Title of Invention

"METHOD AND APPARATUSES FOR CALIBRATING THE SCREEN GRID VOLTAGE OF COLOUR PICTURE TUBES"

Abstract The invention relates to the screen grid calibration (UG2) , also called G2 calibration, of colour picture tubes (1). In this case, it is based, in particular, on television sets having colour picture tubes in which the cut-off points are automatically readjusted by means of so-called automatic cut-off circuits. During G2 calibration, a DC voltage reference corresponding to the black value is set at the cathodes (K) of the colour picture tube, which cathodes are driven by an RGB signal. According to the invention, in a first step, a voltage potential changeover is carried out, by means of an electronic switch (DS), at the control electrodes (G1) of the colour picture tube (1), which control electrodes are at reference potential (earth) for the RGB signal driving. In a second step, the screen grid voltage (UG2) is set in such a way that field and/or line flyback stripes are just visible, and/or are reduced until the field and/or line flyback stripes actually disappear, the transition being utilized as an indicator of the fact that the cathode (K) at the largest positive potential compared with the remaining cathodes (K) is now precisely at a threshold (Vcc) corresponding to the maximum voltage available to the cathodes (K). After this setting of the screen grid voltage (UG2), the control electrodes (Gl) are reset to reference potential by means of the switch (DS).
Full Text 2 FIELD OF INVENTION
The invention relates to a method for calibrating the screen grid voltage of colour picture tubes and in this case is based, in particular, on television sets having colour picture tubes in which the cut-off points are automatically readjusted by means of so-called automatic cut-off circuits. In the case of such television sets, it is customary to use colour picture tubes in which the screen grids (abbreviated to G2) of the three tube systems R,G and B are combined or have a common connection at the colour picture tube base.
BACKGROUND OF THE INVENTION
Such screen grid calibration, referred to as G2 calibration below, is carried out in mass production of television sets, in particular, after a so-called "burn-in test" after the sets have been assembled, in which test the sets are operated as far as possible under operating conditions and which test serves for identifying and filtering out earlier failures. The G2 calibration comprises progressive voltage settings at the screen grids and measurement operations at the control electrodes of the colour picture tube, such as e.g. at the cathodes thereof in the case of the signal driving via the cathodes that is customary nowadays.
OBJECT OF THE INVENTION
The object of the invention is therefore, to provide a method for simplifying the G2 calibration in apparatuses having an automatic cut-off circuit for cut-off point

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regulation of the color picture tube. SUMMARY OF THE INVENTION
This object is achieved by means of the method of the invention according to the features as described hereinbelow.
The invention is based on the following consideration and insights:
A G2 calibration is carried out in order to ensure, in the case of the colour picture tube used in the apparatus, that - in the case of the colour picture tube being driven via its cathodes in the manner that is customary nowdays - VB (video blanking) signal is present at the cathodes in a specific voltage range in order that the available operating voltage Vcc of the video output amplifier stages can be utilized optimally for the modulation and correct presetting is provided for the cut-off point, called cut-off below, of the respective tube system. In this case, it is not sufficient, however, to set the screen grid voltage to a specific value - as shown by Figure 4 - with a given screen grid voltage a relatively large cathode voltage range arises on account of variations for the cut-off of the respective tube system and, given a screen grid voltage of e.g. 300 volts, can exceed, or impermissibly restrict, the voltage range available at the cathodes for signal modulation. The voltage range at the cathodes, which forms a so-called modulation window in this case, is bounded by the operating voltage Vcc of the video output amplifier stages, on the one hand, and by the saturation voltage or behaviour thereof, on the other hand.

