DE1181736B - Method for black control of television signals - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: H 04 η

German class: 21 al -34/31

Number: 1181736

File number: F 39127 VHI a / 21 al

Filing date: February 27, 1963

Opening day: November 19, 1964

The invention relates to a method of blacking out television signals, and in particular for black control of color television signals and / or monochrome television signals. Such color television signals (FBAS signals) can consist of color sync pulses, from image signals, blanking intervals and sync signals or (FBA signals) from color sync pulses, Combine image signals and blanking intervals. Among the monochrome television signals On the one hand, a distinction is made between signals (BAS signals), which are made up of image signals, blanking and Composing sync pulses and, on the other hand, signals (ΒΑ signals) consisting of image signals and blanking intervals exist.

The black level of such television signals (FBAS, FBA, ΒΑ signals) is expediently keyed Black control recorded which on signal components during the blanking intervals on the so-called »Black shoulder« appeals. When it comes to color television signals, their color sync pulses (Burst) are transmitted on the black shoulder, part of this "black shoulder" is claimed for the color sync pulses. According to a known method, a controlled Black control used, which responds to those remaining parts of the "black shoulder", which are not used by the color sync pulses. When it comes to the NTSC method in particular then it would be conceivable to use a black control, which is based on signal components the back porch responding after the color sync pulses. When performing a Such a method, however, creates difficulties insofar as the timing of the color sync pulses relative to the horizontal sync pulses due to transmission errors, in particular is not constant due to group delay errors (in the vicinity of the color subcarrier).

According to a further known method for black control of color television signals according to the NTSC method uses a black control which responds to the point at which the Color sync pulses are. A parallel oscillation circuit is used for this used in series with a clamp circuit to prevent the transmitted Color sync pulses are disturbed by the black control. However, practice shows that while the duration of the image signals dip in the frequency response of the transmitted color television signal, because the choke of the parallel oscillation circuit with the diode capacities of the clamping circuit forms a suction circuit.

Procedure for black control of
Television signals

Applicant:
TV G. mb H.,
Darmstadt, Am Alten Bahnhof 6

Named as inventor:

Dr.-Ing. Helmut Schönfelder, Darmstadt,

Karl-Friedrich Pohle,

Reinheim (Odenw.)

The invention aims to provide a method and a circuit arrangement for black control of Indicate television signals which overcomes the difficulties of known methods.

In a method for black control of color television signals, according to the invention Demodulation of the color sync pulses Impulse ge * - and derived therefrom clamping pulses of the first type, which at a predetermined time interval occur after the color sync pulses. These clamping pulses of the first type are then known per se Way used to control a gated black control stage.

The method according to the invention has the advantage that for each color sync pulse - despite any transmission errors that may occur - a clamping pulse first occurs at a precise time interval Kind is generated that the response of the keyed black control on the back porch guaranteed. Even if there are shifts in the color sync pulses relatively to the horizontal sync pulses, as they are, for example, during the switchover of a TV studio can occur on another, the time interval between these clamping pulses remains constant to the assigned color sync pulse.

Another advantage of the invention is the fact that the clamping pulses of the first type during the Vertical blanking intervals cannot cause interference because they (due to the lack of color sync pulses) are not generated during the vertical blanking period. Finally, the inventive Method also has the advantage that clamping pulses of the usual width of about 1.1 μβεσ Duration can be used for keyed black level maintenance

409 728/160

so that perfect black level maintenance is guaranteed.

Sometimes it is useful to also use clamping pulses of the second type in addition to the clamping pulses of the first type to generate, which occur at a predetermined time interval after the sync pulses. These Clamping pulses of the second type should then be fed to a clamping circuit when the clamping pulses of the first kind are absent. In any case, regardless of whether color television signals or monochrome television signals are transmitted over one and the same channel, a black control with clamping pulses first or second type ensures that automatically always transferred to the black shoulder Responds to television signals.

