US3720781A - High voltage slewing of penetration tube gun - Google Patents

High voltage slewing of penetration tube gun Download PDF

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Publication number
US3720781A
US3720781A US00197467A US3720781DA US3720781A US 3720781 A US3720781 A US 3720781A US 00197467 A US00197467 A US 00197467A US 3720781D A US3720781D A US 3720781DA US 3720781 A US3720781 A US 3720781A
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United States
Prior art keywords
high voltage
shield
tube
gun
crt
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Expired - Lifetime
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US00197467A
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English (en)
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R West
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RTX Corp
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United Aircraft Corp
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Publication date
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/22—Picture reproducers using cathode ray tubes using the same beam for more than one primary colour information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00—Details of colour television systems
    • H04N9/12—Picture reproducers
    • H04N9/16—Picture reproducers using cathode ray tubes
    • H04N9/27—Picture reproducers using cathode ray tubes with variable depth of penetration of electron beam into the luminescent layer, e.g. penetrons

Definitions

  • This invention relates to improvements in arrangements of high voltage in multiple phosphor penetration cathode ray tube circuitry.
  • a cathode ray tube comprises an evacuated glass bulb, necked down at one end wherein an electron beam gun is situated.
  • Various focusing electrodes, grids and sweep generating coils or plates and other apparatus are also located along the necked down portion.
  • the working element of the electron beam gun is the cathode which is nominally held at a low potential.
  • a conductive coating is utilized throughout substantially the entire internal surface of the tube, except immediately adjacent to t-he gun.
  • a thin aluminum layer covers the entire inner surface of the screen (the front face of the tube) and a high voltage (5 kv. to 20 kv. is typical) is applied to this inner conductive layer, and to the conductive coating, which operates to accelerate the electrons to the proper velocity to impact the particles of the phosphor in a fashion to create the light image as desired.
  • the high voltage on this coating creates problems with metal surfaces and circuitry external to the tube; that is to say the coating on the inside of the tube forms a capacitor with any conductive element adjacent the outside of the tube.
  • a conductive coating on the outside of the tube which is typically a carbon wash of some sort. This outer coating is grounded so as to provide the desired isolation.
  • the outer and inner coatings, separated by a dielectric the glass of the tube Wall), form a capacitor.
  • a multiple phospor penetration type tube is one which either has composite phosphors in which an inner phosphor is one color (green or blue), completely surrounded by a different phosphor (such as red), all of these particles together forming the phosphor surface on the screen. If the electron beam impacts the screen with a very high velocity, the inner phosphor will be excited and the light generated will be the color of the inner phosphor; if however the beam impacts the phosphor with a lesser velocity, then only the outer layer is excited and so the other color (such as red) will emanate.
  • Another type of multiple phosphor penetration type tube employs two separate layers of phosphor separated yby an energy sensitive barrier layer.
  • Other penetration CRTs may employ phosphors of different persistence or other characteristics rather than only of different colors.
  • phosphors of different persistence or other characteristics rather than only of different colors.
  • the key to operation of a multiple phosphor penetration type fCRT is to provide a beam of the correct energy on a point by point basis as a picture is being developed on the screen of the CRT.
  • it In order to alter the intensity of the beam from point to point as necessary to excite the desired phosphor in the generation of the picture, it -becomes necessary to switch the high voltage at video rates.
  • the entire system acts much the same as an antenna, creating strong fields about the tube. For instance, switching from 6 to 12,000 volts at video rates, comprising a square wave, provides significant frequency components as high, perhaps, a 50 kHz.
  • an RF shield is placed in front of the screen, which is grounded so as to isolate persons and objects in the vicinity of the front of the screen from the RF eld generated by switching of the high voltage. This in turn provides another significant capacitance between ground and the high voltage acceleration layer within the tube.
  • the total capacitance of the high voltage acceleration layer or anode inside of the tube to ground renders it difficult to change the high voltage by large amounts at a rapid rate. For instance, to change from an acceleration voltage on the order of 6,000 volts to an acceleration voltage on the order of 14,000 volts (which may obtain in a typical large screen application), may require driving as much as several thousand pico farads, which could in turn require as much as two or three amperes. This can be seen to require a power supply capable of delivering on the order of l0 to 20 thousand watts peak.
  • the tube must therefore be blanked out once a voltage change is initiated until steady state conditions can be established with an equipotential layer throughout the screen of the tube. This slows down the rate at which the video can be changed in the tube; other- Wise, defocusing and errors in deection and other picture degradation will result.
  • the object of the present invention is to provide improvements in multiple phosphor penetration CRT systems, and particularly in the high voltage arrangements therein.
  • the anode of a multiple phosphor penetration cathode ray tube is held at a constant potential, and the gun of the cathode ray tube, including the immediate circuitry for operating it, are all slewed upward and downward by the desired voltage differential.
  • the gun and its associated equipment are located within a Faraday shield, whereby the slewing of the high voltage has no effect on the circuitry within the Faraday shield.
  • essentially only two connections are made between the circuitry within the Faraday shield and the outside world; these comprise an alternating current source of power which may conveniently be supplied thereto by a twisted pair fed through a high voltage isolation transformer, and video superimposed on an RF carrier supplied over a coaxial line through a high voltage isolation transformer.
  • the present invention provides significant reduction in the capacitance which has to be driven in a high voltage voltage-switching multiple phosphor penetration cathode ray tube. 'In addition, the present invention avoids the necessity of an RF shield since the high voltage at the screen remains constant. The present invention, by keeping the screen at the same potential at all times, completely eliminates the necessity of establishing steady state conditions each time that the high voltage is switched in order to avoid focus and deflection ambiguities and the resulting degradation of the picture quality.
