US2978608A

US2978608A - Character synthesizing tube

Info

Publication number: US2978608A
Application number: US844144A
Authority: US
Inventors: Jr John E Gaffney
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1956-12-24
Filing date: 1959-10-02
Publication date: 1961-04-04
Anticipated expiration: 1978-04-04

Description

April 4, 1961 GAFFNEY, JR 2,978,608

CHARACTER SYNTHESIZING TUBE Original Filed Dec. 24. 1956 5 Sheets-Sheet 1 INVENTOR JOHN E. GAFFNEYMR- hi5 ATTORNEYS V April 1961 J. E. GAFFNEY, JR 2,978,608

CHARACTER SYNTHESIZING TUBE Original Filed Dec. 24. 1956 5 Sheets-Sheet 2 0 '00. 06.06 0000 9000: G I. 00.00 C... 0....

INVENTOR JOHN E. GAFFNEY,JR.

BY cum M MMA K 5% W his ATTORNEYS April 1961 J. E. GAFFNEY, JR 2,978,608

CHARACTER SYNTHESIZING TUBE Original Filed Dec. 24. 1956 5 Sheets-Sheet 3 w my 40/ INVENTOR'K. JOHN E. GAFFNEYf,;JR.

BY W M hi5 ATTORNEYS.

April 4, 1961 J. E. GAFFNEY, JR

CHARACTER SYNTHESIZING TUBE Original Filed Dec. 24. 1956 5 Sheets-Sheet 4 mDm his ATTORNEYS April 4, 1961 GAFFNEY, JR 2,978,608

CHARACTER SYNTHESIZING TUBE Original Filed Dec. 24. 1956 5 Sheets-Sheet 5 VERTICAL POSITION RESET BEAM UNBLANK (APERTURE) HORIZONTAL POSITION CLOCK INVENTOR JOHN E. GAFFNEY, JR,

/ his ATTg Unite 2,978,608 I CHARACTER SYNTHESIZING TUBE John E. Galtney, In, Poughlreepsie, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Claims. (Cl. 315-22) This invention generally relates to indicating devices and, more particularly, to a cathode ray tube for synthesizing characters on a display screen. This application is a continuation of and was copending with my earlier filed application, Serial No. 630,386, filed December 24, 1956.

In one prior indicator of the cathode ray tube type, one of a whole roster of selectable characters must be chosen by a set of selecting deflection coils. All but one of these possible character forming beams are off the axis of the tube, thereby necessitating the application of specialized focusing fields to counteract the radial nonuniformity of the electric accelerating field produced between the cathode and the anode of the tube due to the use of a plurality of divergent beams. Both the focusing and the selecting deflection fields present technical difiiculties which are overcome by the present invention.

Another disadvantage which is overcome by the pres ent invention is the effect of the nonhomogeneity of the electric or magnetic deflection fields acting upon the character representing beam of the cathode ray tube. In prior devices, the various beams emanate from different geographical locations on the cathode and, therefore, the effect of the electric or magnetic deflection fields on all possible characters is not uniform.

Accordingly, it is one of the objects of the present invention to provide a character synthesizing tube in which any one of the selected characters originates from the same on-axis position.

Another object is to provide a character synthesizing tube of the above character with either a plurality of memory elements in which information is to be stored, or a fluorescent screen on which characters are visible, or both;

A further object of the present invention is to provide a character representing device in which the electric or magnetic deflection fields have the same efiect on each character produced;

A still further object of the present invention is to provide a device for visually producing predetermined characters in response to an electric signal in which the disadvantages of heretofore known devices are overcome.

These and other objects are accomplished in the character synthesizing tube of the present invention by pro-. viding a cathode ray tube with a plurality of independent electron beams capable of being focused upon an incremental area on the tube screen. Obviously, the electron beams may be obtained by using separate electron guns but, for practical purposes, a single electron gun is preferred.

To obtain the desired separate electron beams from a single electron gun, the emitter or cathode is. constructed to present a relatively small lateral dimension andany desired length. In other words, the cathode is much longer than it is Wide. Such a cathode ray beam gen erator provides a single beam which is then subdivided into a plurality of vertically spaced-apart smaller inde res 2 I pendent beams in a lineal array acted upon separately. by an electron lens.

