| 摘要 |
PURPOSE:To make it possible to selectively connect balanced circuits whose impedance has been matched, automatically in a short time, by providing plural balanced circuits which match various two-wire line impedance, respectively, and a circuit for selectively connecting these plural balanced circuits. CONSTITUTION:This circuit is provided with plural balanced circuits 14a-14n having each different impedance to the two-wire line 18, and a change-over switch circuit 20 for switching said balanced circuits 14a-14n and connecting them to the four-wire input terminal 11. And, when the line 18 has been connected to the two-wire input terminal 13, a signal is provided to the input terminal 11. In this case, a balanced circuits 14a-14n is connected to the circuit 20, and when it is not matched, it is integrated by the integrating circuit 24 by outputting an error signal from the differential amplifier to and after that, it is compared with the threshold level which has been set in advance, by the comparator circuit 23, and the logical operation is executed by the feedback logical circuit 22 in accordance with said comparison output. This logical output is decoded by the decoder 21, the circuit 20 is controlled by its output, and the balanced circuits 14a-14n are selectively connected. |
