ITT NOKIA DIGIVISION 7170 VT CHASSIS DIGI B-E CRT TUBE ITT-NOKIA A66ECF00X01 "PLANIGON".

CRT Tube ITT/SEL Planigon A66ECF00X01

In-line gun system for a color picture tube:

Super Precision In-Line ITT SEL.In a color picture tube with an in-line gun system elliptic beam-spot distortion caused by the deflection field is compensated for by pairs of plates in at least one focus electrode. The plates project into the apertures for the electron beams and are located at a distance from the bottom of the focus electrode.

What is claimed is: 1. A color picture tube, comprising:
a screen;
a funnel;
a neck;
a deflection system mounted on said neck at the transition of said neck to said funnel and which contains an inline gun system comprising cathodes and grid and focus electrodes, said focus electrodes having separate apertures each with a continuous edge for guiding electron beams to said screen, at least one of said focus electrodes having plates attached thereto which are located on both sides of the electron beams and are disposed on the screen side of said at least one said focus electrodes; said plates having curved portions which project into said apertures and are arranged in a spaced relationship from the screen side of the aperture of the respective focus electrode; and
one of the grid electrodes contains a slit diaphragm.
2. A color picture tube as claimed in claim 1, wherein:
vertices of said curved portions of said plates for the outer electron beams are located beside the center lines of said apertures for these electron beams in the focus electrode.
3. A color picture tube as claimed in claim 1, wherein:
the distances (w) between opposite ones of said plates
are different for the different electron beams.
4. A color picture tube as claimed in claim 1, wherein:
the distances between said plates and the bottom of the respective focus electrode differ for the individual electron beams.

Description:

BACKGROUND OF THE INVENTION
The present invention relates to a color picture tube.
U.S. Pat. No. 4,086,513 discloses a color picture tube with an in-line gun system in which parallel plates are attached to a focus electrode on both sides of the beam plane. This parallel pair of plates is directed towards the screen and serves to compensate the elliptic distortion of the beam spots by the deflection field, such distorted beam spots reducing the sharpness of the image reproduced. The pair of plates is attached to the focus electrode nearest to the screen. Alternatively, plates can be attached to a focus electrode near the first-mentioned focus electrode on both sides of the beams directed towards the last focus electrode. These plates are mounted at an angular distance of 90 degrees from the first-mentioned parallel pair of plates.
SUMMARY OF THE INVENTION
It is one object of the invention to provide a color picture tube with an in-line gun system causing an improvement in the compensation of the distortion of beam spots.
BRIEF DESCRIPTION OF THE DRAWING
The embodiments of the invention will now be explained with reference to the accompanying drawings, in which:
FIG. 1 is a side view of a color picture tube;
FIG. 2 is a side view of an in-line gun system;
FIG. 3 is a top view of a focus electrode;
FIG. 4 is a section through the focus electrode of FIG. 3 along line IV--IV.
DETAILED DESCRIPTION
FIG. 1 shows a color picture 10 tube comprising a screen 11, a funnel 12, and a neck 13. In the funnel 13, an in-line gun system 14 (drawn in broken lines) is located producing three electron beams 1, 2, 3, which are swept across the screen 11 (1', 2', 3'). A magnetic deflection system 15 is located at the transition from the neck 13 to the funnel 12.







FIG. 2 is a side view of the in-line gun system 14. It has a molded glass disk 20 with sealed in contact pins 21. The contact pins 21 are conductively connected (not shown) to the electrodes of the in-line gun system 14. The contact pins are followed by grid electrodes 23, 24, focus electrodes 25, 26 and a convergence cup 27. Inside the grid electrode 23, cathodes 22 are arranged which are shown only schematically in broken lines. The first grid electrode 23 is also called control grid, and the second grid electrode 24 is also called screen grid. The cathode together with the control grid and the screen grid is called triode lens. The focus electrodes 25, 26 form a focusing lens. The individual parts of the in-line electrode gun 14 are held together by two glass beads 28.
The focus electrode 25 consists of 4 cup-shaped electrodes 25.1 to 25.4, of which two each are joined together at their free edges and thus form a cup-shaped electrode. In all electrodes of the in-line gun system 14, there are three coplanar aperatures through which the electron beams 1, 2, 3 produced by the three cathodes 22 can pass. Three beams 1, 2, 3 are thus produced in the in-line gun system which strike the Luminescent Layer of the screen 11. In order to change the shape of the beam spot to obtain improved sharpness of the reproduced image, a suitable astigmatism is imparted to the in-line gun system. This effect is obtained by a slit diaphragm in the grid electrode 24 of the triode lens and by plates on both sides of the beam plane or on both sides of the beams in the focus electrode(s).
It is necessary to divide the astigmatism of the beam system between the triode lens and the focusing lens. The triode lens forms a smallest beam section which--in analogy to optics--is imaged on the screen with the following lenses. The astigmatic construction of this triode lens also leads to an astigmatism of the aperture angle of the bundle of rays emerging from the triode lens. A larger aperture angle facilitates defocusing of the image of the smallest beam section and the viewer of the color picture tube focuses on the plane with the larger aperture angle, i.e., the vertical and not the horizontal focal line of the astigmatic beam section of the triode lens is imaged on the screen. On the other hand, the aperture angle must not become too large, because then the bundle of rays moves to the bordering region of the imaging lenses. The large spherical aberration of these rather small electrostatic lenses does not permit a sharp image. Therefore, a sufficient astigmatic deformation of the bundle of rays is possible only if it is partly effected in the last focusing lens of the beam system where the aperture angle of the bundle of rays is no longer influenced.
FIG. 3 is a top view of the cup-shaped focus electrode 26. In the bottom of the focus electrode 26, there are three coplanar apertures 30 for the passage of the electron beams 1, 2, and 3, respectively. At the walls 32 of the focus electrode 26 two plates 31 are attached opposite each other, each of which has three curved portions 33. These curved portions 33 project into the apertures 30. The plates 31 can also consist of three individual curved portions 33. In the embodiment shown in FIG. 3, the curved shape of the portions 33 corresponds to an arc of a circle. The shape of the portions 33 can also be elliptic or parabolic or have a similarly curved shape. The distance w ₁ between the opposite vertices of the portions 33 projecting into the central aperture is smaller than the distance w ₂ between the opposite vertices of the portions 33 for the outer apertures 30. Furthermore, the vertices of the portions 33 for the outer apertures are not on the center line of the outer apertures 30. In order to make this clear, the distance of the central points of the apertures 30 from each other is designated by the letter S in FIG. 3. The distance of the vertices of the outer portions 33 from the central vertex in the plate 31 is designated by s ₁ . It is clear that the value s ₁ is smaller than the value S. This makes it possible to influence the angle the outer electron beams 1, 3 make with the central electron beam 2 to achieve static convergence.
FIG. 4 is a section of the focus electrode 26 along line IV--IV of FIG. 3. The apertures 30 in the bottom of the focus electrode 26 have burred holes whose height for the individual apertures can be different. The plates 31, which may be attached to the wall 32 of the focus electrode 26 by weld spots 34, are arranged in a defined spaced-apart relation with respect to the inner edge of the burred holes. The distance from the bottom of the focus electrode 26 to the lower edge of the portions 33 of the plates 31 projecting into the apertures 30 is designated by the letter d. The distance d ₁ for the portion 33 projecting into the central aperture 30 is larger than the corresponding distances d ₂ of the outer portions 33 from the bottom of the focus electrode 26. By varying the distance d, the astigmatism of the focus electrode can be influenced. It is thus possible to choose the distances d of the various portions 33 from the bottom of the focus electrode individually in order to optimize the adjustment of the astigmatism individually for each electron beam. The height of the portions 33 of the plates 31 is designated by the letter b. By varying this height b, the astigmatism of the focus electrode can also be changed. Here, too, it is possible to determine the height b individually for each portion 33 in order to optimize the adjustment of the astigmatism for each electron beam. In the embodiment shown in FIG. 4, the height b ₂ of the outer portions 33 is larger than the height b1 of the inside portion 33.
The plates 31 described above do not only influence the astigmatism of the focusing lens, but also the other lens aberrations, i.e., the spherical aberration and the further higher-order aberrations. This influence is different for each of the embodiments described above. The higher-order aberrations can be seen mainly at the edge of the picture. They can be minimized by a suitable combination of the plates at the electrodes of the focusing length. It is possible, for example, to distribute the correction to the two focus electrodes or to impress too strong an astigmatism on one of the two focus electrodes, with partial compensation at the other focus electrode.
By the use of the plates 31 described above, it is possible to adjust the astigmatism very finely, thus producing an improved sharpness across the entire screen. By the fine adjustment of the static convergence, which is possible as well, the sharpness can also be improved. Furthermore, the dynamic convergence is improved, too.


In-line color picture tube


 Nokia Unterhaltungselektronik GmbH
 
Abstract:
To prevent the formation of a corona (2) in a known in-line color picture tube with an automatic-focusing deflection system and four grids (G1-G4), a rectangular opening is provided on the side of the second grid (G2) facing the first grid (G1). As a result, the luminous spot (1) formed by the electron beam at the center of the screen is converted to a vertical ellipse and the ratio of the axes of the lateral ellipses on the edge of the image is reduced, thus improving the sharpness of the edges. The openings (5) in the first grid (G1) are elongated in the in-line direction, in particular rectangular, the adjacent openings of the second grid (G2) are also rectangular and all the other openings in the other grids (G2, G3, G4) are circular. In this way, the ratio of the axes of the luminous elliptical spot (11) produced by the electron beam at the center of the screen is reduced without adversely affecting the sharpness of the edges.

 1. An in-line colour picture tube with a self-converging deflection system and an electron-beam formation system comprising three beam systems arranged side by side, each of the beam systems comprising a cathode, a first, a second and a third grid and at least one further grid, where one of the said grids is designed as an anode and each grid is provided with an aperture for each of the three beam systems and where:

the aperture (5) for each electron beam in the first grid (G1) is designed to be of elongated and especially rectangular shape and the longer side (1) of the said aperture (5) runs in the in-line direction

the ratio between the longer and the shorter sides of the apertures (5) of the first grid (G1) amounts to between 1.0:0.8 and 1.0:0.96

the aperture (6) for each electron beam on the side of the second grid (G2) facing the first grid (G1) is designed to be right-angled and the longer side (L) of the said aperture (6) runs in the in-line direction

ratio between the sides of the right-angled aperture (6) of the second grid (G2) is equal to or greater than 2 (two)

the shorter side (B) of the aperture (6) of the second grid (G2) is equal to about 1.0 to 1.4 times the shorter side (b) of the aperture (5) of the first grid (G1)

the aperture (7) for each electron beam on the side of the second grid (G2) facing away from the first grid (G1) is designed to be of circular shape

the apertures (8.1, 8.2, 8.3, 8.4) for each electron beam in the third grid (G3) and the aperture (9) for each electron beam in the fourth grid (G4) and of any further grids are designed to be of circular shape.


2. A colour picture tube in accordance with claim 1, characterized in that the diameter of the circular aperture (7) of the second grid (G2) amounts to between about 0.8 and 1.0 times the shorter side (B) of the rectangular aperture (6) of the second grid (G2).

3. A colour picture tube in accordance with claim 1 characterized in that the circular aperture (7) of the second grid (G2) is conically enlarged in the direction of the third grid (G3).

4. A colour picture tube in accordance with claim 1 characterized in that the height of the aperture (5) of the first grid (G1) amounts to about 0.07 to 0.15 mm.

5. A colour picture tube in accordance with claim 1 characterized in that the height of the rectangular aperture (6) of the second grid (G2) amounts to about 0.2 to 0.4 mm.

6. A colour picture tube in accordance with claim 1 characterized in that the height of the circular aperture (7) of the second grid (G2) amounts to about 0.4 to 0.8 mm.

7. A colour picture tube in accordance with claim 5 characterized in that the height of the rectangular aperture (6) of the second grid (G2) and the height of the circular aperture (7) of the second grid (G2) are related to each other in the proportion of about 0.5:1.0.

8. A colour picture tube in accordance with claim 1 characterized in that the cross section area of the circular aperture (7) of the second grid (G2) is about 0.85 to 1.15 times as great as the cross section area of the rectangular aperture (5) of the first grid (G1).

9. A colour picture tube in accordance with claim 1 characterized in that the aperture (5) of the first grid (G1) is made roughly rectangular by designing the two longer sides (23) as straight lines running parallel to each other and joining them at each end by semicircular closure (24).

10. A colour picture tube in accordance with claim 2, characterized in that the circular aperture (7) of the second grid (G2) is conically enlarged in the direction of the third grid (G3).

11. A colour picture tube in accordance with claim 2, characterized in that the height of the aperture (5) of the first grid (G1) amounts to about 0.07 to 0.15 mm.