The control of each electron beam is provided by. suitable circuitry external to the tube. By sweeping the beam array across the screen area alloted to each character, and at the same time cutting predetermined electron beams on and ofl, a desired character may. be produced on the screen. Although the inventive char: acter synthesizing tube is unique in its ability to scan the screen in line sequence, discrete positions on the screen may be selected by the application of suitable control voltages or, indeed, any. desired sequence and any desired speed may be selected. The character syn thesizing tube is useful, therefore, in selecting any one of many memory elements in which information is stored and retained. In such an application the conventional luminescent screen may be replaced by a memory screen made up of many memory elements from which information may be selected at random due to the fact that the beams are off until a selected time on the sweep cycle, or the beam may be left on to pass in turn from'one to the other of the memory elements in a predetermine order.

Other objects and advantages of the present invention will become apparent to one skilled in the art to which the invention pertains from the following detailed description of the preferred embodiment thereof described with respect to the accompanying drawings, in whichi Figure 1 is a perspective view, greatly enlarged, illustrating one embodiment of a cathode ray beam genera tor in accordance with the present invention;

Figure 2 is a perspective view, partially in section, of a cathode ray tube incorporating the invention and illustrating the position of the beam generator, and partially in magnified section to illustrate the illumination of selected spots on the inner face of the cathode ray tube screen to represent selected characters; Figure 3 is a perspective view partially in section 0 the cathode ray tube of Figure 2 taken from another angle;

Figure 4 is a view in perspective, greatly enlarged, of another cathode ray beam generator; 1

Figure 5 is a circuit diagram illustrating one arrangement of components to operate the character synthesiz ing tube of the present invention;

Figure 5A is a partial schematic diagram of a magnetic core matrix'illustrated in Figure 5; and

Figure 6 is a timing chart illustrating the relative timing of control pulses and voltages in the operation of the present invention. Y

Referring to the perspective view of Figure 1, a typ' ical embodiment of the present invention provides a cathode ray beam generator for developing any desired number of vertically spaced-apart electron beams to be focused in a vertical array on an incremental area of a cathode ray tube screen. Included in the generator is a long narrow cathode 10 emitting electrons in a fanshaped beam as determined by side-deflecting plates 11 and12'. A conventional arrangement for indirectly heating the cathode 10 may be utilized. It has been found that for optimum beam density the plates 11 and 12 should be at an angle of approximately With each other.

To subdivide the single electron beam, a curved anode plate 13 provided with a terminal 13a is positioned between the flared ends of the deflecting plates 11 and 12. Since one embodiment of the cathode ray beam generator utilizes seven separate electron beams, seven vertically spaced-apart apertures 15, rectangular in shape, for example, are provided along the central axis of the an,- odeplate 13. Of course, the apertures may be circular ,or of any other desired configuration. The electron beam passing through each aperture in the anode plate 13 is shielded from interacting field effects of the electron, beams passing through adjacent apertures by interconnected electrical conductors 14 adjacent to the apertures, such conductors preferably being maintained at ground potential. In thi manner, seven separate and distinct electron beamsare provided which may be controlled independently of each other. Of course, seven separate electron emitters may be substituted for the above arrangement although such a system would be more com plex and expensive than the above-described structure.

Considering next the control of the seven electron beams, each beam is either on or off. That is, any predetermined electron beam either passes through a grid structure or electron lens to a screen, described hereinafter, or it is cut oif entirely. To achieve the latter effect, the electron beam may be defocused'by suitable elements. Another arrangement to out 01f the beam involves the provision of'an electron mirror effect to reflect the electrons entirely. 'An electron mirror acts identically upon an electron beam as does its optical counter-' part on light. This is accomplished by providing a pofocused on the tube screen at a point determined by a tential distribution which decelerates and reverses the di I section of flow of the impinging beam of electrons.

The beam defocusing type of control, on the other hand, achieves the desired control by'defocusingthe beam sufficiently with an electron lens along the axis of the beam path. This simply causes the beam to be imaged at some spot beyond the aperture plane, causing anapparent disappearance of the spot from the display screen.

. For the purposes of the present invention, however, the

electron mirror type of'beam control is preferred although it is understood that other systems may be used.

