GB2238652A

GB2238652A - Cathode ray tube

Info

Publication number: GB2238652A
Application number: GB9012403A
Authority: GB
Inventors: Adrian Roll
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-06-02
Filing date: 1990-06-04
Publication date: 1991-06-05
Anticipated expiration: 2010-06-04
Also published as: GB9012403D0; GB8912745D0; GB2238652B

Abstract

A colour cathode ray tube in which the electron gun generates a single beam that is scanned across successive groups of red, green and blue phosphor strips, has a beam indexing arrangement in which a glass fibre 22 or 23 is located between each phosphor strip, the light collected by the fibres from the adjacent phosphors being detected and converted into an electrical switching signal to enable modulation of the electron beam from the single gun to correspond with the phosphor being scanned. A lenticular lens (40), Fig. 3 (not shown), whose elements are parallel to the phosphor strips with each element covering two adjacent phosphor groups, may be associated with the screen, which may for example be provided on a flat surface inside the CRT envelope, whereby a 3-D image may be generated by forming respective left and right images using respective left and right groups associated with each element of the lens. <IMAGE>

Description

A CATHODE RAY TUBE This invention relates to a cathode ray tube (CRT) for use in a colour television set.

A conventional colour television CRT compromises three electron guns each of which dir-ects an electron beam at coloured phosphers which are coated on the inside of a glass screen In a trinitrom (trade mark) tubes however, a single electron gun produces three electron beams from three in line cathode.The phosphors may be provided in the form of dots arranged in groups of three. (triads), as in a shadow mask tube, or in horizontal or vertical strips as in lawrence and Tri ni tron tubes respectively. three di ++erent coloured phosphers are used one For each of the chosen red, blue and green primaries Each colour phospher is energised by an electron beam of intensity proportional to the appropriate colour -iol taqes R', G', or B to pr-oduce three coincident rasters which reproduce the red green and blue content of the transmitted picture.

It is an object or the present invention to provide a cathode ray tube for a colour tel ivision which produces a high definition image According to one aspect of the invention there is provided a colour television cathode ray tube comprising a phosphor coated screen; an electron beam generating means which emits an electron beam towards the screen: a light detecting means for detecting the position of the beam in relation to the screen; and switching means for switching the colour voltage supplied to the electron beam generating means in accordance with the position detected by the detecting means. Thus as the electron beam scans the screen the colour voltage may be switched according to the cvolour of the phospher which is impinged by the electron beam.Preferably the colour voltage supplied to the modulating electrode is switched.

The detecting means will comprise a light transmission element, in which 1 light beam is captured from the light emission of the parallel adjacent phosphers. The light emission is produced by the electron beam striking the phosphers stimulating light emission. The light transmission element will te in the form of strips of glass arranged in the form of strips oF glass arranged in the form of a parallel arrays each strip of glass placed parallel to and between adjacent phosphers of the vertically arranged strips of primary colour emitting phosphers.Thus when the electron beam hits a particular coloured phospher it will induce a light beam b a glass transmission strip adjacent the phospher, that light being detected, and resulting electrical signal at the output of the detector is used to govern operation of the switching means. Preferably the detector will be a fast photo-diode.

array parallel with the vertical array of phosphor bands.

Preferably the array is arranged within the tube adjacent the screen.

The screen may incorporate means for the display of a three dimensional image. The. said means may comprise a lenticular screen. The screen and lenticular screen may be separate or of unitar construction. - - The phosphor bands may be etched onto the inner surface of the screen.

Preferably, the conductive elements are also fixed to the interior of the screen. Two cathode ray tubes in accordance with te invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a horizontal section through the cathode ray tube; Figure 2 is a schematic diagram of the electronics system associated with the cathode ray tube; Figure 3 is a horizontal cross section thrcugh the screen of another cathode ray tube i accordance with the invention.

