Circuit connecting subscriber line to telephone exchange - has balanced amplifier whose input is connected to one or other of two supply points (BE 17.4.79)

摘要

The circuit has a balanced amplifier between two supply points at different potentials. It has two inputs and two outputs, the latter connected to the two wires of the subscriber line. Each input terminals of the amplifier is connected to an output of a digital-analogue converter, whose input is connected through a switch to the one or the other supply point. The switch is controlled by a binary digital signal which characterises the voltage required for the subscriber line, and is collected from digital signal generator under exchange control.