Ringing control circuit in a telephone switching system

Claim 1

A ringing control circuit for a telephone exchange system comprising: (a) a plurality of subscriber line circuits in a group, each coupled with a subscriber, (b) a ringing source common to all the subscriber line circuits for providing a continuous ringing signal, (c) a ringing switch means provided for each subscriber for coupling said ringing source to each subscriber, (d) a ring trip circuit common to all the subscriber line circuits provided between said ringing source and the subscribers to detect an answer signal of subscribers, (e) each subscriber line circuit having a subscriber ringing controller for switching said ringing switch means to provide an interrupted ringing signal to a related subcriber, and a subscriber line scan circuit for detecting whether a handset is lifted, (f) said subscriber ringing controller starting ringing upon arrival of a call to the subscriber and finishing ringing upon detection of an answer signal by said ring trip circuit, characterized in that (g) a ringing phase selection means is provided, having as its outputs phased ringing signals equal to or less in number than the number of subscribers in a group, said phased ringing signals being alternatively active, (h) each subscriber line circuit having an AND circuit with two inputs, one input of which is the answer signal provided by said ring trip circuit, and the other input of which is one of the phased ringing signals, (i) an output of said AND circuit causing a subscriber ringing controller to stop the ringing.