FR2640407A1 - Visual display device having a cathode ray tube - Google Patents

Abstract

The brighter display device 40 is formed by a cathode ray tube with beam indexation 11' used in recurrent scanning mode, producing several electron beams Bm1, Bm2 in the cathode ray tube, all of these beams being made to pass onto the same areas of the screen 16, describing the scanning frame. The beams can be made to strike the screen by being superimposed and modulated by the same video signal or being offset in the line-scanning direction by being delayed by a fraction of the line period, or being offset in the field-scanning direction by being delayed by a multiple of the line period, and the video signal intended for the follower beam(s) being retarded by a corresponding interval so that the image is reinforced. The delay of the video signal can be produced in digital form by a memory 44 addressed from one end of the scan to the other by means of a circuit 45 and delay variations due to scanning corrections contained in a correction-card memory 47. The delayed-beam method can be applied to a perforated-mask cathode ray tube.

Description

The present invention relates to display devices using

  cathode ray tubes, and in particular devices to increase the maximum luminance of the screen beyond what is already achievable. Cathode ray tubes, or "cathode ray tubes", are increasingly used in

  aircraft cockpits to produce aircraft

  in color and, when we have to satisfy the double imperative of robustness and high brightness

  of the screen in sunlight, the index tubes

  beam are used in preference to tubes with

most well-known shadow mask.

  The cathode-ray tubes with a perforated mask are

  frent of several operating limitations due to the fragility of the shadow mask structure and its absorption of a very large part of the energy of the electron beam for each of the three beams used to define each color picture element , the dissipation, via the mask, of this energy supplied at a single point surrounding an opening through which the beam passes for an instant, determining the maximum useful beam current in any configuration and, consequently, the

screen brightness.

  These perforated mask cathode ray tubes can produce an image with sufficient brightness when they are operated in so-called cursive writing mode, in which line figures are drawn which occupy any small proportion of the screen surface and which are surrounded by unaddressed areas which allow

  with the shadow mask to dissipate the local absorbed energy-

  when the figures are drawn through the rest

of the shadow mask.

  However, the information to be displayed is more and more often provided by a computer and often in a graphic form, many tubes

  display cathodes must necessarily function-

  ner in recurrent scanning mode, in which a luminous point (which can be constituted by the neighboring points produced by each of the phosphors of a triplet) is repetitively scanned successively along a direction of the screen in the form a line that is moved for each scan in an orthogonal direction to define a field, or frame, of scan lines. A modified form of shadow mask tube uses a mask with slits that extend orthogonally to the direction of the scan

  lines and triplets of phosphors.

  It is clear that we write on a larger proportion of the screen and that the electron beams must be deflected at such a speed that they are on each picture element phosphor for a shorter time. The restoration of the local brightness of the screen by increasing the energies of the electron beams which are superimposed at each point of the shadow mask is prevented by the dissipation of energy via the shadow mask

  when writing successively on all points.

  The beam-indexing cathode ray tube, for its part, does not have such an energy absorbing mask, which allows a beam of more intense

  great to hit the screen directly.

  It usually includes an electron gun assembly which produces a single electron beam focused on a screen coated with phosphor bands excitable by an electron beam, which emit different primary colors, arranged in a network in a repetitive series of triplets according to the colors emitted and it is also provided at regular intervals

  in the repetitive sequence, indexing bands available

  in the same direction, which respond to the beam

  of electrons by emitting detectable radiation through

  to the tube for a detector. The beam indexing tube is used

  in recurrent scanning mode, the modulation of the beams

  electron skins being multiplexed between pathways of a

  electrical chrominance signal associated with the three

  their primary phosphors of the bands of triplets scanned sequentially along each line, the emission of radiation by the indexing bands used to synchronize the multiplexing of the chrominance signals so that the beam hits the band of

correct lumiophore.

  To obtain sufficient image definition in the scanning direction of the lines, the phosphor bands are narrow and possibly separated by guard bands to prevent color impurities, which results in also a limitation on the permitted dimension of the light point

  in the scanning direction of the lines.