The cathode ray tube 10 comprises a electron un 12 which emits an electron a phosphor-coated glass screen 16. Green, red and blue phosphors, 17a, 17b and 17c respectively are arrange in vertical bands on the inner surface 18 of the screen.

The horizontal and vertical position of the electron beam 14 is governed by horizontal deflector plates 2C) and vertical deflector plates ( not shown respectively. Alternativelys horizontal or vertical scanning coils could be used. Both sets of deflector plates or scanning coils can be energized to cause the electron beam 14 to scan the phosphers. n vertical array of glass strips e.g. 22,23 is arranged adjacent the phosphors such that a strip is adjacent and parallel with each vertical phosphor band. Each strip in the array is hit by the scanning electron beam and a light beam is thereby induced in each strip as it is hit.By detecting these light beams it is possible to establish the position of the electron beam with respect to the screen and in particular which phosphor band the electron beam is about to hit. For example a by light beam in strip 22 caused the strip being hit by electron beam 14, indicates that the electron beam is about to impinge on the adjacent green phospher 17a.

as each strip is thin relative to the phosphel band, it does not cast a shadow on the phospher-coated inner surface. Horizontal non-conductive supporting members may correct adjacent strips to strengthen the array.

Each strip is electrically connected to the detecting/switching circuit shown in Fig. 2. The circuit 30 comprises current detecting means 32 whichis connected to each strip at either end thereof and detects each separate current as it is produced across each strip. The connections between the means 32 and each strip, and between the-strips and the walls-of the tube, are insulated or otherwise isolated to prctect the means 32 from the high voltages, typically 25 KV employed- by the final mode and internal graphite coating (eg Aquadog trade mark) employed within the cathode ray tube.

The signal generated by the current detecting means 32 is passed to a high stability switching oscillator 34 and thence to switching means 36 which switches the colour voltage between green, red and blue, supplied to the electron gun according to the colour of the phosphor which it has been detectec is being hit by the electron beam. Thus, for example, when the electron beam hits a green phosphor band the detecting/switching circuit 30 switches the colour voltage supplied to the electron gun to the green component of the input colour voltage, changing the colou voltage when the electron bear nits the next phosphcr. in nis wrv a colour picture is built up having a particularly high definition.

Advantageously, a thin aluminium mirror may be provided, behind the phosphers and the grid, through which the electron beam will readily pass but which reflects light emitted +rom the phosphors to improve the brightness of the picture. The mirror may be provided in the form of a thin coating on the phosphors.

The electron beam should ideally be thinner than the width of each phosphor band to prevent adjacent colours being activated. However, it is envisaged that in practice the width of the electron beam would be slightly greater- than the width of one phospher band.

In either case it would be preferable to contr-ol the passage of the electron beam so that it hesitates on on each phosphor band as it scans the inner surface of the screen. This could be acheived, for example, by superimposing a suitable shaped waveform over the current supplied to the deflector plates or coils to cause the beam to hesitate on each phospher band.

The light detecting means may preferably comprise a fast photo diode. The signal produced by the photo diode could be passed to the oscillator 34 and switching means 36 as previously described.

It is envisaged that cathode ray tubes in accordance with the invention would find particular application in the field of 3D TV as where there is a need to accurately define two slightly spaced 2.part images on the screen. In particular, a cathode ray tube in accordance with the invention could be used in conjunction with a lenticular screen arrangement to project a three dimensional image. A suitable arrangement is shown in Fig. 3. A lenticular screen 40 (curvative exaggerated-for,clarity) is fixed to the outer surface 42 of a glass plate 44 which comprises the screen of the cathode ray tube. Vertical phosphor bands, eg 46 are etched onto the surface cf the plate 44 as described above.In between each phosphor band is located a metal strip, eg 48 in which a current is induced when the electron beam is incident on the adjacent phosphor as described above. A thin aluminium mirror 50 reflects the light emitted by the phosphors in use to enhance the brightness of the image on the Although a two component construction is described, it is envisaged that the phosphors an-' strips might be fixed directly to the surface of the lenticular screen.