12. A colour picture tube in accordance with claim 2, characterized in that the height of the rectangular aperture (6) of the second grid (G2) amounts to about 0.2 to 0.4 mm.

13. A colour picture tube in accordance with claim 2, characterized in that the height of the circular aperture (7) of the second grid (G2) amounts to about 0.4 to 0.8 mm.

14. A colour picture tube in accordance with claim 6, characterized in that the height of the rectangular aperture (6) of the second grid (G2) and the height of the circular aperture (7) of the second grid (G2) are related to each other in the proportion of about 0.5:1.0.

15. A colour picture tube in accordance with claim 2, characterized in that the cross section area of the circular aperture (7) of the second grid (G2) is about 0.85 to 1.15 times as great as the cross section area of the rectangular aperture (5) of the first grid (G1).

16. A colour picture tube in accordance with claim 2, characterized in that the aperture (5) of the first grid (G1) is made roughly rectangular by designing the two longer sides (23) as straight lines running parallel to each other and joining them at each end by semicircular closures (24).

17. A colour picture tube in accordance with claim 3, characterized in that the circular aperture (7) of the second grid (G2) is conically enlarged in the direction of the third grid (G3).

18. A colour picture tube in accordance with claim 3, characterized in that the height of the rectangular aperture (6) of the second grid (G2) amounts to about 0.2 to 0.4 mm.

19. A colour picture tube in accordance with claim 3, characterized in that the height of the circular aperture (7) of the second grid (G2) amounts to about 0.4 to 0.8 mm.

20. A colour picture tube in accordance with claim 3, characterized in that the cross section area of the circular aperture (7) of the second grid (G2) is about 0.85 to 1.15 times as great as the gross section area of the rectangular aperture (5) of the first grid (G1).


DESCRIPTION

The present invention relates to an in-line colour picture tube in accordance with the precharacterizing part of claim 1.

Colour picture tubes provided with a self-converging deflection system suffer from the drawback that the non-homogeneous multiple fields produced by the said system cause distortions of the electron spot produced on the screen, the distortions being such that a circular spot at the centre of the screen, following deflection to the lateral edge of the screen, will be underfocused in the horizontal direction, thereby giving rise to a supine (i.e. horizontal) ellipse with an aureole (or corona) at both the top and the bottom. Though the round shape of the spot remains relatively well preserved after vertical deflections, an aureole is produced as the upper or lower edge of the screen is approached; this aureole always faces inwards, i.e. towards the centre of the screen, and therefore corresponds to overfocusing.

Such spots are produced with electron-beam systems in which the beam apertures are consistently circular. For the reasons just discussed, however, such systems cannot be used.

With a view to avoiding the formation of an aureole, there are known electron-beam systems (cfr. the paper entitled "A High Performance Color CRT Gun With an Asymmetrical Beam Forming Region" by H. Y. Chen and R. H. Hughes, RCA publication ST-5105, presented at the IEEE Chicago Spring Conference on Consumer Electronics, 1980, Chicago, Ill.) in which the apertures of the second grid facing the first grid are rectangular and have a length-to-breadth ratio of about 3:1. Given such apertures in the second grid, one obtains a smaller focusing voltage in the vertical direction than in the horizontal direction and therefore a flatter beam pattern in the area of the upper and lower edge of the screen, this being particularly true as regards the edge rays of the electron beam. In this way one obtains a circular spot in the case of vertical deflection and a spot in the form of an ellipse lying on its side--though with a relatively large axial ratio--in the case of horizontal deflection. The form of the spot at the centre of the screen, however, will in this case be distorted into a standing ellipse with an axial ratio of, say, 1:1.4. Subject to accepting a worsening of the resolution at the centre of the screen, one can thus obtain an improvement in the edge areas.

An electron beam formation system is also known (EP-A 111 872) in which the apertures in the first grid are either of an elongated or a rectangular shape. In this known electron-beam formation system, however, the apertures in the second grid facing the first grid are either circular or elongated in shape, while on the side facing away from the first grid there is provided a rectangular aperture that is common to all three electron beams. This measure is intended to improve the resolution of a colour picture tube of the type described at the beginning hereof by modifying the form of the spot into a horizontal ellipse and preventing the formation of aureoles, above all in the edge areas of the screen. In the known solution this is obtained by means of two asymmetrical lens systems, arranged in sequence and consisting of the grids 1/2 and 2/3, and a symmetrical lens system consisting of the grids 3/4.

An in-line system intended to avoid the formation of vertical aureoles when the spot is deflected horizontally is known from FR-A- 2 437 062. To this end a plate is arranged on the side of the second grid that faces the first grid. This plate is provided with an elongated slit extending in the plane of the electron beam for each of the beams. The apertures in the second grid permitting the passage of the electron beams also terminate in these slits. The effect of these slits arranged in the plane of the beams and their shape is that, as compared with the focusing in the beam plane itself, the electron beams are underfocused in a plane at right angles thereto. This ensures that the spot will be deformed into a standing (vertical) ellipse at the screen centre and a supine (horizontal) ellipse at the lateral edge of the screen. Averaged over the screen as a whole, a better resolution is therefore obtained and this notwithstanding the fact that the resolution at the screen centre is worsened due to this ellipse formation.

The present invention is therefore concerned with further reducing the spot distortions and improving the resolution of the television picture.

This problem is solved by means of the combination of features specified in claim 1. The following effect has been observed when a picture tube is designed in the manner of the present invention:

The spots at the centre of the screen are still characterized by an elliptical distortion, but the vertical diameter of the spot at the centre of the screen is 15 to 25% smaller than in the case of spots produced with the known electron-beam formation systems. Furthermore, the spot dimensions at the edge of the screen do not undergo any substantial modification and, given a proper choice of the focusing voltage, no aureoles will be formed in any part of the screen. Consequently, a considerably improved resolution of the television picture is obtained at the centre of the screen while maintaining good resolution at the edges.

Further advantageous features of the invention are specified in the dependent claims and will be described hereinbelow by reference to an embodiment illustrated by the drawing. For the sake of simplicity, the description will assume a four-grid system, though the invention, of course, is equally applicable to multigrid systems. The figures on the drawing are as follows:

FIG. 1 shows a longitudinal section through an electron beam formation system in accordance with the invention;

FIGS. 2a to 2c show the forms of the spot at different deflection angles of the electron beam on the screen of a colour picture tube with an electron-beam formation system in which the apertures in the grids are consistently circular and at different focusing voltages;

FIG. 3 shows a section view along the line A--A of FIG. 1;

FIG. 4 shows a section view along the line B--B of FIG. 1;

FIG. 5 shows a schematic representation of the apertures in the three grids following the cathode of the electron-beam formation system of FIG. 1 as shaped in accordance with the invention;

FIGS. 6a to 6c illustrate the reduction the distortions of the spot at the centre of the screen when the invention is used, and

FIG. 7 shows another form that may be given to the aperture in the first grid.

FIG. 1 illustrates an electron-beam formation system 1 consisting of thr

ee cathodes 2, which are arranged--one behind the other--in the plane of the figure, the first grid G1, the second grid G2, the third grid G3 and the fourth grid G4, which is connected so as to act as the anode. The individual grids are maintained in position in a known manner by having their lateral edges 3 set into a glass rod 4 while the latter is in a fused state.

Given optimal focusing and apertures 5, 6, 7, 8.1, 8.2, 8.3, 8.4 and 9 in grids G1 to G4 that are of circular shape, such an electron-beam formation system 1 will produce a circular electron spot 11--as illustrated by the unbroken line in FIG. 2a--when the electron beams strike the luminophore layer at the screen centre 10. Following a vertical deflection of the electron beam in the direction of the upper edge 12 of the screen, the spot 11 will become slightly deformed into a vertical ellipse and comprise an aureole (or corona) 13 pointing in the direction of the screen centre 10 (FIG. 2b). The broken circular line 14 in FIG. 2b serves to illustrate the distortions that occur as compared with the perfect circular form.

FIG. 2c shows a laterally displaced spot 11 as produced following a horizontal deflection of the electron beam from the screen centre, say, to the right edge 15 of the screen. The actual luminescent spot is indicated by the broken line 16. It has the form of an ellipse lying on its side (=horizontal ellipse). The spot 11 is continued upwards and downwards by the aureoles 13, thus producing an effective form of the spot as illustrated by the unbroken line 17.

As explained at the beginning, these spot forms are based on the use of the self-converging deflection system.

As was likewise mentioned at the beginning, the formation of the aureoles can be eliminated by raising the focusing voltage. But this will increase the size of the spot at the screen centre 10 and at the upper (and lower) edge 12 of the screen, as indicated by the chain-dotted line 18 in FIG. 2a and the chain-dotted line 19 in FIG. 2b. When deflected in the direction of the lateral edge 15 of the screen, on the other hand, the spot 11 is deformed into a flat ellipse with a large axial ratio lying on its side, this shape being indicated by the chain-dotted line 20 in FIG. 2c.

When use is made of a colour picture tube in accordance with the invention, an improvement of the resolution is already obtained by virtue of the fact that the aperture 6 on the side of the second grid G2 (which is designed as a double grid) facing the first grid G1 is given a rectangular shape, with the longer side extending in the in-line direction, and the aperture 7 on the side of the second grid G2 facing the third grid G3 is of a circular

shape.

Given such a design of the grid apertures and the use of a focusing voltage at which aureoles 13 no longer occur at the screen centre, the spot 11 at the screen centre will be deformed into a vertical ellipse, i.e. the spot 11 will now be underfocused in the vertical axis. This spot form is indicated by the broken line 21 in FIG. 6a. At the same time, however, the spot 11 in the form of a horizontal ellipse that occurs at the lateral edge 15 of the screen following a horizontal deflection is modified in such a way that the previously large axial ratio (line 20) gives way to a small axial ratio. The modified spot 11, which approximates more closely to a circular shape and leads to a better resolution, is shown as the unbroken line 21 in FIG. 6c. As averaged over the screen as a whole, these modified spot forms produce better resolution even though the resolution at the screen centre is slightly worsened. According to the invention, the aperture 5 of the first grid G1 is likewise designed in the form of a rectangle. The longer side 1 of this aperture runs in the in-line direction and the ratio between the longer side 1 (length) and the shorter side b (breadth) is in the range between 1:0.8 and 1:0.96. Rather than being rectangular, the aperture may be given some similar elongated shape with a corresponding axial ratio. It is possible and advantageous, for example, to use an oval aperture or, as shown in FIG. 7, an aperture 5 consisting of the long sides 23, which are straight and parallel to each other, joined by semicircular closures at both ends. Furthermore, the ratio between the longer side L (length) and the shorter side B (breadth) of the rectangular aperture 6 of the second grid G2 is chosen so as to be either equal to or greater than 2 (two). The ratio between the side B of the aperture 6 of the second grid G2 and the side b of the aperture 5 of the first grid G1 should lie approximately in the range between 0.95:1 and 1.4:1. This particular design of the apertures 5, 6, 7 and 8.1 of the qrids G1, G2 and G3 is schematically illustrated in FIG. 5, while FIG. 3 illustrates this embodiment as seen in an end elevation along section A--A of FIG. 1. FIG. 4, on the other hand, shows an end elevation of the grid G1 with the rectangular apertures 5 as seen along the section B--B of FIG. 1. It will be appropriate to make the cross section area of the circular aperture 7 of the second grid G2 about 0.85 to 1.15 times as great as the cross section area of the elongated or rectangular aperture 5 of the first grid G1.

When the apertures 5 are designed as just described, a further improvement of the resolution is obtained by virtue of the fact that the elliptical form of the spot at the screen centre 10 is made to approximate more closely to the circular form and that this is not accompanied by any deleterious distortions of the spot at the lateral edge 15 of the screen. This improvement is illustrated in FIGS. 6a and 6b by means of the unbroken lines 22. The shortening of the major axis of the ellipse 22 drawn as an unbroken line in FIG. 6b as compared with the ellipse 21 drawn as a broken line may amount to up to 25% of the major axis of the ellipse drawn as a broken line.

The height of the aperture 5, i.e. the thickness of the first grid G1 in the area of the aperture 5, amounts to about 0.07 to 0.15 mm, and preferably 0.08 to 0.12 mm.

On the side facing away from the grid G1, the aperture 7 of the second grid G2--which is immediately adjacent to the aperture 6--is designed to be of circular shape and it will be appropriate if this aperture is enlarged in the manner of a cone in the direction of the third grid G3. The diameter of this aperture 7 corresponds to about 0.8 to 1.0 times the length of the side B of the aperture 6. The height of the rectangular aperture 6 of the second grid G2 amounts to about 0.2 to 0.4 mm, preferably 0.25 to 0.3 mm, while the height of the adjacent aperture 7 amounts to about 0.4 to 0.8 mm, preferably 0.5 to 0.6 mm. It will be appropriate for the ratio between the height of the rectangular aperture 6 to the height of the circular aperture 7 to be about 0.5:1.

