US3174070A

US3174070A - Electron beam deflection structure with compensation for beam transit time

Info

Publication number: US3174070A
Application number: US131288A
Authority: US
Inventors: Clifford H Moulton
Original assignee: Tektronix Inc
Current assignee: Tektronix Inc
Priority date: 1961-08-14
Filing date: 1961-08-14
Publication date: 1965-03-16
Anticipated expiration: 1982-03-16

Description

March 16, 1965 c. H. MOULTON 3,174,070

ELECTRON BEAM DEFLECTION STRUCTURE WITH COMPENSATION FOR BEAM TRANSIT TIME Filed Aug. 14 1961 CL/F/ORD H. MOULTON BY BUCKHORN, CHEATl-HM BLORE A T TORNE Y5 of the electron beam.

cathode ray tube to such transient signal voltages.

United States Patent ELECTRON BEAM DEFLEQTEON STRUCTURE This invention relates generally to electron discharge devices, and more particularly to an improved electron beam deflection structure for use in such devices in which a deflection signal voltage is caused to travel along a distributed deflection plate forming part of such deflection structure at substantially the same velocity as that of the electrons in the electron beam in order to extend the upper frequency range and transient signal response of such devices.

The apparatus of the present invention is particularly useful in an electron beam display device, such as the cathode ray tube of a cathode ray oscilloscope, which uses electrostatic vertical deflection of the electron beam in such device. This electrostatic deflection is caused by a signal voltage impressed between a pair of electrically conductive plates, each of which is positioned on opposite sides of the electron beam so that they extend a substantial distance in the direction of electron flow in order to secure adequate deflection of such electron beam. The length of the deflection plates places an upper limit upon the frequencies of the signal voltage which can be irnpessed upon the deflection plates for eifective deflection Since transient signal voltages include extremely high frequencies this deflection plate length also limits the accuracy of the response of the For example, when "the transit time required for an electron to traverse the length of the deflection plates becomes equal to the time required for one full cycle of the highest frequency signal voltage it is desired to display, the resulting electrical field between the deflection plates causes substantially equal deflection of the electron in 'opposite directions as it traverses the plate so that the net deflection is zero for such frequency. In fact, inaccurate deflection occurs whenever such transit time becomes a substantial fraction of the time for one cycle of such frequency.

Distributed deflection plates have been suggested for overcoming the above-discussed deficiencies of ordinary "deflection plates, one example being the electron beam deflection structure disclosed in the United States Patent No. 2,922,074, issued January 19, 1960, which shows a zigzag distributed deflection plate and to which reference may be made for a further discussion of the problem involved. The present invention is an improvement on the electron beam deflection structure of the patent referred to and involves replacing part or" the grounded deflection plate on the opposite side of the electron beam from that of the zigzag distributed deflection plate of the tion structure, which characteristic impedance is the same as that of the transmission line conductor connecting the signal voltage source to the deflection structure, in order to prevent reflection of the signal voltage which will interfere with proper deflection of the electron beam. As a result of this improved deflection structure the electron 3,174,070 Fatented Mar. 16, 1965 ice beam display device will more accurately reproduce and represent as a light image on its fluorescent screen, the signal voltage applie to the improved deflection structure. When this signal voltage is a known square Wave pulse having a short rise time, the deflection structure and circuit of the present invention cause a leveling off in the trailing portion of the image of the reproduced signal voltage presented on the fluorescent screen indicating that the top of the reproduced signal has been flattened until it more accurately represents the original applied square wave pulse.

Therefore one object of the present invention is to provide an improved electron beam deflection structure.

Another object of the invention is to provide an improved electron beam deflection structure in an electron beam display device which more accurately reproduces an electrical signal applied to such deflection structure.

Still another object of the present invention is to provide an improved electron beam deflection structure for a cathode ray tube in order to improve the high frequency and transient signal response of such tube.

