US2672575A - Apparatus for reproducing images in color - Google Patents

Description

March 6, 1954 P, H. WERENFELS APPARATUS FOR REPRODUCING IMAGES IN COLOR 6 Sheets-Sheet 1 Filed Oct. 11 1951 INVENTQR .Rier erarg eh Q ATTORNEY March 16, 1954 p H, WERENFELS 2,672,575

APPARATUS FOR REPRODUCING IMAGES IN COLOR Filed Oct. 11, 1951 3 Sheets-Sheet 2 March 16, 1954 P. H. WERENFELS APPARATUS FOR REPRODUCING IMAGES IN COLOR Fil ed Oct. 11 1951 S Sheets-Sheet I5 INVENTOR fsllgr elf/yelp ORNEY ing directions. phosphors are activated in a given order as the Patented Mar. 16, 1954 APPARATUS FOR REPRODUCING IIWAGES IN COLOR Peter H. Werenfels, Lawrenceville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application October 11, 1951, Serial No. 250,867

3 Claims.

1 This invention relates to improved cathode ray tube apparatus for reproducing images in color.

Color kinescopes have been constructed employing directional color screens that emit light of one primary color or another depending on mounted with the perpendicular bisector of one particular side of the equilateral triangle pointing in opposite directions that are perpendicular to the row. Thus one side of alternate triangles is parallel to the upper edge of a row and the corresponding side of intermediate triangles is parallel to the bottom side of a row. The phosphors may be spots on a plane surface, they may be coated onto three sides of a solid such as a.

pyramid, or, they may be coated on the insides of a hollow hexahedron, etc. The important factor is that the different color responsive phosphors must be arranged so that they can be scanned in one order by a beam tracing a closed nonintersecting path in one direction and in a' reverse order when the beam traces a different closed path but in the same direction. A target formed in this manner Willbe referred to as a directional target. I

The directional target is activated by-a single beam that is rotated about its normal path so as to approach the screen from cyclically chang- The difierent color emissive .in the name of Sziklai, Schroeder and Bedford,

improved results canbe obtained if "the transmitted signal represents the primary colors in one sequence during one interval of time and a reverse sequence during another interval.

It is the principal object of this invention to provide a new and improved way of reversing the sequence in which the different primary colors are emitted by color kinescopes of the type described above.

Briefly this objective may be attained by shifting the centering of the beam or beams of electrons before they are focussed so that a different group of phosphors is scanned. In addition, for reasons that will be treated in detail below, the phase of the rotation of the beam about its normal path must be altered when the centering is changed.

The manner in which this objective maybe reached will be better understood from the detailed description of the drawings in which:

Figures 1 and 1A show the details of a single beam color kinescope that may be employed in the combination of the present invention.

Figure 2 is a view of the phosphor dot screen as it is seen through the mask of the color kinescope of Figure 1,

Figure 3 is a view of certain of the apparatus in Figure 1 useful in explaining the operation of the present invention. 1

Figure 4 illustrates a circuit that may be employed to change the centering of the beam on successive fields. a

Figure 5 is an enlarged view of the phosphor spots employed in one type of directional screen and Figure 6 illustrates a type of coincidence circuit that may be employed.

Referring to the drawings, Figure 1 shows one form of single beam color kinescope that may be used in the present invention. The tube consists of an evacuated envelope l0, having both a conical portion l2 and a'tubular neck portion Id coaxially joined together as shown. The conical portion l2 of the envelope is closed by'a'face plate I5 and closely spacedfrom it is a fluorescent target and screen structure l8 to be described below. Mounted coaxially within the tubular envelope [4 is an electron gun structure for projecting a beam of electrons 20 toward the screen structure'l8. The electron gun is of conventional design and consists of a cathode cylinder 22. i

