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Low Power, High Speed Intensity Control of CRT Electron Beam

IP.com Disclosure Number: IPCOM000044717D
Original Publication Date: 1984-Apr-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Bond, PW: AUTHOR [+2]

Abstract

A major problem with the control of the electron beam intensity in a conventional electron gun for a CRT is the large voltage applied between the cathode and the control grid to control the electron beam intensity. In addition, there is capacitance between the grid and the cathode which must be charged and discharged. At high average date rates, such as presentation of many characters on the CRT screen, the combination of the grid-cathode capacitance and the large and rapid control voltage charges contribute to large currents and high power dissipation in the video driver circuit. Finally, additional power is consumed in the heating of the cathode to high temperatures to emit electrons.

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Low Power, High Speed Intensity Control of CRT Electron Beam

A major problem with the control of the electron beam intensity in a conventional electron gun for a CRT is the large voltage applied between the cathode and the control grid to control the electron beam intensity. In addition, there is capacitance between the grid and the cathode which must be charged and discharged. At high average date rates, such as presentation of many characters on the CRT screen, the combination of the grid-cathode capacitance and the large and rapid control voltage charges contribute to large currents and high power dissipation in the video driver circuit. Finally, additional power is consumed in the heating of the cathode to high temperatures to emit electrons.

Relatively new devices known as cold cathodes, solid state electron emitting devices, or solid state cathodes can replace the heated cathode as an electron source in a CRT. These devices make use of the negative affinity of certain materials and other physical effects to directly emit electrons in a vacuum without a heater. Instead of using a grid to control electron intensity, the solid state cathode may be directly electrically excited or driven by a photon source such as an LED. When electrically excited, the cathode appears as a diode and requires a relatively small voltage swing to turn on and off; hence, much power is saved during high speed operation. The devices themselves are also very fast. CRT intensity can al...