Cathode-ray Tube With Serpentine-shaped Transmission Line Deflection Means

Abstract

Improved high-frequency response, cathode-ray tube for tracking, determining, and recording high frequency, unknown input signals. To this end, the invention provides a sectionalized, round and square cross section CRT having ceramic, vacuumtight lead-ins; impedance matched, insulated, serpentine traveling wave deflection structures; and an electron gun incorporating an anode aperture formed with a protrusion for providing high-electron beam density.

Description

BACKGROUND OF THE INVENTION

Fast cathode-ray tubes are required for a wide variety of industrial and research applications. In the digital-communication and research fields, for example, real-time cathode-ray tubes and oscilloscopes are required that can handle input signals in the range up to at least 50 to 250 MHz, as described in Electronics, July 7, 1969 p. 90 et seq., by Alan J. DeVilbiss. Stated another way, there are many and varied applications that require cathode-ray tubes and oscilloscopes that have the ability to track, determine, and/or record known and unknown, fast real-time input signals, such as pulses with rise times in the range of a few nanoseconds or less.

One fast response cathode-ray tube, hereinafter referred to as a CRT, provides at least one planar, conductive strip means folded into a serpentine configuration. Successively predetermined portions of the serpentine configuration are disposed adjacent to, but spaced from one another along the direction of an electron stream, whereby the electron stream passes each portion in sequence for deflections corresponding to an unknown input signal. Such a system is described in U.S. Pat. No. 3,280,361, by Goldberg et al., and assigned to the EG & G Co., but as described in this patent, the dielectric material used for mounting is attached to the end portions of the serpentine shaped conductive strip means. Thus, this CRT structure lacks rigidity or involves difficult fabrication problems. Moreover, as mentioned in this patent, the impedance matching of the structure thereof is limited since even the end mounted dielectric material thereof may change the impedance of the serpentine strip means. It is additionally advantageous to provide high-electron beam densities in a CRT.

SUMMARY OF THE INVENTION

This invention, which was made in the course of, or under a contract with the United States Atomic Energy Commission, comprises improved CRT structures having rigidly mounted, impedance matched serpentine traveling wave deflection means, which are improvements over the serpentine structure of the above-mentioned patent. To this end, in one embodiment, the serpentine structure of this invention is supported along one whole side thereof and shaped with narrow neck portions for providing a uniform impedance along the overall length thereof. In accordance with further aspects of this invention, push-pull, and mirror image-spaced apart, serpentine conductive strips are provided. It is also an object of this invention to provide improved fabrication means, comprising a modular sectionalized structure and ceramic lead-ins for providing an accurate low-distortion, fast response time, low-reject rate, adjustably fabricated, easy to assemble CRT. In accordance with a still further feature, this invention provides a high density electron beam.

The above and further novel features and objects of this invention will appear more fully from the following detailed description of one embodiment when the same is read in connection with the accompanying drawings, and the novel features will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings where like elements have like reference numbers:

FIG. 1 is a partial, extended view of one embodiment of the CRT of this invention:

FIG. 2 is a partial cross section of the Rossi and sweep plate section of FIG. 1 through II--II;

FIG. 3 is a partial cross section of the signal section assembly of FIG. 1 through III--III;

FIG. 4 is a partial cross section of the electrostatic lens section assembly of FIG. 1 through IV--IV;

FIG. 5 is a partial cross section of the marker section assembly of FIG. 1 through V--V;

FIG. 6 is a partial cutaway view of the gun assembly of the CRT of FIG. 1;

FIG. 7 is a partial cross section of the grid cup and first anode electrode of FIG. 1 through VII--VII, showing the protrusion for increasing the electron density produced by the apparatus of this invention.

DESCRIPTION OF PREFERRED EMBODIMENT

This invention provides a fast, accurate, low distortion, high frequency response CRT for use with a Rossi deflection of 2,200 MHz or higher. Moreover, this invention is useful in tracking, determining and recording fast or high speed known or unknown input signals, such as electrical input pulses in the range from a few nanoseconds to several picoseconds. Accordingly, this invention is particularly useful in a wide range of scientific research applications. However, as will be understood in more detail from the following and also by one skilled in the art of CRT's and oscilloscopes, this invention is useful in any of a wide variety of industrial or research applications involving fast or high frequency CRT input signals, and/or fast writing time, high frequency Rossi deflections or high frequency CRT response times.

