US3177395A - Flat cathode ray tube with increased deflection sensitivity - Google Patents

Description

April 6, 1965 M. R. NAMORDI ETAL 3,177,395

FLAT- CATHODE RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY Filed April 4, 1963 6 Sheets-Sheet 1 FIGJ A SOURCE OF v HDRIZONTAL DEFLECTiON INVENTORS' SHGNAL MOOSHI R. NAMORDI,

SVEND E. HAVN,

THEIR ATTORN EY.

April 6, 1965 M. R. NAMORDI ETAL 3,177,395

FLAT CATHODE RAY -TUBE WITH INCREASED DEFLECTION SENSITIVITY Flled Aprll 4, 1963 6 h h et 2 SOURCE OF HORIZONTAL DEFLECTION SIGNAL INVENTORS MOOSHI R. NAMORDI, SVEND E HAVN,

BY W

THEiR ATTORNEY.

A ril 6 1 6 M. R. NAMORDI ETAL q p 9 5 FLAT CATHODE RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY 'Filed April 4, 1963 6. Sheets-Sheet I5 m s.u v L8 xv SOURCE OF VERTICAL DEFLECTION VOLTAGE INVENTORSZ MOOSHI R. NAMORDI, SVEND E. HAVN,

THEIR ATTORNEY.

M. R. NAMORDI ETAL 177 395 Apnl 1965 FLAT CATHODE RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY Filed April 4, 1963 6 Sheets-Sheet 4 I $5; w 11 la ls l \V $5 s E $2 \l, Q n mm S souRcEoF VD 2 VERTICAL DEFLECTION [VOLTAGE THEIR ATTORNEY.

April 6, 1965 Filed April 4, 1963 DEFLECTION VOLTAGE IN KILOVOLTS M. R. NAMORDI ETAL FLAT CATHODE RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY 6 Sheets-Sheet 5 FIGS 2 3 4 INCHES DISTANCE FROM TOP OF TARGET T0 INTERSECTION WITH ELECTRON BEAM INVENTORS MOOSHI R. NAMORDI, SVEND E. HAVN,

THEIR ATTORNEY,

M. R. NAMORDI ETAL Apnl 1965 FLAT CATHODE RAY TUBE WITH INCREASED 3177395 DEFLECTION SENSITIVITY 6 Sheets-Sheet 6 Filed April 4, 1963 SOURCE OF VERTICAL DEFLECTION VOLTAGE INVENTORS MOOSHI R.NAMORDI, SVEND E. HAVN,

BY WJ- M THEIR ATTORNEY.

3,177,395 FLAT CATHODE RAY TUBE WITH INCREASED DEFLECTION SENSITIVITY Mooshi R. Namordi, Syracuse, and Svend E. Havn,

Liverpool, N.Y., assignors to General Electric Company, a corporation of New York Filed Apr. 4,1963, Ser. No. 270,743

. 7 Claims. (Cl. 315-44) This invention relates to an image display system and more particularly to electron beam deflection arrange-' ments for relatively shallow cathode ray tubes.

An image display system of the type to which this invention pertains is shown and described in cope'nding US. patent application Serial No. 141,862, filed September 29, 1961, now Patent No. 3,155,872, which is assignedto the assignee of the present invention. In such a system, a shallow cathode ray tube is employed having a target area positioned on a front or viewing area of the tube and deflection means are spaced from the target area on the inside of an opposite wall of the picture tube. Suitable operating potentials are applied to the target area andto the deflection means for providing a potential gradient therebetween such that when an electron beam is directed into the space which. separates the target area and the deflection means, the beam is deflected from one extremity of the target to an opposite extremity of the target'in a vertical direction.

United States Patent Horizontal deflection is accomplished by entrance of the electron beam into the space between the target area and deflection means along one of a plurality of spaced parallel paths which are substantially parallel to the target area. It is to be understood that the terms horizontal and vertical scanning are used in a relative sense, for convenience, to denote two mutually perpendicular directions of scanning at the viewing screen.

