| 摘要 |
PURPOSE:To secure a uniform image on the same condition, by cutting a secondary electron signal into two separate portions, low frequency and high frequency, while installing a signal correction device regulating the high frequency portion according to the magnitude of the low frequency portion and thereby forming the image with the corrected signal. CONSTITUTION:A signal correction device 4 for turning a detection secondary electron signal S2 into a correction secondary electron signal S3 for correction is installed in addition. This correction device 4 is fitted with a low-pass filter 42 which passes only a delay circuit 41 having the signal S2 delayed for the specified time long and a low frequency constitutent and calculates a difference between a delay signal S41 and a low frequency signal S42 with a differential amplification circuit 43. On the other hand, also it calculates a difference between a reference level signal S45 of the specified voltage value and the low frequency signal S42 with a differential amplifier 46, then amplifies a high frequency signal S43 with an amplifier 44 in accordance with a gain correction signal S46 out of this differential amplifier 46 and transmits the correction secondary electron signal S3 to a display unit 3. With this, a uniform image can be secured by using the secondary electron signal uninfluenced by any external cause. |