In understanding this invention, reference is made to FIG. 1, which illustrates one embodiment of the CRT 11 of this invention. A source 13 produces a spray 15 of electrons 17 with velocity v, and these electrons are formed into a suitable small diameter beam 19 that accurately passes through suitable focusing and deflecting means, comprising deflecting stations 21, and impinges against a conventional phosphorescent screen 23 at one end of a glass cylinder 25. For properly transporting the beam and impacting it against the screen 23, the CRT 11 advantageously comprises an evacuated electron gun assembly 27, a marker deflection structure 29, an electrostatic lens section 31, although a magnetic lens may alternately be used, a signal deflection structure 33, a high frequency timing and Rossi linear sweep plate means 35, and an evacuated glass cylinder 25 having helical conductor means 37 around the circumference thereof.

It will be understood from the above, that CRT 11 involves complicated and accurately located structures involving stringent standards and requirements. In this regard, the CRT 11 of this invention meets the difficult assembly and high frequency operating requirements involved in industrial and research uses, and overcomes the high-rejection rates known heretofore. To this end the CRT 11 employs a modular design and assembly system that permits physical adjustment and testing of the various parts thereof, and which overcomes or lessens the expensive problems of assembling these parts on a single frame of rods, as was done heretofore.

As shown in FIG. 1, modules 39 which sequentially form the stations 21 for assembly between gun 27 and screen 23, comprise round cross section tubes 41 and square cross section tubes 43, each of which is made of metal and carries round, disc shaped flanges 45 having oppositely mating cylindrical shoulders or niches for coaxial alignment along a single x axis passing azimuthally through and along the center of the modules 39 formed by the round and square cross section tubes. Also, appropriate aperture discs 47 are arranged and heliarc welded between modules 39.

The described modular design is based on the approach of building the deflection structures of stations 21 into the individual modules 39 of the body 49 of CRT 11, and the precise complete mechanical assembly adjustment and critical testing of the individual components of each module 39 before the assembly thereof. The individuals modules 39 of CRT 11 are then joined together by heliarc welds 51 to form the complete CRT 11. As described in more detail hereinafter, the gun 27 and front bulb or screen cylinder 25 are also built as individual sections and joined to the deflection station modules 39 by heliarc welds 51. Likewise, the modular design of CRT 11, has the advantage of ease and economy of assembly while consistently meeting stringent specifications with a low-rejection rate, and without constraints being imposed to compromise the design of CRT 11 for the sake of compatibility with existing equipment and power supplies.

Additionally, this modular assembly of CRT 11 permits completion and final assembly of coaxial lead-ins 53, which permit the mentioned critical tests to be performed. These coaxial lead-ins 53 have ceramic-to-metal vacuum seals 55 designed for both 50 ohm GR connectors and 100 ohm GR connectors. Also, lead-ins 53 provide the correct impedance within 1 ohm for the 50 ohm connectors, and within 3 ohms for the 100 ohm connectors. These seals 55 have the advantage of reliability and vacuum integrity. In this regard also, the sectionalized, tubes 43 permit easy and vacuumtight location and assembly of the coaxial, ceramic, lead-ins 53, which have conductor pins 57 and thin discs 59 of molybdenum for securing the vacuumtight seals 55 between the pins 57 and coaxial ceramic elements 59'.

Basically, the final vacuum seal has been separated from the electrical connections by the described modules 39 of CRT 11. Moreover, the described ready access provided at the ends of the individual modules 39 and the complete inspection and adjustment thereof, permits the individual subassembly of modules 39 in lot quantities. Thus, the final assembly of CRT 11 joins the several main subassemblies after they have been completely checked out and inspected, whereby rejects are caught at an early stage in the assembly and repairs of the parts of modules 39 represent a minor problem.

Another advantage of the described modules 39, comprises the exhaust tubulation 61 (shown in FIG. 1 and FIG. 6), and a cold weld 63 with an annealed copper tubing 65. A pinch-off 67, is also provided. In this regard, this pinch-off 67 has proven to be very reliable in actual production and use, since it has the advantage that no heat is used during the pinch-off process to a degradation of the vacuum in CRT 11.

