Electron gun with low voltage limiting aperture main lens

Details Electron gun with low voltage limiting aperture main lens Electron gun with low voltage limiting aperture main lens

1991-12-09

1993-06-29

O'Shea, Sandra L.

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

313448, 315 15, H01J 2948, H01J 2951

Patent

active

052237648

ABSTRACT:
A limiting aperture disposed in a relatively low voltage and electrostatic field-free region in the main focusing lens portion of an electron gun in a cathode ray tube (CRT) provides reduced electron beam spot size and improved video image contrast and purity in the CRT's display screen. The generally circular limiting aperture is disposed on the axis of the electron gun and within a charged electrode, or grid, within the main focusing lens. The cylindrically shaped, charged grid is elongated along the gun axis and includes generally circular recesses in facing surfaces thereof, which recesses are also disposed on the gun axis and separated by an inner partition defining the limiting aperture. The charged grid is maintained at a voltage V.sub.G, with V.sub.G .ltoreq.0.12 V.sub.A, where V.sub.A is the CRT's anode voltage. With the limiting aperture recessed within the elongated charged electrode, the electrostatic field is essentially zero at the limiting aperture where outer, peripheral electrons in the electron beam are intercepted and removed from the beam for limiting electron beam spot size. The low voltage of the limiting aperture-bearing grid substantially reduces the possibility of secondary electrons reaching the display screen. Most of the secondary electrons are absorbed by the succeeding high voltage grid.

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