Alternatively, the phosphors could be applied to the flat surface of a lenticular screen which would then be mounted behind a conventional screen. Such an arrangement might be prepared in that it would be more visually acceptable in that a television would not have a visible lenticular lens arrangement.

It will be appreciated that the metal strips could be replaced by optical fibres which receive light emitted by the phosphors when impinged by the electron beam.

- Cathode ray tubes in 'accordance, with the invention which are capable of displaying accurate three dimensional images could be used for example in a computer-monitor for computer aided design work or as a flight or driving simulator or as a public television receiver.

Claims

1. A CRT consisting of an evacuated glass envelope with a screen at one end and a single cathode at the other as in diagram 1. On the inner surface of the CRT screen or on a separate flat glass screen mounted internally parallel to the envelope screen, are vertical phosphors which emit when excited by an electron beam, the primary colours for that phosphor, the primary colours being Red, Green and Blue.

The phosphors are mounted so that each phosphor is parallel and next to a different primary colour phosphor on each side, see diagram 3. As the electron beam scans the screen controlled by electromagnetic coils driven by a scanning current or alternatively parallel metal plates 2 sets at right angles parallel to the electron beam mounted internally with a scanning voltage applied to each part of vertical or horizontal scanning plates producing an electrostatic force for the plates, or magnetic force to the electron beam in the case of the scanning cqils. The vertical phosphors are scanned at right angles. Producing high quality television pictures using the standard video received.

CLAIMS 2 2. When used to project three dimensional images a vertical strip lens is placed on the flat screen each lens covers 6 vertical phosphors, and is parallel to them. Two separate pictures viewed from slightly different horizontal viewing angle using two slightly displaced TV cameras to simulate the viewing angle of the eye of a given object or objects, are split into vertical strips and alternate strips are applied to two the two triad sets covered by a single lens. The lens is shaped so that the right eye sees the vertical strip from the left camera and the right eye receives the vertical picture strip from the right camera.

Thus the picture received by the right eye is all the vertical strips from the right camera and the left eye all the strips from the right camera, and the two pictures form a 3D image as viewed by the observer of the TV screen. See DIAG 4.

Amendments to the claims have been filed as follows 1. n CRT consisting of an evacuated glass envelope with a screen at one end and a single cathode at the other as in Figure 1. On the inner surface of the CRT screen or on a seperate flat glass screen mounted internally parallel to the envelope screen, are vertical phosphers which emit when excited by an electron beam, the primary colours for that phospher the primary colours being red, careen and Blue.

The phosphers are mounted so that each phospher is parallel and next to a different primary colour phosphor on each sides see Figure 3. Between and parallel to each pair of adjacent phosphers is situated a light transmission element consisting of a glass strip connected to a light detecting element possibly a fast photo diode which produces at its output pulses of electrical power proportional to the light emitting intensity of the phosphor.This is used to sychronise a switching circuit to switch on the primary colour video element of the corresponding colour phospher being scanned by the electron beam. fis the electron beam scans the screen controlled by electromagnetic coils driven by a scanning current or alternatively parallel metal plates producing an electrostatic force for the plates, or magnetic force to the electron beam electron in the case of scanning coils. The vertical phosphers are scanned at right angles. Producing high quality television pictures using the standard video received.

2. When used to project three dimensional images a vertical strip lens is placed on the flat screen each lens covers 6 vertical phosphors, and is parallel to them. Two seperate pictures viewed from slightly different horizontal viewing angle using two slightly displaced TV cameras to simulate the viewing angle of the eye of a given object or objects, are split intu vertical strips and alternate strips are applied to the two triad sets covered by a single lens. The lens is shaped so that the right eye sees the vertical strips from the right camera and the left eye all the strips from the left camera, and the two pictures form a 3D image as viewed by the observer of the TV screen. See FIG 4.