| 摘要 |
PURPOSE:To prevent brightening line position from being varied by operation of an oscilloscope and the temperature, etc., by measuring DC offset voltage of a vertical axis amplifier and cancelling the offset voltage by feeding back the offset voltage. CONSTITUTION:A switch 16 is actuated by a switch control signal 17 synchronous with an outside signal or a brightness cancelling signal, and input terminal of an attenuator 2 is grounded. And, an offset voltage output 8 from a vertical axis amplifier 3 is converted to a digital value by an A/D converter 10 synchronously with a switch control signal. This digital value is added to an input value of the D/A converter 13 by an adder 12 through a coefficient operator 11, and a result of this addition is converted to an analog value by the D/A converter 13 and put into the vertical axis amplifier 3. It is possible, by doing so, to cancel the offset voltage of the vertical axis amplifier to zero and eliminate necessity of adjustment of the offset voltage. |
