US2915673A - Cathode ray tube apparatus - Google Patents

Description

Dec. 1, 1959 E. ATTI 2,915,673

CATHODE RAY TUBE APPARATUS Filed Dec. 4, 1958 2 sheets-sheet 1 Figi I jug@ Fig. 2

Fig. 3.

"46 Fig. 4

ese

:l-4O `F-/sz INVENTOR 3644 M Eros Atti 1 56 ATTORNEY Dec. 1, 1959 E. ATT: 2,915,673

CATHODE RAY TUBE APPARATUS Filed Dec. 4, 1958 l12 Sheets-Sheet 2 l J /l /l\ United States Patent O CATHODE RAY TUBE APPARATUS Eros Atti, Horseheads, N.Y., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 4, 1958, Serial No. 778,157

6 Claims. (Cl. 315-29) This invention relates to cathode ray tube apparatus and, more particularly, to electrostatic deflection systems for the deflection of electron beams. More specifically the invention relates to a system capable of providing small amplitude deflection of high energy beams.

' In the prior art type of electrostatically deflection systems used Yin cathode ray tubes, two sets of deflection electrodes are provided for sequentially deflectingthe electron beam, one set providing the beam deflection in a first direction and the other set providing the beam deflection in a direction at right angles to the first direction. These deflection electrodes are normally positioned in front of the electron gun, between the electron gun and the display screen. For electron optical reasons it is necessary that the deflection electrodes positioned in this manner be operated at a potential not too different from that of the final anode of the electron gun. Excessive defocusing of the electron beam is prevented in this manner.

Guns providing high energy beams operate at final anode potentials in the kilovolt range. Typical television picture tubes, for instance, operate with the final anode about 15-20 kv. above cathode potential. The use of conventional electrostatic deflection systems as a means to deflect electron beams in this energy range in- Volves serious tube manufacturing problems, and also, serious circuit problems, on account of the basic requirement mentioned above that the deflection electrodes be biased at a potential not too different from the final anode potential. Due to insulation problems it is usually quite unpractical to bring out through the base of the tube the leads of the high potential deflecting electrodes together with the leads of the other electrodes of the gun, operating normally at low potentials. The difliculty here consists in preventing voltage breakdown between the electrodes operating at high potential and those operating at low potential. For this reason the deflection electrode leads have been customarily brought out through the bulb neck or bulb wall at a prohibitive increase in tube cost. This prior system also requires a rather expensive circuit in that high voltage capacitors are needed in order to couple and insulate the deflection electrodes from the output terminals of the deflection driving circuit, normally operating at low potential. The capacitors required rfor this purpose are generally bulky and expensive due to the high voltage insulation-required between the plates of the capacitor. The deflec tion electrodes are normally connected by means of coupling resistors to the final anode so as to be biased at the same direct current potential as the final anode.

From all this it appears that the high voltage insulation requirement of the deflection electrodes adds substantial cost and complexity to both the cathode ray tube and to the circuitry associated with it. Such additional cost and complexity remain the same, regardless of how small the deflection amplitude, a few spot diameters for instance, required in the system. It still remains substantially the same even in the particular case Patented Dec. 1, 1959 ice in which the bandwidth of frequencies within which ,the deflectionvshould occur is limited to a restricted portion of the frequency spectrum, the high frequency band for instance. The invention here described solves entirely these difficulties in those cases in which the deflection amplitude is limited to relatively small angles and furthermore the deflection frequency does notdescend below certain minimum values.

It is accordingly an object of this invention to provide an improved deflection system.

It is another object to provide an electrostatic deflection system suitable for the deflection of high energy beams which eliminates the need of external coupling resistors, high voltage coupling capacitors and associated wiring.

It is another object to provide a simple electrostatic deflection type cathode ray tube which substantially reduces the cost of the tube and of thefdeflection circuit associated with the tube.

