Browse Prior Art Database

Low Cost Three Beam Cathode Ray Tube

IP.com Disclosure Number: IPCOM000082995D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 66K

Publishing Venue

IBM

Related People

Selzo, CA: AUTHOR

Abstract

In a single-gun monochrome cathode-ray tube (CRT) used in conventional data display terminals, as the line scanning rate is increased, greater beam power and higher anode voltages are required to maintain brightness, thus shortening gun life and increasing screen burn. In addition, if a constant line scan rate is maintained as the number of displayed characters is increased flicker occurs. A cathode-ray tube display which eliminates flicker using a three-gun CRT is constructed and operates as follows.

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Low Cost Three Beam Cathode Ray Tube

In a single-gun monochrome cathode-ray tube (CRT) used in conventional data display terminals, as the line scanning rate is increased, greater beam power and higher anode voltages are required to maintain brightness, thus shortening gun life and increasing screen burn. In addition, if a constant line scan rate is maintained as the number of displayed characters is increased flicker occurs. A cathode-ray tube display which eliminates flicker using a three- gun CRT is constructed and operates as follows.

Referring to Fig. 1, the conventional color CRT arrangement is shown in which three individual guns 11, 13 and 15 are directed to a shadow mask 17 to actuate the phosphors on the CRT screen 19. The phosphors are producing colors of blue, green and red when impinged by a CRT beam. As shown in Fig. 2, the guns were mounted to produce three vertical beams on the monochrome phosphor screen 21 without use of the shadow mask. The three beams are simultaneously swept in the conventional fashion so that three horizontal sweeps are caused to occur simultaneously.

In actual operation, to display characters on the CRT, a character generator, not shown, is connected via a signal amplifier to the grids of the three guns. In operation, different data from separate video amplifiers would be supplied to each gun, the signal to each gun being switched on and off to change character density, the brightness being controlled by adjusting the signal level.

Referring to Fig. 3, static and dynamic convergence controls, shown as the centering magnet and dynamic convergence magnets, were adjusted to position the three beams. Generating a character in the conventional horizontal sweep using a 7 x 9 dot matrix, each of the three beams may write a different part of the same character such that complete characters are written in three horizontal sweeps, rather than the nine sweeps required by a single-gun CRT.

An alternate approach to message generation was used to write the intermediate group of characters shown in Fig. 3, in which each bean would write the corresponding row for that character as they are swept across the screen in synchronism. Thus beam 1 would write the character A, beam 2 the character B, and beam 3 the character C so that with the nine horizontal sweeps three lines of characters would be written, but each item would be written by a separate gun. In the bottom row of characters on screen 21 in Fig. 3, all three beans were caused to hit the same spot on the phosphor at the same time, so that the brightness was proportionally increased with the number of beams unblanked.

Other modifications such as two beans adjusted to write the same character position while bean 3 was...