In apparatus of the above character, the excursion of the vertical sweep voltage which must be supplied for vertical scanning is of a high magnitude, and normally is well in excess of a few thousand volts. While low power static, or constant potential, voltages in the order of a few thousand volts or more may be supplied by relatively inexpensive and well-known circuits, a controlled voltage having excursions in this order of magnitude may be economically generated only by resorting to techniques bordering on the outermost fringes of the present stateof-the-art. The problem becomes particularly acute when it is sought to utilize semi-conductorcircuits, and it is highly desirable that such circuits be utilized to more fully exploit the inherent advantages to be gained by utilizing a compact, shallow cathode ray tube. Therefore, it is desirable to minimize the required excursion of the vertishallow cathode ray tube having increased sensitivity to verticaldeflection voltage without requiring the generation of additional alternating current voltages in the system associated therewith.

A further object of this invention is to provide a shallow cathode ray tube having increased sensitivity to vertical deflection voltage without increasing the external dimensions of the tube.

Briefly, in accordance with one form of this invention, the entrance to the throat of the cathode ray tube, or slit through which the collimated electron beam passes after horizontal deflection and prior to entering the space between the target areaand deflection means, is reduced in size to provide an increased voltage gradient for a given diiference in potential between opposed surfaces defining the throat. The initial portion of the throat-defining surface which is disposed toward the front or target side of the tube is then electrically insulated from other conductive surfaces in the tube and maintained at a reduced direct-current potential. The electron transit time through the initial portion of the throat region is thereby increased to provide a longer time for the field produced by the vertical deflection voltage to influence the electron beam. Since the influence of a given electric field upon an electron passing therethrough is related directly to the time during which the electron is in the field, the improved throat of this invention allows the field provided by the vertical deflection voltage to be lessened for a given desired deflection of the electron beam. Thus, the sensitivity of the tube to vertical deflection voltage is increased.

The invention will be explained in more detail in connection with the drawings in which:

FIGURE 1 is a front view of a shallow cathode ray tube;

FIGURE 2 is an external bottom view of FIGURE 1;

FIGURE 3 is a side view of FIGURE 1 at section AA, illustrating the preferred embodiment of this invention; 7

FIGURE 4 is a side view similar to FIGURE 3, illustrating an alternative embodiment of this invention;

FIGURE 5 presents -a graphical comparison of the eflfectiveness of the various embodiments of this invention; and

FIGURE 6 is a side view similar to FIGURE 3, illustrating another alternative embodiment of this invention.

By way of explanation, and not by way of limitation, a specific shallow cathode ray tube is now described to provide a background which highlights and more clearly shows the mode of operation and advantages of the present invention. Referring to the specific form of a shallow cathode ray tube illustrated in FIGURES l and 2, the portion of the tube opposite the bracket I is the image section; the portion opposite the bracket VD, the vertical deflection section; and the portion opposite the bracket HD is the horizontal deflection and collimating section.

As seen in FIGURE 1, an electron gun 2 projects a beam of electrons 3 between pole plates 4, only one of which is visible in the view. The magnetic field set up between pole plates 4 is accomplished in a well-known manner by a yoke 6, deflection coil 8 and source 10 of horizontal deflection signal. The magnetic field causes the beam to scan in a plane parallel to the paper from an extreme position 3' to the other extreme position 3". Magnetic pole plates 12, only one of which is seen in FIGURE 1, are mounted adjacent the outside Wall of the horizontal deflection section HD. Of course, various types of horizontal deflection sections may be used; the one that is the subject matter of the US. patent application Serial No. 141,863 filed September 29, 1961, which is assigned to the assignee of the present invention is preferable. In accordance with this preferred horizontal deflection section, pole plates 12 are joined at their righthand ends by a magnet 14, and they are so shaped that the beam of electrons emerges along parallel vertical paths all in the same plane regardless of where the beam first enters the space between the pole pieces 12. The collimated horizontally scanned beam thus formed enters 69 the throat of the vertical deflection section VD and emerges therefrom to scan target 16.

Various types of image sections may be used; the one that is the subject matter of the US. patent application Serial No. 141,862, filed September 29, 1961, now Patent No. 3,155,872, which is assigned to the assignee of the present invention is preferred. The image section of the shallow cathode ray tube illustrated in FEGURE 3 is in substantial conformity with the teaching of the aforementioned disclosure. Components previously described are indicated by the same numerals. The tube envelope is shown as being made of glass, though other suitable materials may comprise various portions or all of the tube envelope. In the following discussion the term resistive coating or resistive means refers to a means having sufficient resistance so as to not unduly load any source of voltage applied across it, and conductive coating, means or surface refers to means which have an insignificant amount of voltage difference between any two points thereof.

