an inversion operation simply by an H pulse. Therefore, there is no guarantee that the setting and resetting operations of the flip-flop circuit 22 are synchronized 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 provides a burst signal S5 obtained by the burst gate circuit 10,
The signal is applied directly to one fixed contact a of a burst changeover switch 33 which is controlled by the output of the flip-flop circuit 22, and is applied to the other fixed contact b after being delayed by one horizontal scanning period through a 1H delay line 31. Then, the phase detection circuit 34 performs phase detection on the output S9 obtained at the movable contact c using the BY-axis reference demodulation carrier S6 obtained at the output end of the continuous wave oscillation circuit 17 described above.

The output S11 of the phase detection circuit 34 is smoothed by a low-pass filter 35, converted to a DC level voltage, and used as the operation control signal S12 of the flip-flop circuit 22. Here, the DC voltage level of the output S12 of the low-pass filter 35 is selected to a level that forces the flip-flop circuit 22 into a non-operating state when the switching operation is correctly synchronized; It is sized to control and correct circuit 22 to correct operating conditions.

The above configuration operates as follows. If the switching operation of the burst selection switch 33 is correct now,
Since the inversion operation of the flip-flop circuit 22 is correctly synchronized with the phase switching operation of the incoming burst signal S5, the line changeover switch 21 also performs the correct switching operation. At this time, the burst signal S5 obtained at the contact point c of the changeover switch 33 is transmitted from R to Y as shown at time t ₁ , t ₂ .
Occurs at a phase position 45° ahead of the axis. By the way, at the time
When the burst signal shown in Figure 1A is obtained from contact a to contact c at t ₁ , the burst signal at this time is 1H.
It is delayed by the delay line 31, and when contact c switches to contact _b at the next time t2, it becomes contact c again, and when contact c switches to contact a at the next time _t3 , it has already reached the first contact point. This is because the burst signal shown in FIG. C has arrived.

When this burst signal is phase-detected using the RY-axis carrier wave (FIG. 3B) in the phase detection circuit 34, positive pulses are successively obtained at each time point as the detection output S11, as shown in FIG. 3C. Therefore, the low-pass filter 35 sends out a control signal S12 consisting of, for example, a positive DC level voltage, as shown in FIG. 3D. However, this positive DC level control signal S12 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-flop circuit 22 is incorrect, the switching states of the line changeover switch 21 and the burst changeover switch 33 will change as shown in FIG. 4A.
As shown in t ₁₁ , t ₁₂ ..., the burst signal is -(R-
This occurs at a phase position that is 45° behind the Y) 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.

When this burst signal is phase-detected by the RY-axis carrier wave S6 (FIG. 4B) in the phase detection circuit 34, the detected output S11 is obtained at time points t ₁₁ , t ₁₂ . . . in FIG. 4C.
Negative pulse output S11 as shown in ... is continuously obtained. Therefore, the low-pass filter 35 smoothes this negative pulse and sends out a control signal S12 which is a negative DC level voltage output as shown in FIG. 4D. However, this negative DC level control signal S12 forces the flip-flop circuit 22 into a non-operating state, for example, prevents the input of the H pulse to the flip-flop circuit 22, thereby preventing the flip-flop circuit 22 from being triggered. The flip-flop circuit 22 therefore remains in the set or reset state.

When the flip-flop circuit 22 is stopped in this way, the burst changeover switch 33 maintains one switching state (for example, the state switched to the contact a connected to the input end of the 1H delay line 31). Therefore, the burst signal obtained at contact c of the burst changeover switch 33 at this time is at the time point A in FIG.
As shown in t ₂₁ , t _{22 .} . . , the state is alternately switched between a state of 45° leading from the RY axis and a state of 45° behind the −(RY) axis. Therefore, in this state, the phase detection output S11 by the RY-axis carrier wave (FIG. 5B) of the phase detection circuit 34 alternately changes to positive or negative for each scanning line as shown in FIG. 5C. The low-pass filter 35 at this time becomes a pulse.
The smoothed output S12 becomes 0 as shown in FIG. 5D.

When this state occurs, if the flip-flop circuit 22 is triggered and started again in the correct switching state, it will thereafter 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 within the receiver is converted into the currently arriving R-Y axis carrier wave. By performing phase detection using , it is possible to easily correct any errors that occur in the switching operation.

Furthermore, as described above, when the flip-flop circuit 22 is forced into a non-operating state, it is possible to prevent the adverse effect from occurring on the color circuit. Incidentally, although not shown in the drawings, generally in PAL color television receivers, for example, the output of the flip-flop circuit 22 is used to control a color killer when the flip-flop circuit 22 interrupts its switching operation.
This is because when the flip-flop circuit 22 is inactive, the color killer is activated and no color is applied.

