US2922074A

US2922074A - Electron beam deflection structure

Info

Publication number: US2922074A
Application number: US610101A
Authority: US
Inventors: Clifford H Moulton
Original assignee: Tektronix Inc
Current assignee: Tektronix Inc
Priority date: 1956-09-17
Filing date: 1956-09-17
Publication date: 1960-01-19
Anticipated expiration: 1977-01-19
Also published as: FR1245296A; DE1156512B; GB928016A

Description

Jan. 19, 1960 c. H. MOULTON ELECTRON BEAM DEFLECTION STRUCTURE Filed Sept. 17, 1956 FIG.2

26 I E 34 M20 1 FIG.3

oo c 0000 0000 DOUG OOQOOGDOOOOOOOOOOOQO INVEN TOR H. MOULTON CLIFFORD FIG. 6 BY ATTORNEYS United States Patent ELECTRON BEAM DEFLECTION STRUCTURE Clifiord H. Moulton, Portland, Oreg., assignor to Tehtronix, Inc., Portland, 0reg., a corporation of Oregon Application September 17, 1956, Serial No. 610,101

11 Claims. (Cl. 315-23) This invention relates to a deflection structure for a cathode ray tube and more particularly to an improved deflection structure in which a signal voltage is caused to travel along a deflection plate forming part of such structure at substantially the same velocity as that of the electrons in the electron beam of the tube so as to extend the frequency range and transient signal response of such tube.

The structure of, the present invention is particularly useful in cathode ray tubes for cathode ray oscilloscopes. Both horizontal and vertical deflection in such tubes is usually of the electrostatic type. That is to say, two pairs of deflection plates at right angles to each other are usually employed with the individual plates of each pair positioned on opposite sides of the beam of electrons. in order to secure adequate deflection of the beam, the deflection plates must have substantial length in the direction of the beam. This places an upper limit upon the frequencies of the signal voltage which can be eflectively impressed upon the vertical deflection plates. Also, since transient signal voltages involve extremely high frequencies, the length of the plates in the direction of electron travel also limits the accuracy of the response of the cathode ray tube to such transient signal voltages.

It will be apparent that maximum deflection for a Signal voltage of given amplitude will occur when the transit time of an electron in the beam along the length of the plates is less than the time corresponding to a half wave length of the signal voltage and that a partial or complete reversal of the deflection voltages on the vertical deflection plates occurs when the transit time of the electron along the plates exceeds the time represented by such half wave. When the transit time becomes equal to the time corresponding to a full wave of the signal voltage, there is substantially equal deflection in opposite directions to produce zero deflection. Such zero deflection also occurs at harmonics of the lowest frequency which produces zero deflection. The magnitude of the deflection is therefore a function of frequency as well as of amplitude of the signal voltage and the effects discussed above become of importance at frequencies for which the transit time of an electron along the deflection plates is a substantial fraction of the period corresponding to a wave length of the signal voltage.

In accordance with the present invention, a deflection structure is provided in which the signal voltage is propagated along a deflection plate in the direction of electron movement at a velocity which is substantially equal to the velocity of the electrons in the beam. Furthermore, the structure provides for suppression of reflections of such signal voltages so that the resulting deflections becomes substantially independent of the frequency of the applied signal voltage and transient response is very materially improved. In a preferred embodiment of the invention, a deflection plate is provided which has a plurality of conducting elements extending transversely of the electron beam. Each of such conducting elements has a surface forming part of the deflection surface of the deflection plate and the conducting elements have their ends connected together alternately on opposite sides of the deflection plate so as to provide a zigzag path for the signal voltage propagated along the plate. The electrical characteristics of the deflection structure utilizing the plate can be made such that a signal travels the length of the plate at the same speed of the electrons in the electron beam and the signal voltage is eflective at all times to produce a deflection force on the electrons in the beam.