The target to may be comprised of the customary phosphor layer 18 deposited on the inside of the front wall of the glass and an aluminum or other electron permeable metallic coating Zil along its top edge. A resistive coating 24 is formed on the back wall and extends downwardly until it makes an electrical connection at 27 with a conductive lining 25 which extends down along the back wall into the vertical deflection section VD, terminating at the throat thereof. The conductive lining 26 is a means for applying deflection voltage signals to the resistive coating 24 and to the means for deflecting the beam in the lower region of the target 16. A conductor 28 makes electrical contact with the resistive coatings 22 and 24 all along their intersection at the top right corner. In the particular embodiment of a shallow cathode ray tube illustrated, one portion of the throat is defined by a conductive strip 25 which may be an extension of conductive lining 26.

In accordance with the present invention the vertical deflection sensitivity is increased by providing two electrically conductive coatings 21 and 23 in the vertical deflection section of the tube opposite lining 26 and strip 25. Coatings 21 and 23 are electrically isolated and define together one wall of the vertical deflection section. Conductive coating 21 extends from adjacent target 16 toward the entrance to the throat of the vertical deflection section. Preferably, coating 21 is an extension of conductive coating 2% which is coextensive with the target 16. In such event, an appropriate voltage may be supplied to both coatings 2d and 21 through lead 21 which extends through the glass envelope and makes electrical connection with coating 21. Of course, in the example given the lead 21' would be equally effective if connected to coating 29:, such as at the top corner thereof.

In order to provide a suitable operating potential for conductive coating 23, a lead such as 23' may extend through the envelope and make electrical connection with coating 23, as shown. Since the primary object of providing separate coatings 21 and 23 is to increase the transit time of electron beam 3 by allowing coating 23 to have a lesser potential than coating 21, it will be readily apparent that it is not essential that separate leads 21 and 23 be utilized. For example, coating 23 may be maintained at a lesser potential than coating 21 by providing a suitable highly resistive internal connection between coating 21 and coating 23 and providing a suitable connection from coating 23 to an internal point of relatively lower potential or ground inside the tube.

In order to provide maximum vertical deflection sensitivity coating 21 preferably extends from the lower portion of target 16 toward the back of the tube and downwardly in the form of a curve of progressively increasing slope. Also, coating 23, while electrically isolated from coating 21, provides a geometrical extension (i.e. coating 23 is a spatial continuation of coating 21) of the surface .take a variety of forms.

formed by coating 21 and extends downwardly to termimate in a vertically disposed strip 23 which defines with strip 25 the entrance to the throat of the cathode ray tube. The surface defined by coatings 21 and 23 may In a preferred embodiment the surface is generally characterized as a parabola.

By constructing the tube in accordance with the present invention, wherein coatings 21 and 23 are electrically isolated, it is possible to provide two electric fields of relatively independent field strengths in the vertical deflection section. This is achieved by providing voltages of differing magnitudes to the respective coatings.

Generally, for reasons of economy and ease of manufacturing, coating 21 is at the same voltage magnitude as coating 20 and preferably directly connected thereto. Therefore, the voltage supplied to coating 23 is varied to provide the desired voltage difference. By selecting this voltage parameter to be less than the voltage of coating 21, the velocity of the electrons in the throat of the vertical deflection section is lessened. Lessening the electron velocity in the throat causes a longer transit time in this region, allowing a given electric field therein to exert more influenceupon the path of the electron beam. Thus, by providing a longer electron transit time in the throat of the vertical deflection section the required variation in deflection is achieved by an electric field having lesser variations in strength, thereby requiring reduced voltage excursions to produce the field, resulting in a tube of increased sensitivity to vertical deflection voltage.