The essence of the invention and exemplary embodiments thereof are illustrated with reference to FIGS. 1 to 8 described, with the same pulse trains or circuit arrangements shown in several figures the same reference numerals are identified. It shows F i g. 1 to 4 pulse trains,

F i g. 5 is a block diagram of a circuit arrangement for generating clamping pulses of the first type, which occur at a constant time interval after the color sync pulses,

F i g. 6 is a block diagram of a circuit arrangement for generating second clamping pulses and third kind,

F i g. 7 shows the circuit arrangement according to FIG. 6 in a detailed representation,

F i g. 8 is a block diagram of a television receiver with circuit arrangements for generating clamping pulses.

F i g. 1 shows a color television signal α in the area of the vertical blanking interval at the end of an even-numbered field. If the color TV is introduced in Central Europe, it is believed that such a color TV signal from the image signals B and from the lying in the blanking intervals of sync pulses (horizontal synchronizing pulses S, pre-equalizing T, main satellites T, Nachtrabanten T "), and color synchronizing pulses F (burst) consists.

The black level of such a television signal a is expediently recorded by a keyed black control which responds to the porch of such a signal. This black control has the advantage that there is no shift in the operating point if, instead of a BAS signal, only a ΒΑ signal is supplied, as can occur, for example, with through amplifiers. A further advantage of such a black control is to be seen in the fact that the basic brightness does not change as a result of a gain control possibly carried out in television receivers.

The in Fig. 1 shown color television signal α contains color sync pulses on the rear porch. It would be conceivable to generate a sequence of clamping pulses b which occur at a constant interval of about 3.5 iisec after the trailing edges of the sync pulses. With such a large delay of 3.5 μ5εΰ, the black control would respond to the flanks of the main satellite T. A potential jump would then occur, which would cause disturbances. It would also be conceivable to derive clamping pulses c which occur at a constant time interval after the leading edges of the sync pulses S. Such clamping pulses c would have the disadvantage that the black control responds to the synchronous pulse base for the duration of the main satellite T , so that there is a potential jump from the black level to the synchronous pulse base and disturbances are caused.

The F i g. 2 and 3 show the excerpts E and G of the signal α according to FIG. 1 in an enlarged representation. In particular, the horizontal sync pulse S, the pre-satellite T ', the main satellite T, the color sync pulse F, the front and rear porch SCH' or SCH ", the clamping pulses k ', K, m' and also numerical data can be seen that are refer to times in nsec. It is assumed that the duration of the front or rear porch SCH ' or SCH ", and also the duration of the sync pulses, are subject to tolerance changes.

If according to FIG. 2 the color sync pulses F consist of ten periods of an oscillation with the color carrier frequency (4.4296875 MHz), then these correspond to a total duration of the color sync pulses F of about 2.3 nsec. The distance from the trailing edge of the sync pulses to the beginning of the color sync pulses F should be about 0.7 \ isec , so that under these conditions the rear porch SCH " with a duration of 2.1 to 3.5 \ isec for a clamping behind the color sync pulse is available. minus a safety margin of 0.5 μββΰ to both sides of the clamp pulse k 'should this clamping pulse k' only 1.1 nsec continue.

F i g. 3 shows that with a delay of 3.5 \ isec and a width of 1.1 \ isqc the clamping pulse K would actually clamp on the flank of a main satellite T. If one wanted to avoid the associated disturbances, then the clamping pulse width would have to be reduced to at least 0.5 nsec. However, this is not desirable because keyed black controls do not work well under these conditions. In addition, from FIG. 3 the two times H / 2 corresponding to half a line duration can be seen.

F i g. 4 shows several pulse trains that play a role in generating clamping pulses. These are the sequence of sync pulses g, a sequence h of color sync pulses F, a sequence of square-wave pulses /, furthermore pulse sequences k, k ', m, m', n, v, p, p ' and a section of a color television signal q.

By rectifying the color synchronizing pulses F, the square-wave pulses / which are differentiated initially result. The leading edges of rectangular pulses corresponding i differentiating peaks are suppressed while that the trailing edges of the square pulses / relevant differentiating peaks k to generate the clamping pulses k 'of the first type are used.

Clamping pulses k 'of this type have the advantages that they cannot cause any interference during the duration D and that their spacing from the respectively assigned color sync pulse F is precisely guaranteed. Even if the color sync pulses F are shifted relative to the horizontal sync pulses 5 (for example when switching from one television studio to another), the time interval remains

the clamping pulse k! to the assigned color sync pulse F constant.

