| 摘要 |
PURPOSE:To control magnification without degrading the S/N ratio of a circuit by compensating the reduction component of a deflection current which is caused by improving the degradation of the S/N ratio due to an attenuator with a variable resistance circuit, adjusting the gain of a voltage amplifier. CONSTITUTION:The maximum and minimum values of the output signal of a scanning signal generator 1 which is attenuated by an attenuator 6 to enlarge magnification are detected by the maximum value detector 8 and the minimum value detector 9. The absolute value as the difference of these two values is calculated by an absolute value detector 10 and sent to a hysteresis circuit 11. The hysteresis 11 compares a preset reference value with the output value of the absolute value detect or 10. It increases also the resistance value by sending a command to a variable resistance circuit 4 and the gain of an amplifier by sending it to a voltage amplifier 7. This can improve the degradation of the S/N ratio due to the attenuator, compensate the reduction of the deflection current which is applied to an electron beam deflection coil 3, and control a high magnification without degrading the S/N ratio of the circuit. |
