| 摘要 |
PROBLEM TO BE SOLVED: To provide a scanning circuit for a scanning electron microscope having an improved signal-to-noise ratio of a scanning signal. SOLUTION: Magnification is controlled in the enlarging direction according to magnification data to a magnification control circuit 2, and an output voltage Va of the magnification control circuit 2 is increased proportion to it. When the output voltage Va is set so that the formula Va<=Vm/n is satisfied, with Vm being the maximum output voltage of the magnification control circuit 2, then a switch SW1 is turned off, and only a switch SW2 is turned on, to select a resistor R2. Here, n is the optimum value of the system and also a value which is characteristic of the device. Then the magnification is further increased with the switch SW2 being on, when the point satisfying the formula Va<=Vm/n is reached, then the switch SW2 is turned off, and only the switch SW3 is turned on, to select the resistor R3.
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