If there is no color television signal and therefore no color sync pulses either, then clamping pulses of the second type m 'are expedient, which occur at a constant distance after the trailing edges of the associated sync pulses g . These are derived from the pulses m .

In some cases it is advantageous to have clamping pulses available for the duration D when the color television signal is present. A pulse sequence η is derived from the pulses m , the pulses of which only occur during the duration D. This can be brought about, for example, using the square-wave pulses i , by means of which all those pulses of the pulse train m that do not occur during the duration D are suppressed. The additive mixing of the pulse trains k and η produces the pulse train p, which can be used either directly or after reshaping as a clamping pulse train p 'of the third type. This pulse sequence ρ is thus composed of two pulse sequences k and η which are phase-shifted from one another. With the corresponding clamping pulses p ' , clamping to the black level of the signal q is achieved both outside and during the entire vertical blanking interval.

F i g. 5 shows a block diagram of a circuit arrangement for generating the clamping pulses of the first type (&'). In this case, a remote color amplitude limiter can be disconnected via terminal 20. These synchronizing pulses g are delayed in step 37 by time t (FIG. 3) and differentiated in the differentiating step 38. In the adjoining limiter 39, differentiating peaks corresponding to the leading edges of the synchronizing pulses are suppressed, so that only those differentiating peaks m are fed to the gate 41 which correspond to the trailing edges of the synchronizing pulses.

It would be conceivable to supply the pulse sequence ν via terminal 42, the pulses of which occur during the duration D and which are intended to ensure that the gate 41 is only open during this duration D. A pulse train η could then be removed from the output of the gate 41. However, it is more expedient to supply the pulse train i instead of the pulse train ν, which is carried out in a manner similar to that of FIG. 5 is derived. The pulse sequences η and k are added in the adding stage 43, and the sequence of the clamping pulses p ′ is fed to the clamping stage 29 via the switching point 44 by transforming the pulse sequence ρ obtained.

As long as there are color sync pulses F , the pulse trains i and k are derived from them and the gate 41 is blocked. If, on the other hand, no color sync pulses are supplied via terminal 20, then the pulse train m is derived from the sync pulses g. If the color sync pulses are only absent for the duration D , then will

sehsignal (a FBAS signal or an FBA signal) 30 as a result of the effect of the now

roughly in the manner of the partially shown in FIG. 1 and 4 shown signals α and q, respectively. Square-wave pulses are supplied via terminal 22 and the gate 23 is controlled in such a way that only the color sync pulses F are allowed through. The pulse sequence i is then emitted by the following constant light 24, amplified in the amplifier 25 and differentiated in the differentiating stage 26. In the following limiter 27, the differentiating peaks corresponding to the leading edges of the pulses i are suppressed and only the differentiating peaks k corresponding to the trailing edges are allowed through. These are reshaped and, in particular, widened in the pulse shaper 28, so that the clamping pulses k ' are produced which are fed to the clamping stage 29.

The color television signal supplied at the input is supplied to the output of the circuit arrangement 33 via the amplifiers 31 and 32, respectively. In this case, using the clamping stage 29, a keyed black control is carried out in a manner known per se. The circuit point 34 is thus connected to a source of constant potential via the clamping stage 29 and via terminal 35 during the duration of the clamping pulses k 'in a low-resistance manner. During the rest of the time (between the clamping pulses k ') , the clamping stage 29 represents a relatively large resistance, so that the color television signal transmitted to the output 33 is not disturbed.

F i g. 6 shows the block diagram of a circuit arrangement by means of which clamping pulses of the second type (m ') or of the third type (p') can be generated. Either a color television signal (FBAS signal or an FBA signal) or a monochrome television signal (BAS signal or BA signal) is supplied via terminal 20. In addition, the sync pulses g are supplied via terminal 21, which may also derive the pulse sequence η from the supplied color television signal or monochrome television signal using an open gate 41. After adding the pulse sequence k and η , the pulse sequence p is produced, from which the sequence of clamping pulses p 'is then derived.