As regards the subsequent grid G3, the apertures 8.1 --which are in the immediate vicinity of the apertures 7--are circular, as are the subsequent apertures 8.2, 8.3 and 8.4 of the third grid G3 and the aperture 9 of the fourth grid G4.

The elongated or rectangular aperture 5 in the first grid G1, together with the neighbouring rectangular aperture 6 of the second grid G2, constitutes an asymmetrical beam-forming lens, while the circular apertures 7 and 8.1 of the second and third grids G2 and G3 constitute a symmetrical beam-forming lens. The decisive beam formation therefore takes place in the area of the grids G1/G2.

In one embodiment the dimensions of the aperture 5 in the first grid G1 were 0.55×0.65 mm with a height of 0.08 mm, the dimensions of the rectangular aperture 6 on the side of the second grid G2 facing the first grid G1 amounted to 0.7×2.2 mm and the diameter of the circular aperture 7 on the side of the second grid G2 facing away from the first grid G1 amounted to 0.65 mm. In an electron-beam formation system (electron gun) having the aforesaid dimensions the electron beam produced a spot at the screen centre that, as compared with the spot produced in the conventional manner, was more than 25% smaller in the vertical direction.



Electron-gun system NOKIA GRAETZ ITT CRT Tube.

In a cathode-ray tube with a thick grid No. 2 (24) in the electron-gun system, current transfer into grid No. 2 (24) may result in a lack of picture sharpness. To avoid this error, the aperture (4) in grid No. 2 (24) has a widening (6) of conical shape or stepped diameter.

1. Electron-gun system for cathode-ray tubes comprising at least one cathode and at least three electrodes, the second of which is a screen grid, which are arranged one behind the other and have apertures through each of which an electron beam can pass, characterized in that the aperture (4) in the screen grid (24) has an unwidened part and a conical widening (6) on its side facing the third electrode (25), whereby current transfer into the screen grid and the third electrode is greatly reduced. 2. An electron gun system for cathode ray tubes, comprising:
at least one cathode;
at least three electrodes, said electrodes and said cathode being arranged one behind the other and having apertures through each of which an electron beam can pass, the aperture of the second electrode having a widening on its side facing the third electrode, said widening being conical in shape and extending over part of the depth of the aperture, and that the other part of the depth satisfies the relationship a divided by d is less than or equal to 0.5, where d is the diameter of the unwidened part of the aperture and a is the depth of the unwidened part of the aperture.
3. An electron-gun system as claimed in claim 2, characterized in that on its side facing the third electrode (25), in the area of the opening (4), the second electrode (24) bears a plate (8) containing the conical widening (6). 4. An electron gun system for cathode ray tubes, comprising:
at least one cathode;.
5. An electron gun system for cathode ray tubes, comprising:
at least one cathode;
at least three electrodes, said electrodes and said cathode being arranged one behind the other and having apertures through each of which an electron beam can pass, the apertures of the second electrode having widenings on sides facing the third electrode, each of said widenings being formed by a step wherein the diameter (d1) of the widened part satisfies the relation d1=d0+2ctanα, where d0 is the diameter of the unwidened part of the aperture (4), c is the depth of the widened part, and α≥10°.
6. Electron-gun system for cathode-ray tubes comprising at least one cathode and at least three electrodes, the second of which is a screen grid, which are arranged one behind the other and have apertures defined by cylindrical surfaces through each of which an electron beam can pass, characterized in that the aperture (4) in the screen grid (24) has a conical widening defined by a conical surface contiguous with the cylindrical surface on its side facing the third electrode (25), whereby current transfer into the screen grid and the third electrode is greatly reduced.

Description:

The present invention relates to an electron-gun system for cathode-ray tubes and more particularly, an electron gun system having at least one cathode and at least three electrodes which are arranged one behind the other and have apertures through each of which an electron beam can pass.
Electron-gun systems for cathode-ray tubes comprising a cathode as well as grid and focusing electrodes are known from (DE-OS 32 12 248) corresponding to U.S. Pat. No. 4,682,073. To achieve a thin electron beam and, thus, a small electron spot on the screen of the cathode-ray tube, it is necessary to make grid No. 2 relatively thick. This means that the aperture in grid No. 2 must have a great depth, it being quite possible that the depth of the aperture is equal to the diameter of the aperture.
With such a design of grid No. 2, it may happen that during the period from the turning on of the cathode-ray tube to the creation of stable space-charge conditions around the cathode, the electron beam expands, touching the wall of the aperture in grid No. 2. The electrons touching the wall of the aperture in grid No. 2 cause the emission of secondary electrons which reach grid No. 3, also called "focusing electrode". Such leakage currents are first unmeasurably small, but with increasing service life, measurable currents in the pA range occur at grid Nos. 2 and 3 for short times because due to deposition of evaporated cathode materials into the aperture of grid No. 2, the secondary-electron yield of initially about 1 multiplies. These leakage currents cause a change in the voltage across grid No. 2 - it becomes more positive - and in the voltage across the focusing electrode, which becomes more negative. Due to these changes in potential, the electron beam is not optimally focused for short periods of time, which leads to a lack of picture sharpness. In unfavorable cases, even self-blocking may be caused by total current transfer into grid Nos. 2 and 3.
It is the object of the present invention to provide an electron-gun system for cathode-ray tubes having a thick grid No. 2 in which no lack of picture sharpness is caused by current transfer into grid Nos. 2 and 3.
This object is attained by making the aperture in grid No. 2 so that it becomes wider at its side facing grid No. 3. Further advantageous features of the invention are achieved by making the aperture widening conical in shape, and in particular, that the conical widening extends over part of the depth of the aperture, and that the other part of the depth satisfies the relation a divided by d is less than or equal to 0.5, where d is the diameter of the aperture and a is the depth of the unwidened part of the aperture. Other features of the invention include the widening of the aperture has an angle of at least 10°, and preferably 15°. In another embodiment, the side of grid No. 2 facing grid No. 3 bears a plate containing the conical widening. The widening may also be in the form of a step, wherein the diameter of the widened part between the step and the side of the grid facing grid No. 3 satisfies the relationship d1=d0+2c tanα, where d0 is the diameter of the unwidened part of the aperture, c is the depth of the widened part, and α is greater than or equal to 10°.
Embodiments of the invention will now be explained with reference to the accompanying drawings, in which:
FIG. 1 is a side view of a cathode-ray tube;
FIG. 2 is a side view of an electron-gun system;
FIG. 3 is a cross-sectional view of a first embodiment of a grid No. 2;
FIG. 4 shows the detail Z of FIG. 3;
FIG. 5 is a cross-sectional view of a second embodiment of a grid No. 2;
FIG. 6 is a cross-sectional view of a third embodiment of a grid No 2;
FIGS. 7a and 7b show the details X and Y of FIG. 6;
FIG. 8 is a cross-sectional view of a further embodiment, and
FIG. 9 shows the detail X of FIG. 8.
FIG. 1 shows a cathode-ray tube 10 comprising a screen 11, a funnel section 12, and a neck 13. There are singlegun and multigun tubes. In multigun tubes, the electron guns are either separate from each other or combined into one mechanical assembly The present invention relates to all these forms of electron-gun systems even though it will be explained as applied to a multibeam electron-gun system of integrated construction.
The neck 13 of the cathode-ray tube 10 houses an electrongun system 14 (indicated by broken lines) which generates three electron beams 1, 2, 3 These beams are scanned (1', 2', 3') across the screen 11 by a magnetic deflection system 15 located in the junction region of the funnel section 12 with the neck 13.
FIG. 2 shows the electron-gun system 14 in a side view. Seen in the beam direction, the system 14 comprises a grid No 1, designated 23, a grid No. 2, 24, first and second focusing electrodes 25 and 26, and a convergence cup 27. Grid No. 1, 23, contains cathodes 22, which are indicated by dashed lines This grid is also called the "control grid", and grid No. 2, 24, the "screen grid". The cathode, the control grid, and the screen grid are referred to as a "triode lens"The focusing electrodes 25, 26 constitute a focusing lens. The individual parts of the system are held together by two glass rods 28 The electrical connections of the system 14 are not shown for the sake of clarity.
All electrodes of the system 14 contain three apertures which are arranged in a horizontal line and through which can pass the electron beams generated by the three cathodes 22, which later land on the phosphor screen 11.
FIG. 3 shows grid No. 2, 24, in a sectional view. Indicated above this grid is the first focusing electrode 25. In this embodiment, grid No. 2 has the shape of a cup whose bottom 5 contains the aperture 4 for the electron beam. The other apertures for the other electron beams are not visible in this sectional view. The aperture 4 has a great depth, i.e., its diameter d is approximately equal to the thickness of the bottom 5 of the grid. On the side of the grid facing the first focusing electrode 25, the aperture 4 has a widening 6 which is conical in shape.
FIG. 4 shows the detail Z of FIG. 3. The conical widening 6 need not extend over the entire depth of the aperture 4. In the example shown, the aperture 4 has a depth a over which its sidewalls are parallel to the central axis of the aperture 4. This portion is followed by the conical widening 6. The conical widening has an angle α of at least 10°, preferably 15°. For the relation of the depth a of the aperture 4 to the diameter d, the condition a/b≤0.5 should be satisfied.
FIG. 5 shows a second embodiment of grid No. 2. In this embodiment, grid No. 2 is made from thin metal sheet. Here, too, the conical widening 6 includes an angle α of at least 1O°, and the relation a/d≤0.5 is satisfied.
FIG. 6 shows a third embodiment of grid No. 2. It has the shape of a cup, and the bottom 7 of the cup contains the rectangular aperture 4. A plate 8 resting on the bottom 7 contains an aperture aligned with the aperture 4 and having a conical widening 6. This structure of grid No. 2 permits an astigmatic beamforming element in the grid to be combined in a simple manner with the plate 8 containing the conical widening 6.
FIGS. 7a and 7b show the details X and Y, respectively, of FIG. 6. The details X and Y represent two sections through the grid 24 which are displaced relative to each other by 9O°. The plate 8 contains a rotationally symmetric aperture consisting of a cylindrical portion of depth a and the conical widening 6. The widening again has an angle α of at least 1O°. It does not extend over the entire depth of the aperture but passes into the portion whose depth is designated a and whose sidewalls are parallel to the central axis of the aperture 4. Here, too, the condition a/d≤=0.5 should be satisfied. The depth of the aperture 4 in the bottom 7 is designated by b, the width by e, and the length by f, and this portion of the aperture acts as an astigmatic beam hole.
FIG. 8 shows a further embodiment of grid No. 2. Here, the widening 6 is formed by a step, and its depth is designated c. In this embodiment, too, the grid can have the shape of a cup whose bottom 7 contains the aperture 4. The bottom 7 then bears the plate S, whose aperture is aligned with the aperture 4 and has the diameter d1 (FIG. 9). This diameter is greater than the diameter dO of the aperture in the bottom 7, so that the step is obtained Here, the condition d1=d0+2ctanα should be satisfied, where α≥10°. FIG. 9 shows the detail X of FIG. 8. In this embodiment, too, the bottom 7 may contain a rectangular aperture which acts as an astigmatic beam hole.

 Support device for a picture tube component

A support device for a deflection unit (10) for a picture tube comprises pins (17) which in a longitudinal direction carry a thread (19) over part of their circumferences. The pins run in guide bores, which are constructed so as to exhibit a recess of not less than the angular circumference of the thread. Each pin is at first so aligned in relation to the associated guide bore that the thread runs in the above-mentioned recess. In this position (after the deflection unit has been aligned), each pin is pushed until it contacts the tube cone (18.K). Then each pin is turned by 90°, thus ensuring that the above-mentioned thread cuts into the non-recessed wall of the guide bore. This ensures that each pin is fixed in position, and simultaneously, due to the lead of the thread, a tension is set between deflection unit and tube. The support device thus constructed has the advantage that the tension force between the deflection unit and the tube cone can be set precisely. This insures that the optimum setting is not lost due to different tension forces acting at the locations of the different support elements, as was the case when conventional support elements were used.

 Nokia (Deutschland) GmbH

1. Support device for a picture tube components (10), with more than one support element, characterized in that each support element (17, 17.5, 17.6) comprises a pin (17, 17.5, 17.6) that can be freely moved in the support direction, inside a guide (16, 16.5, 16.6) having a smooth inner surface, and can be arrested in any position inside this guide (16, 16.5, 16.6), said pin (17, 17.5, 17.6) having a thread (19) extending in a longitudinal direction over a part of its circumference and said guide (16, 16.5, 16.6) having a recess (21) of not less than the angular circumference of the thread (19), whereby the thread (19) may fit in the recess (21) to allow free longitudinal movement of the pin (17, 17.5, 17.6) in the guide (16, 16.5, 16.6) to any desired arresting position where the pin (17, 17.5, 17.6) can be locked by rotation so that the thread (19) engages the inner surface of the guide (16, 16.5, 16.6).

