US2912615A - Cathode ray tubes for colour television - Google Patents

Description

Nov. 10, 1959 LPBSZYNSKF 2,912,615

CATHODE RAY TUBES FOR COLOUR TELEVISION Filed Feb. 27, 1958 2 Sheets-Sheet 1' lllllll IlllllIlllllllllllllllllllllllli Illlilllllllllllllllll FIG.1.

I121) 6121-01 H. G. .Lubzynak/ I Nov. 10, 1959 LUBSZYNSKI I 2,912,615

CATHODE- my TUBES FOR COLOUR TELEVISION Filed Feb. 27, 1958 2 Sheets-Sheet 2 FIG. 4.

TUNED AMP AND SHAPER Inventor CATHODE RAY TUBES FOR COLOUR TELEVISION Hans Gerhard Lubszynski, Waltham St. Lawrence, England, assignor to Electric & Musical Industries Lim ted, Hayes, Middlesex, England, a company of Great Britain Application February 27, 1958, Serial No. 717,881

Claims priority,,application Great Britain February 28, 1957 Claims. (Cl. 315-12) This invention relates to colour-picture reproducing tubes and relates to apparatus embodyingsuch tubes for reproducing coloured pictures from colour television signals.

There have been various proposals for producing a colour-picture reproducing cathode ray tube employing a single gun for the picture reproduction. Usually, in such tubes, the fluorescent screen is composed of a multiplicity of parallel phosphor strips, adapted to emit light of difierent colours when excited by the cathode ray beam. For example in one proposed form of tube, the strips are regularly arranged in groups of three strips, the strips in each group emitting red, green and blue light respectively when excited. Such a tube is arranged for use so that the strips are vertical, that is traverse to the scanning lines. With tubes according to such proposals, a sensing device is required for keeping the correct phase relationship of the scanning beam position and the received-colour information. However, such sensing devices introduce difficulties inasmuch as a compensating system, pilot beam, or other undesirable complication is needed.

The object of the present invention is to reduce such diificulties.

According to the present invention there is provided a cathode ray tube, suitable for reproducing coloured images from colour television signals, comprising a screen and an electron gun for directing an electron beam to said screen, said screen comprising a plurality of regularly arranged luminescent strips adapted when excited by the beam to emit light of different colours, and regularly arranged indexing zones substantially parallel to said strips, said zones each comprising materials having different secondary electron emission co-etficients" selectively presented to the beam toproduce a repetitive characteristic variation of the secondary electron emission co-eflicient within each zone in the direction of said strips. For example if the screen has a thin aluminum or other metallic fihn deposited over the luminescent strips, in well known manner, the indexing zones may be provided by depositing material having, a relatively high secondary electron emission co-efiicient compared with aluminium, over only the red phosphor strips, say, said material being deposited so as to comprise a fine pattern of strips extending across. the red strips and so spaced that the aluminium or other metallic film is exposed between the strips of the said material.

In apparatus for reproducing coloured pictures' from colour television signals and embodying a cathode ray tube according to the invention, there may be provided means for deflecting the beam of said tube according to a television raster of which the lines are transverse to said luminescent strips, means for modulating the beam of said tube in response to signals of video frequencies corresponding to received television signals, means for imposing a wobble on the beam of said tube during lines of said raster, the variation of the secondary 2,912,615 Patented Nov. 10, 959

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electron emission co-eflicient within said zones being predetermined in relation to said wobble to produce in the secondary electron emission from said screen a variation of a frequency distinguishable from said video frequencies, and indexing means responsive to said variation of the secondary electron emission for timing the modulation of said beam in relation to the passage of the beam across said luminescent strips.

In order that the invention may be clearly understood and readily carried into eifect, the invention will be described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic view of the end face of a cathode ray tube according to one example of the invention, showing the structure of the fluorescent screen of Such tube,

. 1 and 2, and

Figure 2 is a cross section of a fragment of the end face to a larger scale than Figure l,

Figure 3 illustrates'part of a television receiver em bodying a cathode ray tube such as illustrated in Figures Figure 4 is a diagram explanatory of the operation of the receiver illustrated in Figure 3.

