DE1065454B - Circuit arrangement for the automatic setting of the basic brightness of a television set - Google Patents

Description

GERMAN

In the circuits known up to now, the basic brightness of the television picture, i. H. the so-called Black level, derived from the porch or the sync pulses. The black level is given in terms of voltage by the direct current component of the television signal. Because this DC component is lost as a result of the capacitive coupling between the individual amplifier stages in the device, it must be added to the signal in front of the picture tube. This happens with the known devices by the so-called black level maintenance. Either the The largest signal voltage obtained by peak rectification, i.e. the voltage of the peak value of the Sync pulse, or with the so-called keyed black level maintenance that from the transmitter im Connection to the synchronous impulses transmitted rear porch of the signal mixture used. With such a derivation of the basic brightness, the image appears with weakly incident transmitters under certain circumstances too dark and with very strong stations too bright. It is therefore with the known ones Circuits a setting of the basic brightness, for example by means of a potentiometer, by hand provided so that the observer can set the most favorable brightness value in each case. the correct setting of the basic brightness of a television set, however, falls to the untrained user experience has shown that the device is very difficult. However, if the device is set incorrectly, the transmission quality will decrease the same not fully exploited.

The invention is concerned with the task of an automatic setting of the basic brightness achieve. This is achieved in that one derived from the beam current of the picture tube, only during the time of the black image content is taken from an integrating network and as a control voltage to an electrode of the picture tube that is decisive for the basic brightness is created.

It is basically already known to use a black control on the TV amplifiers black image content, but not in connection with the setting of the basic brightness of the display tube and not as a function of the beam current of this tube.

Compared to the known circuits, the invention has the advantage that the basic brightness of the electrical quantity decisive for the visual impression, namely the beam current, directly is derived, so that the tube aging of the picture tube and operating voltage fluctuations be eliminated. .

According to a further development of the invention, the circuit arrangement is used

for automatic adjustment

the basic brightness of a television set

Applicant:

Siemens-Electrogeräte Aktiengesellschaft,

Berlin and Munich, Munich 2, Oskar-von-Miller-Ring 18

Horst Pelka, Munich, has been named as the inventor

for this purpose a circuit arrangement with an electronic Switch, which as a result of temporal blanking during the duration of the television signal mixture existing blanking gaps for the sync pulses and as a result of amplitude-dependent blanking is activated by the light image content only during the black image content.

The drawing shows a schematic diagram to explain the circuit arrangement according to the invention by way of example, the current flowing to the booster voltage source being used as a variable proportional to the beam current for generating the control voltage. It is assumed that there is at least one point in each image, the amplitude of which corresponds to the image black value. The television signal mixture α fed to the input E of this circuit arrangement is taken from the external resistor R _{1 of} the output stage and applied to the cathode of the picture tube B. The beam current creates a voltage at the resistor R ₂ , via which the booster voltage Boo is applied to an electrode of the picture tube B , which is fed to the integrating network N via the electronic switch S, if it is closed, and via the amplifier V. This voltage supply does not take place during the recording of the entire television signal mixture, but only during the time of the blackest pixel. For this purpose, the tube Ro ₁ is initially provided, which during the duration of the blanking gaps present in the television signal mixture and encompassing the sync pulses and the front and rear black stairs in time and through the bright

905 628/157

Image content of the television signal mixture α is blanked as a function of the amplitude, that is to say it is only conductive during the black image content. The temporal blanking during the duration of the blanking intervals of the television signal mixture is carried out, for. B. taken from the winding W _{1 of} the flyback transformer T , the grid G _{1 of} the tube Ro ₁ supplied negative blanking pulses. Since 'these blanking pulses occur during the blanking gaps, the tube Ro _{1 is} practically impermeable in time coincidence with them, so that at this time the integrate. the network N is not supplied with voltage. For in Undurc'hlässigwerden Ro of the tube ₁ the voltage drop of the tube Ro ₁ disappears at the anode resistance so that a positive pulse is supplied as a result of abrupt increase of the voltage at the anode to the grid of the further tube Ro. ₂ As a result, oppositely directed control pulses occur at the anode resistor and the cathode resistor of the tube Ro _{2 of} such a magnitude that the electronic switch 5 ^{1 is} opened so that the voltage derived from the beam current of the picture tube B does not reach the network N. Outside this period of time, the tube Ro ₁ is only conductive if there is no voltage tapped from the television signal mixture α _{at the grid G 3 of} the tube Ro ₁ , the amplitude of which is smaller than that of the blackest pixel. As soon as the tube Ro ₁ becomes conductive during the blackest pixel, the voltage on the grid of the tube Ro ₂ becomes more negative, so that the control pulses already mentioned at the anode resistor and the cathode resistor appear with opposite polarity as before. The electronic switch S is thus closed, so that the voltage derived from the beam current reaches the network N. On the other hand, as soon as a voltage tapped from the composite television signal is applied to the grid G _{3 of} the tube Ro ₁ , the amplitude of which is smaller than that of the blackest image point, the tube Ro ₁ becomes impermeable and controls the tube Ro ₂ again in such a way that the latter during the duration of the blanking gaps electronic switch ^ opens, so no voltage on the

Λ Network N has arrived.

According to the described mode of operation of the electronic switch S controlled by the tubes Ro ₁ and Ro ₂ , the integrating network N receives a voltage derived from the beam current of the picture tube

ίο only supplied during the time of the black image content. A corresponding control voltage is then taken from the integrating network N and sent to an electrode that is decisive for the basic brightness. the picture tube, e.g. B. the Wehnelt cylinder applied.

Claims (2)

Patent claims: 1. Circuit arrangement for the automatic setting of the basic brightness of a television set, characterized in that one of the jet stream ao derived from the picture tube, integrating only during the time of the black picture content The voltage supplied to the network is taken from it and sent as a control voltage to one for the basic brightness decisive electrode of the picture tube is applied. 2. Circuit arrangement according to claim 1, characterized in that the beam current The voltage derived from the picture tube is applied via an electronic switch, which as a result of temporal blanking during the duration of the blanking gaps present in the television signal mixture for the sync pulses and as a result of amplitude-dependent blanking by the bright Image content is only closed while the image content is black. Considered publications: "Radio Mentor", 1955, issue 11, pp. 692/693; "Funk und Ton", 1951, No. 10, p. 509. For this. 1 sheet of drawings © 909 '628/157 9. 59