Ringing-current and loop-current supply for telephony - has amplifier connected between incoming and outgoing line amplifiers to reduce echo and side-tone

摘要

The supply can be fabricated as a monolithic component and is intended for PCN telephone exchange systems. Controlled current sources form part of a hybrid circuit. The loop current on the two wire side of the hybrid is modulated via two current sources by the output of the incoming amplifier on the fair wire side. Signals from the 2-wire side are transmitted to the outgoing line on the 4-wire side by an outgoing amplifier. A third amplifier is connected between the incoming and outgoing terminals on the 4-wire side for side tone and echo attenuation.