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Browse Prior Art Database

Focus Auto-Adjustment for CRT Display

IP.com Disclosure Number: IPCOM000047872D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Harahata, M: AUTHOR [+2]

Abstract

This article describes a technique for focus auto-adjustment for CRT displays which measures the brightness on the display screen while varying the focus voltage and sets the best focus point at the minimum brightness. At the best focus, or at the minimum beam spot diameter, there occurs a space between adjacent two scan lines, as shown in Fig. 1, and thus the area S of the luminescent regions on the phosphor screen goes to minimum and beam current density Id goes to maximum since Id x S is constant when varying the focus voltage. However, "the brightness per unit area at the luminescent regions" vs "Id" characteristics are sublinear, as shown in Fig. 2.

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Focus Auto-Adjustment for CRT Display

This article describes a technique for focus auto-adjustment for CRT displays which measures the brightness on the display screen while varying the focus voltage and sets the best focus point at the minimum brightness. At the best focus, or at the minimum beam spot diameter, there occurs a space between adjacent two scan lines, as shown in Fig. 1, and thus the area S of the luminescent regions on the phosphor screen goes to minimum and beam current density Id goes to maximum since Id x S is constant when varying the focus voltage. However, "the brightness per unit area at the luminescent regions" vs "Id" characteristics are sublinear, as shown in Fig. 2. Consequently, at the best focus, or at the minimum S and the maximum Id, the luminance energy on the screen given by the product of (the brightness per unit area at the luminescent regions) x (S) goes to minimum. For the above reason, the best focus point can be determined by searching the minimum brightness point while varying the focus voltage. Fig. 3 shows the present focus auto-adjustment system. The present method can be applied not only to monochrome displays but to color displays. The present method has the advantages of short adjustment time, easy measurement and low cost.

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