Therefore, for that cathode which is at the highest potential in the modulation window, a cathode voltage is defined for which the cut-off is achieved by appropriate setting of the screen grid voltage, in order to ensure that, at the respective cathode, the video signal-or the corresponding RGB signal-lies optimally in the modulation range bounded by the operating voltage Vcc and the saturation voltage of the video output amplifier stages. In practice, however, in television sets with cathode control of the colour picture tube and automatic cutoff regulation, instead of the actual cut-off, a cathode voltage level which is known as a quasi cut-off and is defined by the circuit design is set with the aid of the screen grid voltage and corresponds to the test current of the cut-off regulating circuit, in which case-as already mentioned-the setting is oriented to that cathode which, compared with the remaining cathodes, has the respectively highest level with respect to the reference potential. In a cathode voltage level of this type, it is possible to take account of tolerances and/or ageing effects of the picture tube, in order that, during cut-off regulation, there is a reserve, in particular for the occurrence of maximum tolerances and/or ageing effects, which suffices to ensure that the RGB signals cannot be shifted into saturation of the video output amplifier stages, or-in the event of a tolerance- and/or ageing-dictated shift in the other direction-the cut-off points do not drift beyond the available operating voltage Vcc, the consequence of which would be that the tube could no longer be inhibited in the event of black and blanking levels and flyback stripes would thus occur. Consequently, it appears to be necessary to measure the cathode voltage.

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For the G2 calibration according to the invention, however, it is possible to avoid measuring the cathode voltages as follows: the relatively large tube-dictated tolerances between the desired cut-off voltage of the cathode respectively at the highest voltage potential and the screen grid voltage to be set for this are in this case not included in the G2 calibration by way of measurement of the cathode voltages, rather a different criterion is advantageously used, namely making flyback stripes visible or the threshold in this respect from which flyback stripes actually become visible. This exploits the fact that, as is known, voltages lying above the respective cut-off are applied to the cathodes during the line and field flyback, in order to ensure that the cathode currents are blanked, that is to say prevented, during the respective time required for this. However, since the signal value "black" usually already lies in the cut-off, in connection with blanking the term "blacker than black" is used. If the screen grid voltage is then increased, the respective voltages between the cathodes and Wehnelt cylinders must also be increased correspondingly in order that the colour picture tube can still be inhibited. If the cathodes reach the maximum available voltage, limited by the operating voltage Vcc of the video output amplifier stages, the colour picture tube can no longer be inhibited when the screen grid voltage is increased further, with the result that flyback stripes become visible.
Therefore, if the screen grid voltage is increased until flyback stripes occur and the screen grid voltage is subsequently reduced until the flyback stripes actually disappear again, it is possible to ensure that the cathode voltage of the cathode

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ray system whose cut-off is at the respectively highest voltage potential compared with the remaining cathode ray systems corresponds exactly to the maximum available cathode voltage. As a result, the maximum voltage range for signal modulation is available for this cathode.
In order to reliably avoid flyback stripes, however, it is customary to provide a certain voltage amount as a reserve. Furthermore, the ageing behaviour of the colour picture tube has to be taken into account. Due to cathode wear, the electric field strength between the cathodes and the Wehnelt cylinders decreases during the life of a colour picture tube. This wear is compensated for by increasing the cathode voltages with the aid of the automatic cut-off regulation, just called cut-off regulation below. The relationship between the ageing of a colour picture tube and the ageing-dictated shift in the cathode voltage, representing the cut-off, as a result of the cut-off regulation is illustrated in FIG. 3. This means that the screen grid voltage would then have to be reduced again to ensure that the resulting cut-off voltage of that cathode which-in comparison with the other two cathode ray systems-is at the respectively highest voltage potential is less than the maximum available cathode voltage determined by a specific amount (that is to say the abovementioned reserve plus a regulating range to be taken into account) (practical values: -10% . . . -15%).
By virtue of the invention, however, settings of the screen grid voltage to the value which corresponds to the maximum available cathode voltage are advantageously avoided. Instead, provision is made for changing over the Wehnelt cylinders of the colour picture tube which are at reference potential to a

