WO2004038755A1

WO2004038755A1 - Display device having a flat display panel

Info

Publication number: WO2004038755A1
Application number: PCT/IB2003/003622
Authority: WO
Inventors: Johannes Penninga; Joseph W. J. M. Van Der Heijden
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2002-10-28
Filing date: 2003-08-13
Publication date: 2004-05-06
Also published as: JP2006504237A; AU2003253180A1; EP1559125A1; KR20050059298A; TW200419619A

Abstract

The raster geometry performance of a CRT can be improved, especially in 1/2EW (EW inner pincushion), by means of a proper choice of the inner panel shape. The inner panel surface of the CRT of the inventive display device has been given more curvature along the vertical (NS) axis and/or the horizontal (EW) axis than usual for the conventional almost spherical panels. In particular the sagittal height in the corners is 5-12 mm larger than that at the ends of the long axis, the inner pincushion error being smaller than 2 mm. The invention is of particular interest for RF tubes, because the flat outer surface of the panel allows more freedom for the inner shape of the panel. The invention is in particular applicable to 16:9 aspect ratio Real Flat display tubes, but also to 4:3 aspect ratio Real Flat display tubes.

Description

Display device having a flat display panel

The invention relates to a display device having a cathode ray tube which comprises an evacuated envelope having a substantially flat rectangular display panel having a long axis and a short axis the inside surface of which is formed with a phosphor screen, a color selection electrode being arranged adjacent the phosphor screen, the envelope accommodating a means for generating a plurality of electron beams, the display device further comprising means for deflecting the electron beams across the phosphor screen.

Display devices of the type mentioned in the opening paragraph are known. Such display devices are used, inter alia, in television receivers and computer monitors. The invention also relates to a cathode ray tube for use in a display device of the type described in the opening paragraph.

The invention further relates to a display panel for use in a cathode ray tube of the type described in the opening paragraph.

Known cathode ray tubes comprise an evacuated envelope having a display panel the inside of which is provided with a phosphor screen. A color selection electrode is arranged adjacent the phosphor screen. The envelope comprises means for generating electron beams. The electron beams excite phosphors of the phosphor screen. In operation, the electron beams are deflected across the phosphor screen, thereby generating images. When a person watches a cathode ray tube, he will see these images after they have been transmitted through the glass, hi the last few years the trend has been to manufacture flatter display windows. The quality of the image produced, as realized within the framework of the invention, is governed in a complex manner by the shape of the display panel. In this connection, an important aspect is raster distortion. Raster distortion reduces picture quality. Raster distortion is to be understood to mean herein a picture error which causes straight lines to be reproduced as curved lines.

A general problem for the designers of the deflection means, or deflection units: DUs, is the limited penetration depth of the higher-order multipoles of the magnetic field. Consider a DU with a pure dipole field for the line coil and the frame coil. This DU will give a strongly pincushion-shaped raster geometry in EW as well as in NS direction. The EW pincushion is corrected by EW modulation of the line current as a function of the frame current (EW correction ), such that the raster shape at outmost East and outmost West is straight. Unfortunately, this correction has a greater effect on the outmost EW lines than on the V2EW lines. After correction, there remains a so-called EW inner pincushion error that is hard to get rid of by adaptation of the coil design in the DU. The NS pincushion distortion is corrected by means of six-pole modulation in the coils and static NS magnets. Also for NS, when the raster is made straight in North and South, there remains a similar problem: pincushion errors at NS (NS inner pincushion) as this six-pole and the multipoles, due to the magnets, cannot penetrate deep enough into the tube to act sufficiently on the 5 NS raster. Often an attempt has been made to solve this ^NS with a ten-pole: The effect of such a ten- pole is in principle correct, but the penetration depth is still less than that obtained with the six-pole. Therefore, the raster is indeed improved in the F'G'H points (end of l^NS), but in the STUN points (halfway the ¹/£ΝS line) the raster is not affected at all (see Fig. 3 A), giving an undulating, so-called "seagull-wing", raster distortion. Said raster problems are more severe as the screen panel is flatter or the deflection angle is larger.

It is an object of the invention to provide a cathode ray tube of the type set forth in the opening paragraph, which cathode ray tube comprises a substantially flat display panel having an improved picture quality, in particular as regards inner pincushion. To this end, the cathode ray tube according to the invention is characterized in that the inside surface of the display panel is curved such that the sagittal height at the corners is 5-12 mm larger than the sagittal height at the ends of the long axis, the inner pincushion raster distortion being smaller than 2 mm.

