| 摘要 |
PURPOSE:To obtain an electron beam describing device which can draw a figure with high accuracy, by providing a shield guard on a blanking board thereby blocking the current flowing through a mirror body when the blanking voltage is changing. CONSTITUTION:A shield guard 19 is located between a mirror body 9 and a blanking board 4 and insulated through an insulator 11 from the blanking board 4, while connected through a guard wire 20 to the ground side of a blanking switch 15 to maintain the same potential with the mirror body 9. Consequently when the blanking switch 15 is switched from open to closed state to discharge the positive charge at the left side of the blanking board 4, the discharge current I2 of the stray capacitance C1' will not flow through the mirror body but through the guard wire 20, thereby it doesn't influence on the electron wire. Consequently good unblanking operation is performed resulting in a clear figure at the starting section with high accuracy. |