  It is however difficult to focus a beam of great intensity until a point of small dimensions is obtained and, even with guard bands

  between neighboring phosphors, a limitation is imposed

  sée with the beam current and therefore with the

  screen brightness. This is mitigated in some

  taine measure by focusing the beam to obtain a "point" which is elongated orthogonally to the direction of scanning of the lines, that is to say along the bands, in the direction of scanning the field, but this is limited by the distance of separation of lines of

neighboring sweep.

  The subject of the invention is a cathode-ray tube display device and a method for operating such a device which makes it possible to display

  brighter recurring scan images.

  An embodiment of the invention is described below by way of example in relation to the appended drawings, in which: - Figure 1 is a sectional view of a cathode ray tube with beam indexing with the circuits d associated attack of a first form of device

  display according to the invention, in which two

  electrons produced in the cathode ray tube are superimposed on the screen; - Figure 2 is a view, similar to Figure 1, of a second form of display device according to the invention, in which the beams

  of electrons used in the cathode ray tube are deca-

  strips at the screen, and delay means are associated with one of the modulation grids of the cathode ray tube; and - Figure 3 is a view, similar to Figure 2, of a third form of device

  display according to the invention showing a different form

  Modulation signal delay means rent.

  FIG. 1 therefore represents a visual display device 10 for displaying images of the type

  multi-color raster scan television,

  that is to say in color, which comprises a cathode ray tube with beam indexing 11 and associated drive and control circuits 12 which are both well known in their details and are not described

here only in outline.

  The cathode ray tube includes an envelope under

  vacuum 13 containing not one but two electro-cannons

  sections 141 and 142 forming a pair of cathodes, each being associated with a control grid 141 ′, 142 ′ and with usual electrodes for accelerating the electrons and

  focusing, beam (not shown) by the-

  which a pair of electron beams Bml and Bm2 is formed between the cathode and a final anode 15 supported in the vicinity of a screen portion 16 on which are formed bands of red green and blue phosphors 17R, 17V, 17B, respectively, separated from each other

  others by guard bands 18. The lumino- bands

  color-emitting phores are grouped into a repeating series of triplets, each comprising a luminophore

  of each color. In this description,

  when we designate a phosphor by a color, it is

  refers to the color of the main visible radiation

  cipally emitted by this phosphor when it is excited by an accelerated electron beam between the barrel

  electrons and the anode, and striking this phosphor.

  The beams are focused in such a way

  that they hit the screen in the form of circular dots

  widths or ellipticals of size slightly greater than the width of the bands in the direction of the width of the bands, whereby they produce the maximum amount of excitation of the phosphor of a band they strike, while the color the light emitted is preserved by the guard bands separating the

  neighboring bands of phosphors of different colors.

  At regular intervals across the screen,

  indexing strips 19 consist of a lumino-

  phore or other matter which responds to the excitation of electron beams to emit radiation, which may be invisible, or produce a secondary emission of electrons towards the back of the tube in the envelope

  this one, and these indexing tapes can be worn

  guard bands 18 or occupy part of

following colored bands.

  The control circuits 12 include a

  power supply 20 to produce a difference in poten-

  tiel between the anode 15 and the cathodes by which the energy of each electron beam is defined and, consequently, the quantity of light produced by the cathode ray tube, or luminosity or luminance of the displayed image. In the embodiment shown in

  Figure 1, the cathodes are aligned one with respect to

  port to another in such a way that the two bundles

  are focused at the same point on the screen and combine

  to define a light emitting point whose

  brightness is determined by the two beams. Consi-

  let’s for the moment run a beam, say the Bml beam. The image is formed, that is to say that a contrast is given to it, by modulation of the beam current by the component video signals "red", "green" and "blue" coming from a source (not shown) such as a camera or a computer graphics generator at the video multiplexer 21 which, in

  function of color synchronization signals pro-

  coming from a formatting circuit 22, applies each of the chrominance signals in turn to a video amplifier 23! and from there to the control grid 14'1 of the cathode ray tube to modulate the current of the electron beam. The formatting circuit 22 can also receive signals synchronizing with the signals

  video from their source.

