DE1950017C3 - Identification circuit for a PAL color television receiver - Google Patents

Description

40

(169) connected to the pulse signal input (55) is characterized in that the PAL phase switch signal generator (53) in the connection between the pulse signal input (55) and the named trigger circuit input (171) one with its input to the output (107) of the Pnlarity correction circuit (109) connected blocking circuit (164,165,167) contains (Fig.5).

6 Identification circuit according to Claim 5, characterized in that the blocking circuit (164 165,167) contains a transistor (164) whose base is connected to the output (57) of the polarity correction circuit (109), whose collector is connected to the input (169) of the trigger circuit ( 171) and via a resistor (167) to the pulse signal input (55) ^{and whose} em'ker is connected to ground (Fig. 5).

7 identification circuit according to one of the preceding claims, characterized in that this one coincidence circuit (75) with a first input (73), which with an output (71) of the synchronous demodulation arrangement (37) is connected, a second input (77) which is connected to a Output (27) of the color subcarrier regeneration circuit (25) is connected, and a color cancellation signal output (79) contains (Fig. 1).

8. Identification circuit according to claim 7 together with claim 3 or claim 4, characterized characterized in that the second input (77) of the coincidence circuit (75) via an amplitude demodulator (118) with said output of the color subcarrier regeneration circuit and the first Input (73) is connected to the output (107) of the polarity correction circuit (109) (FIG. 4).

9. Identification circuit according to one of the preceding claims, characterized in that a Input (23) of the passive integrator (25) with an output (7) of a PAL decoding arrangement (1) is coupled to which the color sync signal quadrature component of constant phase arises and an input (61) of the synchronous demodulator (37) with an output (5) of the PAL decoding arrangement (1), at which the color sync signal generator component of alternating phase arises, is coupled.

f.

Flip-flop to correct the PAL phase and controls the color switch.

The invention is based on the object of providing an identification circuit of the type mentioned at the beginning create in which intermediate stages for the signals to be compared are avoided as much as possible, so that a largely error-free control is assured. this is achieved if, according to the invention, the passive regenerator is connected to a phase-locked circuit and the demodulator circuit of the regenerated reference color carrier and the burst signal with the phase changing by 180 ° from line to line for synchronous demodulation, whereby a Feed path one from the PAL phase switch signal generator controlled phase (polarity) switch contains, and if this synchronous demodulator the Provides voltage for the phase control circuit of the regenerator.

For the sake of completeness it should be noted that from "Radio Mentor" 7.196G, page 595, an identification circuit is known in which a second synchronous demodulation arrangement for automatic phase compensation the color carrier regeneration circuit is used.

In a circuit arrangement according to the invention it is achieved that if a incorrect switching status of the PAL phase switch signal generator the phase deviation of the reference color carrier regeneration circuit with a passive integrator practically adjusts to 90 ° with respect to the desired phase. Thereby the mentioned Synchronous demodulation arrangement then from a maximum voltage. This voltage serves as an identification signal for establishing the correct switching status of the PAL phase switch signal generator. When the switching state is correct, the synchronous demodulation arrangement tries output voltage is due to the presence of that synchronous demodulation arrangement in the phase locked loop of the reference color carrier regeneration circuit practically set to zero. There will then be as close a match as possible to the Phase of the reference color carrier signal with that due to the component with the constant phase of the color sync signal represented phase.

Exemplary embodiments of the invention are illustrated in the drawings and are described below described in more detail. Show it

F i g. 1 is a limited block diagram of an inventive Identification circuit,

Fig. 2 is an error voltage phaser deviation diagram to illustrate the behavior of the circuit according to FIG. 1 if the switching status of the PAL phase switch signal generator,

F i g. 3 is an error voltage-phase deviation diagram; by which the Benehrren the circuit of Fig. 1 in an incorrect switching state of the PAL phase switch signal generator is displayed,

F i g. 4 is a simple block diagram of an identification circuit according to the invention, wherein the 90 ° phase rotating network to maintain the correct Position of the color difference signal demodulation axes among each other is included in a reactance circuit of the automatic phase control,

FIG. 5 is a simple circuit diagram of part of the circuit according to FIG. 4, which is suitable for an embodiment in integrated circuit technology is suitable,

F i g. 6 is an error voltage-phase deviation diagram. the behavior of the circuit according to FIG. 5 represents.

