US2776388A

US2776388A - Electron-discharge device

Info

Publication number: US2776388A
Application number: US354171A
Authority: US
Inventors: Adler Robert
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1953-05-11
Filing date: 1953-05-11
Publication date: 1957-01-01
Anticipated expiration: 1974-01-01

Description

Jan. 1, 1957 R. ADLER 2,776,388

ELECTRON-DISCHARGE DEVICE Filed May 11, 1953 ROBERT ADLER INVENTOR.

,l-ns ATTORNEY.-

United States Patent ELECTRON-DISCHARGE DEVICE Robert Adler, Northfield, Ill., assignor to Zenith Radio Corporation, a corporation of Illinois Application May 11, 1953, Serial No. 354,171

Claims. (0 313-72) This invention relates to electron-discharge devices and more particularly to such devices of the beam deflection type.

The advantages of beam deflection tubes for certain applications have long been known in the art. For example, such tubes are inherently well adapted for balanced operation and are particularly well suited for applications in which direct-current coupling is required. However, beam deflection tubes have not been extensively used because of several considerations with respect to which grid-controlled tubes have presented superior operating characteristics. Specifically, grid-controlled tubes have generally been considered capable of providing materially greater space current than beam deflection tubes, although this limitation has largely been overcome by the provision of sheet-beam deflection tubes. It has also been possible to achieve materially greater transconductances with grid control than with electrostatic deflection; however, there are many applications in which the characteristically lower transconductance of beam deflection tubes is not to be considered a disadvantage.

In spite of the progress which has been made in the development of beam deflection tubes, optimum utilization of their desirable characteristics has not been achieved. In particular, the advantage of inherent adaptation to balanced operation is largely counterbalanced by a tendency to draw excessive beam current to the deflectors in response to the application of large signal voltages, thus undesirably loading the input circuit. This tendency may be reduced by increasing the spacing between the deflectors, but this compromise is accompanied by a decrease in the already relatively low transconductance of the input system. Moreover, the deflector bias required to focus the beam on the output electrode system is also decreased as the deflector spacing is increased, with the result that direct-current coupling to the positively biased output electrodes of the preceding stage is no longer feasible.

. It is, therefore a primary object of the present invention to provide a new and improved beam deflection tube in which stable transconductance is achieved over a wide range of positive bias potentials applied to the input deflectors.

It is a further object'of the invention to provide a new and improved beam deflection tube capable of accommodating relatively large input signal voltages without drawing excessive deflector current, and to achieve this improved operating characteristic while maintaining the transconductance of the deflector system substantially unchanged or even somewhat increased.

It is a corollary object of the invention to achieve these objectives with a structure adapted to mass production on an economical basis and without materially complicating the structure of known beam deflection tubes.

The beam deflection tube constructed in accordance with the invention comprises means including a cathode for projecting a sheet-like electron beam of substantially rectangular cross-section toward an output electrode system including at least two anodes. A pair of electrostatic-deflection electrodes are disposed between the beam projecting means and the output electrode system, flanking the normal or undeflected path of the beam. The tube further comprises an accelerating electrode, spaced from the deflection-control electrodes by a distance less than the spacing between the deflection-control elem trodes, in the form of a conductive plate having an elongated slot in register with the beam, together with a screen grid, directly connected to the accelerating electrode and including a plurality of spaced conductive elements effectively covering the slot in the accelerating electrode, to provide a screened aperture system which cooperates with the deflection-control electrodes to form a projection lens for focusing the electron beam on the output electrode system.

The features of the present invention which are believed to be novel are set forth with particularity inthe appended claims. The invention, together with further objects and advantages thereof, may best be understood,-.-

however, by reference to the following description taken in connection with the accompanying drawing, in the. several figures of which like reference numerals indicate.

like elements, and in which: 7

Figure 1 is a cross-sectional view of a novel beam defiection tube constructed in accordance with the invention; and

Figure 2 is a schematic circuit diagram of a system in,

which the tube of Figure 1 is particularly useful.

ln Figure l, a new and improved beam deflection tubeconstructed in accordance with the present invention comprises an electron-emissive cathode 10 provided withan.