There are other parameters which may be varied in order to achieve a particular desired result by utilizing the present invention. The width 29 of the entrance to the throat defined by strips 23" and 25 may be varied, and vertical deflection sensitivity is largely determined by this parameter. Decreasing width 29 increases the vertical deflection sensitivity. The relative areas in the vertical deflection section covered by coatings 21 and 23 may be varied. In general, it has been found that increasing the dimension 30, which is the horizontal width, or horizontal projection of coating 23, increases the vertical deflection sensitivity.

The primary criterion which limits selection of the aforementioned parameters in the direction of maximized vertical deflection sensitivity is associated with impingement of electron beam 3 upon coating 23, rather than upon target 16, when it is desired to scan the lower portion of target 16. The tendency of electron beam 3 to impinge upon coating 23 also increases as the aforementioned parameters are varied to achieve maximum vertical deflection sensitivity. It is apparent that a great number of varied combinations and permutations of these parameters may be utilized successfully to achieve improved vertical deflection sensitivity.

Particularly effective results have been obtained with the shallow cathode ray tube illustrated in FIGURE 3 by providing a width 29 equal to inch, by making dimension 30 substantialy equal to width 29 and by providing a potential of seven kilovolts to coating 23 through lead 23'. In such a shallow cathode ray tube, satisfactory vertical scanning was achieved by applying to conductive lining 26 through lead 26', a vertical deflection voltage from source 32 having maximum limits of excursion of 6.1 and 1.8 kilovolts. Cathode ray beam 3 was thereby caused to vary between path 33 and path 31 to effect a complete vertical scan as the voltage from source 32 varied from 6.1 kilovolts to 1.8 kilovolts.

By way of pointing out the improved vertical deflection sensitivity achieved by using the arrangement of the present invention, a shallow cathode ray tube of structure similar to that of FIGURE 3, but having a single equipotential surface extending from coating 20, rather than the separate coatings 21 and 23 of this invention, required a vertical deflection voltage varying between the limits of 8.2 kilovolts and 1.6 kilovolts. The controlled voltage excursion required by the shallow cathode ray tube not constructed in accordance with the present invention was thus 6.6 kilovolts, whereas the controlled voltage excursion which provides similar results using the teaching of this invention is only 4.3 kilovolts, a reduction of over 35%. Such a substantial increase in vertical deflection sensitivity greatly lessens the burden cast upon the generator circuit of source 32.

FIGURE 4 illustrates an alternative embodiment of this invention. For the purpose of showing that the invention is not dependent upon a specific variety of shallow cathode ray tube, the tube shown in FIGURE 4 has been selected different from the tube of FIGURE 3. In particular, the tube of FIGURE 4 features a resistive coating 41 formed on the back wall and extending downwardly to the entrance of the throat of the vertical deflection section where coating 41 is connected to a conductive strip 42. Source 32 of vertical deflection voltage is connected by conductor 42 to conductive strip 42. It will be noted that this structure differs from that of FIGURE 3 wherein resistive coating 24 extended downwardly to cover only a portion of the back wall and was connected at 27 to a conductive lining 26 which extended down the remaining portion of the back wall.

In the embodiment of this invention shown in FIGURE 4, a conductive coating 43 is connected electrically to conductive coating 20 near the lower region of target 16. Preferably, conductive coating 43 is an extension of conductive coating 20. Coating 43 extends from the lower region of target 16 backwardly and downwardly in a curve of progressively increasing slope to a termination adjacent the entrance of the throat of the vertical deflection section. Horizontally spaced from the termination of conductive coating 43 is a conductive strip 44, which together with strip 42 defines the entrance to the throat of the vertical deflection section. The throat width is defined by dimension 45, which is the horizontal distance between strips 44 and 42.

In order to point out the advantages of the two specifically illustrated embodiment of this invention, as well as to provide a comparison of the relative effectiveness of the two specific embodiments, reference is now had to FIGURE 5. In the interest of providing a controlled comparison, the curves of FIGURE 5 are plotted from data obtained using a shallow cathode ray tube of the type shown in FIGURE 4. In the graph of FIGURE 5, deflection voltage in kilovolts is plotted on the ordinate and the position at which the electron beam impinges upon or intersects with the target is measured on the abscissa as distance from the top of the target.

