Subscriber line interface circuitry with common base audio isolation stage

Abstract

Methods and apparatus for coupling outgoing analog audio signals to a subscriber line are described. A subscriber line interface circuit apparatus couples an outgoing audio signal to the subscriber line through a common base isolation stage. In one embodiment, linefeed driver control signals for controlling battery feed to the subscriber line are received on the same signal lines as the outgoing audio signal. In various embodiments, the common base isolation stage comprises a plurality of bipolar junction transistors coupled in a common base configuration or a plurality of field effect transistors coupled in a common gate configuration.

1 . A method comprising the steps of:
 a) receiving an outgoing audio signal; and   b) coupling the audio signal to a subscriber line through a plurality of transistors coupled in a common base configuration.