Condition for the proper functioning of this circuit according to FIG. 6, however, is that the phase shift effected in step 37 is set in such a way that the pulses m derived from the sync pulses g occur during the duration of the square-wave pulses i. However, since the pulses m are narrow compared to the square pulses i , shifts between the color sync pulses F (of the pulse train K) and the horizontal sync pulses S (of the sync signal g) of up to about ± 1 μξ & ο can occur without disturbances being expected.

It can happen that a color television signal (FBAS- or FBA signal) and during other times a monochrome television signal (BAS or BA signal) is transmitted. Since a well-working black control is important in all cases, it is advisable to using an automatically responsive circuit arrangement to ensure that in any case - regardless of which of the signals (FBAS or FBA or BAS or BA signal) is transferred - a properly working black control is carried out.

The circuit arrangement according to Fi g. 6 now has the additional advantage that it guarantees perfect black control of the signal transmitted via terminal 20 to output terminal 33 in any case. When a monochrome television signal is transmitted, clamping pulses m 'are applied to the clamping stage 29. If, on the other hand, a color television signal is supplied via terminal 20, then a pulse train ρ is emitted by the adder 43 and converted into clamping pulses p ' .

F i g. 7 shows details of the circuit arrangement according to FIG. 6. The pulse sequence g is fed to stage 37 via terminal 21 , which causes a delay t. This signal is then amplified in the amplifier 51 , differentiated in the differentiating stage 38 and fed to the gate 41. The output of this gate is connected to the impedance converter 53 via the circuit point 52 .

Color synchronizing pulses F are supplied via terminal 54 and rectified in the rectifier 24 . The output signal is then fed to a further impedance converter 56 via the impedance converter 55 and the limiter 27 and the pulse sequence i is emitted from its output via the circuit point 56 ' and the gate 41 is thus controlled. In addition, the pulse sequence / is fed to the impedance converter 57 via the differentiating stage 26. The two interconnected outputs of the impedance converters 53 and 57 cause the signals to be added, and the resulting composite signal is converted into clamping pulses with the help of the pulse shaper 28, the limiter 58, the amplifier 59 and the impedance converter 60, which can be removed via terminal 44 .

113, 114 1 kß

115 22 kß

116 470 Ω

Capacitors

120 10 μΡ

121 0.15 _μ Ρ

122 150 μΡ

123, 124 0.15 µΡ

125 100 pF

126 100 μΡ

127, 128, 129 200 pF

130, 131, 132, 141 0.15 µΡ

Diodes

133 type F 34

135 type OA 72

Term 136 Type BV 401

Spool 137 type BV 640/6

Terminals 139 and 140 are positive

In the preferred embodiment, 25 poles (+12 V) or with the negative pole (-12 V)

connected to a DC voltage source.

F i g. 8 shows a block diagram of a television receiver, both for reproduction monochrome

the following switching elements are used:

Transistors

61 to 75 type SFD 229

76 AF 118

77 2 N 708

78 OC 468

Resistances
80 1 M.O 81 56 kß 83.82 180 ß 84 33 kß 85.86 470 Ω 87 270 Ω 88 15 kß 89 1 kß 91 10 kß 92 470 Ω 93 10 kß 94 2.2 kß 95 220 kß 96 1.5 kss 97 100 Ω

98 10 kß

99, 100 1.2 kSS

101 2.2 kSS

102 103 104 105

1.8 kss
470 Ω
5.6 kss
10 kß

106 680 ß

107 470 ß

108 1 kß

109, 110 10 k

111 12 kß

112 1.5 kss

Pictures as well as for the reproduction of colored pictures should be suitable. This television receiver consists of the following circuit arrangements known per se : input amplifier 142, oscillator and mixer 143, intermediate frequency amplifier 144, video detector 145, amplitude limiter 146, vertical and horizontal oscillator 147, deflection generator 148, picture tube 149, rectifier for audio intermediate frequency 150, audio intermediate frequency amplifier 151, audio rectifier and amplifier 152, loudspeaker 153, color synchronization stage 154, synchronous demodulators 155, matrix 156, clamping stages 157, 158, 159, delay stages 160, 161.

In addition, a stage 162 for separating the color sync pulses, a stage 163 (see FIG. 6) and a vector oscilloscope 164 are also provided.

