DE1100081B - Circuit arrangement for black control in a multi-standard television receiver - Google Patents

Description

The invention relates to a circuit arrangement in a television receiver for reception of television signals modulated onto a carrier wave in both a positive and a negative sense, in which the same demodulator is used for both types of modulation and the output electrode is one Video tube by means of a switch and, depending on the modulation sense, either with the Control grid or the cathode of a picture tube is connected. ίο

With combination receivers that meet the above-mentioned conditions, it was not previously possible to the black level under all circumstances in a sufficiently reliable manner on the display tube reintroduce if he z. B. due to the capacitive coupling between the control electrodes Display tube and the previous stage has been lost.

It is known for standard receivers that the video signal, whose black level has been lost, an electron tube that is blocked by gate pulses while the sync pulses occur, in such a way that the current flows through this tube during the occurrence of the black level in the video signal assumes its maximum value, the tube having a voltage that is dependent on this maximum value is taken and this voltage together with the video signal from a control electrode of the picture tube to keep the black level constant.

In a circuit arrangement of the type mentioned for multi-standard reception, it was known to use an additional reversing stage in the case of receiving programs with positive modulation, which allows only a single identical pulse separation stage for both negative and positive modulation to use. If you use a similar method with such a circuit arrangement wanted to keep the black level constant for both types of modulation on the one for standard receivers well-known way, then, one would put together the so obtained from the black level dependent voltage and the video signal require a second, additional inverter.

It has therefore been proposed to reduce the black level in multi-standard receivers when receiving in positive Meaning television signals modulated onto a carrier wave with the help of the brightest picture signal components to set; this method seemed the easiest. However, practice has shown that such a built receiver not entirely satisfactory 5a can work. There are fluctuations in the black value, which under certain circumstances can lead to a considerable Can lead to impairment of image reproduction.

Circuit arrangement
for black control in one
Multi-standard remote control

Applicant:

NV Philips' Gloeilampenfabrieken,
Eindhoven (Netherlands)

Representative: Dipl.-Ing. K. Lengner, patent attorney,
Hamburg 1, Mönckebergstr. 7th

Claimed priority:
Netherlands 6 April 1956

Peter Johannes Hubertus Janssen

and Wouter Sineulers, Eindhoven (Netherlands),

have been named as inventors

The circuit arrangement according to the invention counteracts this disadvantage and has the characteristic on that the video signal with both types of modulation of an electron tube, possibly using an inverting stage, is fed in such a way that during the occurrence of the black value in the video signal the current in the main circuit of this tube assumes its maximum value, and that one of this Maximum value-dependent voltage taken from the output circuit of the tube and a control electrode is fed to the picture tube to keep the black level constant, with gate pulses a Control electrode of the electron tube are fed to this during the occurrence of the sync pulses lock.

The circuit arrangement is particularly advantageous when automatic gain control in the receiver is used. The control voltage for this is for the two modulation systems of the same tube circuit taken, and their size is determined by the maximum amplitudes of the demodulated signal, which is still provided with the direct current component. In the case of negative modulation, these are the Vertex of the sync pulses and, with positive modulation, the brightest image components, i.e. H. the maximum White that is present in the picture at a given moment. The latter means that if the

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brightest parts in the recorded; Scene during - The signal 20, with positively directed synchro, some times are gray or almost black, as a result of impulses, is also transmitted via the contact arm 31 of the the automatic gain control these parts in the switch 22 and the capacitor 32 to the anode The picture on the display tube is permanently white to tube 33, the circuit of which is used to control the if not the black level is fixed again to a reliable 5 black level on the display tube is set in the picture. gain. The connection point of the contact arm 31

An example of the circuit arrangement after the Er and the capacitor 32 will also remove the signal is explained in more detail with reference to the drawing, assume that the synchronous pulse, not shown is fed to the separation stage.