internal indirect heater element 11, a slotted focusing electrode 12, and an accelerating electrode 13 formed of,

a conductive plate and provided with a central aperture or slot 14 opposite the emissive surface of cathode 10. Cathode 10, focusing electrode 12, and accelerating electrode 13 constitute an electron gun for projecting a sheet-like electron beam of substantially rectangular cross-section along a predetermined center plane 15 bisecting the aperture or slot 14 of accelerating electrode 13 and the emissive. surface of cathode 10. The tube further comprises an out-l put electrode system including a pair of

anodes

16 and 17 preferably, although not essentially, disposed on opposite sides of the center plane 15 and in a common transverse plane. Alternative output electrode systems, as for example an apertured anode followed by a conductive plate for collecting electrons passing through the aperture of the first anode, may be employed, as is well known in the art. The tube also comprises a pair of electrostatic-

deflection electrodes

18 and 19, flanking the tube center plane 15 and disposed intermediate accelerating electrode 13 and

output electrode system

16, 17.

Deflectors

18 and 19 may advantageously be formed as simple parallel rods or wires, as illustrated in the drawing, or may comprise opposed deflection plates or the like as is well known in the art, The tube may also advantageously comprise a box-like suppressor electrode system 20 including a suppressor vane 21 extending along the center plane 15 between

output anodes

16 and 17 in a manner which is also well known in the art.

That portion of the tube thus far described may be of entirely conventional construction. However, in accordance with the present invention, the tube further comprises a screen grid 22 constructed of a plurality of spaced conductive elements effectively covering slot 14 of accelerating electrode 13. Preferably, screen grid 22 is disposed intermediate accelerating electrode 13 and deflection-

control electrodes

18 and 19, although other constructions in which the screen grid is placed in the plane of the accelerator slot or even closely adjacent slot 14 on the side of accelerator 13 facing focusing electrode 12 may be employed. Screen grid 22 is preferably formed of a plurality of spaced parallel wires extending in a direction transverse to the tube center plane 15 and eflectively covering aperture 14 of accelerating electrode 13 to form a screened aperture system which cooperates with

deflectors

18 and 19 to constitute a projection lens for focusing the electron beam on or in the plane of

output electrode system

16, 17. The tube may also advantageously comprise a. second screen grid 23 between

deflectors

18, 19 and

output anodes

16, 17;

screen grids

22 and 23 may conveniently be formed as a single winding of continuous wire supported by a pair of conventional grid support posts or wires 24, with the

deflectors

18 and 19 encompassed by the winding constituting screen grids 22. and 23. Preferably, the screen grid winding is formed in the manner illustrated-in the drawing, with the two efiective screen grid portions-22 and 23 of substantially planarconfiguration intersectingthe beam axis at right angles.

All of the electrodes have a substantial longitudinal extent in a direction perpendicularto the plane of the drawing to provide a high-currentsheetbeam. The entire electrode system may be mounted in any suitable manner within a glass or metal envelope 25, which is then evacuated and gettered in accordance with well known practices in the art.

In operation, when suitable-operating potentials are applied to the respective electrodes of the device of Figure 1, a sheet-like electron beam of substantially rectangular cross-section is projected through slot- 14 of accelerating electrode 13. Upon the application of alternating signal voltages to electrostatic-deflection electrodes 18-and 19, the beam is deflected'back and forth across the tube center plane 15 to energize suitable load circuits associated with the

respective anodes

16 and 17. In these more general aspects, the operation of the tube of Figure 1 is entirely conventional.

Conventional beam deflection tubes, not provided with screen grid 22, have exhibited an undesirable tendency to draw excessive input deflector current in response to the application of large input signal voltages. This tendency is readily understandable when it is considered that, when the input signal amplitude is increased, the deflection amplitude may also be increased to the point where the electron beam grazes or actually impinges on the deflection-control electrodes. Thus, the input deflectors may draw beam current and produce an undesirable loading eflect on the associated input circuit. In order to reduce this tendency to draw deflector current, the spacing between the input deflectors may be increased, to permit a larger deflection amplitude without causing the beam to graze the deflection-control electrodes. However, in conventional beam deflection tubes, any'increase in the spacing between the deflectors is necessarily accompanied by a decrease in the deflection sensitivity and the input transconductance. More importantly, this expedient also results in a decrease in the positive bias potential required for the deflectors to insure focus of the beam in the plane of the output electrode system. In practice, it has been found that in order to accommodate input signal voltages of the magnitude oftendesired, it has been necessary to increase the separation between the deflectors to such an extent that the deflector potential required for proper focusing drops to cathode potential or even lower. In such a case, it is no longer possible to employ directcurrent coupling from the output anodes of ,a preceding stage, which are normally maintained at positive operating potentials.