A control grid cylinder 24 coaxiallysurrounds the electron emitting end of the cathode 22 and has an apertured plate structure closing one end thereof and closely spaced from the cathode. A shield electrode or grid 26' constitutes a short thimble-like electrode having an aperture in the bottom thereof for the passage of electrons therethrough. Spaced along the tubular neck portion Hi and coaxial with the other electron gun parts is a tubular first anode electrode 28, having an enlarged portion at the end facing the fluorescent screen I 8.- A- second anode electrode is formed by a conductive coating 30 on the inner of a converging nature and cause the electrons to form into a beam having a minimum cross section or cross-over point 56,be tw een the tubular electrode 28 and the screen It. beam, after passing through this cross-over point 56, tends to diverge before striking the screen H3. The diverged beam is bent away from the central axis of the tube by a rotating radial magnetic field. As is well known in the art, such a izleld can begenerated by applyingcurrent of one phase to afi-rst pair of coils that are diametrically. mounted about the neck of the .tubaand applying current of a different phase to a second pairof coilsthat are mounted with their axis at 9Q?-to, the first pair. For simplicity, the coils are shown as one yoke 3|. The focusing coil 3% serves to-converge the electrons within the beam and also .to direct the beam to the same point in the region of thetarget 18. shown, this pointis the. same point on a mask 44; that the beam would havestruck. if the coils were not used. Thus, the beam substantially generates a cone.of revolutionhaving an apex at thelmask .44.-

The electron beam 20 andhencethe apexot the cone, of revolution may becaused to scan over thesurface of themask 44 in any desired pattern or raster.

from topto the-bottom of the screen. [8. The scanning of the beam is produced by. scanning fieldsestabIishedby twopairs of scanning coils included in the yoke .40. Each pairof coils may be connected to well known circuits producing saw-tooth currents forv providing both line and frame scansion of the beam.

In the screen structure l8 the masking electrode 44=is positioned in front of atransparent phosphor supporting sheet 45. electrode 44 is formed: from thin metallic foil which is opaque tothe electronsof the beam 20. A plurality of apertures 48 are formed through the metal foil of the masking electrode 44. Supported onthe surface of the transparent plate,

46 are areas 50 of phosphor coating which are positioned in the path of the beam 20 passing through apertures 48.

In the enlarged section of the screen 18 shown in Figure 1A it can be seen that if the electron b'amapproaches the target from any one of the directions indicated as X, Y or Z, the electrons oflthebeam will pass through the-apertures of themasking electrode 44 and strike those phosphor spots which arein line with the beam path.

coincident with these directions. When the beamapproaches the target along a path X it strikes only those phosphor coatedspots indicated by R, which luminesce with a red light.

In a similar manner, when the beam approaches.

The electron In the embodiment.

However, in tubes of this type, the 7 conventional scanning consistsofparallel lines,

The masking,

10 2 spots in sequence.

circle with its center at a point l3. If the ouring the target along a path Z will strike those phosphor areas indicated by the letter B, which luminesce with a blue light.

'1 hus, the combined efi'ects of the rotating field oi coils and that of the focusing coil 34 result in beam is being first displaced from its normal path and then redirected alonga new path to strike the. surface oftarget lcfrom sequentially different directions so as to strike the phosphor The cross sectional area of the beam at the mask 44 may be large enough to cover a plurality of the apertures 48. Electrons pass through each of theapertures covered by the beam to form a; sectional beams having a direction depending on the rotational angle of the main beam about its normal path. As the main beam rotates, the sectional beams also rotate and scan circular paths on the screen i8 having centers 10. In Figure 2 certain groups of phosphor dots 10 are so arranged that their geometriccenters. coincide with thecenteixof the circular-path traced on the screen I8 by thesectional beams. Assuming for the moment that the beam .20 is not scanning a raster, but is rotating aboutits normal position in a clockwise direction, it can be -seen from an examination of Figure 2 thatthe sectional beams i0 will-scan aroundithe red; blue, and green phosphor spots of the groups! the order named; Nowif the centersof the substantially circular paths tracedby thelsectional beams are shifted to the corresponding points E2, the beam scans.red,.green, and blue phosphor spotsin the order named. This-order of scanning the spots isjust=the reverse of the order centering is as it passes throughthe beam rotation coils. Whether the meansemployed is electrostatic or electromagnetic the shiftshould be in a direction that is the opposite from the direction to 12; that is from T2 to 10. The

