US2216266A - Two-stage oscillograph - Google Patents

Description

1940. P. T. FARNSWORTH TWO-STAGE OSCILLOGRAFH Filed March 22-, 193'! k IN V EN TOR. PHIL o 7. Eve/vs WORTH Patented Oct. 1, 1940 UNITED STATES TWO-STAGE OSCILLOGRAPH Philo T. Farnsworth, Springfield Township, MontgomeryCounty, Pa., assignor, by mesneassignments, to Farnsworth Television & Radio 'Corporation, Dover, Del., a corporation of Delaware Application March 22, 1937, Serial No. 132,323

1'7 Claims.

My invention relates to oscillographs, and particularly-to a two-stage cathode'ray oscillograph for television use, and embodies the broad principle of image amplification set forth in my prior 5 application entitled Electron image amplifier,

Serial No. 461,l10,filed June 14, 1930, now Patent No. 2,085,742, granted July 6, 1937.

Among the objects of my invention are: To provide a cathode ray oscillograph of greater sensitivity; to provide a more eificient oscillograph for television and other uses; to provide means for developing'an amplified cathode ray beam within an oscillograph; to provide a method of increasing the beam power within an os'cillograph available for image production fora given value of primary beam'current; to provide means for producing a morebrilliant visual image from a given primary beam; and to provide an oscillograph wherein an electron beam is utilized toproduce an incandescent line image, and'said line image is utilized 'to produce an entire image or will be specifically pointed out in the de scription forming a part of this specification, but I do not limit myself to the embodiment of the invention herein described, as various forms may be adopted within the scope of the claims.

My invention consists, briefly, in providing within an oscillograph tube an incandescible electrode of width equal to that of the desired picture and height roughly equal to one picture element, across which each line of the picture to be produced shall in turn be scanned, whereby the electrode shall be incandesced ineach elementary length thereof to a degree, correspond ing to the light intensity of the corresponding picture element: the. incandescent line image thus produced, consisting of thermionic electron and secondarily emitted electrons, is inturn directed upon a viewing or projecting screen, with successive line image's displaced from each other by a suitable deflecting field to form an entire image By making the first electrode of highly emissive material, the number of electrons producing each element of the entire image may be increased without increasing the emission from the gun, and a more brilliant image may be therebyobtained'without increasing the accelerating potentials or the size of the gun.

Referring to the drawing: Figure 1 is a schematic sectional view of an oscillograph employing my invention.

Figure 2 is a cross-sectional schematic view, 5 taken along line 2--2 of Figure 1, showing the o1. H's-7.5)

structure of the intermediate electrode enlarged in proportion to the "remainder of the tube.

The brilliance of an image produced in a cathode ray oscillograph is dependent upon a number of factors, among which are the average number 5 of electrons in the cathode ray beam and the construction of the screen upon which the image is produced. In the Farnsworth application entitled Incandescent light source, Serial No. 67,889, filed March 9, 1936, now matured into 10 U. S. Patent No. 2,089,054, issued August 3, 1937, it was pointed out that the essen'tialrequirements for brilliance in an incandescible screen are that the screen mass be small and that heat losses shall be by radiation rather than by conduction: is in that application and in variousrelated cases, a type of-screen construction believed to offer a satisfactory answer to the problem was described,

- and the type of screen utilized in this'oscillograph tron emission at low energy loss, since the energy 30 utilized therein is confined to the region of maximum emission per unit of power absorbed. This may better be understood by reference to the drawing, 'a'more detailed description of which is as follows: I

In Figure 1 'I have shown a cathode ray tube embodying my invention. A long, evacuated, cy-' lindrical envelope I of glass or similar insulating material is terminated at one end-by a reentrant stem 2, and at the opposite end by an enlarged o rounded head 4. An electron gun 5 is supported at the end of envelope I near the-reentrant stem 2. In the figure, I have represented this gun conventionally as composed of a' filamentary cathode 6 supported by leads land 9 sealed 5 through the press I0 terminatingthe reentrant stem 2, an apertured control electrode H supported by a lead l2 sealed through the press l0, and a gun-type anode l4 carried by a supporting lead l5 sealed through the wall of envelope I. 50 However, any combination of anode, cathode and control electrode which will produce a modulated electron beam is deemed a full equivalent ofthe gun 5, as shown. 1