2. Support device in accordance with claim 1, wherein the pin includes an elastic end cap for compressively engaging said picture tube.

3. Support device in accordance with claim 1, wherein the thread has a predetermined pitch.

4. Support device in accordance with claim 1, wherein the thread has zero pitch.

5. Support device in accordance with claim 4, wherein said pin includes an elastic end cap for compressively engaging said picture tube.

6. Support device for a picture tube components (10), with more than one support element, each support element (17, 17.5, 17.6) comprising a pin (17, 17.5, 17.6) that can be freely moved in the support direction, inside a guide (16, 16.5, 16.6) having a smooth inner surface, and can be arrested in any position inside this guide, said pin (17, 17.5, 17.6) having a thread (19) extending in a longitudinal direction over a part of its circumference and said guide (16, 16.5, 16.6) having a recess (21) being not less than the angular circumference of the thread so that the thread (19) may fit in the recess (21) to allow free longitudinal movement of the pin (17, 17.5, 17.6) in the guide (16, 16.5, 16.6) to any desired arresting position where the pin can be locked by rotation so that the thread (19) engages the inner surface of the guide (16, 16.5, 16.6).

characterized in that each guide (16.6) comprise an adhesive channel (28) formed in the smooth inner surface for introduction of adhesive for gluing a pin (17.6) in the guide (16.6).


7. Support device in accordance with claim 6, wherein the adhesive channel has a width that exposes only a portion of the circumference of said pin.

8. Support device for a picture tube component (10), with more than one support element, characterized in that each support element (17.6) comprises a pin that can be freely moved in a support direction, inside a guide (16.6) having an inner surface, and can be arrested in any position inside said guide, said pin having grooves (27) over at least a part of its circumference and said guide (16.6) having an adhesive channel (28) formed in the inner surface for the introduction of adhesive for gluing the pin (17.6) in the guide.

9. Support device in accordance with claim 8, wherein the adhesive channel has a width that exposes only a portion of the circumference of said pin.

10. Support device in accordance with claim 8, wherein the pin includes an elastic end cap for compressively engaging said picture tube.

Description:

TECHNICAL FIELD

The invention relates to a support device for a picture tube component, especially for a deflection unit. Generally, the deflection unit is clamped in position with the aid of a clamping ring at the neck of the picture tube, and it is supported on the tube cone with the aid of the support device.

PRIOR ART

As soon as a deflection unit already firmly linked to the neck of the picture tube is aligned so as to ensure that imaging characteristics are satisfactorily provided within specified tolerances, the unit must be fixed in the position reached on the tube. In the current state-of-the-art, this is achieved either by turning screws mounted in a retainer part until they are flush against the tube cone, or by pushing wedges between the above-mentioned retainer part and the tube cone. In both methods of fastening, it has turned out to be difficult to perform this fixing procedure so as to ensure that the set position of the deflection unit is retained. It must be noted that the deflection unit is firmly mounted inside the aligning unit, as is the picture tube. If now an operator tightens one of the above-mentioned screws more than the others, then the retainer part will move somewhat out of true, thus causing an elastic force to build up, which relaxes when the tube with the fixed deflection unit is removed from the aligning unit. There is a similar effect when one of the fixing wedges is pressed more firmly between cone and retainer part than the others.

Both when using screw-shaped support elements and wedge-shaped support elements, it is accordingly not assured that the aligned position of the deflection unit will be retained when this is released from the aligning device.

The long-standing problem was accordingly to provide a support device for a deflection unit for a picture tube constructed so as to ensure that the deflection unit does not alter its position when, after being fixed on the picture tube inside an aligning device, it is removed from this device.

SUMMARY OF THE INVENTION

The support device described in this invention is characterized by the fact that each support element can be moved in the support direction inside a mounting, and that inside this mounting it can be arrested in more than one setting position. A support device of this kind is especially suited for adjusted retention of a deflection unit, but can also be used for adjusted retention of a magnetic multipole unit, for example.

In order to illustrate the advantages of the invention, let it be assumed that the support element is a pin, which is guided in a mounting aligned on the picture tube, and can be glued in the bore in any desired setting position. If, after this desired alignment has been achieved, this pin is moved so as to arrive flush against the picture tube, the pressing force onto the pin does not affect in any way the retainer part of the deflection unit, since the pin can be moved freely in the bore in the retainer part. It is not until the pin has been glued in the bore that it can transmit a force between picture tube and deflection unit. If, however, the pin is essentially inelastic, then even after gluing no misadjusting force will be exerted.

The fact that a force between picture tube and deflection unit can only be a force resulting from an elastic deformation of the moved pin can be utilized in order to selectively set a tension force between picture tube and deflection unit. If, for example, the pin exhibits at its front end contacting the picture tube a cap made of elastic material, this latter will be deformed in dependence on the pressing force of the pin onto the tube. This pressing force can be designed to be relatively uniform, so that at all support points the same tension force is exerted, thus ensuring that the alignment position achieved is retained unaltered. Such a relatively precise adjustment of a prestressing force was not possible when using conventional support elements. When conventional screws were used, these would all have to be tightened with the same torque, and it would have to be ensured that the torque is not affected by friction, but is dependent only on the prestressing force being achieved. This condition is in practice never satisfied, since the parts used are made of plastic, meaning that some screws are very easy to turn, and some very difficult. The torque is thus substantially determined by friction, and for this reason identical torques will not produce identical prestressing forces. The situation is similar when conventional wedges are used; with the aid of a relatively slight thrust force, a wedge can enable a relatively high prestressing force to be achieved. However, when identical thrust forces are applied to different wedges, the result will be different tension forces, since the thrust force is highly dependent on the friction of the wedge between itself and the picture tube and itself and the retainer part. It must also be noted that in practice wedges with different angles are used, in order to bridge different distances between deflection unit and picture tube at different points. Even given identical friction forces and identical thrust forces, there will be different tension forces when wedges with different angles are used.

On the other hand, as already explained, the tension force when an elastic pin is used depends solely on the pressing force used, provided that there is no very great friction between pin and bore. The latter phenomenon can be easily prevented, however, since it is not of the slightest importance whether the pin fits snugly in the bore.

For quick attachment of a support element in the mounting, it is of especial advantage when the support element and the mounting possess catches which permit the support element to move only towards the picture tube. Here the component is fixed in position when the adjustment end position is reached. However, between different fixing positions there is a travel difference (depending on the lock function), which may easily lead to slightly differing tensions.

It is most especially advantageous when the support element is constructed in the form of a pin, which in a longitudinal direction carries a thread over a part of its circumference, and when the guide is constructed so as to exhibit a recess of not less than the angular circumference of the thread. As long as the support element is seated in the guide so as to ensure that the partial thread is running in the recess, it can be moved to and fro in the guide with a very slight force. Once it has been moved into the desired position, it merely needs to be turned a little, in order to be fixed in position in relation to the guide. Depending on the lead of the thread, the pin, when turned for fixing purposes, will be given a further forward movement in relation to the guide, by a specified amount. In this way a precisely defined tension can be set, depending solely on the lead of the thread and the turning angle used.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1: Side view of a deflection unit fixed in position of a picture tube (only partially depicted);

FIG. 2: Plan view of the deflection unit in accordance with FIG. 1;

FIG. 3: Side view of a pin-shaped support element with partial thread;

FIGS. 4A and 4B: Cross-sections through a guide with a pin in accordance with FIG. 3, once in the adjustment-movement position (FIG. 4A) and once in fixing position (FIG. 4B);

FIG. 5: Longitudinal section through a guide with a moving pin with catches; and

FIG. 6: Longitudinal section through a guide with a pin which can be glued inside the guide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The deflection unit (10) in accordance with FIGS. 1 and 2 comprises a retainer part with a front retaining ring (11) and a rear clamping ring (12). The retainer part carries a (diagrammatically

depicted) deflection winding (13) and contacts (14).

At the circumference of the retaining ring (11), there are three support feet (15) under identical angular distances. Each support foot (15) possesses a guide bore (16) (FIG. 4), with a pin (17) mounted inside it. Each pin (17) acts as a support element for supporting the deflection unit (10) on the cone (18.K) of the tube. At the tube neck (18.H), the deflection unit is attached with the aid of the clamping ring (12). The construction of the pins (17) and the associated guide bores (16) can be seen in FIGS. 3 and 4. Each pin (17) possesses in a longitudinal direction two partial threads (19), each of which extends over a part of the pin's circumference and a non-threaded surface 19a. The tips of the threads exhibit a larger circumference than the rest of the pin, which is constructed without a thread. This can be seen especially clearly in FIG. 4A. The guide bore (16) exhibits two recesses, which match the partial threads (19) and are constructed so as to ensure that the pin (17) can be moved inside the guide bore (16) quite easily when it is inserted into the bore in such a way that the partial threads (19) are aligned with the recesses (21), and the non-threaded surface 19a is aligned with the non-recessed surface 21a, as shown in FIG. 4a. In this position (4A), each pin (17) can be moved to and fro at will in the associated guide bore, and especially until contacting the tube cone (18.K). If the pin (17) is turned by 90°, the partial thread (19) cuts into the non-recessed parts of the wall of the guide bore (16). This ensures that the pin (17) is fixed in position in the guide bore (16), and simultaneously it is moved by a small distance, depending on the direction of turn, the angle of turn, and the lead of the thread concerned.

In order to fix a deflection unit in position on a picture tube, the following procedure is adopted, with the aid of support elements constructed to the above design. First of all, the deflection unit is pushed in the conventional manner over the picture tube neck (18.H), and then attached in a specified longitudinal position at the tube neck by tightening a clamping screw (22) at the clamping ring (12). Then the tube and the deflection unit (10) are contacted, and in operation of these components the deflection unit (10) is adjusted with the aid of an adjuster device until imaging characteristics are within specified tolerances. In the aligned position, the deflection unit (10) now has to be permanently fixed. It is here that the pins (17) described above come into use; in the position shown in FIG. 4A, they are pushed against the tube cone (18.K). For forces operating between deflection unit (10) and tube cone (18.K), it is immaterial how strong the pressing forces on the pins (17) are, or in particular whether the forces are identical at all pins or not. When a particular pin (17) is moved against the tube cone (18.K), it is then turned by 90° into the position shown in FIG. 4B, with the turn being performed in the direction causing a further forward movement onto the tube cone relative to the deflection unit (10). This turning movement fixes the pins (17) in position, simultaneously causing the adjusted position of the deflection unit (10) being fixed as well. Due to the small forward movement of the pins during fixing, a small tension is achieved between deflection unit (10) and tube, resulting in an especially secure seat of the deflection unit (10). The adjusted position is not altered thereby. The extent of the tension, given a fixed turn of 90° in all cases, depends only on the lead of the thread, meaning that it can be specified by this latter.

The pins (17) shown in FIGS. 1-3 carry a widened head with a slit (24) for turning purposes. However, it is not necessary for there to be a widened head, and instead of a slit, for example, an outer or inner multi-cornered configuration can be provided. In addition, the pin can be modified so that instead of two partial threads (19) more or fewer partial threads are provided. If only one partial thread is provided, the advantage is that when fixing in position, for example, the pin can be turned by 270°, in order to achieve an especially great fixing tension, if this should be necessary.

The pin (17.5) and the guide bore (16.5) in accordance with FIG. 5 carry catches (25.17 and 25.16 respectively), which are aligned so as to ensure that they permit the pin (17) to move towards the picture tube cone (18.K). At its front end, the pin (17.5) is fitted with a rubber cap. When the deflection unit is being fixed in position, the pin is pressed against the tube cone with a specified force, thus compressing the rubber cap (26) somewhat. The longitudinal-movement position of the pin (17.5) in the guide bore (16.5) is determined by the locking function achieved in each case. When the deflection unit is released by the aligning device, the elastic deforming force of the rubber cap (26) ensures that the deflection unit is braced with a specified force against the tube.

Pins having a rubber cap (26) as shown in FIGS. 5 and 6 and threads (19) as shown in FIG. 3 but with a zero pitch can be used to practice the invention. In such a case the pins are inserted into the guides and are pressed against the tube cone with a specified force so that the caps compressively engage the tube cone. The pins are then rotated so that the zero pitch threads engage the surface of the guide and fix the pins in a position with the rubber cap compressed. In this manner the specified force is exerted on the tube by the rubber caps so that the deflection unit is securely seated.

In the embodiment shown in FIG. 6, a pin (17.6) with grooves (27) is provided. The associated guide bore (16.6) possesses an adhesive channel (28) formed in the surface of the guide bore and having a width that exposes only a portion of the circumference of said pin for gluing the grooved pin (17.6) when this latter has been pushed as far as the picture tube cone. The grooved pin (17.6) is also at its front end fitted with a rubber cap (26) for the purpose explained above. An adhesive channel (28) and glue can also be used in conjunction with threaded pins to provide a more secure fixation of the pins.