"reason for this will become clear from the following discussion of the electron optics of thetube of Figure 1. essential components of the electron-optic system are illustrated in Figure 3. The electron gun shown in Figure 1 directs a beamof electrons along the principal. axis of the tube-to a point 0 that is centrally located with respect to the rotating magnetic field-set up by the beam rotation coils. In normal operation, the beam 20is bent away from the principal axis of the tube and rotatdi The paths 27 my and g indicate different positions the beam 20 may assume as the radial magneticfield established by the coils rotates. The loci of the beam in the plane of thefocusing coil 34 is a rent in the focusing coils is properly adjusted, the origin""0 of the beam is imaged atthe point i."-" I'his"latter poinft is at the, apertures of the mask and iseffectively the focal or cross-over point. With nopurrent flowing in the deflection coils 40; thebea-m would generate a cone of revolution having its apex at the point 2'. Now if the beam is deflected, the apex scans to a point It should be noted that the focusing coils serve to'focus at'th'e point i or 2" as the case may be, j both the electrons within the beam and the beam itself, regardless of its position in the loci.

In one embodiment of this invention, the beam is shifted from the point I) to the point as it "passes" through the beam rotation coils.

Thus the loci of the beam in the plane of the focusing coil 34 is indicated by the dotted circle I having a center 16.

As is well known to those Skilled in the art, this change in the angle of If the rows of phosphor spots The of the beam and perpendicular to the direction 0, 0. The shift in centering might also be efiected by electrostatic plates that set up an electrostatic field along the line 0, 0'. Normal centering of the beam and hence theraster 'on the tube may be effected by controlling the amount of steady current flowing in the deflection coils 40. Thus normal centering acts the same as a steady amount of deflection, and the center of deflection is still the same as illustrated by the deflected beam in Figure 3 that strikes the screen at 2'. When the normal centering control is adjusted, the beam still lands at the same place with respect to the phosphor groups. displace the electron paths toward the focusing field, however, the electrons approach the screen from a different direction and land at a different place on the screen I8 with respect to the phosphor groups. The shifting of the centering could take place at other points than the axial position of the beam rotation coils but must take place before the focusing field is reached.

This shift in the beam in one direction, up-

ward and to the right as shown in Figure 3, ac- 'tually displaces the scanned raster and hence signals representing a certain point in the scene being reproduced are reproduced at two different positions as the beam is shifted to effect a reverse sequence of color reproduction. This 'misregistration is negligible if the groups of phosphors are small in comparison with the maximum amount of detail to be reproduced. If the groups are relatively large, the horizontal displacement can be corrected by changing the phase of the incoming video signals that are "used to modulate the intensity of the beam or beams with respect to the scanning action of the beam.

Figure 4 illustrates the manner in which the centering of the beam of the tube shown in Figure 1 may be shifted on successive fields. The transmitted signal is detected on a standard receiver 90 and applied to the grid of the color tube and to the deflection circuit 92 in the normal manner. The signals are also applied to a color synchronizing circuit 94 such as described in RCA Bulletins on Color Television and UHF October 1949. A sampling oscillator 96 is controlled by the synchronizing circuit 94 and provides the energy that is to be applied to the beam rotation coils. The sampling frequency applied by the oscillator 96 is applied to the grid of an amplifier 98 via a delay line I00 and to the grid of an amplifier I02 directly. The plates of the ampli- If the change in centering is such as to a beam rotation coil 60. Thus if the amplifier 98 is conducting, the sampling frequency is applied to the beam rotation coil 60 with a delay determined by the delay line I00 and if the amplifier is cut off and amplifier I02 is conducting, the sampling frequency is applied directly to the beam rotation coil 60 without any delay. The reasons for this delay will be discussed more fully in connection with Figure 5.