The structure of the deflection plate of the present invention lends itself to the provision of a deflection structure which has the same characteristic impedance as an input conductor, such as a coaxial cable. That is to say, the deflection plate of the present invention may be positioned between a pair of conducting plate members so that the deflection plate, in efiect, forms a continuation of the central conductor of the coaxial cable and the conducting plate members, referred to, form an effective continuation of the outer conductor of the coaxial cable. In such a structure, the deflection plate of the present invention is positioned closer to one of such conducting plate members than the other and diverges from such other conducting plate member from the entrance end of the structure for electrons toward the outlet end for such electrons to provide a diverging passage between the deflection plate and such other conducting plate member. The inductance per unit length of the deflection structure containing the deflection plate may be varied by varying the length of the transverse conducting elements and their spacing from each other and the capacitance per unit length can be varied by varying the width of the deflection plate and the associated conducting plate members and also the spacing between the deflection plate and one of the conducting plate members. By properly varying the factors mentioned, the deflection plate structure may be caused to have the characteristic impedance of any of the usual flexible commercial coaxial cables employed in test instruments while, at the same time, providing a velocity of signal voltage propagation along the plate which is within the range of velocities which can be imparted to electrons in the electron beam. Also, the outlet end of the deflection structure can be terminated in the characteristic impedance of the coaxial cable and deflection structure so that reflections of the signal voltage back along the deflection plate and the coaxial cable are substantially eliminated.

It is therefore an object of the present invention to provide an improved deflection structure for cathode ray tubes which has improved frequency and transient response.

Another object of the invention is to provide an improved deflection plate for the cathode ray tubes of oscilloscopes in which a signal voltage is applied at one end of the deflection plate and travels along a zigzag path so as to have a net velocity in the direction of propagation of electrons in the electron beam of the tube which is substantially the same as that of the electrons in such beam.

Another object of the invention is to provide a deflection structure for the beam of a cathode ray tube in which a signal is propagated along a deflection plate in the direction of the electrons in the electron beam of such tube at a rate substantially equal to the velocity of the electrons in the beam and in which the deflection structure has substantially the same characteristic impedance as the connector structure for connecting said plate to a signal source and in which the other end of the deflection structure can be terminated in such characteristic impedance.

A further object of the invention is to provide a deflection plate structure for a cathode ray tube in which a deflection plate is positioned between a pair of conductpedance substantially the same as that of a coaxial cable employed for impressing a signal upon one end of the deflection structure and in which adeflection plate causes the signal voltage pressed thereonto travel in a zigzag path with a net Velocity of the direction of the electron beam substantially equal .to the velocity of the electrons in such beam and in which such structure provides for terminating the other end of the structure at the characteristic impedance of such structure. 2

Other objects and advantages of the invention will ap pear in the following description of a preferred embodiment shown in the attached drawings of which:

Fig. 1 is a diagrammatic vertical cross section of a cathode ray tube embodying the deflection structure of the present invention;

Fig. 2 is a vertical cross section through the deflection structure of the present invention and also diagrammatically showing the electrical connections thereto;

Fig. 3 is a vertical cross section taken on the line 3-3 ofFig.2; i w

Fig. 4 is a plan of the deflection invention with parts broken away; 1

Fig. 5 is a plan of the deflection plate of the present invention in its condition before installation in the deflection plate structure of Figs. 2 to 4; and

Fig. 6 is a side elevation view of one of the insulating supporting plates for the deflection plate of Fig.5.