The embodiments relate to designs of guide bores and pins which are matched to each other so as to ensure that the pins can be moved inside the guide bore without exerting great force, but can be fixed in more than one adjustment positions, preferably in any desired adjustment position, in relation to the guide. Combinations of guides and pins with these characteristics can be produced in many further embodiment forms, e.g. also in dowel-like embodiment forms, i.e. with configurations in which a wedge is driven into the pin after the latter has been pushed forward as far as the tube cone, in order to expand the pin and thus to clamp it in the guide. It is advantageous to slit the pin for such a purpose.

The pins shown in the embodiments are additionally so constructed that they enable a specified tension to be achieved between deflection unit and tube cone. A tension of specified size can, however, also be implemented by ensuring that the support feet (15) are withdrawn by the aligning device with a specified force while the pins are being pushed forward to the tube and while they are being fixed in position. After the deflection unit has been released by the aligning device, the elastic restoring force of the support feet (15) ensures the desired tension force. Pins having zero pitch threads are particularly useful in this case. It must be pointed out that it is not necessary for three support feet (15) to be provided in the deflection unit; a different number may also be possible.

The embodiment relates solely to a deflection unit. Pins which can be moved and arrested in the manner described can, however, also be used to retain other components in the position adjusted, e.g. for magnetic multipoles, of the type used for setting convergence and colour purity, for example. In an application of this sort, the pins can be supported on the tube neck, or on the deflection unit in front of it.



Foreign References:
CA1014454A    1977-07-26        411/417   
DE2451288A1    1975-05-15           
DE2641847A1    1978-03-23           
DE2814575A1    1979-10-11           
DE3010262A1    1981-09-24           
DE3106900A1    1982-09-16           
GB1025076A    1966-04-06        358/248   
GB1586100A    1981-03-18           
Other References:
Soviet Inventions Illustrated-Section E1: Electrical Derwent Publications, Ltd.-London (1987). 

 Color picture tube with shadow mask mounting means
 
  Hold members are used for abutting a shadow mask on the pins in the rim portion of the faceplate of a color picture tube. These hold members are of a two-part design and connected to one another with the aid of means permitting a transverse movement in relation to the axis of symmetry of the color picture tube. These means may consist either of a swivel joint or of a straight line motion device. During the first insertion of the shadow mask into the faceplate, any possible tolerances of the pins can be compensated for because the possible transverse movement of the hold members. The spacing between the shadow mask and the phosphor screen is not affected.

 Standard Elektrik Lorenz AG

1. A color picture tube comprising:

a faceplate, the inside surface of said faceplate being coated with a layer of phosphor;

a shadow mask;

a plurality of means for mounting said shadow mask in proximity of said faceplate, each said mounting means including:

a pin carried by said faceplate

a two part hold member, a first part of said hold member being retained on said pin, a second part of said hold member being retained on said shadow mask, and means coupling said first part with said second part whereby said first and second parts can move relative to each other in a direction transverse to the longitudinal axis of said picture tube during assembly of said shadow mask to said faceplate, said first and second parts being immovably connected to one another after assembly of said shadow mask to said faceplate, said first part being a substantially flat planar first element, said second part being a substantially flat planar second element.


2. A color picture tube in accordance with claim 1, wherein:

said first and second parts of each hold member overlap each other and, within the overlapping range, are joined to one another with the aid of swivel joint.


3. A color picture tube in accordance with claim 2, wherein:

said swivel joint comprises a tubular rivet.


4. A color picture tube in accordance with claim 3, wherein:

said first part comprises two shoulders which are each provided with a guide flap extending around an end of said second part.


5. A color picture tube in accordance with claim 2, wherein:

said swivel joint comprises a first guide flap at the rim portion of said first part, said guide flap extending around said second part, and two further guide flaps at an end of said first part opposite said guide flaps and which extend around an end of said second part.


6. A color picture tube in accordance with claim 1, wherein:

said first and second parts are coupled to one another such that motion of said first part relative to said second part can occur only along a straight line.


7. A color picture tube in accordance with claim 6, wherein:

said first part has four guide flaps which embrace said second part to limit relative motion between said first and second parts to a straight line.


8. A color picture tube in accordance with claim 2 wherein:

said shadow mask is frameless; and

each said second part is mounted to said shadow mask and simultaneously serves as a corner reinforcement for said shadow mask.


9. A color picture tube in accordance with claim 3 wherein:

said shadow mask is frameless; and

each said second part is mounted to said shadow mask and simultaneously serves as a corner reinforcement for said shadow mask.


10. A color picture tube in accordance with claim 6 wherein:

said shadow mask is frameless; and

each said second part is mounted to said shadow mask and simultaneously serves as a corner reinforcement for said shadow mask.


Description:

BACKGROUND OF THE INVENTION

The invention pertains to a color picture tube.

German OS No. 32 15 742 describes a type of color picture tube in which the pins for supporting the mask are fused under such an angle into the rim portion of the faceplate that its longitudinal axes extend parallel in relation to the electron beam deflected toward the respective corner. The free ends of the pins are conical, and the hold members are of a two-part design. A first part of the hold members has an almost triangular shape and is provided with a large hole at its end not secured to the mask. This hole is partially covered by a second part mounted to the first part, having a smaller opening. The openings in the second parts, are engaged by the pins when the picture tube is assembled.

Prior to installing the mask into the faceplate, the two parts of the hold members are not firmly connected to one another, but are held by springs and lugs. The mask is inserted into the faceplate by using or interposing a spacing gauge, and only thereafter the parts of the hold members are mounted to one another.

SUMMARY OF THE INVENTION

It is one object of the invention, to provide a color picture tube of the type mentioned hereinbefore, in which compensation of tolerances between the shadow mask and the pins in the faceplate is possible in the course of the first insertion, in a simple way and with the aid of simple hold members.

In accordance with the principles of the invention a color picture tube includes a plurality of support members to support a shadow mask at a predetermined distance from the phosphor screen and to automatically compensate for tolerances. The hold members are of two piece design and are connected to each other such that the two pieces may move relative to each other transversely in relation to the axis of symmetry of the picture tube. Each hold member is carried on one pin in the rim portion of the faceplate.

In accordance with the invention, the two pieces of each hold member are coupled either by a swivel joint or a straight line motion means. When the shadow mask is first inserted into the faceplate, any possible tolerances of the pins are compensated for by transverse movement of the hold members. The spacing between the shadow mask and the phosphor screen is not effected.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood from a reading of the following detailed description in conjunction with the drawing in which:

FIG. 1 is the top view of a face plate with a shadow mask inserted;

FIGS. 2A and 2B are the top and the side views, respectively, of a first embodiment of the hold members;

FIGS. 3A and 3B are top and side views, respectively, of a second embodiment of the hold members;

FIGS. 4A and 4B are top and side views, respectively, of a third embodiment of the hold members; and

FIG. 5 is the side view of a fourth embodiment, partly in a sectional elevation.

DETAILED DESCRIPTION

FIG. 1 shows only the faceplate 1 with the inserted shadow mask 2 of a conventional type of color picture tube. The X axis, the Y axis and the diagonals D1 and D2 are clearly shown. The surface of the rim porton 4 of the face plate 1 on which the faceplate is connected to the cone by means of solder glass (frit), is indicated by the reference numberal 3. Faceplate 1 carries the phosphor layer (not shown) on its inner side. At the point of intersection of the diagonals D1 and D2 with the rim portion 4 of the faceplate 1, pins 5 are provided which, via hold members 6, carry the shadow mask. The hold members 6 engage the rim portion 7 of the shadow mask 2.

The axis of symmetry (longitudinal axis) of the color picture tube, at the point of intersection of the X axis with the Y axis, is perpendicular to the drawing plane. The holding members for mask 2 do not absolutely have to be in the corners of the faceplate 1, but may equally well be provided for in the points of intersection of the X and Y axes with the rim portion 7 of the shadow mask 2 and the rim portion 4 of the faceplate 1.

FIGS. 2A and 2B show a first embodiment of a hold member 6 in two different views. The hold member 6 consists of two parts 6a and 6b which overlap each other. Part 6a has an almost triangular hole 8 at its free end through which the pin 5 extends. Part 6b has a recess 9 at its free end. Recess 9 is symmetrically positioned in relation to the longitudinal axis of hold member 6, so that the part 6b ends in two prongs 10a and 10b. Prongs 10a, 10b are connected to the rim portion 7 of the shadow mask 2.

Parts 6a and 6b are movable relative to one another by a swivel joint provided for in the overlapping area of the parts 6a and 6b. In this embodiment of the hold member 6, the swivel joint consists of a tubular rivet 11.

The free end of the part 6a is narrower than its area covered by the part 6b. Because of this, part 6a has two shoulders 13, with the rim portion thereof lying on a circular arc. This circular arc is determined by a radius stretching from the tubular rivet 11 up to the shoulders 13. In the center of each shoulder 13 there is provided a guide flap 12. Both guide flaps 12 are laid around the rim portion of part 6b. This rim portion of part 6b forms part of a circular arc which is determined by the aforementioned radius. The longitudinal axes of guide flaps 12 pass through the tubular rivet 11. With this arrangement of the guide flaps 12, the two parts 6a and 6b of the hold member 6 are held almost in one plane, and the tubular rivet 11 is relieved without this affecting or restricting the rotary motion of the parts with respect to one another.

FIGS. 3A and 3B show a second embodiment of a hold member 6, in which the swivel joint, compared to that of the first embodiment, is of a more simple design. Part 6a, at its end covered by the part 6b has a cutout 14, and the recess 9 between the prongs 10a, 10b in part 6b extends to the bottom of the cutout 14. Near bottom of the cutout 14, the recess 9 is restricted by a circular arc. At the point of intersection of the longitudinal axis of the hold member 6 with the cutout 14, a guide flap 15 is disposed on part 6a. Flap 15 extends around the rim portion of the part 6b within the area of the recess 9. Accordingly, in this embodiment the swivel joint connecting the parts 6a and 6b is formed in a simple way by the two guide flaps 12 and by the guide flap 15 lying opposite to them.

FIGS. 4A and 4B show a third embodiment of a hold member. In cases where a lateral displacement between the two parts 6a and 6b of the hold member 6 is sufficient, this type of embo

diment can be chosen. Part 6a is again provided at its shoulders with guide flaps 12 which are bent around the part 6b. The shape of the shoulders is simplified in that its rim portion is perpendicular to the longitudinal axis of hold member 6. In the same way, part 6b is provided with shoulders whose rim portion is also perpendicular to the longitudinal axis of the hold member. At the rim portion of the end of part 6a, as covered by the part 6b, two further guide flaps 17 are provided which are bent around the shoulders on the part 6b. The possible lateral movement of the parts 6a and 6b with respect to each other is restricted by the respective limit stop of a guide flap 12 against the narrow free end of the part 6a, or of a guide flap 17 against a prong 10 and the free end of the part 6b.

For a color picture tube employing a frameless shadow mask 2, the hold members 6 may also be designed in accordance with the embodiment of FIG. 5. In this case, part 6b of the hold members simultaneously serves as a corner reinforcement 18 for the shadow mask 2. Within the overlapping of parts 6a and 6b a tubular rivet 11 serves as the swivel joint. For stiffening, part 6a may be provided with folded rim portions 19.

Before the shadow mask 2 is installed into the faceplate 1, the hold members 6 are connected at the respective points either to the rim portion 7 of the shadow mask 2, or directly to the shadow mask, or to the shadow mask via an intermediate member. The shadow mask 2 is inserted into the faceplate 1 and hold members 6 are simultaneously slipped on to pins 5. Because of the movability of the two parts of the hold members, there is thus effected a compensation of tolerances due to possible movement transversely in relation to the axis of symmetry of the color picture tube. In so doing, the spacing of the shadow mask from the layer of phosphor remains unchanged. After that, the hold members are fixed in their assumed position in that the parts of the hold members are connected to one another, for example, by way of spot welding with the aid of a laser beam.

The novel, simple types of hold members 6 can be mounted outside the color picture tube and secured to the shadow mask. Because of this, the spacing between the shadow mask and the layer of phosphor is fixed after the insertion to the faceplate, so that no spacing gauges are required. The compensation for any possible tolerances in direction transversely in relation to the axis of symmetry of the color picture tube is then carried out in the was as already described hereinbefore.

It is also possible to firmly connect the hold members to the then simpler designed pins within the rim portion of the faceplate, and to provide the detachable connection between the shadow mask and the ends of the hold members applied to this point.

  Color picture tube having internal conductive coatings
 
 In a color-picture tube, the conductive coating on the inside of the cone is a suspension without organic constituents. The conductive coating on the inside of the neck, which is contiguous to the conductive coating on the inside of the cone, consists of the aforementioned suspension with an addition of organic constituents. A sharp and scratch-resistant boundary between the conductive coating in the neck and the uncoated area of the neck is thus obtained.

