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Automatic Beam Intensity Matching for Multiple-Beam Cathode Ray Tubes

IP.com Disclosure Number: IPCOM000037347D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Beck, VD: AUTHOR [+2]

Abstract

In order for a multiple-beam cathode ray tube (MBCRT) to produce an image with a high perceived quality, the brightness of the individual beams must be matched. Failure to match the brightnesses of the beams produces bright or dark streaks in the image. In order to meet the stringent requirements of beam matching, it is necessary to adjust each of the beams to the same intensity. Intensity differences between beams come from non-uniform drifts, warm-up, aging, and variations in manufacture of the individual cathodes. Manual adjustment is difficult because when the intensity of a given beam is changed, the intensities of the beams immediately above and below appear to be altered in the sense opposite to that of the central beam.

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Automatic Beam Intensity Matching for Multiple-Beam Cathode Ray Tubes

In order for a multiple-beam cathode ray tube (MBCRT) to produce an image with a high perceived quality, the brightness of the individual beams must be matched. Failure to match the brightnesses of the beams produces bright or dark streaks in the image. In order to meet the stringent requirements of beam matching, it is necessary to adjust each of the beams to the same intensity. Intensity differences between beams come from non-uniform drifts, warm-up, aging, and variations in manufacture of the individual cathodes. Manual adjustment is difficult because when the intensity of a given beam is changed, the intensities of the beams immediately above and below appear to be altered in the sense opposite to that of the central beam. Because of these difficulties it is desirable to automate the process of beam matching; however, the intensity of individual beams must be measured in order to do this. A method is described herein for measuring and adjusting beams in monochrome and color MBCRTs.

Automatically converging color CRTs frequently use an ultraviolet (UV) phosphor deposited in the form of small chevrons on the back of the shadow mask to measure the intensities of beams. The UV output of this phosphor is detected with a PIN diode (a diode having a layer of intrinsic, i-type, semiconductor material sandwiched between the p- and n- regions) looking at the phosphor through a clear area in the dagging on the funnel of the CRT bottle. As each of the beams in the color CRT crosses a chevron, its position can be deduced, and correction signals applied to bring the three color beams into convergence.

In the case of the MBCRT, there is no shadow mask and patterning of the beam intensity sensing phosphor is unnecessary as spatial information is not required. In addition, a low-efficiency UV phosphor can be used...