Referring more particularly to the drawings, the deflection plate structure ltl of the present invention is positioned within the glass envelope 12 of a cathode ray tube having a phosphor coating 14 on the interior of the large end of the envelope 12. The envelope 12 of the tube is provided with a conventional plug 16 having the usual pins 17 for insertion into a socket, the pins 17 furnishing electrical connections to an electron gun 18 which may be a conventional type providing a beam 243 of electrons which first pass between conventional horizontal deflection plates 22 and then through .the vertical deflection structure of the present invention andthereafter impinge upon the screen formed by the phosphor coating 14 and the end of the envelope 12 of the tube. The deflection structure 10 includes a deflection plate 24 positioned between a pair of

conductingplate members

26 and 28 with the deflection plate 24 nearer the conducting plate member 26 than the conducting plate member 28. The electron beam indicated by the line 20 in Fig. 2, enters the deflection structure at the entrance end 3} thereof. It passes between the deflection plate .2 and the conducting plate member 28 and leaves the deflection structure 10 through the outlet end 31 of the deflection structure. During its passage through the deflection structure, the beam 20 is deflected vertically in Fig. 2 by a signal voltage propagated along the deflection plate 24 from the inlet end 34 of the deflection structuretothe outlet end 31.

The preferred form of the deflection plate 24 is most clearly shown in Figs. 4 and 5 Such plate is a thin sheet of conducting material, preferably a spring metal which will withstand bending, for example, a sheet of Phosphor bronze. The deflection structure 10, including both the deflection plate 24 and the

plates

26 and 28, preferably tapers so as to be wider at its outlet end 31 than at its inlet end 30. The deflection plate 24 has a plurality of riarrowslots 32 extending inwardly alternately from opposite edges thereof, theinner ends of the slots overlapping to provide laterially extending conductor elements 33 which extend transversely ofthe beam of electrons 20 and provide a zigzag path for a signal voltage propagated alo ng the deflection plate from the inlet end 30 of the structure to the outlet end thereof. In the plate shown, the conductor elernen ts are all of the same length but the width'of the elements is made progressively smaller and the width of the slots between such elements correspondingly larger from the inlet to the outl l structure of the present of the deflection structure. The portions of the deflection plate 24 between the slots at the opposite edges of the deflection plate terminate in small support tabs 34 and such support tabs engage side support elements 36 in the form of thin sheets of insulating material, for example, mica. The support elements 36 are of substantially the same length as the deflection plate 24 and conducting

plate members

26 and 28 and have formed therein a plurality of rows of small apertures 38 and 39. The row of apertures 38 is positioned between t'wo rows of apertures 3) and nearer one of the rows of apertures 39. The apertures 38'are' spaced to correspond to the tabs 34 on the deflection plate 2.4 and such tabs are inserted into the aper'tures38 of supporting'platesso at each side of the deflection plate 24. The tabs 34 are then bent over as shown in Fig. 3. The two conducting

plate members

26 and 28 are also provided with similar tabs 34 which extend through the apertures 39 in the support element 36 and are bent'over as'shown in Fig. 3. This structure providesa rigid boxlike structure in which the deflection plate 24 is rigidly supported by the support elements 3.6 in properly spaced relationship with the conducting plate members .26 and 28 which are also rigidly supported by the support elements 36. The support elements 36 may be supp'orted'within the envelope 12 of the cathode ray tube in any desired manner. The envelope 12 may be provided with a suitable connector structure 42 adjacent the inlet end '33 of the deflection structure 10 providing for external connection to the deflection plate 24 and conducting

plate members

26 and 28. Also, the envelope 12 may be provided with a connector structure 44 adjacent the outlet end 31 of the defiection structure 10, the connector structures each having a pair of conductors extending through the walls of the envelope 12 and sealed therein in anysuitable or conventional manner.

As indicated in Fig. 2, the central conductor 46 of a coaxial cable 48 may be connected to the deflection plate 24 at the inlet end 30 of the deflection structure and the grounded outer cylindrical conductor 0 may be connccted to the conducting

plate members

26 and 28. At the outlet end 31 of such deflection structure 10, the conducting

plate members

26 and 28 maybe connected together and also preferably to ground. The outlet end of the deflection plate 214 are also connected to the conducting plate members 2t? and 28 through a resistor 52 which preferably has a" value of resistance equal to the characteristic impedance of the coaxial cable The resistor 52 may obviously'be positioned internally of the envelope 12 but the structure shownin Fig. 1 provides for external connection of the defl ron structure to the resistor 52.