When screen grid 22 is provided between accelerator 13 and

deflectors

18, 19, in accordance with the present invention, screen grid 22 and slotted accelerator 13 to gether constitute a screened aperture system which cooperates with

deflectors

18 and 19 to form a projection lens for focusing the beam in the plane of the output system. Since the conductive elements of screen grid 22 intersect the center plane of the sheet beam at right angles, the only ripples or disturbances in the equipotential surface presented by the screen grid occur in a plane trans verse to that in which beam focus is required. The refractive power of the electron lens constituted by the deflectors and the preceding accelerating system is increased, and the bias potential required to be applied to the deflectors to achieve focusing in the plane of the output electrode system, for a given deflector spacing, is also increased in the positive direction. Consequently, the separation between the deflectors may be increased to a greater extent in order to reduce the tendency to draw excessive deflector current without causing the deflector potential required for proper beam focus to be reduced belowthe average potential of the output electrodes of a preceding stage. Moreover, it has been discovered that when screen grid 22 is provided in accordance with the present invention, such increase in the separation between the input deflectors not only entails no reduction in deflection sensitivity or input transconductance, but is actually accompanied by-a small though noticeable increase in transconductance.

The second screen grid 23 and the suppressor system 20, -21- are preferably included "to provide pentode-type operating characteristics. Second screen grid 23 provides a post-deflection accelerating field which is particularly' advantageous for the purpose of directing the deflcted electrons to the output anode'on the same side of the center plane 15 on which they leave the transverse deflection field established by

deflectors

18 and 19 and for the additional purpose of further increasing the positive deflector potential required for beam focus and further reducing the amount of beam current drawn by the deflectors, while the

suppressor system

20, 21 prevents the generation of spurious output signal components attributable to secondary electron emission.

The beam deflection tube of the present invention is particularly, although not exclusively, useful in a system of the type illustrated schematically in Figure 2, in which a pair of

triode amplifiers

30 and 31 are employed to provide a balanced input signal to a beam deflection tube 32 of the type illustrated in Figure 1. The cathodes of

triodes

30 and 31 are connected to ground, and the

anodes

33 and 34 are connected to a suitable source of positive unidirectional operating potential, conventionally designated B+, through respective load resistors 35' and 36. The

control grids

37 and 38 of

triodes

30 and 31 are returned to ground through

respective signal sources

39 and 40. In order to utilize to advantage all of the beneficial attributes of the invention,

signal sources

39 and 40 are preferably of the type having essential directcurrent components and may constitute, for example, photosensitive cells whose outputs are to be compared.

Anodes

33 and 34 of

triodes

30 and 31 are directly connected todeflectors 18 and 19 respectively of beam deflection tube 32. Cathode 10, focusing electrode 12, and suppressor 21 may be directly connected to ground, and accelerating electrode 13 and

screen grids

22 and 23 may be connected together and to B+.

Anodes

16 and 17 are connected to B+ through respective output resistors 4Laud 42. The use of the common symbol B-lto indicate positive operating potential connections is not to be construed as requiring all connections so designated to be returned to a single operating potential, but it is contemplated that the positive operating potentials applied to the several points of the circuit designated B-l 'may be of either the'same-or different values, depending on the requirements-of thercircuit.