The primary prerequisite to successful electron beam control is to provide isolation of each beam from the others in order that it may be turned on'or off without interfering with the other beams. That is, the field effect of one set of beam controlelectrodes as well as the space charge effect produced by the electron beam upon which it acts must be minimized. To this end,

elongated grids

20 and 21, forming an electron lens, utilize supporting dielectric material, indicated generally by the numerals 22 and 23, to provide a plurality of

rectangular apertures

24 and 25, respectively, preferably equal in number to the cathode apertures 15. Permanently interconnected

electrical conductors

26 and 27 on the

grids

20 and 21, respectively, form closed loops about each of the apertures 24 and to isolate the electron beams passing therethrough from any appreciable interacting field eifects, their effect being identical with that of the electrodes 14.

The grid control elements comprise electrically conductive facings 28 supported by the dielectric material in the

apertures

24 and 25. Each of the facings 28 receives a control voltage from a terminal 29 extending through an opening 30, separate electrical conductors (not shown) connecting each terminal 29 to separate pins 41 (Figure 2) extending from the base of a cathode ray tube 40. Thus, only seven connections for each of the two grids are required. Through these simplified connections, a control voltage may be maintained independently at each of the grid apertures. In certain instances, all of the terminals of one of the grids may be tied to a common potential.

If desired, each of the apertures may contain a fine Wire mesh at the potential of the conductive facings 28. -It will be understood that such wire mesh may be used with or without the facing 28. In addition, the grid control elements may be self-supporting in which event the dielectric structure may be eliminated.

Under normal operation of the tube, the control elements 28 at the

apertures

24 and 25 are maintained at such potentials that the beam formed by the related cathode aperture 15 is in an off condition. When an appropriate signal is received at related terminals 41, P

separate beam deflection circuit to be described hereinafter. More particularly, if the electron mirror effect is used, the facings 28 in the grid 21 may be maintained at a fixed positive'potential of,'f0r example, 200 volts, and the facings 28 in the grid 20 may be held normally at a negative 200 volt potential. By applying a positive 150 volt potential to selected facings 28 on the grid 20, selected beams may be turned on. This demonstrates the electron mirror effect, the surface of the mirror being between the grids20 and 21.

With the provision of seven vertically spaced-apart I electron beams, each being capable of separate and independent control, the next requirement for the operation of the present character synthesizing tube is that the seven beams, as a unit, be deflected horizontally and vertically to a predetermined position on the tube screen.

Referring now to Figure 2 of the drawings, the cathode 10, the beam forming plate 13 and the

grids

20 and 21 are shown in operating position within an evacuated container 42 of the cathode ray tube 40. It should be understood that the size of the cathode, anode and grid structures has been greatly exaggerated in Figures 2 and 3 in the interests of clarity. 2 4 and 25 in the

grids

20 and 21 may be on the order of .010 to .030 inch square, for example. Electrical connections (not shown) are provided between each ofthe separate components within the evacuated container 42 and the pins 41, only a representative number of which are shown for simplicity. As such connections are well known in the art, a detailed description thereof is deemed unnecessary here- 1 A second anode 43 (Figure 3) may be provided in the envelope 42 in accordance with conventional cathode raytube construction in order to accelerate the elechorizontal deflection plates 45 and by vertical deflection plates 46, such-beams thereby impinging on desired areas of a screen 47. A conventional phosphorescent coating may be provided on the screen. If desired, a storage type screen may also be utilized in which event the information may be read from the screen by scanning it.

A magnetic field may be provided by a coil 43 (Figure 3) to reduce the beam column height by converging the beams, as shown in Figure 3, to reduce the character size. In other instances such a magnetic field may be employed to increase the column height by diverging the electron beams, if desired.

Another arrangement to provide a plurality of independent electrons beams spaced apart in a lineal array is shown in Figure 4. In this structure, a cathode 100, indirectly heated in a conventional manner, is flanked by a pair of side bafiles 101. Grids 102 spaced from and extending in front of the cathode are supported by strips 103, separate grids being energized through terminals 102:: to control electrons emitted from separate areas of the cathode. A finc wire mesh may be provided across the opening defined by the wires of each individual grid, if desired. It will be understood that the grid-cathode structure has been greatly enlarged, the distance between horizontal grid wires being on the order of .015

tial of this anode by a connection to a terminal 105a thereon.

The theory of operation of this beam forming structure In practice, the'apertures I willbe-understoodwhenitis compared to a conventional three element vacuum tube. Thus, each of the grids 102 forms with an area of the cathode and the anode 105 a triode controlled by appropriately varying the cathodegrid potential gradient. Furthermore, by setting the potential on the anode 105 sufliciently low, the generation of an electron beam is prevented regardless of the gridcathode potential.