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different or positive voltage potential which preferably takes account of the cathode voltage reserve explained above and of the effect of the cut-off regulation on the signal modulation range. This potential changeover occurs in each case at the beginning of the G2 calibration. Only then is the screen grid voltage set, in which case the operation of making flyback stripes or the like visible on the screen or the visibility threshold in this respect can advantageously be utilized as a setting criterion in this case as well. Afterwards, the potential changeover is reversed and the G2 calibration is thus ended.
The voltage difference to be provided for the potential changeover according to the invention can be determined e.g. empirically or with the assistance of diagrams like the diagrams shown in Figure. 3 and Figure. 4.
The G2 calibration according to the invention thus has the advantage that a single screen grid voltage setting is performed and advantageously measurement at the cathodes of the colour picture tube is rendered unnecessary. In addition there is a significant advantage, in particular for mass production of television sets, in that G2 calibration can be carried out with the rear panel of the TV set housing or case having been mounted.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention is explained in more detail below using an exemplary embodiment with the aid of the drawing. In the accompanying drawing,

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Figure. 1 shows one of the RGB signal-processing signal paths with the colour picture tube of a television set,
FIG. 2 shows diagrams for illustrating the G2 calibration,
FIG. 3 shows the relationship between the ageing of a colour picture tube and the ageing-dictated shift in the cut-off as a result of the cut-off regulation, and
FIG. 4 shows the dependence and variation range of the cut-off on the screen grid voltage of a colour picture tube,
where mutually corresponding parts are provided with the same reference symbols.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
Figure. 1 illustrates a block diagram to show one of the identical colour channels of an RGB colour signal-processing circuit with cut-off regulation of the respective tube system of a colour picture tube 1. For the G2 calibration of the colour picture tube 1, a potentiometer P having a tap is provided, which is intended to be arranged on the chassis of a television set and preferably be accessible for the G2 calibration through the rear panel of the housing of the said

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television set in a manner known per se. The tap of the potentiometer P, which is arranged between reference potential (earth) and a positive DC voltage +UB, is connected to the screen grid G2 of the respective tube system of the colour picture tube 1. Thus the screen grids G2 can be set to a common positive screen grid voltage +UG2 and the G2 calibration can preferably be carried out jointly for all three systems.
The colour picture tube 1 is preferably intended to be driven via its cathodes K, in which case the control grids Gi of the colour picture tube 1, which control grids are designed as Wehnelt cylinders, should be connected to reference potential (earth) as is known. A measuring transistor 3 arranged between the cathode K of the respective tube system and the output of a corresponding video output amplifier stage 2 is provided, for measurement of the dark current, in the respective colour channel. For measuring the dark current, a cut-off measurement line is keyed in, in a known manner, in the respective colour channel during a field blanking interval by means of a blanking and measurement pulse generator circuit 5 which is arranged upstream of an addition stage 6 in the course of the RGB colour signal path.
The addition stage 6 in the respective colour channel controls the video output amplifier stage 2, via an output stage 7, with a summation signal. When the video signal is being processed, the summation signal is composed of the signal voltage of an RGB signal and a voltage which is updated e.g. in each case in a field-by-field manner and is stored in a storage capacitor C as a regulation

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voltage for the cut-off regulation of the RGB signal. When the regulation voltage--called cut-off regulation voltage below-is being determined, on the other hand, the pulse voltage of the cut-off measurement line that has been keyed and the cut-off regulation voltage resulting from the comparison of the voltage Urn, which is measured across the measuring resistor 4, with a reference voltage Uref form the summation signal.
When the cut-off regulation voltage is being determined, the voltage Urn measured across the measuring resistor 4 is fed via a series circuit formed by a buffer stage 8 and the voltage source for generating a reference voltage Uref to the inverting input of an operational amplifier 9, which is designed as a comparator and whose non-inverting input is connected to reference potential via a storage capacitor G_, which is provided for storing a voltage proportional to the leakage current. A sampling switch SL is provided for the e.g. field-by-field updating of this voltage which compensates for the influence of the leakage current. By means of the sampling switch SL, the reference voltage source Uref can be connected to the non-inverting input of the operational amplifier 9 in such a way that it is bridged together with the two inputs of the operational amplifier 9 during the measurement and storage of the voltage proportional to the leakage current. The switch position illustrated is adopted when the cut-off regulation voltage is being determined.
The cut-off regulation voltage which is generated by the operational amplifier 9 designed as a comparator and is updated in accordance with the respective