In operation, respective single-ended signals having significant direct-current components are applied from

sources

39 and 40 to control

grids

37 and 38 of mode closed in the'abovc-identified copending applicationsmay have the following characteristic dimensions:

amplifiers

30 and 31. As previously indicated, these sig- Inches nals may be derived from a pair of photosensitive cells Spacing from cathode 10 to focusing electrode 12-- .005 the outputs of which are to be compared. If the illu- 5 Width of slot m focus ng electrode 12 .030 mination of the two photocells is different, the average Spacing between focusing electrode 12 and accelvoltage drops appearing across

load resistors

35 and 36 crating electrode 13 .056 are correspondingly difierent, with the magnitude of the Width of slot 14 .030 difference indicating the desired output diflerence read- Distance from accelerating electrode 13 to screen ing. The output voltages developed across resistors 35 10 grid 22 .012 and 36 are applied to

deflectors

18 and 19 respectively Diameter of

deflectors

18 and 19 .040 of beam deflection tube 32 to establish a transverse de- Separation between deflectors 18 and 19-. .060 fiection field proportional to the voltage difference be- Di tance from screen grid 22 to screen grid 23 .140

tween anodes

33 and 34. The division of beam current Distance from screen grid 23 to centers of deflectors between

anodes

33 and 34 is proportioned to the deflec- 15 18 and 19---- .113 tion field between

deflectors

18 and 19, and correspond- DiSiP-HCS from scffiin grid 23 10 anodes 16 and ing amPlified output voltages F acress All of the sheet metal electrodes were constructed of put resistors 41 and 42. The deviation of either of these Stock and extended for a direction perpendicular voltages from the anode Source i may be to the plane of the drawing for a distance of 5 inch. ployed as an indication of the desired difference read- 20

Screen grids

22 and 23 were wound as a single formed solenoidal winding of .004 diameter wire having a pitch ,Through the 9 l of Screen gnd m accordance of 32 turns per inch. The entire electrode assembly was with the present f the sepfuatlon i deflectors mounted in a conventional miniature tube envelope be- 13 and 19 P be Increased 9 avmd 39 deflector tween a pair of mica spacers in a conventional manner. current whlle at same retammgihe advan' 25 A tube constructed in this manner delivered a total antages of P and balanced Opel-anon: More ode current of 12 milliamperes at an accelerating volt- Over the reducnon transconductance occasloned by age of 250 volts, and exhibited the following transconthe increased separation between

deflectors

18 and 19 ductances: required to avoid excessive deflector current is smaller than the increase effected by the addition of screen grid 220 mlcromhos at a deflector Potent"ll of 22, so that a net increase in the input transconductance Volt? i achieved 320 mrcromhos at a deflector D. C. potent al of +75 volts h i i f Figure 2 i mflrely an illustrative 420 mrcromhos at a deflector D. C. potentialof volts ample f one system in which a tube constructed in 270 rn'lcromhos at a deflector D. C. potential of 0 volts cordance with the invention may be employed and the 35 160 mlcromhos at a deflector D. C. potential of 35 volts benefits and advantages of invention achiellcd- With a balanced A. C. voltage of 120 volts peak-to-peak ever, beam deflection tubes constructed in accordance li to the d fl t 13 and voltage at least with the invention y also be p y t0 advantage four times in excess of the A. C. voltage required to as VideO amplifiers PW!er amplifiers in television effect complete transfer of the beam between anodes ceivefs or the like, in y Other circuit system 40 16 and 17the total D. C. current drawn by deflectors P y g m deflecfitm mbes- The invention is of

P

18 and 19 remained 5O microamperes or less throughiiculal' advantage in connection 'With the! new and out the range of D. C. deflector potentials from -35 proved beam deflection tubes and synchronizing control lt to +150 1 systems described and claimed in one or more of the Thus the invention provides a new and improved beam following copending applications: deflection tube affording the advantages of stable trans Inventor Serial No. Filing Date Title John G. Spmoklpn 246,768 September 15, 1951...- Television Receiver.

259,063- November 30, 1951- 0.-.. Robert Adler.

263,737, 'now Patent 323,752, now Patent December 28, 1951--- 2 November 17, 1952. November 17, 1952.

December 3, 1952 January 12, 1953 Do. Television Receiver Scanning System. Television Receiver.

In the systems described in the above-mentioned copending applications, a beam deflection tube is employed as an element in the feedback loop of a scanning oscillator, with a large A. C. signal appearing between its deflectors and with automatic frequency control being effected by varying the D. C. potential difference between the same deflectors in accordance with the output voltage from a balanced phase detector. The stable trausconductance over a wide range of D. C. deflector voltages and the low beam current drawn by the deflectors, even at large peak-to-peak input signals, achieved by the tube of the present invention are of especial advantage in connection with a system of this type.