A further object of the invention is to provide an improved distributed defiection plate for use in the deflection structure of a cathode ray tube so that a signal voltage applied to the distributed deflection plate travels along a zigzag path determined by such plate at a net velocity in the direction or" travel of electrons in the electron beam of such tube which is substantially equal to that of the electrons in such beam and a portion of such applied signal voltage reverses its direction of travel in order to correct the deflection of the electron beam so that the cathode ray tube more accurately reproduces the wave shape of such applied signal voltage.

Still another object of the present invention is to provide an improved deflection structure for an electron beam in a cathode ray tube which results in more accurate high frequency and transient signal voltage deflections and which at the same time forms a transmission line having the same characteristic impedance as that of a transmission line conductor used to connect one end of such deflection structure transmission line to a signal voltage source and in which the other end of such deflection structure transmission line is terminated in such characteristic impedance for preventing signal voltage reflection so that such cathode ray tube more accurately reproduces such signal voltage.

Other objects and advantages of the present invention will appear in the following description of preferred embodiments thereof, shown in the attached drawings, of which:

FIG. 1 is a diagrammatic cross-sectional view of a cathode ray tube having a deflection structure in accordance with the present invention.

FIG. 2 is a partly diagrammatic vertical cross-section through the deflection structure of the present invention schematically showing one embodiment of the electrical circuit connections thereto.

FIG. 3 is a vertical cross-section taken along the line S3 of FIG. 2.

FIG. 4 is a plan view showing portions of a preferred embodiment of the distributed deflection plate used in the deflection structure of the present invention.

FIG. 5 is a fragmentary view similar to a portion of FIG. 2 showing the preferred embodiment of the electrical circuit connections to the deflection structure of FIG. 2.

FIG. 6 illustrates the form of a square wave signal voltage as it is reproduced by a cathode ray tube having a deflection structure made in accordance with the present invention compared to that reproduced by previous deflection structures.

A conventional cathode ray tube having an improved vertical deflection structure made in accordance with the present invention is shown in FIG. 1. This cathode ray tube may include an envelope 1%), of glass or similar insulating material, having a fluorescent screen 12 coated on the inner surface of one end of the envelope and a conventional electron gun 14 supported inside such envelope at the other end thereof for emitting a beam 15 of electrons which impinge upon the fluorescent screen. Between the electron gun 14 and the fluorescent screen 12 are positioned horizontal deflection plates 15 of a conventional type and a vertical deflection structure 18 in accordance with the present invention. A connector plug 19 providing for connections to electrodes in the cathode ray tube is shown mounted on the electron gun end of the envelope it It should be understood that the cathode ray tube shown is merely representative of any conventional cathode ray tube, and that the improved deflection structure of the present invention may be used in other electron discharge devices.

The vertical deflection structure 18 of FIG. 1 is shown in more detail in FIGS. 2 to 4. This deflection structure includes upper and lower electrically

conductive members

20 and 22 diverging from each other and also includes an elongated upper distributed deflection plate section 24 and a short lower distributed deflection plate section 26 having a structure similar to that of upper section 24 and electrically connected thereto by means of a connection 27 at the electron beam outlet end of deflection structure 18. The pair of conducting

members

20 and 22 and the distributed

deflection plate sections

24 and 26 are supported in spaced relationship by two insulator supports 28 in the form of thin sheets of insulating material, such as mica, so that the longer section 24 of the distributed deflection plate is positioned closer to the upper conducting member 20 than the lower conducting member 22, in order to form with lower member 22 and the short section 26, a passageway for the electron beam 15. The short section 26 of the disributed deflection plate is thus placed on the opposite side of the electron beam 15 from long section 26 and forms with the short lower conducting member 22 a twopiece element approximately equal in length to the upper member 20. The inlet end of the deflection structure 18 may be connected to a source of signal voltage by a coaxial cable 30 so that the inlet ends of the pair of conducting

members

20 and 22 are connected to the grounded outer cylindrical conductor 32 of the coaxial cable and the inlet end of the long section 26 of the distributed deflection plate is connected to the inner central conductor 34 of the coaxial cable.