Furthermore, when the correct switching operation is performed as described above, a gate circuit may be provided on the output side of the phase detection circuit 34, and this gate circuit may be gated by, for example, the pulse signal S11 shown in FIG. 3C. For example, the possibility of malfunctions occurring can be further reduced.

Furthermore, in the above embodiment, the phase of the demodulation reference carrier wave for the R-Y signal is inverted for each scanning line, but instead of this, the demodulation reference carrier wave is fixed and the subtraction circuit 27 The phase of the color signal may be changed by inserting a phase inverter and a line changeover switch in the path of the color signal obtained at the output end.

Furthermore, in the above, the burst signal S5 is
Although the ACC detection circuit 11 and the killer detection circuit 10 detect the waves and control the ACC amplifier circuit 9 and the killer amplifier circuit 13, respectively, these detection circuits 11 and 12 are omitted and replaced with
The output S12 of the low-pass filter 35 obtained by smoothing the output S11 of the phase detection circuit 34 may be used for control.

Furthermore, in the above description, the inverting operation of the flip-flop circuit 22 is forcibly suppressed when the flip-flop circuit 22 performs an erroneous switching operation, but instead, the inverting operation of the flip-flop circuit 22 itself is not suppressed, and the switching output is not sent out. It may be controlled as follows. In this case, if the correct switching operation is restored, the voltage level of the low-pass filter 35 is inverted accordingly, so that the inhibition of switching output can be automatically canceled.

FIG. 6 shows another embodiment of the present invention, in which the 1H delay line 31 is omitted and the changeover switch 33 is shown with the same reference numerals assigned to corresponding parts as in FIG. 2 to show only the essential parts. The contacts a and b may be connected to both ends of the 1-delay line 25 of the demodulation circuits 20 and 23 for the BY signal and the RY signal. In this way, one 1H daylay line can be omitted. Note that 40 is a burst gate circuit for increasing the accuracy of operation. At this time, as described above with reference to FIG. 2, the output of the burst filter 35 is
It may also be used as a control signal for the ACC amplifier circuit 9 and the killer amplifier circuit 13.

As described above, according to the present invention, it is possible to correctly switch the phase of a burst signal based on the currently arriving carrier wave, but a phase detection circuit is used to output a determination as to whether or not the phase switching of the burst signal is correct. By using a low-pass filter and a low-pass filter, the configuration can be simplified compared to the conventional configuration. In addition, by making a corrective action based on the currently arriving signal only when the line switching action is incorrect, and not performing the corrective action when the line switching action is correct, the negative effects of external noise can be avoided while the line switching action is being performed correctly. Therefore, 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. Fifth
This figure is a signal waveform diagram for explaining the operation of FIG. 2, and FIG. 6 is a block diagram showing another embodiment of the present invention. 2... Receiving circuit, 5... Trap circuit, 6...
Brightness processing circuit, 7... Matrix circuit, 8... Bandpass filter, 9... ACC amplifier circuit, 10
... Burst gate circuit, 11 ... ACC detection circuit, 12 ... Killer detection circuit, 13 ... Killer amplifier 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 changeover switch, 22...flip-flop circuit, 23...R
-Y signal demodulation circuit, 25...1H delay line,
26...addition circuit, 27...subtraction circuit, 31...
1H delay line, 33... Burst selection switch, 34... Phase detection circuit, 35... Low pass filter, 40... Burst gate circuit.

Claims (1)

[Claims] 1. The first and second color subcarriers having a phase difference of 90 degrees from each other are individually amplitude-modulated by mutually independent first and second color difference signals, and the first color is modulated for each scanning line. The phase of the burst signal is used as a phase reference of the reference color subcarrier to invert the phase of the subcarrier and transmit it to the receiver, and the receiver identifies the phase state of the first carrier. The phase of the burst signal is set to the first
In response to the phase inversion of the carrier wave, the second
In a color television receiver that changes the axis of the carrier wave symmetrically,
1H to delay the above burst signal by 1H time
A delay line, a burst signal switching circuit that is connected to both ends of this 1H delay line and selectively takes out the input and output of the 1H delay line, and the output of this burst signal switching circuit is connected to the second terminal.
A phase detection circuit that performs phase detection using a carrier wave, and a line switching circuit that switches the phase of the switching circuit and the demodulating carrier wave or the carrier color signal in accordance with the phase detection output are synchronized to perform a switching operation for each scanning line, or A line synchronous switching circuit characterized by comprising a switching signal generation circuit that generates a switching signal that does not cause a switching operation.