Ringing circuit for centrally controlled telephone exchange junction - has alternating signal source, and bipolar electronic switch output connected to subscriber and timer

摘要

The ringing circuit is designed to present to a called subscriber a continuous call tone followed by a discontinuous call tone. The ringing circuit has an alternating signal source and a first bipolar electronic switch fitted with two input terminals. The input terminals are supplied from the alternating signal source. Its two output terminals are connected to the called subscribers line and to a control terminal fed by a timing signal generator. The signal generator is controlled by the central control unit.