Front end circuit structure for a subscriber line circuit interface.

摘要

A front end circuit structure for a subscriber line circuit interface employs a controllable amplifier including a switching converter. The switching converter includes a capacitor coupled across a two-wire subscriber line and supplies an auxiliary voltage to the line. The amplifier includes an input adder having an output coupled to the switching converter for controlling the magnitude of the auxiliary voltage with one input of the adder adapted to receive a feedback control signal which is developed by monitoring the voltage across the output. Another input to the adder receives line input signals for the line circuit. The amplifier is controlled in operation by an off hook detector which provides an output signal when the subscriber lines goes off hook to cause the amplifier to operate and further includes ring control logic which is also coupled to the amplifier and activates the amplifier during the presence of a ring control signal. In this manner, the amplifier is operative only during an off hook condition of the line and during ringing generation. The amplifier, based on its structure in the line circuit, provides all basic line functions such as DC current, ringing, voice and remote metering signals.