Key telephone line shunt detector circuit

摘要

A line circuit is disclosed for controlling communications over a communication pair between a switching machine and a key telephone station. The line circuit includes a dual sensitivity shunt detector arrangement (103, 104, 105) for improved detection of dc transients and ac ringing voltage signals appearing across the pair. A current diverter circuit (104) switches the sensitivity of the shunt detector arrangement depending on the operating state of the key telephone station.