 Nokia Graetz GmbH

1. A color-picture tube comprising:

a cone;

a first conductive coating without organic constituents on the inside of said cone;

a neck adjacent said cone; and

a second coating on an area inside said neck, said second coating being contiguous to said first coating and consisting of a suspension of said first coating with an addition of organic constituents.


2. A color-picture tube in accordance with claim 1, wherein:

said organic constituents consist of polyvinyl pyrrolidone.


3. A color-picture tube in accordance with claim 1, wherein:

the boundary line between said first coating and said second coating coincides with the seal line between said neck and said cone.


4. A color-picture tube in accordance with claim 1, wherein:

said second coating slightly overlaps said first coating.


Description:

BACKGROUND OF THE INVENTION

The present invention relates to a color-picture tube and to a method of manufacturing the color-picture tube.

DE-OS No. 27 42 741 discloses a color-picture tube having a conductive coating on the inside of the cone. The coating is made of graphite, iron oxide, and a silicate binder. The entire inside of the neck of the color-picture tube is coated with a film of vaporizable material, e.g., polyvinyl alcohol. This film serves to protect the neck during the insertion of the electron-gun system. After the electron-gun system has been mounted, the film in the neck is vaporized.

To avoid sparkover between the conductive coating in the cone, which is at high electric potential, and the electron-gun system, there must be a sharp boundary between the conductive coating and the uncoated area. The thickness of the coating must be very uniform, and the boundary region between the coated and uncoated areas must be very smooth, because otherwise material of the coating would easily crumble away at bulging transitions, particularly when the centering and contact springs of the electron-gun system are moved over the boundary.

DE-OS No. 29 03 735 discloses a method of applying a conductive coating to the cone of a color-picture tube which comprises the steps of covering the areas which are to remain free of the coating with a lacquer film, then depositing the conductive coating, and finally washing away the lacquer film and the conductive coating resting on the film.

SUMMARY OF THE INVENTION

One object of the invention is to provide a color-picture tube of the above kind in which there is a sharp and scratch-resistant boundary between the conductive coating and the uncoated area in the neck.

A further object is to provide a simple method of manufacturing such color-picture tubes.

In a color-picture tube in accordance with the invention, the conductive coating on the inside of the cone is a suspension without organic constituents and a conductive coating is provided on the inside of the neck, which is contiguous to the conductive coating on the inside of the cone, and consists of the aforementioned suspension with an addition of organic constituents. A sharp and scratch-resistant boundary between the conductive coating in the neck and the uncoated area of the neck is thus obtained.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood from a reading of the following detailed description in conjunction with the drawing in which:

FIG. 1 is a perspective view of a color-picture tube, partly broken way and partly in section; and

FIG. 2 to 5 show different steps of the method of manufacturing the color-picture tube.

DETAILED DESCRIPTION

FIG. 1 shows the cone 1 and the neck 2 of a color-picture tube 13 which further comprises a mask-faceplate assembly 14 (outlined by dashed lines and slightly lifted) and a base 15. At the upper rim of the cone 1, the sea

l surface to which the mask-faceplate assembly 14 is to be joined is designated 3. The first conductive coating on the inside of the cone 1 is shown dotted and is designated by the reference numeral 4. This coating 4 extends down to the seal line 5 between the neck 2 and the cone 1. On the inside of the neck 2, there is a portion with a second coating 6 (shown hatched) which is contiguous to the first coating 4. The boundary between this second coating 6 and the uncoated area in the neck 2 is designated 7. The second coating 6 may extend beyond the seal line 5 and overlap the first coating 4, as shown in FIG. 1.

The coating 4 contains no organic constituents and consists, for example, of a graphite suspension with an admixture of iron powder or other nonconductive inorganic constituents for setting the electric resistance, such as TiO2, AL2 O3, and SiO2, and a silicate binder. The coating 6 consists of the suspension of the coating 4 with an admixture of organic constituents. The organic constituents are, for example, polyvinyl pyrrolidone, polyvinyl alcohol, casein, and polyvinyl acetate. The use of a suspension without organic constituents for the first coating 4 permits short frit-sealing times which joining the mask-faceplate assembly 14 to the cone 2, and shorter pumping times at a lower peak temperature, without any adverse effects on the tube vacuum and tube life. To avoid the disadvantage of an unsharp and non-abrasion-resistant boundary between this suspension and an uncoated area, the first coating 4 is adjoined by the second coating 6, which is a suspension that gives a sharp boundary.

The method of making the color-picture tube of FIG. 1 will now be described with the aid of FIGS. 2 to 5. The carefully cleaned cone 1 and the neck 2 joined thereto are covered with the first conductive coating by any of the conventional techniques. In the example of FIG. 2, the first coating is applied by pouring in the suspension through the end 9 of the tube that is guided along the boundary 8. In this manner, the entire inside surface of the cone 1 and the entire inside surface of the neck 2 are covered with this coating (shown dotted). Then, the anode contact in the cone 1 is uncovered by blowing (not shown), and the first conductive coating 4 is dried. The drying is done with infrared lamps 10, of which only one is shown in FIG. 3. The distance h between the lower edge of the infrared lamp 10 and the seal surface 3 is chosen so that the coating 4 will dry between the boundary 8 and the seal line 5 while remaining wet between the seal line 5 and the free end of the neck. This can also be accomplished with an infrared lamp located at a fixed distance h by suitably adjusting the heating power of the lamp.

As shown in FIG. 4, the wet portion of the coating 4 below the seal line 5 is then removed by rinsing out the neck 2 with the suspension of the subsequently applied second coating. To do this, a tube 11 is introduced into the neck 2 from below. The suspension 6a (shown hatched) of the subsequent second coating emerges from the upper end of the tube 11, which rises slightly above the seal line 5. The suspension 6a also washes over a small portion of the dried coating 4 in the transition region from the cone 1 to the neck 2, but this portion is not washed away. Only the wet coating below the seal line 5 is removed and replaced by the suspension of the second coating. After removal of the tube 11, this second coating in the neck 2 is dried with, e.g., a heater fan. The area which is to remain free of the second coating 6 in the neck 2 is then rinsed with alkali hydroxides, preferably a 0.5 to 10% sodium hydroxide solution, and then cleaned with a wiper 12 and water. In a preferred embodiment, the rinsing is done with a 0.5 to 2% sodium hydroxide solution. Thereafter, the neck may be cleaned with hydrofluoric acid. Finally, the neck is rinsed inside and outside with demineralized water. For cleaning the outside of the neck, a ring brush (not shown) may be used.

This is a divisional of co-pending application Ser. No. 844,109 filed on Mar. 26, 1986, now U.S. Pat. No. 4,762,733.

 Color picture tube with mounting structure for a shadow mask
 
  In a color picture tube, the shadow mask is suspended in a way such that the pins inserted into the rim portion of the faceplate are aligned vertically in relation to the axis of symmetry of the color picture tube. The free ends of the pins are of spherical design, and comprise a conical part. Two-piece, trapezoidal hold members for the shadow mask rest on the pins. Each of the hold members is resiliently pressed upon the pins by a locking spring.
 
   Standard Elektrik Lorenz AG
   
1. A color picture tube comprising:

a faceplate;

a shadow mask including a rim portion;

a magnetic shield adjacent said rim portion;

a plurality of mounting structures for mounting said shadow mask in proximity to said faceplate, each of said plurality of mounting structures comprising:

a support pin having one end portion fused in said faceplate, an intermediate portion which is generally conical in shape, and a generally spherical other end portion;

a support angle having a first and a second end wherein said first end is attached to said magnetic shield and said second end is carried by said support pin;

a generally trapezoidal shaped, flat hold member attached to said rim portion of said shadow mask, said flat hold member having its narrow end pointing toward said support pin and having a hole in said narrow end adapted to receive said support pin;

a "V"-shaped locking spring having one end mounted on said support angle and abutting said intermediate portion and having its other end pressing said hold member toward the center of said spherical shaped other end portion; and

wherein the longitudinal axis of said support pin is perpendicular to the axis of symmetry of said picture tube.


2. A color picture tube in accordance with claim 1, wherein:

each said pin comprises a constriction between said intermediate portion and said other end portion.


3. A color picture tube in accordance with claim 1, wherein:

each said pin is symmetrical above its longitudinal axis.


4. A color picture tube in accordance with claim 1, wherein:

each said pin is formed from sheet metal.


5. A color picture tube in accordance with claim 1, wherein:

each said pin is of solid construction.


6. A color picture tube in accordance with claim 1, wherein:

each said hold member comprises first and second overlaying parts, said first part having flaps on its sides which fold over and embrace said second part.


7. A color picture tube in accordance with claim 1, wherein:

said hole is triangular with a diameter smaller than the diameter of said spherical shaped other end portion.


8. A color picture tube in accordance with claim 1, wherein:

said other end of said spring comprises two prongs.


9. A color picture tube in accordance with claim 8 wherein:

each of said prongs includes a bent portion for engaging said hold member.


10. A color picture tube in accordance with claim 8, comprising:

a bulge on each of said prongs, each said bulge engaging said hold member.


Description:

BACKGROUND OF THE INVENTION

This invention pertains to a color picture tube.

In particular, the invention pertains to a color picture tube of the type having a shadow mask mounted in the proximity of the faceplate by means of pins which are disposed in the corners of the faceplate which with hole containing supports on the shadow mask. The supports are retained at the pins with the aid of locking springs.

German Pat. No. 31 25 095 teaches a color picture tube in which the pins for supporting the mask are fused into the rim portion of the faceplate at such an angle that their longitudinal axes extend parallel in relation to the electron beam deflected toward the respective corner. The free ends of the pins are of conical design, and the hold members are oblong and of one piece. Two part clamping members are used for locking the hold members on the pins.

SUMMARY OF THE INVENTION

One object of the invention is to provide a color picture tube having a holding arrangement for its mask which permits easy insertion and removal of the mask during the manufacture of the color picture tube and which, in the event of forces acting thereupon from the outside, does not exert any unbuttoning forces.

In accordance with the principles of the invention a color picture tube which has a frameless shadow mask is suspended in such a way that the pins inserted into the rim portion of the faceplate are aligned vertically in relation to the axis of symmetry of the color picture tube. The free ends of the pins are of spherical design and comprise a conical part. Two-piece trapezoidal hold members for the shadow mark rest on the pins. Each of the hold members is resiliently pressed upon the pins by a locking spring.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood from a reading of the following detailed description in conjunction with the drawings in which:

FIG. 1 is a top view on to a faceplate of a picture tube with an inserted mask;

FIG. 2 is a side view in the direction as indicated in FIG. 1 of a hold member for supporting the mask in one corner of the faceplate;

FIG. 3 is an enlarged view of the hold member of FIG. 2;

FIG. 4 is a section taken on line A-B of FIG. 3;

FIG. 5 is a section taken on line C-D of FIG. 3;

FIG. 6 is a side view of a second embodiment of the hold member;

FIG. 7 is a section taken along line A--A of FIG. 6; and

FIG. 8 is a section taken through a pin.

DETAILED DESCRIPTION

FIG. 1 shows a faceplate 1 with an inserted mask 2 of a conventional type of color picture tube.

For reference purposes, FIG. 1 shows an X axis, a Y axis and diagonals D1, D2. The frit surface on the rim portion 4 of the faceplate 1 is indicated by the reference numeral 3. The faceplate 1 carries a phosphor layer on its inside. At the point of intersection of the diagonals D1 and D2 with the rim portion 4 of the faceplate 1, pins 5 are provided which, via hold members 6, carry the mask. The hold members 6 engage on the rim portion 7 of the mask 2.

The axis of symmetry of the color picture tube, in the point of intersection of the X axis with the Y axis, is vertically on the drawing plane. The hold members for the mask may alternatively be provided at the intersection of the X and the Y axes with rim portion 7 of mask 2 and rim portion 4 of faceplate 1.

As seen in FIG. 2, pin 5 has one end fused into the rim portion 4 of the faceplate 1. Pin 5 is inserted into the rim portion 4 as to be vertical relative to the tube axis. The free end of pin 5 carries two-part hold member 6 which, via corner reinforcement 8, is connected to the outside of rim portion 7 of the mask 2. The hold member 6 is so aligned to extend perpendicular relative to electron beam E as deflected into this corner. Moreover, the pin 5 carries a support angle 9. The magnetic shielding 10 of the color picture tube is mounted to the end of support angle 9. At the end of support angle 9 abutting on pin 5, an almost V-shapedly bent locking spring 11 is mounted. The free end of the spring presses the support member 6 resiliently upon the pin 5.