  The circuits 12 include a beam deflection signal generator and an amplifier 24, also synchronized with the formatting circuit 22, and deflection coil means 25 which cause the electron beam to carry out a repetitive line scan across strips of phosphors, perpendicular to their length, that is to say in the plane of the figure. Field orthogonal scanning circuits also exist, but are not

shown for simplicity.

  A photodetector or, if appropriate, a detector & secondary emission, 26 is arranged to receive the emissions from the indexing bands 19, and an indexing signal produced therein and applied via the amplifier 27 to the formatting circuit 22 represents the crossing of the indexing strips by an electron beam animated by a

  sweeping movement in the direction of a line.

  The fixed spatial relationships between the bands of color phosphors and the indexing bands allow the formatting means to provide a synchronized signal on the electron beam scanning the bands of red, green and blue phosphors, whereby the multiplexer can transmit the "red", "green" and "blue" video signals synchronized with the crossing of the respective phosphor and produce the color image by varying the current of the electron beam

with these video signals.

  The gate 142 ', which controls the beam Bm2, is connected to receive the modulation signals coming from the output of the video multiplexer 21 via the driver amplifier 232 so that during each scan, the two beams are modulated by the same information and that the light points superimposed on the screen

appear as a single point.

  It will be understood that the energy of the beam hits

  Any particular phosphor strip can be made larger than with a single beam without resorting to an individual beam current which prevents focusing of the beams sufficiently to obtain a light spot of similar dimensions which

  avoids excitation of neighboring phosphor bands.

  Thus, thanks to the simple device consisting in dividing the energy of the electron beam between two beams and in modulating the beams with the same chrominance signal information, it is possible to obtain a beam current of greater intensity and greater brightness than the image formed on the screen. In a recurrent scanning cathode ray tube, the image observed results from a very brief excitation

  of a particular part of the phosphor of the screen

  popped at field scan intervals, or at double field scan intervals if interleaving is used, followed by a relatively short phosphor emission decay interval and a relatively long non-emission interval which is not perceived because the eye of the observer integrates these repeated emissions to make an image of them

seemingly regular.

  It will be understood that within the limits of any field sweep, this image can be enhanced and appear brighter by increasing the intensity of the light emitted by the screen by delaying one beam relative to the other so that the different beams hit the same portion of the screen one after the other, delayed in time but modulated by the same image information also delayed in

the weather.

  Turning now to FIG. 2, it can be seen that it represents a second embodiment 30 of a display device according to the invention under the

  form of a sectional view of a cathode ray tube with indexa-

  tion of beam with the driving circuits similar to those of FIG. 1, so that the same elements are designated by the same reference numerals, but different in that, in the tube 11 ', the barrels with

  electrons / cathodes 143, 144 are aligned with one another

  port to each other and to the screen so that the beams Bml and Bm2 strike the screen at a predetermined distance from each other in the direction of the scanning of the lines and, in the control circuits 12 ' , by the presence of modulation signal delay means 31 mounted between the chrominance signal multiplexer

  21 and the gate amplifier 232.

  The distance d at the screen between the points of impact of the beams is chosen such that they are at points in correspondence with respect to the bands of phosphors 17R, 17V and 17B and to the bands

indexing 18.

  In the screen construction shown, the indexing bands 18 appear at a step equal to two bands of phosphors which, of course, repeat in triplets, so that the points in correspondence

  appear at a step equal to six bands of phosphors.

  The same reasoning applies to other provisions

screen.

  The distance d is thus a multiple of six

  times the pitch of the phosphor strips and, depending on the frequency

  quence of line scanning by the beam, defines a delay between the following beam Bm2 hitting the same point on the screen as the beam Bml. The delay means 31 are adjusted to produce such a delay interval in the modulation signal applied to the gate 142 'so that the same video information element modulates the two beams Bml and Bm2 when they strike a particular part of screen phosphor,

  that is, any indexing band.