The distributed deflection plate 2446 is so positioned with respect to conducting

members

20 and 22 that the deflection structure 18 forms a transmission line which is an extension of coaxial cable 50 and has substantially the same characteristic impedance as that of the coaxial cable. When the transmission line including the deflection structure is terminated in its characteristic impedance, such as by two parallel resistors 36, reflections of signal voltages applied to the deflection structure 18 through coaxial cable 30 are thereby prevented. The resistors 36 are connected between the two adjacent ends of the short distributed deflection plate section 26 and the short lower conducting member 22. Also the electron beam outlet end of member 22 may be connected to ground along with the outlet end of upper conducting member 20.

As shown in FIG. 4, the preferred embodiment of the distributed deflection plate 24 is a thin fiat sheet of eleclrically conducting material such as spring metal, for example, phosphor bronze which will withstand the bending involved in manufacture assembly. This distributed deflection plate may be formed in the zigzag tapered shape of FIG. 4 which is produced by a plurality of narrow slots 38 extending inwardly from the opposite edges of the tapered metal sheet in an alternating manner. The inner edges of the slots 38 overlap to provide laterally extending conductor elements 40 which may be positioned transverse to the electron beam 15 in order to provide an electrically conductive zigzag path for propagating signal voltages along the distributed deflection plate 24 so that the velocity of the signal voltage in the direction of travel of the electron beam 15 is substantially equal to the velocity of electrons in such electron beam.

The distributed deflection plate 24 is provided with a plurality of small supporting tabs 42 along the outer edges of conducting elements 40 which are inserted into rows of holes provided in insulator supports 28 and bent over to hold the distributed deflection plate between the insulating supports as shown in FIG. 3. The outer edges of unslotted conducting members 2t) and 22 are also provided with small supporting tabs similar to those on distributed deflection plate 24 so that they, too, may be held by supports 28 upon insertion of these tabs into the holes in such supports and bending such tabs. The resulting deflection structure 13 is a rigid box-like structure in which the pair of conducting members 29 and 22 and the distributed deflection plate sections 24- and 26 are rigidly supported in proper space relationship. The insulator supports 28 may be held within the envelope 1d of the cathode-ray tube in any suitable manner, and may be connected to external circuits by suitable connectors 44 through the side of the envelope 10.

The improved operation of the deflection structure of the present invention over that shown in US. Patent No. 2,922,074, previously referred to, is best described by referring to FIG. 6 which shows the image of a square wave pulse of signal voltage as it is reproduced by a cathode ray tube having a deflection structure made in accordance with the present invention compared to that reproduced by the deflection structure of the patent referred to above. As shown in FIG. 6, the wave shape produced by the deflection structure of such patent is shown at 56 as a solid line. It should be noted that the top of this wave shape is not flat, but has a small, sharp, overshoot pea; 52 at its leading edge and a gradually increasing amplitude reaching a maximum value 54 near its trailing edge. If the characteristic impedance termination in the deflection structure of the patent is omitted so that the outlet end of that deflection structure is open-circuited, the resulting wave shape is that shown by dashed curve 56 which is obviously undesirable because it does not accurately reproduce the applied square wave. If, on the other hand, the characteristic impedance termination of the patent is short-circuited, the resulting Wave form follows the dotted curve 58 which is obviously also undesirable. Also in both cases substantially the total signal is reflected back through the transmission line. By partly short-circuiting the characteristic impedance termination of the patent, for example by making it of a less resistance than the characteristic impedance of the transmission line, it is possible to produce a substantially flat top curve by leveling off the maximum 54-. However, such a partial shortcircuit causes an undesirable partial reflection of the signal voltage back through the transmission line formed by the deflection structure.