As most clearly shown in FIG. 3, pin 5 has a conical part 13 which carries the spherical end 12. The diameter of the spherical end 12 is larger than the smallest diameter of the conical part 13, so that a constriction 14 exists between the conical part 13 and the spherical end 12. Support member 6 rests on the spherical end 12. The support angle 9 is placed onto the conical part 13 of the pin 5. Locking spring 11 extends in a bend to contact a point of support angle 9 lying above the conical part 13, and is secured to that end of the support angle 9 which as shown in FIG. 3 points downward. The apex of the bend of locking spring 11 abuts on the portion of the

spherical end 12 pointing toward the constriction 14, and thus presses the support angle 9 on to the conical part 13. Somewhat behind the point where the locking spring touches the support angle 9, the spring is bent off in such a way that its free end 16 presses upon the hold member 6. This prevents hold member 6 from slipping off the spherical end 12 of pin 5. The free end 16 of the locking spring 11 ends in a bend 17 pointing toward the hold member 6. In the apex of bend 17, bulgings 18 are provided for, so that only small bearing surfaces result. The forces exerted by the locking spring 11 via the bulgings 18 upon the hold member 6 extend in the direction indicated by arrow K, toward the center point of the spherical end 12 of the pin 5.

The sectional view of FIG. 4 taken along the line A-B of FIG. 3, shows the parts of the support angle 9 and locking spring 11 resting on pin 5. The support angle 9 and locking spring 11 are both provided with a central incision, so that they both end in two prongs 19 and 20, respectively. These prongs 19 and 20, for example, are joined to one another by weld spots 21. The width of the incision in the locking spring 11 is chosen to be larger than the diameter of the constriction 14, but smaller than the diameter of the spherical end of the pin 5. The width of the incision in the support angle 9 is chosen to be larger than the diameter of the constriction 14, but smaller than the larger diameter of the conical part 13. Therefore, the support angle with the locking spring can be placed from above on to the conical part 13 of the pin 5. The support angle 9 is thereafter pressed against the enlarging end of the conical part 13 and is secured in this position by bent portion 15 of locking spring 11 abutting on the spherical end 12.

The inwardly bent portion 17 of the locking spring 11 is likewise provided with an incision extending in the center so that locking spring 11 ends in two prongs which press symmetrically upon hold member 6.

In FIG. 5, the incision or notch in the support angle 9 is clearly shown. At the rim portion of the support angle, the incision is larger than further toward the inside, and it ends up in a circular cutout. Support angle 9 thereby embraces the conical part 13 of the pin 5 throughout a large part of the circumference. Thus, support angle 9 is secured in its final position and prevented from being pulled off in the upward direction.

FIG. 6 is a side view of a second embodiment of the hold member. Conical part 13 extends in a direction opposite to that of the hitherto described pin. The thinner end of the conical part 13 points toward the fused end of the pin 5. The locking spring 11 is now V-shaped and mounted with its one end to the horizontally extending portion of the support angle 9. The other end of the locking spring again ends up in two prings, each of which is provided with a bulge 18. Bulges 18 press resiliently against the hold member 6. The pressing force is directed toward the center of the spherical end 12. By mounting the locking spring to the horizontal part of the support angle 9, the angle is pulled on the conical part 13 against the spherical end 12.

The holder includes parts 6a and 6b. Part 6a of the hold member engages the spherical end of the pin 5. Part 6b of the hold member carries the corner reinforcement of the mask 2. Part 6a is of a somewhat thicker design and rigid, whereas part 6b has resilient properties. On the part 6b, flaps 22 are provided for, which capture and engage part 6a. In addition, thereto, the parts 6a and 6b are joined to one another by spot welding.

FIG. 7 is a sectional view taken along the line A--A of FIG. 6. From this it can be seen that hold member 6 has a trapezoidal shape; the one end points toward the pin 5, and the base side points toward the corner reinforcement (fillet) 8. The upper piece of the hold member is formed by part 6a and the lower piece is formed by the part 6b. A triangular hole 23 is provided in the proximity of the upper rim portion of the part 6a. Due to its triangular form, hole 23 engages spherical end 12 of the pin 5 at three points. Corner reinforcement 8 which carried the mask 2 is mounted on the lower resilient part 6b. A recess 24 is provided in both part 6b and on the associated part of the corner reinforcement 8 thus preventing the electron beam from being shadowed during its deflection into the respective corner.

FIG. 8 is a sectional view taken through a pin 5. On the right side of the line of symmetry there is shown a pin which was either turned from a rod length of circular cross section, or extrusion moulded. On the left of the line of symmetry there is shown a pin shaped from a sheet metal part. All pins 5 are rotation-symmetrical and have a spherical end 12. Between the end as fused in the glass of the faceplate 1, and the spherical end 12, there is provided a conical part 13 and, in the first embodiment of the hold member, a constriction 14. Relative thereto, the thinner end of the conical part 13 points toward the spherical end 12. In the pin 5 of the second embodiment of the hold member, the thinner end of the conical part 13 points toward the end of the pin 5 which is fused (sealed) in the glass of the faceplate.

As a particular advantage relating to the hitherto described arrangement for holding the mask in position inside the color picture tube is that angular variations between the pin (5) and the hold member (6) will have no influence upon the quality of the mask seating.

In some types of color picture tubes there is no room for the hold member between the mask and the rim portion of the faceplate. In these cases, the mask may be provided with a corner reinforcement (fillet) lying within, with the hold member being secured thereto.

Foreign References:
GB2097996A    1982-11-10        313/402

ITT NOKIA  DIGIVISION 7170 VT  CHASSIS  DIGI B-E   ITT DIGIT2000 CATHODE RAY TUBE (Kinescope) driver with kinescope current sensing circuit:


A television receiver includes a kinescope and a current sensing transistor for conveying amplified video signals to the kinescope, and for providing at a sensing output terminal an output signal related to the magnitude of kinescope current conducted during given sensing intervals. A clamping circuit clamps the sensing output terminal during normal image intervals, and unclamps the sensing output terminal during the sensing intervals. The clamping circuit facilitates interfacing the sensing transistor with utilization circuits which process the sensed output signal, and assists to maintain a proper operating condition for the sensing transistor.


1. In a video signal processing system including an image reproducing device for displaying video information in response to a video signal applied thereto, apparatus comprising:
a video output driver stage with a video signal input and a video signal output for providing an amplified video signal;
means for conveying said amplified video signal to said image reproducing display device, said conveying means having a sensing output for providing thereat a sensed signal representative of the current conducted by said image reproducing display device;
utilization means responsive to said sensed signal; and
clamping means for selectively clamping said sensing output during normal image intervals, and for unclamping said sensing output during intervals when said sensed signal representative of current conducted by said image reproducing display device is subject to processing by said utilization means; wherein
said clamping means comprises clamping transistor means with an output first electrode coupled to said sensing output, a second electrode coupled to an operating potential, and an input third electrode coupled to said sensing output, the conduction of said clamping transistor means being controlled in accordance with the magnitude of said sensed signal as received by said third electrode; and
said clamping transistor means is self-keyed to exhibit clamping and non-clamping states in response to said sensed representative signal.
2. Apparatus according to claim 1, wherein:
said video output stage comprises a video amplifier with a video signal input and a video signal output for providing said amplified video signal; and
said conveying means comprises an active current conducting device with an input first terminal for receiving said amplified video signal, an output second terminal for conveying said amplified video signal to said image reproducing display device, and a third terminal for providing said sensed signal.
3. Apparatus according to claim 2, wherein
said active current conducting device is a transistor with a base input for receiving said amplified video signal, an emitter output for providing said amplified video signal to said image reproducing display device, and a collector output for providing said sensed signal.
4. Apparatus according to claim 1, wherein
said first and second electrodes define a main current conduction path of said clamping transistor means.
5. Apparatus according to claim 4, wherein
said clamping means includes resistive means coupled to said sensing output for providing a voltage in accordance with the magnitude of said sensed signal; and
said third electrode of said clamping transistor means is coupled to said resistive means.
6. Apparatus according to claim 1, and further comprising
filter means for bypassing high frequency signal components at said sensing output.
7. In a video signal processing system including an image reproducing device for displaying video information in response to a video signal applied thereto, apparatus comprising:
a video output driver stage coupled to said image reproducing display device for providing an amplified video signal thereto, and having a sensing output for providing thereat a sensed signal representative of the current conducted by said image reproducing display device;
control means responsive to said sensed signal for developing a control signal;
means for coupling said control signal to said image reproducing display device to maintain a desired conduction characteristic of said image reproducing display device; and
clamping means for selectively clamping said sensing output during normal image intervals, and for unclamping said sensing output during intervals when said control means operates to monitor said sensed signal; wherein
said clamping means comprises clamping transistor means with an output first electrode coupled to said sensing output, a second electrode coupled to an operating potential, and an input third electrode coupled to said sensing output, the conduction of said clamping transistor means being controlled in accordance with the magnitude of said sensed signal as received by said third electrode; and
said clamping transistor means is self-keyed to exhibit clamping and non-clamping states in response to said sensed signal.
8. Apparatus according to claim 7, wherein
said control means includes digital signal processing circuits; and
said control means includes an input analog-to-digital signal converter network.
9. In a video signal processing system including an image reproducing device for displaying video information in response to a video signal applied thereto, apparatus comprising:
a video amplifier with a video signal input for receiving video signals, and a video signal output for providing an amplified video signal;
a signal coupling transistor with an input first electrode for receiving said amplified video signal from said video amplifier, an output second electrode for providing a further amplified video signal to said image reproducing display device, and a third electrode for providing a sensed signal representative of the magnitude of the current conducted by said image reproducing display device;
utilization means responsive to said sensed signal; and
clamping means for selectively clamping said third electrode of said coupling transistor during normal image intervals, and for unclamping said third electrode during interval when said sensed representative signal is subject to processing by said utilization means, said clamping means comprising clamping transistor means with an output first electrode coupled to said third electrode of said signal coupling transistor, a second electrode coupled to an operating potential, and an input third electrode coupled to said third electrode of said signal coupling transistor, the conduction of said clamping transistor means being controlled in accordance with the magnitude of said sensed signal as received by said input third electrode of said clamping transistor means.
10. Apparatus according to claim 9, wherein
said coupling transistor is an emitter follower transistor with a base input electrode, an emitter output electrode, and a collector output electrode corresponding to said third electrode.

Description:

This invention concerns a video output display driver amplifier for supplying high level video output signals to an image display device such as a kinescope in a television receiver. In particular, this invention concerns a display driver stage associated with a sensing circuit for providing a signal representative of the magnitude of current conducted by the kinescope during prescribed intervals.
Video signal processing and display systems such as television receivers commonly include a video output display driver stage for supplying a high level video signal to an intensity control electrode, e.g., a cathode electrode, of an image display device such as a kinescope. Television receivers sometimes employ an automatic black current (bias) control system or an automatic white current (drive) control system for maintaining desired kinescope operating current levels. Such control systems typically operate during image blanking intervals, at which time the kinescope is caused to conduct a black image or a white image representative current. Such current is sensed by the control system, which generates a correction signal representing the difference between the magnitude of the sensed representative current and a desired current level. The correction signal is applied to video signal processing circuits for reducing the difference.
Various techniques are known for sensing the magnitude of the black or white kinescope current. One often used approach employs a PNP emitter follower current sensing transistor connected to the kinescope cathode signal coupling path. Such sensing transistor couples video signals to the kinescope via its base-to-emitter junction, and provides at a collector electrode a sensed current representative of the magnitude of the kinescope cathode current. The representative current from the collector electrode of the sensing transistor is conveyed to the control system and processed to develop a suitable correction signal.
In accordance with the principles of the present invention, there is disclosed a kinescope current sensing arrangement wherein a current sensing device is coupled to a kinescope for providing at an output terminal a signal representative of the magnitude of the kinescope current. A clamping circuit clamps the output terminal to a given voltage during normal image trace intervals. During prescribed kinescope current sensing intervals, however, the clamping circuit is inoperative and the sensed signal representative of the kinescope current is developed at the output terminal. The clamping circuit advantageously facilitates interfacing the current sensing device with control circuits for processing the sensed signal, and assists to maintain a proper operating condition for the current sensing device which, in a disclosed embodiment, also conveys video signals to the display device. In accordance with a feature of the invention, the clamping circuit is self-keyed between clamping and non-clamping states in response to the representative signal at the output terminal.
In the drawing:
FIG. 1 shows a circuit diagram of a kinescope driver stage with associated kinescope current sensing and clamping apparatus in accordance with the present invention; and
FIG. 2 depicts, in block diagram form, a portion of a color television receiver incorporating the current sensing and clamping apparatus of FIG. 1.
In FIG. 1, low level color image representative video signals r, g, b are provided by a source 10. The r, g and b color signals are coupled to similar kinescope driver stages. Only the red (r) color signal video driver stage is shown in schematic circuit diagram form.
Red kinescope driver stage 15 comprises a driver amplifier including an input common emitter amplifier transistor 20 arranged in a cascode amplifier configuration with a common base amplifier transistor 21. Red color signal r is coupled to the base input of transistor 20 via a current determining resistor 22. Base bias for transistor 20 is provided by a resistor 24 in association with a source of negative DC voltage (-V). Base bias for transistor 21 is provided from a source of positive DC voltage (+V) through a resistor 25. Resistor 25 in the base circuit of transistor 21 assists to stabilize transistor 21 against oscillation.
The output circuit of driver stage 15 includes a load resistor 27 in the collector output circuit of transistor 21 and across which a high level amplified video signal is developed, and opposite conductivity type emitter follower transistors 30 and 31 with base inputs coupled to the collector of transistor 21. A high level amplified video signal R is developed at the emitter output of follower transistor 30 and is coupled to a cathode electrode of an image reproducing kinescope via a kinescope arc current limiting resistor 33. A resistor 34 in the collector circuit of transistor 31 also serves as a kinescope arc current limiting resistor. Degenerative feedback for driver stage 15 is provided by series resistors 36 and 38, coupled from the emitter of transistor 31 to the base of transistor 20.
A diode 39 connected between the emitters of transistors 30 and 31 as shown is normally reverse biased and therefore nonconductive by the voltage difference across it equalling the sum of the two base-emitter voltage drops of transistors 30 and 31, but is forward biased and therefore rendered conductive under certain conditions in response to positive-going transients at the emitter of transistor 30, corresponding to the output terminal of driver stage 15. The arrangement of transistor 31 prevents the amplifier feedback loop including transistors 20, 21 and 31 and resistors 36 and 38 from being disrupted, thereby preventing feedback transients and signal ringing from occurring. Additional details of the arrangement including transistors 30 and 31 and diode 39 are found in my copending U.S. patent application Ser. No. 758,954 titled "FEEDBACK DISPLAY DRIVER STAGE".
The emitter voltage of transistor 30 follows the voltage developed across load resistor 27, and transistor 30 conducts the kinescope cathode current. Substantially all of the kinescope cathode current flows as collector current of transistor 30, through a kinescope arc current limiting protection resistor 37a, to a clamping network 40. Transistor 30 acts as a current sensing device in conjunction with network 40 as will be explained. Clamping network 40 in this example is self-keyed to exhibit clamping and non-clamping states in response to the magnitude of the current conducted by transistor 30.
Clamping network 40 is common to all three driver stages of the receiver, as will be seen subsequently in connection with FIG. 2, and is coupled to the green and blue signal driver stages via protection resistors 37b and 37c. Network 40 includes clamping transistors 41 and 42 arranged in a Darlington configuration, and series voltage divider resistors 43 and 44 which bias clamp transistors 41 and 42. A high frequency bypass capacitor 46 filters signals in the collector circuit of transistor 30 in a manner to be described below. The series combination of a mode control switch 49 and a scaling resistor 48 is coupled across resistors 43 and 44. A voltage related to the magnitude of kinescope current is developed at a terminal A and, as will be explained with reference to FIG. 2, the voltage at terminal A can be used in conjunction with a feedback control loop to maintain a desired kinescope operating current condition which is otherwise subject to deterioration due to kinescope aging and temperature effects, for example.
Assuming switch 49, the function of which will be explained below, is open, the kinescope cathode current flowing in the collector of transistor 30 is conducted to ground via resistors 43 and 44. When this current causes a voltage drop across resistor 44 to sufficiently forward bias the base-emitter junctions of transistors 41 and 42, transistor 42 will conduct in a linear region, and will clamp terminal A to a voltage VA according to the following expression, where V _BE41 and V _BE42 are the base-emitter junction voltage drops of transistors 41 and 42: VA=(V _BE41 +V _BE42 ) (R43+R44)/R44
During normal image intervals typically there are greater than approximately 25 microamperes of current conducted by transistor 30, which is sufficient to render transistors 41 and 42 conductive for developing clamping voltage VA at terminal A. At other times, as will be discussed, transistors 41 and 42 are rendered nonconductive whereby clamping action is inhibited and a (variable) voltage is developed at node A as a function of the magnitude of the kinescope cathode current, for processing by succeeding control circuits.
Illustratively, the arrangement of FIG. 1 can be used in connection with digital signal processing and control circuits in a color television receiver employing digital signal processing techniques, as will be seen in FIG. 2. Such control circuits include an input analog-to-digital converter (ADC) for converting analog voltages developed at terminal A to digital form for processing.
When the control circuits are to operate in an automatic kinescope black current (bias) control mode, wherein during image blanking intervals the kinescope conducts very small cathode currents on the order of a few microamperes, approximating a kinescope black image condition, clamp transistors 41 and 42 are rendered nonconductive because such small currents flowing through resistors 43 and 44 from the collector of transistor 30 are unable to produce a large enough voltage drop across resistor 44 to forward bias transistors 41 and 42. Consequently terminal A exhibits voltage variations, as developed across resistors 43 and 44, related to the magnitude of kinescope black current. The voltage variations are processed by the control circuits coupled to terminal A to develop a correction signal, if necessary, to maintain a desired level of kinescope black current conduction by feedback action. In this operating mode switch 49, e.g., a controlled electronic switch, is maintained in an open position as shown in response to a timing signal VT developed by the control circuits.
When the control circuits are to operate in an automatic kinescope white current (drive) control mode wherein during image blanking intervals the kinescope conducts much larger currents representing a white image condition, switch 49 closes in response to timing signal VT, thereby shunting resistor 48 across resistors 43 and 44. The value of resistor 48 is chosen relative to the combined values of resistors 43 and 44 so that the larger current conducted via the collector of transistor 30 divides between series resistors 43, 44 and resistor 48 such that the magnitude of current conducted by resistors 43 and 44 is insufficient to produce a large enough voltage drop across resistor 44 to render clamping transistors 43 and 44 conductive. Unclamped terminal A therefore exhibits voltage variations related to the magnitude of kinescope white current, which voltage variations are processed by the control circuits to develop a correction signal as required. As used herein, the expression "white current" refers to a high level of individual red, green or blue color image current, or to combined high level red, green and blue currents associated with a white image.
With the illustrated configuration of transistors 41 and 42 clamping voltage VA is relatively low, approximately +2.0 volts. The clamping voltage could be provided by a Zener diode rather than the disclosed arrangement of Darlington-connected transistors 41 and 42, but the disclosed clamping arrangement is preferred because Zener diodes with a voltage rating less than about 4 volts usually do not exhibit a predictable Zener threshold voltage characteristic, i.e., the "knee" transition region of the Zener voltage-vs-current characteristic is usually not very well defined. In addition, the disclosed transistor clamp operates with better linearity than a Zener diode clamp and radiates less radio frequency interference (RFI).
The relatively low clamping voltage is compatible with the analog input voltage requirements of the analog-to-digital converter (ADC) at the input of the control circuits which receive the sensed voltage at terminal A as will be explained in greater detail with respect to FIG. 2. In this example the ADC is intended to process analog voltages of from 0 volts to approximately +2.5 volts, and the clamping voltage assures that excessively high analog voltages are not presented to the ADC during normal video signal intervals.
The relatively low clamping voltage also assists to prevent transistor 30 from saturating, which is necessary since transistor 30 is intended to operate in a linear region. To achieve this result and to maximize the cathode current conduction capability of transistor 30, the clamping voltage should be as low as possible to maintain a suitably low bias voltage at the collector of transistor 30. On the other hand, the value of arc current limiting resistor 37a should be large enough to provide adequate arc protection without compromising the objective of maintaining the collector bias voltage of transistor 30 as low as possible. Operation of transistor 30 in a saturated state renders transistor 30 ineffective for its intended purpose of properly conveying video drive signals to the kinescope cathode, and for conveying accurate representations of cathode current to clamping network 40 particularly in the white current control mode when relatively high cathode current levels are sensed. In addition, undesirable radio frequency interference (RFI) can be generated by transistor 30 switching into and out of saturation. Also, when saturation occurs transistor base storage effects can result in video image streaking due to the time required for a transistor to come out of a saturated state.
Thus clamping network 40 advantageously limits the voltage at terminal A to a level tolerable by the analog-to-digital converter at the input of the control circuits coupled to terminal A, and protects the analog-to-digital converter input from damage due to signal overdrive. Network 40 also provides a collector reference bias for transistor 30 to prevent transistor 30 from saturating on large negative-going signal amplitude transitions at its emitter electrode. The clamping voltage level is readily adjusted simply by tailoring the values of resistors 43 and 44.
Capacitor 46 bypasses high frequency video signals to ground to prevent transistor 30 from saturating in response to such signals. Capacitor 46 also serves to smooth out undesirable high frequency variations at terminal A to prevent potentially troublesome signal components such as noise from interfering with the signal processing function of the input analog-to-digital converter of the control circuits, e.g., by smoothing the current sensed during the settling time of the analog-to-digital converter.
The latter noise reducing effect is particularly desirable, for example, when the input ADC of the control circuits coupled to terminal A is of the relatively inexpensive and uncomplicated "iterative approximation" type ADC, compared to a "flash" type ADC. The operation of an iterative ADC, wherein successive approximations are made from the most significant bit to the least significant bit, requires a relatively constant or slowly varying analog signal to be sampled during sampling intervals, uncontaminated by noise and similar effects.
The value of capacitor 46 should not be excessively large because a certain rate of current variation should be permitted at terminal A with respect to kinescope cathode currents being sensed. If the value of capacitor 46 is too small, excessive voltage variations, particularly high frequency video signal variations, will appear at terminal A, increasing the likelihood of transistor 30 saturating. The speed of operation of the clamp circuit itself is restricted by an RC low pass filter effect produced by the base capacitance of transistor 41 and the equivalent resistance of resistors 43 and 44.
FIG. 2 shows a portion of a color television receiver system employing digital video signal processing techniques. The FIG. 2 system utilizes kinescope driver amplifiers and a clamping network as disclosed in FIG. 1, wherein similar elements are identified by the same reference number. By way of example, the system of FIG. 2 includes a MAA 2100 VCU (Video Codec Unit) corresponding to video signal source 10 of FIG. 1, a MAA 2200 VPU (Video Processor Unit) 50, and a MAAA 2000 CCU (Central Control Unit) 60. The latter three units are associated with a digital television signal processing system offered by ITT Corporation as described in a technical bulletin titled "DIGIT 2000 VLSI DIGITAL TV SYSTEM" published by the Intermetall Semiconductors subsidiary of ITT Corporation.
In unit 10, a luminance signal and color difference signals in digital form are respectively converted to analog form by means of digital-to-analog converters (DACs) 70 and 71. The analog luminance signal (Y) and analog color difference signals r-y and b-y are combined in a matrix amplifier 73 to produce r, g and b color image representative signals which are processed by preamplifiers 75, 76 and 77, respectively, before being coupled to kinescope driver stages 15, 16 and 17 of the type shown in FIG. 1. A network 78 in unit 10 includes circuits associated with the automatic white current and black current control functions.
The high level R, G and B color signals from driver stages 15, 16 and 17 are coupled via respective current limiting resistors (i.e., resistor 33) to cathode intensity control electrodes of a color kinescope 80. Currents conducted by the red, green and blue kinescope cathodes are conveyed to network 40 via resistors 37a-37c, for producing at terminal A a voltage representative of kinescope cathode current conducted during measuring intervals, as discussed previously.
VPU unit 50 includes input terminals 15 and 16 coupled to terminal A. Through terminal 15 the VPU receives the analog signal from terminal A and, via an internal multiplex switching network 51, the analog signal is supplied to an analog-to-digital-converter (ADC) 52. Terminal 16 is connected to an internal switching device (corresponding to switch 49 in FIG. 1) which, in conjunction with scaling resistor 48, controls the impedance and therefore the sensitivity at input terminal 15. High sensitivity for black current measurement is obtained with resistor 48 ungrounded by internal switch 49, and low sensitivity for white current measurement is obtained with resistor 48 grounded by internal switch 49.
The digital signal from ADC 52 is coupled to an IM BUS INTERFACE unit 53 which coacts with CCU unit 60 and provides signals to an output data multiplex (MPX) unit 55. Multiplexed output signal data from unit 55 is conveyed to VCU unit 10, and particularly to control network 78. Control network 78 provides output signals for controlling the signal gain of preamplifiers 75, 76 and 77 to achieve a correct white current condition, and also provides output signals for controlling the DC bias of the preamplifiers to achieve a correct black current condition.
More specifically, during vertical image blanking intervals the three (red, green, blue) kinescope black currents subject to measurement and the three white currents subject to measurement are developed sequentially, sensed, and coupled to VPU 50 via terminal 15. The sensed values are sequenced, digitized and coupled to IM Bus Interface 53 which organizes the data communication with CCU 60. After being processed by CCU 60, control signals are routed back to interface 53 and from there to data multiplexer 55 which forwards the control signals to VCU 10.