When cathode 6 is heated by a battery l6 or equivalent source of energy, electrons are emitted therefrom and attracted toward anode H by a positive potential placed thereon by a battery 11, or an equivalent direct current source, through lead IS. The number reaching said anode is controlled in accord with a charge built up on the control electrode II by a signal current applied thereto through an input lead 19, condenser 20, and supporting lead l2. The gun 5 thus directs a signal-modulated beam of electrons along-the axis of tube I in accord with well known practice, the electrons being accelerated by a positive potential produced by a battery 2| on an intermediate electron emitting electrode 22, diametrically disposed in a horizontal plane across envelope l, as more clearly indicated in Figure 2.

An electrostatic shield 24 covers the inner wall of envelope I from a point near the gun 5 tea point slightly beyond electrode 22, although insulated therefrom. By virtue of a connection 25 to the gun anode lead 15, shield 24 is maintained at anode potential, and prevents, unwanted disturbance of the electrons traveling from gun to screen. This shield may be a metal cylinder inserted in the envelope, or may beformed by evaporating a conducting coat on the wall; a metal sleeve disposed about the exterior of envelope! would serve the same purpose. I n a a The modulatedbeam is caused to traverse electrode 22 by the magnetic field set up by diametrally spaced coils 26 (indicated schematically as one coil), connected to a sawtooth os cillator 21 tuned to the proper high scanning frequency, and the impact of the; beam upon electrode 22 heats it to a; degree of incandescent varying along its length in accord with the variable light intensity of the picture element in corresponding position. A battery 29 may be used to heat electrode 22 to a dull red glow, in order that all the energy in thebeam may be utilized in producing visible changes. 5 Otherwise, a considerable proportion ,of the beam energy would be wasted in heating the electrode to incandescence. If desired, this polarizing heat might be supplied by directing infra-red radiations upon the electrode 22 from a lamp, or an auxiliarygun might be provided, to direct an unmodulated stream-f electrons upon the said electrode.

The electrode 22, in its preferred form, is

formed by winding about 250 turns per inch of fine refractory wire, such as tungsten, upon a mandrel having a diameter'of about .003 inch, and then etching the coil in hot sodium nitrite until the wire diameter is reduced to .00025 inch. Itis supported by spot-welding the ends, under tension, to leads 23 and 28 sealedithrough the envelope i. This method of forming acoil to be incandesced has been described in the pending Farnsworth application entitled fIncandescent light source, Serial No. 67,889, filed March 9, 1936, now matured into U. S. Patent No. 2,089,- 054, issued August 3, 1937, and as there pointed out, the efliciency is high, due to the small mass to be heated and the high percentage of heat loss by radiation as opposed to conduction.

The electron line image thus produced, composed of secondarily emitted electrons thrown out by impact of the beam, and thermionic emission due to incandescence, is attracted along the tube toward a viewing or projecting screen 30, which is preferably formed of a numberof coils similar to electrode 22, held parallelly in aplane in ac-f cordance with the teaching of the Farnsworth application, cited supra. Various other or the 'trode 22.

applicant's screens may be used alternatively therewith, and are deemed full equivalents thereof.

The electronic line image from the intermediate electrode 22 is accelerated toward the projecting or picture screen 30 by a high positive potential from a battery 3| or equivalent source of direct current. The electron image components tend to spread out, due to the mutual repulsion oftheir negative charges, but are prevented from doing so by the field set up about solenoid 32 when energized by a battery 34..

These magnetic focusing means cause the electrons to travel in mean rectilinear paths from electrode 22 to screen 30, and thus maintain the same relative intensity at screen 30 as at elec- Successive line images are deflected by the field set up in diametrally placed coils 35, indicated schematically as a single coil, by sawtooth oscillator 36 operating at low scanning frequency.