YThese and other objects are effected by my invention as will be apparent from the following description taken inaccordance with the accompanying drawing, throughout which like reference characters indicate like parts,

ray tube (emi illustrated in Fig. l, partly in section;

Fig. 3 is amodification of the illustration shown in Fig. 2; p v f Fig. 4 illustrates another modification of the deflection system shown in Fig. 2;

Fig. 5 is a schematic view of a cathode ray tube utilizing an auxiliary deflection system and embodyingv the principles of my invention; f

Fig. 6 is an enlarged cross sectional view of a portion of the structure illustrated in Fig. 5; and

Fig. 7 is a sectional view taken along lines VII--Vll of'Fig. 6.

Referring in detail to Fig. 1, there is shown a cathode ray. tube embodying my invention. The tube is comprised of an envelope 12 having a tubular neck portion 14, a flared portion 16 and a face plate 18. The face plate 18 of the envelope has a fluorescent coating 20v of a suitable phosphor material deposited on the inner surface thereof. An electrically conductive coating isalso normally provided on the face plate portion and is illustrated in the specific embodiment as an electron permeable coating 22 of a suitable material such as aluminum deposited on the exposed surface of the fluorescent coating 20. The flared portion 16 of the envelope is also provided with ank electrically conductive coating 24 of a suitable electrically conductive material such as carbon or aluminum and which extends into the neck portion 14 of the envelope. An electron gun 30 is mounted within the neck portion of the envelope. The electron gun 30 consists essentially of a beam forming and'modulating system followed by a principal focusing electron lens electrode system. The conductive coating 24 on the inner surface of the flared pole portion 16 serves as an anode of the cathode ray tube to which a suitable voltage is applied by means of an external terminal 26. The electron gun 30 shown in the specific embodiment is wellknown in the art and is described more fully in U.S. Patent 2,773,212 by J. A. Hall and issued December 4, 1956 entitled Electron Gun and assigned to'the same assignee. f The beam forming section of the electron gun consists generally of an indirectly heated cathode, a control grid and a screen grid electrode. The principal focusing lens consists of a first anode, a focusing electrode and a second anode. These elements are not illustrated in Fig. 1 as the electron gun lstructure is we11- 3 known in the art and any suitable electron gun may be utilized which generates a suitable electron beam.

Referring to Fig. 2, there is shown a portion of the second or final anode 36 of the electron gun 30 and the deflection system within the neck of the cathode ray tube. The deection system consists of two spaced pairs of plates. The first pair of plates 3S and 40 positioned adjacent to the final anode 36 consists of the two parallel plate members 38 and 4t). The plates 38 and 40 are of electrically conductive material. The design and configuration of electrostatic plates 38 and 4i) for deflec` tion of electron beams is well-known in the art and no further discussion is necessary here. The pair of plates 38 and 40 provide the means of deflecting the electron beam in a plane parallel to the drawing sheet in response to suitable deflection signals applied across them.

A resistor 42 connects the upper plate 38 of the vertical deiection pair to the final anode 36 while the lower plate 4G is connected through a resistor 44 to the final anode 36. In the specific embodiment shown the resistors 42 and 44 are shown as separate from the electron gun structure but it is obvious that they may be made up of the supporting means connecting the detlecting electrodes to the final gun anode. For example, the support members might be of a partially conductive material rather than the high insulating material more commonly used to support and hold the various electrodes of the electron gun in a unitary structure. It is also possible to apply a conductive coating on the surface of these insulating members to provide the necessary resistances or leakage paths between the detiection plates and the final anode. In the specific embodiment shown in Fig. 7 a hollow rod tvpe of partially conducting support is being used. The detiecting plates 112 and U4 are connected electrically to the final anode electrode W6 by means of the transverse or surface conduction offered by the material constituting the spacer member 106. An electrically conductive member 46 is attached to the upper plate 3S and is in electrical Contact with a conductive coating 48 applied on the inner surface of the neck portion 14. In the specific embodiment shown the electrical contact is made by spring action of the member 46 against the inner coated surface 48 of the neck. The lower detiection plate member 40 makes contact with another conductive coating 50. also applied to the inner surface of the neck, in a similar manner by the electrode connecting member 52. Two conductive coatings 54 and 56 are provided on the outer surface of the tube neck 14 corresponding in area and opposite respectively to the internal upper coating 48 and to the lower internal coating S0. The coatings 48. 50. 54 and 56 are of a suitable electrically conductive material such as carbon or a silver paint. The two coatings 4S and 54 facing each other constitute the plates of a capacitor, which is coupled to the upper deliecting electrode 38. Since the glass of the neck portion i4 between said plates provides a high dielectric constant material of high dielectric strength and of low dielectric loss, a very suitable capacitor is obtained.