Either a color television signal or a monochrome television signal is thus tapped from the node 165 and fed to the stages 146, 155, 160 and 162. In the amplitude limiter 146 , the sync pulses g are separated and fed to the vertical and horizontal oscillator 147 and the stages 162 and 163. In stage 162 , the color sync pulses h are separated from the color television signal, if necessary, and these color sync pulses h are supplied on the one hand to the color synchronization stage 154 and on the other hand to the stage 163 . Clamping pulses rri or p 'are emitted from the output of stage 163 via circuit point 44 and via delay stage 161 , depending on whether a monochrome television signal or a color television signal is available at circuit point 165. In both cases, these clamping pulses m ' and p' cause the clamping stages 157, 158, 159 to respond to the porch of the transmitted remote

65 visual signals.

The outputs of the synchronous demodulators 155 supply the / - or ß-signal in a known manner. These become on the one hand the matrix 156 and on the other hand

supplied to the vector oscilloscope 154. Through the end points of the pointers 166, 167 and 168, respectively thus the phase angle of the / signal or the Ö signal or the color sync pulses are identified, provided a corresponding test signal is transmitted. The television receiver according to FIG. 8th is particularly suitable as a test receiver and can be used, for example, in television studios. Included stages 142 to 145 and 150 to are sometimes not required because the television signals are transmitted via cable can be fed directly to the node 165.

Claims (20)

