| 摘要 |
PURPOSE:To prevent the influence of the current, which is flowed to a referral resistance, upon the potential of the output, by providing an FET constituting a switch on both conductors of each input route and receiving the pontential of an output conductor by an operational amplifier and flowing a current to the referral resistance by this output. CONSTITUTION:When an input signal I1 is selected, a backward bias is applied to a diode D1 to turn off it. Then, an FET Q1 is turned on to obtain the input signal I1 in an output terminal O. The potential of the output terminal O is received by an operational amplifier A having a high input impedance, and the output is applied to referral resistances Z1-Zn. Though a current is not flowed to the referral resistance Z1 because the other end is biased backward, currents are flowed to resistances Z2-Zn through diodes D2-Dn to turn off FETs Q2-Qn. The input current is hardly flowed to the amplifier A, and thus, an accurate output is obtaind in the output terminal O. |