Similarly, the two electrode coatings Si) and 56 provide a capacitor coupled to the lower detiecting electrode 4t). The outer electrodes S4 and 56 of the coupling capacitors are attached to a suitable deflection signal source 6fl, so that a deflection signal is applied between the deecting electrodes 33 and 40.

The second pair of plates 7) and .72 or horizontal detiection plates are positioned vertically and at right angles to the vertical deection plates 38 and 40. The plate 7@ is connected by suitable electrically conductive means 74 to a conductive coating 76 on the inner surface of the tube neck 14. while a corresponding conductive coating 78 is provided on the outer surface of the neck to provide a capacitive connection from the plate 70 to the exterior of the envelope. The plate 72 is connected in a similar manner by means of a connector 80,

inner coating 82 and a corresponding outer coating 84. The plate 70 is connected through a resistor 7l to the anode 36 and the other plate 72 is connected through a resistor 73 to the anode. A suitable deflection voltage is applied across the two exterior conductive coatings 78 and 84 by source 88 to provide the necessary horizontal deliection of the electron beam. The structure illustrated in Fig. 2 can provide symmetrical or balanced deliection of the electron beam along both coordinate axes which are vertical and horizontal.

In the operation of the device the electron beam generated by the electron gun will pass through the tirst pair of deflection plates 3S and 40 and in accordance with the deiiection signal applied by the source di) be defiected in a vertical direction. ln passing through the second pair of deflection plates 7@ and 72 the electron beam will be deflected in a horizontal direction corresponding to the signal applied from the source 88.

In Fig. 3 a modified version is shown in which one of the vertical deection plates 4i? and one of the horizontal deflection plates '72 is connected to a common coupling capacitor formed by a conductive coating 99 on the inner surface and a corresponding conductive coating 92 facing 9i) on the outer surface. The plates 40 and 72 are electrically connected to the anode 36. This common external element coating 92 is connected to both sources 60 and 88 of deflection voltage. This system is simpler but, of course, will provide unbalanced deflection.

In Fig. 4 there is illustrated a detiection system which provides only one axis of detiection. This system may be utilized where deliection in only one direction is desired or where an auxiliary deiiection of the beam in one direction is desired at the same time that the beam is scanning a conventional raster, for instance, by means of an external magnetic yoke provided around the neck of the tube. The structures illustrated in Figs. 2, 3 and 4 provide a system which will operate in those applications where the deflection signals do not go below a certam frequency. This is due to the fact that as the frequency decreases the impedance offered by the coupling capacitors increases. The lower frequency limit attainable will depend upon the maximum value allowed for the coupling resistors within the tube and of course, the size of the coupling capacitors, the thickness of the glass, etc. The size of the coupling capacitor becomes smaller as the frequency of operation increases so that practical coupling capacitors of the order of a square centimeter may be considered sufficient for many applications involving high frequency small amplitude deection.

Referring in detail to Fig. 5, there is shown another cathode ray tube in which electrostatic deflection is provided within the electron gun to provide a relatively small detiection of the electron beam. An electrostatic or an electromagnetic detiection system may be utilized in conjunction with this detiection system to provide the conventional raster scan. The electron gun shown in Fig. 5 is similar to that shown in Fig. l with the modification in the first anode of the principal focusing lens system. This modification consists of providing detiection electrodes within the skirt or tubular portion of the anode as shown in more detail in Figs. 6 and 7. The deflection electrodes are located in a substantially equal potential region. By providing the auxiliary deflection system within this region of the gun, the deflection takes place very near to the beam crossover where the beam has small cross section. This, of course, permits the best shaping and spacing of the deflection electrodes to assure maximum beam detiection sensitivity.

