Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1980-12-04
1983-09-27
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
315371, 358 73, H04N 927
Patent
active
044069774
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a power supply circuit, provided with a voltage control circuit with negative feedback for applying a rapidly changing high voltage to the anode of a penetron type cathode ray tube for a color display system, and with a deflection voltage correcting unit for obtaining color independent pictures on the screen of the cathode ray tube.
To increase the legibility of a display, a multicolor tube is employed. Owing to the short working distance, it is undesirable to use a shadow-mask tube for this purpose; a penetron tube gives considerably better results. The penetron tube has two different phosphor layers. With a certain anode voltage the electrons excite mainly the first phosphor layer, while with a certain higher anode voltage, the electrons are sufficiently accelerated to penetrate the barrier layer between the two phosphor layers and excite the second phosphor layer. The two anode voltages light up the screen in a certain color; with intermediate anode voltages mixed colors are obtainable. Four-color displays are in common use. In such color displays, the electron beam will hit the screen at a different place for each color with a specific deflection voltage; as the electrons continually acquire a different acceleration by the anode voltages corresponding with the various colors. The deflection voltages should therefore be corrected by a fixed factor for each color. To switch the anode voltage from a first to a second value, a certain time will elapse before the anode voltage settles to its second value and stabilizes. In this switching period, the beam electrons are subjected to a change in acceleration, causing positional errors to be displayed, even if fixed correction factors are applied to the deflection voltages for the individual colors, unless the display is blanked during the switching.
A power supply circuit as set forth in the opening paragraph is known from the German Offenlegungsschrift 26 19 520, in which the deflection voltages are permanently corrected by a fraction of the anode voltage. To improve the long-term stability of the circuit, it is preferable to avoid a direct coupling between the deflection channels and the anode voltage.
SUMMARY OF THE INVENTION
According to the invention a deflection voltage correcting unit is thereto controlled by at least a correction signal derived from an input voltage of the voltage control circuit. This correction signal is therefore directly related to the control voltage of the voltage control circuit with negative feed-back. With an input voltage typical of a certain color, the voltage control circuit can be set in such a way that the control voltage, and hence the correction signal, are adjusted to a value corresponding with this color. This however requires an exceptionally broad range of the control voltage. It is therefore preferable that the deflection voltage correcting unit comprises a coarse and a fine correcting circuit, wherein the coarse correcting circuit is controlled by a signal typical of a particular display color and the fine correcting circuit by the correction signal derived from an input voltage of the voltage control circuit. The control voltage and hence the correction signal for the fine correcting circuit can then be continually adjusted to zero. In the coarse correcting circuit the deflection voltages are corrected by a fixed factor required for each color, while in the fine correcting circuit errors due to imperfections in the switching of the anode voltage are compensated. If now the voltage control circuit is divided into a coarse and a fine control, and the correction signal for the fine correction circuit is derived from the control voltage of the fine control of the voltage control circuit, the errors which would arise through variations in the anode voltage could be compensated in the deflection voltage very accurately. In particular, the compensation of the errors, which would arise during the settling time while switching the anode voltage, give the voltage con
REFERENCES:
patent: Re28631 (1975-11-01), Waehner et al.
patent: 3805253 (1974-04-01), McLanaghan
patent: 3887829 (1975-06-01), Owens, Jr.
patent: 3887840 (1975-06-01), Maytum
patent: 4088928 (1978-05-01), Waehner
patent: 4092566 (1978-05-01), Chambers et al.
Blum Theodore M.
Briody Thomas A.
Burk Robert C.
Goodman Edward W.
Hollandse Signaalapparaten B.V.
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