In Fig. 1, a PAL decoding arrangement 1 has an input 3, a first output 5 and a second Output 7. When a modulated PAL reference color carrier signal is received at input 3, the first appears Output 5 the component with the changing and at the second output 7 the component with the constant phase of this reference color carrier signal. Outputs 5 and 7 are one with inputs 9 and 11, respectively Demodulator and matrix arrangement 13 connected.

The second output 7 of part 1 is also connected to an input 15 of a gate circuit 17. the Gate circuit 17 also has an input 19, to which pulse pulses are fed, and an output 21, at which a color burst signal component with a constant phase appears. The output 2 is with an * input 23 of a color subcarrier regenerator 25 connected, which according to the invention must be of the passive type and hereinafter referred to as a passive integrator referred to as.

According to the invention, an output 27 of the passive integrator 25 is connected to an input 29 of a phase switch 31 connected. There is also an output 33 of the phase switch 31 with a reference carrier input 35 of a synchronous demodulation arrangement 37 and a control signal output 39 of the demodulation arrangement 37 is connected to a control signal input 41 of a phase control circuit 43. The phase locked circuit 43 is connected to the passive integrator 25 via a line 45. The phase switch 31 gives at output 33 a reference color carrier signal whose phase changes by 180 ° from line to line.

The output 33 of the phase switch 31 is also connected to an input 47 of the demodulation arrangement 13 connected. With the aid of a phase-rotating network, the output 33 of the phase switch can be used 31 output reference color carrier signal is a reference signal for synchronous demodulation of the dem Derive input 9 supplied color signal component with the changing phase.

The phase changeover switch 31 has an input 49 which is connected to an output 51 of a PAL phase changeover signal generator 53 is connected. A control signal for the phase changeover switch 31 is sent to this output 51 receive. The phase switching signal generator 53 contains a two-part circuit, which is through an input 55 the same applied line-frequency pulse signal, for example a line retrace voltage, controlled will. The switching state of the phase switch 53 can be with the help of a detection signal that a Input 57 of the same is supplied, correct. The input 57 is for this purpose with an output 59 of the synchronous demodulation arrangement 37 connected.

The synchronous demodulation arrangement 37 has a signal input 61, which is connected to an output 63 of a Gate circuit 65 is connected. An input 67 of the gate circuit 65 is connected to the first output 5 of the PAL decoding arrangement 1. The gate circuit 67 also has an input 69 to which a key signal is fed will. At the signal input 61 of the synchronous demodulation arrangement 37, the component is thereby with the changing phase of the burst signal. In the synchronous demodulation arrangement 37 This color sync signal component, whose phase can be seen from line to line by! 80 ° changes with the help of the the reference carrier input 35, also changing in phase from line to line by 180 ° Reference signal demodulated. This reference signal has

under the influence of the phase control circuit 43 in the correct switching state of the phase switching signal generator a phase that is practically 90 ° from that of the The color synchronizing signal component which is fed to the signal input 61 differs, and if it is incorrect Switching state a phase that is practically the same as the above or deviates 180 ° from it.

The synchronous demodulation arrangement 37 also has an output 71, which after a further Elaboration of the invention with an input 73 of a coincidence circuit 75 is connected. Another Input 77 of coincidence circuit 75 is connected to output 27 of passive integrator 25. Just in the presence of a color signal at the input 3 and in the correct switching state of the phase switch 31, the coincidence circuit 75 is at one Color erasing signal output 79 from a signal that is transmitted via an input 81 connected to the output 79 of the Demodulation and matrix arrangement 13 unlocks this arrangement so that it can be supplied to three outputs 83, 85 and 87 of the same can output demodulated color difference signals.

The output 27 of the passive integrator is to supply a reference signal with a non-changing phase with an input 89 of the demodulation and matrix arrangement 13 connected.

The mode of operation of the detection circuit, insofar as this is important for understanding the invention, will now be illustrated with reference to FIGS. 2 and 3 explained in more detail. First of all, it is assumed that the switching state of the phase switching signal generator 53 is correct. Furthermore, in the unregulated state, the initial phase of the reference color carrier signal at the output 27 of the passive integrator φοι compared to the desired phase φο is assumed. The control voltage V at the output 39 of the synchronous demodulation arrangement 37 is then V ₀ (see FIG. 2). This control voltage will attempt to readjust the phase of the output signal of the passive integrator up to the value φο via the phase control circuit 43. If the initial _{phase φ o 2 were} compared to the desired phase φ ₀ , a control voltage V ₀ 2 would arise at the output 39, which would readjust the phase of the signal at the output 27 of the passive integrator 25 to φ ° via the phase control circuit. If the output signal of the passive integrator has the desired phase φ ₀ , the phase difference between the voltages at the inputs 35 and 61 of the synchronous demodulation arrangement 37 is 90 °. No signals are then produced at the outputs 71 and 59 of the synchronous demodulation arrangement 37, so that no color blocking signal is produced at the coincidence circuit 75 and no detection signal is produced at the phase switching signal generator 53.