The distance from the top to the bottom of target 16 is four inches, and it will be noted that the abscissa of the graph of FIGURE 5 shows deflection voltages for a complete vertical scan of the target. The difference between the deflection voltage at extremes of each curve is a measure of the vertical deflection sensitivity of, the particular embodiment represented by the curve. Curve 51 shows the deflection voltage sensitivity of a shallow cathode ray tube of the type shown in FIGURE 4, but not incorporating the present invention. Specifically, the

. curves constructed from data obtained by utilizing a continuous conductive strip extending from the bottom of target 16 and describing a generally parabolic curved path downwardly to the entrance of the throat of the vertical deflection section. No conductive strip, such as 44, was used and the width of the entrance to the throat was equal to one-half inch. A vertical deflection voltage having a peak-to-peak excursion of 9.3 kilovolts was required to obtain a complete vertical scan of target 16.

Curve 52 shows the vertical deflection sensitivity of a shallow cathode ray tube constructed as shown in FIG- URE 4, and having a dimension 45, of the entrance to the throat of the vertical deflection section, equal to fourtenths of an inch. However, for curve 52 the potential of strip 44 was made equal to that of conductive coatings 20 and 43, that is to say, ten kilovolts. Curve 52, then, serves primarily to show the substantial increase in vertical deflection sensitivity achieved by narrowing the entrance to the throat. It can be seen that the .vertical deflection voltage excursion, peak-to-peak, is 7.1 kilovolts. By this change alone, the vertical deflection sensitivity has been increased by more than 20% over that of the prior embodiment characterized by curve 51.

Curve 53 is constructed from data taken with a shallow cathode ray tube constructed in accordance with and supplied with the potentials indicated in FIGURE 4. The potential of conductive strip 44 was lowered from ten kilovolts as used in the tube characterized by curve 52, to seven kilovolts. The result may be seen to be a further decrease in the required peak-to-peak excursion of the vertical deflection voltage. As shown, the value is 6.3 kilovolts. The vertical sensitivity is increased more than 30% curve 51.

Curve 54 is plotted from data obtained by utilizing the embodiment of this invention shown in FIGURE 6, wherein a shallow cathode ray tube is used of the type wherein the resistive coating extends completely down the back wall of the image section, as in FIGURE 4. It is apparent that the vertical deflection section of the tube otherwise is similar to that shown in FIGURE 3. The embodiment of FIGURE 6 is more effective in increasing vertical deflection sensitivity than the specific embodiment of this invention shown in FIGURE 4. In particular, the peak-to-peak excursion of the deflection voltage has been reduced to 5.7 kilovolts, almost a 40% decrease in the required deflection voltage excursion 0f the arrangement characterized by curve 51.

' Finally, the dashed curve 55 is shown to provide more complete disclosure of the vertical deflection voltage characteristics of the shallow cathode ray tube structure of FIGURE 3, utilizing the embodiment of this invention shown therein, as discussed before. The improvement in vertical deflection volt age sensitivity indicated by curve 55, when compared to curve 54, results from the more effective tube structure of FIGURE 3, as contrasted to the tube structure of FIGURE 6, and forms no part of the present invention. Specifically, the use of a conductive portion on the back wall of the image section is part of the subject matter of the aforementioned US. patent application Serial No. 141, 862, now Patent No. 3,155,872.

There has been shown and described herein an improved vertical deflection system for a shallow cathode ray tube. The invention has been described in conjunction with two specific embodiments of a shallow cathode ray tube. It will be apparent to those skilled in the .art that the teaching of this invention may be applied to other analogous electron-optic systems to obtain the improved results shown herein. Also, while this invention has been described with reference to two specific embodiments thereof, it should be understood that many modifications and variations of the specific structure disclosed will occur to those skilled in the art, and it is therefore intended that the scopeof this invention be defined solely by reference to the following claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is as follows:

1. In a shallow cathode ray tube system having an electron target, deflection means disposed in spaced relationship opposite said target and defining a space therebetween, a source of electrons for generating an electron beam generally parallel to said target and a vertical deflection section including a throat through which the beam passes prior to entry into the space between said target and deflection means and impinging on said target, the improvement comprising:

(a) first conductive means extending from adjacent said target toward the entrance to the throat of said section and defining one portion of a wall of said section;

above the arrangement characterized by (b) second conductive means, electrically isolated from said first conductive means, and defining a second portion of said wall including the entrance to said throat; and

(0) means arranged to maintain said second conductive means at a lower voltage level than said first conductive means, whereby the transit time of electrons in said throat is increased and the vertical deflection sensitivity of said tube is improved.

