| 摘要 |
PURPOSE:To improve the contact reliability of contacts, by connecting the contacts corresponding to the first and second attenuation of the attenuation selection switch to the input terminal and ground of common potential respectively. CONSTITUTION:The selection attenuator used for the vertical axis amplifier of an oscilloscope is inserted between the stages of the amplifier. The output signal of the preamplifier is inputted to the terminal 1, the output resistance of the preamplifier is sufficiently smaller than the sum of the resistors 4 and 5, and the input resistance to the next stage amplifier is sufficiently greater than the parallel resultant value of the resistors 4 and 5. The value of the resistor 7 is selected equal to the sum of the resistors 4 and 5. In the condition where the common terminal of the switch 3 connected to the terminal 1 corresponding to the first attenuation factor, the input current almost flows to the contact of the switch 3 and the resistor 7. When the common terminal of the switch 3 is connected to the common potential corresponding to the second attenuation rate, the input current almost flows to the common potential through the contact and the resistor 5. Thus, since the current flowing to the contact of the switch has almost equal current value as the input current, the contactness reliability can be increased in comparison with conventional fine current. |
