Browse Prior Art Database

Character Tilt Correction

IP.com Disclosure Number: IPCOM000090946D
Original Publication Date: 1969-Aug-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Wolf, JW: AUTHOR

Abstract

Cathode ray tube displays employ compensating circuits or devices for eliminating pincushion which otherwise occurs as a result of the angular sweep of the cathode ray beam to the corners of the display screen. If only the main deflection system is corrected and the character drawing circuitry is uncorrected, the characters appear in the correct position on the screen but are tilted in the corners of the screen due to the pincushion effect.

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Character Tilt Correction

Cathode ray tube displays employ compensating circuits or devices for eliminating pincushion which otherwise occurs as a result of the angular sweep of the cathode ray beam to the corners of the display screen. If only the main deflection system is corrected and the character drawing circuitry is uncorrected, the characters appear in the correct position on the screen but are tilted in the corners of the screen due to the pincushion effect.

CRT 10 has main position and character stroke deflection yokes 12 and 14. These are driven by the circuitry to provide characters, specified by a digital character stroke generator 16, at a position on the CRT screen designated by registers 18. The X and X analogue inputs for the push-pull windings of the XP yoke winding are connected alternatively through gate 20 under the control of the high-order bit line 22 of the X position register. Thus if, the character is to be displayed in the upper half of the CRT screen, the X analogue signal is delivered on line 24. Otherwise, line 24 receives the X signal.

The Y position value is decoded at 26. Lines controlled by 26 are connected to Parallel emitter resistors RE for transistor 28 having a collector resistor RL. Transistor 28 multiplies the signal on line 24 by the quantity RL/RE and conducts, in addition, a current component which is a function of the Y position alone. The base of transistor 30 is connected through a parallel bank of resistors 32 under the control of decoder 26 to provide a collector current. This is an inverse function of the Y position alone and this current modifies the output of 28 so that the net signal on line 34 is a function of the product of th...