DE1537479A1 - Circuit in a PAL color television receiver for synchronizing the line-frequency switch - Google Patents

Description

Switching in a PAL color television receiver for Synchronization of the line-frequency switch, according to patent application T 34 350 VIIIa / 21al

In a PAL color television receiver there is a line rate switch required to switch the phase of a color carrier or a reference carrier line-frequency. The frequency of such Switch can be made by line sync pulses or line return pulses be synchronized. In addition, the correct switching phase of this switch must be ensured.

In the main patent (patent application T 34 350 VTIIa / 21al) is one Circuit for synchronizing such a line-frequency switch described in which a switched from line to line Reference carrier (R-Y) and the received alternating burst can be combined and by rectifying the combined signals a manipulated variable for the correction the switching phase of the line-frequency switch * is obtained.

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The circuit according to the main patent allows operation without interference at a relatively short distance. The invention has the AVSS based on the object to provide a drive for the line-frequency switch, wherein the operating states of the line rate

so

Clearly differentiated with the correct and incorrect switching phase that he is a color killer and possibly can also be used to switch a color carrier trap on and off.

The invention relates to a circuit in which the switched Reference carrier (R-Y) and the alternating burst signal are combined in a phase comparison circuit to to gain a control voltage for the half-line frequency generator. The invention consists in that the DC control voltage is fed to the half-line frequency generator in such a way that the generator is shut down if the line-frequency switch is in the wrong switching phase and always the same electrode path of the line-frequency switch controlled by the generator is permeable, so that the output from the switch is switched The reference carrier is always the same when the generator is shut down

and
The phase position is such that the switched reference carrier (RY) or the Farvsvnchronimpuls is rotated by such an amount in the phase before the combination that a voltage that cancels the shutdown is emitted when the generator is shut down.

The invention is explained in more detail below with reference to the drawing. 3 '_

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FIg. 1 shows the block diagram and FIG. 2 shows a detailed diagram of a circuit according to the invention. In FIG. 1, the color sync signal 1, separated from the color signal and alternating from line to line, is fed to a passive or active reference carrier generator 2 (which may contain retuning circuits). From the reference carrier generator 2, the reference carrier is fed to a demodulator 4a, for example the (BY) demodulator, on the one hand via a 9Q ° phase rotating member 3 and, on the other hand, to a line-frequency switch 5, the so-called _β PAL switch. The PAL switch 5 supplies at its output, controlled by a half-line frequency generator 6 ″ for the (RY) demodulator .4b, an (RY) reference carrier whose phase is switched from line to line by 180 °. The (RY) carrier is also used to determine the phase position of the half-line frequency? To readjust the generator 6 in such a way that the switching phase of the PAL switch 5 coincides with the switching phase of the PAL switching on the transmitter side. (ID). For this purpose, in the circuit according to the main patent, the (RY) carrier switched from line to line and the alternating color sync signal 1 are fed to a phase discriminator 7, which has an output dependent on the mutual phase position of these two signals. DC voltage V_ supplies. This DC voltage V

s s

is used as a manipulated variable the half-line frequency generator 6 in such The sense that the generator is influenced, in particular shut down, if the switching phase is incorrect. The size of the DC voltages with the correct or incorrect pushing phase is between OV or a small voltage on the one hand and a large one

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Spatinungpert, on the other hand. 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, for example a DC amplifier 8, is arranged between the phase discriminator 7 and the half-cell frequency generator 6, which depending on the control DC voltage V to the generator 6, a large BSW. sets small fixed DC voltage. A further safeguarding of the correct switching phase is achieved in that the CR-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 control DC voltage is positive when the switching phase is correct and negative when the switching phase is incorrect (or vice versa).

1. Generator 6 is running properly

2. ■■ · "■ _ 6 goes wrong

3. "6 is not running

4. There is no color sync signal

The voltages of the lines η and η + 1 are sieved in such a way that a DC voltage "middle word" sets. In cases 1 and 3 results in the same voltage sequence + U, OV, + U ..., so that a bsw keeping the generator in operation setting state results. Case 2 with negative voltage ensures that / '- 5 -

909839/0652

Line η Line η + 1 + tr OV OV -U + U OV OV OV (generator
stands still)

the generator is switched on. Depending on the time constant of the control loop, the generator 6 can immediately start up again result in correct switching. The shutdown of the generator at The absence of a color sync signal enables a color killer to be connected to the generator 6, which saves additional circuits will"

In the circuit shown in FIG. 2, the control DC voltage of the discriminator reaches a DC amplifier 10. When the DC control voltage is low, the transistor 10 is blocked and the voltage of -60V is applied to the base via the resistor 11 of the transistor 12, which is thereby also blocked. In this way the generator 6 containing the transistor 12 is shut down « If the control voltage is high, the transistor 10 becomes conductive and the negative voltage of -24V is across the transistor Internal resistance 10 and the resistor 13 in parallel with the capacitor 14 at the base of the transistor 12 »As a result, the generator 6 oscillates. Since the transistor 12 is always blocked at its base, it arrives in its blocked state, a more positive voltage to the anode of the fiehalldlode 15, which becomes conductive as a result. This is always the same Hekroden distance 15 permeable and at a standstill Generator 6 always arrives - as desired - a reference carrier of constant phase position to demodulator 4b. The output voltage of the Switch 5 is rotated in phase by 45 ° by means of a phase shifter 9 composed of a resistor 16 and a capacitor 17. With this «value optimal results were achieved. With

other, different phase rotations can, however, be the desired one Also achieve effect.

909839/0652

Claims (3)

Claims Specimen copy May not be changed 1 «circuit in a PAL Parb television receiver for the synchronization of the line-frequency switch, which switches the phase of a reference carrier used for demodulation from line to line by 180 ° and is controlled by a half-line frequency generator, whereby by phase comparison of the received, alternating color sync signal and the switched Reference carrier a control DC voltage for the generator is obtained, according to patent .... (patent application T 34 350 Villa / 2IaI, characterized in that the control DC voltage is fed to the half-line frequency generator (6) so that the generator (6) in the wrong switching phase of the line-frequency switch (5) is stopped and the same electrode path (15) of the line-frequency switch (5) controlled by the generator is always permeable, so that the switched reference carrier output by the switch is and set the generator (6) always has the same phase position that the switched reference carrier (R-Y) or color sync pulse (1) before the combination (7) by such an amount in the (9)
Phase is rotated so that when the generator (6) is stopped, a voltage that cancels the shutdown is output. 2. Circuit according to claim 1, characterized «that the switched reference carrier (RY) or the color sync signal (1) before the combination (7) are rotated in phase by 45 ° * - 7 _ 909839/06 52 - T - W 7220 3. Circuit according to claim 1 or 2, characterized in that that when the generator (6) is stopped, a manipulated variable that blocks the color channel is obtained. 909839/0652 8 blank page