Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Patent
1986-04-03
1987-01-27
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
H01J 2958
Patent
active
046396446
ABSTRACT:
A cathode-ray tube display system having a dynamic focus circuit to compensate for the inherent defocusing of an electron beam resulting from differences in the distance the beam must travel between an electron gun projecting such beam and a display screen as the beam is moved from position to position about the screen. The circuit is fed by a variable focusing signal having a predetermined bandwidth extending from zero hertz to a predetermined frequency. A combining network is included in the circuit for combining a reference voltage, an amplified, capacitively-coupled first portion of the applied variable focusing signal, and an amplified second portion of the applied signal to produce, at a focus electrode, a composite focusing signal. The produced composite focusing signal has a nominal focusing voltage level produced in response to the reference voltage and selected to provide proper focusing of the beam when the beam is positioned at the center of the screen. The combining network attenuates the nominal focusing voltage level to a predetermined factor thereof at the output of an amplifier used to amplify the second portion of the applied signal. Circuit components are selected to provide the circuit with a substantially uniform transfer function, relating the applied signal to the composite focusing signal, that is frequency independent over the bandwidth of the applied signal. Thus, the composite focusing signal provides accurate focusing when the beam remains fixed at a single, off-center position on the screen, as well as when the beam is moved about the screen.
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Blum Theodore M.
Cain D.
Dawson Walter F.
Raytheon Company
Sharkansky Richard M.
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