It is now assumed that the Zwcitciler of the phase switching signal generator 53 is in the incorrect sound state. Then the phase of the reference signal at the input 35 of the synchronous demodulation arrangement 37 will deviate 180 ° from that of the case described above and the characteristic which the control voltage V at the output 39 represents as a function of the phase angle φ of the reference signal around input 35 will be as is shown in Fig.3. One to an initial phase φ _Ο | corresponding voltage Vo / now has a polarity opposite to the polarity in the previous case and via the phase control circuit 43 the phase deviation φ of the signal at the input 35 compared to the desired phase φ «will now be larger instead of smaller, as in the case of correct switching state of the phase switch 53 was the case. Because the color subcarrier regenerator 25 is now a passive integrator, this phase rotation will not be able to exceed 90 ° and the control voltage V will have its maximum value Vi ', which in this case is shown negatively. In a similar way, with an initial phase φο2 and a control voltage Vo ₂ ', the phase control circuit will strive for a phase deviation of -90 °, to which a control voltage W represented as maximum positive in this case ίο belongs. In these two cases, the synchronous demodulation arrangement 37 also emits a large signal at its outputs 71 and 59. The signal at output 71 will then cause the color to be deleted, and the signal at output 59 will correct the switching state of the phase changeover signal generator 53 and move it from the incorrect to the correct state.

The identification circuit according to FIG. 4 is in part

according to FIG. 1 structured accordingly. For that part the same reference numerals are used as in FIG. 1 and it will refer to the description of the same

Description of the FIG. 1 referenced.

The most important differences with the circuit according to FIG. 1 are as follows. The phase switch 31 is behind the output 5 is added to the color signal path. In the phase switch 31 is now from line to line Phase of the modulated reference color carrier signal rotated by! 80 °. Instead of gates 65 and 17, in In this case, electronic changeover switches 91 and 93 were added. Connect these changeover switches 91,93 during the occurrence of the color sync signal, the outputs 5 and 7 of the decoding arrangement 1 with the Inputs 61 and 23 of the synchronous demodulation arrangement 37 and the passive integrator 25. During the remaining part of the time, the changeover switches 91, 93 connect the outputs 5 and 7 of the decoding arrangement 1 to the inputs 9 and 11 of the Demodulation and matrix arrangement 13. The output 27 of the passive integrator 25 is via a phase-rotating network 95 of 90 ° with a Reference signal input 97 of the demodulation and matrix arrangement 13 is connected. After another Elaboration of the invention is an output 99 of this phase-rotating network 95 with an input 101 of a phase inversion and distribution circuit 103 is connected. A control signal input 105 of the phase reversal and distribution circuit 103 is connected to the Control signal output 39 of the synchronous demodulation arrangement 37 connected. About the connection 45 is as a result, a reference carrier voltage is fed to the passive integrator, the phase of which depends on the Control signal by 90 ° or by 270 ° from which the voltage at the output 27 of the passive integrator 25 deviates and the amplitude of which is dependent on the control signal fed to the control signal input 105. This will under the influence of the control signal at input 105 a Phase correction of the output signal of the passive integrator 25 obtained.

Another difference with the circuit of FIG. 1 is that the input 57 of the PAL-Phascnunv switching signal generator 53 and the input 73 of the coincidence speed 75 for the color deletion by means of a signal Output 107 of a polarity correction circuit 10i are connected. Two inputs 111 and 113 of the polarity correction sound 109 are mil outputs 115 and 117, respectively, of the phase inversion and distribution scarf ment 103 connected. The entrance 77 of the coincidence

Circuit 75 is connected to output 27 of passive integrator 25 via an amplitude detector 118 .

The circuit diagram of the phase reversal and distribution circuit 103, the polarity correction circuit 109 and the PAL phase switching signal generator 53 of the circuit according to FIG. 4 is shown in FIG. The mode of action of this combination is also explained below with reference to FIG.