The fluorescent screen of the cathode ray tube shown in Figures 1 and 2 comprises vertical red, green and blue phosphor strips. In practice these strips are narrow so that a large number can be deposited but the width is exaggerated in the drawing for the convenience of illustration. The colour of the light emitted by the individual phosphor strips is denoted in the drawing by R, G, B and the strips of one group are denoted by the references 1, 2 and 3. The section in Figure 2 is taken through the red strip 1. On top of the phosphor strips a thin aluminium film 4 is deposited in well known manner. On topbf the aluminium film 4 a fine pattern of horizontal indexing strips is deposited or otherwise provided in zones above every one of the red phosphor strips. Some of the indexing strips are denoted by the reference 5. The indexing strips are, however, shown in only 2 phosphor strips in Figure 1 for convenience of illustration. These strips are'formed of material having a secondary electron emission co-eflicient as diiferent as possible from that of the aluminium at the primary voltage used for the scanning beam. For example the secondary electron emitting material may be aluminium oxide (A1 0 or magnesium oxide (MgO). For example if the secondary emitting material is aluminium oxide, it may be deposited by selectively oxidising the aluminium film 4, in known manner. Alternatively the strips may be formed of carbon so as to have a substantially lower secondary electron emission coeflicient than the alumin- To enable indexing signals to be derived in response" to the preferential secondary electron emission from the indexing strips 5, the usual second anode 6 of the tube (see Figure 3, where the tube is denoted by the reference 7) is separated from the aluminum film 4 so that it can be used as a collector of secondary electrons. In the receiver which is partly shown in Figure 3, a load resistor 8 is provided having one end connected to the aluminum film 4 and its other end connected to a source of high positive potential, denoted as E. H. T. The second anode 6 is maintained at a somewhat higher potential than the film 5 by a potential source 9, inorder to saturate the secondary electron emission from the strips 5. Signals set'up across the resistor 8 in response to secondary electron emission from the film 4 and the strips 5 are applied to a tuned amplifier and shaping circuit 10 which produces pulses, such as that indicated by reference 11, corresponding to the passage of the beam in the tube 6 across the red phosphor strips. The pulses are used as indexing signals and, suitably delayed by a delay line 12, are applied to colour gates l3, l4 and '15, where they function to feed video signals corresponding to the red, green and blue components of an image to one of the electrodes in the gun of the cathode ray tube 6 so that the beam is modulated by these video signals. By virtue of the indexing signals, the application of the respective component video signals is correctly timed in relation to the passage of the beam across the phosphor strips I, G and B. y r

The generation of the indexing signals is dependent upon the imposition of a Wobble on the beam of a tube during each line scan. This Wobble is imposed by means of the circuit 16 which is adapted to superimpose a sinusoidal component on the normal field defiecting waveform, the frequency of this component being approximately strip frequency, that is the frequency with which the beam traverses the phosphor strips R, G and B,

' assuming a linear line scan. Circuits for producing the normal line and field scanning waveforms are not represented in Figure 3, since they may be entirely conventional. The dotted line 17 in Figure 4 represents the track of the scanning spot 18 as the beam crosses one of the red phosphor strips, the general line scanning direc tion being denoted by the arrow 19. The amplitude of the wobble produced by the circuit 16 is such that in crossing a red phosphor strip the spot crosses and recrosses several of the indexing strips '5, so that the width and separation of the strips '5' must be such that there are several of these strips in the distance between adjacent lines of the raster traced on the screen of the tube 7. As indicated in Figure 4, there may be five strips 5 in the line pitch of the screen. The graph 20 exemplifies the variation in secondary electron emission collected by the anode 6 as the beam crosses a red phosphor strip, a maximum in the graph 20 occurring when the spot 18 is centred on one of the stripsS and a minimum occurring when the spot 18 is centred in the space between two of the strips 5. The current in the resistor 8, which will vary in response to: the secondary emission from the aluminum film 4 and the strips 5; therefore exhibits a high frequency modulation superimposed on any variationdue tothe video signals. Moreover during the interv'als denoted in Figure 4 as t1, t2 and 13, corresponding to the times when the passage of the beam across the beam 5 is substantially linear the high frequency modulation -will have a substantially constant frequency. The amplifier is tuned to this frequency so that it produces output signals responsive substantially only to the secondary electron emission from the strips 5 and subthe beam on the corresponding line. Provided that the beam is never-biassed below a given level, say 40 a, the modulation of the current in the resistor 8 is always present when the beam crosses a red strip but is present at no other time. Assuming moreover that the highest video frequency in the signals applied to modulate the beam in the tube 7 corresponds to the triplet frequency, this modulation frequency will be substantially above the highest video frequency.

