Craig & Antonelli
Ringing control apparatus
 A ringing control apparatus comprises a bidirectional switching circuit connected in series to a ringing source, which generates an alternating current of a large amplitude, for delivering to a called subscriber the AC signal as an interrupted ringing signal, a phase detector circuit in the form of a zero level detector for detecting the phase of the AC signal generated from the ringing source, and a control circuit for generating a signal for turning on and off the switching circuit in synchronism with the output signal of the phase detector circuit. The delivery of the ringing to the called subscriber is started at a point of time when the ringing voltage comes to a zero level and is stopped at a point of time when the ringing current comes to a zero level, thereby to prevent generation of a surge voltage. 
Hitachi, Ltd.
H
H04M
inventional
Takafumi Takuji Tatsuru
Kojima Mukaemachi Miyoshi