| 摘要 |
PURPOSE:To improve the SN ratio of a scanning signal by providing a feedback point change-over circuit for switching the feedback point to the input side of a reference resistance change-over circuit, or to the output side of an amplifier. CONSTITUTION:A feedback point change-over circuit 9 for switching a feedback point to the input side of a reference resistance change-over circuit 8, or to the output side of an amplifier 5, is provided. That is, when the resistors r1-rn having the resistance value, in which a current flowing to the feedback resistance 7 can not be neglected as it is, are selected, the output side of a scanning coil 6, that is, the input side of the reference resistance change-over circuit 8 and the side of the feedback resistance 7 are made to be interrupted by switching the feedback point to the output side of the amplifier 5. Thereby, the feedback resistance 7 and the input resistance 4 having small resistance values can be used, thus reducing a thermal noise besides reducing a current noise of the amplifier 5 so as to improve the SN ratio of a scanning signal.
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