The described modular assembly system of this invention is also advantageous in the accurate assembly, testing and adjustment of the traveling-wave deflection structures 69 of the deflection stations 21 of this invention. Referring to FIG. 2, for example, the serpentine shaped, traveling-wave, delay-line structure 69 of Rossi, sweep plate deflector 35, is rigidly mounted along both edges 71 of the delay line structure 69 in grooves 73 in spaced apart insulators 75 and brazed to the insulators 75. Moreover, by means of careful assembly and spring contacts 77 for the electrical connections 79 of lead-ins 53, which is all made possible by the described modular design of this invention, the spacings, alignment, and electrical characteristics of these elements are maintained within a few thousands of an inch or less.

This invention is also advantageous since it provides a serpentine-shaped, traveling-wave, delay-line, deflection structures 69 that has the desired impedance. Referring to FIG. 3, for example, signal deflector 33 has a serpentine-shaped, traveling-wave, delay-line, charged particle (electron) deflection structure 69 that is photoetched from a uniform thickness plate having little or nil magnetism properties, and a cross section formed to provide the desired impedance when rigidly mounted and assembled in insulators 75 on both edges 71 thereof. To this end, as shown in FIG. 3, the assembled serpentine deflection structure 69 has a variable cross section that is uniformly adjusted to be 50 or 100 ohms, which is checked by a high-resolution TDR along its length. This particular, described serpentine structure 69 thus gives a unique narrow cross section around the serpentine turns. This provides high frequency, undistorted response, thereby to insure that the electron beam 19 is in step with the voltage signal e.g., an unknown pulse) impressed on this variable cross section, serpentine structure 69 & is synchronous therewith in phase. Thus, this (unknown) signal can be compared accurately with a high frequency sine reference wave signal, e.g., in the opposite direction. Moreover, this specific serpentine structure 69 having the described balanced, uniform impedance along its length, provides the particular advantage of sensitivity, whereby the beam scan, i.e., how far the beam 19 can be deflected without distortion, is increased. Additionally, the writing speed is increased, faster input or unknown signals can be tracked, and resonant, higher frequency Rossi deflection signals can be employed without distortion.

Still further, a uniform easily adjustable spacing between parallel, periodic, "turns" 81 of the serpentine structure 69 is provided, these spacings can be wider, more closely controlled in accordance with CRT 11 design and impedance matching requirements of the allied equipment without any constraints being imposed to comprise the tube design for the sake of compatibility with existing equipment and power supplies, the serpentine structure 69 can be longer, the power requirements are less, and low-stray capacitance is provided consistently and reproducibly in production quantities.

Advantageously, each serpentine structure 69, comprises a molybdenum delay line uniformly about 10 mils thick. However, this thickness dimension may be up to 20 mils. Also, the ends 83 curve for a rigid attachment to connections 79, while the edges 71 are brazed to ceramic insulators 75 by metallizing i.e., with solder fill.

The system of this invention has the further advantage that two-spaced apart, parallel serpentine delay-line structures 69 can be adjustably assembled in deflector 33 for 10-20 volt, 0-2,000 MHz signals, and these signals can be 180.degree. out of phase in the two respective serpentine structures 69 for balanced push-pull operation. To this end, these two serpentine structures can be assembled, and are advantageously mirror images of each other in accordance with the accurate sectionalized and adjustable assembly system of the modules 39 of this invention.

The round cross section tubes 41 of modules 39 have the added advantage of spacing the walls thereof far from the structure assembled therein. Thus, the impedance of the serpentine signal deflector 33 is easily assembled, tested, and controlled in a rigid, shockproof subchassis.

