| 摘要 |
PURPOSE:To realize drawing of fine pattern by measuring nonlinear distortion of deflection voltage waveform, calculating a distortion correcting value from this value, mixing a distortion correcting signal with a deflection signal having nonlinear distortion and forming a deflection signal having good linearity. CONSTITUTION:When a signal VS which attenuates a deflection signal VSout in synchronization with a synchronous signal Scnt rises linearly, the time until it becomes equal to the reference voltage Vref output from a computer 20 is measured. The distortion of waveform of deflection voltage VSout is measured 19 by measuring 23 a count time for each rise like a step from the minimum voltage VL to the maximum voltage VH. Based on this calculated value, the computer 20 reverses the polarity of reference value to generate a corrected value in proportional to a deviation. The computer 20 moreover stores 27 a corrected value using a digital value at the timing where the measuring time is divided into n-point, reads 28 such value through control with the synchronous signal Scnt and converts it into analog signal through the D/A converter in order to generate a corrected signal VSb. This signal is then mixed with a deflection signal VSa. Thereby, a deflection signal having good linearity can be obtained. |