In Fig. 5, the input 101, to which the reference color carrier signal received from the output 27 of the passive integrator 25 and rotated by 90 ° in phase by the phase-rotating network 95 is fed, is connected via a capacitor 119 to the base of a transistor 121 . The base of this transistor 121 is connected to a supply source Vi via a resistor 123. This supply source Vi also has the base of a transistor 125 which, together with the transistor 121 and a transistor 127, which is included in a common part of the emitter lines of the transistors 121 and 125 , forms a phase reversal circuit. The emitters of transistors 121 and 123 are connected to the collector of transistor 127 via resistors 129 and 131, respectively. The emitter of the transistor 127 is connected to ground via a resistor 133. The base of the transistor 127 is connected to a supply source V2 which _{outputs a lower voltage than the supply source V 1} .

The collector currents of transistors 121 and 125 are influenced by the reference color carrier signal at the base of transistor 121 in antiphase.

The collector of transistor 121 is connected to the emitters of two transistors 135 and 137 which form part of a current distribution circuit. The collector of transistor 125 is connected to the emitters of two transistors 139 and 141 which form part of another power distribution circuit. The base electrodes of these transistors 137 and 139 are connected to one another and to a capacitor 143 . The base electrodes of the transistors 135 and 141 are connected to one another and to a capacitor 145 . The other ends of the capacitors 143 and 145 are grounded. The collectors of transistors 137 and 141 are connected to output line 45 . The collector of the transistor 135 is connected to the output 117 and via a resistor 146 to a supply source V ₃ which emits a higher voltage than the supply source Vi. The collector of the transistor 139 is connected to the output 115 and via a resistor 148 to the supply source V3. The ends of the capacitors 143 and 145 connected to the aforementioned base electrodes are each connected to a gate circuit at the input 105, to which the synchronously demodulated in the synchronous demodulation arrangement 37 is fed.

The capacitor 143 is connected to the collector of a transistor 147 and to the emitter of a transistor 149. The emitter of the transistor 147 and the collector of the transistor 149 are connected to the input 105 . The base electrodes of the transistors 147 and 149 are connected to an input 151 to which a pulse which coincides in the line with the color sync signal is fed.

The capacitor 145 is connected to the collector of a transistor 153 and to the emitter of a transistor 155. The emitter of the transistor 153 and the collector of the transistor 155 are connected to the input 105 . The base electrodes of the transistors 153 and 155 are connected to an input 157 , to which a pulse is fed which appears during the line return and before the occurrence of the color sync signal.

If a pulse appears at input 157 , transistors 153 and 155 are conductive and the capacitor

S 145 is charged up to the voltage that is present at the input 105 at the moment. If a pulse occurs somewhat later at the input 151 , the transistors 147 and 149 are conductive and the capacitor 143 is charged up to the demodulated color synchronization signal voltage which is present at the input 105 at the moment. A voltage difference arises across capacitors 143 and 145 , which is a measure of the amplitude and polarity of the demodulated color sync signal. This amplitude and polarity are again a measure of the phase deviation of the reference color carrier emitted by the passive integrator 25 in relation to the desired phase φ o of the reference color carrier. The phase of the color synchronizing signal fed to the input 61 of the synchronous demodulation arrangement is a measure of the desired phase and deviates 90 ° therefrom.

If the phase difference between the color sync signal at input 61 and the reference color carrier signal at input 35 of the synchronous demodulation system is exactly 90 °, then the amplitude of the modulated color sync signal at input 105 is zero. The capacitors 143 and 145 have the same voltage and the transistors 135 and 137 or 139 and 141 carry a practically equal part of the currents supplied by the transistors 121 and 125, respectively. The AC component provided by transistors 137 and 145 at output 45 will be zero. If the phase difference mentioned deviates from 90 °, a will appear between the capacitors 143 and 145

3S voltage differences arise and the currents are distributed unevenly. If the voltage difference between the capacitors 143 and 145 is positive, the transistor 137 carries a larger part of the current supplied by the transistor 121 than the transistor 135 and the transistor 141 carries a smaller part of the current supplied by the transistor 125 than the transistor 139. The sum of the currents supplied by transistors 141 and 137 at output 45 is then supplied for the most part by transistor 137 , so that the phase of the alternating current component therein is determined by the phase of the alternating current component supplied by transistor J21. It can easily be seen that with a negative voltage difference between the capacitors 143 and 145, the alternating current component supplied by the transistor 141 will predominate over that supplied by the transistor 137 at the output 45. The entire alternating current component at the output 45 will then have the phase of the alternating current through the transistor 125 which is in phase opposition to that in the other transistor 121 of the phase number circuit. The polarity of the voltage difference between capacitors 143 and 145 thus determines whether the phase of the alternating current and thus of the reference color carrier signal at output 45 is 0 ° or 180 ° with respect to the phase of the signal at output 101 . The size of the voltage difference determines the amplitude of the incoming alternating current components. With the help of this AC component, the phase of the output voltage of the passive integrator 25 is corrected until the phase difference between the color sync signal at the input 61 and the 25 nm input from the passive integrator 35 of the synchronous demodulation arrangement