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measurement cycle is in this case stored for the cut-off regulation via a sampling switch S in the storage capacitor C. The switch position illustrated is adopted during RGB signal processing.
In the case of the circuit section which has been described thus far and is known per se, the measurement pulse generator circuit 5, the stages 6, 7 and 8, the operational amplifier 9, the sampling switches S and SL, and the reference voltage Uref are part of a video processor 11 designed as an integrated circuit.
The connection of the control grids G; of the colour picture tube 1 to reference potential is established, according to the invention, by means of an electronic switch DS designed as a changeover switch.
With this switch DS, which is arranged e.g. together with the video output amplifier stages 2 on a so-called picture tube printed circuit board (not illustrated), according to the invention-as described in more detail below-for the G2 calibration a voltage potential changeover is carried out at the control grids Gi of the colour picture tube 1.
The switch DS can be realized e.g. in a simple manner by means of a voltage divider comprising non-reactive resistors and an npn transistor T to be operated as an electronic switch. To that end, the emitter of the transistor T is connected to reference potential (earth). The collector-emitter path of the transistor and a first resistor Rl are connected in parallel with one another and are connected via

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a second resistor R2 to a positive operating voltage +UB', which can be derived e.g. from the positive operating voltage +Vcc of the video output amplifier stages 2. The parallel circuit formed by the collector-emitter path of the transistor T and the first resistor Rl is furthermore connected to the control grids G.sub.l of the colour picture tube 1 via a third resistor R3. The base of the transistor T, which forms the control input of the switch DS, is connected to the positive operating voltage +UB' via a fourth resistor R4.
The control signal ST fed to the base of the transistor T for the purpose of controlling the switch DS is such that the transistor T is turned on, that is to say operates in the saturation mode, for normal operation of the television set, with the result that the control grids Gi practically carry the reference potential. For the G2 calibration, on the other hand, the transistor T is turned off, with the result that the control grids Gi carry a voltage potential which is determined by a divider ratio which is practically formed by the first (Rl) and second (R2) resistors and can be advantageously predetermined-in particular taking account of the cathode voltage reserve already explained and the effect, likewise already explained, of the cut-off regulation on the signal modulation range as a result of the colour picture tube ageing effects.
Since just two signal states are necessary for the control signal ST, the latter can also be generated by means of a microprocessor which is used in any case in contemporary television sets, with the result that the G2 calibration can advantageously be carried out by means of an apparatus operating command

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that is to be appropriately provided. With the assistance of an optical measuring apparatus with sensors which can be used to evaluate the screen of the television set during the G2 calibration in accordance with a setting criterion, it is possible, moreover, to completely automate the G2 calibration.
The principle behind the G2 calibration is described below with reference to similar diagrams a) and b) illustrated in FIG. 2, where diagram a) is supposed to be based on a G2 calibration which is described in DE 198 55 628.4, which was not published before the priority date, while diagram b) is supposed to illustrate the G2 calibration in accordance with the present invention.
The diagrams a) and b) illustrate, by way of example, in addition to the profile of the screen grid voltage UG2, the respective profile of the cathode voltage Ucathode for the cut-off as a function of the screen grid voltage setting, called UG2 setting below. The respective ordinate of the diagrams a) and b) is a scale for the screen grid voltage UG2, the cathode voltage Ucathode and the cathode current Icathode- The voltage values which are specified here on the ordinate and are assigned to the cathode K are by way of example and refer e.g. to the reference potential (earth).
A cathode voltage profile of this type is typical for cut-off regulation. On account of the cut-off regulation, the cut-off of the respective tube system of the colour picture tube 1 correspondingly follows the screen grid voltage profile as far as the maximum voltage value which is available to the cathodes K for modulation