The invention is based on the following recognition: A degree of freedom not really exploited before is the shape of the inner surface of the display panel. For curved (i.e. non-real flat) screens, where the outside panel more-or-less follows the inner screen panel, it was not feasible to experiment with alternative shapes of the inner panel surfaces due to unacceptable reflections of ambient light when the tube is switched off. For display tubes where the outside screen is flat, in particular so-called Real Flat tubes, however, one has to deal only with much less disturbing second reflections. If use is made of a spherically curved inner panel surface with a certain predetermined glass wedge in the corner, then there is the freedom to make the inner surface more curved along the vertical axis and/or more curved along the horizontal axis. It is a main feature of the invention that the inside surface of the display panel is curved such that the sagittal height at the corners is 5-12 mm larger than the sagittal height at the ends of the long axis. It is the gist of the invention that, if during the design of a display tube for a display device having a given deflection unit the above rule is met, it is possible to make the inner pincushion raster distortion smaller than 2 mm. It has been found that inner pincushion raster distortions smaller than 2 mm do not disturb the viewing impression (perception). By properly adapting the sagittal height at the ends of the short axis to that in the corners and at the ends of the long axis it is in particular possible to make the inner pincushion raster distortion (sometimes termed "East- West innerpin", or "EW innerpin") smaller than 1.5 mm, and even equal to or smaller than 1 mm. When considering the simulation data in Table I it will be appreciated that at a constant difference between the sagittal heights in the corners and at the end of the long axis (or: East) of 7.5 mm, the difference between the sagittal height in the corners and at the end of the short axis (or: North) can vary from 1 to 9 mm in order to meet the object of making EW innerpin smaller than 2 mm. From the viewpoint of glass-stability it would be attractive to use a small value for the difference between the sagittal height in the corners and that at the end of the short axis, in particular less than 2.5 mm. Tubes manufactured using the above design principle lead to good results, in particular if the color selection means is a shadow mask of the iron type, or a mask of the tension type. However, if the mask is of the Invar type, mask microphony becomes a parameter of concern. It is a further feature of the invention that the difference between the sagittal heights in the corner and at the end of the short axis is at least 2.5 mm. h that case mask microphony, also of Invar type masks, is sufficiently small.

According to a still further feature of the invention the relative sagittal height RSH, preferably lies between 0.70 and 0.95, the relative sagittal height being the quotient of the sagittal height at the end of the diagonal across the inner panel surface and the sum of the sagittal heights at the ends of the long axis and at the end of the short axis.

Within the inventive range of sagittal heights which lead to EW innerpin values of less than 2 mm, the above condition provides an acceptable flatness impression.

Further embodiments and advantages of the invention will be described with reference to the Figures. The invention will be explained in greater detail by means of a few exemplary embodiments of the cathode ray tube according to the invention and with reference to the accompanying drawings, in which:

Fig. 1 is a schematic cross-sectional view of a cathode ray tube; Fig. 2 is a partly perspective view of the inner surface of a display panel, showing how the sagittal heights are defined;

Figs. 3 A and 3B are views of a display panel showing reference points as used in the art;

Figs. 4 and 5 are diagrams showing the dependence of inner pincushion distortion on the sagittal height in the corners with respect to that in the North.

The Figures are not drawn to scale. In the Figures, corresponding parts generally bear the same reference numerals.

A cathode ray tube, in this example color display tube 1 , comprises an evacuated envelope 2 which includes a display panel 3, a cone portion 4 and a neck 5. In the neck 5 there is provided an electron gun 6 for generating three electron beams 7, 8 and 9 in one plane, the in-line plane, in this case the plane of the drawing. A display screen 10 is situated on the inside surface 15 of the display panel 3. Said display screen 10 comprises a large number of phosphor elements luminescing in red, green and blue. On their way to the display screen 10, the electron beams 7, 8 and 9 are deflected so as to scan the display screen 10 by means of deflection unit 11 and pass through a color selection electrode 12 (which is arranged in front of the display window 3 and) which in this case is formed by a thin shadow mask plate having apertures 13. The color selection electrode is suspended in the display window by means of suspension means 14. The three electron beams 7, 8 and 9 pass through the apertures 13 of the color selection electrode at a small angle and, consequently, each electron beam impinges on phosphor elements of only one color.

