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AssigneeU.S. Philips Corporation
InventorWouter van den Berg
Estimating the term…
An automatic control for the optimum control voltage during the line flyback time between the control electrode and the cathode of an ACT gun in a television pick-up tube. A variation in the cathode potential during the line flyback requires inter alia an adaptation of the control electrode potential. Without this adaptation a too small beam current on the target would result in an insufficient erasing action while a too large beam current would result in an inadmissible dark current with the risk of persistence upon display (afterglow). In the circuit arrangement a measurement of the beam current is effected through a specific choice of the lens pulse duration at the gun, which beam current becomes available for the erasing action on the target during the line flyback time, and through comparison with a reference value a variable pulse generator is controlled for supplying the control electrode pulse with a given pulse height during the line flyback time.
A circuit arrangement suitable for use in a television pick-up tube provided with an anti-comet tail electron gun, formed with a cathode, a control electrode, anode electrodes and a lens electrode for generating during line scan times and line flyback times an electron beam having different values for the beam diameter, beam current intensity and beam potential upon impingement of a target present in the tube under the control of a control voltage between the control electrode and the cathode having a cathode potential and a lens voltage between the lens electrode and an adjacent anode electrode, one line period being constituted by the line scan time and a line blanking time comprising the line flyback time and a beam blanking time, said circuit arrangement comprising an input means for coupling generator including a potential divider having a plurality of connection points, a plurality of switch means for coupling said points to the output of the variable pulse generator under the control of a switching signal, the potential divider including a controllable resistor coupled to said first input, further being coupled to said second input to which the adjustable source is coupled.
Dependencies are inferred from the claim text.