To illustrate the manner in which the single column electron beam array is deflected, a suitable voltage applied between the horizontal deflection plates 45 and between the vertical deflection plates 46'directs the array, for example, to a column 50 on the screen 47, as shown by the magnified section of Figure 2. Solid dots indicate an on beam and blank circles indicate the spot where that electron beam would have been focused had it not been blanked oil.

In column 50, all seven of the vertically spaced-apart electron beams are on as indicated by the seven solid 'dots on the screen 47. By changing the voltage between the horizontal deflection plates 45 while holding the voltage constant between the vertical deflection plates 46, the single column of seven electron beams is deflected to the next column position 51. Coincident with the change in horizontal position of the beams, the second, third, fifth and sixth electron beams, counting downwardly from the top, are cut off, as indicated by the small blank circles in the column 51. Thus, only the top, middle and bottom beams impinge upon the screen. The seven beams are continuously stepped across the screen 47 as predetermined beams are cut on" and off at a rapid rate to form the selected characters. In the example shown in Figure 2 of the drawings, the letter E is printed at the first character position with the letters S, T, and a partially formed E, following the T. In Figure 3, the letters formed on the screen 47 appear from the front with the electron beam array shown in a position to complete the second letter B.

The timing of the beam array shift is shown in the timing chart of Figure 6 which will be explained in greater detail hereinafter. As the voltage on the vertical deflection plates 46 is held constant, the horizontal position voltage is varied in a sequential step fashion to move the single column electron beam array across the selected character position.

For the purpose of furtherillustrating the invention,

'it will be assumed that the cathode ray tube 40 has sufficient area on its display screen 47 for an array of 128 characters across by 64 characters down. Such an array has been chosen arbitrarily for use in the proposed character synthesizing tube although the invention is not limited to any particular array or number of characters. Since each character position on this tube screen is composed of five vertical columns of seven spots (spaces at drawings. Considering first the operation of that portion of the block diagram enclosed by broken lines and labeled horizontal display position selector, during the time intervals T7 and T of the machine cycle preceding the generation and display of the next character, a computer (not shown) sends into a register 52 a binary coded positioning signal which corresponds to one position out "of the l 28 horizontal positions on the tube face on which it is desired that the next character appear.

The binary coded positioning signal is transformed by a digital-tol analog' converter 53 to provide a voltage on a line 54 that will index the selected character. at column 2 of. a given character space, column 1 actually comprising space between adjacent characters.

Another digital-to-analog converter 55 produces a horizontal position step voltage, indicated in the time sequence chart of Figure 6, to step the electron beam array across the tube face 47. The converter 55 does this incrementally since it steps the output voltage when pulses are fed to it at times T to T The stepped voltage is added to the horizontal positioning voltage from the line 54 by an analog voltage adder 56, the composite voltage being fed into a horizontal deflection amplifier 57 which, in turn, energizes the plates 45 to move the beam array horizontally, step by step, across the selected character position.

To determine on which line the characters are to be formed, a predetermined vertical deflection of the elec tron beam array must be obtained. In response tosuit able binary code signals from the computer, a register 58 positioned in a unit termed a vertical-display position selector produces output signals if such coded signals are received coincidentally with time T pulses. A digital-toanalog converter 59 receives the binary signals from the register 58 and generates a voltage providing the desired vertical deflection for one of the 64 selectable rows of characters. The vertical deflection voltage is amplified by a suitable amplifier 6t) and applied to the vertical deflection plates 46 of the tube.

At the same time that horizontal and vertical positioning signals are being applied to the deflection plates, predetermined ones of the seven electron beam are unblanked (turned on) at selected intervals. The control of the unblanking is initiated by a binary coded character signal from a character selection bus leading from the computer. This coded signal is applied to an appropriate decoding tree 61 which is composed of magnetic cores or diodes, in a unit labeled character decoder. The decoding tree 61 selects and applies a voltage pulse to one of sixty four, for example, character selection output wires 62 corresponding to the coded character from the computer. v

The wires 62 selectively couple energizing potentials to a core matrix 63 which generates coded output signals on seven output conductors 64 corresponding to the seven vertical electron beam positions. For example, the core matrix 63 may take the form of the circuit shown in Figure 5A. Five columns of seven high remanence magnetic cores 63a form the matrix, the output conductors 64 being connected to individual windings on the cores in corresponding rows. A second connection to the core windings has been omitted since it merely leads to a suitable potential. Five input conductors 65 receiving pulses at times T to T as shown in Figure 5, energize windings on corresponding columns of the magnetic cores 63a.