It has been found that the improved deflection structure shown in FIG. 2 of the present invention will produce a wave shape such as indicated by the dash-dot curve 60 in FIG. 6 thus eliminating the maximum 54 and providing an essentially flat top wave except for the small peak 52 resulting in more accurately reproducing the applied square wave.

An explanation of the improved Wave shape is that the signal voltage impressed across the input end of the deflection structure results in a deflection voltage which travels forwardly along such structure at a rate determined by the length of the zigzag path provided by the plate section 24 and then continues across the connection 27 and rearwardly along the deflection structure again at a rate determined by the length of the zigzag path provided by the plate section 26 to the terminating resistors 36 where the signal energy is largely absorbed. The rearwardly traveling deflection voltage cancels out that part of the original deflection of the electron beam which produced the gradual increase to the maximum 54, indicated on the screen of the cathode ray tube.

FIG. shows another embodiment of the invention in which a time delay circuit including an inductor 62, a capacitor 64 and two parallel resistors 66 is employed to provide a further phase shift between the applied and the reflected signal voltage. The outlet end of the distributed deflection plate section 24 is partially terminated by the capacitor 64 connected in series with parallel resistors 66 to the outlet end of grounded upper conducting member 20, and a delaying inductor 62 is connected between the outlet ends of

sections

24 and 26. The signal voltage is delayed slightly by inductor 62 before reaching the termination resistors 36 and if the time constant of the circuit consisting of capacitor 64 and resistors 66 is equal to the time constant of the circuit including inductor 62 and termination resistors 36, reflections back along the deflection structure and coaxial cable are minimized. This results in an even more level curve portion 60 than that obtained by the connection 27 of FIG. 2, but no attempt has been made to show that vertical deflection of the electron beam in a cathode ray oscilloscope having a cathode ray tube with the improved vertical deflection structure of the present invention becomes substantially independent of frequency over a Wide range from zero to an upper cut oil frequency of many hundred megacycles, and that the reproduced signal voltage seen on the fluorescent screen of cathode ray tube more accurately represents the wave shape of the signal voltage applied to the vertical deflection structure. Also, it should be'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 vertical and horizontal deflection of the electron beam may be produced by a deflection struc ture in accordance with the present invention. In addition, the shape of the distributed deflection plate may be ent invention may be varied without departing from the I spirit of the invention and it is not intended to limit the scope of the invention to the preceeding detailed description, but that scope is to be determined only by the following claims.

I claim: 1. An electron beam deflection structure comprising: first means positioned on one side of said beam and providing an electrically conductive path for propagating signal voltages along said structure at substantially the same velocity as electrons in said beam and in the direction of travel of said electrons, second means positioned on the other side of said beam and providing an electrically conductive path for propagating said signal voltages along said structure in a direction generally parallel to said beam, and connection means for thereafter delivering said signal voltages from said first means to said second means for propagation along said structure by said second means thereby modifying the deflection of said electron beam so that it more accurately repro- 6 duces the waveform of the applied signal voltages.

2. An electron bean deflection structure comprising:

first means positioned on one side of said beam and providing an electrically conductive path for propagating signal voltages along said structure at substantially the same velocity as electrons in said electron beam and in the direction of travel of said electrons,

second means positioned on the other side of said beam and providing an electrically conductive path tor propagating said signal voltages along said structure in a direction generally parallel to said beam,

and connection means for thereafter delivering said signal voltages from said first means to said second means for propagation along said structure in a direction opposite to the direction of travel of said electrons.

3. A distributed deflection structure for deflecting a beam of electrons when a signal voltage is applied to said structure, said structure comprising:

a first section positioned on one side of said beam and extending substantially parallel to said beam and having means to provide an electrically conductive zi zag path along a surface of said first section for propagating signal voltages along said structure at substantially the same velocity as the electrons in said beam and in the direction or" travel or" said electrons,

a second section providing a similar zigzag path and being positioned on the other side of said electron beam so that a surface of said second section extends in spaced relationship to said surface of said first section for a distance less than the total length of said first section,

and electrical connection means for said first and second sections so that the signal voltage after it has traveled along said first section is caused to reverse direction and to travel along said second section in a direction opposite to that of the electrons in said beam to thereby modify the deflection of said electron beam so that it more accurately reproduces the waveform of the applied signal voltage.

