| 摘要 |
PURPOSE:To attempt improvement of the S/N ratio in a single exposure at the sacrifice of minute informations more or less, by dividing detected signals into two, and providing one path with a connected circuit which screens the signals exceeding the fixed frequency, and guiding this output signals to a cathode-ray tube. CONSTITUTION:A secondary electron detector 8 is arranged on the upper part of a sample 4. Its output is amplified by an amplifier 9 and divided into two. In one ciucuit, the pulse signals which do not exceed a fixed value are screened by an AD converter 10 and a filter circuit 11 and converted into analog signals by a DA converter 12. To the output terminal of this converter, a +V clamp circuit 13a and a -V clamp ciucuit 13b are mutually connected and in parallel and each clamp circuit is composed of amplifiers and diodes respectively. The output terminal of each clamp circuit is connected to the output terminal of an analog amplifier 16 which is inserted in the branched other path and supplied to the brightness modulation grid of a cathode-ray tube 7 through an output amplifier 17. This can obtain an excellent picture with less visual roughness which can be observed without any hardness. |