Itwill be noted fthat the high and low frequency scanning coils 26 and 35 are shown in Figure 1 as occupying nearly the, same angular position about the axis of envelope I, although their effect is exerted normal to each other. The reason for this position is found in the influence of solenoid 3'2. Thefield due to coil 2 traverses the beam horizontally along electrode 22, while the resultant field, due to coil 35' and solenoid 32, produces a vertical defiectionof the line image. The field of solenoid .32 may, de-' pending on thestrength oi thecurrent from battery 34 and the spacing of the parts, influence the field produced by coils 26.x Theresultant field, which will be rotated about the axis of the tube to a degree dependent on the strength or the solenoid field component, would cause a deflection of the beam Iromgun along a diameter at an angle to the horizontah, In practice, this is corrected by rotating coils 26 aboutthe tube until horizontal deflection is again secured; similarly, coils 35 may be rotated until the resultant field produces a vertical deflection of the line image. These adjustments may be checked visually by maintaining a square image on screen 30.

Screen 30 may-be polarized by means, not

shown in the drawing, similar tothose used" with electrode 22, and the entireelectronic impact utilized to. produce'an intensely incandescent image of the televised pictured or scene.

The end 4 of the tube has been made large to provide ample heat radiating surface.

The incandescent image may be projected through a suitable focusing lens system 31,

shown schematically, upon a suitable viewing.

screen, not shown, or for direct observation.

In short, by forming upon an intermediate electrode successive incandescent line images,

and utilizing these intense line images to pro-:

duce the'entire image, I am, able to secure a much more intense image without increasing the beam power or raising the accelerating potential. on the projecting screen, and am able to eiil'ect amazes screen capable of emitting light when bombarded j with electrons from said linear electrode and positioned on the other side of said linear elec--* positively relative to said anode, and meansfor charging said two-dimensional screen positively with relation to said linear electrode.-

3. Apparatus in accordance with the recitation of claim 1, wherein the two-dimensional screen is a screen incandescible upon electron impact therewith. c

4. Apparatus in accordance with claim 1,

refractory electron emitting wire of substantially .00025' inch wire diameter, said coil having approximately 250 turns per inch with a coil diam eter of substantially .003 inch. Y

5. A 'cathode ray oscillograph comprising an evacuated envelope having-therein a cathode, a control electrode and a gun type anode, cooperating, when energized as an electron gun, to produce a modulated beam of electrons of elemental cross section, an intermediate electron emitting electrode extending across said envelope, alined with said gun anode and having dimensions corresponding to one picture line, means positioned to move electrons from said beam linearly and cyclically over the long dimension of said electron emitting electrode to produce heating thereof and consequent electron emission, a picture screen capable of producing light upon electron impact therewith positioned in the path of electron emission from said electron emitting electrode, and a second scanning means positioned to move electrons emitted from said electron emitting electrode across said picture screen to produce an image on said picture screen corresponding to the modulations of the modulated beam.

6. A cathode ray oscillograph as recited in claim 5, having a magnetic solenoid surrounding the electron path between the intermediate screen and the second screen.

'7. A cathode ray oscillograph as recited in claim 5, wherein the modulations of the initial beam correspond to television signals, wherein the electron emission from the intermediate screen corresponds to a complete line of a television picture, and wherein the image on the second screen corresponds to the complete picture area.

8. A cathode ray oscillograph as recited in claim 5, wherein the first scanning means is a high frequency movement, and wherein the second scanning means accomplishes a low frequency scansion movement.

9. In combination, a screen whose surface emits light when bombarded with electrons, a thermionic cathode providing a stream of electrons directed at said screen, means for energizing said cathode to a temperature slightly less than that at which said cathode emits electrons in substantial quantities, a source of picture signal modulated electrons, means for bombarding said cathode with electrons from said source to raise the instantaneous temperature of said cathode in accordance with the modulation of electrons from said source, the electrons thereupon-emitted by said cathode being modulated in i accordance with'said-picture signals, and means for scanning said screen in a pre-determined pat-v tern of lines with the streamof electrons emitted by said cathode. to produce on said screen a visual image. 1' 1 1 Y 10. In combination, a screen whose surface emits light when bombarded with electrons, an elongated cathodezproviding along its lengtha stream of electrons directed at said screen, means for modulating the stream of electrons flowing from said cathode to provide at successive in tervals, .of time electronic images of successive lines ofa picture to be reproduced on said screen,

and means, for sweeping said stream of electron r} over said-screen ina direction transverse to the axis of said cathode.