4. An electron beam deflection structure comprising:

a pair of spaced, electrically conductive members positioned on opposite sides of said beam,

means including a distributed deflection plate section positioned between said pair of members and spaced therefrom, and positioned nearer to one of said members than the other and on one side of said electron beam,

said means providing an electrically conductive path for propagating signal voltages along said deflection structure with a velocity substantially equal to that of the electrons in said beam and in the direction of travel of said electrons,

and second means including a distributed deflection plate section providing an electrically conductive path for thereafter propagating said signal voltages along said structure in a direction opposite to that of said electron beam.

5. A deflection structure for causing deflection of a beam of electrons traveling in a predetermined direction through said structure when a signal voltage is applied to said deflection structure, said structure comprising:

a pair of electrically conductive members spaced from each other to provide a path therebetween for said beam, and diverging in the direction of travel of the electrons in said beam,

a distributed deflection plate section positioned between said pair of members and spaced therefrom and positioned nearer to one of said members than the other and on one side of said beam,

said section including means to provide an electrically conductive zigzag path for propagating signal voltages along said structure with a velocity substantially 4 equal to that of the electrons in said beam and in the direction of travel of said electrons,

and a second distributed deflection plate section having means to provide an eiectrically conductive zigzag path for propagating signal voltages along said structure at substantially said velocity in a direction generally parallel to said beam,

said second section being positioned on the other side of said beam and in alignment with the other conducting member.

6. An electron beam deflection apparatus comprising:

a deflection structure including;

a pair of spaced, electrically conductive members,

a first distributed deflection plate section positioned between said pair of members and spaced therefrom and positioned nearer to one of said members than the other and on one side of said beam,

said distributed deflection plate section including means to provide an electrically conductive path for propagating signal voltages along said deflection structure with a velocity substantially equal to that of the electrons in said beam and in the direction of travel of said electrons,

and a second distributed deflection plate section connected to said first and having means to provide an electrically conductive path for propagating said signal voltages along said structure at substantially said velocity and in a direction generally opposite to that of said electrons,

and a termination impedance connected between said second means and the other of said members,

said impedance being substantially equal to the characteristic impedance of said deflection structure in order to prevent reflection of said signal voltages.

7. A deflection apparatus for causing deflection of a beam of electrons when a signal voltage is applied to said apparatus, said apparatus comprising:

a deflection structure providing a path therethrough for said beam of electrons including;

a pair of electrically conductive members spaced from each other to provide a path therebetween for said beam, and diverging in the direction of travel of electrons in said beam,

said distributed deflection plate section having means to provide an electrically conductive zigzag path for propagating signal voltages along said distributed deflection plate with a velocity substantially equal to that of said electrons and in the direction of travel of said electrons,

and a second distributed deflection plate section having means to provide an electrically conductive zigzag path for propagating signal voltages along said struc ture at substantially said velocity in a direction generally parallel to said beam,

said second section being positioned on the other side of the electron beam from said first section and in alignment with said other member,

a termination impedance substantially equal to the characteristic impedance of said deflection structure connected between said second section and the other of said members,

a delay impedance connected between said first section and said second section,

and a compensation impedance connected between said first section and said one member and having a time constant equal to that of said delay impedance and said termination impedance.

