Amplifiers.

摘要

A two wire balanced line drive amplifier in a semiconductor subscriber's line interface unit has two output amplifiers each capable of feeding a controlled current to a respective one of the wires. The differential voltage on the line is monitored and feedback as a negative-feedback voltage combined with the input signal voltage. This combination is applied to a reference impedance (22). The resulting current in this impedance controls the current fed to the line by the output amplifiers G1, G2. In one embodiment the control is direct via controlled current sources for example prevision current mirrors and in another embodiment a current mirror controls the current to one wire and the current to the other wire is controlled indirectly via circuitry arranged to maintain equal voltage excursions on the two wires of the line.