JPH033991B2 - - 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 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 sent as a phase reference for the color subcarrier to identify the phase of the other color whose phase is not switched. Carrier wave (hereinafter referred to as phase-locked carrier wave)
By rotating each adjacent scanning line by ±45° with respect to the phase of is being done.
Incidentally, for the n-th line, as shown in Figure 1A, the phase of the phase-inverted carrier wave (RY signal side) is advanced by 90 degrees with respect to the phase of the phase-fixed carrier wave (B-Y signal side), and the burst is generated. A phase relationship is created in which the signal phase is further advanced by 45 degrees. Also the next nth
For the +1st line, as shown in Figure 1B, the phase of the phase-inverted carrier wave is delayed by 90 degrees with respect to the phase-locked carrier wave, and the burst signal is further
Delay by 45°. Thereafter, as shown in FIG. 1C and D for the n+2nd, n+3rd, . . . lines, the same phase relationship as described above for the nth and n+1st lines is alternately obtained. ing.

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. 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 a receiver, the phase of this burst signal is detected on the receiver side, and the phase switching operation of the demodulating carrier wave is synchronized with that on 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 1D, it is necessary 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. good. 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. It is demodulated by the circuit 3 and given to the speaker 4.

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 amplification circuit (ACC amplification circuit). 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 control 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 S5 rotates by 90 degrees for each scanning line, but 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 S5 is equivalently averaged. , thus the B-Y signal of the phase-locked carrier wave and the -
A (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. Performs 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 reference carrier wave for demodulation whose phase is inverted for each scanning line is transmitted from the movable contact c to the R-Y signal demodulation circuit 23 for demodulation. Supplied as a reference carrier.

On the other hand, the output S4 of the killer amplifier 13 described above is delayed by one horizontal period in the 1H delay line 25, and then output without delay in the adder circuit 26.
S4 and is subtracted from the non-delayed output S4 in the subtraction circuit 27. Thus, the output terminals of the adder circuit 26 and the subtracter circuit 27 have B
-Y-axis color signal component S7 and RY-axis color signal component S8 are obtained, and these signals S7 and S8 are applied to BY demodulation circuit 20 and RY demodulation circuit 21, respectively.

In this way, the B-Y demodulation circuit 20 and the R-Y
B-Y signal and R-Y obtained from demodulation circuit 21
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 supplies the burst signal S5 obtained by the burst gate circuit 10 to the 90° phase lead circuit 31 and the 90° phase lag circuit 32, and sends the outputs to the outputs of the flip-flop circuits 22, respectively. Therefore, the fixed contacts a and b of the burst changeover switch 33, which are controlled, are respectively applied. And the output obtained at movable contact c
S9 is phase-detected in the phase detection circuit 34 using the BY-axis reference demodulation carrier S10 obtained at the output end of the 90° phase shift circuit 19 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; The size is selected to control the flip-flop circuit 22 and correct it to the correct operating state.

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 S9 obtained at the contact point c of the changeover switch 33 is transmitted at times t ₁ , t _{2 .} . . of FIG.
The phase changes sequentially by ±45° around the axis.

When this burst signal S9 is phase-detected using the BY-axis carrier wave (FIG. 3B) in the phase detection circuit 34, positive pulses are continuously obtained at each time point as the detection output S11 as shown in FIG. 3C. . Therefore, the low-pass filter 35 smoothes this positive pulse, thereby sending out, for example, a positive DC level voltage output S12 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 12 performs an inverting operation due to 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 -(B-
The phase is erroneously synchronized to a state where the phase changes sequentially by ±45° around the Y) axis.

