| 摘要 |
PURPOSE:To set the offset voltage accurately at zero, by setting the positive and negative power supplies under a floating state (or its approximate state) from an earth and detecting and amplifying the potential difference between the intermediate potential point and the earth to feedback said potential difference. CONSTITUTION:The currents I1 and I2 flow to resistances Rb and Rg1 as well as to resistances Rg2 and Rf in the directions shown by arrow marks respectively owing to the presence of the offset voltage of a differential amplifier (Q1 or Q2). The current I1 is equal to the current I2 since the power supply + or -VCC is floated, and I=(Vg1-Vg2)/(Rg1+Rg2) is satisfied for the current I. At the same time, the potential Vb at the middle point of the power supply is set as Vb=(Rb+Rg1)I and the DC output potential V0 is set as V0=-(Rf+Rg2)I respectively. While Vg1=Rg1Vb/(Rb+Rg1) is satisfied for the voltage Vg1 of an input terminal. Then Vg1 is equal to 0 if the resistance Rb is infinite. The current I is substituted for the above-mentioned equation of Vb, and Rb infinity is taken into consideration. Thus Vg1-Vg2=0, i.e., Vg1=Vg2=V0=0 is satisfied. Then the DC output of a direct-coupled amplifier is set accurately at zero. |