Referring to FIG. 4, the lens 31, which is likewise assembled with similar advantages in a round cross section tube 41, utilizes a mechanical mount that provides precise centering of the through coaxial lens elements 85 with respect to the electron beam within a few mils. The lens 31, which is advantageously an electrostatic lens, also incorporates an adjustment feature precisely to orientate the ends 87 of the lens elements 85 in lens 31 perpendicular to the axis of the electron beam 19. This adjustment is accomplished by using two micrometer heads to provide the tilt adjustment in the vertical and the horizontal plane. After this alignment procedure, which also comprises clamping the lens elements 85 and lens 31 relatively in place, the micrometer heads are removed. In this regard the described modular design permits the testing, adjustment and assembly of interchangeable lenses 31. For this adjustment procedure, the effect of the electron beam is advantageously used as an indication for the proper lens alignment whereby the lens 31 is perpendicular to the electron beam 19 within 1/2.degree. or less.

Referring to FIG. 5, the structure in the square-cross section tube of the marker 29, on the other hand, requires less spacing. Additionally this square-cross section permits the lead-ins 53 to be off center to line up with the widely spaced ends 83 of the closely spaced, periodic, "turns" 81 of the serpentine structure 91 of this marker 29.

The electron source 13, which is illustrated in FIG. 6, is a negative-grid, high-density beam, gun 27 having a beam collimating and electrical field curving anode electrode 97 which forms an annular protrusion 99 at the input end 101 of flat plate 103. This gun 27 differs from conventional structures in that the protrusion 99 forms a sleeve around the beam 19 toward grid 105 as shown in FIG. 7. Compared to conventional anodes, the anode electrode 97 of this invention increases the electron beam current by a factor of 1.8 or more on production quantities of tubes 11.

The effect of the protruding sleeve formed by protrusion 99 is to change the curvature of equipotentials 107 in accelerating region 109 of electron gun 27. This change in the curvature is such that electric field 111 produced by the cathode-anode structure 113 is modified to have a convergent effect on the electron beam 19, rather than a divergent effect experienced by a plain aperture 115 in a flat plate 103 without a protrusion 99. The above-described convergent effect illustrated by dashed lines 117, provides a higher electron beam current passing through the limiting aperture 115.

Advantageously, the connections 119 of the electron gun 27, which is illustrated in FIG. 6, have a potting compound 121 that insures the reliability of the connections and resistance to arcing, thereby reliably maintaining the same under severe environmental conditions of shock, vibration, humidity, dirt or dust.

To insure that the CRT 11 maintains a high-vacuum under usage and long shelf life, the parts thereof receive an extensive high-vacuum processing cycle. To this end, all the metal parts undergo a 1,000.degree. C. high-vacuum firing for 1 hour prior to assembly to outgas the parts. After the assembly process, the completed section is subjected to a 450.degree. C. vacuum bakeout. Prior to assembly, the glass bulb of cylinder 25, which is illustrated in FIG. 1, with the phosphor screen 23 and an aquadag resistive spiral 37 with a chrome oxide resistive coating has a 380.degree. vacuum bakeout for 1 hour. This bakeout removes a large part of the evolved gaseous products from the assembly of cylinder 25 and the whole bulb assembly 125.

After this vacuum bakeout of the bulb assembly 125, the CRT 11 is assembled and the entire CRT undergoes a 380.degree. C. bakeout during the 8-hour exhaust and vacuum processing cycle. This extensive exhaust and vacuum processing cycle has been a major factor in achieving uniformly high-emission current from the cathode 127 and in achieving long-life in production quantities of CRT 11.

In one example for the above-described assembly cycle, the tubes 41 and 43 and the flanges 45 therefor are assembled, vacuum brazed in a furnace and leak checked. Finish machining of flanges 45 then provides concentric diameters and shoulders for both flanged ends 131 of each respective tube 41 and 43. To this end a mandrel in one end 131 provides for machining both ends to provide flat ends 131 to 1 mil having a 32 micron finish, and concentricity to 1 mil.

An assembly jig then registers on each of the respective machined shoulders of the flanged tubes 41 and 43 and spot welding accurately places the internal elements 133 therein. Also the lead-ins 53 are assembled in tubes 41 and 43 respectively, heliarc welded in place, and connected to the internal elements 133. Thereafter, these lead-ins 53 and internal elements 133 are electrically checked and adjusted, e.g., with time domain reflectometers for adjusting the impedances thereof for minimum reflectance.

The completed modules 39 are individually vacuum baked at 1,000.degree. C., assembled in line with their shoulders 135 in ends 131 mating with each other, and heliarc welded. Leak checking of this assembly then prepares for pump out, bakeout at 400.degree. C., metal pinch-off, etc.