The characteristic impedance of the deflection structure 10 may be rnade substantially the same as that of the coaxial cable 48 or other trans mission line employed for supplying a signal voltag e to the inlet end of the deflection structure. That is to say, the characteristic impedance of the deflection structure is a function of its inductance per unit length andits capacitance per unit length, The inductance per unit lerigtli li i y be varied over a substantial range by varying'th'e length and width of the slots 32 and, similarly, the capacitance per unit length may be varied over a considerable'r'a'nge by varying the width of the deflection plate 24 and conducting

plate members

26 and 28 and also varyingthe distance between the deflection plate 24 and the conducting plate member 26. It is entirely possible to provide a deflection structure with a substantially constant characteristic impedance equal to any of the coaxial cables commercially available and conventionally employed test instruments. Furthermore, such characteristic impedances may be obtained while providing a net velocity of signal propagation in the dir ection of the travel of electrons in electron beam 20, which is sr rbstantially the same as the velocity of such electrons. Since the characteristic impedance of the deflection structure is substantially the same as that of the coaxial cable 48 and the outlet end of the deflection structure is terminated in a resistor having a value substantially equal to such characteristic impedance, reflections of signal voltage are substantially eliminated and a signal voltage applied through the coaxial cable 48 to the inlet end of the deflection structure travels along the deflection plate 24 at the same speed as the electrons in the beam 29 and is absorbed by the terminating resistor 52. Vertical deflection in cathode ray oscilloscope tubes having the vertical deflection structure of the present invention becomes substantially independent of frequency from zero frequency to an upper cutoff frequency which may be several hundred megacycles and the response to transient signal voltages is very materially increased.

While the cathode ray tube illustrated is particularly adapted for connection to the output of a single-ended amplifier or other signal source having one side grounded, it is entirely possible to employ two properly spaced and diverging deflection plates 26 connected to the output of a push pull amplifier or other double-ended source of signal voltage so that signal voltages in phase opposition travel along such deflection plates at the same speed as the electrons in the beam being deflected. Such a deflection structure may also have the same characteristic impedance as a balanced line connected to the input end of the deflection structure and the outlet end of such structure may be similarly terminated in its characteristic impedance. Also, it is obvious that the relative positions of the vertical deflection structure and the horizontal deflection plates may be reversed so that the electron beam first passes through the vertical deflection structure and that either, or both, the vertical and horizontal deflection may be produced by deflection structures having a zigzag path for a signal voltage propagated along a deflection plate.

While I have disclosed the preferred embodiment of my invention, it is understood that the details thereof may be varied and that the scope of the invention is to be determined by the following claims.

I claim:

1. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate comprising a plurality of electrical conducting elements extending transversely of said direction and spaced from each other in said direction to provide a series of parallel elements with adjacent ends and narrow slots between said elements, each of said elements having a surface in alignment with a'similar surface on the next adjacent elements to provide said one surface, each of the intermediate elements of said series having one end electrically conductively connected to the adjacent end of the next preceding element in said series and its other end electrically conductively connected to the adjacent end of the next succeeding element in said series to provide a zigzag electrically conductive path along said one surface for signal voltages propagated along said plate in said direction.

2. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being a sheet of electrical conducting material having a plurality of slots spaced from each other in said direction and each extending inwardly from one edge of said plate and terminating short of the opposite edge of said plate to provide a plurality of series connected electrically conducting elements, said elements extending transversely of said direction and being spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from opposite edges of said plate to provide a zigzag electrically continuous conductive path through said elements for signal voltages propagated along said plate in said direction.

3. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being a thin plate of metal having a plurality of slots spaced from each other in said direction and each extending inwardly from one edge of said plate and terminating short of the opposite edge of said plate to provide a plurality of series connected electrically conducting elements extending transversely of said direction and spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from opposite edges of said plate to provide a zigzag electrically continuous conductive path through said elements for signal voltages propagated along said plate in said direction.

4. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being a thin sheet of metal having a greater length than width and tapering in width from a relatively narrow width at one end to a relatively wider width at the other end, said plate having a plurality of slots spaced from each other in said direction and each extending inwardly from one edge of said plate and terminating short of the opposite edge of said plate to provide a plurality of elongated conducting elements extending transversely of said direction and spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from opposite edges of said plate to provide a zigzag conductive path through said elements for signal voltages propagated along said plate in said direction.

5. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being a thin sheet of metal having a greater length than Width and tapering in width from a relatively narrow width at one end to a relatively wider width at the other end, said plate having a plurality of slots spaced from each other in said direction and each extending inwardly from one side edge of said plate and terminating short of the opposite edge of said plate to provide a plurality of elongated conducting elements extending transversely of said direction and spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from opposite edges of said plate to provide a zigzag conductive path through said elements for signal voltages propagated along said plate in said direction, said elements all being of substantially the same length and progressively decreasing in width from said one end to said other end, said slots correspondingly progressively increasing in width from said one end to said other end.

6. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being a sheet of electrical conducting material having a plurality of slots spaced from each other in said direction and each extending inwardly from one edge of said plate and terminating short of the opposite edge of said plate to provide a plurality of electrical conducting elements extending transversely of said direction and spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from opposite edges of said plate to provide electrically conductive connections between said elements alternately at opposite sides of said plate and a zigzag electrically conductive path through said elements for signal voltages propagated along said plate in said direction, the connections between said elements terminating in supporting tabs extending outwardly from the edges of said deflection plate for attachment to a supporting structure.

7. A deflection plate for causing deflection of a beam of electrons traveling in a predetermined direction along one surface of said plate when a signal voltage is applied to said plate, said plate being of thin sheet metal having a plurality of slotsspaced from each other in said direction and each extending inwardly from one edge of said plate and terminating short of the oppositeedge ofsaid plate to provide a plurality ofelectiical conducting elements extendingtransversely of said direction and spaced from each other in said direction by said slots, alternate ones of said slots extending inwardly from oppositeedges of said plate to provide electrically conductiveconnections between said elements alternately at opposite sides of said plate and a electrically conductive zigzag path through said elements for signal voltages propagated along said plate in said direction, the connections between said elements at said ends of said elements terminating in bendable upp ng bs x e din ou ward y rom h edges of s id deflectibn P at fo a ta hmen to a s p porting structure. I

8. A deflection structure for a cathode ray tube having means therein for producing a beam of electrons, said structure comprising a pair of conducting plate members spaced from each other for receiv n said beam between s plates, i Plate m m r .d er ins rqm-fiaeh ethe in the direction 'of electron travel in said beam and providing inlet and outlet ends for said beam, at third plate member positioned between said conducting plate members and nearer one of said conducting plate members than the other so as to be positioned on one side of said beam, said third plate member being constrn cted of a plurality of conducting elements extendingtransversely of said beam and having adjacent ends and being spaced from each other in said direction by narrowslots to provide a series of parallel elements, each of the intermediate elements of said series having one end conductively connected to the adjacent end of the next precedingelement in said series and its other end conductively c nnec ted to the adjacent end of the next succeeding element in 'said series to provide a zigzag conductive paththrough said elements for signal voltages propa ated ai ng said third plate member, and supporting means for said plate members. i i

9. A deflection structure for a cathode ray tube having means therein for producing a beam ofelectrons, said structure comprising a pair of conducting plate members spaced from each other for receiving said' beambetween said plates, said plate members diverging from each other in the direction of electron travel in' said beam and providing inlet and outlet ends for said beam, a thiird' plate member positioned between said'c'onducting plate members and nearer one of said conducting plate members than the other so as to be'positioned on one side of said beam, said third plate member being constructed of a plurality of conducting elements extending transversely of said beam and having adjacent ends and being spaced from each other in said direction by narrow slots to provide a series of parallel elements, each of the intermediate elements of said series having one end conductively connected to the adjacent end of the next preceding element in said series and its other end conductively connected to the adjacent end of the next succeeding element in said series to provide a zigzag conductive path through said elements for signal voltages propagated along said third plate member, and supporting means for said plate members comprising insulating members secured to and extending between the lateral edges of said plate members, said plate members being wider adjacent said outlet end than adjacent said inlet end.