709639/119

37 supplied reference color carrier signal is practically 90 °. The control signal at output 39 is the same practically zero when the PAL phase switching signal generator 53 has the correct switching state. Knows the PAL phase switching signal generator 53 the incorrect Switching state on, the control signal at the input 105 of the phase reversal and distribution circuit 103 is the Increase the phase difference between the input signals of the synchronous demodulation arrangement 37 to the try by dividing the alternating current component of the output signal at output 45 of the phase reversal and distribution circuit 103 will then aim for a maximum value instead of the value zero, as it is in the correct Switching state is the case. Basically, the phase control is based on FIG. 2 and 3 given Explanation.

Except for the alternating current component supplied by transistors 137 and 141 at output 45 the control signal at input 105 also has an influence on that of each of the transistors 139 and 135 at the Outputs 115 and 117 of the phase reversal and distribution circuit 103 supplied direct current component and thereby the voltage difference between the collectors of said transistors.

If the voltage on capacitor 143 is positive compared to the voltage on capacitor 145, then flows through transistor 139 receives most of the direct current supplied by transistor 125 and through the transistor 135 is the smallest part of the direct current supplied by transistor 121. Those from transistors 121 and 125 supplied direct currents are practically the same. The direct current through transistor 139 then becomes be greater than that through transistor 135 and the voltage drop across collector resistor 148 greater than that at the collector resistor 146. With a different polarity of the voltage difference between the Capacitors 143 and 145 also get the voltage difference between the collectors a different one Polarity.

At the outputs 115 and 117 there is a voltage difference, its size and polarity Measure for the voltage difference between the capacitors 143 and 145 and thus for the Amplitude and polarity of the synchronously demodulated false synchronous signal fed to input 105 and thus a measure of the phase deviation between the color burst signal and the reference color carrier signal at the inputs of the synchronous demodulation arrangement 37.

Any JDC voltage difference between the outputs 115 and 117 becomes the Inputs 111 and 113 of the polity correction circuit 109 supplied. The input 111 is connected to the base of a transistor 159 and to the emitter of a Transistor 161 connected. Entrance 113 is on Base of transistor 161 and at the emitter of transistor 159. The collectors of transistors 159 and 161 are connected to one another and to the output 107 and are connected to ground via a resistor 163 placed. In this exemplary embodiment, transistors 159 and 161 are of the pnp type, in contrast to this to the other transistors according to FIG. 5, which are of the npn type.

If there is no tension difference between the Inputs 111 and 113 of the polarity correction circuit are present, neither of the two transistors is 159 and 161 are conductive and the voltage at output 107 is then zero. If the entrance 111 opposite the

S input 113 is negative, transistor 159 conducts when the voltage difference has exceeded a certain threshold value determined by the transistor type and when the polarity of the transistor 161 is reversed. In both cases the voltage drop across the resistor increases 163 in the common collector line and thus at output 107.

As a function of the angle φ between the desired and the undesired phase of the reference color carrier At the output 27 of the passive integrator 25, the output voltage V at the output 107 has a profile on how this is shown in FIG. 6 is shown in sketch form. With the aid of this voltage, the coincidence circuit 75 for color erasure and the PAL phase switching signal generator 53 controlled.

The voltage at the output 107 is fed to the input 57 of the PAL phase switching signal generator 53. the Input 57 is connected to the base of a transistor 164, the emitter of this transistor is connected Dimensions. The collector of the transistor 164 is through a resistor 165 to a supply source, through a Resistor 167 is connected to input 55 and directly to an input 169 of a two-part 171. An output 173 of the two-divider 171 is at the output 51 of the PAL phase switching signal generator 53.