8. A deflection apparatus for causing deflection of a beam of electrons when a signal voltage is applied to said apparatus, said apparatus comprising:

a deflection structure providing a path therethrough for said beam of electrons and including;

a pair of electrically conducting members spaced from each other to provide a path therebetween for said beam, and diverging in the direction of travel of the electrons in said beam,

a distributed deflection plate section positioned between said pair of members and spaced therefrom and positioned nearer to one of said members than the other and on the one side of said beam,

and a second distributed deflection plate section having means to provide an electrically conductive zigzag path for propagating signal voltages along said structure at substantially said velocity in a direction generally parallel to said beam,

said second section being positioned on the other side of the electron beam from said first section and in alignment with the other of said members,

a termination impedance including two parallel resistors and substantially equal to the characteristic impedance of said deflection structure connected between said second section and said other member,

a delay impedance including an inductor connected between said first section and said second section,

and a compensation impedance including two parallel resistors in series with a capacitor connected between said first section and said one member and having a time constant equal to that of said delay impedance and said termination impedance.

9. An electron beam display device comprising:

an envelope,

a fluorescent screen supported inside one end of said envelope,

a cathode supported inside said envelope at the other end thereof,

means supported in said envelope for focusing, accelerating and deflecting an electron beam emitted by said cathode,

said means including an electron beam deflection structure having a pair of spaced, electrically conductive members,

a distributed deflection plate section positioned between said conducting plate members and spaced therefrom and positioned nearer to one of said members than the other and on one side of said electron beam,

said distributed plate section having means to provide an electrically conductive path for propagating signal voltages along said deflection structure with a velocity substantially equal to that of the electrons in said beam and in the direction of travel of said electrons,

and a second distributed deflection plate section having means to provide an electrically conductive path for propagating said signal voltages along said structure at substantially said velocity and in a direction opposite to that of said electrons,

10. A cathode ray tube comprising:

an envelope,

a fluorescent screen coated on the inner surface of one end of said envelope,

a cathode supported inside said envelope at the other end thereof,

means supported in said envelope for focusing, accelerating and deflecting the electron beam emitted by said cathode,

said means including a deflection structure for causing the deflection of a beam of electrons traveling in a predetermined direction through said structure when a signal voltage is applied to said deflection structure,

said structure having a pair of electrically conductive members spaced from each other to provide a path therebetween for said beam, and diverging in the direction of electron travel of the electrons in said beam,

said distributed deflection plate section having means to provide an electrically conductive zigzag path for propagating signal voltages along said structure with a velocity substantially equal to that of said electrons and in the direction of travel of said electrons,

said second section positioned on the other side of the electron beam from said first section and in alignment with said other of said conducting members,

References Cited in the file of this patent UNITED STATES PATENTS 2,064,469 Haeff Dec. 15, 1936 2,535,317 Pierce Dec. 26, 1950 2,922,074 Moulton Jan. 19, 1960

Claims

1. AN ELECTRON BEAM DEFLECTION STRUCTURE COMPRISING: FIRST MEANS POSITIONED ON ONE SIDE OF SAID BEAM AND PROVIDING AN ELECTRICALLY CONDUCTIVE PATH FOR PROPAGATING SIGNAL VOLTAGES ALONG SAID STRUCTURE AT SUBSTANTIALLY THE SAME VELOCITY AS ELECTRONS IN SAID BEAM AND IN THE DIRECTION OF TRAVEL OF SAID ELECTRONS, SECOND MEANS POSITIONED ON THE OTHER SIDE OF SAID BEAM AND PROVIDING AN ELECTRICALLY CONDUCTIVE PATH FOR PROPAGATING SAID SIGNAL VOLTAGES ALONG SAID STRUCTURE IN A DIRECTION GENERALLY PARALLEL TO SAID BEAM, AND CONNECTION MEANS FOR THEREAFTER DELIVERING SAID SIGNAL VOLTAGES FROM SAID FIRST SAID TO SAID SECOND MEANS FOR PROPAGATION ALONG SAID STRUCTURE BY SAID SECOND MEANS THEREBY MODIFYING THE DEFLECTION OF SAID ELECTRON BEAM SO THAT IT MORE ACCURATELY REPRODUCES THE WAVEFORM OF THE APPLIED SIGNAL VOALTAGES.