In order to shift the beam as previously discussed, the present apparatus supplies current to the centering coil 19 during one field and a different amount of current to this coil during a succeeding field. In order to effect th'isresult, the horizontal and vertical sweep signals supplied by the deflection circuit 92 are applied to a coincidence circuit I06 which is described in detail in connection with Figure 6. The coincidence circuit provides a pulse at the beginning of every other field. These pulses are applied to trigger a multivibrator I 08. The multivibrator I08 may be a free running type having a cycle equal to two fields or it may be a monostable multivibrator that is triggered to an unstable state by the coincidence pulse, reverting to its stable state at the end of a field. In either case, the multivibrator l08 will provide, as is well known to those skilled in the art, oppositely phased rectangular waves as illustrated by the wave forms H0 and H2; These wave forms are applied to the grids of the amplifiers 98'and I02 respectively so that one is conducting while the other is non-conducting and vice versa. Thus during one field the sampling frequency supplied by the oscillator 98 is applied to the beam rotation coils 50 via the amplifier 98 and the delay line I00, and in the next field it is applied directly to the beam rotation coil 60.

One output of the multivibrator I08 is applied to an amplifier H4, the plate of which is connected to 18+ via the beam centering coil I9. Hence when the amplifier H4 is rendered conductive by the positive portion of the wave form H2 a large amount of current fiows through the centering coil 19. When the amplifier H4 is cut off during a negative portion of the'wave form H2 the amount of current flowing through the beam centering coil 79 may be substantially zero. The amount of current fio'wing through the beam centering coil 19 when the amplifier l M is conductive may be adiusted by rheostat H6 that is connected in parallel with the beam centering coil I9. When the amplifier I I4 is non-conductive, the amount of current flowing through the beam centering coil I9 can be controlled by a rheostat H8 that is connected be tween. the plate of the amplifier l I4 and ground.

The overall operation of the apparatus in Figure 4 is as follows. During one field the amplifier 98 may be cut off and the sampling frequency from the oscillator '96 is applied directly to the beam rotation coils 60. At the same time,

the amplifier H4 is rendered conductive and current flows through the beam centering coil 79 so as to shift the beam from the points I0 on the phosphor screen of Figure 2 to the points '12. During the next field, however, the amplifier 90 is rendered conductive and the amplifier I02 is cut off, with the result that the sampling beam, strikes the, phosphorscreen vof Figure) at points 10.-

The following. discussion .relates to the reasons for the use of the delay linev I in the apparatusof Figure 4. Figure shows .an enlarged View of some of the phosphor spots. When thelocus traced by the rotating beam is centered at the points '52, and assuming that the beam rotation is in. a clockwise direction, the order of color reproduction is red, green, blue,v red, etc. When the beam is shifted so that the center of [its locus is at the points 10,- the same direction of rotation will scan the red, blue, green, red spots in sequence. This sequence, as previously noted, is the reverse of the sequence when it follows a path centered at [2. Assume that thebeam is centered atthe point 12 and that the resultant magnetic field is such that the beam strikes a red phosphor spot I20. If the beam. is now shifted by the action of the beam centering coil i9 soas to follow a circular path having H! for a cententhe beam strikes a point midway between the red phosphor spot H29 and abluephosphor spot !22. However, at this time the signal transmitted representsred and not a combination of red and blue. Therefore, in order to insure thatthebeam lands on the red spot, the phase of the beam rotation must be retarded by 6O". The delay line Hi0 must therefore introduce a delay of one-sixth of a cycle of the sampling frequency supplied by the oscillator 96;

Figure 6 illustrates one form-that the coincidence circuit H35. of Figureb mayv assume. A multi-grid tube I is biased to cut off by placing a positive potential on its cathode as shown. The horizontal flyback pulses are applied to .a grid 12! by an ordinary RC coupling network. The

vertical fiyback pulses are differentiated by an RC coupling network 128 before being applied to a grid I29. When the two feedback pulses occur simultaneously, as is the case on every other field, the cut off bias on the cathode of c the tube 25 is overcome and a pulse appears at its plate. It is this pulse that triggers the multivibrator H18.