The manner of connecting a single character selection output conductor 62, representing the letter E, has been illustrated in Figure 5A. Thus, the conductor 62 leads to windings on the cores 63a corresponding to the dots that must be illuminated to form an E, namely the top, middle and bottom rows and the left column.

In operation, a potential is maintained on the E conductor 62 while that character position is scanned. However, the cores 63a will not be switched by such potential alone since corresponding windings will not furnish the required switching magnetomotive force. Energization of the T conductor 65 by a pulse at time T adds an additional coercive force to the left column of cores, this being sufficient to switch them and provide output voltages output lines will supply potentials to the grid facings 28 in Figure 1 or the grids 102 in Figure 4.

While the electron beam array is being moved from one character position to another, or to a new row, a Suitable blanking potential is applied to a control electrode by a conductor 68. For example, the control electrode may be the plate 13 in Figure l or the anode 105 in Figure 4. This potential is normally furnished by an unblanked amplifier 69. A set-reset circuit 70, which may comprise a trigger circuit stable in two conditions, supplies a continuous D.-C. voltage at level 1 to the amplifier 69 in response to a pulse at time T to unblank the tube 40. A further pulse received by the trigger 70 at time T turns off the D.-C. voltage and restores the circuit to its condition so that a blanking signal is carried on the line 68. The interval during which the tube is blanked in this manner for reset is indicated in Figure 6 by the legend Reset.

At the same time that a signal representing a particular character to be printed on the screen is fed into the decoding tree 61, the same signal is fed into an OR circuit 71 in a machine start unit, as shown in Figure 5. The OR" circuit 71 is of the type which provides an output signal if there is a pulse on any one of the input leads. The output of the OR circuit is fed into an AND circuit 72 also receiving pulses from a clock 73 synchronized with the computer. The AND circuit 72 provides an output pulse at each instant that pulses from the clock 73 and from the OR circuit 71 coincide. Each output pulse from the AND circuit 72 causes a clock pulse counter 74, which may comprise a ring counter, to advance one step and supply pulses on the outputs T to T at the corresponding times. These pulses are supplied to various units in the systems, as described above, so that the indicator circuits are synchronized with the computer.

It will be evident from the foregoing that the indicator circuits incorporating the inventive cathode ray tube 40 may be substituted for a conventional printer to display the output of a computer. A high speed camera may be synchronized with the computer to obtain information from the tube screen 47. If a storage type screen 47 is used, it may be scanned to provide signals representative of the output information.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiment, it will be understood that various omissions, substitutions and changes in the form and details of the device illustrated, and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

I claim:

1. A cathode ray tube indicator comprising an evacuated envelope enclosing an electron beam generator providing a plurality of independent beams spaced apart in a lineal array, a screen to receive the electron beam array, deflection means between the beam generator and the screen to control the position of the electron beam array on the screen, and grid means adjacent the electron beam generator to turn selected ones of said plurality of electron beams on and off" as they are deflected along the screen to form selected characters thereon.

2. A cathode ray tube indicator comprising an evacuated envelope enclosing cathode means to provide an electron beam, electrode means in the path of the beam to subdivide it into a plurality of independent beams 'spaced apart in a lineal array, a screen to receive the "electron beam array, deflection means between the electrode means and the screen to control the position of the electron beam array on the screen, and grid means adjacent the electron beam generator to turn selected ones of said plurality of electron beams on and off as they are deflected along the screen to form selected characters thereon.

3. .A cathode 'ray tube indicator comprising an evacuated envelope enclosing a cathode source of electrons, beam forming electrode means adjacent to said cathode to provide a plurality of independent electron beams spaced apart in a lineal array, a screen to receive the electron beam array, deflection means between the beam forming electrode means and the screen to control the position of the electron beam array on the screen, grid means in the path of said plurality of electron beams to turn selected ones on and off as they are deflected along the screen to form selected characters thereon.