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and is called "blanking" threshold below. As is known, depending on the circuit design used, the operating voltage Vcc of the video output amplifier stages 2 or else a fixed DC voltage offset may correspond to the "blanking" threshold. A further increase in the screen grid voltage UG2 can then no longer be corrected by the cut-off regulation-before that the said correction was effected by a corresponding shift in the cut-off along the cathode voltage profile parallel to the screen grid voltage profile-, with the result that cathode current Icathode starts to flow and field and/or line flyback stripes, just called flyback stripes below, thus become visible.
Proceeding e.g. from a predeterminable UG2 presetting in accordance with a value A on the respective abscissa of the diagrams a) and b), and with the feeding of a black picture into the television set -e.g. by means of a video signal generator (not illustrated)-, in the case of the G2 calibration described in DE 198 55 628.4 in a first step, the screen grid voltage +UG2 is increased until flyback stripes become visible. In this case, the fact that flyback stripes become visible is utilized as an indicator of the fact that the cathode K at the largest positive voltage potential compared with the remaining cathodes K is already bordering the "blanking" threshold. In the diagram a), an abscissa value B, starting from which a further increase in the screen grid voltage UG2 leads to the cathode current I.sub.cathode flowing and thus flyback stripes become visible, corresponds to the "blanking" threshold. In a second step, the screen grid voltage +UG2 is then reduced until the flyback stripes actually disappear-or just remain visible and can thus be measured by means of optical sensors-, the

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transition being utilized as an indicator of the fact that the cathode K at the largest possible voltage potential is now at the "blanking" threshold. Investigations have shown that the transition can be detected by the human eye with such accuracy that errors are practically precluded. Instead of using the human eye for detecting the transition, it is also possible to use measuring apparatuses with optical sensors.
In a third and thus last step, in the case of the G2 calibration described in DE 198 55 628.4, the screen grid voltage +UG2 is then reduced by a specific amount, in order to have a corresponding margin for maximum ageing effects of the colour picture tube 1 as well as a cathode voltage reserve (already mentioned) for the purpose of reliably avoiding flyback stripes. An abscissa value C, which identifies the screen grid voltage setting at the end of both the G2 calibration described in DE 198 55 628.4 and the G2 calibration according to the invention, is supposed to correspond to this amount.
In the case of the G2 calibration according to the invention, which is likewise intended to proceed from the UG2 presetting in accordance with abscissa value A with a black picture being fed in, as the first step--in contrast to the G2 calibration described in DE 198 55 628.4-provision is made for changing over the control grids Gi from reference potential to a positive voltage potential. The voltage difference that is provided in this case is intended to correspond to the abovement'oned margin for maximum colour picture tube ageing effects and cathode voltage reserve.

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A corresponding voltage difference AU at the respective cathode K corresponds to the changeover of the control grids d from reference potential to the positive voltage potential. It brings about a parallel shift in the profile of the cathode voltage Ucathode for the cut-off in such a way that the "blanking" threshold at the cathode K at the largest positive voltage potential (compared with the remaining cathodes K) is displaced to the abscissa value C, which identifies the screen grid voltage setting at the end of a G2 calibration. The profile of the cathode voltage Ucathode, which profile is shifted in parallel, is represented by means of the dash-dotted line D.
According to the invention, in a second step, practically all that is necessary is to set the screen grid voltage +UG2to a voltage value which corresponds to the abscissa value C, since, starting from this set value, as a result of the voltage potential changeover according to the invention at the control grids Gi, a cathode current Icathode starts to flow and flyback stripes thus become visible. In this case, the transition at which the flyback stripes actually become visible or just disappear is used as a setting criterion for the G2 calibration in this case as well.
In a further departure from the G2 calibration described in DE 198 55 628.4, all that is then needed, in the third and thus final step, is to reset the control grids d to reference potential, whereby the parallel shift in the cathode voltage profile representing the cut-off is reversed and the G2 calibration is ended.
The present invention thus has the advantage that practically only a single G2 setting step is necessary for the G2 calibration.