  • the present invention is readily implementable using standard technology without signicant penalties in cost, weight or size.
  • a cathode ray tube 1 is provided with a fixed high voltage Supply 2 which is connected to an anode electrode 3 on the CRT to provide the acceleration voltage to the anode of the CRT.
  • the CRT 1 may be provided with an external conductive coating 4 which is grounded to isolate structure external of the tube 1 from the high voltage on the anode, as is known in the art.
  • the CRT is also provided with a focus coil 5 which is driven by suitable focus circuitry 6 which may be of the type well known in the art and which is not described further herein.
  • a deflection coil 7 is driven by a symbol generator 8 which may in turn receive signals from apparatus, such as a computer, a radar system or other apparatus, the data output of which is to be displayed.
  • the symbol generator 8 also provides video to a modulator 9l which modulates the video on an RF carrier provided thereto from an RF carrier source 10.
  • a high voltage switching power supply 12 is controlled by the symbol generator 8 so as to provide a swing in high Voltage applied to the gun 14 of the CRT 1.
  • the high voltage supply 12 is connected to a Faraday shield structure 16, which completely surrounds the gun 14 and circuitry utilized to operate the gun 14.
  • the Faraday shield 16 may take the form of a hollow aluminum cylinder, or other shapes of other conductive materials as may be desired in any given utilization of the present invention. As shown in the figure, the Faraday shield 16 is supported by an insulating disc 15 which slips over the neck of the tube.
  • Additional support may be provided by similar insulating discs located midway within the shield (but eliminated herefrom for simplicity) which may conveniently have the CRT tube socket (not shown) fastened thereto, whereby the Shield 16 will derive support from the base (not shown) of the tube; however, the Faraday shield 16 may be supported by external structure or in any other way found suitable.
  • a detector and amplifier 18 of a common type which is utilized to drive the control grid 20 of the CRT.
  • a suitable power supply for the video amplifier is included within the Faraday shield 16; this may typically comprise a 80 Volts supply 22.
  • a SOO-volt supply 24 is provided to maintain the potential of the screen grid 26 of the CRT.
  • Power ⁇ for the power supplies 22, 24 is provided by a twisted pair of leads 2S which is connected externally of the Faraday shield 16 to a medium frequency power supply 30, which may typically supply 6.3 volts (to match the heater voltage of the CRT) at about 50 kHz.
  • a high voltage isolating transformer 32 which may comprise a ferrite core with suitable insulation and a proper assemblage of windings in accordance with well known teachings of the art.
  • one wire 34 of the twisted pair comprises ground and is connected to the Faraday shield 16.
  • One side of the heater is similarly grounded to the shield 16, and the other side of the heater is connected directly to the other wire 38 of the twisted pair 28 along with the power supplies 22, 24.
  • the cathode 46 of the CRT is connected directly to the shield 16 so that it is slewed between upper and lower DC voltages applied thereto by the switching high voltage supply 12.
  • the video detector and amplifier 18 derives the video input from a coaxial line 42 which is coupled through a single turn to a high voltage isolating transformer which may typically comprise an iron dust core (or it may be an air core) which is coupled to a primary 46 driven by the modulator 9.
  • the transformer 43 may be designed in any desired fashion so as to satisfy the requirements of the carrier (which may typically be mHz.) provided by the source 10.
  • the symbol generator 8 causes the high voltage switching supply 12 to change from one voltage to another so that the total acceleration voltage between the cathode 40 and the anode 3 of the CRT changes from one voltage to another.
  • the fixed high voltage supply 2 might be at a potential of positive 9 kv. and, in a two-level penetration type application, the switching high voltage supply 12 may typically provide minus 4 kv. and plus 4 kv. Thus the total acceleration voltage would vary from 5 kv. to 13 kv.
  • more than two voltage levels may be supplied by the switching high voltage power supply 12; for instance, in a tube capable of generating four different colors, four different voltages may be provided by the switching high voltage supply 12.
  • the magnetic coupling provided by the high voltage isolation transformer 43 in coupling the video from the outside world into the Faraday shield 16 is essential in order to isolate the high voltage DC of the Faraday shield 16 from the circuitry outside thereof.
  • the video signal would be superimposed on the high voltage, and it would be impossible to isolate the circuitry within the Faraday shield 16 from the high voltage.
  • the shield 16 should be sucient to provide substantially complete RF shield of the components 14, 18, 22 and 24 from the outside world, so that they can function together in their own world which is many volts elevated from the surrounding structure outside the shield 16.
  • a multiple penetration cathode ray tube apparatus adapted to provide significant rapid alteration of the cathode ray beam accelerating voltage, comprising:
  • a multiple penetration cathode ray tube having an anode and an electron gun including a cathode;
  • shielded circuit means disposed within said shield, said shield providing substantially complete RF shielding of said shielded circuit means, said shielded circuit means providing operating potentials and signals referenced to said shield for operating said electron gun in response Ato signals applied thereto by said external circuit means through said high voltage isolation means;
  • a switching high voltage supply capable of providing at least two different voltages connected at least to said shield and to said cathode.
  • said external circuit means includes video means providing a video signal modulated on an RF carrier;
  • said shielded circuit means includes a video detector and ampliiier dispos-ed in said shield and operating with the potential of said shield as a reference potential;
  • said isolation means includes'a high -voltage isolation RF transformer having a primary coupled to said video means and a single turn secondary coupled through the central conductor of a coaxial cab-le to said video detector and amplifier, the outer conductor of said coaxial cable being connected to said shield.
  • said external circuit means includes a medium frequency power source
  • said isolation means includes a high voltage isolation transformer having a primary coupled to said medium frequency power source, and connection means comprising a twisted pair connected to a secondary of said transformer and applying the voltage therefrom between said shield and said shielded circuit means.
  • said external circuit means includes a medium frequency power source
  • said isolation means includes a high voltage isolation transformer having a primary coupled to said medium frequency power source, and connection means comprising a twisted pair connected to a secondary of said transformer and applying the voltage therefrom between said shield and said shielded circuit means.
  • Apparatus according to claim 4 wherein said electron gun includes a screen grid and said shielded circuit means further includes a power supply for said screen grid powered by said twisted pair.