Fig. 1 the switching position for negative modulation io The anode of the tube 33 is also on the and resistance 34! with the controllable contact of the

Figure 2 illustrates that for positive modulation. see the positive voltage source and earth lying

In FIG. 1, the potentiometer 35 at the intermediate frequency circuit 1 is connected. Consequently, the The incoming signal is fed to the demodulator circuit, the anode of the tube 33 to a medium potential from the rectifier 2 and the parallel circuit 15 are placed. The signal 20 is this potential the capacitor 3 and the resistor 4 consists. superimposed. Between the control grid and the Ka-Bei the specified polarity of the diode 2 occurs when the tube 33 is the resistor 36, wherein one in the negative sense to a carrier wave on this cathode by means of the parallel connection of the modulated television signal at resistor 4 a demo resistor 37 and the capacitor 38 to ground modulated signal, the sync pulse of which is negative 20. The control grid of the tube 33 is also are directed, as shown schematically at 5. connected to one side of the capacitor 39, des-this Signal is fed to the control grid circuit of the tube 6 sen other side gate pulses 40 in such a way fed. In the anode circle of this tube there is a sense that the tube 33 during the occurrence derstand 7, from which a signal is taken which is below the sync pulses of the at the anode of the tube 33 other signal 20 occurring at a control electrode of the display tube 25 is blocked. The Maxi fed will. voltage that is still anode current in tube 33

The cathode of the tube 6 is connected to the cathode that allows the flow, i.e. the maximum anode current, to be connected to the tube 8, which is used in a known manner to generate an automatic gain control voltage ter of the signal 20 through the front and rear black school witnesses, in other words. At the common cathode resistor 9 of 30 by the black level. The maximum anode current tubes 6 and 8, a signal of the shape 10 occurs. This requires the maximum voltage that is connected to the parallel control grid of the tube 8 with earth. The circuit 37, 38 occurs, and the time constant of which is tube is set in such a way that during the largest one selected such that this voltage during part of the signal the tube is blocked; only the line period remains almost constant.
Peak of the signal, in the case of negative modulation that is the 35. In a certain embodiment of the switching peak of the sync pulses, 'come over the device, which has proven itself well, is the i? C-time blocking point. The anode circuit of the tube is constantly fed with the parallel circuit 37, 38 at 625 images by rectified voltage pulses 11, lines about 5000 line periods and at 819 images the line deflection circuit (not shown) has about 7000 line periods.

can be taken. These pulses charge via the capacitor 14 serving as the anode tension grid 28 of the display tube 25, the resistance source. If 41. Shortly after the occurrence of the sync pulse, current begins to flow in the tube 8, the charge is withdrawn from the signal 20, ie also at the cathode of the Wie-capacitor 14, which is black via the display tube available, and is added again in diederstand 13. As a result, the voltage across the resistor 13 is reduced to the control grid. A part of this output tube via the resistor 41, which is connected in parallel to the par resistor, to which a smoothing capacitor 15 allele circuit 37, 38 maximum voltage developed, is supplied at 16 with the control voltage, which is taken from the automatic gain control until the next Synzur occurs, chronimpulses remains almost constant. The verschiededie in a known way one or more of ¹ De- NEN voltage settings for the display tube 50 modulator circuit of the receiver before and now selected in such a 2, 3, 4, that during the erwähngehenden high or Zwischenf requenzstuf en to-th occurrence of the black reference value which will be led again. Gaiberöhre is currently blocked. During the occurrence

The cathode of the tube 17 is also connected to the synchroninipulse in the signal 20, the re-cathode circuit of the tube 6 remains connected, and the control tube is blocked, while after each sync grid the tube 17 is connected to earth. In the anode chronological pulse of the black level of the signal again from this tube there is a resistor 18, to which a new one is brought to the blocking point.
Signal 19 is taken, but otherwise only when the previous one was based on the requirement

is used with positive modulation. assumed that the black level of the front and

The resistor 7 will correspond to a signal of the shape 20 60 back porch of the signal. By taken from the contact arm 21 of the order error and less precise setting of transmitters switch 22 and the capacitor 231 to the cathode 24 'this is often not or not constantly the case. Around the display tube 25 is guided. The cathode 24 can counter this disadvantage, the control gateist Via the resistor 26 with the positive voltage of the tube 33 effective pulse through integration voltage source and delayed through resistor 27 to ground 65 so that the two blacks are also connected. The control grid 28 of the display tube shoulders the video signal with be blanked, so 25 is connected to the capacitor 29, whose other then the darkest image components Represent the other side by means of the contact arm 30 of the switching black level.