4. A cathode ray tube indicator comprising an evacuated envelope enclosing a cathode source of electrons,v

beam forming electrode means adjacent to said cathode to provide a plurality of independent electron beams spaced apart in a lineal array, a screen to receive the electron beam array, deflection means between the beam forming electrode means and the screen to control the position of the electron beam array on the screen, grid means adjacent to the beam forming electrode means including two electrodes each formed by a lineal array of apertures, first electrically conductive elements adjacent to each of the apertures to shield the plurality of electron beams one from the other and minimize interacting field effects, second electrically conductive elements defining the apertures adapted to receive beam control potentials to turn selected ones of said plurality of electron beams on and off as they are deflected along the screen to form selected characters thereon.

5. A device as defined in claim 4 in which said two grid electrodes are formed of a dielectric material providing said apertures, the second electrically conductive element comprising a facing on the interior of said apertures.

6. A device as defined in claim 4 in which the second electrically conductive elements include a wire mesh in said apertures.

7. A cathode ray tube indicator comprising an evacuated envelope enclosing a cathode source of electrons, beam forming electrode means adjacent to said cathode to provide a plurality of independent electron beams spaced apart in a lineal array, a screen to receive the electron beam array, deflection means between the beam forming electrode means and the screen to control the position of the electron beam array on the screen, grid means including two electrodes each formed by a lineal array of apertures, first electrically conductive elements adjacent to each of the apertures to shield the plurality of electron beams one from the other and minimize interacting field effects, second electrically conductive elements defining the apertures adapted to receive beam control potentials, and terminal means to connect each of said second conductive elements to external control circuits for providing said control potentials to turn selectct ones of said plurality of electron beams on and oil as they are deflected across the screen to form selected characters thereon.

8. A device as defined in claim 7 in which said two grid electrodes are formed of a dielectric material providing said apertures, the second electrically conductive element comprising a facing on the interior of said apertures.

9. A device as defined in claim 7 in which the second electrically conductive elements include a wire mesh in said apertures.

10. A cathode ray tube indicator comprising an evacuated envelope enclosing an elongated cathode source of electrons, beam forming electrode means adjacent to said cathode to direct said electrons into a fan-shaped beam, plate means interposed across the fan-shaped beam to divide it into a plurality of independent electron beams spaced apart in a lineal array, a screen to receive the electron beam array, deflection means between the cathode source and the screen to control the position of the electron beam array on the screen, and grid means adjacent to the plate means to turn selected ones of said plurality of electron beams .on" and ofi" .as they are deflected across the screen to form selected characters thereon.

11. A cathode ray tube indicator comprising an evacu-v a lineal array, a screen to receive the electron beam array, deflection means between the cathode source and the screen to control the position of the electron beam array on the screen, grid means adjacent to the plate means including two electrodes each formed by a lineal array of apertures, first electrically conductive elements adjacent to each of the apertures to shield the plurality of electron beams one from the other and minimize interacting field efiects, second electrically conductive elements defining the apertures adapted to receive beam control potentials to turn selected ones of said plurality of electron beams on and oif as they are deflected along the screen to form selected characters thereon.

12. A cathode ray tube indicator comprising an evacuated envelope enclosing a cathode source of electrons, a plurality of grids adjacent to said cathode source, said grids controlling the emission of electrons from a plurality of areas on the cathode to provide a plurality of independent electron beams spaced apart in a lineal array, a plate positioned in front of the grids in the path of the electron beams having an aperture elongated in the direction of the array to limit the width of the electron beam array, a screen to receive the electron beam array, de-

flection means between the plate and the screen to control stepped across the screen 10 the position of the electron beam array on the screen, the grids adapted to receive beam control potentials to turn selected ones of said plurality of electron beams on and off as they are deflected along the screen to form selected characters thereon.

13. A device as defined in claim 12, in which elec trically conductive elements are positioned between the grids to shield the plurality of electron beams one from the other and minimize interacting field efifects.

14. A method of producing selected characters on a cathode ray tube screen comprising the steps of providing a plurality of spaced apart electron beams in a lineal array, stepping the beam array across the screen, and turning selected ones of the beams on and off as they are stepped across the screen to form selected characters thereon.

15. A method of producing selected characters on a cathode ray tube screen comprising the steps of providing a supply of electrons, dividing the electrons into a plurality of spaced-apart electron beams in a lineal array, stepping the beam array across the screen, and turning selected ones of the beams on and off as they are to form selected characters thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,691,156 Saltz et al. Oct. 5, 1954 2,734,187 Rajchman Feb. 7, 1956 2,741,722 Shields Apr. 10, 1956 2,760,108

Wilson et a1. Aug. 21, 1956