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A further advantage is that with the G2 calibration according to the invention, which is not oriented, therefore, to a cathode voltage level corresponding to the quasi cut-off, the actual production tolerances of the colour picture tube 1 are also detected at the same time, since the flyback stripes are used for the setting criterion.
The voltage difference provided as a margin for maximum ageing effects and the cathode voltage reserve can be determined in a relatively simple manner using the diagrams illustrated in Figure. 3 and Figure. 4.
In FIG. 3, using a diagram, the relationship between the ageing of a colour picture tube and the ageing-dictated shift in the cut-off as a result of the cut-off regulation Is illustrated by way of example in Figure. 3. In this case, vertical bars B show the respective variation range of the cathode voltage for the cut-off as a function of the ageing in weeks (from 1 to 60 weeks), while the respective average value is represented with the aid of squares Q.
FIG. 4 uses a diagram to show the dependence and variation range of the cut-off on the screen grid voltage +UG2- In this case, the abscissa represents the voltage difference in volts between a cathode K and the corresponding control grid Gi of the colour picture tube 1, the said control grid being designed as a Wehnelt cylinder. This voltage difference simultaneously corresponds to the cathode voltage, since, in accordance with Figure. 1, the control grids Gi are practically connected to reference potential via the electronic switch DS during normal

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operation of the television set. The same should also be applied correspondingly with regard to the ordinate which represents the voltage difference in volts between the screen grid G2 and the corresponding control grid Glf of the colour picture tube 1.
This diagram, which is based on a typical colour picture tube, illustrates that there is a relatively wide range between an assumed cathode voltage Ucathode for the cut-off and the screen grid voltage +UG2 required therefor. Therefore, a use of different colour picture tubes leads, with regard to the voltage potential changeover of the control grids Gi in accordance with the invention, to differences which-as is shown below-do not, however, necessitate individual adaptations of the voltage potential changeover according to the invention to the colour picture tubes.
where
Ucathode(a) = the cathode voltage during the G2 calibration,
These differences can be calculated using the following mathematical relationships (I) to (IV):


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Uci(a) =a voltage potential of e.g. +30 volts on account of the changeover of the control grid Gl in accordance with the invention, and

where
Ucathode(n) =the cathode voltage after the G2 calibration,
UGi(n) =the voltage potential of practically 0 volts on account of the resetting of the control grid Gl to reference potential in accordance with the invention.
and
Assuming that the screen grid voltage +UG2 is constant, and on the basis of the voltage potential changeover according to the invention at the control grids Gl from reference potential to a positive voltage potential of e.g. +30 volts, the previous equations (I) and (II) produce, by way of the elimination of the screen grid voltage +UG2, the following equations


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where, using equation (IV), the influence of the voltage potential changeover according to the invention on the cut-off can then be calculated in a simple manner.
Since the range from Smin, to Smax is dependent on the gun of the respective picture tube type,-taking such a diagram as a basis-the voltage potential changeover, according to the invention, of the control grids Gl from reference potential to a positive voltage potential of e.g. uniformly +30 volts, for the colour picture tubes listed below, results in the following relatively slight cathode voltage differences with regard to the cut-off:
Coty M gun : ±4.5 volts (Videocolor),
Vector gun : ±1.8 volts (Videocolor) and DF-III gun : ±2.2 volts (Toshiba)
On account of the slight difference, there is the advantage that it is not necessary to individually adapt the voltage potential changeover, according to the invention, of the control grids Gl to different guns of picture tubes.

