| 摘要 |
PURPOSE:To eliminate the need for a call signal current limit resistor and a high withstand voltage changeover switch by applying a call signal of a low output to an input signal of a non-inverting amplifier via a switch circuit in a circuit transmitting a high voltage call signal to a subscriber terminal device. CONSTITUTION:A low withstand voltage switch 14 connects an input terminal of the non-inverting amplifier 5' to the position of an input terminal 12 during talking and a talking current flowing from a power supply of the non-inverting amplifier 5' to a power supply of an inverting amplifier 6 is fed to a subscriber line via the terminals 1, 2. At the incoming call to the subscriber terminal device, since the switch 14 connects the input terminal of the amplifier 5' to the position of a call signal oscillator 15, the call signal from the oscillator 15 is inputted to the amplifier 5' via the switch 14, amplified to a prescribed level so as to energize a bell of the subscriber terminal device. |
