| 摘要 |
To generate a ringing signal by means of a subscriber line interface circuit having two final stages (A), each for supplying an individual subscriber line wire (LA, LB), one (LA) of the subscriber line wires is connected to one of the input terminals of an operational amplifier, the other input terminal of which being connected to the interconnecting point between two series connected resistors having the same resistance, the output terminal of the operational amplifier being connected, via a first resistor (ZT), to a current input terminal (R) of the subscriber line interface circuit for generating a first current, while a signal generator (U), via a second resistor (ZR), is also connected to said current input terminal (R) for generating a second current, said final stages (A) of the subscriber line interface circuit being supplied with current from said current input terminal (R) to drive the final stages (A) to generate the ringing signal.
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