Fig. 2 is a partly perspective view of the inner surface of a display panel. The points of the surface can be described by a function z = f(x,y), where z is the distance between a point and the tangent plane in the center of the surface, and x and y are the customary denominating letters for the coordinates along the long and the short axis, respectively, for a point on the surface, z is commonly termed the sagittal height. x_max and y_max are, respectively, the x and the y coordinate of a point at the end of the long and the short axis. The z-axis extends perpendicularly to the tangent plane in the center of the surface of the display window and is indicated in the Figure. The short axis is referred to as the y-axis, the long axis is referred to as the x-axis. Said axes extend perpendicularly to each other and to the z-axis. Both the inside surface and the outside surface can be described in such a manner. In Fig. 2, the sagittal height z_max in the corners is indicated by line segment 21 and the sagittal height at the end of the long axis z_max(x_max,0) and the sagittal height at the end of the short axis z_raax(0,y_maχ) by line segments 22 and 23, respectively. The ends of the short and the long axes are given by the extreme points of the above-described raster in the x-direction and the y-direction, respectively.

Such a surface z(x,y) can be characterized in approximation by the formula

z( , y) = a₂₀ (— )² + a₀₂ (^)² + a₀₄ (-^)⁴ + a₂₂ (-^-)² (-^-)² max max J max max J max a₂o, ao2_> ao₄ and a₂₂ constants Simulations have been carried out using 36 inch WSRF tubes the inner panel surface of which meets the above formula. Table I hereafter shows how variation of the sagittal heights influences the

East- West inner pincushion distortion.

In all examples the sagittal height in the corners was 7.5 mm larger than the sagittal height at the ends of the long axis.

Table 1

Data relating to 24, 28, 32 and 36 inch WSRF tubes and 29 and 34 inch 4:3 RF tubes, in the designing of which the inventive concept was used, are presented in Table LI. i all tubes the (East- West) inner pincushion distortion was below 2 mm. Table II

Fig. 3 A schematically shows a view of a display panel on which reference points as used in the art are indicated. The (rectangular) display panel has a long axis x and a short axis y.

Fig. 3B shows a simplified version of Fig. 3 A on which only the Vz East- West points K, L, M, N are indicated. Two raster lines are shown which should go through K, L, M, N, but they don't: this is a case of East- West inner pincushion distortion. A distortion δ is measured at e.g. L in mm. Fig. 4 shows in diagrammatic form panel simulation data relating to a 24 inch

WSRF display panel. Along the horizontal axis the sagittal height in the comers, SHc is presented in mm, along the vertical axis the difference between the sagittal height in the comers, SHc, and the sagittal height in North, SHN, is presented in mm. The diagram shows diagonal lines of constant raster inner pincushion distortion (in mm). This simulation is for a constant difference of 7 mm between the sagittal height in the comers and the sagittal height in East.

A similar diagram is presented in Fig. 5 for a 36 inch WSRF tube. This simulation is for a constant difference of 9 mm between the sagittal height in the comers and the sagittal height in East. Summarizing, the invention relates to a CRT having an improved raster geometry performance especially in M-EW (EW inner pincushion) which is achieved by means of a proper choice of the inner panel shape. The inner panel surface of the inventive CRT has been given more curvature along the vertical (NS) and/or the horizontal (EW) axis than usual for the conventional almost spherical panels. In particular the sagittal height in the comers is 5-12 mm larger than that at the ends of the long axis, the inner pincushion error being smaller than 2 mm. The invention is of particular interest for RF tubes, because the flat outer surface of the panel allows more freedom for the inner shape of the panel.

The invention is in particular applicable to 16:9 aspect ratio Real Flat display tubes, but can also be applied in 4:3 aspect ratio Real Flat display tubes.

Claims

CLA S:

1. A display device having a cathode ray tube which comprises an evacuated envelope having a substantially flat rectangular display panel, having a long axis and a short axis, the inside surface of which is provided with a phosphor screen, a color selection electrode being arranged adjacent the phosphor screen, the envelope accommodating a means for generating a plurality of electron beams, the display device further comprising means for deflecting the electron beams across the phosphor screen, characterized in that the inside surface of the display panel is curved such that the sagittal height at the comers is 5-12 mm larger than the sagittal height at the ends of the long axis, the inner pincushion raster distortion being smaller than 2 mm.

2. Display device as claimed in claim 1, wherein the inner pincushion raster distortion is at most 1 mm.

3. Display device as claimed in claim 1, wherein the difference between the sagittal height of the inner panel surface in the corners and that at the ends of the short axis is at least 2.5 mm.

4. A display device as claimed in claim 3, wherein the color selection electrode is an Invar type shadow mask.

5. A display device as claimed in claim 1 , characterized in that the relative sagittal height, RSH, ranges between 0.70 and 0.95.

6. A display device as claimed in claim 1, characterized in that the aspect ratio of the display window is 16:9.

7. A display device as claimed in claim 1, characterized in that the aspect ratio of the display window is 4:3.

8. A cathode ray tube for use in a display device as claimed in claim 1.