  The delay may be longer than a line scan period, but shorter than the field period, so that the offset impact points are on different scan lines from the frame and, in a convenient form, the delay may be an integer multiple of the line scan period so that the two beams strike the same band, but within

  different lines of the scan frame.

  The delay means 31 may have any suitable form to provide a delay interval ranging from a few microseconds when the beams strike the strip in the same line of the frame up to a few hundred microseconds when they strike the strip in different lines

of the frame.

  For short delays, it is convenient

  to use fixtures, such as cut-out devices

  load range, which delay analog modulation signals but, for longer delays, it is

  better to use digital storage methods

  such as shift registers or memories

  addressable such as RAM.

  Such digital storage is the most

  useful when the video signals that produce the af-

  files are digitally processed in certain equipment or in a computer and the delay means can then be conveniently introduced before the

  digital signals be converted to analog form

  to be applied as modulation signals to

a control grid.

  Turning to Figure 3, we see that it represents

  feels a third embodiment of a display device 40 according to the invention in the form of a sectional view of a cathode ray tube with beam indexing 11 ′ with driving circuits 12 "similar to those of

  Figure 2, so that the same elements are desi-

  identified by the same reference numbers, but different

  rents regarding the application of signals

video.

  The video signals of the three primary colors (RGB) are produced in digital generation circuits 41 which can be a computer or a special circuit card generating video signals, and are applied by data lines 42 to a multiplexing unit 43 RGB and digital / analog conversion (DAC), corresponding to signal multiplexer 21 of

  devices 10 and 30, which receives the synchronization signal

  sation of the image formatting means 22 for drawing therefrom, and supplying the driving amplifier 231 with analog signals to control the grid of the color corresponding to the impact position of the head beam

  (Bm2) determined from the indexing system.

  Data lines 42 also transmit

  the signals to a delay memory 44 which is controlled by means of read / write input / output means 44 ′, by addressing means 45 controlled or synchronized themselves by the formatting means of image 22 so as to memorize each of the digital video signal words during a predetermined delay interval before applying them to an RGB and DAC multiplexing unit 46 similar to unit 42, but controlled by the addressing means 45 au place of

formatting means 22.

  The analog output signal of the convert-

  digital / analog 46 is applied to the amplifier

  attack ficitor 232 and grid 142 'with the

appropriate delay.

  It will be understood that the digital delay circuits and the digital / analog conversion can take other suitable forms and that, for example, multiplexing can be part of the write operations in the delay memory, so that the only data of memorized signal are those that

  will be applied to grid 142 '.

  It is recalled that the duration of the delay is something immaterial and, as it is a function only of the interval between the writing of the video data in a memory and their reading in this memory, it is easy to change , even in operation and

continuously.

  It will be understood that it is not unusual to apply corrections to the scanning of the screen of a

  cathode ray tube by an electron beam for corri-

  manage various distortions caused by the geometry of the tube and by interactions of deflection fields, that is to say that the deflection forces vary according to the position of the beam in the envelope of the tube in order to ensure that the point at which it strikes

  the screen follows a uniform scanning pattern.

  We will also understand that when there is more

  of an electron beam and when they are intention-

  nally offset as in the invention, but subject to the same deflection forces, the action of the scanning correction forces on the head beam can have the effect that any following beam is slightly displaced from its nominal trajectory by

  scanning at a point such that it strikes a strip of light

  nophores of "wrong" color or overlaps two bands

phosphors. -

  The device 40 of FIG. 3 can be

  modified to include a correction memory 47 functions

  operating under the control of write / read addressing means 45, whereby it is possible to

  vary the delay applied to the video signal depending on

  tion of the position of the head beam in the scan

  of the field. Conveniently, the variable delay can com-

  take a map of the variations of the follower beam from its nominal beam position with respect to the head beam for each position of the head beam in the frame, that is to say for each indexing strip or each triplet of phosphor strips crossed when subjected to correction forces

sweep.