Patent claims: 1. A method for black control of color television signal, which are composed of image signals and color sync pulses, characterized in that by demodulating the color sync pulses (F) pulses (0 obtained and therefrom clamping pulses of the first ao type (k ') are derived, which at a predetermined time interval occur after the color sync pulses and are used in a manner known per se for keyed black control of a color television signal. 2. The method according to claim 1, characterized in that in addition to the Kletnmimpuls of the first type (& ') additionally clamping pulses of the second type (τη') are generated, which in a given, but another time interval after the sync pulses (g) occur, which also used in a manner known per se for keyed black control of a color television signal will. 3. The method according to claim 1 and 2, characterized in that a clamping circuit is alternately supplied with a sequence of clamping pulses of the first type (Jc ') or a sequence of clamping pulses of the second type (m ^r ) . 4. The method according to claim 1 and 2, characterized in that the clamping pulses of the first type (&') and the clamping pulses of the second type (m') are combined such that a single sequence of clamping pulses of the third type (p ') is produced. 5. The method according to claim 1, characterized in that the generated clamping pulses of the first type (k ') occur temporally about 0.3 to 0.6 μβεο after the last oscillation of the associated color sync pulses (F). 6. The method according to claim 1, characterized in that the generated clamping pulses of the first type (k ') have a duration of 1.0 to 1.5 μεεο. 7. The method according to claim 1, characterized in that the color sync pulses (F) consist of about ten to twelve individual oscillations of the color subcarrier frequency and begin about 0.5 to 0.8 μβεΰ after the trailing edge of associated sync pulses (g) and on the back porch (SCH ") lie. 8. The method according to claim 1, characterized in that the color sync pulses (F) rectified and in this way square-wave pulses (0, which occur during the duration of the color sync pulses (F), that these square-wave pulses (0 are differentiated, the differentiating peaks accordingly the leading edges are suppressed and the differentiating peaks (k) corresponding to the trailing edges of these square-wave pulses (/) are fed as control pulses to a pulse shaper (28), from whose output the clamping pulses of the first type (k ') are emitted. 9. The method according to claim 2, characterized in that the clamping pulses of the second type (τη ') occur at a constant time interval of preferably 1.4 to 1.8 μβεο after the trailing edges of associated sync pulses (g), which arise from the horizontal sync pulses (S ) and the satellite (T, T, T ") put together. 10. The method according to claim 4, characterized in that the clamping pulses of the first type (k ') and those clamping pulses of the second type im') which are assigned to the satellites (T, T, T ") are added and in this way a single sequence is obtained from pulses (p) which are used either directly or after reshaping as clamping pulses of the third type (p ') for gated black control of a remote sensor signal. 11. The method according to claim 1, characterized in that the clamping pulses of the first type (k!) Are fed to a clamping stage of a television receiver in a manner known per se. 12. Procedure! according to claim 2, characterized in that the clamping pulses of the second type (m ') are fed to a clamping stage of a television receiver in a manner known per se. 13. The method according to claim 4, characterized in that the KlemqpimpuJse of the third type (//) in a manner known per se of a clamping step a television receiver. 14. The method according to claim 1 and 3, characterized in that the clamping pulses of the second type (m ') are always fed to the clamping circuit (29) when a gate (41) is open through which the sync pulses (g) or derived therefrom Pulses (m) or the clamping pulses of the second type (m ') are passed that the gate (41) is controlled by square-wave pulses (0, that if necessary the color sync pulses (F) - preferably by rectification - square-wave pulses (0 are derived, which the Lock the gate (41). 15. The method according to claim 14, characterized in that the sync pulses (g) are differentiated, the differentiating peaks, which correspond to the leading edges, suppressed and the differentiating peaks (m), which correspond to the trailing edges of the synchronous pulses (g) , the gate (41 ) are supplied. 16. The method according to claim 14, characterized in that the synchronizing pulses (g) or pulses derived therefrom (m) are delayed in time such that the pulses (m) fed to the gate (41) occur during the duration of the square-wave pulses (ΐ). 17. Circuit arrangement for carrying out the method according to claim 1 and 9, characterized in that the color synchronizing pulses (F) are fed to a rectifier (24) and in this way the square-wave pulses (0) are derived, that these square-wave pulses (i) of a differentiating stage (26) and the differentiated signal is fed to an amplitude limiter (27) which only detects those differentiating peaks (k) assigned to the color sync pulses (F). 409 728/160 are corresponding to the trailing edges of the rectangular pulses (/), and are forwarded that these differentiating peaks (k) fed to a pulse shaper (28) and a clamping pulses of the first type (k ¹⁾ of the clamping step (29). 18. Circuit arrangement for carrying out the method according to claim 2, characterized in that the synchronizing pulses (g) are fed to a delay stage (37) and then to a differentiating stage (38) and an amplitude limiter (39) which emits only those differentiating peaks (m), which correspond to the trailing edges of the synchronizing pulses (g) so that these differentiating peaks (m) are fed to a pulse shaper (28) and passed on to the clamping stage (29) as clamping pulses of the second type (m '). 19. Circuit arrangement for carrying out the method according to claim 3 and 14, characterized in that the color sync pulses (F) are fed to a rectifier (24) and in this way the rectangular pulses (0 are derived that these rectangular pulses (ζ) of a differentiating stage (26 ) and the differentiated signal is fed to an amplitude limiter (27) which only emits those differentiating peaks (k) assigned to the color sync pulses (F) which correspond to the trailing edges of the square-wave pulses (0) so that the sync pulses (g) of a delay stage (37) and then fed to a differentiating stage (38) and an amplitude limiter (39) which emits only those differentiating peaks (m) which correspond to the trailing edges of the synchronizing pulses (g) so that these differentiating peaks (m) are fed to the gate (41) which is open during the duration of those clamping pulses of the second type (rri) which are assigned to the satellites (T, T, T ") and therefore only e Inen part (pulses n) of the differentiating peaks (m) lets through that these passed pulses (ri) and the differentiating peaks (k) assigned to the color sync pulses (F) are added in an adder (43) and that from the output of this adder (43) the single sequence of pulses 0?) and either directly or after being converted into a pulse shaper (28) as a sequence of clamping pulses of the third type (/>') fed to the clamping stage (29). 20. Circuit arrangement according to claim 19, characterized in that the delay stage (37) is designed in such a way that the synchronizing pulses (g) and subsequently also those thereof derived pulses (m) during the duration of those square-wave pulses (0 which occur through Rectification of the color sync pulses (F) can be derived. Considered publications:
"Principles of Color Television" by The Hazel- tine Laboratories Staff, New York, John Wiley & Sons, Inc., 1956, p. 172; Electronics, February 1952, pp. 96 and 97. For this purpose 2 sheets of drawings 409 728/160 11.64 Q Bundesdruckerei Berlin