10. A deflection structure for a cathode ray tube having means therein for producing a beam of electrons, said structure comprising a pair of conducting plate members spaced from each other for receiving said beam between said plates, said plate members diverging from each other in the direction of electron travel in said beam and providing inlet and outlet ends for said beam, a third plate member positioned betweeen said conducting plate members and nearer one of ,saidconducting plate members than theother so as rape positioned on one side of said beam, said third plate member being constructed of a plurality of conducting elements extending transversely of said beam having adjacent ends and spaced from each other in said direction by narrow slots to provide a series of parallel elements, each of the intermediate elements of said series having one end conductively connected to the adjacent end of the next preceding element in said series and its other end conductively connected to the adjacent end of the next succeeding element in said series to provide a zigzag conductive path through said element for signal voltages propagated along said third plate member, supporting means for said plate members, conducting means extending to the exterior of said tube from said inlet end to provide for impressing a signal voltage between said third plate member and said conducting plate members and conducting means extending to the exterior of said tube from said outlet end.

11. A deflection system for a cathode ray tube having means therein for producing a beam of electrons, said system including a deflection structure comprising a pair of conducting plate members spaced from each other for receiving said beam between said plates, said plate members diverging from each other in the direction of electron travel in said beam and providing inlet and outlet ends for said beam, a third plate member positioned between said conducting plate members and nearer one of said conducting plate members than the other so as to be positioned on one side of said beam, said third plate member being constructed of a plurality of conducting elements extending transversely of said beam and having adjacent ends and being spaced from each other in said direction by narrow slots to provide a series of parallel elements, each of the intermediate elements of said series having one end conductively connected to the adjacent end of the next preceding element-in said series and its other end conductively connected to the adjacent end of the next succeeding element in said seriesto provide a zigzag conductive path through said elements for signal voltages propagated along said third plate member, supporting means for said plate members, said deflection structure including conducting means extending to the exterior of said tube adjacent said inlet end of said structure to provide for impressing a signal voltage between said third plate member and said conducting plate members, a connector structure for connecting said conducting means to a' source of signal voltage, said deflection structure having substantially the same characteristic impedance as said connector structure, and means for terminating said outlet end of said deflection structure with a value of resistance substantially equal to said characteristic impedance.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,469 Haefi Dec. 15, 1936 2,195,456 Hollmann Apr. 2, 1940 2,293,539 Gray Aug. 18, 1942 2,409,992 Strobel Oct. 22, 1946 2,535,317 Pierce Dec. 26, 1950 2,609,520 Pierce Sept. 2, 1952 2,630,544 Tiley Mar. 3, 1953 2,698,398 Glinzton Dec; 28, 1954 2,708,236 Pierce May 10, 1955 2,827,588 Guenard et a1 Mar. 18, 1958 2,832,001 Adler Apr. 22, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2922 074 Janaary l9 i960 Clifford H Moulton It is hereby cer'ziiiied that error appears in the prineed speciiicaiion oi" the above numbered pateni requiring c-orrec'tion and ihat *ihe said Letters Paizent should; read as correcied belowo Column 5 line 21 for "plates 26" read plates 24 Signed and sealed ihis 5H1 day of July 1960,

(SEAL) Atfiest:

KARL Ho AXLINE Attesting officer ROBERT C. WATSON Commissioner of Patents