Merely by way of illustration and in no sense by way of limitation, a beam deflection tube constructed in acconductance over a wide range of direct voltage bias conditions for the input deflectors, low deflector current, and increased transccnductance and deflection sensitivity. The tube is of general utility in any system in which the use of beam deflection tubes is feasible, being of particular advantage in environments requiring or permitting balanced operation and/or direct-current coupling.

While a particular embodiment of the present invention has been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An electron-discharge device of the beam-deflection cordance with the invention for use in the systems distype comprising: an electron gun including an elongated apropos eteetron emissi'v'e cathode a a an accelerating electrode having a naribwslot parallel to said cathode for projecting along a predetermined center plane a sheetlike electron beam of snstantiauy rectangular cross-section; a pair of deflection=control electrodes flanking said center plane and spaced from each other by a distance greater than the spacing between said accelerating electrode and said deflection-controlelectrodes; an output system including a pair of output electrodes; and a screen grid directly connected to said accelerating electrode and including a plurality of spaced conductive elements effectively covering said slot to provide a screened aperture system which, together with said deflection-control electrodes, constitutes a projection lens for focusing said electron beam on said output system.

2. An electron-discharge device of the bCalli-dCfiBCtiCn type comprising: an electron gun including an elongated electron emissive cathode and an accelerating electrode having a narrow slot parallel to said cathode for projecting along a predetermined center plane a sheetlike electron beam of substantially rectangular cross-section; a pair of defiecti'on control electrodes flanking said center plane and spaced from each other by a distance greater than the spacing between said accelerating electrode and said deflection'cont'rol electrodes; an output system including a pair'of output electrodes; and a screen grid, directly connected to said accelerating electrode and including a plurality of spaced conductive elements extending transversely across said center plane, interposed between said accelerating electrode and said deflection-control electrodes.

3. An electron-discharge device of the beam-deflection type comprising: an electron gun including an elongated electron-emissive cathode and an accelerating electrode having a narrow slot parallel to said cathode for projecting along a predetermined center plane a sheetlike electron beam of substantially rectangular cross-section; a pair of deflection-control electrodes flanking said center plane and spaced from each other by a distance greater than the spacing between said accelerating electrode and said deflection-control electrodes; an output system including a' pair of output electrodes; a screen grid, directly connected to said accelerating electrode and including a plurality of conductive elements extending transversely across said center plane, interposed between said accelerating electrode and said deflection-control electrodes; and a second screen grid interposed between said deflectioncontrol electrodes and said output electrode system.

4. An electron-discharge device of the beam-deflection t'y'p'e comprising: an electron :gun including an elongated electron-emissive cathode and an accelerating electrode havinga narrow 'sl'ot parallel to said cathode for project ing along a predetermined center plane a sheetlike electron beam of substantially rectangular cross-section; a pair of deflection-control electrodes flanking said center plane and spaced from each other by a distance greater than the spacing between said accelerating electrode and said deflection-control electrodes; an output system including a pair of output electrodes; a screen grid, directly connected to said accelerating electrode and including a plurality of conductive elements extending transversely across said center plane, interposed between said accelerating electrode and said deflection-control electrodes; and a second screen grid integral with said first screen grid and interposed between said deflection-control elec' trodes and said output electrode system.

5. An electron-discharge device of the beam-deflection type comprising: an electron gun including an elongated electron-emissive cathode and an accelerating electrode having a narrow slot parallel to said cathode for projecting along a predetermined center plane a sheetlike electron beam of substantially rectangular cross-section; a pair of deflection-control electrodes flanking said center plane and spaced from each other by a distance greater than the spacing between said accelerating electrode and said deflection-control electrodes; an output system'including a pair of output electrodes; a screen grid, directly connected to said accelerating electrode and including a plurality of conductive elements extending transversely across said center plane, interposed between said accelerating electrode and said deflection-control electrodes; a second screen grid integral with said first screen grid and interposed between said deflection-control electrodes and said output electrode system; and means interposed between said second screen grid and said output electrode system for'suppressing secondary electron emission from said output electrodes.

References Cited in the file of this patent