Computer graphics processing and selective visual display system – Data responsive crt display control – Data responsive deflection control
Patent
1996-05-23
2000-01-04
Hjerpe, Richard A.
Computer graphics processing and selective visual display system
Data responsive crt display control
Data responsive deflection control
345 12, 345 14, G09G 108
Patent
active
060115270
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube system which uses an auxiliary deflection winding for convergence correction. Such an auxiliary convergence correction winding or yoke is commonly used in projection television systems where each one of multiple cathode ray tubes generates a unique color image. When the color images are optically combined, slight correction is necessary in order that the multiple images exactly match.
In some systems, a convergence yoke is positioned close enough to the deflection yoke so that deflection currents are induced in the convergence yoke. Such induced currents in the convergence yoke may cause undesirable deflection of the electron beam. The Applicant has found that such induced currents cause an apparent stretch of the image near the beginning of horizontal scan.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cathode ray tube display system in which image distortion, due to currents induced in a convergence correction yoke by the deflection yoke, is corrected.
More specifically, the invention provides a cathode ray tube system which includes a kinescope, a deflection yoke and a correction yoke mounted thereon. The deflection yoke is energized by sawtooth wave currents to generate magnetic fields for scanning an electron beam across the face of the kinescope. The correction yoke, when energized, generates magnetic fields which correct for beam landing errors in the kinescope. Since the correction yoke is affected by stray fields from the deflection yoke, in order to compensate for the effect of the stray fields on the correction yoke, a source of compensation current is fed to the correction yoke near the beginning of a deflection sawtooth wave.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic drawing of a cathode ray tube having a deflection yoke and a convergence correction yoke.
FIG. 2 shows waveform diagrams of the current that is induced in the convergence correction yoke by the horizontal deflection winding for different values of correction yoke winding circuit impedances.
FIG. 3 is a schematic circuit diagram, in block form, of a cathode ray tube display system, according to the invention, which compensates for the currents in the correction yoke which are induced by the deflection yoke.
FIG. 4 is a detailed circuit diagram of a correction arrangement for three cathode ray tubes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a cathode ray tube 10 having an electron gun 12 which generates an electron beam and directs it toward the face of the cathode ray tube. Deflection yoke 14 magnetically scans the beam across the face of the tube while convergence correction yoke 16 corrects for beam landing errors. It is to be noted that convergence correction yoke 16 and deflection yoke 14 are in close proximity, so that stray fields which are generated by deflection yoke 14 tend to induce currents in correction yoke 16.
FIG. 2 shows waveforms of the current which is induced in convergence correction yoke 16 by the horizontal deflection field from deflection yoke 14. Curve 18 shows the current which is induced in correction yoke 16 when yoke 16 is terminated by zero impedance (a short circuit). This waveform closely approximates the waveform of the horizontal deflection current. However, when convergence correction yoke 16 is terminated by a 40 ohm impedance, which is the approximate value of the output impedance of the amplifier which drives the convergence correction yoke, the shape of the induced current changes to the shape shown by curve 20. Curve 20 is a pulse occurring at the beginning of horizontal trace and having a duration of about 15% of the horizontal trace interval. The induced current reaches its baseline about 4 microseconds (.mu.S) after the start of video.
FIG. 3 shows a schematic diagram, in block form, of a circuit for correcting for the current which is induced in the convergence yoke by the horizontal deflection winding of the deflection yoke. Convergen
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Hjerpe Richard A.
Laks Joseph J.
Sragow Daniel E.
Thomson Consumer Electronics Inc.
Tran Henry N.
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