Referring in detail to Fig. 5, there is shown a cathode ray tube having an envelope 12 similar to that described with respect to Fig. l. The envelope l2 consists of a neck portion T14, flared portion 16 and face plate t8. The phosphor screen 29 is deposited on the inner surface of the face plate i8. An electrically conductive coating 24 is provided on the inner surface of the envelope and lextends back into the neck portion 14. The coating 24 is provided with a suitable voltage by means of an exterior terminal 26. An electrically conductive coating 96 is provided on a portion of the outer surface of the flared portion 16.

An electron gun 100 is positioned within the neck portion of substantially conventional design with the exception of the first anode. In Fig. 5, there'is shown a control grid 102, a screen grid 104, a first anode 106, a focusing electrode 108 and a second anode 110.

Referring in detail to Figs. 6 and 7, two closely spaced deflection electrodes 112 and 114 of suitable electrically conductive material are positioned inside of the first anode 106. The deflection electrodes 112 and 114 are fastened to a tubular insulating member 116 by means of fastening member 118. One of the plates 114 is electrically connected to the first anode electrode 106 by means of a sliding spring contact 116. The other plate 112 is connected to the first anode 106 through a resistance, the value of which may be of the megohm order. In Fig. 5 the resistance is provided by means of the layer 122 of resistive material applied inside the tube neck 14 and connecting the conductive coating 24 to the internal conductive layer 124. A fiexible spring contact member 126 connects the deflection plate 112 to the conductive layer 124. Also, in Fig. 5 the conductive coating 124 is annular in shape lwhile the conductive layer 128 required to form the coupling capacitor is applied to the outer surface of the tube in correspondence of the inner conductive layer 124. The inner coating 124 will operate at the D.C. potential of the first anode 106 while the external conductor 128 will operate at a D.C. potential substantially that of ground.

The other plate 114 may be considered as capacitively coupled to ground by means of the external conductive coating 96 on the flared portion 16 of the cathode ray bulb and the internal conductive coating 24. The coating 24 is at the same potential as the first anode 106.

In the operation of the device in the absence of any deflection signals applied to the neck coupling capacitor 124- 128 from source 130, the two deflection plates 112 and 114 are at the same potential as that of the first anode 106 and the electron beam passes undeflected through the deflection plates 112 and 114. When the voltage from the deflection source 130 is applied to the neck coupling capacitor the voltage is transmitted to the deflection plates 112 and 114 through the two capacitors 124-128 and 24-96 which are in effect in series. Since the deflection plate 114 connected to the flared portion coupling capacitor is at a fixed potential all of the alternating current voltage minus the voltage drop across the coupling capacitor is applied to the upper deflection plate 112 which swings above and below the main biasing voltage that of the final anode 106. Because of the small amount of deflection voltage applied, on account of the small deflection amplitude required compared to the voltage of the first anode, there is practically no focusing effect suffered by the beam due to the deflection undergone within the deflection plates. The voltage drop due to the coupling capacitor occurs mainly across the neck coupling capacitor 124-128 since it is of much smaller value than the filter capacitor 24-96. It has been found that this system provides a sensitivity of approximately 20 volts per millimeter for a final anode voltage of 16 kilovolts. For deflection frequencies of the order megacycles per second the width of the conductive coatings 124 and 128 may be made of the order of one centimeter.

In the structure shown in Figs. 7 and 8 the deflection system is substantially a spring package unit. A slot in the cylinder of the first anode 106 permits the insertion of the complete unit within the first anode 106. An aperture disc 132 is also provided which prevents the deflection system from distorting the prefocusing field between the screen grid 104 and the first anode 106.