  The variations thus reported may include variations in position which, when read, are related to the scanning frequency to define variations in the delay interval by appropriate processing circuits (such as a computer in 41), then added to the nominal delay interval, or can be stored directly as variations of the nominal delay interval. The simplest way, however, is to store the variations as delay intervals each combined with the nominal delay interval, i.e. as the effective delay interval to be used for each beam position and signaled so by the means of

image formatting 22.

  It will be understood that, although the invention has

  was described with reference to a cathode ray tube with indexa-

  two beams, it is not limited

  number of beams, how the

  bundles are formed, nor even to the type of cathode ray tube

  as long as the beams follow the same path

roof with each sweep.

  For example, the cathode ray tube illustrated has separate electron guns / cathodes to produce the individual beams. A cathode construction can be provided which produces an elongated beam along an axis, usually the longitudinal direction of the strips, and subjected at the level of different zones of this beam to the action of individual control grids in a similar manner. to that of 141 'and 142'. In such a case, the areas of the beam strike the screen to effectively form two separately adjustable modular points of light in the direction of scanning the field and to operate with a delay interval.

  of a scan line period in a corresponding manner

  laying down to that described above o two beams

  tincts are thus shifted. Furthermore, the display device according to the invention can incorporate a cathode-ray tube with a perforated mask in which a group of three beams directed by an opening of the perforated mask towards a triplet of phosphors on the screen, corresponds to the normal single beam d '' a beam indexing tube. A cathode-ray tube with a shadow mask according to the invention can use two or more groups of three beams, each group being directed towards different parts of the

  mask perforated so that everyone does not provide and

  put an improved dissipation by the mask.

  It is also possible to use a single group of three beams aligned in such a way that they

  are directed to different openings but

  close to the shadow mask, thanks to which each beam reaches a different portion of the screen scanned in a frame and can have an increased intensity thanks to the time which separates the impacts of the three beams on the same part of the screen, which provides all the visual information for this part with a slight degradation in color purity due to the fact that the

  phosphors are excited at slightly different times

famous.

  The embodiment of the display device

  sheet 10 of FIG. 1, in which the multiple beams are superimposed, is naturally not applicable to the tube with a shadow mask with regard to superimposed groups of beams for the reasons of

  heat absorption problems discussed above.

  It will be understood that in the context of the pre-

  feel description, say that the same modulation is

  applied to more than one beam means that the same instantaneous part of a modulation signal which moves as a function of time is applied to the two beams without necessarily modulating them at the same level

signal.

Claims (14)

