Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1996-05-23
1998-07-21
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
H01J 2956
Patent
active
057839131
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a raster distortions correcting device for a picture tube of a video display apparatus.
Typically, in, for example, projection television receivers, North-South pincushion distortions, resulting in curved displayed horizontal lines of a cross-hatched pattern, are corrected by generating a convergence current component in a convergence winding. When the cathode ray tube (CRT) of a projection receiver having rear projection lens has a relatively flat phosphor surface, the convergence current component is obtained by modulating or multiplying a horizontal rate parabola signal with a vertical rate sawtooth signal and applying the modulated signal to an amplifier that is coupled to the convergence winding.
In order to reduce the distance from the CRT faceplate to the screen on which the displayed image is made visible to the viewer, a curved phosphor surface is utilized having a radius of curvature of the type that tends to increase North-South pincushion distortions relative to what would be obtained had the aforementioned phosphor surface been flat. Similarly, outer North-South pincushion distortions, i.e., at the top/bottom of the displayed image, are corrected by the aforementioned current in the convergence winding with a higher degree of modulation than is required when the phosphor surface of the CRT is flat. The result is that the distortions of the displayed lines at the top/bottom of the cross-hatched pattern are corrected. Disadvantageously, the high degree of modulation tends to introduce inside North-South pincushion distortions, midway between the screen center and the screen top and bottom edges.
In a raster distortion correction arrangement, embodying an inventive feature, a vertical rate sinusoidal signal modulates a horizontal rate parabola signal. The modulated signal is applied to the convergence winding to provide S-shaping of the vertical rate sawtooth signal so as to reduce the inside pincushion distortion. The sinusoidal signal is produced by low pass filtering and phase shifting a vertical rate parabola signal. The vertical rate parabola signal is produced by integrating a vertical rate sawtooth signal.
Typically, the vertical rate sawtooth signal is obtained in a sawtooth signal generator from a pulse signal that is produced in a counter. When the television receiver is tuned for receiving a composite video signal, the counter changes state at a rate that is determined by the receiver horizontal oscillator which is phase locked to a horizontal synchronizing signal of the received composite video signal.
During a transient interval that occurs, for example, after the user effectuates television signal channel change, the synchronizing signal is absent. Such situation can also occur when synchronization lock is lost because of other reasons. During this interval the horizontal oscillator is free running at a frequency very close to its horizontal value. The vertical counter count is altered so that the vertical frequency is locked to the horizontal oscillator but at a vertical frequency that is 10% lower than in normal television signal reception. This feature maintains the integrity of on screen displayed images and provides fast vertical phase lock when normal television signal reception is resumed. The result is that, when the synchronizing signals are absent, the frequency of the counter output pulse signal is lower by about 10% than during normal television signal reception.
Consequently, the amplitude of each of the vertical rate sawtooth signal and of the vertical rate parabola signal tends to increase. The increased amplitude may produce a DC or average voltage level shift of the vertical rate parabola signal. Such different DC voltage remains as long as normal television signal reception has not resumed.
The DC, average level reverts back to its normal level after normal television signal reception has resumed. However, a transient interval that elapses while the DC level is being restored may be long enough to produce a transient picture distortion. The
REFERENCES:
patent: 3700958 (1972-10-01), Haferl
patent: 3721857 (1973-03-01), Haferl
patent: 4335333 (1982-06-01), Ramsay et al.
patent: 4378516 (1983-03-01), Smith
patent: 4642530 (1987-02-01), Rodriguez-Cavazos
patent: 4668897 (1987-05-01), Haferl
patent: 4682085 (1987-07-01), Haferl et al.
patent: 4687972 (1987-08-01), Haferl
patent: 4777411 (1988-10-01), O'Connor et al.
patent: 4777412 (1988-10-01), Leonardi
patent: 4795949 (1989-01-01), Wilber
patent: 4810939 (1989-03-01), Watanabe et al.
patent: 4827193 (1989-05-01), Watanuki et al.
patent: 4972127 (1990-11-01), Rodriguez-Cavazos et al.
patent: 5034664 (1991-07-01), Fernsler et al.
Blum Theodore M.
Henig Sammy S.
Laks Joseph J.
Thomson Consumer Electronics Inc.
Tripoli Joseph S.
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