2. In a shallow cathode ray tube system having an electron target, deflection means disposed in spaced relationship opposite said target and defining a space, therebetween, a source of electrons for generating an electron beam generally parallel to said target and a vertical deflection section including a throat through which the beam passes prior to entry into the space between said target and deflection means and impinging on said target, the improvement comprising:

(a) first conductive means extending from adjacent said target toward the entrance to the throat of said section and defining the major portion of a wall of said section;

(11) second conductive means, electrically isolated from said first conductive means, and disposed in the entrance to the throat of said section; and

(c) means arranged to maintain said second conductive means at a lower voltage level than said first conductive means, whereby the transit time of electrons in said throat is increased and the vertical deflection sensitivity of said tube is improved.

3. In a cathode ray tube system having an image section comprising an electron target and a conductive electron-permeable coating on said target, deflection means disposed in spaced relationship opposite said coating and defining a space therebetween, a source of electrons for generating an electron beam generally parallel to said target, and a vertical deflection section including a throat through which the electron beam passes prior to entry into the space between said target and coating and impinging on. said target, the improvement comprising:

(a) first conductive means connected to said coating and extending toward the entrance to the throat of said vertical deflection section to define a portion of one wall of said section;

(b) second conductive means electrically isolated from said first conductive means, and extending into the entrance to said throat to define another portion of said wall; and

(0) means arranged to maintain said second conductive means at a lower voltage level than said first conductive means, whereby the transit time of electrons in said throat is increased and the vertical deflection sensitivity of said tube is improved.

4. The cathode ray tube of claim 3 wherein said first conductive means defines a first surfiace of progressively increasing slope extending from said target toward said throat.

5. The cathode ray tube of claim 4 wherein said second conductive means defines a second surface which is a geometrical extension of said first suriiace and which extends to the entrance portion of said throat.

6. The cathode ray tube of claim 5 wherein the horizontal width of said second conductive means is substantially equal to the width of the entrance to said throat.

7. The cathode ray tube of claim 5 wherein said first and second conductive means define a surface having a generally parabolic cross-section.

References Cited by the Examiner UNITED STATES PATENTS DAVID G. REDINBAUGH, Primary Examiner.

Claims (1)

1. IN A SHALLOW CATHODE RAY TUBE SYSTEM HAVING AN ELECTRODE TARGER, DEFLECTION MEANS DISPOSED IN SPACED RELATIONSHIP OPPOSITE SAID TARGET AND DEFINING A SPACE THEREBETWEEN, A SOURCE OF ELECTRONS FOR GENERATING AN ELECTRON BEAM GENERALLY PARALLEL TO SAID TARGET AND A VERTICAL DEFLECTION SECTION INCLUDING A THROAT THROUGH WHICH THE BEAM PASSES PRIOR TO ENTRY INTO THE SPACE BETWEEN SAID TARGET AND DEFLECTION MEANS AND IMPINGING ON SAID TARGER, THE IMPROVEMENT COMPRISING: (A) FIRST CONDUCTIVE MEANS EXTENDING FROM ADJACENT SAID TARGET TOWARD THE ENTRANCE TO THE THROAT OF SAID SECTION AND DEFINING ONE PORTION OF A WALL OF SAID SECTION; (B) SECOND CONDUCTIVE MEANS, ELECTRICALLY ISOLATED FROM SAID FIRST CONDUCTIVE MEANS, AND DEFINING A SECOND PORTION OF SAID WALL INCLUDING THE ENTRANCE TO SAID THROAT; AND (C) MEANS ARRANGED TO MAINTAIN SAID SECOND CONDUCTIVE MEANS AT A LOWER VOLTAGE LEVEL THAN SAID FIRST CONDUCTIVE MEANS, WHEREBY THE TRANSIT TIME OF ELECTRONS IN SAID THROAT IS INCREASED AND THE VERTICAL DEFLECTION SENSITIVITY OF SAID TUBE IS IMPROVED.

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