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Browse Prior Art Database

DAC Controllable Raster - Horizontal Centering Circuit

IP.com Disclosure Number: IPCOM000099885D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Jahandoost, HH: AUTHOR [+2]

Abstract

Disclosed is an adaptation of a horizontal centering circuit having two transistors and a current source to allow DAC (digital-to-analog converter) voltage controllability.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 99% of the total text.

DAC Controllable Raster - Horizontal Centering Circuit

       Disclosed is an adaptation of a horizontal centering
circuit having two transistors and a current source to allow DAC
(digital-to-analog converter) voltage controllability.

      In high quality CRT monitors, it is often desirable to employ
centering circuits for both the vertical and the horizontal axes.
Vertical centering circuits generally are simple, but horizontal
centering circuits usually are not. A simple modification to a
commonly used horizontal centering circuit allows for DAC voltage
controllability.

      The proposed circuit is shown in the figure.  The function of
R2 and Q3 and the OP-AMP is to provide a current sink to the resistor
R1.  The voltage potential across R1 is directly proportional to the
magnitude of the voltage-controlled current sink.  Since the two
transistors Q1 and Q2 are used as emitter followers, the voltage
across R1 "steers" an induced net DC current in the horizontal yoke.
Therefore, this current sink translates control to the floating Q1
and Q2 transistor pair from the ground referenced input - a DAC
voltage or any other control voltage.  The net DC offset current
induced in the horizontal yoke is a function of the amount of current
"borrowed" during a part of the deflection cycle.  By using current
"borrowed" from one part of the cycle and "steering" this current
back through the horizontal yoke itself, the raster and image can be
shifted left or right. ...