| 摘要 |
PURPOSE:To prevent the mixing of noises in an unnecessary area and improve the analysis precision by setting only a necessary portion in an electron beam scan area as a counting area. CONSTITUTION:The working voltage range of individual window comparators 10, 11 can be optionally adjusted by adjusting lower limit reference voltage adjusting volumes VR1, VR3 and upper limit reference voltage adjusting volumes VR2, VR4 provided on each window comparator. When both an X-axis scan signal (x) and a Y-axis scan signal (y) are within their working voltage ranges respectively, aperture signals (a) are outputted from an AND circuit 12. That is, the signals (a) are generated while an electron beam is scanning a certain rectangular area in the whole scan area. Multiple aperture circuits 9 of such a structure are connected in parallel, and their outputs (a) are summed up in an OR circuit 13 to become a gate control signal (g). |