Advantageously, fiducial marks 137 and the serial number of CRT 11 are abraded onto the internal surface of the glass faceplate 129. These fiducial marks serve the purpose of increasing the precision of the recovery and analysis of the recorded data. These fiducial marks provide a fixed reference on the face of CRT 11 to obtain increased precision when correlating calibration films with the recorded data.

In one example for producing these fiducial marks 137, the marks 137 and the patterns thereof are first cut into a thin metal mask by photoetching. The pattern is transferred to the internal surface of the glass by an abrasive process of blowing an abrasive onto the glass on which the mask has been cemented.

To this end the metal mask is cut from 3 mil stock, the fiducial marks are photoetched into the mask, cement attaches the mask to the inside of face 139, an eraser removes the excess cement, and an air driven abrasive abraids the glass.

Controlled illumination of the fiducial marks 137 is provided by edge lighting with an electroluminescent tape around the edge of the face 139 of bulb assembly 125. The electroluminescent tape is held in position by being molded into a sleeve of insulating material (not shown) in which the high-voltage lead is also molded. Better illumination has been obtained without any intermediate material between the electroluminescent tape and the glass of bulb assembly 125 than clear plastic or cement.

The described CRT 11 provides an oscilloscope having many advantageous performance and assembly features. In terms of sensitivity in volts per trace width, scan in trace widths, writing speed in trace widths per second and bandwidth, the described high-density electron beam 19, vacuumtight lead-ins, specific, variable cross section serpentine structure 69, and the described modular assembly system provides superior results for ultrashort and high frequency pulsework, without sacrificing other operating characteristics even with existing auxiliary equipment and existing CRT design requirements. The low, controlled, uniform impedances and low-stray capacitances are specifically and actually provided for long periodic serpentine structures having wide spacing between the "turns" 81 thereof. Also, the described system of this invention, provides an accurate, rigid, shockproof, insulated assembly in round and square cross section modules 39 that are bakedout, leak-checked, and electrically tested, and selectively adjusted to provide long-operating lifetime, high-performance, and low-reject rates in production quantities. In actual practice low-stray capacitances of 0.4 .mu..mu.f are provided at 100 ohm levels for signal rise times of 10.sup.-.sup.10 seconds or less. Other actual parameters achieved with this invention, comprise 0.50 ns. maximum transmission rise times, 4.+-.0.2 ns. transit times, 50.+-.2.OMEGA. marker serpentine structures, Rossi systems with VSWR of 1.4, beam currents with dynamic cutoff of 200 v. above static and static cutoff of 350 v..+-.50 v.

Claims

What is claimed is:

1. A cathode-ray tube oscilloscope for tracking ultrashort pulses, comprising source means having an anode, a cathode and a grid for producing a beam of electrons, means for focusing said beam of electrons for transporting the same along a longitudinally extending axis, means for producing light from said focused beam along said axis, and deflecting means for deflecting said focused beam from said axis a distance corresponding to an ultrashort input signal for providing a reference time scale for the continuous time calibration of said input signal from the light produced from said focused electron beam relative to said axis, said deflecting means having a serpentine-shaped transmission line formed with narrow and curving neck portions of continuously variable width and cross section that connect continuous equally spaced straight sections transverse to said longitudinally extending axis by curving around the turns of said serpentine-shaped transmission line to provide a uniform low impedance between the ends of said transmission line along its entire length.

2. The invention of claim 1 in which said serpentine-shaped transmission line has spaced apart insulators along the entire length thereof on both sides of said transmission line for rigidly mounting the same in said cathode ray tube oscilloscope.

3. The invention of claim 1 having an anode forming an aperture and a protrusion extending toward said grid for receiving and collimating said electrons in a high-density beam.

4. The invention of claim 3 in which said protrusion produces a convergent effect on said electron beam.

5. The invention of claim 1 in which said deflecting means forms spaced apart serpentine-shaped transmission lines that are arranged in space to form a mirror image of each other on either side of said axis for push-pull operation by pulses that are 180.degree. out of phase and in step with the electrons in said beam.