By using a substantially symmetrical sawtooth waveform for producing the wobble, the frequency modula tion of the indexing signals which is evident in the graph can be substantially eliminated if desired.

The indexing strips need not be-located in zones which may be arranged "in regularly spaced rows which bear a register with phosphor strips of a specified colour but i known relationship to the spacing of the phosphor strips.

Moreover instead of forming a screen of phosphor strips such as R, G and B, which emit light of difierent colours when excited by the cathode ray tube, the same effect, can be produced by employing a phosphor which emits substantially white light and by providing a colour filter of strip form in front of the phosphorm. In this case the zones in which the secondary electron emitting material is provided need to bear a known relationship to the strips of the colour filter.

What I claim is:

1. A cathode ray tube, suitable for reproducing coloured pictures from colour television signals, comprising a luminescent screen and an electron gun for directing an electron beam tosaid screen, said screen comprising a plurality of regularly arranged strips which emit light of diiferent colours when the screen is excited. by the beam, and regularly arranged indexing zones substantially parallel to said strips, said zones :each comprising materials having different secondary electron emission co-efiicients selectively presented to the beam to provide a repetitive variation of the secondary electron emission co-efficient within each Zone in the direction of said strips.

2. A "cathode ray tube, suitable for reproducing coloured pictures from colour television signals, comprising a screen and an electron gun for directing an electron beam to said screen, said screen comprising a plurality of regularly'arranged luminescent strips adapted when excited by the beam to emit light of different colours, and regularly arranged indexing zonessubstantially parallel to said strips, said zones each comprising materials having 'dilferent'secondary electron emission coefiicients selectively presented to the beam to provide a repetitive variation of the secondary electron emission .directing an electron beam to said screen, said screen comprising aplurality of regularly arranged strips which emitlight of different colours when the screen is excited by the beam, and regularly arranged' indexing"zones substantia'lly parallel to said strips, said .zones each comprising material having a relatively high secondary electron emission c'o-efficient and materialhaving a relatively low secondary electron emission co-efiicient alternately presented to the beam in narrow strips transverse to said luminescent strips, to provide a repetitive variation :of the secondary electron emission co efiicient within each zone in the direction of said strips 5. Apparatus for reproducing coloured pictures from colour television signals; comprising'a'cathode ray tube having a luminescent screen ,and an electron gun for directing an electron beam to isa'idscreen; said screen comprising a plurality of regularly arranged-strips which emit-light of different colours when the screen iii-excited by the beam, and regularly arranged indexing zones sub stantiallyparallel to'said strips, said zones each comprising materials having different secondary electron emission co-efiicients selectively presented to the beam to provide a repetitive variation of the secondary electron emission co-efiicient Within each zone in the direction of said strips; meansfor deflecting the beam of 7 said tube according to a television raster of which the lines are transverse to said strips; means for modulating the beam of said tube .in response to signals of video frequencies corresponding to received television signals; means for imposing a wobble on the beam or saidtube during lines of said raster, the variation of the secondary electron emission co-eificient Within said zones being predetermined in relation to said wobble to produce in the secondary electron emission in said screen variations of a frequency distinguishable from said video frequencies, and indexing means responsive to said variations of the secondary electron emission for timing the modulation References Cited in the file of this patent UNITED STATES PATENTS Moore Dec. 4, 1956

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