ters 22 is laid on earth. The sync pulses of the. It is noteworthy that it is not necessary Signals 20 make the control grid 28 more negative. 70 the tube 33 completely through the control grid

effective impulse to block. It is sufficient that during the occurrence of the sync pulses and possibly also the black shoulders of the signal at the anode of the tube 33, the cathode current is reduced so far that the maximum cathode current is caused by the black level in the signal at the anode of the tube mentioned.

In FIG. 2, the same circuit arrangement is shown as in FIG. 1, but with the changeover switch 22 in the positive modulation position. When receiving a modulated in a positive sense on a carrier wave TV signal then arises at the resistor 4 .Signal with positively directed sync pulses, such as it is shown at 42. A signal of the shape 43 then appears at the cathode of the tubes 8 and 17 Control voltage for automatic gain control, which is taken from the circuit at 16 then controlled by the brightest image components in the signal 42, that is to say by the maximum white.

A signal 44 is taken from the anode of tube 6 and a signal 45 is taken from the anode of tube 17. That Signal 44 becomes the control grid by means of contact arm 30 of changeover switch 22 and capacitor 29 28 of the display tube 25, and the cathode 24 of this tube is through the capacitor 23 and the Contact arm 21 placed on earth. The sync pulses of the signal 44 make the control grid of the display tube so again more negative.

The signal 45 is fed to the anode of the tube 33 by means of the contact arm 31 and the capacitor 32. As with negative modulation, the anode of this tube is then also the video signal positively directed sync pulses supplied. The effect of this part of the circuit is therefore the same those with negative modulation, and ian the display tube the black level is always in the Lock point set.

Claims (2)

Patent claims: 1. Circuit arrangement in a television receiver for receiving both in the positive as well as television signals modulated onto a carrier wave in the negative sense, in which the same Demodulator is used for both types of modulation and the output electrode of a video tube by means of a switch and, depending on the modulation sense, either with the control 40 45 grid or the cathode of a picture tube, characterized in that the video signal for both types of modulation is fed to an electron tube (33), if necessary using an inverter (17), in such a way that the current in the main circuit is maintained during the occurrence of the black level in the video signal this tube assumes its maximum value, and that a voltage dependent on this maximum value is taken from the output circuit of the tube (33) and fed to a control electrode (28) of the picture tube (25) to keep the black level constant, gate pulses (40) to a control electrode of the electron tube (33) are supplied, which block them during the occurrence of the sync pulses. 2. Circuit arrangement according to claim 1, characterized in that the anode DC voltage The video signal is superimposed on the electron tube (33) with positively directed sync pulses is and this signal by means of a switch (22) the output circuit one for the relevant Modulation sense suitable video amplifier tube (6,17) is removed in the receiver, the Control grid of the first-mentioned tube (33) connected to one end of a resistor (36) the other end of which is connected to the cathode circuit of this tube, and the control grid this tube is also coupled to one layer of a capacitor (39), the other layer of which Gate pulses (40) are supplied in such a way that during the occurrence of the sync pulses on the anode of this tube the voltage in the control grid circuit is reduced so much that the Current intensity in the output circuit of this tube remains below the value that would be in the presence of it of the black level occurs in the video signal, the cathode of this tube having one end of a Resistance (37) is connected, the other end of which is connected to earth, and this resistance is bridged by a capacitor (38), the coating of which is connected to the cathode of the tube one end of a resistor (41) is connected, the other end of which is connected to the control grid (28) the picture tube (25) is connected. Considered publications:
U.S. Patent No. 2,618,703;
"Funkschau", 1955, issue 16, p. 337. 1 sheet of drawings © 109 527/225 2.