  1. Visual display device comprising a recurrent scanning cathode ray tube (11, 11 ′) having a screen (16) carrying a network of triplets of phosphors, (17R, 17 17B) emitting color and capable of operating for produce multiple beams   of individually modifiable electrons (Bml, Bm2)   pant the phosphors of the network of triplets, scanning means (24, 25) operable to give a repetitive scanning movement to the beams producing for each beam, an impact on the screen (16) which forms a raster of line scans offset from each other in an orthogonal direction to form a field such that the fields for all the beams are spatially superimposed, characterized in that the individually modifiable electron beams (BM1, BM2) are arranged relative to each other to strike phosphors in correspondence with the network of triplets of phosphors (17R, 17v, 17B), in that modulation means (14'l, 14'2, 231, 232, 31, 43, 44, 44 ', 45, 46) can work to modulate the intensity of   each electron beam according to a modulus signal   electrical representation representative of a visual image   produce on the screen, so that the same modu-   lation is applied to the different beams (Bml, Bm2) when they strike the phosphors on the same portion of the superimposed fields to reinforce the excitement of these phosphors.   2. Device according to claim 1, charac-   terized in that the beams (Bml, Bm2) are directed towards the screen (16) so as to strike the latter at   different positions of the screen on which each do   this is animated by a sweeping movement as the head beam or as the follower beam, and in that the modulation means (14'1, 14'2, 231, 232, 31, 43, 44, 44 ', 45, 46) include delay means (31, 44, 44 ') operable to delay the modulation signal applied to each beam (Bml, Bm2) which follows the leading beam in each described frame by a time interval related to the separation distance of the point of impact of this beam from the head beam in the direction of scanning of the beams (Bml, Bm2).   3. Device according to claim 2, charac-   terized in that each time interval is inferior   less than a field scan interval.   4. Device according to claim 2 or 3, characterized in that the cathode ray tube (11, 11 ') is of the beam indexing type, in which the screen (16) comprises several triplets of phosphor strips (17R , 17V, 17B) and several indexing bands (19), each band extending in the direction of scanning the field, arranged in a network in the direction of scanning the lines of the frame, and in   which beams (Bml, Bm2) are directed to frap-   per corresponding portions of the triplet network of phosphor bands (17R, '17V, 17B) and bands indexing (19).   5. Device according to claim 4, charac-   terized in that the beams (Bml, Bm2) are directed   to strike the same bands, offset in the direction   tion of scanning the field of an integer of line scans.   6. Device according to claim 4, charac-   terrified in that the delay means (31, 44, 44 ')   include a digital delay line that can work   to delay the modulation signal in digital form.   7. Device according to one of claims 2   to 6, characterized in that it comprises correction means (47) which can operate to vary the   delay of the modulation signal applied to each beam   track follower from one end to the other of the frame as a function of the variations of the instantaneous relative positions between said follower beam and the head beam due to non-linearities of the scanning and to corrections of scanning applied so that the beam of head describes a uniform frame.   8. Device according to claim 7, charac-   terized in that the correction means (47) comprises   attempt a correction memory in which is   t, for each follower beam, a function linked to the effective separation distance between this beam and the head beam in the scanning direction for each addressable position where the head beam strikes   the screen (16) and reading means capable of operating   ner according to the instantaneous position of the head beam throughout the field scan for   read said memorized function for each beam followed   enter a delay in the modulation signal tion in accordance with it.   9. Device according to claim 8, charac-   terized in that the function reported in the correction memory is the instantaneous value of the interval   delay of the tracking beam modulation signal.   10. Device according to claim 8, characterized in that the function reported in the correction memory is an offset in the nominal delay interval or in the nominal separation distance between the follower beam and the head beam. 11. A method of forming a visual display comprising the steps of producing in a tube   with cathode rays (11, 11 ') color several beams   electron beams (Bml, Bm2) individually modular to focus the beams (Bml, Bm2) on a screen (16) so as to excite phosphors (17R, 17v, 17B) emitting radiation, to animate each of the beams of '' a repetitive scanning movement along a frame of scanning lines, the lines being offset with respect to each other in an orthogonal direction to form a field of scanning lines,   characterized in that the fields are spatially superimposed   and in that the intensities of each of the   swiping skins are modulated   according to electrical modulation signals representing   of a visual image to be produced on the screen, so that the same modulation is applied to   different beams when they hit the same carriers   overlapping fields to reinforce emissions of these portions.   12. The method of claim 11, charac-   terized in that the beams (Bml, Bm2) are caused to strike the same portions of the screen (16) defining the lines   of the frame as head beams or as follower beams   set in time, whereby the beams strike instantly -   ment of physically shifted portions of the screen (16), and in that the modulation signals applied to each follower beam are delayed by a delay interval comprising said time lag.   13. The method of claim 12, applied   than a cathode ray tube with beam indexing   hoop (11, 11 '), in which the phosphors emitting radiation (17R, 17V, 17B) comprise triplets of bands of phosphors emitting lights of different colors, and beam indexing bands (19)   which extend substantially orthogonally to the direction   line scanning, characterized in that said time shift is a function of the scanning frequency and the separation distance between the beam indexing bands (19) and the beams   phosphors (17R, 17V, 17B) emitting the same color.   14. Method according to claim 12 or 13, characterized in that the delay interval between the modulations of the head beam and each follower beam is varied as a function of the variations in offset between them due to variations in the forces of sweep deviation applied to the head beam across the field scan to define a uniform frame.