DE1537479C3 - Circuit in a PAL color television receiver to correct the switching phase of the line-frequency switch - Google Patents

Description

correct (identification). For this purpose, in the circuit according to the main patent, the (ft-Y) carrier switched from line to line and the alternating color sync signal 1 are fed to a phase discriminator 7, which supplies a DC voltage V _{s dependent on the mutual phase position of these two signals at its output} . This DC voltage V _s is fed as a manipulated variable to the half-line frequency generator 6 in such a way that the generator is influenced, in particular shut down, if the switching phase is incorrect. The magnitude of the DC voltages with the correct or incorrect switching phase is between 0 V or a small voltage value on the one hand and a high voltage value on the other. In some cases, the given voltage difference is not sufficient to maintain the correct switching phase of the PAL switch 5 with certainty. For this purpose, a blocking stage, z. B. a DC amplifier 8 is arranged, which applies a large or small fixed DC voltage to the generator 6 depending on the control DC voltage V _s. A further safeguarding of the correct switching phase is achieved in that the (i? -Y) carrier supplied by the PAL switch 5 and alternating from line to line is fed to the phase discriminator 7 via a 45 ° phase rotating member 9. This ensures that the DC control voltage V _s becomes positive when the switching phase is correct and negative when the switching phase is incorrect (or vice versa). With the circuit described so far, the following DC control voltages V _s result in different operating states:

Row η Row η + 1

1. Generator 6 is running correctly .... + U

2. Generator 6 is running incorrectly OV

3. Generator 6 does not run + U

4. The color sync signal remains off OV

OV
-U
OV

OV (Genetor 6 stops)

The voltages of lines η and n + 1 are screened in such a way that a DC voltage mean value is established. In cases 1 and 3 the result is the same voltage sequence + U, OV, -fU. . ., so that a state that holds or sets the generator in operation results. Case 2 ensures with negative voltage that the generator is stopped. Depending on the time constant of the control loop, the generator 6 can immediately select the correct one when it starts up again

ίο result in switching phase. The shutdown of the generator in the absence of a color sync signal enables a color killer to be connected to the generator 6, which saves additional circuits.

In the case of the FIG. 2, the control DC voltage of the discriminator 7 reaches the DC amplifier 8 with a transistor 10. When the control DC voltage V _s is low, the transistor 10 is blocked, and the voltage of -60 V is across the resistor 11 at the base of the transistor 12, which thereby is also blocked. In this way, the generator 6 containing the transistor 12 is stopped. When the control DC voltage is high, the transistor 10 becomes conductive, and the negative voltage of -24 V lies across the transistor internal resistance 10 and the resistor 13 parallel to the capacitor 14 at the base of the transistor 12. As a result, the generator 6. The transistor 12 always oscillates is blocked at its base, a more positive voltage reaches the anode of the switch diode 15 in its blocked state, which thereby becomes conductive. This means that the same electrode path 15 of the switch 5 is always permeable, and when the generator 6 is stopped, a reference carrier of constant phase always reaches the demodulator Ab, as desired Phase rotated by 45 °. Optimal results were achieved with this value. However, the desired effect can also be achieved with other, different phase rotations.

1 sheet of drawings

Claims (1)

1 2 is combined, whose during the duration of the color claims: synchronous signal occurring, rectified output voltage depending on the correctness 1. Switching in a PAL color television receiver the switching phase of the line-frequency switch as Catcher to correct the switching phase of the line 5 manipulated variable controls the generator. The object of the present invention is to generate a reference carrier from line to line, to switch over a control circuit for the line frequency and to create a switch of line frequency, in which the generator synchronizes the operating frequency pulses state of the switch is controlled with correct and incorrect, the received switching phase being so clearly differentiated from line to io that the line is switched by 90 ° in phase color as a chrominance channel switch and for the single and synchronous signal and which can be used in the phase switching off of a color carrier trap.
tete reference carrier to a phase comparison stage. This object is achieved by the set out in claim 1, the output voltage of which is achieved as the invention described above. Advantageous execution size depending on the correctness of the 15 ments of the invention are specified in the dependent claims switching phase the line-frequency switch control. ert, according to patent 1278494, characterized in that a circuit has been proposed that controls the manipulated variable (V _s ) the (DT-PS 12 63 820) in a PAL color generator (6) so that If the television receiver is wrong, the generator controlling the line-frequency switch switching phase of the line-frequency switch (5) 20 is controlled by a manipulated variable in which the switching phase is stopped and the same distance switching phase is corrected, which is the same as the phase shifting (15) of the switch controlled by the generator (6) the output voltage of the generator with (5) is permeable, so that the switch (5) of a switched reference carrier emitted from the alternating color sync signal always has the same phase voltage when the generator (6) is idle with half-line frequency identification span. So there is a so-called position and that the switched reference carrier low-frequency phase comparison between the half (RY) or the color sync signal (1) before the line-frequency switching voltage itself and a supply to the phase comparison stage (7) by half-line frequency identification voltage. Such an amount rotated in phase is color subcarrier-frequency phase comparison for extraction (phase shifter 9) that when the generator is stopped, a manipulated variable such as the one in the main patent and in the rator (6) a disconnection of the present invention is carried out is delivered. does not follow there. The one from line to line in the phase 2. A circuit according to claim 1, characterized in that the reference carrier switched by 180 ° indicates that the switched reference is not used to obtain the manipulated variable for correcting the carrier (RY) or the synchronous signal (1) 35 switching phase. the phase discriminator (7) via a phase By stopping the rotator according to the invention (9) with a phase shift of 45 °, the puller always leads in the same defined switching position will. ment and the phase rotation of the reference carrier 3. A circuit according to claim 1 or 2, thus achieved that at the output of the phase comparison marked that when the gene is stopped 40 stage with wrong and correct switching phase a defirator (6) at the output of the phase discriminator niert, greatly different voltage arises. (7) The manipulated variable that occurs as a manipulated variable for blocking This is then used to shut down the generator when the color channel is used. wrong switching phase and can also be used to operate a color killer circuit or a color 45 carrier trap serve. The invention is hereinafter based on the Drawing explained using an exemplary embodiment. In it shows F i g. 1 shows a block diagram of the invention and
50 Fig. 2 a practically executed circuit of a The main patent relates to a circuit in part of the circuit of FIG.
PAL color television receiver for correcting the In F i g. 1 the separated from the chrominance signal, Switching phase of the line-frequency switch, which supplies the color synchronous phase alternating from line to line of a locally generated color carrier 55 generator 2 serving to demodulate the color carrier frequency signal 1 to a passive or active reference carrier signal (which, if necessary, switches over from line to line by 180 ° and from Contains voice circuits). The reference carrier is controlled from the reference carrier geneeinem of line-frequency impulses synchronizing rator 2 via a th generator, the received 90 ° phase rotating member 3 the (BY) demodulator Aa color sync signal from line to line by 90 ° in and on the other hand the PAL switch 5 supplied. Which of the phase is switched. 60 PAL switch 5 supplies at its output, controlled The invention according to the main patent is based on a half-line frequency generator 6, for the task of creating a novel, particularly interference-free (i? -Y) demodulator 4 b an (i? -Y) reference carrier, free-of-motion circuit for correcting the whose phase is switched by 180 ° from line to line - switching phase of the line-frequency switch in a tet. The (/? - Y) reference carrier will also be used to create a PAL color television receiver. 65 used to determine the phase position of the half-line frequency This object is achieved in that the emp generator 6 readjusts in such a way that caught color sync signal with the in the phase the switching phase of the PAL switch 5 with the switching 180 ° switched color carrier in one stage phase of the sender-side PAL switchover