When this burst signal is phase-detected by the BY-axis carrier wave S10 (FIG. 4B) in the phase detection circuit 34, the detection output S11 is obtained at time points t ₁₁ and t ₁₂ in FIG. 4C.
A series of negative pulses as shown in . . . are obtained. Therefore, the low-pass filter 35 smoothes this negative pulse and sends out a negative DC level voltage output S12 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 contact b on the 90° delay circuit 32 side). Therefore, the signal S9 obtained at the contact point c of the changeover switch 33 at this time becomes a signal obtained by delaying the phase of the burst signal S5 by 90 degrees, as shown in FIG. 5A. In other words, the burst signal is as shown in Figure 5A.
As shown in the time points t ₂₁ , t ₂₂ ..., the state has advanced 45 degrees from the -(RY) axis (the time points t ₁₁ , t ₁₃ in FIG. 4A mentioned above)
. . ) and a state delayed by 45 degrees from the RY axis (states at time points t ₂ , t ₄ . . . in FIG. 3A described above). Therefore, in this state, the phase detection output S11 by the carrier wave of the BY axis of the phase detection circuit 34 becomes a pulse that alternately changes to positive or negative for each scanning line as shown in FIG. The smoothed output S12 of the low-pass filter 35 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 in the receiver is converted into the currently arriving B-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 is provided on the output side of the phase detection circuit 34, and this gate circuit is gated by, for example, the pulse signal S11 of FIG. 3C. This can further reduce the possibility of malfunctions occurring.

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.

FIG. 6 shows another embodiment of the present invention, and as shown in FIG. Although a circuit 34 is provided separately, in the embodiment shown in FIG. 6, the BY signal demodulation circuit 20 is also used for abnormality identification.

That is, a changeover switch 41 controlled by the burst gate pulse S15 is provided on the input side of the B-Y signal demodulation circuit 20, and one fixed contact a is connected to the output end of the addition circuit 26, and a movable contact c is connected to the BY signal demodulation circuit 20. At the same time, the movable contact c of the changeover switch 33 is connected to the other fixed contact b of the changeover switch 41.

Further, the output of the BY signal demodulation circuit 20 is applied to a low-pass filter 43 through a gate circuit 42 whose opening is controlled by a burst gate pulse S15 to smooth it, and the operation of the flip-flop circuit 22 is controlled by the DC level voltage. do.

In the configuration shown in FIG. 6, during the burst period, the switch 41 is switched to the contact b side by the burst gate pulse S15, and the output S9 of the changeover switch 33 is switched to the contact b side.
is input to the BY signal demodulation circuit 20, and during other periods, the switch 41 is switched to the contact a side to provide the output of the addition circuit 26 to the BY signal demodulation circuit 20. However, the output of the B-Y signal demodulation circuit 20 is sent to the low-pass filter 43 through the gate circuit 42 only during the burst period.
4D, a DC voltage level output corresponding to the switching state of the changeover switch 41 is obtained at the output terminal of the low-pass filter 43, thereby controlling the operation of the flip-flop circuit 22.

In this way, exactly the same effect as described above with respect to FIG. 3 can be obtained.

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 the judgment output 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 conventional configuration can be simplified accordingly. 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, FIGS. Figure 5 is a signal waveform diagram for explaining the operation of Figure 2;
The figure is a block diagram showing another embodiment of the 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...
90° phase lead circuit, 32...90° phase lag circuit, 3
3... Burst selection switch, 34... Phase detection circuit, 35... Low pass filter, 41... Changeover switch, 42... Gate circuit, 43... Low pass filter.

Claims (1)

[Claims] 1. 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 amplitude is modulated for each scanning line. The phase of the first color subcarrier is inverted and transmitted to the receiver, and the burst signal is used as a phase reference of the reference color subcarrier to allow the receiver to identify the phase state of the first color subcarrier. In the color television receiver, the phase of the burst signal is changed with respect to the axis of the second carrier wave in correspondence with the inverted state of the phase of the first carrier wave, using the phase change. a first phase shift circuit that advances the phase of the burst signal by τ/2; a second phase shift circuit that delays the phase of the burst signal by τ/2; and a switching circuit that selectively takes out the outputs of the first and second phase shift circuits. , synchronizing a phase detection circuit that detects the phase of the output of this switching circuit with the second 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. 1. A line synchronization switching circuit comprising a switching signal generating circuit that generates a switching signal that causes a switching operation to be performed or not to be performed for each scanning line.