In the embodiment of the invention discussed above, the beam would nominally strikethe screen iii-at the points 10. The order of scanning .the spots was reversed by shifting the beam so that it would normally strike the screen. 18 ofv the points 12. Little or no current would thenbe passed through the beam shiftingcoil- Hl'when the path. of the beam was to be centered-at the points E9 and a predetermined-amount of current would be in the coil 19 when the beam is to be shifted so as to trace paths centered at points '12. The beam might normally be centered at any point on a line between the points Til-and E0 in which case the current through the coil 19 would flow in one direction when the path of the beam on the screen I8 is to be at points 12 and in the opposite direction when the path of thebeam is to be centered at points 10. If the beam would normally land at points on the screen 18 that are not along a line 12-10, then two sets of beam shifting coils providing intersecting fields would have to be used. Current through one of them would center the path traced by the beam at points 72 and current through the other would center the path traced by the beam on the screen l8 .at points 10.

Thebeam could also be shifted downward so of Figure 4 by one half cycle of the beam rotationalfrequency.

It is not necessary that the center of the path tracedbythe beam or the screen 18 be shifted to thenearest group of phosphors that provides reversal of the primary colorreproduction. The shift can skip any number of groups as long as the groups traced afterthe shiftarle such that rotation about them in same direction produces a reversal inthe sequence with which the phosphors of the diiferent primary colors are scanned.

The apertures 48 in the mask 44 could also be oriented differently with respect to the phosphor groups without interfering with the present invention.

Having thus described the invention whatis claimed is:

1. Cathoderaytube apparatus comprisingin combination a directional target having diiferent colorphosphors mounted in groups along each line of the raster, an electron gun adapted to direct a beam of electrons toward said target along a given path, means for bending said. electrons away from said path, the plane in which said bending occurs being rotated, means for focusing said beam in the region of said target,- means for deflecting said beamso that it scans a raster at said target, means located between. said gun and said focusing means for directing the electrons along a given path during, a first interval and for directing said electrons along a diiferentpath. during a second interval whereby said rotating beam scans the difierent color phosphors on said directional target in one sequence during the first interval and in, reverse sequence during the second interval.

2. Apparatus for reproducing images in color in response to signals that are derived by sampling at a rate greater than line frequency the primary colors of ascene in one order for a first interval of time and in a reverse order during a second interval of time comprising in combination a cathode ray tube, ,a directional color screen mounted in said tube, an electron gun adapted to direct a beam of electrons toward said screen along .a given path,,means for bending said beam away-from said path, the .plane of said bending beingrotated, means for focusing said'beam at a. point in the region of .said screen, means for laterally shifting said beam before it passes through said focusing means, means for causing said beam to scana raster on said screen,.means for controlling-said beam shifting means so that the beam follows one path during said first interval and a different path during said second interval, and means for changing the phase of said rotating plane during said second interval.

3. Apparatus for reproducing images in color from color signals that are derived by sampling each of a plurality of primarycolors from a scene in one sequence for a first interval of time and in reverse sequencelfor a. second interval of time comprising in combination a target comprise-:1 of a phosphor dot screen, an apertured mask mounted infront of said screen, an electron gun adapted to project a beam of electrons toward said screen, means for establishing a rotating radial magnetic field that is perpendicular .to said beam, a foc using. coiladapted to converge said 2,672,575 9 10 electrons at the apertures in said mask, said ing the magnitude of said transverse magnetic focusing coil being mounted so as to act on said field different during only one of said intervals. electrons after they have passed through said ro- PETER H. WERENFELS.

tating magnetic field, a deflection yoke adapted to cause said focussed electrons to scan a raster 5 References Cited 1n the file of this Patent at said target, means for establishing a trans- UNITED STATES PATENTS verse magnetic field that is at right angles to said beam, said latter means being mounted so as to 7 D i g A 1951 shift said beam at a point before it enters the in- 2 Q 1952 fiuence of said focusing field, and means for mak- 10 I Fnen e a e a

Images