Browse Prior Art Database

Flyback Pulse Inverter Circuit for CRT Set Up

IP.com Disclosure Number: IPCOM000121553D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 90K

Publishing Venue

IBM

Related People

Eagle, DJ: AUTHOR [+3]

Abstract

Described is a display circuit to invert the polarity of the horizontal scan flyback pulse during the setting up of a cathode ray tube (CRT) in order that the pulse polarity matches the polarity used in the final display product. Failure to match polarities results in a measurable convergence shift.

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This is the abbreviated version, containing approximately 52% of the total text.

Flyback Pulse Inverter Circuit for CRT Set Up

      Described is a display circuit to invert the polarity of
the horizontal scan flyback pulse during the setting up of a cathode
ray tube (CRT) in order that the pulse polarity matches the polarity
used in the final display product. Failure to match polarities
results in a measurable convergence shift.

      The advantage of the disclosed circuit is flexibility. It may
be used as a pulse inverter (either from positive to negative or from
negative to positive) or simply as an isolation circuit which could
have safety advantages in some environments.  The cost of the
circuitry involved is low but makes it possible for CRT manufacturers
to use their existing commercial flyback generators to accurately set
up CRTs for displays using either polarity of flyback pulse.

      With CRT-based display products, the performance of the CRT is
key to the overall customer acceptability of the final product.  One
of the important factors is convergence performance.  Traditionally
this is the subject of many complaints, depending exclusively on the
quality of the CRT. Convergence is dependent on the polarity of the
horizontal flyback pulse used.  Most displays have used
positive-going flyback pulses.  With higher specification displays
there is a tendency to move towards drives with negative-going
flyback pulses because implementation of regulator circuits is
greatly simplified by using a negative-going flyback pulse.

      CRT manufacturers use standard commercial units to drive the
CRTs during set-up; units are indestructable and robust enough to
cope with any fault condition encountered. But they lack flexibility.
Whilst it is possible to adjust the horizontal frequency, it is not
possible to adjust the polarity of the flyback pulse.  The
traditional bias towards positive-going flyback pulses resulted in
commercial units offering only positive polarity.  So even if a CRT
is to be used in a display with a negative-going flyback pulse, it
will be set up using a positive-going flyback pulse.  T...