If a balanced type beam deflection in lieu of the unbalanced deflection is desired it is only necessary to have the deflection electrode 114 connected through a resistance to the first anode 106 and then connected to a similar coupling capacitor similar to the neck coupling capacitor. The coupling capacitor shown on the neck may take many types and shapes and if desired the annular capacitor could be designed into two semi-annular capacitors, one of each would be used for each set of plates.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

1 claim as my invention:

l. A cathode ray tube comprising an envelope and having therein a display screen, an electron gun for generating an electron beam, deflection means for deflecting said electron beam, said defiection means comprising a pair of plates, means for establishing a difference in potential between said plates, said means comprising a voltage source positioned external to said cathode ray tube, and connecting means between said voltage source and said plates, said connecting means comprising a conductive coating on outer surface of said envelope and a corresponding one on the inner surface of said envelope, electrical means connecting said inner surface coating to one of said plates and electrical means connecting said outer surface coating to said voltage source.

2. A cathode ray tube comprising an envelope and having therein an electron sensitive target, means for generatingl an electron beam, electrostatic deflection means for deflecting said electron beam, said electro-static deflection means comprising two plates positioned within said envelope such that the electron beam passes between said plates, a first conductive coating provided on the inner surface of said envelope, electrical means connecting one of said plates to said first conductive coating, a second conductive coating positioned on the outer surface of said envelope and opposite to said first conductive coating to form a capacitor, and means connected to and supplying deflection voltages to said second conductive coating for establishing deflection field between said plates.

3. A cathode ray tube comprising, an envelope and having therein a target, an electron gun for generating an' electron beam to bombard said target, deflection means for deflecting said electron beam to scan a raster on said target, said electron gun comprising, a cathode, a control grid, a screen grid electrode and a first accelerating anode in the order named, auxiliary deflection means positioned within said accelerating anode, said deflection means comprising two plates positioned within said accelerating electrode such that the electron beam passes between said plates, a deflection voltage source, a first electrically conductive coating on the exterior surface of said envelope connected to said voltage source and a second electrically conductive coating on the inner surface connected to one of said plates.

4. A cathode ray tube comprising, an envelope and having therein a target, means for generating an electron beam to bombard said target, deflection means for deflecting said electron beam to scan a raster on said target, said electron beam generating means comprising, a cathode, a control grid, a screen grid electrode and a first accelerating anode in the order named, auxiliary deflection means positioned within said accelerating anode, said deflection means comprising two plates positioned within said accelerating electrode such that the electron beam passes between said plates, means connected to and supplying the deflection voltages to said deflection plates, said means comprising a source of deflection voltage an inner and outer conductive coating provided on the wall of said envelope to form the plates of a capacitor with the glass wall forming the dielectric, circuit means connecting said deection source to said outer coating and means connecting csaid inner coating to one of said deflection plates.

5. A cathode ray tube comprising, an envelope and having therein a target, means for generating an electron beam to bombard said target, deflection means for deecting said electron beam to scan a raster on said target, said electron beam generating means comprising, a cathode, a control grid, a screen grid electrode and a rst accelerating anode in the order named, auxiliary deflection means positioned within said accelerating anode, said deection means comprising two plates positioned within the said accelerating electrode such that the electron beam passes between said plates at a point, rneans` connected to and supplying the deflection voltages to said deflection plates, said means comprising a voltage source coupled through capacitance members to said deliection plate, said capacitance members comprising an inner and outer conductive coating provided on the wall of said envelope positioned directly opposite to form the plates of the capacitance members with the glass wall forming the dielectric.

6. A cathode ray tube comprising, an envelope and having therein a target, means for generating an electron beam to bombard said target, deection means for deecting said electron beam to scan a raster on said target, deflection means positioned to deflect said electron earn, said deflection means comprising two plates, means connnected to and supplying deilection voltages to each said deflection plates, said means comprising a voltage source coupled through a capacitance member to said deflection plate, said capacitance member comprising an inner cuter conductive coating provided on the wall ci said envelope positioned directly opposite to form the plates of the capacitance member with the glass wall forming the dielectric.

No references cited.

Images