Landscapes

  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
  • Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)
US00197467A 1971-11-10 1971-11-10 High voltage slewing of penetration tube gun Expired - Lifetime US3720781A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US19746771A 1971-11-10 1971-11-10

Publications (1)

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US3720781A true US3720781A (en) 1973-03-13

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US00197467A Expired - Lifetime US3720781A (en) 1971-11-10 1971-11-10 High voltage slewing of penetration tube gun

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US (1) US3720781A (esLanguage)
CA (1) CA973639A (esLanguage)
FR (1) FR2159284B1 (esLanguage)
GB (1) GB1386139A (esLanguage)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1981000182A1 (en) * 1979-06-27 1981-01-22 Hollandse Signaalapparaten Bv Power supply circuit
US4517494A (en) * 1981-11-09 1985-05-14 Sharp Kabushiki Kaisha Screening structure for a cathode ray tube display
US4999542A (en) * 1973-12-03 1991-03-12 Harris Data Communications, Inc. Data processing display terminal

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4999542A (en) * 1973-12-03 1991-03-12 Harris Data Communications, Inc. Data processing display terminal
WO1981000182A1 (en) * 1979-06-27 1981-01-22 Hollandse Signaalapparaten Bv Power supply circuit
US4390896A (en) * 1979-06-27 1983-06-28 Hollandse Signaalapparaten B.V. Power supply circuit
US4517494A (en) * 1981-11-09 1985-05-14 Sharp Kabushiki Kaisha Screening structure for a cathode ray tube display

Also Published As

Publication number Publication date
FR2159284A1 (esLanguage) 1973-06-22
GB1386139A (en) 1975-03-05
CA973639A (en) 1975-08-26
FR2159284B1 (esLanguage) 1978-07-21

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