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WE CLAIM
1. Method for calibrating the screen grid voltage (UG2) of a colour picture tube (1) of a colour television set having an automatic cut-off regulation, the cut-off regulation having a DC voltage reference (Uref) corresponding to a black value being set at the cathodes (K) of the colour picture tube (1), which cathodes are driven by a RGB signal, with the steps,
in the first step, a voltage potential changeover is carrier out at the control electrodes (Gl) of the colour picture tube (1), which control electrodes are a reference potential during normal operation of the television set, without disabling the DC voltage reference of the automatic cut-off regulation,
in the second step, the screen grid voltage (Ita) is set to a voltage value at which field and/or line flyback stripes are visible, and then the screen grid voltage (UG2) is reduced until the field and/or line flyback stripes disappear, for setting the screen grid voltage (UG2) to a value which the cathode (K) with the largest positive potential as compared with the remaining cathodes (K) is now at a threshold (Vcc) corresponding to the maximum voltage available to the cathodes (K),
and in a further step, the control electrodes (Gl) are reset to said reference potential again.

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2. Method as claimed in claim 1, wherein a voltage difference (M) is
provided for the voltage potential changeover of the control electrodes
(Gl) of the colour picture tube (1), a margin for the compensation of
ageing effects of the color picture tube (1) as a result of cut-off regulation
plus a cathode voltage reserve corresponding to the said voltage
difference.
3. Method as claimed in claim 2, wherein a uniform voltage difference (AA) is
provided for the voltage potential changeover of the control electrodes
(Gl) in the event of different types of colour picture tubes (1) being used.
4. Method as claimed in claim 1, wherein the calibration of the screen grid
voltage (UG2) is carried out with a rear panel of the housing of the
television set having been mounted.
5. Method as claimed in one or more of the preceding claims 1 to 4, wherein
the screen grid voltage (Ita) is calibrated when a black picture is fed in.
The invention relates to the screen grid calibration (UG2) , also called G2 calibration, of colour picture tubes (1). In this case, it is based, in particular, on television sets having colour picture tubes in which the cut-off points are automatically readjusted by means of so-called automatic cut-off circuits. During G2 calibration, a DC voltage reference corresponding to the black value is set at the cathodes (K) of the colour picture tube, which cathodes are driven by an RGB signal.
According to the invention, in a first step, a voltage potential changeover is carried out, by means of an electronic switch (DS), at the control electrodes (G1) of the colour picture tube (1), which control electrodes are at reference potential (earth) for the RGB signal driving. In a second step, the screen grid voltage (UG2) is set in such a way that field and/or line flyback stripes are just visible, and/or are reduced until the field and/or line flyback stripes actually disappear, the transition being utilized as an indicator of the fact that the cathode (K) at the largest positive potential compared with the remaining cathodes (K) is now precisely at a threshold (Vcc) corresponding to the maximum voltage available to the cathodes (K). After this setting of the screen grid voltage (UG2), the control electrodes (Gl) are reset to reference potential by means of the switch (DS).

Documents:

00190-cal-2000 abstract.pdf

00190-cal-2000 claims.pdf

00190-cal-2000 correspondence.pdf

00190-cal-2000 description (complete).pdf

00190-cal-2000 drawings.pdf

00190-cal-2000 form-1.pdf

00190-cal-2000 form-18.pdf

00190-cal-2000 form-2.pdf

00190-cal-2000 form-26.pdf

00190-cal-2000 form-3.pdf

00190-cal-2000 form-5.pdf

00190-cal-2000 letters patent.pdf

00190-cal-2000 others.pdf

00190-cal-2000 priority document others.pdf

00190-cal-2000 reply f.e.r.pdf


Patent Number 203819
Indian Patent Application Number 190/CAL/2000
PG Journal Number 10/2007
Publication Date 09-Mar-2007
Grant Date 09-Mar-2007
Date of Filing 31-Mar-2000
Name of Patentee DEUTSCHE THOMSON-BRANDT GMBH
Applicant Address HERMANN-SCHWER-STR.3, D-78048 VILLINGEN-SCHWENNINGEN,
Inventors:
# Inventor's Name Inventor's Address
1 LUBCKE GEROLD IN DER SCHMELZE 22 , D-77716 HASLACH
PCT International Classification Number H04N17/04 ,H04N 9/72
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 19916740.0 1999-04-13 Germany