U.S. Philips Corporation

Martinus H Van Den Broek

Aart A Van Gorkum

Jan Zwier

Robert H Fastenau

Jan D Westra

A monochrome cathode ray tube having an electromagnetic deflection unit (9) and a directly adjoining integrated focusing multipole correction unit (10) which serves both to generate a static focusing field and to generate higher order multipole correction fields to correct for spot distortion errors. In particular quadrupole fields are generated to correct for astigmatism errors.

Cathode ray tube having a magnetic focusing lens

Positive ions which are generated in a vacuum tube (1) and can adversely affect the electron emission of a cathode (3) are collected for the major part by a screen grid or diaphragm (5), which forms part of a positive electron lens (4,5). In the case of a semiconductor cathode having a circular emission region (13) having a diameter larger than that of the opening in the screen grid (5), this emission region (13) is struck only by positive ions generated in a small region between the cathode (3) and a first grid (4). These ions moreover have a comparatively low energy so that the emission behavior is to only a limited extent adversely affected by sputtering by positive ions which would remove cathode material (33), such as cesium.

Cathode-ray tube having an ion trap

A cathode-ray tube comprising in an evacuated envelope a diode electron gun for generating an electron beam. The electron gun includes a cathode arranged on an axis with its emissive surface extending substantially perpendicularly to the axis, and an anode extending substantially perpendicularly to the axis and having an aperture opposite to the cathode, the electron beam being focused on a target by means of at least one focusing lens. The cathode-ray tube is a picture display tube, the target is a display screen, and the spacing between the anode and the cathode of the diode electron gun is smaller than 200 .mu.m. The electron beam generated in the operating tube, viewed in the direction of propagation, is focused to form a cross-over immediately after the anode by a positive electron lens. The cross-over, which is displayed on the display screen by means of the focusing lens, has a current density on the axis which is larger than three times the current density in the point of intersection of the axis with the cathode. Because of this high current density crossover, a comparatively large electron beam current (1-5 mA) spot is formed on the display screen having a diameter which is smaller than the diameter of the spot formed by known cathode-ray display tubes having triode electron guns. The part of the anode including the aperture preferably consists of a thin metal foil which extends perpendicularly to the axis, and the thickness d of the foil divided by the radius r of the aperture is smaller than 1 (.sup.d /r&lt;1). Such a tube is particularly suitable for use as a projection television tube or a D.G.D.-tube.

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Eindhoven, Netherlands

Martinus H Van Den Broek