| 摘要 |
PURPOSE:To enhance stability by connecting a fixed resistor constituting a zero adjusting circuit to a point whose potential undergoes the approximately same change as that at a current input end of the transistor of a second detecting resistor part corresponding to a first detecting resistor part. CONSTITUTION:A zero-point adjusting circuit having the following constitution is provided. The circuit comprises a variable resistor VR1 and a fixed resistor R6 which is connected to the sliding terminal of the resistor VR1. The terminals at both ends of the variable resistor VR1 are connected to the current input ends of the first and second detecting resistors R1 and R2. The fixed resistor R6 is connected to a point which undergoes the approximately same potential change as that at the current input end of a transistor T in the second detecting resistor part R2 corresponding to the first detecting resistor part. Namely, the fixed resistor R6 is connected to a point (d) which undergoes the approximately same potential change as that at a point (a) of the terminal of a differential amplifier Q on the side of a current IA. When the change in potential difference at the point (a) and the point (d) is constant even if the input is changed, bias currents ia and ib are constant. Since the zero adjusting circuit is formed of only the resistors and connected between the two points where the potential change due to the input change is changed in the same direction by the same amount, interference to a span caused by the zero adjustment is eliminated. |
