| 摘要 |
PURPOSE:To uniformly maintain a beam quantity obtained from all of the electron beam sources regardless of a time lapse with a simple constitution, by comparing a beam current quantity emitted from respective beam source with a reference value, providing a means which controls the beam current quantity, and repeating periodically an operation to increase or decrease the beam current quantity by prescribed unit. CONSTITUTION:A beam current generated from a cathode 10 to an anode direction is interrupted by a beam interruption signal 60 impressed on a G4 electrode 16 for a horizontal blanking period, and during that period, a beam is permitted to run in a G3 electrode. And the beam is detected by a current detecting part 50, and is compared with a certain prescribed level by a comparator 51. When a difference in a compared result is large, one is subtracted from data latched at a latch circuit 54 by an adder/subtractor 52, and when it is small, the data on which one is added, is generated, and the data after addition/subtraction is written at the address of a memory 53. Such operation is performed for all of the electron electron beams on a screen, and is repeated with a certain period, thereby, a negative feedback control is performed so as to set the beam current at a regulated value.
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