All electronic interface for telephony system

摘要

A line circuit for connecting a subscriber line to a telephony system that avoids the use of electro-mechanical elements such as relays. A bridge circuit includes a bilateral current gate in each of the tip and ring lines that can couple or inhibit signals from passing between the subscribed lines and the system. When the bilateral current gates are in an inhibit mode, an on-hook current source energizes the tip and ring lines. A detector senses when the subscriber goes off-hook, and also the dial pulses. After the current gate goes into a coupling mode, the on-hook current source and detector are electrically inactive, and an off-hook current source thereafter provides current to the tip and ring conductors.