11. In combination, a screen whose "incre mental surface areas emit light when bombarded with electrons, a substantially linear cathode providing along its length a stream of electrons directed at said screen, means for modulating the stream of 'electronsemitted by said cathode to provide at successive intervals of time electronic images of successive ones of a system of lines which together, form a picture on said. screen, and means forsweeping with substantially constant velocity said stream, of electrons over said screen in a direction transverse to the axis ofv said cathode. I

12. The combination o'fa screen whose surface emits luminous energy when bombarded with electrons, an elongated cathode providing along its length a stream of electrons directed atv said screen, means for causing said electrons to bombard said screen, means for modulating the stream of electrons flowing from said cathode to provide at successive intervals of time electronic images of successive ones of a system of lines which together form a picture on said screen, means for focusing said stream of electrons upon said screen as a line of finite length and optimum breadth, and means for sweeping said stream of electrons over said screen in a direction at an angle to the axis of said cathode.

13. The combination, in a recording system, of a screen whose incremental surface areas emit light when bombarded with electrons, an elongated thermionic cathode providing along its length a stream of electrons directed at said screen, means for energizing said cathode to a temperature slightly less than that at which said cathode emits electrons in substantial quantities, means for increasing the instantaneous temperature of incremental lengths of said cathode to a temperature at which said incremental lengths of said cathode emit electrons in increased quantities, said last named means modulating the stream of electrons flowing from said cathode to provide at successive intervals of time electronic images of successive ones of a pattern of lines which together form a picture on said screen, and means for sweeping said stream of electrons over said screen in a direction transverse to the axis of said cathode.

14. In a recording system, the combination of I stream to provide at successive intervals of time Q electronic images of successive ones of a pattern of lines which together form a picture on said screen, and means for sweeping-said stream of electrons over said screen in a direction transverse to the plane of said stream of electrons.

15. In combination, a screen whose surface emits light when bombarded with electrons, an elongated cathode providing along its length a stream of electrons directed at said screen, a

second source of electrons,.meansifor bombarding said cathode along its length with electrons from said'second named source, the electrons from said second named-source being modulated through successiveintervals oftime in accordance with'the light and shadow of successive ones of a pattern of lines which together form a picture to be reproduced'on said screenyrneans responsive to the bombardment of said cathode ,by electrons from said second named source for producing a modulation of the stream of electrons flowing from said cathode toward said screen to provide at successive intervals of time electronic images of successive ones of said pattern of lines which together form a picture on said screen, and means for sweeping'said stream of electrons emitted by said cathode over said screen in a direction transverse to the axis of said cathode.

16. In combination, a screen whose surface emits light when bombardment with electrons, an elongated cathode providing along its length a stream of electrons directed at said screen, a source of electrons modulated with picture signals, means for periodicallysweeping said cathode alongits length with modulated electrons from said second named source, each such peri-J odical traversal of said cathode by said electrons efiecting themodulation of the stream of electrons emitted by said cathodein accordance with the values of light, and shadow along the length of a respective one of a system'of lines which form the picture to be reproduced on said screen,

and means for sweeping said stream of electrons over said screen in a direction transverse to the axis of said cathode. I a

17-. The combination, in a recording system, .01 a screen whose surface emitslight when bombarded with electrons, a source of electrons modulated with picture signals, an elongated thermionic cathode providing along its length a stream of electrons directed at said screen, means for energizing said cathode to a temperature slightly less than that at which said cathode emits electrons in substantial quantities, means for periodically sweeping said cathode along its.- length-with modulated electrons from said first electrons overvsaid screen ina direction trans-,

verse to the'axis of said cathode. I

PHILO T. FARNSWORTH.

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