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Novel Width Compensation Against Brightness Variations

IP.com Disclosure Number: IPCOM000101851D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 76K

Publishing Venue

IBM

Related People

Gibbs, TK: AUTHOR [+2]

Abstract

A method is described of correcting display width changes against brightness variations caused by CRT beam current loading in a display monitor. The correction can be accurately scaled making the correction more accurate and effective.

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This is the abbreviated version, containing approximately 53% of the total text.

Novel Width Compensation Against Brightness Variations

       A method is described of correcting display width changes
against brightness variations caused by CRT beam current loading in a
display monitor.  The correction can be accurately scaled making the
correction more accurate and effective.

      In a conventional non-interlaced display monitor, the EHT
supply is normally not stabilized.  Changes in EHT supply will
reflect in consequent changes of width.  Thus, when the beam current
(brightness) of a monitor is altered over a large range, this will
reflect in a change of EHT and consequently a noticable change in the
display width.  The disclosure shows that width compensation can be
achieved by simple means but with an accuracte control of scaling to
make compensation more effective than conventional methods.

      Referring to Fig. 1, when the beam current of the monitor is
increased, the loading of the B+ (90 V) is increased, and due to its
a finite output impedance the 90 V rail voltage will tend to fall.
As the power supply is monitoring the level of the 90 V supply, when
it detects a fall it increases the mark space ratio in an attempt to
maintain the 90 V supply constant at its original level. This has a
secondary effect of also marginally increasing the 22 V supply as the
beam current increases.  This characteristic can be used to
advantage.

      Fig. 1 shows that the width control takes the form of a DC
input to the diode modulator...