Subscriber line interface circuit for controlling AC and DC output impedance

摘要

A subscriber line interface circuit (SLIC) sets AC and DC output impedances as seen by first and second transmission signals. The common mode variation and differential variation of the first and second transmission signals is AC-sensed to provide a common mode feedback signal and a differential feedback signal which in turn controls the AC output impedance. The DC component of the first and second transmission signals is blocked allowing downstream amplifiers to operate at reduced power supply potentials. The DC variation of the first and second transmission signals is also sensed for providing a DC feedback signal to control the DC output impedance.