When the voltage at input 57 of the PAL phase switch signal generator 53 is zero, the transistor 164 is not conductive and pulses arriving at the input 55 of the line frequency are passed practically unhindered to the input 169 of the two-divider 171, the

its output 173 emits a so-called square-wave signal of half the line frequency. With a positive Voltage at input 57, like this in the case of an incorrect phase of the passive integrator 25 issued reference color carrier occurs, the

Voltage at input 57 is positive and transistor 164 is conductive. The pulses fed to input 55 then become strong due to the series connection of the resistor 167 and the conductive transistor 164 weakened and can no longer let the two-part 171 work. The positive voltage on Input 57 occurs in the event of an incorrect switching state of the PAL phase switch 53, which is caused by the above-mentioned Blocking process of the impulses is automatically corrected to the correct switching state, whereby the

so the voltage at input 57 becomes zero again.

In the event of an incorrect switching state of the PAL phase number converter 53 at the output 107 of the polarity correction circuit 109 occurring positive voltage is also the input 73 of the coincidence circuit 75

SS fed. A then arises at the output 79 of the same Color clear signal. If the switching status of the PAL phase switch signal generator53 is incorrect, then there is none Color rendering possible. The color blocking signal at the output 79 only disappears when the input 73 is the

<So voltage zero and at the same time at input 77 the from Amplitude demodulator 118 demodulated reference turbocharger signal is available. The latter is namely an indication of the presence of a color burst signal at the input 23 of the passive integrator 25.

For this purpose 3 sheets: Drawings

Claims (5)

Claims: 10 1. Identification circuit for synchronizing the switching phase of a half-line frequency, from Line pulses controllable PAL phase switching signal generator in a PAL color television receiver, which includes a passive reference color carrier regenerator, the reference color carrier a demodulation circuit which controls a signal for synchronizing the PAL switching phase and for the Color switch supplies, characterized that the passive regenerator (25) is connected to a phase control circuit (43) and of the demodulation circuit (37) the regenerated reference color carrier (from 25, 27) and the burst signal (from 5) with the phase changing by 180 ° from line to line for synchronous demodulation are supplied, with a supply path one of the PAL phase switching signal generator (53) controlled phase (polarity) switch (31), and that this synchronous demodulator (37) supplies the voltage for the phase control circuit (43) of the regenerator (25). 2. Identification circuit according to claim 1, wherein a virtually 90 ° phase rotating network is connected with an input to an output of the color subcarrier regeneration circuit, thereby characterized in that an output (99) of the phase-rotating network (95) with an input (101) a phase reversal stage (103; 121, 125, 127) is connected to two outputs in antiphase, each output having a power distribution circuit (135, 137,139,141) connected to it, which Power distribution circuits each have an input (105), which is connected to the control signal output (39) the synchronous demodulation arrangement (37) is connected, and a common output (45), which is connected to the color subcarrier regeneration circuit (25) and at least one identification signal output (115,117), the one with an entrance (57) for supplying the signal for synchronizing the switching phase of the PAL phase switching signal generator (53) is connected (Fig. 5). 3. Identification circuit according to claim 2, the power distribution circuits each having one Output (115, 117) included with the named input (57) of the PAL phase switch ters (53) is connected, characterized in that the invention relates to an identification the outputs (115,117) of the power distribution switching circuit for synchronizing the switching phase lines via a polarity corrector circuit (109) of a half-line frequency, controlled by line pulses with the mentioned input (57) of the PAL-phased PAL-phase switching signal generator in a PAL- switching signal generator (53) are connected (Fig. 5). Color television receiver that has a passive reference color 4. Identification circuit according to claim 3, including a carrier regenerator, wherein the reference color wheel thereby characterized in that the Polaritätskorrek- 55 drives a demodulation circuit that a gate circuit (109) two transistors (159, 161) signal for synchronizing the PAL switching phase and contains, whose base electrodes each deliver with the emitter for the color switch. of the other transistor and with an output In a known circuit of this type according to (111, 113) of another power distribution circuit »radio technology« No. 13, 1968, pages 489 to 490, that becomes (139, 141; 135, 137) are connected and their 60 color sync signal initially via a τ 45 ° switch Collectors fed to one another and to the input and thus brought into the same phase position and (57) of the PAL phase switch signal transmitter (53) controls a quartz filter as a passive regenerator. the are bound (Fig. 5). locally generated reference color carriers obtained will be the 5. Identification circuit according to one of the on (B- ^ / - demodulator and via a PAL switch and Proverbs 3 or 4, the PAL phase switching 6s amplifier being fed to the (R- Y) demodulator. The signal generator (53) a pulse signal input (55) to the switched reference color carrier is further checked by supplying line return pulses and one from an amplitude rectifier and supplies a trigger circuit (171) of which an input that is too low in amplitude sends a switching signal to the 35